Optical coherent imager and method for sensing coherent light that share input / output paths

Abstract

To provide an optical coherent imager comprising a shared path for transmitting and receiving an optical signal by utilizing polarization diversity, an optical coherent imager including an array of optical coherent sensing units, and a method for sensing coherent.SOLUTION: In a coherent sensing unit 100, regarding a polarization varied free space-to-waveguide coupler 101 which functions as both a transmitter and a receiver, in a case where a polarization state of an input optical signal Ein arriving at the coupler is orthogonal with a polarization state of an output optical signal Eout outputted from the coupler, the input optical signal is internally coupled to an input coupling waveguide 122 which is different from an output coupling waveguide 121. As the transmitter, the output optical signal Eout that is outputted is propagated in a direction outside of an x-y plane (namely, a propagation direction of Eout has a z component other than zero), and polarized together with polarization that is determined by a design of the coupler, and as the receiver, the input optical signal Ein is coupled to the coherent sensing unit.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] [Related applications] This application claims priority to U.S. Provisional Application No. 63 / 147,733, filed on 9 February 2021, the entire contents of which are incorporated herein by reference for all purposes. [Statement concerning research or development sponsored by the federal government] This invention was made possible with the support of the U.S. Government under grant number 2015160 from the National Science Foundation. The U.S. Government reserves certain rights to this invention. [Technical field] The present invention relates to an optical coherent imager having a common input / output path and a method for sensing coherent light. More specifically, the present invention relates to an optical integrated circuit having a shared input / output path based on polarization diversity and a method for sensing coherent light. [Background technology]

[0002] An optical coherent imager is an active imaging system that includes an array of photodetectors (referred to herein as “sensors”) and a light source (typically a coherent light source such as a laser). The light source not only serves the purpose of illuminating the target but also provides a local oscillator (LO) for optical coherent detection (also known as “optical heterodyne detection”). Such optical coherent imagers can be used in applications such as 3D frequency-modulated continuous wave (FMCW) LiDAR and optical coherence tomography (OCT). The illumination light reflected (or scattered) by the target and received by the imager is referred here as the received optical target signal, or simply the target signal.

[0003] Conventionally, to perform optical coherent detection, optical coherent imagers operate by coherently coupling the LO in free space with the target signal using bulk optics before detection is performed by the imager's sensor. In contrast, optical coherent imagers with a detection sensor based on photonic integrated circuit (PIC) technology allow the mixing of the LO and the target signal on a photonic chip (also referred to herein as the “PIC chip”). More specifically, a PIC-based sensor comprises an array of coherent sensing units that act as the active sensing pixels in a conventional detection array such as a CCD or CMOS image sensor. Instead of performing optical detection directly at the pixels as in a conventional detection array, the coherent sensing units of a PIC-based sensor couple the target signal from free space to multiple waveguides on the PIC chip via waveguide couplers. The target signal, appearing as a waveguide mode within the waveguides, can be manipulated and processed using various photonic components implemented on the PIC chip. This includes coherent mixing with the LO using a 2x2 optical coupler and detection by a photodetector. Here, the LO (low-energy light) can appear as a waveguide mode by introducing the LO light to the PIC chip via a coupler. Recent developments in monolithic and heterogeneous integration of lasers on PIC chips may even allow the light source to be integrated onto the same PIC chip as a PIC-based sensor.

[0004] For target illumination, active imagers generally employ two approaches: (1) full-field illumination and (2) finite-field illumination using a scanning beam.

[0005] In full-field illumination, the target scene is filled with illumination light, and the entire instantaneous field of view (FOV) of the sensor receives light signals reflected or scattered from the scene. Advantages of the full-field approach include high frame rates and simplified data post-processing output formats, as the sensor can acquire images like a conventional camera. A significant drawback of the full-field approach is that the illumination laser power is spread over a wide area, resulting in fewer photons reflected or scattered by each sensing unit of the imager sensor. Consequently, the full-field approach requires high sensitivity in the imager sensor, often necessitating the use of expensive materials unusual in sensor manufacturing. Furthermore, the full-field approach may limit the active imager to being operated at distances constrained by the maximum illumination laser power, due to practical factors such as eye safety.

[0006] In finite-field illumination using a scanning beam, the target scene is scanned by the illumination laser beam by manipulating the laser beam using some kind of scanning mechanism. At each scan position, only a finite FOV of the imager sensor receives the target signal. This finite FOV depends on the spot size of the illumination laser beam and the imaging optics of the imager. Because the FOV used in the finite-field illumination approach is small, the laser power is concentrated in a smaller area, resulting in more photons being received by the imager sensor at the corresponding FOV. Therefore, the finite-field illumination approach can typically operate an active imager over longer distances than the full-field illumination approach given the same illumination laser power.

[0007] For optical coherent imagers operating with a finite-field illumination approach using PIC-based sensors, it is desirable to implement the beam scanning mechanism on the same PIC chip as the sensor to reduce the manufacturing cost of the imager. Common beam scanning mechanisms that can be implemented on a PIC chip include optical phased arrays (OPAs). Nevertheless, the photonic component for the beam scanning mechanism (referred to here as the "transmitter") is typically implemented in an area of ​​the PIC chip separate from the detection area, which includes the free-space versus waveguide coupler of the PIC-based sensor (referred to here as the "receiver"). Such separation may require separate optical systems for the transmitter and receiver to direct the illumination beams to the target and maximize the coupling of the target signal to the receiver.

[0008] In optical coherent imagers utilizing finite-field illumination, it is sometimes desirable for the transmitter and receiver to share the same optical system for illuminating the target and receiving the target signal, respectively. More preferably, the optical paths of the output probe beam and the incident target signal are the same. Advantages of such input / output path-sharing imagers include a simplified optical system and simplified calibration between the transmitter and receiver. More specifically, a simplified optical system can lead to more efficient use of laser power by allowing the imager to supply LO light only to the coherent sensing unit that receives the signal from the target during the beam scanning process.

[0009] [References] 1. Lawrence C. Gunn, III, Thierry J. Pinguet, Maxime J. Rattier, and Jeremy Witzens, "POLARIZATION SPLITTING GRATING COUPLERS," U.S. Patent Application No. 7,006,732 B2, filed December 12, 2003. 2. Bing Shen, Peng Wang, Randy Polson, and Rajesh Menon, "Integrated metamaterials for efficient and compact free-space and waveguide coupling," Optics Express, Vol. 22, pp. 27175–27182 (2014). 3. Xia Chen and Hon K. Tsang, "Polarization-Independent Lattice Coupler for Silicon-on-Insulator Nanophotonic Waveguides," Optics Letters, Vol. 36, No. 6, pp. 796-798 (2011). 4. Junming Zhao, Lianhong Zhang, Jensen Li, Yijun Feng, Any Dyke, Sajad Haq, Yang Hao, "Wide-angle multi-octave broadband waveplate based on a field conversion approach," Scientific Reports, 5, 17532 (2015). 5. Paolo Pintus, Duanni Huang, Paul Adrian Morton, Yuya Shoji, Tetsuya Mizumoto, John E. Bowers, "Broadband TE Optical Isolators and Circulators in Silicon Photonics via Ce:YIG Coupling," Journal of Lightwave Technology, Vol.37, No.5, p.1463 (2019). [Overview of the project] [Problems that the invention aims to solve]

[0010] This disclosure provides an optical coherent imager implemented on an optical integrated circuit (PIC) that enables a shared path for transmitting and receiving optical signals by utilizing polarization diversity. The disclosure also provides an optical coherent imager including an array of optical coherent sensing units for simplifying the design and calibration of the imager, and a method for coherent sensing by the optical coherent imager. [Means for solving the problem]

[0011] In one embodiment, the present disclosure provides an optical coherent sensor comprising a plurality of coherent sensing units and polarization converters disposed on the coherent sensing units. Each coherent sensing unit includes a polarization-diversifying optical coupler capable of directing an optical signal having a first polarization state between free space and a first waveguide and a optical signal having a second polarization state between free space and the first waveguide, one or more 2x2 optical couplers optically coupled to the polarization-diversifying optical coupler via at least one of the first and second waveguides, and one or more photodetectors optically coupled to the 2x2 optical couplers.

[0012] In one embodiment, the polarization-diversifying optical coupler comprises a first subcoupler and a second subcoupler.

[0013] In one embodiment, one of the first and second subcouplers is polarization-dependent, which optimally couples with an optical signal in a predetermined polarization state, and the other of the first and second subcouplers is polarization-independent, which optimally couples with an optical signal in any polarization state.

[0014] In one embodiment, the second subcoupler is positioned on the first subcoupler and is vertically separated from the first subcoupler.

[0015] In one embodiment, the first and second subcouplers are arranged on a photonic substrate and are separated from each other laterally.

[0016] In one embodiment, the polarization converter guides an output optical signal from one of the first and second subcouplers into an optical path in free space, separates the input optical signal from the optical path into a first optical signal having a first polarization state and a second optical signal having a second polarization state, and one or both of the first and second optical signals are spatially displaced by the polarization converter so that the first and second optical signals are incident on the first and second subcouplers, respectively.

[0017] In one embodiment, the polarization converter comprises at least one polarization-dependent beam separator.

[0018] In one embodiment, the polarization converter comprises one or more polarization converters that rotate a linearly polarized optical signal by a predetermined angle.

[0019] In one embodiment, at least one of the polarization converters is a Faraday rotator.

[0020] In one embodiment, the polarization converter comprises one or more quarter-wave plates.

[0021] In one embodiment, the polarization-diversifying optical coupler further comprises a third subcoupler. In one embodiment, the first, second, and third subcouplers are arranged on a photonic substrate and are separated from each other laterally.

[0022] In one embodiment, the polarization converter guides the optical signal output from one of the first, second, and third subcouplers into an optical path in free space, separates the input optical signal from the optical path into a first optical signal having a first polarization state and a second optical signal having a second polarization state, and one or both of the first and second optical signals are spatially displaced by the polarization converter so that the first and second optical signals are incident on two of the first, second, and third subcouplers, respectively.

[0023] In one embodiment, the polarization-diversifying optical coupler further comprises a fourth subcoupler.

[0024] In one embodiment, the polarization converter guides the output optical signal from two of the first, second, third, and fourth subcouplers into an optical path in free space, and separates the input optical signal from the optical path into a first optical signal having a first polarization state and a second optical signal having a second polarization state. One or both of the first and second optical signals are spatially displaced by the polarization converter so that they are incident on two of the first, second, third, and fourth subcouplers, respectively.

[0025] In another embodiment, the disclosure provides an optical coherent imager comprising the optical coherent sensor described above and an imaging optical system including a plurality of lenses. The imaging optical system is arranged such that the optical coherent sensor is positioned in close proximity to the image plane of the imaging optical system.

[0026] In yet another embodiment, the disclosure includes the steps of emitting one or more output optical signals from an optical coherent imager to one or more targets along one or more optical paths corresponding to one or more field of view positions of the optical coherent imager, The steps include receiving one or more input optical signals reflected from a target illuminated by an output optical signal using an optical coherent imager along the optical path, The steps include: using a polarization converter of an optical coherent imager to convert each input optical signal into a first optical component having a first polarization state and a second optical component having a second polarization state orthogonal to the first polarization state; The steps of guiding the first and second optical components of an input optical signal to one or more photodetectors of an optical coherent sensor of an optical coherent imager by one or more polarization-diversifying optical couplers on the optical coherent sensor, The steps include: guiding the first and second optical components of the input optical signal to one or more photodetectors of the optical coherent sensor by one or more polarization-diversifying optical couplers on the optical coherent sensor of the optical coherent imager in order to determine target information at each field of view by performing heterodyne detection by local emission at each field of view of the optical coherent imager; This provides a method for optical coherent imaging, including [specific technology / method].

[0027] In one embodiment, emitting an output optical signal includes the steps of generating one or more source optical signals from a light source, converting the source optical signals into individual output optical signals having a first radiated polarization state using a polarization-diversifying optical coupler, and emitting the output optical signals from the polarization-diversifying optical coupler.

[0028] In one embodiment, after outputting an output optical signal from a polarization-diversifying optical coupler, the method further includes the step of converting each of the output optical signals from a first output polarization state to a second output polarization state using a polarization converter of an optical coherent imager.

[0029] In one embodiment, converting an input optical signal involves rotating each first polarization state of the input optical signal by a first predetermined polarization angle, and rotating each second polarization state of the input optical signal by a second predetermined polarization angle.

[0030] In one embodiment, transforming an input optical signal involves spatially displacing at least one of the first and second components of the input optical signal according to first and second polarization states, so that the first and second components are incident on the first and second subcouplers of the polarization-diversifying optical coupler, respectively. [Brief explanation of the drawing]

[0031] Those skilled in the art will understand that the drawings are primarily illustrative and not intended to limit the scope of the disclosed subject matter. The drawings are not necessarily to scale. In some cases, different aspects of the disclosed subject matter may be shown in the drawings in an exaggerated or enlarged manner to facilitate the understanding of different features. [Figure 1A] This is a plan view showing a coherent sensing unit for transmitting and receiving optical signals based on polarization diversity according to one embodiment of the present disclosure. [Figure 1B] A perspective view showing a polarization-diversified free-space versus waveguide coupler according to one embodiment of the present disclosure. [Figure 2] This is a perspective view showing a polarization-diversified free-space paired waveguide coupler according to another embodiment of the present disclosure. [Figure 3] This is a perspective view showing a polarization-diversified free-space paired waveguide coupler according to a further embodiment of the present disclosure. [Figure 4A] This is a side view showing a polarization separation configuration for internally coupling optical signals according to one embodiment of the present disclosure. [Figure 4B] Figure 4A is a side view showing a polarization separation configuration for output coupling of optical signals. [Figure 4C] This is a side view showing the polarization separation configuration of Figure 4A for input coupling and output coupling of optical signals. [Figure 5A] This is a perspective view showing a polarization conversion configuration realized by the Faraday effect according to one embodiment of the present disclosure. [Figure 5B] This is a top view showing the polarization state of the optical signal in Figure 5A. [Figure 5C] This is a side view showing a polarization conversion and separation configuration incorporating the polarization conversion configuration of Figure 5A and the polarization separation configuration of Figure 4C according to one embodiment of the present disclosure. [Figure 6A] This is a perspective view showing a polarization conversion configuration realized by a quarter-wave plate according to another embodiment of the present disclosure. [Figure 6B] This is a top view showing the polarization state of the optical signal in Figure 6A. [Figure 6C] This is a side view showing a polarization conversion and separation configuration incorporating the polarization conversion configuration of Figure 6A and the polarization separation configuration of Figure 4C according to another embodiment of the present disclosure. [Figure 7A] This is a plan view showing a coherent sensing unit for transmitting and receiving optical signals based on polarization diversity according to another embodiment of the present disclosure. [Figure 7B] This is a plan view showing a coherent sensing unit for transmitting and receiving optical signals based on polarization diversity according to yet another embodiment of the present disclosure. [Figure 8] This is a plan view showing a coherent sensing unit for transmitting and receiving optical signals based on polarization diversity according to a further embodiment of the present disclosure. [Figure 9] This is a plan view showing a coherent sensing unit for transmitting and receiving optical signals based on polarization diversity according to yet another embodiment of the present disclosure. [Figure 10A] This is a top view showing three waveguide polarization diversification free-space versus waveguide couplers according to one embodiment of the present disclosure. [Figure 10B]Figure 10A is a perspective view showing the coupler. [Figure 10C] This is a side view showing a polarization conversion separation configuration for use with three waveguide polarization diversification free-space versus waveguide couplers for coupling optical signals according to one embodiment of the present disclosure. [Figure 10D] This is a side view showing the configuration shown in Figure 10C, which is used for internal coupling of optical signals. [Figure 10E] Figure 10C is a top view showing the polarization state of the optical signal. [Figure 10F] Figure 10D is a top view showing the polarization state of the optical signal. [Figure 11A] This is a perspective view showing three waveguide polarization diversification free-space versus waveguide couplers according to another embodiment of the present disclosure. [Figure 11B] This is a side view showing a polarization conversion separation configuration for use with three waveguide polarization diversification free-space versus waveguide couplers for coupling optical signals according to another embodiment of the present disclosure. [Figure 11C] This is a side view of the configuration shown in Figure 11B, which is used for internal coupling of optical signals. [Figure 11D] Figure 11B is a top view showing the polarization state of the optical signal. [Figure 11E] Figure 11C is a top view showing the polarization state of the optical signal. [Figure 12A] This is a side view showing a polarization conversion separation configuration for use with three waveguide polarization diversification free-space versus waveguide couplers for coupling optical signals according to further embodiments of the present disclosure. [Figure 12B] This is a side view showing the configuration shown in Figure 12A, which is used for internal coupling of optical signals. [Figure 12C] Figure 12A is a top view showing the polarization state of the optical signal. [Figure 12D] Figure 12B is a top view showing the polarization state of the optical signal. [Figure 13A] This is a top view showing three waveguide polarization diversification free-space versus waveguide couplers according to further embodiments of the present disclosure. [Figure 13B]Figure 13A is a perspective view showing the coupler. [Figure 13C] This is a side view showing a polarization conversion separation configuration for use with three waveguide polarization diversification free-space versus waveguide couplers for coupling optical signals according to further embodiments of the present disclosure. [Figure 13D] This is another side view of the configuration shown in Figure 13C. [Figure 13E] This is a side view showing a configuration as shown in Figure 13C, which is used for internal coupling of optical signals. [Figure 13F] This is another side view of the configuration shown in Figure 13E. [Figure 13G] Figures 13C and 13D are top views showing the polarization state of the optical signal and its path position on the xy-plane. [Figure 13H] Figures 13E and 13F are top views showing the polarization state of the optical signal and its path position on the xy plane. [Figure 14] The plan view of a coherent sensing unit for transmitting and receiving optical signals based on polarization diversity according to one embodiment of the present disclosure is shown, wherein the polarization of the transmitted optical signal is adjustable. [Figure 15A] This is a top view showing four waveguide polarization diversification free-space versus waveguide couplers according to one embodiment of the present disclosure. [Figure 15B] Figure 15A is a perspective view showing the coupler. [Figure 15C] This is a side view showing a polarization conversion separation configuration for use with four waveguide polarization diversification free-space versus waveguide couplers for coupling optical signals according to one embodiment of the present disclosure. [Figure 15D] This is another side view showing the configuration shown in Figure 15C. [Figure 15E] Figures 15C and 15D are top views showing the polarization state of the optical signal and its path position on the xy-plane. [Figure 15F] This is a side view showing a configuration as shown in Figure 15C, which is used for internal coupling of optical signals. [Figure 15G] This is another side view showing the configuration shown in Figure 15F. [Figure 15H] Figures 15F and 15G are top views showing the polarization state and path position of the optical signal on the xy plane. [Figure 16A] This is a top view showing four waveguide polarization diversification free-space versus waveguide couplers according to another embodiment of the present disclosure. [Figure 16B] Figure 16A is a perspective view showing the coupler. [Figure 16C] This is a side view showing a polarization conversion separation configuration for use with a four waveguide polarization diversification free-space versus waveguide coupler for coupling optical signals according to another embodiment of the present disclosure. [Figure 16D] This is a side view showing the configuration shown in Figure 16C, which is used for internal coupling of optical signals. [Figure 16E] Figure 16C is a top view showing the polarization state of the optical signal. [Figure 16F] Figure 16D is a top view showing the polarization state of the optical signal. [Figure 17A] This is a perspective view showing four waveguide polarization diversification free-space versus waveguide couplers according to further embodiments of the present disclosure. [Figure 17B] This is a side view showing a polarization conversion separation configuration for use with four waveguide polarization diversification free-space versus waveguide couplers for coupling optical signals according to further embodiments of the present disclosure. [Figure 17C] This is a side view showing the configuration shown in Figure 17B, which is used for internal coupling of optical signals. [Figure 17D] Figure 17B is a top view showing the polarization state of the optical signal. [Figure 17E] Figure 17C is a top view showing the polarization state of the optical signal. [Figure 18A] This is a plan view showing a coherent optical sensor according to one embodiment of the present disclosure. [Figure 18B] This figure shows a row of coherent sensing units in a coherent sensing array according to one embodiment of the present disclosure. [Figure 19A] This is a plan view showing a coherent optical sensor according to another embodiment of the present disclosure. [Figure 19B] This is a plan view showing a coherent sensing unit group according to one embodiment of the present disclosure. [Figure 20A] A plan view of a coherent optical sensor according to a further embodiment of the present disclosure is shown. [Figure 20B] This is a plan view showing a coherent sensing unit group according to another embodiment of the present disclosure. [Figure 20C] This is a plan view showing a Mach-Zehnder interferometer-based optical switch according to one embodiment of the present disclosure. [Figure 21A] This is a side view showing an optical coherent imager according to one embodiment of the present disclosure. [Figure 21B] This is an enlarged view of the imaging device shown in Figure 21A, near the final image plane. [Figure 21C] Figure 21B shows polarization maps of examples of normal and extraordinary rays on the final image plane across the field of view of an optical coherent imager. [Figure 22A] This is a side view showing an optical coherent imager according to another embodiment of the present disclosure. [Figure 22B] This is a side view showing a ray propagating through a polarization-dependent beam separator that causes angular displacement and a ray propagating through a polarization-dependent beam separator that causes lateral displacement according to an embodiment of the present disclosure. [Figure 23] This flowchart shows a method for optical coherent imaging using polarization diversification that enables a shared path for transmitting and receiving optical signals, according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0032] The following detailed description includes systems, methods, techniques, and instruction sequences illustrating embodiments of the present disclosure. The following description includes many specific details to provide an understanding of various embodiments of the subject matter of the invention for illustrative purposes. However, it will be apparent to those skilled in the art that embodiments of the subject matter of the invention can be implemented with or without these specific details. Generally, instruction instances, protocols, structures, and techniques well known to those skilled in the art are not necessarily described in detail.

[0033] Figure 1A is a plan view showing a coherent sensing unit 100 for transmitting and receiving optical signals based on polarization diversity according to one embodiment of the present disclosure. Multiple coherent sensing units 100 can be used to form a coherent sensor array of an optical coherent imager. Figure 1B is a perspective view showing a polarization wave diversification free-space pair waveguide coupler 101 of the coherent sensing unit 100 according to one embodiment of the present disclosure. The coherent sensing unit 100 may be mounted on a photonic substrate using photonic integrated circuit (PIC) technology. The surface of the photonic substrate can be represented by a plane extending along the x and y axes of the coordinate system shown in Figures 1A and 1B. The photonic components of the coherent sensing unit 100 mounted on the photonic substrate may or may not be covered by cladding. Such components may or may not be embedded in the cladding. For simplicity, the photonic substrate and cladding are not shown in Figures 1A and 1B, and are not shown in other figures of the present disclosure. Furthermore, in the following description of this disclosure, the target detected by the optical coherent imager is assumed to be located along the positive z-direction, away from the substrate surface and, where applicable, any optical components on the substrate surface. For simplicity, the target is not explicitly shown in the drawings.

[0034] The photonic waveguides on the PIC chip have various common designs such as ridge waveguides, rib waveguides, embedded waveguides, slot waveguides, etc., but are not limited thereto. According to some embodiments, the waveguide of the coherent sensing unit 100 of the present disclosure is manufactured with dimensions along the z direction that are smaller than the dimensions on the x - y plane according to the coordinate system of the embodiments shown in FIGS. 1A and 1B, and is made to support various waveguide modes including transverse electric (TE) mode, transverse magnetic (TM) mode, TE and TM modes, but is not limited thereto. Here, the TE mode may refer to a waveguide mode having a dominant electric field component transverse to the propagation direction of the mode and the surface of the photonic substrate where the waveguide exists, while the TM mode may refer to a waveguide mode having a dominant magnetic field component transverse to the propagation direction of the mode and the surface of the photonic substrate where the waveguide exists. Those skilled in the art should be familiar with such common designs of waveguides and the various modes supported by these waveguides.

[0035] As shown in FIG. 1A, the light source signal E S may be supplied to the coherent sensing unit 100 through the waveguide 121. On the other hand, the local oscillator (LO) E LO may be supplied to the coherent sensing unit 100 through the waveguide 123. The light source signal E S and the LO E LO may or may not come from the same light source. Here, the light source may or may not be mounted on the same PIC chip with the coherent sensing unit 100. According to some embodiments, through an appropriate design of a system and method for coupling the light source (or light sources) that generates the light source signals E S and E LO in the waveguide of the PIC chip with the coherent sensing unit 100, the light source signal E S can be made to appear as a fundamental TE mode in the waveguide 121, L O E LOThis can be made to appear as a fundamental TE mode within waveguide 123. Such designs are well known to those skilled in the art. According to another embodiment, the light source signal E S This can be intentionally made to appear as a TM mode or TE mode other than the basic TE mode within the waveguide 121. Similarly, according to some embodiments, LO E LO This can be intentionally made to appear as a TM mode or TE mode other than the fundamental TE mode within waveguide 123.

[0036] As shown in Figure 1A, the polarization-diversified free-space paired waveguide coupler 101 (hereinafter referred to as "coupler 101" for simplicity) may function as both a transmitter and a receiver. It is a pair of waveguide couplers connected to waveguides 121 and 122, where the main role of waveguide 121 is to guide signal light to coupler 101, and the main role of waveguide 122 is to receive internally coupled light from coupler 101. However, according to some embodiments, the internally coupled light from coupler 101 can also be directed to waveguide 121. Therefore, with respect to coupler 101, waveguide 121 may be considered an output coupled waveguide, and waveguide 122 may be considered an input coupled waveguide. A notable feature of the polarization-diversified free-space versus waveguide coupler 101 is the input optical signal arriving at the coupler 101 (E in Figure 1A). in The polarization state of the output optical signal (E in Figure 1A) output from the coupler 101 is determined by the polarization state of the output optical signal (E in Figure 1A). out When orthogonal to the polarization state of the light, the input optical signal is internally coupled and directed to an input coupled waveguide (waveguide 122 in Figure 1A) that is different from the output coupled waveguide (waveguide 121 in Figure 1A). Hereafter, free space may refer to a vacuum, air, a region on the surface of the coupler, or any homogeneous medium with a boundary that has a length scale much longer than the wavelength of the optical signal propagating through it (e.g., at least 10 times).

[0037] As a transmitter, the coupler 101 receives the light source signal E from the waveguide 121. S output optical signal E outIt can be coupled in free space and used for target illumination by an optical coherent imager. The output optical signal E output by the coupler 101 out It propagates in directions outside the xy-plane (i.e., E out The propagation direction of the polarization (having a z component other than zero) is polarized with polarization determined by the design of the coupler 101. According to some embodiments, the polarization may be one of a pair of orthogonal linear polarizations according to a coordinate system defined by the design of the coupler 101. Here, the coordinate system may be the same as or different from the coordinate system defined by the x, y, and z axes shown in Figures 1A and 1B. According to other embodiments, the polarization may be one of a pair of orthogonal polarizations other than a pair of linear polarizations, such as right circular polarization and left circular polarization, and two orthogonal elliptical polarizations.

[0038] As a receiver, the coupler 101 receives the input optical signal E in The input optical signal E can be coupled to the coherent sensing unit 100. in This is essentially an optical signal from the aforementioned target (or target signal). The input optical signal E is coupled by the coupler 101. in The input optical signal E in Depending on the polarization state, the input optical signal E can be directed towards either or both waveguides 121 and 122. in The polarization component depends on the design of the coupler 101. According to some embodiments, the output optical signal E out Input optical signal E orthogonal to the polarization in The first polarization component is the internally coupled optical signal E in(wg)1 It is preferable that the input optical signal E be guided into waveguide 122. in The input optical signal E orthogonal to the first polarization in The second polarization component is the internally coupled optical signal E in(wg)2 It is preferable that it be guided into waveguide 121. Further details about the two polarization components that are internally coupled in coupler 101 are described below with reference to Figure 1B. Internally coupled optical signal E in(wg)1This is preferably processed by the remaining circuitry of the coherent sensing unit 100. As shown in Figure 1A, the internally coupled optical signal E in(wg)2 The light source signal E S It propagates in the opposite direction to the propagation direction. According to some embodiments, the internally coupled optical signal E in(wg)2 It is preferable that this be left undisturbed without affecting other parts of the PIC chip that comprises the sensing unit 100. According to some embodiments, such as the embodiment shown in Figure 7A, but not limited thereto, the internally coupled optical signal E in(wg)2 This may be handled by several other parts of the PIC chip that include the sensing unit 700.

[0039] In Figure 1A, the coupler 101 is depicted as a single entity, but the coupler 101 may include a single photonic component or multiple photonic components. In some embodiments, the coupler 101 may be realized by a polarization-divided free-space versus waveguide coupler. Examples of polarization-divided free-space versus waveguide couplers include, but are not limited to, the polarization-divided grating couplers described in U.S. Patent No. 7,006,732, “Polarization-Divided Grating Coupler,” and “Integrated Metamaterials for Efficient and Compact Free-Space and Waveguide Coupling,” Optics Express 22, 27175-27182 (2014), which describe metamaterial-based polarization-divided free-space versus waveguide couplers. Other examples of polarization-divided free-space versus waveguide couplers include, but are not limited to, those realized through plasmonic effects, photonic micro / nanostructures, or both. Other embodiments of the coupler 101 are described below with reference to Figures 2 and 3. Furthermore, according to some embodiments, the coupler 101 may comprise one of a TE-TM mode converter, a splitter, and a combiner. In some embodiments, the coupler 101 may comprise a single layer of photonic material. In other embodiments, the coupler 101 may comprise multiple layers of photonic material, the photonic materials of the different layers may be the same or different.

[0040] Referring to Figure 1B, according to some embodiments, the light source signal E propagates toward the coupler 101. S This may appear as a transverse electric (TE) mode within waveguide 121. As an example, the light source signal ES shown in Figure 1B propagates in the negative y direction with a dominant electric field component along the x direction. Next, the coupler 101 couples the light source signal ES into free space to produce an output optical signal E polarized according to the polarization determined by the design of the coupler 101. out This can generate the output optical signal E out The output optical signal E can be linearly polarized along the x-direction in Figure 1B. In some cases, the output optical signal E out It is preferable that the propagation is in a direction perpendicular to the substrate surface. For example, E shown in Figure 1B out It propagates in the z direction. Also, the output optical signal E out In some cases, the signal may propagate in a direction that is not perpendicular to the substrate surface, i.e., at an angle to the substrate surface.

[0041] As shown in Figure 1B, the input optical signal E in This consists of two orthogonal polarization components, namely the first polarization component E in1 and the second polarization component E in2 It may include one or both of the following. Input optical signal E in This is the first polarization component E in1 If it contains only, the second polarization component E in2 It is understood that the amplitude is zero, and vice versa. The coupler 101 controls the first polarization component E in1 The two are internally coupled, and the internally coupled optical signal E in(wg)1 It is preferable that it be designed to be guided into waveguide 122. Here, the first polarization component E in1 The output optical signal E out It is orthogonal to the polarization of the first element. Similarly, the coupler 101 is perpendicular to the second polarization component E in2 The two are internally coupled, and the internally coupled optical signal E in(wg)2 It is preferable that it be designed to be guided into waveguide 121. This is because the light source signal E S It propagates in the opposite direction to the propagation direction. The first polarization component E is internally coupled and guided into waveguide 122. in1The output optical signal E out The second polarization component E is orthogonal to the polarization of the first component, and is internally coupled and guided into waveguide 121. in2 This is the first polarization wave E in1 It is orthogonal to the output optical signal E. out and input optical signal E in Because the second polarization E can propagate along the same or different directions, in2 The output optical signal E out The polarization may be the same as or different (down to the proportionality constant). Input optical signal E coupled to waveguides 121 and 122 in The specific polarization component depends on the design of the coupler 101.

[0042] According to some embodiments, the coupler 101 may be designed to optimally internally couple the optical signal according to a preferred polarization standard called a coupled polarization standard. According to some embodiments, one of the components of the coupled polarization standard is the output optical signal E output by the coupler 101. out The polarization may be the same as that of the other. For example, as shown in Figure 1B, the coupled polarization reference may be a linear polarization reference (e.g., x-polarized and y-polarized). The coupler 101 then processes the input optical signal E in The first linearly polarized component E in1 (For example, polarized along the y-direction) can be internally coupled and guided into waveguide 122. Here, the first linearly polarized component E in1 This is the output optical signal E of linear polarization. out It lies on a plane (e.g., the yz plane) that is orthogonal to the polarization (e.g., the x-direction) and parallel to the first component of the coupled polarization reference (i.e., the y-direction). Similarly, according to the linear polarization reference, the coupler 101 is positioned on the input optical signal E in The second linear polarization component E in2 (For example, along the direction on the xz plane in Figure 1B) can be internally coupled and directed towards waveguide 121. Here, the second linearly polarized component E in2 This is the output optical signal E of linear polarization. out The polarization (i.e., in the x-direction) and the second component of the coupled polarization reference (i.e., in the x-direction) lie on a plane (i.e., the xz plane), and the second polarization E in2is the first polarization E in1 It is orthogonal to this.

[0043] The coupler 101 receives the input optical signal component E from free space. in1 The internally coupled optical signal E is then coupled into the waveguide 122. in(wg)1 This can be produced. According to some embodiments, the internally coupled optical signal E in(wg)1 This can appear as a TE mode within waveguide 122. For example, the internally coupled optical signal E in(wg)1 It propagates in the positive x-direction in Figure 1B, along with the dominant electric field component along the y-direction. Similarly, the coupler 101 receives the input optical signal component E from free space. in2 The internally coupled optical signal E is then coupled into the waveguide 121. in(wg)2 This can be produced. According to some embodiments, the internally coupled optical signal E in(wg)2 This can appear as a TE mode within waveguide 121. For example, the internally coupled optical signal E in(wg)2 It propagates in the positive y-direction in Figure 1B, along with the dominant electric field component along the x-direction.

[0044] In some embodiments, the optical signal E is internally coupled within the waveguide 122. in(wg)1 If present, it may appear as a single waveguide mode. According to some embodiments, the single waveguide mode may be a basic TE mode. According to other embodiments, the single waveguide mode may be a basic TM mode. According to further embodiments, the single waveguide mode may be a mode other than the basic TE mode or the basic TM mode. In other embodiments, the optical signal E is internally coupled within waveguide 122. in(wg)1 If present, it may manifest as a combination of multiple waveguide modes.

[0045] Similarly, in some embodiments, the optical signal E is internally coupled within the waveguide 121. in(wg)2If it exists, it may appear as a single waveguide mode. According to some embodiments, the single waveguide mode may be a fundamental TE mode. According to other embodiments, the single waveguide mode may be a fundamental TM mode. According to further embodiments, the single waveguide mode may be a mode other than the fundamental TE mode or the fundamental TM mode. In other aspects, an optical signal E internally coupled within waveguide 121 in(wg)2 If it exists, it may appear as a combination of multiple waveguide modes.

[0046] The coupler 101 is intended to separate the orthogonally polarized components of an optical signal into two separate waveguides 121 and 122, but it is not uncommon for some embodiments of the coupler 101 to have cross-coupling occur. For example, referring to FIG. 1B, even if the input optical signal E in is linearly polarized along a direction orthogonal to the polarization of E out and is on a plane parallel to the first component of the linear polarization reference (e.g., the input optical signal is E in1 ), in addition to a part of E in guided to waveguide 122, a part of E in other than zero may be guided to waveguide 121. Similarly, in some embodiments, even if the input optical signal E in is linearly polarized along a direction on a plane parallel to the polarization of E out and the second component of the linear polarization reference (e.g., the input optical signal is E in2 ), in addition to a part of E in guided to waveguide 121, a part of E in other than zero may be guided to waveguide 122. Further, in some embodiments, in addition to a part of E out coupled to free space as the output optical signal E by the coupler 101, E S a part of E SA small amount of non-zero polarity may propagate directly to the waveguide 122 via the coupler 101. Such cross-coupling may be considered an imperfection in the design of the coupler 101. According to some embodiments, the coupler 101 is preferably designed to maximize the coupling between each polarization component and their intended waveguide while minimizing cross-coupling.

[0047] According to some embodiments, even in Figure 1B, E out and E in Even if the input optical signal E is drawn at different spatial positions on the surface of the coupler 101, in This is the output optical signal E emitted from the coupler 101. out It is preferable that the coupling to the coupler 101 occurs at the same spatial position on the surface of the coupler 101 as the spatial position of the input optical signal E in This is the output optical signal E emitted from the coupler 101. out It is preferable that the coupling to the coupling 101 occurs at a spatial position on the surface of the coupling 101 that is different from the spatial position of the coupling.

[0048] In some embodiments, the coupler 101 outputs the optical signal E out It radiates into free space, and simultaneously inputs the optical signal E in The output optical signal E can be coupled to the sensing unit 100. In another embodiment, the coupler 101 can output the optical signal E at different time points. out It radiates into free space, and the input optical signal E in It can be coupled to the sensing unit 100. Generally, the optical signal E in and E out The light signal E may propagate along the same direction or along different directions, but in Figure 1B, the light signal E in and E out They are depicted as propagating along different directions.

[0049] Referring back to Figure 1A, component 102 receives the internally coupled optical signal E from waveguide 122. in(wg)1 and LO E from waveguide 123 LOThis is a 2x2 optical coupler that mixes the two signals and splits the mixed signal to direct them to waveguides 124 and 125. Embodiments of the 2x2 optical coupler 102 include, but are not limited to, directional couplers and multimode interferometers (MMIs). The mixing ratio and splitting ratio of the 2x2 optical coupler 102 depend on the design of the coupler 102. In some embodiments, the 2x2 optical coupler 102 may have a splitting ratio of 50 / 50. In other embodiments, the 2x2 optical coupler 102 may have a splitting ratio other than 50 / 50.

[0050] In some embodiments, the internally coupled optical signal E propagates within the waveguide 122. in(wg)1 and LO E propagating within waveguide 123 LO It is preferable that these appear as the same waveguide mode. In other embodiments, the internally coupled optical signal E propagates within the waveguide 122. in(wg)1 and LO E propagating within waveguide 123 LO It is preferable that these appear as different waveguide modes. Internally coupled optical signal E propagating within waveguide 122 in(wg)1 and LO E propagating within waveguide 123 LO When the internally coupled optical signal E propagates within waveguide 122, according to some embodiments, the 2x2 optical coupler 102 may further include one or more mode converters in one or both of its input ports (i.e., waveguides 122 and 123). in(wg)1 and LO E propagating within waveguide 123 LO One or both of these are converted and appear as the same waveguide mode. According to another embodiment, the 2x2 optical coupler 102 does not have to include such a mode converter, and the internally coupled optical signal E propagates within the waveguide 122. in(wg)1 And LO E propagates within waveguide 123, appearing as a different waveguide mode. LO They can still be mixed, divided, and directed.

[0051] In Figure 1A, component 103 is a square-law photodetector (responding to the power of the optical signal proportional to the square of the electric field) that receives and detects an optical signal from waveguide 124. Similarly, in Figure 1A, component 104 is a square-law photodetector that receives and detects an optical signal from waveguide 125. According to some embodiments, the 2x2 optical coupler 102 may be a 50 / 50 2x2 optical coupler, and the coupler 102 may form a balanced optical heterodyne detection device together with photodetectors 103 and 104. According to some embodiments, one of the photodetectors 103 and 104 may be omitted from the coherent sensing unit 100. Here, the remaining other photodetector can form a single-detector optical heterodyne detection device together with coupler 102, which may or may not be a 50 / 50 coupler.

[0052] According to some embodiments, the photodetectors 103 and 104 may appear as a single composite photodetector having two optical inputs connected to waveguides 124 and 125. A coupled photodetector with two optical inputs can measure any one or more of the intensity, sum of intensity, and difference of intensity of the optical signals from the two inputs.

[0053] According to some embodiments, the photodetectors 103 and 104 may be connected to an output electronic circuit comprising any one or more electronic components such as a transimpedance amplifier (TIA), transistors, diodes, resistors, capacitors, and electrical switches, but the electronic components are not limited to these. The output electronic circuit is used to process the electrical outputs of the photodetectors 103 and 104. This output electronic circuit is not shown in Figure 1A.

[0054] In Figure 1A, the coherent sensing unit 100 may include components not explicitly shown, including any one or more electro-optic and thermo-optic components for one or more of the following: phase, amplitude, frequency, wavelength, and time control. The electro-optic and thermo-optic components are not limited to these.

[0055] Figure 2 is a perspective view showing a polarization-diversified free-space versus waveguide coupler 200 according to another embodiment of the present disclosure. The coupler 200 comprises two subcouplers 201 and 202 mounted on different layers of a PIC chip. According to some embodiments, one of the two subcouplers 201 or 202 may be designed to optimally couple an optical signal to a particular polarization state, and the other subcoupler may be designed to optimally couple an optical signal to a corresponding orthogonal polarization state. For example, subcoupler 201 may be designed to optimally couple an input / output optical signal E1 linearly polarized along a particular direction (e.g., along the x-direction). On the other hand, subcoupler 202 may be designed to optimally couple an input / output optical signal E2 linearly polarized along a direction orthogonal to the polarization of E1 (e.g., along the y-direction). Subcouplers 201 and 202 may or may not be aligned to the same xy positions.

[0056] Referring to Figure 2, subcoupler 201 may be, but is not limited to, a free-space pair-waveguide coupler, such as a grid coupler. It may optimally couple with an optical signal E1 polarized according to a certain polarization (e.g., linear polarization along the x-direction) and minimally couple with an optical signal E2 polarized according to a polarization orthogonal to the polarization of E1 (e.g., linear polarization along the y-direction). Similarly, subcoupler 202 may be, but is not limited to, a free-space pair-waveguide coupler, such as a grid coupler. It may optimally couple with an optical signal E2 polarized according to a certain polarization (e.g., linear polarization along the y-direction) and minimally couple with an optical signal E1 polarized according to a polarization orthogonal to the polarization of E2 (e.g., linear polarization along the x-direction). Subcouplers 201 and 202 may or may not be of the same design. Generally, the pair of orthogonal polarized optical signals E1 and E2, which are optimally coupled to one of the subcouplers 201 and 202 and minimally coupled to the other, may be any of a pair of orthogonal linearly polarized, right-circularly polarized and left-circularly polarized signals, or a pair of orthogonal elliptically polarized signals.

[0057] In Figure 2, orthogonal optical signals E1 and E2 are depicted for illustrative purposes at different spatial locations on the surfaces of subcouplers 201 and 202. Generally, subcoupler 201 can be optimally coupled with optical signal E1 and minimally coupled with E2 at the same or different spatial locations on its surface. Similarly, generally, subcoupler 202 can be optimally coupled with optical signal E2 and minimally coupled with E1 at the same or different spatial locations on its surface.

[0058] In Figure 2, optical signals E1 and E2 are depicted propagating along the z-direction, which is perpendicular to the plane of the substrate surface. In general, optical signals E1 and E2 can propagate along directions that are perpendicular to or perpendicular to the plane of the substrate surface. Furthermore, optical signals E1 and E2 may propagate along different directions, but in Figure 2, they are depicted propagating along the same direction.

[0059] In Figure 2, mutual coupling between subcouplers 201 and 202 can be minimized by selecting an appropriate vertical isolation 299 between them. The vertical isolation 299 is preferably formed by placing a photonic material layer (or air gap) with a thickness of 50 nanometers to 5 millimeters between subcouplers 201 and 202. In general, the selection of isolation 299 depends on a combination of various factors. These factors include, but are not limited to, the PIC technology, the manufacturing process, the photonic material used between subcouplers 201 and 202, the wavelength of signal E1, the wavelength of signal E2, the design of subcoupler 201, and the design of subcoupler 202.

[0060] According to some embodiments, the subcoupler 201 may comprise a single layer of photonic material. According to other embodiments, the subcoupler 201 may comprise multiple layers of photonic material, and the photonic materials of the different layers may be the same or different. Similarly, according to some embodiments, the subcoupler 202 may comprise a single layer of photonic material. According to other embodiments, the subcoupler 202 may comprise multiple layers of photonic material, and the photonic materials of the different layers may be the same or different.

[0061] According to some embodiments, for use in the coherent sensing unit 100 of Figure 1A, the subcoupler 201 of Figure 2 may be used as a transmitter, while the subcoupler 202 of Figure 2 may be used as a receiver. Here, the subcoupler 201 as a transmitter is further from the target, and the subcoupler 202 as a receiver is closer to the target. In this situation, the waveguide 221 of Figure 2 may be the same as (or equivalently connected to) the waveguide 121 of Figure 1A as an output coupling waveguide. On the other hand, the waveguide 222 of Figure 2 may be the same as (or equivalently connected to) the waveguide 122 of Figure 1A as an internal coupling waveguide. According to other embodiments, for use in the coherent sensing unit 100 of Figure 1A, the subcoupler 201 of Figure 2 may be used as a receiver, and the subcoupler 202 of Figure 2 may be used as a transmitter. Here, the subcoupler 201 as a receiver is further from the target, and the subcoupler 202 as a transmitter is closer to the target. In this situation, waveguide 221 in Figure 2 may be the same as (or equivalently connected to) waveguide 122 in Figure 1A as an internal coupling waveguide, while waveguide 222 in Figure 2 may be the same as (or equivalently connected to) waveguide 121 in Figure 1A as an output coupling waveguide.

[0062] Figure 3 is a perspective view showing a polarization-diversified free-space versus waveguide coupler 300 according to a further embodiment of the present disclosure. The coupler 300 comprises two subcouplers 301 and 302, which are implemented as two separate couplers on the same layer of the PIC chip. According to some embodiments, one of the two subcouplers may be designed to optimally couple with an optical signal having one polarization state, and the other subcoupler may be designed to optimally couple with an optical signal having another polarization state. According to some embodiments, the two polarization states may be orthogonal to each other. According to other embodiments, the two polarization states may not be orthogonal to each other. For example, subcoupler 301 may be designed to optimally couple with an optical signal E1 that is linearly polarized along the x-direction, while subcoupler 302 may be designed to optimally couple with an optical signal E2 that is linearly polarized along the y-direction.

[0063] Referring to Figure 3, subcoupler 301 may be a free-space-to-waveguide coupler, such as a grid coupler. The free-space-to-waveguide coupler may optimally couple with an optical signal E1 polarized according to a specific polarization (e.g., linear polarization along the x-direction), or minimally couple with an optical signal having a polarization orthogonal to the polarization of E1 (e.g., linear polarization along the y-direction), but the free-space-to-waveguide coupler is not limited to a grid coupler. Similarly, subcoupler 302 may be a free-space-to-waveguide coupler, such as a grid coupler. The free-space-to-waveguide coupler may optimally couple with an optical signal E2 polarized according to a specific polarization (e.g., linear polarization along the y-direction), or minimally couple with an optical signal having a polarization orthogonal to the polarization of E2 (e.g., linear polarization along the x-direction), but the free-space-to-waveguide coupler is not limited to a grid coupler. Subcouplers 301 and 302 may or may not be of the same design.

[0064] In other embodiments, one of the subcouplers 301 and 302 may be designed to optimally couple with an optical signal having a polarization state, while the other subcoupler may be a polarization-independent free-space paired waveguide coupler designed to optimally couple with an optical signal having any polarization state. An example of a polarization-independent free-space paired waveguide coupler is described in “Polarization-Independent Lattice Coupler for Silicon Nanophotonic Waveguides on Insulators,” Optics Letters Vol. 36, No. 6, p. 796 (2011). Referring to Figure 3, on the one hand, subcoupler 301 may be a free-space paired waveguide coupler such as a lattice coupler. The lattice coupler may optimally couple with an optical signal E1 polarized according to one polarization (e.g., linear polarization along the x-direction), or minimally couple with an optical signal having a polarization orthogonal to the polarization of E1 (e.g., linear polarization along the y-direction). On the other hand, subcoupler 302 may be a polarization-independent free-space paired waveguide coupler that optimally couples with an optical signal E2 having any polarization. Here, the optical signal E2 may or may not be orthogonal to the optical signal E1.

[0065] In Figure 3, cross-coupling between subcouplers 301 and 302 can be minimized by selecting an appropriate lateral separation 399 between the subcouplers. The lateral separation 399 can be formed by placing subcouplers 301 and 302 on the same substrate surface at a distance of 50 nanometers to 5 millimeters. In general, the selection of the lateral separation 399 depends on a combination of factors. These factors include, but are not limited to, PIC technology, manufacturing process, photonic material used as the medium between subcouplers 301 and 302, wavelength of signal E1, wavelength of signal E2, design of coupler 301, and design of coupler 302.

[0066] According to some embodiments, the sub-coupler 301 may include a single layer of photonic material. According to other embodiments, the sub-coupler 301 may include multiple layers of photonic material, and the photonic materials of different layers may be the same or different. Similarly, according to some embodiments, the sub-coupler 302 may include a single layer of photonic material. According to other embodiments, the sub-coupler 302 may include multiple layers of photonic material, and the photonic materials of different layers may be the same or different.

[0067] In FIG. 3, the optical signals E1 and E2 are depicted as propagating along a direction perpendicular to the plane of the substrate surface, i.e., the z-direction. In general, the optical signals E1 and E2 can propagate along a direction that may or may not be perpendicular to the plane of the substrate surface. Further, although the optical signals E1 and E2 may propagate along different directions, the optical signals E1 and E2 are depicted as propagating along the same direction in FIG. 3.

[0068] According to some embodiments, for use in the coherent sensing unit 100 of FIG. 1A, the sub-coupler 301 of FIG. 3 may be used as a transmitter and the sub-coupler 302 of FIG. 3 may be used as a receiver. In such a situation, the waveguide 321 of FIG. 3 may be the same (or equivalently connected) as the waveguide 121 of FIG. 1A as an output coupling waveguide. On the other hand, the waveguide 322 of FIG. 3 may be the same (or equivalently connected) as the waveguide 122 of FIG. 1A as an internal coupling waveguide.

[0069] FIG. 4A is a side view showing a polarization separation configuration for internally coupling optical signals according to an embodiment of the present disclosure. FIG. 4B is a side view showing the polarization separation configuration of FIG. 4A for coupling optical signals. FIG. 4C is a side view showing the polarization separation configuration of FIG. 4A for input coupling and output coupling of optical signals. The polarization separation configurations shown in FIGS. 4A, 4B, and 4C are used together with the polarization diversity free space to waveguide coupler 300 of FIG. 3 to direct optical signal E1 (coupled to sub-coupler 301) and optical signal E2 (coupled to sub-coupler 302) for propagation along a common optical path in free space. Here, the common optical path is between the optical component 401 and the target.

[0070] The polarization separation configuration includes a polarization-dependent beam separator 401, as shown in FIG. 4A. According to some embodiments, the polarization-dependent beam separator 401 may be a birefringent beam displacer. According to some embodiments, the birefringent beam displacer may be made of one or more materials including, but not limited to, calcite crystal, alpha barium borate crystal, yttrium vanadate crystal, or rutile crystal. Birefringent beam displacers are well known in the art. According to other embodiments, the polarization-dependent beam separator 401 may be a polarization-dependent beam separator other than a birefringent beam displacer. Examples include, but are not limited to, birefringent wedges, polarization beam splitters, polarization-dependent diffraction gratings, polarization-dependent metalenses.

[0071] According to some embodiments, the polarization-dependent beam separator 401 may be a component separate from the PIC chip including the polarization diversity free space to waveguide coupler 300 as shown in FIG. 4A. According to other embodiments, the polarization-dependent beam separator 401 may be attached to the surface of the PIC chip including the coupler 300. According to further embodiments, the polarization-dependent beam separator 401 may be within the PIC chip constituting the coupler 300 or may be a part thereof.

[0072] In the case of optical signal reception, according to the embodiment in Figure 4A, the input optical signal E in The beam should reach the polarization-dependent beam separator 401 from the target. The polarization-dependent beam separator 401 receives the input optical signal E in The input optical signal can be split into two optical signals E1 and E2, the polarizations of which are orthogonal to each other. The splitting of the optical signals may depend on the polarization of the input optical signal. One of the optical signals E1 and E2 is the normal ray (o-ray) and the other is the extraordinary ray (e-ray). For example, optical signal E1 may be the o-ray and optical signal E2 may be the e-ray. In addition to the general usage in the case of birefringent beam separators, the terms "o-ray" and "e-ray" used here generally refer to two orthogonal polarization lines split by the polarization-dependent beam separator 401. Here, the splitting is defined by the properties of the polarization-dependent beam separator.

[0073] The polarization of optical signals E1 and E2 depends on the dielectric constant of the material of the polarization-dependent beam separator 401, the orientation of the optical axis 498, and the input optical signal E in It depends on the incident angle of the input optical signal E. in The incident angle is close to the normal to the surface of the polarization-dependent beam separator 401. Therefore, the polarization-dependent beam separator 401 can be manufactured, and the optical axis 498 is preferably oriented such that when output from the polarization-dependent beam separator 401, the o-line (E1) is polarized along the x-direction and the e-line (E2) is polarized along the y-direction.

[0074] According to some embodiments, the o-line and e-line (e.g., optical signals E1 and E2 in Figure 4A) may be displaced laterally upon emergence from the polarization-dependent beam separator 401. The lateral displacement may depend on one or more factors, including the geometry (e.g., shape and thickness), the dielectric constant of the material, and the orientation of the optical axis 498 of the polarization-dependent beam separator 401, as well as the input optical signal E in This includes, but is not limited to, the wavelength and angle of incidence of the input optical signal E. inIn the case of near-perpendicular incidence, line E1 can propagate along the first optical path with a first lateral displacement (for example, as shown in Figure 4A, E1 propagates along the input optical signal E with zero lateral displacement). in (Continue along the path). On the other hand, line E2 receives the input optical signal E, as shown in Figure 4A. in The light may propagate along the second optical path with a second lateral displacement 499 relative to the path. Here, the second optical path of the e-line E2 is different from the first optical path of the o-line E1, and the second lateral displacement of the e-line E2 is different from the first lateral displacement of the o-line E1.

[0075] According to some embodiments, the optical signals E1 and E2 can be incident on the subcouplers 301 and 302 at an angle close to perpendicular incidence, as shown in Figure 4A. According to other embodiments, the optical signals E1 and E2 can be incident on the subcouplers 301 and 302 at an angle other than perpendicular incidence. Input optical signal E in The polarization and propagation direction of the o-line E1 and e-line E2 can be determined by Maxwell's equations, depending on the arbitrary incident angle and the characteristics of the polarization-dependent beam separator 401 (geometric shape, dielectric constant, optical axis orientation, etc.).

[0076] According to some embodiments, the subcoupler 301 may be configured to optimally couple with the o-wire E1 based on its polarization and propagation direction, where the polarization and propagation direction of the o-wire E1 may be predetermined. Similarly, according to some embodiments, the subcoupler 302 may be configured to optimally couple with the e-wire E2 based on its polarization and propagation direction, where the polarization and propagation direction of the e-wire E2 may be predetermined. For example, as shown in Figure 4A, the input optical signal E inThe incident angle may be close to the normal to the surface of the polarization-dependent beam separator 401, and the optical axis 498 may be oriented at an angle on the yz plane. Therefore, subcoupler 301 may be configured to optimally couple with the o-ray E1 propagating along the z direction and polarized along the x direction. On the other hand, subcoupler 302 may be configured to optimally couple with the e-ray E2 propagating along the z direction and polarized along the y direction. The lateral spacing 399 between subcouplers 301 and 302 may be determined by incorporating information about the lateral spacing 499 between the o-ray E1 and the e-ray E2.

[0077] According to other embodiments, subcoupler 301 may not be configured to optimally couple with o-wire E1 based on its polarization. That is, the optimal polarization for coupling with subcoupler 301 may not be the same as the polarization of o-wire E1. Similarly, according to other embodiments, subcoupler 302 may not be configured to optimally couple with e-wire E2 based on its polarization. That is, the optimal polarization for coupling with subcoupler 302 may not be the same as the polarization of e-wire E2. According to further embodiments, subcoupler 301 may not be configured to optimally couple with o-wire E1 based on the propagation direction of o-wire E1. Similarly, according to further embodiments, subcoupler 302 may not be configured to optimally couple with e-wire E2 based on the propagation direction of e-wire E2.

[0078] According to some embodiments, the subcoupler 301 may be a polarization-independent coupler and may be configured to optimally couple with the o-wire E1 based solely on the propagation direction of the o-wire E1. Similarly, according to some embodiments, the subcoupler 302 may be a polarization-independent coupler and may be configured to optimally couple with the e-wire E2 based solely on the propagation direction of the e-wire E2.

[0079] In the case of optical signal transmission, as shown in Figure 4B, the optical signal E1 output from subcoupler 301 may be polarized according to the polarization of the o-line defined by the polarization-dependent beam separator 401 (e.g., linear polarization along the x-direction, as shown in Figure 4B). Similarly, the optical signal E2 exiting subcoupler 302 may be polarized according to the polarization of the e-line defined by the polarization-dependent beam separator 401 (e.g., linear polarization along the y-direction, as shown in Figure 4B). The propagation of optical signals through the polarization-dependent beam separator 401 is reversible. Therefore, after passing through the polarization-dependent beam separator 401, the optical signals E1 and E2 are coupled and propagate along the optical path away from the upper surface of the polarization-dependent beam separator 401 to form the output optical signal E out This can result in (for example, a path that continues the path of optical signal E1 with zero lateral displacement, as shown in Figure 4B). Here, optical signals E1 and E2 are coherent with each other, and the output optical signal E out The light is polarized according to the polarization, amplitude, and relative phase of the optical signals E1 and E2.

[0080] According to some embodiments, the optical signals E1 and E2 output from the polarization-dependent beam separator 401 may not completely overlap spatially. As a result, the output optical signal E out The polarization of the output optical signal E1 and E2 may change spatially. According to some embodiments, the polarization-dependent beam separator 401 and subcouplers 301 and 302 have a spatial overlap between optical signals E1 and E2, and the output optical signal E1 has a dominant polarization state (i.e., greater than 50%). out It would be preferable to configure it so that it can produce [the desired result].

[0081] Polarization-dependent beam separator 401 can be used with coupler 300 to transmit and receive optical signals, and one of subcouplers 301 and 302 transmits the output optical signal E out It can be used to transmit the input optical signal E. On the other hand, the other of subcouplers 301 and 302 receives the input optical signal E. in It can be used to receive the optical signal E. out and Ein The optical signal can propagate along a common optical path between the optical component 401 and the target. As shown in Figure 4C, on the one hand, the optical signal E1 output from the subcoupler 301 is polarized according to the polarization of the o-line defined by the polarization-dependent beam separator 401. After passing through the polarization-dependent beam separator 401, the optical signal E1 is output to the optical signal E out This can generate optical signals E1 and E out The polarization is the same. For example, if the optical signal E1 output from the subcoupler 301 is polarized along the polarization of the o-line of the polarization-dependent beam separator 401 (i.e., linearly polarized along the x-direction), the output optical signal E out The optical signal E1 is output from the polarization-dependent beam separator 401 with the same polarization (i.e., along the x-direction) and can propagate along the optical path away from the polarization-dependent beam separator 401 (for example, a path that continues the path of the optical signal E1 without lateral displacement, as shown in Figure 4C).

[0082] On the other hand, according to some embodiments, the input optical signal E in The output optical signal E is polarized according to the polarization of the e-line defined by the polarization-dependent beam separator 401. out It is preferable for the signal to propagate in the reverse direction along the same optical path. After passing through the polarization-dependent beam separator 401, the input optical signal E in This can generate an optical signal E2 which is coupled to the subcoupler 302, and the optical signal E in The polarization of E2 is the same. For example, as shown in Figure 4C, the input optical signal E, which is linearly polarized along the y-direction, is incident on the upper surface of the polarization-dependent beam separator 401 in a direction perpendicular to the y-direction. in This can produce an optical signal E2 that is linearly polarized along the y-direction and coupled with the subcoupler 302. Here, the optical signal E2 is displaced laterally by the polarization-dependent beam separator 401. As shown in Figure 4C, the output optical signal E out and input optical signal E in The polarizations of the two optical signals E1 and E2 are orthogonal to each other. In one embodiment, the input optical signal E in The polarization of the output optical signal Eout If the polarization is not perpendicular to the input optical signal E in It is preferable that the wire be divided into wire o and wire e. Here, as shown in the embodiment of Figure 4A, wire o can be connected to sub-coupler 301 and wire e can be connected to sub-coupler 302.

[0083] According to some embodiments, the roles of subcouplers 301 and 302 may be interchangeable, and as a result, the output optical signal may be e-line E2 instead of o-line E1 as shown in Figure 4C.

[0084] As shown in Figure 4C, the coupled polarization reference may be formed by a pair of polarizations of optical signals that optimally couple with subcouplers 301 and 302. According to some embodiments, the coupled polarization reference may be the same as the o-line and e-line polarizations corresponding to the polarization-dependent beam separator 401. According to other embodiments, the coupled polarization reference may be different from the o-line and e-line polarizations corresponding to the polarization-dependent beam separator 401.

[0085] According to some embodiments, the difference between the coupled polarization reference and the polarization of the o-line and e-line corresponding to the polarization-dependent beam separator 401 is preferably minimized by a suitable design of the optical coherent imager. Such a suitable design may include optical components (such as one or more lenses) to ensure that the input and output optical signals propagate along a direction that maintains near-perpendicular incidence on the surface of the polarization-dependent beam separator 401. Such a suitable design may also include optical components (such as one or more lenses) to ensure that the input and output optical signals are coupled to the subcouplers 301 and 302 at an incidence angle close to the optimal coupling direction of the subcouplers 301 and 302.

[0086] Referring to Figure 4C, if the coupled polarization reference may differ from the polarization of the o-line and e-line corresponding to the polarization-dependent beam separator 401, the optical signal output-coupled by the coupler 300 can produce two output optical signals emerging from the polarization-dependent beam separator 401. Here, the two output optical signals are the optical signals corresponding to the o-line and e-line. Under these circumstances, the optical signal E1 emitted by the subcoupler 301 is the output optical signal E out The same output line O and output optical signal E out This may result in an output e-line propagating along a different optical path than the optical path (not shown). In the case of an optical coherent imager that uses polarization diversity to enable a shared path for transmitting and receiving optical signals, the output e-line in this situation can be ignored because an input optical signal sharing the same optical path as the output e-line may not be able to be coupled with the internal coupling subcoupler 302, as illustrated in Figure 4C.

[0087] According to some embodiments, either or both of the subcouplers 301 and 302 in Figure 4C may be polarization-independent free-space paired waveguide couplers. Using a polarization-independent free-space paired waveguide coupler, the input optical signal E can be coupled regardless of the polarization of the o-line and e-line corresponding to the polarization-dependent beam separator 401. in It may be possible to optimally combine them.

[0088] In some optical coherent sensing situations, the optical signal reflected by a target may have the same principal polarization component as the optical signal illuminating the target. Such situations include, but are not limited to, specular reflection and reflection of light from a glossy target surface. Therefore, to optimize the received signal, it may be desirable to use a polarization conversion mechanism along with a coherent sensing unit that utilizes polarization diversity in the input and output optical signals.

[0089] FIG. 5A is a perspective view showing a polarization conversion configuration 510 realized by the Faraday effect according to an embodiment of the present disclosure. The polarization conversion configuration 510 is configured to input-couple and output-couple an optical signal with a coupler 101, and includes a Faraday rotator 501 and an optional polarization rotator 502. FIG. 5B is a top view showing the polarization state of the optical signal in FIG. 5A.

[0090] In FIG. 5A, the Faraday rotator 501 is an optical component disposed between the target and the polarization diversity free-space waveguide coupler 101. The Faraday rotator 501 may be configured to rotate a linearly polarized optical signal by a certain angle (e.g., 45 degrees). For example, as shown in FIG. 5A, the coupler 101 can emit an optical signal E1 linearly polarized along the x direction. Next, the Faraday rotator 501 can rotate the polarization of the optical signal E1 by 45 degrees to generate an optical signal E2 linearly polarized along a direction making an angle of 45 degrees with respect to the x direction.

[0091] In FIG. 5A, an optional polarization rotator 502 (referred to as a "polarization rotator" for simplicity in this specification) is disposed between the target and the Faraday rotator 501. Examples of the polarization rotator 502 include, but are not limited to, a quartz rotator. In FIG. 5A, the polarization rotator 502 may be configured to further rotate the polarization of the optical signal E2 by a certain angle. For example, as shown in FIG. 5A, the polarization rotator 502 rotates the polarization of the optical signal E2 linearly polarized along a direction making an angle of 45 degrees with respect to the x direction by 45 degrees to generate an optical signal E3 linearly polarized along the y direction.

[0092] The polarizing rotor 502 is a reciprocal optical component; that is, the polarization rotation by the polarizing rotor 502 is independent of the propagation direction of the optical signal. As shown in Figure 5A, the polarizing rotor 502 can rotate the polarization of an input optical signal E4, which has the same linear polarization as E3, by an angle (e.g., 45 degrees) to produce an optical signal E5 with the same polarization as E2. In contrast, the Faraday rotor 501 is a non-reciprocal optical component. Because the propagation direction of E5 is opposite to that of E2, the Faraday rotor 501 can rotate the polarization of the optical signal E5 by an angle (e.g., 45 degrees) to produce an optical signal E6 that is linearly polarized along a direction perpendicular to the polarization of the optical signal E1 (i.e., the y-direction as shown in Figure 5A). According to some embodiments, the angular rotation brought about by the Faraday rotor 501 may not be affected by the angle of incidence of the optical signal to the Faraday rotor 501, as it is influenced by the length of the propagation path of the optical signal within the Faraday rotor 501. Furthermore, the magnetic field strengths along the propagation path during polarization rotation may mutually compensate for each other. The operating principle of a Faraday rotor is well known to those skilled in the art.

[0093] According to some embodiments, an optional polarizing rotator 502 can be used to convert the polarization of E3 to one of the polarization reference components defined by the coupler 101. As an example, the polarization reference defined by the coupler 101 in Figure 5A is linear polarization along the x and y directions. According to other embodiments, any polarizing rotator 502, which may be a quartz rotator, can be used to enable broadband polarization rotation when used with the Faraday rotator 501. Conventional polarizing rotators, such as quartz rotators, are sensitive to the angle of incidence of the input optical signal. According to some embodiments, the polarizing rotator 502 is preferably a polarizing rotator that can accept the input optical signal over a wide angular range while maintaining the intended phase shift. Examples of such wide-angle polarizing rotors include, but are not limited to, artificial photonic structures designed using a field conversion approach, as described in "Wide-Angle Multi-Octave Broadband Waveplate Based on a Field Conversion Approach," Scientific Reports, 5, 17532 (2015).

[0094] According to some embodiments, the components of the polarization conversion configuration 510 may be shown as separate components, as shown in Figure 5A. According to other embodiments, some or all components of the polarization conversion configuration 510 may appear as a single coupled component. Furthermore, according to some embodiments, the polarization conversion configuration 510 may be a separate optical assembly from the PIC chip comprising the polarization diversification free-space paired waveguide coupler 101, as shown in Figure 5A. According to other embodiments, some or all components of the polarization conversion configuration 510 may be mounted on the surface of the PIC chip comprising the coupler 101. According to further embodiments, some or all components of the polarization conversion configuration 510 may be located within or part of the PIC chip comprising the coupler 101.

[0095] In Figure 5A, for illustrative purposes, the propagation paths of the input coupled optical signals E1, E2, and E3 are depicted separately from those of the output coupled optical signals E4, E5, and E6. Generally, the propagation paths of input coupled signals and output coupled signals may or may not be spatially different. Furthermore, in Figure 5A, for illustrative purposes, the optical signals E1, E2, E3, E4, E5, and E6 are shown propagating along the z-direction and are incident perpendicularly to the coupler 101, Faraday rotator 501, and polarizing rotator 502. Generally, the propagation direction of the optical signals may be perpendicular to these components, or it may be at an angle of incidence other than perpendicular.

[0096] Figure 5C is a side view showing a polarization conversion separation configuration for use with a coupler 300 according to one embodiment of the present disclosure. Here, the polarization conversion configuration 510 of Figure 5A is incorporated into the polarization separation configuration of Figure 4C. As shown in Figure 5C, the polarization-dependent beam separator 401 is positioned between the coupler 300 (including subcouplers 301 and 302) and the polarization conversion configuration 510 (including a Faraday rotor 501 and a polarizing rotor 502). The polarization-dependent beam separator 401 of Figure 5C may be used to allow optical signals coupled to subcouplers 301 and 302 to propagate along a common optical path, where the common optical path lies between the polarization-dependent beam separator 401 and the target. For example, as shown in Figure 5C, the subcoupler 301 can output an optical signal E1 to free space, which is linearly polarized along a direction defined by the subcoupler 301 (e.g., the x-direction in Figure 5C). As shown in Figure 5C, and also referring to Figures 4C and 5A, on the one hand, optical signal E1 can produce an optical signal E3 that is linearly polarized along a direction perpendicular to the direction of E1 (e.g., the y-direction). On the other hand, input optical signal E4 has the same polarization as E3 and propagates along a common optical path with output optical signal E3. However, in the reverse direction, an optical signal E6 that is linearly polarized along a direction perpendicular to the polarization of E1 (i.e., the y-direction) can be produced via the polarization rotor 502, the Faraday rotor 501, and the polarization-dependent beam separator 401. Furthermore, optical signal E6 is spatially separated from the path of E1 so that it can be coupled with the subcoupler 302.

[0097] According to some embodiments, the components of the polarization conversion configuration 510 and the polarization-dependent beam separator 401 may be shown as separate components, as shown in Figure 5C. According to other embodiments, some or all components of the polarization conversion configuration 510 and the polarization-dependent beam separator 401 may appear as a single coupled component. Furthermore, according to some embodiments, the polarization conversion configuration 510 and the polarization-dependent beam separator 401 may be a separate optical assembly from the PIC chip comprising the polarization-diversified free-space paired waveguide coupler 300, as shown in Figure 5C. According to other embodiments, some or all components of the polarization conversion configuration 510 and the polarization-dependent beam separator 401 may be mounted on the surface of the PIC chip including the coupler 300. According to further embodiments, some or all components of the polarization conversion configuration 510 may be mounted on the surface of the PIC chip, and the polarization-dependent beam separator 401 may be located within or as part of the PIC chip constituting the coupler 300.

[0098] In Figure 5C, for illustrative purposes, optical signals E1, E3, E4, and E6 are shown propagating along the z-direction and incident perpendicularly to the coupler 300, polarization-dependent beam separator 401, Faraday rotor 501, and polarization rotor 502. In general, the propagation direction of the optical signals may be perpendicular to these components, or at angles of incidence other than perpendicular.

[0099] Figure 6A is a perspective view showing a polarization conversion configuration realized by a quarter-wave plate 601 according to another embodiment of the present disclosure. In this embodiment, polarization conversion is realized by a phase delay by the quarter-wave plate. In Figure 6A, the quarter-wave plate 601 is an optical component positioned between the target and the polarization diversification free-space paired waveguide coupler 101. The quarter-wave plate 601 may be configured to convert linearly polarized optical signals into circularly polarized optical signals through appropriate orientation of its optical axis. For example, as shown in Figure 6A, the quarter-wave plate 601 can convert an optical signal E1, which is linearly polarized along the x-direction, into an optical signal E2 that is right-circularly polarized with respect to the propagation direction of E2 (the positive z-direction). Figure 6B is a top view showing the polarization state of the optical signal in Figure 6A.

[0100] As shown in Figure 6A, the optical signal E3 has polarization with the same circular rotation direction as the polarization rotation direction of E2, but propagates in the opposite direction to the propagation direction of E2 (i.e., E2 and E3 are effectively opposite-handed). The quarter-wave plate 601 may be used to convert the optical signal E3 to produce an optical signal E4 that is linearly polarized along a direction perpendicular to the polarization of E1. For example, as shown in Figure 6A, the quarter-wave plate 601 converts the optical signal E3, which is left-circularly polarized with respect to the propagation direction (negative z-direction), to an optical signal E4 that is linearly polarized along the y-direction.

[0101] According to some embodiments, the quarter-wave plate 601 may be a separate component from the PIC chip comprising the polarization-diversified free-space paired waveguide coupler 101, as shown in Figure 6A. According to other embodiments, the quarter-wave plate 601 may be mounted on the surface of the PIC chip constituting the coupler 101. According to further embodiments, the quarter-wave plate 601 may be located within or part of the PIC chip constituting the coupler 101.

[0102] In Figure 6A, for illustrative purposes, the propagation paths of the input coupled optical signals E1 and E2 and the propagation paths of the output coupled optical signals E3 and E4 are depicted separately. Generally, the propagation paths of the input coupled signals and the output coupled signals may or may not be spatially different. Furthermore, in Figure 6A, for illustrative purposes, the optical signals E1, E2, E3, and E4 are shown propagating along the z-direction and incident perpendicularly to the coupler 101 and the quarter-wave plate 601. Generally, the propagation direction of the optical signals may be perpendicular to these components, or it may be at an incident angle other than perpendicular.

[0103] Figure 6C is a side view showing a polarization conversion separation configuration for use with a coupler 300 according to another embodiment of the present disclosure, where the polarization conversion configuration of Figure 6A is incorporated into the polarization separation configuration of Figure 4C. As shown in Figure 6C, the polarization-dependent beam separator 401 is positioned between the coupler 300 (including subcouplers 301 and 302) and the quarter-wave plate 601. The polarization-dependent beam separator 401 in Figure 6C may be used to allow optical signals coupled to subcouplers 301 and 302 to propagate along a common optical path, where the common optical path lies between the polarization-dependent beam separator 401 and the target. For example, as shown in Figure 6C, the subcoupler 301 can output an optical signal E1 to free space, which is linearly polarized along a direction defined by the design of the subcoupler 301 (e.g., the x-direction in Figure 6C). As shown in Figure 6C, and also referring to Figures 4C and 6A, on the one hand, optical signal E1 can produce an optical signal E2 that is right-circularly polarized with respect to the propagation direction of E2 (e.g., along the positive z-direction). On the other hand, input optical signal E3 has polarization in the same circular rotation direction as the polarization rotation direction of E2 and propagates along a common optical path with output optical signal E2, except in opposite directions (i.e., E3 is left-circularly polarized with respect to the propagation direction). The input optical signal E3 may pass through a quarter-wave plate 601 and a polarization-dependent beam separator 401 to produce an optical signal E4. Optical signal E4 is linearly polarized along a direction perpendicular to the polarization of E1 (e.g., the y-direction in Figure 6C) and is spatially separated from the path of E1, so that optical signal E4 can be coupled with subcoupler 302.

[0104] According to some embodiments, the quarter-wave plate 601 and the polarization-dependent beam separator 401 may appear as separate components, as shown in Figure 6C. According to other embodiments, the quarter-wave plate 601 and the polarization-dependent beam separator 401 may appear as a single combined component. Furthermore, according to some embodiments, the quarter-wave plate 601 and the polarization-dependent beam separator 401 may be a separate optical assembly from the PIC chip comprising the polarization-diversified free-space paired waveguide coupler 300, as shown in Figure 6C. According to other embodiments, either or both of the quarter-wave plate 601 and the polarization-dependent beam separator 401 may be mounted on the surface of the PIC chip comprising the coupler 300. According to further embodiments, either or both of the quarter-wave plate 601 and the polarization-dependent beam separator 401 may be within or part of the PIC chip constituting the coupler 300.

[0105] In Figure 6C, for illustrative purposes, optical signals E1, E2, E3, and E4 are shown propagating along the z-direction and incident perpendicularly to the coupler 300, the polarization-dependent beam separator 401, and the quarter-wave plate 601. In general, the propagation direction of the optical signals may be perpendicular to these components, or at angles of incidence other than perpendicular.

[0106] In some applications of optical coherent sensing, a target may reflect or scatter the light signal illuminating the target so that the returned light signal has a substantially different polarization from the polarity of the illuminating light signal. To optimize the received signal, it may be desirable for the coherent sensing unit to be able to detect input light signals in all polarization states.

[0107] Figure 7A is a plan view showing a coherent sensing unit 700 for transmitting and receiving optical signals based on polarization diversity, according to another embodiment of the present disclosure. The coherent sensing unit 700 in Figure 7A is similar to the coherent sensing unit 100 in Figure 1A. The main difference between the coherent sensing unit 700 and the coherent sensing unit 100 is that, according to the embodiment of the coherent sensing unit 100 shown in Figure 1A, the coherent sensing unit 700 receives an input optical signal E coupled by a coupler 101 and led to a waveguide 121. in It can also process the components of [the other component].

[0108] More specifically, referring to Figure 7A, the light source signal E S This is supplied to the coherent sensing unit 700 via waveguide 731, and to the local oscillator (LO)E LO The signal is supplied to the coherent sensing unit 700 via waveguide 734. In Figure 7A, component 705 is a 2x2 optical coupler. Since there is no signal input from waveguide 733, the 2x2 optical coupler 705 receives the light source signal E from waveguide 731. S Divide E S It can function as a split coupler that directs a portion of the signal as an optical signal E1 to the polarization-diversifying free-space versus waveguide coupler 701 via waveguide 721. S Some of it may be used for other purposes (for example, as in the coherent sensing unit 710 in Figure 7B), or it may simply be considered a loss. In the latter case, to avoid back reflection, the E passing through waveguide 732 S It may be necessary to properly attenuate some of the E passing through waveguides 721 and 732. S The ratios depend on the division ratio and loss of the 2x2 optical coupler 705, respectively. According to some embodiments, the 2x2 optical coupler 705 may be a 50 / 50 2x2 optical coupler. According to other embodiments, the 2x2 optical coupler 705 may have a division ratio other than 50 / 50.

[0109] In Figure 7A, the polarization-diversifying free-space versus waveguide coupler 701 (referred to here as "coupler 701" for simplicity) is similar to coupler 101 of the coherent sensing unit 100 in Figure 1A, which functions as both a transmitter and a receiver. It is a waveguide coupler connected to waveguides 721 and 722.

[0110] Referring to Figure 7A, the coupler 701 converts the optical signal E1 from the waveguide 721 into an output optical signal E that can be used for target illumination by the optical coherent imager. out It can be coupled in free space as such. Output optical signal E output by coupler 701 out It propagates in directions outside the xy-plane (i.e., E out The propagation direction has a non-zero z component and is polarized with polarization defined by the design of the coupler 701.

[0111] Referring to Figure 7A, the coupler 701 receives the input optical signal E in The input optical signal E can be coupled to the coherent sensing unit 700. The input optical signal E can be coupled by the coupler 701. in The input optical signal E in Depending on the polarization state, the input optical signal E can be directed towards either or both waveguides 721 and 722. in The polarization component depends on the design of the coupler 701. According to some embodiments, the output optical signal E out The polarization and the input optical signal E orthogonal to it in The polarization component of is preferably guided into waveguide 722 as an internally coupled optical signal E2. Input optical signal E guided into waveguide 722 in The polarization component of the input optical signal E is orthogonal to it. inThe polarization component can be guided into waveguide 721 as an internally coupled optical signal E3. The internally coupled optical signal E3 propagates in the opposite direction to the propagation direction of optical signal E1. Since there is no signal input from waveguide 732, the 2x2 optical coupler 705 can function as a split coupler, splitting the internally coupled optical signal E3 from waveguide 721 and guiding a portion of E3 as an optical signal E4 through waveguide 733 to 2x2 optical coupler 712. A portion of E3 passes through waveguide 731 and the light source signal E S It can also propagate in the opposite direction to the propagation direction. According to some embodiments, the components of E3 in waveguide 731 may be left unaffected by the rest of the PIC chip comprising the sensing unit 700. The portions of E3 passing through waveguides 731 and 733, respectively, depend on the division ratio and loss of the 2x2 optical coupler 705.

[0112] In Figure 7A, the coupler 701 is depicted as a single entity, but the coupler 701 can generally comprise a single optical component or multiple optical components. According to some embodiments, the coupler 701 can be realized by a polarization-divided free-space pair waveguide coupler, similar to the coupler 101 shown in Figures 1A and 1B. According to other embodiments, the coupler 701 may be realized by two couplers 200, where waveguides 221 and 222 may be the same as waveguides 721 and 722 (i.e., waveguide 721 is waveguide 221 and waveguide 722 is waveguide 222, or waveguide 721 is waveguide 222 and waveguide 722 is waveguide 221). According to further embodiments, the coupler 701 may be realized by the coupler 300 of Figure 3. Here, waveguides 321 and 322 may be the same as waveguides 721 and 722 (i.e., waveguide 721 is waveguide 321 and waveguide 722 is waveguide 322, or waveguide 721 is waveguide 322 and waveguide 722 is waveguide 321). In yet another embodiment, the coupler 701 is realized by coupler 300, and the polarization-dependent beam separator 401 in Figure 4C is used together with the coherent sensing unit 700, and the output optical signal E out and input optical signal Ein The beams can be allowed to propagate along a common optical path, which lies between the polarization-dependent beam separator 401 and the target. According to some embodiments, the coupler 701 may also comprise a TE-TM mode converter, a splitter, and a combiner, similar to the coupler 101 in Figures 1A and 1B.

[0113] Furthermore, according to some embodiments, the polarization of the output and input optical signals can be rotated by using the Faraday rotor 501 and an optional polarizing rotor 502, as shown in Figures 5A and 5C, together with the coupler 701. According to some embodiments, the quarter-wave plate 601 shown in Figures 6A and 6C may be used with a coupler 701 to convert the output optical signal into a linearly polarized, circularly polarized, or elliptically polarized optical signal, depending on the polarization of the output optical signal.

[0114] In Figure 7A, component 706 separates LO from waveguide 734 and directs a portion of LO to LO E LO ,1 is led to waveguide 723, and a portion of LO is directed to LO E LO ,2 is a split coupler that leads to waveguide 735. The portion of LO passing through waveguides 723 and 735 respectively depends on the split ratio and the loss of split coupler 706. According to some embodiments, split coupler 706 may be a 50 / 50 split coupler. According to other embodiments, split coupler 706 may have a split ratio other than 50 / 50.

[0115] In Figure 7A, component 702 receives the internally coupled optical signal E2 from waveguide 722 and the LO E from waveguide 723. LO It is a 2x2 optical coupler that mixes 1 and 1 and splits the mixed signal and directs it to waveguides 724 and 725. According to some embodiments, the 2x2 optical coupler 702 may be similar to the 2x2 optical coupler 102 of the coherent sensing unit 100 in Figure 1.

[0116] In Figure 7A, component 703 is a square-law photodetector that receives and detects an optical signal from waveguide 724. Similarly, in Figure 7A, component 704 is a square-law photodetector that receives and detects an optical signal from waveguide 725. According to some embodiments, photodetectors 703 and 704 may be similar to photodetectors 103 and 104 of the coherent sensing unit 100 in Figure 1.

[0117] According to some embodiments, the photodetectors 703 and 704 may be connected to an output electronic circuit that includes, but is not limited to, one or more electronic components such as a transimpedance amplifier (TIA), transistors, diodes, resistors, capacitors, and electrical switches. These are used to process the electrical output of the photodetectors 703 and 704. This output electronic circuit is not shown in Figure 7A.

[0118] In Figure 7A, component 712 receives the internally coupled signal E4 from waveguide 733 and the LO E from waveguide 735. LO This is a 2x2 optical coupler that mixes 2 and splits the mixed signal and directs it to waveguides 736 and 737.

[0119] In Figure 7A, component 713 is a square-law photodetector that receives and detects an optical signal from waveguide 736. Similarly, in Figure 7A, component 714 is a square-law photodetector that receives and detects an optical signal from waveguide 737. According to some embodiments, photodetectors 713 and 714 may be the same as photodetectors 703 and 704.

[0120] According to some embodiments, the photodetectors 713 and 714 may be connected to an output electronic circuit comprising, but not limited to, one or more electronic components from among transimpedance amplifiers (TIAs), transistors, diodes, resistors, capacitors, and electrical switches. These are used to process the electrical outputs of the photodetectors 713 and 714. This output electronic circuit is not shown in Figure 7A. According to some embodiments, the output electronic circuit connected to the photodetectors 713 and 714 may form a single electronic circuit together with the output electronic circuit connected to the photodetectors 703 and 704. According to other embodiments, the output electronic circuit connected to the photodetectors 713 and 714 may be separate from the output electronic circuit connected to the photodetectors 703 and 704.

[0121] According to some embodiments, the coherent sensing unit 700 may include components not explicitly shown, including, but not limited to, one or more electro-optical and thermo-optical components for one or more of the phase, amplitude, frequency, wavelength, and temporal control.

[0122] Figure 7B is a plan view showing a coherent sensing unit 710 for transmitting and receiving optical signals based on polarization diversity, according to yet another embodiment of the present disclosure. The coherent sensing unit 710 in Figure 7B is similar to the coherent sensing unit 700 in Figure 7A. The main difference between the coherent sensing unit 700 and the coherent sensing unit 710 is that in the coherent sensing unit 710, LO E LO The light source signal E is passed to waveguide 732. S As a result of this, waveguide 734 is connected to waveguide 732.

[0123] Figure 8 is a plan view showing a coherent sensing unit 800 for transmitting and receiving optical signals based on polarization diversity, according to a further embodiment of the present disclosure. The coherent sensing unit 800 in Figure 8 is similar to the coherent sensing unit 700 in Figure 7A. The main difference between the coherent sensing unit 800 and the coherent sensing unit 700 is that in the coherent sensing unit 800, an optical circulator 805 is used to replace the 2x2 optical coupler 705 of the coherent sensing unit 700 to guide the flow of optical signals. Examples of optical circulators 805 include, but are not limited to, optical circulators based on heterogeneous Ce:YIG / silicon waveguides in a Mach-Zehnder interferometer (MZI) configuration, as described in "Broadband TE Optical Isolators and Circulators in Silicon Photonics Through Ce:YIG Bonding," Journal of Lightwave Technology, Vol. 37, No. 5, p. 1463 (2019).

[0124] According to the embodiment shown in Figure 8, the optical circulator 805 is a 3-port optical circulator that routes optical signals in a circular direction. More specifically, the optical circulator 805 can route optical signals in a clockwise direction. Optical signals input from waveguide 731 are led to waveguide 721, optical signals input from waveguide 721 are led to waveguide 733, and optical signals input from waveguide 733 are led to waveguide 731.

[0125] In Figure 8, the optical circulator 805 is coupled to waveguides 721, 731, and 733. Subsequently, waveguide 732 of the coherent sensing unit 700 in Figure 7 may be omitted from the coherent sensing unit 800 in Figure 8. The optical circulator 805 receives the light source signal E in waveguide 731. SThe optical signal E1 can be generated in waveguide 721 by routing the signal. The internally coupled optical signal E3 received by coupler 701 can be guided through waveguide 721 to optical circulator 805. Here, optical circulator 805 can route the internally coupled optical signal E3 to waveguide 733 to generate optical signal E4.

[0126] According to some embodiments, the optical circulator 805 may be a 4-port optical circulator, such as one implemented by a 4-port MZI-based optical circulator, instead of a 3-port optical circulator. The waveguide 732 of the coherent sensing unit 700 in Figure 7 may be held within the coherent sensing unit 800 in Figure 8. In such a scenario, the 4-port optical circulator may be coupled to waveguides 721, 731, 732, and 733. Here, the 4-port optical circulator routes the optical signal from waveguide 731 to waveguide 721, from waveguide 721 to waveguide 733, from waveguide 733 to waveguide 732, and from waveguide 732 to waveguide 731.

[0127] In Figure 8, using an optical circulator 805 within the coherent sensing unit 800 to replace the 2x2 optical coupler 705 within the coherent sensing unit 700 is ideal for the light source signal E passing through the waveguide 732. S It would be desirable to have the advantage of avoiding some of the losses. Nevertheless, current state-of-the-art on-chip optical circulators have insertion loss (>10dB). This may still be too high to offer any advantage over using the 2x2 optical coupler 705 in the configuration of the coherent sensing unit 700.

[0128] Figure 9 is a plan view showing a coherent sensing unit 900 for transmitting and receiving optical signals based on polarization diversity, according to yet another embodiment of the present disclosure. The coherent sensing unit 900 is similar to the coherent sensing units 700, 710, and 800, which detect input optical signals in any polarization state. The main difference between the coherent sensing unit 900 and the coherent sensing units 100, 700, 710, and 800 is that the coherent sensing unit 900 includes a polarization-diversified free-space paired waveguide coupler that directs an internally coupled optical signal having any polarization state to a waveguide different from the waveguide that carries the output optical signal.

[0129] More specifically, referring to Figure 9, the light source signal E S This is supplied to the coherent sensing unit 900 via waveguide 921, and to the local oscillator (LO)E LO This is supplied to the coherent sensing unit 900 via waveguide 934.

[0130] In Figure 9, the polarization-diversified free-space versus waveguide coupler 901 (referred to as “coupler 901” for simplicity in this specification) is a set of three waveguide couplers connected to waveguides 921, 922, and 933. Coupler 901 can function as both a transmitter and a receiver.

[0131] Referring to Figure 9, the coupler 901 receives the output optical signal E1 (light source signal E) from the waveguide 921. S (essentially the same as) output optical signal E out It can be coupled in free space as such. This can be used for target illumination by an optical coherent imager. The output optical signal E output by the coupler 901 out It propagates in directions outside the xy-plane (i.e., E out The propagation direction has a non-zero z component and is polarized in a polarization state defined by the design of the coupler 901.

[0132] As a receiver, the coupler 901 receives the input optical signal E inThe input optical signal E can be coupled to the coherent sensing unit 900. The input optical signal E can be coupled by the coupler 901. in The input optical signal E in Depending on the polarization state, the input optical signal E can be directed towards either or both waveguides 922 and 933. in The polarization component depends on the design of the coupler 901. According to some embodiments, the output optical signal E out The polarization and the input optical signal E orthogonal to it in The polarization component is preferably guided into waveguide 922 as an internally coupled optical signal E2, and the input optical signal E guided into waveguide 922 in The polarization component of the input optical signal E is orthogonal to it. in The polarization component is preferably guided into waveguide 933 as an internally coupled optical signal E3.

[0133] In Figure 9, the coupler 901 is depicted as a single entity, but the coupler 901 can generally comprise a single optical component or multiple optical components. Embodiments of the coupler 901 are shown in Figures 10A, 11A, and 13A, which are described in more detail below. According to some embodiments, the coupler 901 can also comprise a TE-TM mode converter, a splitter, and a combiner, similar to the coupler 101 in Figures 1A and 1B.

[0134] In Figure 9, the split coupler 906 is LO E LO The waveguide 934 is separated, and a portion of LO is taken to LO E LO ,1 is led to waveguide 923, and a portion of LO is LO E LO The LO is led to waveguide 935 as 2. The portions of LO passing through waveguides 923 and 935, respectively, depend on the splitting ratio and loss of the splitting coupler 906. According to some embodiments, the splitting coupler 906 may be a 50 / 50 splitting coupler. According to other embodiments, the splitting coupler 906 may have a splitting ratio other than 50 / 50.

[0135] In Figure 9, component 902 receives the internally coupled optical signal E2 from waveguide 922 and the LO E from waveguide 923. LO It is a 2x2 optical coupler that mixes 1 and 1 and splits the mixed signal and directs it to waveguides 924 and 925. According to some embodiments, the 2x2 optical coupler 902 may be similar to the 2x2 optical coupler 702 of the coherent sensing unit 700 in Figure 7A.

[0136] In Figure 9, component 903 is a square-law photodetector that receives and detects an optical signal from waveguide 924. Similarly, in Figure 9, component 904 is a square-law photodetector that receives and detects an optical signal from waveguide 925. According to some embodiments, photodetectors 903 and 904 may be similar to photodetectors 703 and 704 of the coherent sensing unit 700 in Figure 7A.

[0137] In Figure 9, similar to the 2x2 optical coupler 712 of the coherent sensing unit 700 in Figure 7A, component 912 receives the internally coupled optical signal E3 from waveguide 933 and the LO E from waveguide 935. LO It is a 2x2 optical coupler that mixes 2 and 2. The mixed signal is then split and led to waveguides 936 and 937.

[0138] In Figure 9, component 913 is a square-law photodetector that receives and detects an optical signal from waveguide 936. Similarly, in Figure 9, component 914 is a square-law photodetector that receives and detects an optical signal from waveguide 937. According to some embodiments, photodetectors 913 and 914 may be similar to the photodetectors 713 and 714 of the coherent sensing unit 700 in Figure 7A.

[0139] Figure 10A is a top view showing three waveguide polarization diversification free-space versus waveguide couplers 1000 according to one embodiment of the present disclosure. Figure 10B is a perspective view showing the coupler 1000 shown in Figure 10A. Figure 10B further shows polarized output and input optical signals E coupled to subcouplers 1001 and 1002. 10 , E 23 , and E 33The coupler 1000 comprises two subcouplers 1001 and 1002, as shown by the dashed lines in Figure 10A. According to some embodiments, subcoupler 1001 may be realized by either a polarization-diversified free-space-to-waveguide coupler 101, as shown in Figure 1B, or a polarization-diversified free-space-to-waveguide coupler 200, as shown in Figure 2. On the other hand, subcoupler 1002 may be realized by a free-space-to-waveguide coupler, including but not limited to a lattice coupler, which is coupled to a single waveguide. According to other embodiments, subcoupler 1002 may be realized by a polarization-independent free-space-to-waveguide coupler.

[0140] Referring to Figure 10A, waveguide 921 is connected to subcoupler 1001 as an output coupling waveguide, and waveguide 922 is connected to subcoupler 1001 as a first input coupling waveguide. Waveguide 933 is connected to subcoupler 1002 as a second internal coupling waveguide. Here, waveguides 921, 922, and 933 are the same as waveguides 921, 922, and 933 of the coherent sensing unit 900 shown in Figure 9.

[0141] As shown in Figures 10A and 10B, one of the main functions of the subcoupler 1001 is to act as a transmitter for output coupling of optical signals for target illumination. The optical signal E1 in waveguide 921 is output by the subcoupler 1001 as optical signal E 10 It is preferable that the output is coupled to free space as shown in Figure 1B, similar to the coupler 101. 10 The optical signal E is polarized according to the design of the subcoupler 1001. For example, as shown in Figure 10B, the optical signal E 10 It is linearly polarized along the x-direction.

[0142] As shown in Figures 10A and 10B, another main function of the subcoupler 1001 is to act as a receiver that inputs and couples the input optical signal to the coherent sensing unit 900. Here, the polarization state of the input optical signal is orthogonal to the polarization of the output optical signal. Output optical signal E 10 An input optical signal E having polarization orthogonal to it.23 The input optical signal E2 is internally coupled by the subcoupler 1001, generating an internally coupled optical signal E2 within the waveguide 922. Similar to the coupler 101 in Figure 1, the input optical signal E2 is optimally input-coupled by the subcoupler 1001. 23 The polarization is determined according to the design of the subcoupler 1001. For example, as shown in Figure 10B, the optical signal E is optimally internally coupled. 23 It is linearly polarized along the y-direction.

[0143] As shown in Figures 10A and 10B, the main function of the subcoupler 1002 is to act as a receiver that inputs and couples the input optical signal to the coherent sensing unit 900. Here, the polarization state of the input optical signal is orthogonal to the polarization of the input optical signal coupled to the waveguide 922 by the subcoupler 1001. Optical signal E 23 An input optical signal E having polarization perpendicular to the polarization of the input optical signal E. 33 The input optical signal E3 is internally coupled by subcoupler 1002, and an internally coupled optical signal E3 is generated in waveguide 933. Similar to subcoupler 1001, the input optical signal E3 is optimally coupled by subcoupler 1002. 33 The polarization is determined according to the design of the subcoupler 1002. For example, as shown in Figure 10B, the optical signal E is optimally internally coupled. 33 It is linearly polarized along the x-direction, and the output optical signal E 10 This is the same as polarization.

[0144] Figure 10C is a side view showing a polarization conversion decoupling configuration 1010 for use with three waveguide polarization diversification free-space versus waveguide couplers for coupling optical signals, according to one embodiment of the present disclosure. Figure 10D is a side view showing the configuration 1010 shown in Figure 10C used for internal coupling of optical signals. The polarization conversion decoupling configuration 1010 receives an input optical signal E arriving at the coupler 1000. 23 and E 33 And the output optical signal E emitted by the coupler 1000 10This allows the light to propagate along a common optical path, which is located between the configuration 1010 and the target. The polarization conversion separation configuration 1010 comprises a Faraday rotator 1051, an optional polarization rotator 1052, and a polarization-dependent beam separator 1041, as shown in Figures 10C and 10D. For illustrative purposes, Figure 10E is a top view showing the polarization state of the optical signal in Figure 10C. Similarly, Figure 10F is a top view showing the polarization state of the optical signal in Figure 10D.

[0145] In the case of optical signal transmission, as shown in Figures 10B and 10C, the subcoupler 1001 of the coupler 1000 outputs and couples the optical signal E1 from the waveguide 921, and the optical signal E 10 This can generate the optical signal E. This is linearly polarized according to the design of the subcoupler 1001 (e.g., linearly polarized along the x-direction) and propagates from the subcoupler 1001 into free space (e.g., towards the positive z-direction). As shown in Figures 10C and 10E, the Faraday rotor 1051 generates the optical signal E. 10 By rotating the polarization of the light by a certain angle (for example, 45 degrees), the optical signal E 11 This can cause E 11 (It is linearly polarized along the direction at an angle of 45 degrees with respect to the x direction). The optional polarization rotor 1052 is similar to the polarization rotor 502 in Figure 5C, and E 11 The polarization of the light signal E is rotated by a certain angle (for example, 45 degrees) 12 It can produce (for example, E 12 (This is linearly polarized along the y-direction). The polarization-dependent beam separator 1041 is similar to the polarization-dependent beam separator 401 in Figure 4C, and the optical signal E (which may appear as an o-line depending on the configuration of the polarization-dependent beam separator 1041) 12 and along the intended optical path (for example, without lateral displacement) 12 The optical signal E propagates along the same optical path. 13 It is preferable that it be configured to generate the optical signal E 13 is, E 12It may be polarized with the same polarization (i.e., linearly polarized along the y-direction). Then the optical signal E 13 This can be used for target illumination. Similar to the polarizing rotor 502 in Figures 5A and 5C, according to some embodiments, the function of an optional polarizing rotor 1052 is to allow the optical signal output from the polarization-dependent beam separator 1041 for target illumination to be polarized along the same direction as one of the polarization reference components defined by the coupler 1000. (For example, the optical signal E in the embodiment of Figure 10C) 10 (Orthogonal to the polarization of the light).

[0146] According to some embodiments, any polarization rotor 1052 in the polarization conversion separation configuration 1010 may be omitted, and as a result, the optical signal E 11 It is preferable that an output optical signal having the same polarization state as the target illumination is used. In such a situation, the polarization-dependent beam separator 1041 uses the optical signal E 11 By aligning the optical axis of the polarization-dependent beam separator 1041 according to the polarization direction, the signal E is optically obtained. 11 This can be output from the polarization-dependent beam separator 1041 as a single optical signal propagating along the intended optical path. (e.g., E without lateral displacement) 11 (Continue the path). According to some embodiments, the polarization-dependent beam separator 1041 receives the optical signal E 11 The subcoupler 1001 is preferably configured such that it can appear as an o-line according to the configuration of the polarization-dependent beam separator 1041.

[0147] In the case of optical signal reception, the input optical signal from the target propagates along the same optical path but in the opposite direction. (See Figure 10C for optical signal E) 13 This is the input optical signal E shown in Figure 10D. 20 and E 30 It is preferable to include one or both of the two input optical signal components having the same polarization as the optical signal E. 20 is the optical signal E 13 Linearly polarized along the same direction as the polarization, the optical signal E 30 is the optical signal E20 It is linearly polarized along the direction perpendicular to the polarization. For example, as shown in Figure 10D, E 20 It is linearly polarized along the y-direction, E 30 It is linearly polarized along the x-direction.

[0148] Referring to Figures 10D and 10F, the input optical signal E 20 The beam passes through the polarization-dependent beam separator 1041, as shown in Figure 10C. 12 An optical signal E having the same polarization (i.e., linear polarization along the y-direction) 21 This can be generated. Here, the optical signal E 21 It is preferable that it appears as an o-line with respect to the polarization-dependent beam separator 1041. Considering the reciprocity of light propagation, the polarization rotor 1052 is E 21 By rotating the polarization of the light signal E in Figure 10C by a certain angle (for example, 45 degrees), 11 A linearly polarized optical signal E along the same direction as the polarization of the light signal E. 22 This can be produced. However, the optical signal E 22 The propagation direction is the optical signal E 11 Because it is opposite to the propagation direction of the optical signal E, the Faraday rotator 1051, which breaks the reciprocity of light propagation, 22 By rotating the polarization of the light by a certain angle (for example, 45 degrees), the optical signal E 23 is the optical signal E 10 It has linear polarization that is orthogonal to the polarization of (i.e., along the y-direction). Next, the optical signal E 23 This can be internally coupled by the subcoupler 1001 to produce an internally coupled optical signal E2 directed towards the waveguide 922, as shown in Figure 10B.

[0149] Referring to Figures 10D and 10F, the optical signal E 30 E is transmitted via the polarization-dependent beam separator 1041. 20 Since it is linearly polarized along the direction perpendicular to the polarization, the optical signal E 30 is the optical signal E 21 It propagates along a spatially different optical path from the optical path of E. 21 Optical signal E having polarization orthogonal to the polarization of 31This can be produced. According to the embodiment in Figure 10D, the input optical signal E 31 The light is linearly polarized along the x-direction, and the optical signal E 21 It propagates along the optical path in the same direction, but is displaced laterally in the negative x-direction. As shown in Figure 10D, the optical signal E 31 It is preferable that it appears as an e-line with respect to the polarization-dependent beam separator 1041. Next, the polarization rotor 1052 is E 31 By rotating the polarization of the light by a certain angle (for example, 45 degrees), the optical signal E 22 A linearly polarized optical signal E along a direction perpendicular to the polarization of the light E. 32 It can generate the optical signal E. The Faraday rotor 1051 generates the optical signal E. 32 By rotating the polarization of the light by a certain angle (for example, 45 degrees), the optical signal E 23 A light signal E having linear polarization perpendicular to the polarization of (i.e., along the x-direction) 33 This can generate the optical signal E 33 These are internally coupled by the subcoupler 1002, which can generate an internally coupled optical signal E3 directed towards the waveguide 933, as shown in Figure 10B.

[0150] According to some of the embodiments described above, the optional polarizing rotor 1052 is omitted, E 11 It is preferable that an optical signal with the same polarization as the one shown in Figure 10C be used for target illumination. Therefore, the optical signal E 11 An input optical signal from a target propagating in the opposite direction along the same optical path can contain one or both of the two input optical signal components having the same polarization. 22 and E 32 This is shown in Figure 10D, where the optical signal E 22 is the optical signal E 11 Linearly polarized along the same direction as the polarization, the optical signal E 32 is the optical signal E 22 The light is linearly polarized along a direction perpendicular to its polarization. In this situation, the optical signal E 11 The polarization-dependent beam separator 1041, configured according to the polarization direction of the optical signal E, 22 In contrast, the optical signal E 22The optical path is the same as E 11 It is possible to create an optical path in the opposite direction to the optical path. On the other hand, the optical signal E 32 The polarizer can propagate along a separate, spatially distinct optical path that is displaced differently from the polarizer rotor 1052. For example, the input optical signal E32 propagates along the optical path in the same direction as the optical signal E22, but is displaced laterally in a direction on the xy plane, not in the negative x direction as shown in Figure 10D. To compensate for the different direction of the lateral displacement, it may be necessary to adjust the position of the subcoupler 1002 on the substrate surface accordingly.

[0151] According to some embodiments, the components of the polarization conversion separation configuration 1010 may be shown as separate components, as shown in Figure 10C. According to other embodiments, some or all components of the polarization conversion separation configuration 1010 may appear as a single coupling component. Furthermore, according to some embodiments, the polarization conversion separation configuration 1010 may be a separate optical assembly from the PIC chip comprising the polarization diversification free-space paired waveguide coupler 1000, as shown in Figure 10C. According to other embodiments, some or all components of the polarization conversion separation configuration 1010 may be mounted on the surface of the PIC chip including the coupler 1000. According to further embodiments, some or all components of the polarization conversion separation configuration 1010 may be located within or part of the PIC chip constituting the coupler 1000.

[0152] In Figures 10B, 10C, and 10D, for illustrative purposes, the optical signal is depicted as propagating along the z-direction and being incident perpendicularly to the coupler 1000, polarization-dependent beam separator 1041, Faraday rotator 1051, and polarization rotator 1052. In general, the direction of propagation of the optical signal may be perpendicular to these components, or it may be at an incidence angle other than perpendicular.

[0153] Figure 11A is a perspective view showing three waveguide polarization diversified free-space versus waveguide couplers 1100 according to another embodiment of the present disclosure. The three waveguide polarization diversified free-space versus waveguide couplers 1100 (referred to herein for simplicity) comprises three subcouplers 1101, 1102, and 1103, as shown by the dashed lines in Figure 11A. According to some embodiments, each of the subcouplers 1101, 1102, and 1103 may be realized by a free-space versus waveguide coupler including, but not limited to, a lattice coupler coupled to a single waveguide. According to other embodiments, each of the subcouplers 1102 and 1103 may be realized by polarization-independent free-space versus waveguide couplers.

[0154] Referring to Figure 11A, waveguide 921 is connected to subcoupler 1101 as an output coupling waveguide, waveguide 922 is connected to subcoupler 1102 as a first input coupling waveguide, and waveguide 933 is connected to subcoupler 1103 as a second input coupling waveguide. Here, waveguides 921, 922, and 933 in Figure 11A are the same as waveguides 921, 922, and 933 of the coherent sensing unit 900 in Figure 9.

[0155] As shown in Figure 11A, the main function of the subcoupler 1101 is to act as a transmitter for output coupling of the optical signal for target illumination. The optical signal E1 in the waveguide 921 is output by the subcoupler 1101 to the optical signal E 01 The output is coupled to free space as the emitted optical signal E. 01 The light signal E is polarized according to the design of the subcoupler 1101. For example, the light signal E 01 As shown in Figure 11A, the light is linearly polarized along the x-direction.

[0156] As shown in Figure 11A, the main function of the subcoupler 1102 is to function as a receiver that input couples the input optical signal to the coherent sensing unit 900 in Figure 9. Here, the polarization state of the input optical signal is orthogonal to the polarization of the output optical signal. Referring to Figure 11A, the output optical signal E 01 An input optical signal E having polarization orthogonal to it.24 The input optical signal E2 is internally coupled by the subcoupler 1102, which generates an internally coupled optical signal E2 within the waveguide 922. 24 The polarization is determined according to the design of the subcoupler 1102. As an example, the optimally internally coupled optical signal E 24 As shown in Figure 11A, the light is linearly polarized along the y-direction.

[0157] As shown in Figure 11A, the main function of the subcoupler 1103 is to function as a receiver that inputs and couples the input optical signal to the coherent sensing unit 900 in Figure 9. Here, the polarization state of the input optical signal is orthogonal to the polarization of the input optical signal coupled to the waveguide 922 by the subcoupler 1102. Referring to Figure 11A, the optical signal E 24 An input optical signal E having polarization orthogonal to it. 34 The input optical signal E3 is internally coupled by the subcoupler 1103, and an internally coupled optical signal E3 is generated within the waveguide 933. The input optical signal E3 is optimally internally coupled by the subcoupler 1103. 34 The polarization is determined according to the design of the subcoupler 1103. For example, the optimally internally coupled optical signal E 34 As shown in Figure 11A, the light is linearly polarized along the x-direction.

[0158] Figure 11B is a side view showing a polarization conversion separation configuration 1110 for use with a three waveguide polarization diversification free-space versus waveguide coupler 1100 for coupling optical signals according to another embodiment of the present disclosure. Figure 11C is a side view showing the configuration 1110 shown in Figure 11B used for internal coupling of optical signals. As shown in Figures 11B and 11C, the configuration 1110 receives an input optical signal E arriving at the coupler 1100. 24 and E 34 And the output optical signal E emitted by the coupler 1100 01This allows the light to propagate along a common optical path, which is located between the configuration 1110 and the target. The polarization conversion separation configuration 1110 comprises a Faraday rotator 1151, an optional polarization rotator 1152, and polarization-dependent beam separators 1141 and 1142, as shown in Figures 11B and 11C. For illustrative purposes, Figure 11D is a top view showing the polarization state of the optical signal in Figure 11B. Similarly, Figure 11E is a top view showing the polarization state of the optical signal in Figure 11C.

[0159] The polarization conversion separation configuration 1110 in Figures 11B and 11C is similar to the polarization conversion separation configuration 1010 in Figures 10C and 10D. The main difference between configuration 1110 and configuration 1010 is that configuration 1110, as shown in Figures 11B and 11C, has an additional polarization-dependent beam separator 1142 positioned between the Faraday rotor 1151 and the polarization-diversifying free-space versus waveguide coupler 1100. More specifically, component 1141 in Figures 11B and 11C is a polarization-dependent beam separator similar to the polarization-dependent beam separator 1041 in Figures 10C and 10D. Component 1152 in Figures 11B and 11C is an optional polarization rotor similar to the polarization rotor 1052 in Figures 10C and 10D. The component 1151 in Figures 11B and 11C is a Faraday rotor similar to the Faraday rotor 1051 in Figures 10C and 10D.

[0160] Referring to Figures 11A and 11B, the subcoupler 1101 of the coupler 1100 receives the output optical signal E 01 The signal can be output into free space. According to some embodiments, an additional polarization-dependent beam separator 1142 in configuration 1110 causes the optical signal E01 to be displaced laterally on the xy plane, and the optical signal E 01 It is preferable that the system be configured to produce an optical signal E10 having the same polarization. Here, the optical signal E 01 It is preferable that the optical signal E appears as an e-line with respect to the polarization-dependent beam separator 1142. As shown in Figure 11B, 01The light is linearly polarized along the x-direction, and the output optical signal is displaced in the positive x-direction. Similar to the polarization conversion separation configuration 1010 in Figure 10C, the Faraday rotor 1151, polarization rotor 1152, and polarization-dependent beam separator 1141 of the polarization conversion separation configuration 1110 are used to displace the optical signal E in Figure 11B. 10 Convert the optical signal E 13 This can be generated. As shown in Figure 11B, the optical signal E 13 is the optical signal E 01 It is linearly polarized along the direction perpendicular to the direction (i.e., the y-direction).

[0161] In the case of optical signal reception, the optical signal E in Figure 11B 13 The input optical signal from a target propagating along the same but opposite optical path can contain one or both of the two polarized input optical signal components. These are as shown in Figure 11C, input optical signal E 20 and E 30 This is the same as the signal E. Here, the optical signal E 20 is the optical signal E 13 Linearly polarized along the same direction as the polarization, the optical signal E 30 is the optical signal E 20 It is linearly polarized along a direction perpendicular to the polarization of the light. For example, as shown in Figure 11C, E 20 It is linearly polarized along the y-direction, E 30 The light is linearly polarized along the x-direction. Similar to the polarization conversion separation configuration 1010, the polarization-dependent beam separator 1141, polarization rotor 1152, and Faraday rotor 1151 of the polarization conversion separation configuration 1110 are used to control the optical signal E in Figure 11C. 20 Convert the optical signal E in Figure 11B. 10 Optical signal E having polarization orthogonal to the polarization of 23 This can be produced. As shown in Figures 11B and 11C, the additional polarization-dependent beam separator 1142 of configuration 1110 generates the optical signal E 23 However, the optical signal E in Figure 11B 01 It is configured to generate an optical signal E24 having polarization perpendicular to the polarization of the light. It then propagates along the optical path and reaches the subcoupler 1102. That is, the optical signal E 24This may appear as an o-ray with respect to the polarization-dependent beam separator 1142. Next, the optical signal E 24 This can be internally coupled by the subcoupler 1102 to produce an internally coupled optical signal E2 directed towards the waveguide 922, as shown in Figure 11A.

[0162] Similarly, the polarization-dependent beam separator 1141, polarization rotor 1152, and Faraday rotor 1151 of the polarization conversion separation configuration 1110 are used to control the optical signal E in Figure 11C. 30 Convert the optical signal E in Figure 11C. 23 Optical signal E having polarization orthogonal to the polarization of 33 This can be achieved. The configuration of the additional polarization-dependent beam separator 1142 allows the optical signal E 33 It is displaced laterally on the xy-plane, and the optical signal E 24 Optical signal E having polarization orthogonal to the polarization of 34 This can generate an optical signal E 10 The optical signal E that produces 01 The method is the same, but the direction is reversed. As shown in Figure 11C, the optical signal E 33 The optical signal E is linearly polarized along the x-direction, displaced toward the negative x-direction, and similarly linearly polarized along the x-direction. 34 This occurs. The E of the optical signal 01 Similarly, the optical signal E 33 It is desirable that this appears as an e-line with respect to the polarization-dependent beam separator 1142. Next, the optical signal E 34 This can be internally coupled by the subcoupler 1103 to generate an internally coupled optical signal E3 directed towards the waveguide 933, as shown in Figure 11A.

[0163] According to some embodiments, any polarization rotor 1152 in the polarization conversion separation configuration 1110 is often omitted, and as a result, the optical signal E 11It is preferable that an output optical signal having the same polarization state as the target illumination is used. Similar to the omission of any polarization rotor 1052 from the polarization conversion separation configuration 1010, the omission of the polarization rotor 1152 in the polarization separation configuration 1110 may require the reconstruction of the polarization-dependent beam separator 1141. For example, the optical signal E 11 This is done by orienting the optical axis of the polarization-dependent beam separator 1141 according to the polarization direction. To compensate for different orientations of the optical axis of the polarization-dependent beam separator 1141, the positions of either or both of the subcouplers 1102 and 1103 may also need to be adjusted on the substrate surface accordingly.

[0164] Similar to the polarization conversion separation configuration 1010, according to some embodiments, the components of the polarization conversion separation configuration 1110 may be shown as separate components, as shown in Figure 11B. According to other embodiments, some or all components of the polarization conversion separation configuration 1110 may appear as a single coupling component. Furthermore, according to some embodiments, the polarization conversion separation configuration 1110 may be a separate optical assembly from the PIC chip comprising the polarization diversification free-space paired waveguide coupler 1100, as shown in Figure 11B. According to other embodiments, some or all components of the polarization conversion separation configuration 1110 may be mounted on the surface of the PIC chip comprising the coupler 1100. According to further embodiments, some or all components of the polarization conversion separation configuration 1110 may be located within or part of the PIC chip comprising the coupler 1100.

[0165] In Figures 11A, 11B, and 11C, for illustrative purposes, the optical signal is shown to propagate along the z-direction and be incident perpendicularly to the coupler 1100, polarization-dependent beam separators 1141 and 1142, Faraday rotator 1151, and polarization rotator 1152. In general, the direction of propagation of the optical signal may be perpendicular to these components, or it may be at an incidence angle other than perpendicular.

[0166] Figure 12A is a side view showing a polarization conversion separation configuration 1210 for use with a three waveguide polarization diversification free-space versus waveguide coupler 1100 for coupling optical signals according to a further embodiment of the present disclosure. Figure 12B is a side view showing the configuration 1210 shown in Figure 12A used for internal coupling of optical signals. Configuration 1210 receives an input optical signal E arriving at the coupler 1100. 24 and E 34 And the output optical signal E emitted by the coupler 1100 01 This allows the light to propagate along a common optical path, which is located between the configuration 1210 and the target. As shown in Figures 12A and 12B, the polarization conversion separation configuration 1210 comprises a Faraday rotator 1251, an optional polarization rotator 1252, polarization-dependent beam separators 1241 and 1242, and an optional quarter-wave plate 1261. For illustrative purposes, Figure 12C is a top view showing the polarization state of the optical signal in Figure 12A. Similarly, Figure 12D is a top view showing the polarization state of the optical signal in Figure 12B.

[0167] The polarization conversion separation configuration 1210 in Figures 12A and 12B is a modified embodiment of the polarization conversion separation configuration 1110 in Figures 11B and 11C. The main changes from configuration 1110 to configuration 1210 are as follows: (1) The polarization rotor 1252 of configuration 1210 is configured to produce polarization rotation in the opposite direction to the rotation direction produced by the polarization rotor 1152 of configuration 1110, if present. (2) The polarization-dependent beam separator 1241 of configuration 1210 is configured, for example, by orienting the optical axis of the polarization-dependent beam separator 1241 in the opposite direction to the lateral displacement produced by the polarization-dependent beam separator 1242, if present, if any lateral displacement occurs. (3) Configuration 1210 includes an additional quarter-wave plate 1261 placed between the polarization-dependent beam separator 1241 and the target. Therefore, the polarization-dependent beam separator 1242 in configuration 1210 is the same as the polarization-dependent beam separator 1142 in configuration 1110, and the Faraday rotor 1251 in configuration 1210 is the same as the Faraday rotor 1151 in configuration 1110.

[0168] On the other hand, referring to Figure 12B, modifications (1) and (2) of the above-described configuration 1210 result in an optical signal E having a path length. 20 , E 21 , E 22 , E 23 , and E 24 This optical path may be obtained. This optical path is compared with the corresponding optical path of configuration 1110 shown in Figure 11C, and the optical signal E 30 , E 31 , E 32 , E 33 , and E 34 This is similar to the path length of the optical path. Therefore, in modified examples (1) and (2), the optical signals E arriving at subcouplers 1102 and 1103 respectively are similar. 24 and E 34 It is desirable to have the advantage of minimizing the phase difference between them. Referring to Figure 12A, modifications (1) and (2) described above have the advantage of minimizing the optical signal E on the surface of the subcoupler 1101 when the optional polarizing rotor 1252 is present. 01The optical signal E is located at a position and direction on the surface of the polarization-dependent beam separator 1241 that is similar to the emission position and direction of the optical signal E. 13 It can also be made possible to emit. Therefore, modifications (1) and (2) may have another advantage in that by using the output optical signal from the subcoupler 1101 of the coupler 1100, simplified optical alignment for the installation of the polarization conversion separation configuration 1210 with the coupler 1100 is possible.

[0169] On the other hand, referring to Figures 12A and 12C, the circularly polarized light signal E is obtained by the modified example (3) described above. 1C This makes it possible to use it for target illumination. More specifically, the quarter-wave plate 1261 can illuminate a linearly polarized light signal E 13 Convert to a circularly polarized light signal E for target illumination. 1C This can be generated. As shown in Figures 12A and 12C, the optical signal E 13 The light is linearly polarized along the x-direction, and the optical signal E 1C It is right-circularly polarized with respect to its propagation direction. In the case of optical signal reception, the optical signal coming from the target can be decomposed according to any two orthogonal polarizations. As shown in Figures 12B and 12D, the input optical signal from the target propagating in the negative z direction has two polarization components E 2C and E 3C It may include either or both of the following, where one is right-circularly polarized with respect to the propagation direction and the other is left-circularly polarized. As shown in Figures 12B and 12D, with respect to the negative z direction, E 2C It is right-circularly polarized, and E 3C This is left-circularly polarized light. As shown in Figure 12B, the quarter-wave plate 1261 receives the optical signal E 2C Convert to linearly polarized optical signal E 20 This generates an optical signal E 3C Convert E 20 A light signal E having polarization orthogonal to it. 30 This can be produced. As shown in Figures 12B and 12D, E 20 It is linearly polarized along the x-direction, E 30The light is linearly polarized along the y-direction. In some embodiments, using a circularly polarized light signal instead of a linearly polarized light signal for target illumination, as enabled by modification (3), may have the advantage of minimizing the possibility of significant signal loss due to certain properties of the target or target surface. Such significant signal loss may occur, but is not limited to, situations in which the target surface preferentially reflects linearly polarized light that happens to be orthogonal to the linearly polarized illumination signal. A circularly polarized illumination signal always contains a pair of orthogonal linearly polarized components that can avoid the loss of the reflected signal under such circumstances.

[0170] According to some embodiments, any polarization rotor 1252 in the polarization conversion separation configuration 1210 may be omitted. Similar to the omission of any polarization rotor 1152 from the polarization conversion separation configuration 1110, the omission of the polarization rotor 1252 in the polarization conversion separation configuration 1210 may require the reconstruction of the polarization-dependent beam separator 1241 and the quarter-wave plate 1261. For example, the optical signal E 11 This is done by orienting the optical axes of the polarization-dependent beam separator 1241 and the quarter-wave plate 1261 according to the polarization direction. The positions of either or both of the subcouplers 1102 and 1103 may also need to be adjusted on the substrate surface accordingly to compensate for different orientations of the optical axes of the polarization-dependent beam separator 1241 and the quarter-wave plate 1261.

[0171] Similar to the polarization conversion separation configuration 1110, according to some embodiments, the components of the polarization conversion separation configuration 1210 may be shown as separate components, as shown in Figure 12A. According to other embodiments, some or all components of the polarization conversion separation configuration 1210 may appear as a single coupling component. Furthermore, according to some embodiments, the polarization conversion separation configuration 1210 may be a separate optical assembly from the PIC chip comprising the polarization diversification free-space paired waveguide coupler 1100 shown in Figure 12A. According to other embodiments, some or all components of the polarization conversion separation configuration 1210 may be mounted on the surface of the PIC chip comprising the coupler 1100. According to further embodiments, some or all components of the polarization conversion separation configuration 1210 may be located within or part of the PIC chip comprising the coupler 1100.

[0172] In Figures 12A and 12B, for illustrative purposes, the optical signal is shown to propagate along the z-direction and be incident perpendicularly to the coupler 1100, polarization-dependent beam separators 1241 and 1242, Faraday rotator 1251, polarizing rotator 1252, and quarter-wave plate 1261. In general, the direction of propagation of the optical signal may be perpendicular to these components, or it may be at an incidence angle other than perpendicular.

[0173] Figure 13A is a top view showing three waveguide polarization diversification free-space versus waveguide couplers 1300 according to a further embodiment of the present disclosure. Figure 13B is a perspective view showing the coupler 1300 shown in Figure 13A. Furthermore, Figure 13B shows polarized output and input optical signals E coupled to subcouplers 1301, 1302, and 1303, respectively. 01 , E 24 , and E 34This figure shows the three waveguide polarization diversified free-space versus waveguide couplers 1300 (referred to as “coupler 1300” for simplicity in this specification) comprise three subcouplers 1301, 1302, and 1303, as shown by the dashed lines in Figures 13A and 13B. According to some embodiments, each of the subcouplers 1301, 1302, and 1303 may be realized by free-space versus waveguide couplers, including but not limited to lattice couplers, which are coupled to a single waveguide. According to other embodiments, each of the subcouplers 1302 and 1303 may be realized by polarization independent free-space versus waveguide couplers. Coupler 1300 is a modified embodiment of coupler 1100 shown in Figure 11A. Subcoupler 1301 of coupler 1300 in Figures 13A and 13B is similar to subcoupler 1101 of coupler 1100 in Figure 11A. The subcoupler 1302 of the coupler 1300 in Figures 13A and 13B is similar to the subcoupler 1102 of the coupler 1100 in Figure 11A. The subcoupler 1303 of the coupler 1300 in Figures 13A and 13B is similar to the subcoupler 1103 of the coupler 1100 in Figure 11A. Comparing the coupler 1300 and the coupler 1100, the spatial arrangement of the subcouplers of the coupler 1300 may be advantageous for some embodiments of the coherent sensing unit 900 in Figure 9 (e.g., it is more compact).

[0174] Figure 13C is a side view showing a polarization conversion separation configuration 1310 for use with three waveguide polarization diversification free-space versus waveguide couplers 1300 for coupling optical signals according to further embodiments of the present disclosure. Figure 13D is a side view showing an alternative to the configuration 1310 shown in Figure 13C. Figure 13E is a side view showing a configuration 1310 as shown in Figure 13C used for internal coupling of optical signals. Figure 13F is a side view showing an alternative to the configuration 1310 shown in Figure 13E. As shown in Figures 13C and 13E, the configuration 1310 receives an input optical signal E arriving at the coupler 1300. 24 and E 34 And the output optical signal E emitted by the coupler 1300 01This allows the light to propagate along a common optical path, which is located between configuration 1310 and the target.

[0175] For illustrative purposes, Figure 13G is a top view showing the polarization state and path position of the optical signal in the xy plane in Figures 13C and 13D. Figure 13G also includes an inset showing a top view of the coupler 1300, indicating the positions of subcouplers 1301, 1302, and 1303 in the xy plane as a reference for the path position of the optical signal in Figure 13G. Similarly, Figure 13H is a top view showing the polarization state and path position of the optical signal in the xy plane in Figures 13E and 13F. The path position in the xy plane in Figure 13H can refer to the positions of subcouplers 1301, 1302, and 1303 shown in the inset of Figure 13G.

[0176] According to Figures 13C, 13D, 13E, and 13F, the polarization conversion separation configuration 1310 comprises a Faraday rotor 1351, an optional polarization rotor 1352, polarization-dependent beam separators 1341 and 1342, and an optional quarter-wave plate 1361.

[0177] The polarization conversion separation configuration 1310 shown in Figures 13C, 13D, 13E, and 13F is a modified embodiment of the polarization conversion separation configuration 1110 in Figures 11B and 11C. The main changes from configuration 1110 to configuration 1310 are as follows: (1) The polarization-dependent beam separator 1341 of configuration 1310 is configured by orienting the optical axis of the polarization-dependent beam separator 1341 in a manner that affects any lateral displacement present, and, if an optional polarization rotor 1352 is present, by orienting the optical axis of the polarization-dependent beam separator 1341 in a direction on the xy plane perpendicular to the lateral displacement caused by the polarization-dependent beam separator 1342. (2) Configuration 1310 includes an additional quarter-wave plate 1361 positioned between the polarization-dependent beam separator 1341 and the target. Therefore, the polarization-dependent beam separator 1342 of configuration 1310 is the same as the polarization-dependent beam separator 1142 of configuration 1110, the Faraday rotor 1351 of configuration 1310 is the same as the Faraday rotor 1151 of configuration 1110, and the polarization rotor 1352 of configuration 1310 is the same as the polarization rotor 1152 of configuration 1110.

[0178] More specifically, in the polarization conversion separation configuration 1310, the polarization-dependent beam separator 1342 causes a lateral displacement along the x-direction (if present), as shown in Figures 13C and 13E. On the other hand, the polarization-dependent beam separator 1341 causes a lateral displacement along the y-direction, if present, as shown in Figures 13D and 13F. This is in contrast to the polarization conversion separation configurations 1110 and 1210, in which the polarization-dependent beam separators, if present, cause a lateral displacement along the x-direction.

[0179] Similar to the polarization conversion separation configuration 1210 in Figures 12A and 12B, referring to Figures 13E and 13F, the modification (1) of the above-described configuration 1310 results in the optical signal E compared to the corresponding optical path of the configuration 1110 shown in Figure 11C. 30 , E 31 , E 32 , E 33 , and E34 Optical signal E having an optical path length similar to the path length of the optical path of 20 , E 21 , E 22 , E 23 , and E 24 It is desirable to obtain the optical path shown in Figures 13E and 13F. 2C and E 3C Each of these undergoes one lateral displacement as it propagates from the quarter-wave plate 1361 to the coupler 1300 through the polarization-dependent beam separator 1341, the polarization rotor 1352, the Faraday rotor 1351, and the polarization-dependent beam separator 1342. Thus, in modification (1), the optical signals E that reach the subcouplers 1302 and 1303 respectively undergo one lateral displacement. 2C and E 3C It would be desirable to have the advantage of minimizing the phase difference between them.

[0180] On the other hand, referring to configuration 1310 in Figures 13C and 13D, similar to configuration 1210 in Figures 12A and 12B, the above modification (2) provides a circularly polarized light signal E to the target illumination. 1C It would be good if it were also possible to use [this].

[0181] According to some embodiments, any polarization rotor 1352 in the polarization conversion separation configuration 1310 may be omitted. Similar to the omission of any polarization rotor 1252 from the polarization conversion separation configuration 1210, the omission of the polarization rotor 1352 in the polarization separation configuration 1310 may require the reconstruction of the polarization-dependent beam separator 1341 and the quarter-wave plate 1361. For example, it may be necessary to reconfigure the optical signal E 11 The optical axes of the polarization-dependent beam separator 1341 and the quarter-wave plate 1361 are oriented according to the polarization direction. The positions of either or both of the subcouplers 1302 and 1303 may also need to be adjusted on the substrate surface accordingly to compensate for different orientations of the optical axes of the polarization-dependent beam separator 1341 and the quarter-wave plate 1361.

[0182] Similar to the polarization conversion separation configuration 1110, according to some embodiments, the components of the polarization conversion separation configuration 1310 may be shown as separate components, as shown in Figure 13C. According to other embodiments, some or all components of the polarization conversion separation configuration 1310 may appear as a single coupling component. Furthermore, according to some embodiments, the polarization conversion separation configuration 1310 may be a separate optical assembly from the PIC chip comprising the polarization diversification free-space paired waveguide coupler 1300, as shown in Figure 13C. According to other embodiments, some or all components of the polarization conversion separation configuration 1310 may be mounted on the surface of the PIC chip comprising the coupler 1300. According to further embodiments, some or all components of the polarization conversion separation configuration 1310 may be located within or part of the PIC chip comprising the coupler 1300.

[0183] In Figures 13B, 13C, 13D, 13E, and 13F, for illustrative purposes, the optical signal is shown to propagate along the z-direction and be incident perpendicularly to the coupler 1300, polarization-dependent beam separators 1341 and 1342, Faraday rotator 1351, polarizing rotator 1352, and quarter-wave plate 1361. In general, the direction of propagation of the optical signal may be perpendicular to these components, or it may be at an incidence angle other than perpendicular.

[0184] The coherent sensing units 100, 700, 710, 800, and 900, shown in Figures 1A, 7A, 7B, 8, and 9 respectively, can generate output optical signals with fixed polarization relative to the target illumination. In some applications of optical coherent sensing, it may be desirable to be able to dynamically adjust the polarization state of the illumination light signal.

[0185] Figure 14 shows a plan view of a coherent sensing unit 1400 that transmits and receives optical signals based on polarization diversity, according to one embodiment of the present disclosure, wherein the polarization of the transmitted optical signal is adjustable. The coherent sensing unit 1400 is similar to the coherent sensing units 700, 710, 800, and 900, which detect input optical signals in any polarization state. The main difference between the coherent sensing unit 1400 and the coherent sensing unit 900 is that the coherent sensing unit 1400 includes a polarization-diversified free-space paired waveguide coupler, which can be used to output couple output optical signals having any polarization state. Furthermore, the internally coupled optical signals in any polarization state can be directed to a waveguide different from the waveguide carrying the output optical signal.

[0186] More specifically, referring to Figure 14, the light source signal E S1 and E S2 At least one of these is supplied to the coherent sensing unit 1400. Light source signal E S1 and E S2 These are respectively led to the coherent sensing unit 1400 through waveguides 1421 and 1431. According to some embodiments, the light source signal E S1 and E S2 They may come from the same light source. In this situation, E S1 and E S2 The resulting output optical signals can be coherently coupled to form a single optical signal. According to other embodiments, the light source signal E S1 and E S2 The light may come from different light sources. Either or both of waveguides 1421 and 1431 may be connected to an optional phase shifter used to adjust the relative phase between the optical signals in waveguides 1421 and 1431. As an example, in Figure 14, waveguide 1431 is connected to a phase-shifted light source signal E S2 It may be connected to a phase shifter 1451 that directs the optical signal E4 to waveguide 1432. According to some embodiments, the phase shifter 1451 may be an electro-optic phase shifter or a thermo-optic phase shifter, but is not limited to these. Local oscillator (LO)E LOThis is supplied to the coherent sensing unit 1400 via the waveguide 1434.

[0187] In Figure 14, the polarization-diversified free-space versus waveguide coupler 1401 (referred to as “coupler 1401” for simplicity in this specification) is a set of four waveguide couplers connected to waveguides 1421, 1422, 1432, and 1433. Coupler 1401 can function as both a transmitter and a receiver.

[0188] Referring to Figure 14, the coupler 1401 receives the optical signal E1 (light source signal E) from the waveguide 1421. S1 The optical signal E4 from waveguide 1432 (which is essentially the same as E4) can be coupled in free space as one or more output optical signals. This may be used for target illumination by an optical coherent imager. The output optical signals output by coupler 1401 propagate in a direction outside the xy plane (i.e., E4). out The propagation direction has a non-zero z component). The output optical signal is polarized in a polarization state defined by the design of the coupler 1401. According to some embodiments, the output optical signal resulting from optical signal E1 may be orthogonally polarized with respect to the output optical signal resulting from optical signal E4. According to some embodiments in which optical signals E1 and E4 are coherent, the output optical signal is polarized in a single output optical signal E having the polarization state defined by the design of the coupler 1401, as well as the amplitude and relative phase of optical signals E1 and E4. out It can appear as such.

[0189] As a receiver, the coupler 1401 receives the input optical signal E in The input optical signal E can be coupled to the coherent sensing unit 1400. The input optical signal E can be coupled by the coupler 1401. in The input optical signal E in Depending on the polarization state, the input optical signal E can be directed towards either or both waveguides 1422 and 1433. inThe polarization component depends on the design of the coupler 1401. According to some embodiments, the output optical signal E1 is non-zero. out The polarization component of the input optical signal E is orthogonal to it. in The polarization component of is preferably guided into waveguide 1422 as an internally coupled optical signal E2. Then, the input optical signal E guided into waveguide 1422 in The polarization component of the input optical signal E is orthogonal to it. in The polarization component of is preferably guided into waveguide 1433 as an internally coupled optical signal E3. According to other embodiments in which the optical signal E4 is non-zero, the emitted optical signal E generated from the optical signal E4 out The polarization component of the input optical signal E is orthogonal to it. in The polarization component of is preferably guided into waveguide 1433 as an internally coupled optical signal E3. Then, the input optical signal E guided into waveguide 1433 in The polarization component of the input optical signal E is orthogonal to it. in The polarization component is preferably guided into waveguide 1422 as an internally coupled optical signal E2.

[0190] In Figure 14, the coupler 1401 is depicted as a single entity, but the coupler 1401 can generally comprise a single photonic component or multiple photonic components. Embodiments of the coupler 1401 are shown in Figures 15A, 16A, and 17A, which are described below. According to some embodiments, the coupler 1401, like the coupler 101 in Figures 1A and 1B, can also comprise a TE-TM mode converter, a splitter, and a combiner.

[0191] In Figure 14, the split coupler 1406 is connected to waveguide 1434 via LO E LO Divide it and make a part of LO into LO E LO ,1 is led to waveguide 1423, and a portion of LO is LO E LOThe LO is led to waveguide 1435 as 2. The portions of LO passing through waveguides 1423 and 1435, respectively, depend on the splitting ratio and loss of the splitting coupler 1406. According to some embodiments, the splitting coupler 1406 may be a 50 / 50 splitting coupler. According to other embodiments, the splitting coupler 1406 may have a splitting ratio other than 50 / 50.

[0192] In Figure 14, component 1402 receives the internally coupled optical signal E2 from waveguide 1422 and the LO E from waveguide 1423. LO It is a 2x2 optical coupler that mixes ,1 and splits the mixed signal and directs it to waveguides 1424 and 1425. According to some embodiments, the 2x2 optical coupler 1402 may be similar to the 2x2 optical coupler 902 of the coherent sensing unit 900 in Figure 9.

[0193] In Figure 14, component 1403 is a square photodetector that receives and detects an optical signal from waveguide 1424. Similarly, in Figure 14, component 1404 is a square photodetector that receives and detects an optical signal from waveguide 1425. According to some embodiments, photodetectors 1403 and 1404 may be similar to photodetectors 903 and 904 of the coherent sensing unit 900 in Figure 9.

[0194] In Figure 14, similar to the 2x2 optical coupler 912 of the coherent sensing unit 900 in Figure 9, component 1412 connects the internally coupled optical signal E3 from waveguide 1433 and the LO E from waveguide 1435. LO It is a 2x2 optical coupler that mixes 2 and 2, and splits the mixed signal and sends it to waveguides 1436 and 1437.

[0195] In Figure 14, component 1413 is a square-law photodetector that receives and detects an optical signal from waveguide 1436. Similarly, in Figure 14, component 1414 is a square-law photodetector that receives and detects an optical signal from waveguide 1437. According to some embodiments, photodetectors 1413 and 1414 may be similar to photodetectors 913 and 914 of the coherent sensing unit 900 in Figure 9.

[0196] Figure 15A is a top view showing four waveguide polarization diversification free-space versus waveguide couplers 1500 (hereinafter referred to as “coupler 1500” for simplicity) according to one embodiment of the present disclosure. Figure 15B is a perspective view showing the coupler 1500 shown in Figure 15A. Figure 15B further shows polarized output and input optical signals E coupled to subcouplers 1501, 1502, 1503, and 1504, respectively. 01 , E 24 , E 34 , and E 04 The coupler 1500 comprises four subcouplers 1501, 1502, 1503, and 1504, as shown by the dashed lines in Figure 15A. According to some embodiments, each of the subcouplers 1501, 1502, 1503, and 1504 may be realized by a free-space paired waveguide coupler, including but not limited to a grid coupler, which is coupled to a single waveguide. According to some embodiments, each of the subcouplers 1502 and 1503 may be realized by a polarization-independent free-space paired waveguide coupler. Coupler 1500 is a modified embodiment of coupler 1300 as shown in Figure 13A, with the addition of a subcoupler 1504 connected to waveguide 1432 of the coherent sensing unit 1400 in Figure 14.

[0197] Figure 15C is a side view showing a polarization conversion separation configuration 1510 for use with four waveguide polarization diversification free-space versus waveguide couplers 1500 for coupling optical signals according to one embodiment of the present disclosure. Figure 15F is a side view showing a configuration 1510 as shown in Figure 15C, used for internal coupling of optical signals. Configuration 1510 receives an input optical signal E arriving at the coupler 1500. 24 and E 34 And the output optical signal E emitted by the coupler 1500 01 and E 04This allows the signals to propagate along a common optical path, which is located between configuration 1510 and the target. Figure 15D is another side view showing configuration 1510 as shown in Figure 15C. Figure 15G is another side view showing configuration 1510 as shown in Figure 15F. Embodiments of the optical paths and polarization states of the output optical signals resulting from optical signals E1 and E4, and the input optical signals resulting from E2 and E3, are shown in Figures 15C, 15D, 15F, and 15G. For simplicity, waveguides 1421, 1422, 1432, and 1433 are not explicitly shown in Figures 15C, 15D, 15F, and 15G.

[0198] For illustrative purposes, Figure 15E is a top view showing the polarization state and path position of the optical signals in the xy plane as shown in Figures 15C and 15D. Figure 15E further shows an inset of a top view of the coupler 1500 showing the positions of subcouplers 1501, 1502, 1503, and 1504 in the xy plane as a reference for the path position of the optical signals in Figure 15E. Similarly, Figure 15H is a top view showing the polarization state and path position of the optical signals in the xy plane as shown in Figures 15F and 15G. The inset of Figure 15H is a top view showing the coupler 1500 showing the positions of subcouplers 1501, 1502, 1503, and 1504 in the xy plane as a reference for the path position of the optical signals in Figure 15H.

[0199] The polarization conversion isolation configuration 1510 shown in Figures 15C, 15D, 15F, and 15G is essentially the same as the polarization conversion isolation configuration 1310 shown in Figures 13C, 13D, 13E, and 13F, except that the quarter-wave plate 1361 is omitted. It is used to generate a circularly polarized output optical signal for target illumination. The coherent sensing unit 1400, operating with the coupler 1500 and the polarization conversion isolation configuration 1510, can generate an output optical signal for target illumination having any polarization state, including linearly polarized, circularly polarized, or elliptically polarized, by adjusting the amplitude and relative phase of the optical signals E1 and E4 in waveguides 1421 and 1432. According to some embodiments, in order to generate an output optical signal having a specific polarization state using the polarization conversion isolation configuration 1510, the subcouplers 1501, 1502, 1503, and 1504 of the coupler 1500 may need to be designed and configured in the following manner: Optical signal E 13 and E 43 To minimize the spatial variation of the polarization of the output optical signal coupled from, the output optical signal E is used as shown in Figures 15C, 15D, and 15E. 13 and E 43 Maximize the spatial overlap.

[0200] In Figures 15B, 15C, 15D, 15F, and 15G, for illustrative purposes, the optical signal is shown to propagate along the z-direction and be incident perpendicularly to the coupler 1500, polarization-dependent beam separators 1541 and 1542, and Faraday rotator 1551. In general, the direction of propagation of the optical signal may be perpendicular to these components, or it may be at an incidence angle other than perpendicular.

[0201] Figure 16A is a top view showing a four waveguide polarization diversification free-space versus waveguide coupler 1600 (hereinafter referred to as “coupler 1600” for simplicity) according to another embodiment of the present disclosure. Figure 16B is a perspective view showing the coupler 1600 shown in Figure 16A. Figure 16B further shows polarized output and input optical signals E coupled to subcouplers 1601 and 1602. 10 , E 40, E 23 , and E 33 The coupler 1600 comprises two subcouplers 1601 and 1602, as shown by the dashed lines in Figure 16A. According to some embodiments, each of the subcouplers 1601 and 1602 may be realized by either a polarization-diversified free-space versus waveguide coupler 101 shown in Figure 1B, or a polarization-diversified free-space versus waveguide coupler 200 as shown in Figure 2. Coupler 1600 is a modified embodiment of coupler 1000 shown in Figure 10A and has an additional waveguide 1432 connected to the subcoupler 1602 of the coherent sensing unit 1600 in Figure 16A for output coupling of the optical signal E4.

[0202] In Figure 16B, for illustrative purposes, the output optical signal E 10 and input optical signal E 23 However, it is depicted as coupling with subcoupler 1601 at different spatial positions. Generally, the output optical signal E 10 and input optical signal E 23 According to some embodiments, the subcoupler 1601 can be coupled at the same spatial position, or according to other embodiments, at a different spatial position. Similarly, the output optical signal E 40 and input optical signal E 33 According to some embodiments, it can be coupled with the subcoupler 1602 at the same spatial position, or according to other embodiments, at a different spatial position.

[0203] Figure 16C is a side view showing a polarization conversion decoupling configuration 1610 for use with a four-waveguide polarization diversified free-space paired waveguide coupler 1600 for coupling optical signals according to another embodiment of the present disclosure. Figure 16D is a side view showing the configuration 1610 shown in Figure 16C used for internal coupling of optical signals. For illustrative purposes, Figure 16E is a top view showing the polarization state of the optical signals in Figure 16C. On the other hand, Figure 16F is a top view showing the polarization state of the optical signals in Figure 16D. The polarization conversion decoupling configuration 1610 is essentially the same as the polarization conversion decoupling configuration 1010 shown in Figures 10C and 10D. Embodiments of the optical paths and polarization states of the output optical signals resulting from optical signals E1 and E4, and the input optical signals resulting from optical signals E2 and E3, are shown in Figures 16C, 16D, 16E, and 16F. For simplicity, waveguides 1421, 1422, 1432, and 1433 are not explicitly shown in Figures 16C and 16D.

[0204] In Figures 16B, 16C, and 16D, for illustrative purposes, the optical signal is shown propagating along the z-direction and incident perpendicularly to the coupler 1600, polarization-dependent beam separator 1641, Faraday rotator 1651, and polarization rotator 1652. In general, the direction of propagation of the optical signal may be perpendicular to these components, or it may be at an incidence angle other than perpendicular.

[0205] Figure 17A is a perspective view showing four waveguide polarization diversification free-space versus waveguide couplers 1700 (hereinafter referred to as “coupler 1700” for simplicity) according to a further embodiment of the present disclosure. Figure 17A further shows polarized output and input optical signals E coupled to subcouplers 1701, 1702, and 1703. 01 , E 04 , E 24 , and E 34The diagram shows that the system comprises three subcouplers 1701, 1702, and 1703, as indicated by the dashed lines in Figure 17A. According to some embodiments, subcoupler 1701 may be realized by either a polarization-diversified free-space versus waveguide coupler 101, as shown in Figure 1B, or a polarization-diversified free-space versus waveguide coupler 200, as shown in Figure 2. On the other hand, each of subcouplers 1702 and 1703 may be realized by a free-space versus waveguide coupler that includes, but is not limited to, a lattice coupler coupled to a single waveguide. According to other embodiments, each of subcouplers 1702 and 1703 may be realized by a polarization-independent free-space versus waveguide coupler. Coupler 1700 is a modified embodiment of coupler 1100 shown in Figure 11A, and in addition to output coupling of optical signal E1 from waveguide 1421, it includes an additional waveguide 1432 connected to subcoupler 1701 of coherent sensing unit 1700 in Figure 17A for output coupling of optical signal E4.

[0206] In Figure 17A, for illustrative purposes, the output optical signal E 01 and output optical signal E 04 However, it is depicted as coupling with subcoupler 1701 at different spatial positions. According to some embodiments, the output optical signal E 01 and output optical signal E 04 To maximize the spatial overlap of the two output optical signals, it can be coupled with the subcoupler 1701 at the same spatial position. According to another embodiment, the output optical signal E 01 and output optical signal E 04 It can be coupled with the sub-coupler 1701 at different spatial positions.

[0207] Figure 17B is a side view showing a polarization decoupling configuration 1710 for use with a four waveguide polarization diversification free-space pair waveguide coupler 1700 for coupling optical signals, according to a further embodiment of the present disclosure. Figure 17C is a side view showing the configuration 1710 shown in Figure 17B, used for internal coupling of optical signals. For illustrative purposes, Figure 17D is a top view showing the polarization state of the optical signals in Figure 17B. On the other hand, Figure 17E is a top view showing the polarization state of the optical signals in Figure 17C. The polarization decoupling configuration 1710 is essentially the same as the polarization decoupling configuration 1110 shown in Figures 11B and 11C. Embodiments of the optical paths and polarization states of the output optical signals resulting from optical signals E1 and E4, and the input optical signals resulting from optical signals E2 and E3, are shown in Figures 17B, 17C, 17D, and 17E. By using the polarization decoupling configuration 1710 with the coupler 1700, the following is preferably ensured: Optical signal E 13 and E 43 The polarization of the coherent coupled optical signal from the optical signal E 01 and E 04 Because the polarization of the coherent coupled optical signal from E is essentially the same, 01 , E 10 , E 11 , E 12 , and E 13 The optical path length is the signal E 04 , E 40 , E 41 , E 42 , and E 43 It is essentially the same as the optical path length. For simplicity, waveguides 1421, 1422, 1432, and 1433 are not explicitly shown in Figures 17B and 17C.

[0208] In Figures 17A, 17B, and 17C, for illustrative purposes, the optical signal is depicted propagating along the z-direction and incident perpendicularly to the coupler 1700, polarization-dependent beam separators 1741 and 1742, Faraday rotator 1751, and polarization rotator 1752. In general, the direction of propagation of the optical signal may be perpendicular to these components, or it may be at an incidence angle other than perpendicular.

[0209] Figure 18A is a plan view showing a coherent light sensor 1800 according to one embodiment of the present disclosure. The coherent light sensor 1800 comprises a coherent sensing array 1810 and optical routing circuits 1820 and 1830 mounted on a PIC chip.

[0210] In Figure 18A, the optical routing circuit 1820 is LO E LO It is used to route to the coherent sensing array 1810. For example, the optical routing circuit 1820 in Figure 18A is used for LO E LO The signals are routed to different rows of the coherent sensing array 1810. The optical routing circuit 1820 includes a network of optical waveguides, and LO E LO The flow is controlled by multiple optical switches within the network. For example, in Figure 18A, the optical routing circuit 1820 includes optical switches 1821, 1822, and 1823, which may be, but are not limited to, Mach-Zehnder interferometer (MZI) based optical switches or MEMS based optical switches.

[0211] It is understood that other implementations of the optical routing circuit 1820 are also possible. For example, the optical routing circuit 1820 in Figure 18A may be in the form of a binary tree. The optical switch is LO E LO The signal is sent from the input to one or more output ports of the switch. According to some embodiments, the optical switch 1821 in Figure 18A sends the LO E in waveguide 1824. LO It can be directed towards one or both of waveguides 1825 and 1826.

[0212] The optical routing circuit 1830 receives the light source signal E SIt is used to route to the coherent sensing array 1810. According to some embodiments, the optical routing circuit 1830 may have a similar structure to the optical routing circuit 1820. In one embodiment, the optical routing circuit 1830 may be in the form of a binary tree comprising optical switches 1831, 1832, and 1833. According to other embodiments, the optical routing circuit 1830 may have a different structure from the optical routing circuit 1820.

[0213] In Figure 18A, the coherent sensing array 1810 comprises an array of coherent sensing units 1801. In one embodiment, the coherent sensing array 1810 comprises 24 coherent sensing units 1801 arranged in a 4x6 rectangular format (i.e., 4 rows and 6 columns). Figure 18B shows a row of six coherent sensing units in the coherent sensing array 1810 according to one embodiment of the present disclosure.

[0214] In Figure 18A, each coherent sensing unit 1801 of the coherent sensing array 1810 is connected to two waveguides that function as optical input ports for the coherent sensing unit. According to some embodiments, the coherent sensing unit 1801 may be a coherent sensing unit 100 as shown in Figure 1A. According to other embodiments, the coherent sensing unit 1801 may be a coherent sensing unit 700 as shown in Figure 7A. According to yet another embodiment, the coherent sensing unit 1801 may be a coherent sensing unit 800 as shown in Figure 8. According to yet another embodiment, the coherent sensing unit 1801 may be a coherent sensing unit 900 as shown in Figure 9.

[0215] In Figure 18A, two waveguides connected to the coherent sensing unit 1801 are used to transmit the light source signal E S and LO E LO The signal can be led to the sensing unit 1801. For example, referring to Figure 18B, the waveguide 1843 leads to the light source signal E SIt is preferable that this be used to guide the coherent sensing unit 1801 connected to waveguides 1843 and 1844 in Figure 18B. Waveguide 1844 is LO E LO It is preferable to use it to guide the same coherent sensing unit. The split coupler is used to connect the light source signal E S and LO E LO To distribute the light source signal E to different coherent sensing units 1801, it is preferable to use it within the coherent sensing array 1810. As shown in Figure 18B, split couplers 1811, 1812, 1813, 1814, and 1815 are used to distribute the light source signal E S The signal can be distributed to six coherent sensing units 1801. The split couplers 1811, 1812, 1813, 1814, and 1815 may have the same or different split ratios. Light source signal E S According to some embodiments that distribute the LO E evenly to six coherent sensing units 1801, split coupler 1811 may have a split ratio of 5:1, split coupler 1812 may have a split ratio of 4:1, split coupler 1813 may have a split ratio of 3:1, split coupler 1814 may have a split ratio of 2:1, and split coupler 1815 may have a split ratio of 1:1. Similarly, according to the embodiment in Figure 18B, split couplers 1851, 1852, 1853, 1854, and 1855 may be used to perform LO E LO This can be distributed to six coherent sensing units 1801. Here, split couplers 1851, 1852, 1853, 1854, and 1855 are LO E LO The power may be distributed equally among the six coherent sensing units 1801, or not, as is the case with the split couplers 1811, 1812, 1813, 1814, and 1815.

[0216] The coherent light sensor 1800 in Figure 18A may also include a laser source, an electrical control circuit, and an electrical readout circuit, which are not explicitly shown in the figure.

[0217] Figure 19A is a plan view showing a coherent photosensor 1900 according to another embodiment of the present disclosure. The coherent photosensor 1900 receives a light source signal E through an optical routing circuit in an H-tree topology. S The system comprises an array of coherent sensing units 1901 coupled to each other. For example, a coherent photosensor 1900, as shown in Figure 19A, appears as a three-level H-tree having eight coherent sensing units 1901. The H-tree optical routing circuit within the coherent photosensor 1900 is constructed by a network of waveguides coupled to a plurality of optical switches 1902. The optical switches 1902 in Figure 19A may be similar to the optical switches 1821, 1822, 1823, 1831, 1832, and 1833 of the coherent photosensor 1800 in Figure 18A.

[0218] As shown in Figure 19A, each of the coherent sensing units 1901 receives the light source signal E S It is preferable that the light source signal E be coupled to a single waveguide that supplies it to a coherent sensing unit. S This may be used as both a light source signal for target illumination and LO for heterodyne detection in the coherent sensing unit 1901. According to some embodiments, each of the coherent sensing units 1901 may be a coherent sensing unit 710 as shown in Figure 7B. According to other embodiments, each of the coherent sensing units 1901 may be a coherent sensing unit 100 as shown in Figure 1A, a coherent sensing unit 700 as shown in Figure 7A, a coherent sensing unit 800 as shown in Figure 8, or a coherent sensing unit 900 as shown in Figure 9. Here, a split coupler is used to supply the light source signal E to each coherent sensing unit 1901. S The light source signal E is used as the light source signal. S Part of and for the coherent sensing unit LO E LO E used as SIt can be divided into parts. According to a further embodiment, each of the coherent sensing units 1901 may be a coherent sensing unit group 1910, as shown in Figure 19B. The coherent light sensor 1900 in Figure 19A may also include a laser source, an electrical control circuit, and an electrical readout circuit, which are not explicitly shown in the figure.

[0219] Figure 19B is a plan view showing a coherent sensing unit group 1910 according to one embodiment of the present disclosure. In one embodiment, the coherent sensing unit group 1910 comprises a plurality of coherent sensing units 1911 arranged in an H-tree topology. For example, the coherent light sensor 1910 in Figure 19B appears as a two-level H-tree having four coherent sensing units 1911. In Figure 19B, component 1913 receives the light source signal E S This is a split coupler that is preferably used to split the light source signal ES so that a portion of it is supplied to each of the coherent sensing units 1911 of the coherent sensing unit group 1910. According to some embodiments, the split ratio of the split coupler 1913 may be 50 / 50 in order to evenly distribute the source signal to all of the coherent sensing units 1911 of the coherent sensing unit group 1910. In Figure 19B, component 1912 is the light source signal E supplied to each coherent sensing unit 1911. S The light source signal E as a light source signal S A portion of the light source signal E as the LO of the coherent sensing unit. S This is a split coupler that is suitable for use in dividing a part into two. The split ratio of the split coupler 1912 may or may not be 50 / 50.

[0220] In Figure 19B, each of the coherent sensing units 1911 may be a coherent sensing unit 100 as shown in Figure 1A, a coherent sensing unit 700 as shown in Figure 7A, a coherent sensing unit 800 as shown in Figure 8, or a coherent sensing unit 900 as shown in Figure 9.

[0221] Figure 20A is a plan view showing a coherent light sensor 2000 according to a further embodiment of the present disclosure. The coherent light sensor 2000 comprises a sensing region 2010 and optical routing circuits 2020 and 2030 mounted on a PIC chip. According to some embodiments, the sensing region 2010 comprises a plurality of coherent sensing unit groups 2001. Each coherent sensing unit group 2001 comprises a plurality of coherent sensing units that emit an output light signal for target illumination, and the polarization of the output light signal is adjustable.

[0222] In Figure 20A, the optical routing circuit 2020 is a local oscillator E LO It may be used to route the light from the light source E to the coherent sensing unit group 2001 within the sensing region 2010. According to some embodiments, the optical routing circuit 2020 may be similar to the optical routing circuit 1820 of the coherent light sensor 1800. In Figure 20A, the optical routing circuit 2030 is used to route the light from the light source E S It may be used to route to a coherent sensing unit group 2001 within the sensing region 2010. According to some embodiments, the optical routing circuit 2030 may be similar to the optical routing circuit 1830 of the coherent light sensor 1800.

[0223] Figure 20B is a plan view showing a coherent sensing unit group 2001 according to another embodiment of the present disclosure. The coherent sensing unit group 2001 comprises a plurality of coherent sensing units 2002 that emit output light signals having adjustable polarization for target illumination. For illustrative purposes, Figure 20B depicts the coherent sensing unit group 2001 as including four coherent sensing units 2002. Each coherent sensing unit 2002 is LO E LOThe system comprises one input waveguide for internal coupling and two input waveguides for internal coupling of light source light. Here, the amplitude and relative phase of the light source light in the two waveguides determine the polarization state of the output light signal radiated from the coherent sensing unit 2002. According to some embodiments, the coherent sensing unit 2002 may be realized by a coherent sensing unit 1400, as illustrated in Figure 14.

[0224] As shown in Figure 20B, each coherent sensing unit group 2001 is LO E LO Multiple split couplers 2051, 2052, and 2053 are provided to distribute to each of the coherent sensing units 2002 of the coherent sensing unit group 2001. According to some embodiments, the split couplers 2051, 2052, and 2053 distribute to each of the coherent sensing units 2002 of the coherent sensing unit group 2001. LO The components may be distributed equally, or they may not be distributed at all, similar to the split couplers 1851, 1852, 1853, 1854, and 1855.

[0225] As shown in Figure 20B, each coherent sensing unit group 2001 receives light from the light source E S It can be equipped with an optical switch 2021 that divides it into two parts. Then, the light source E S The two parts are preferably distributed to each coherent sensing unit 2002 via a split coupler. For example, light source E S A portion of the light may be distributed to the coherent sensing unit 2002 via split couplers 2011, 2012, and 2013. According to some embodiments, the split couplers 2011, 2012, and 2013 distribute the light source E to each coherent sensing unit 2002 of the coherent sensing unit group 2001. S It may be similar to the split couplers 1811, 1812, 1813, 1814, and 1815, which may or may not distribute the light evenly. Similarly, the light source E SSome of these may be distributed to each coherent sensing unit 2002 via split couplers 2014, 2015, and 2016, similar to split couplers 2011, 2012, and 2013. According to some embodiments, a coherent sensing unit group 2001 may include waveguide crossovers 2022 that allow optical signals to cross each other with minimal loss and crosstalk in a compact PIC layout.

[0226] Figure 20C is a plan view showing a Mach-Zehnder interferometer-based optical switch 2021 according to one embodiment of the present disclosure. The optical switch 2021, which is a Mach-Zehnder interferometer, includes a phaser 2031 that controls the output portion of the optical switch 2021. According to some embodiments, the phaser 2031 may be an electro-optic phaser or a thermo-optic phaser.

[0227] The coherent light sensor 2000 in Figure 20A may include a laser source, an electrical control circuit, and an electrical readout circuit, which are not explicitly shown. Similarly, the coherent sensing unit group 2001 in Figure 20B may include an electrical control circuit and an electrical readout circuit, which are not explicitly shown.

[0228] Figure 21A is a side view showing an optical coherent imager 2100 according to one embodiment of the present disclosure. The optical coherent imager 2100 comprises a coherent photosensor 2101, a polarization conversion separation assembly 2102, and an imaging optical system 2103. The optical coherent imager 2100 also includes, but is not limited to, any one or more of a laser source, an electronic controller, an electronic interface, and a digital signal processor, which are not explicitly shown in Figure 21A for simplification.

[0229] The coherent photosensor 2101 in Figure 21A is a sensor comprising multiple coherent sensing units of the present disclosure. According to some embodiments, the coherent photosensor 2101 may be one of the coherent photosensors 1800, 1900, and 2000 shown in Figures 18A, 19A, and 20A, respectively. An output optical signal is emitted from the coherent photosensor 2101 for target illumination. The output optical signals emitted from different coherent sensing units of the coherent photosensor 2101 via the imaging optical system 2103 can produce illumination beams at different field-of-view positions, so that each field-of-view position corresponds to a coherent sensing unit of the coherent photosensor. Details of the imaging optical system 2103 in Figure 21A are shown for illustrative purposes only. Other optical setups may be used for the imaging optical system 2103. Depending on the specific design of the coherent sensing unit used in the coherent photosensor 2101, according to some embodiments, the polarization conversion isolation assembly 2102 may be one of the configurations shown in Figures 4C, 5A, 5C, 6A, 6C, 10C, 11B, 12A, 13C, 15C, 16C, and 17B. The polarization conversion isolation assembly 2102 may be used to allow the output optical signal emitted from the coherent photosensor 2101 for target illumination and the input optical signal (i.e., target signal) received by the coherent photosensor 2101 to propagate along a common optical path, where the common optical path lies between the assembly 2102 and the target 2104.

[0230] In Figure 21A, ray 2171 shows an example of the optical path at a field of view position of the optical coherent imager 2100, and ray 2172 shows an example of the optical path at another field of view position of the optical coherent imager 2100. The imaging optical system 2103 may have at least one image plane. The polarization conversion separation assembly 2102 may be positioned close to the image plane of the imaging optical system 2103. For example, in Figure 21A, the polarization conversion separation assembly 2102 is positioned close to the coherent photosensor 2101 located at the final image plane 2161 of the imaging optical system 2103.

[0231] Figure 21B is a magnified view of the imager 2100 in the vicinity of the final image plane 2161 as shown in Figure 21A. For illustrative purposes, in Figure 21B, the polarization conversion separation assembly 2102 may be shown as the polarization conversion separation configuration shown in Figure 6C. As shown in Figure 21B, for each field of view position of the optical coherent imager 2100, input optical signals from targets that share a common optical path with respect to the output optical signal may be spatially separated on the final image plane by the polarization-dependent beam separator 401. In Figure 21B, spatial separation 2198 is the spatial separation of the input ray 2171 and the output ray 2171 provided by the polarization-dependent beam separator 401. Spatial separation 2199 is the spatial separation of the input ray 2172 and the output ray 2172 provided by the polarization-dependent beam separator 401. According to some embodiments, the imaging optical system 2103 may have image-spatial telecentricity, which allows the spatial separation by the polarization-dependent beam separator 401 to be uniform across the entire field of view of the optical coherent imager 2100. Therefore, the spatial separation 2198 of ray 2171 may be similar to that of ray 2172, 2199. Furthermore, the angular range 2188 of ray 2171 may also be similar to that of ray 2172, 2189. In such a situation, the polarization-diversified free-space versus waveguide coupler of the coherent sensing unit within the coherent optical sensor 2101 may be designed to optimally couple with the optical signal according to a common incidence angle (e.g., perpendicular incidence), a common angular range, and, where applicable, a common spacing between subcouplers. In other embodiments where the imaging optical system 2103 does not have image-space telecentricity, each of the polarization-diversifying free-space versus waveguide couplers of the coherent sensing unit in the coherent light sensor 2101 may be individually designed to optimally couple with the optical signal according to the specifications of the polarization conversion separation assembly 2102 and the imaging optical system 2103.

[0232] Figure 21C is a polarization map showing examples of normal rays (o-rays) and extraordinary rays (e-rays) for a polarization-dependent beam separator 401 on a coherent photosensor 2101 across the field of view of the optical coherent imager in Figure 21B. In Figure 21C, polarization 2191 shows an example of o-ray polarization, and polarization 2192 shows an example of e-ray polarization. For example, according to the orientation of the optical axis 498 on the xz plane in Figure 21B, o-ray polarization is linear polarization with a major component along the y-direction. On the other hand, e-ray polarization is linear polarization with a major component along the x-direction. According to some embodiments where the imaging optical system 2103 is precisely image-space telecentric, both o-ray and e-ray polarization may be non-uniform across the field of view of the optical coherent imager. According to other embodiments, such as the embodiment shown in Figure 21C, if the imaging optical system 2103 is not precisely image-space telecentric, the o-ray and e-ray polarizations may deviate from uniformity. According to some embodiments, the polarization-diversified free-space versus waveguide coupler of the coherent sensing unit in the coherent photosensor 2101 may be designed such that non-uniformity is negligible. According to other embodiments, each of the polarization-diversified free-space versus waveguide couplers of the coherent sensing unit in the coherent photosensor 2101 may be individually designed to optimally couple with the optical signal according to changes in the polarization of the o-line and e-line across the field of view of the imaging optical system 2103.

[0233] Figure 22A is a side view showing an optical coherent imager 2200 according to another embodiment of the present disclosure. The optical coherent imager 2200 comprises a coherent photosensor 2201, an imaging optical system 2203, and a polarization conversion separation assembly comprising components arranged with the optical components of the imaging optical system 2203. As an example, the polarization conversion separation assembly comprises polarization-dependent beam separators 2241 and 2242, a Faraday rotor 2251, a polarizing rotor 2252, and a quarter-wave plate 2261. This polarization conversion separation assembly is similar to the polarization conversion separation configuration 1210 in Figures 12A and 12B, except for the use of a polarization-dependent beam separator 2241 that provides angular displacement instead of the lateral displacement provided by the polarization-dependent beam separator 1241 in configuration 1210. According to some embodiments, the polarization-dependent beam separator 2241 may be a birefringent wedge. In Figure 22A, ray 2271 shows an example of the optical path at a field of view position of the optical coherent imager 2200, and ray 2272 shows an example of the optical path at a different field of view position of the optical coherent imager 2200.

[0234] Figure 22B is a side view showing a ray propagating through a polarization-dependent beam separator 2241 that produces angular displacement and a ray propagating through a polarization-dependent beam separator 2242 that produces lateral displacement, according to an embodiment of the present disclosure. Referring to Figure 22B, the polarization-dependent beam separator 2242 can cause lateral displacement in the input ray, and this lateral displacement depends on the polarization of the ray. For example, in Figure 22B, when the ray passes through the polarization-dependent beam separator 2242, the x-polarized and y-polarized components of the ray are displaced laterally by different displacements. In contrast, the polarization-dependent beam separator 2241 produces angular displacement in the input ray, and this angular displacement depends on the polarization of the ray. For example, in Figure 22B, when the ray passes through the polarization-dependent beam separator 2241, the x-polarized and y-polarized components of the ray are displaced by different angles.

[0235] Referring back to Figure 22A, the polarization-dependent beam separator 2242 is positioned close to the image plane of the imaging optical system 2203, while the polarization-dependent beam separator 2241 is positioned close to the focal plane of the imaging optical system 2203. The angular displacement caused by the polarization-dependent beam separator 2241 on the focal plane can effectively produce a lateral displacement on the image plane. The use of the polarization-dependent beam separator 2241 may have the advantage of allowing greater flexibility in various locations for arranging optical components in the imaging optical system 2203, including but not limited to the polarization-dependent beam separators 2241 and 2242, the Faraday rotator 2251, the polarizing rotator 2252, and the quarter-wave plate 2261.

[0236] As shown in Figure 22A, the Faraday rotator 2251, the polarizing rotator 2252, and the quarter-wave plate 2261 are preferably positioned within the imaging optical system 2203 where the angle of incidence of the light ray is relatively small (i.e., close to perpendicular incidence). According to some embodiments, some polarization-dependent components may have larger performance tolerances than others for specific applications of optical coherent imaging. For example, the Faraday rotator 2251, which is tolerant of the angle of incidence of the light ray, may be positioned at any position between the polarizing rotator 2252 and the polarization-dependent beam separator 2242. As another example, the quarter-wave plate 2261 may be positioned where the change in the angle of incidence of the light ray is greater at different field-of-view positions. The quarter-wave plate 2261 can convert a linearly polarized output optical signal at normal incidence to a circularly polarized optical signal, and convert a linearly polarized output optical signal at incidence angles other than perpendicular incidence to an elliptically polarized optical signal. Therefore, the change in the angle of incidence on the quarter-wave plate 2261 at different field-of-view positions can essentially result in different elliptical polarizations for illumination at different positions in the target scene. This may not pose a significant problem for the relevant applications of optical coherent imaging. Furthermore, some embodiments of the coherent photosensor 2201, such as the coherent photosensor 2000 shown in Figure 20A, can enable dynamic polarization adjustment, thereby mitigating the problem of different elliptical polarizations for illumination at different positions in the target scene.

[0237] In Figure 22A, the components of the polarization conversion and separation assembly are arranged individually with the optical components of the imaging optical system 2203. According to some embodiments, one or more components of the polarization conversion and separation assembly may be arranged collectively with the optical components of the imaging optical system 2203.

[0238] Figure 23 shows a flowchart of an optical coherent imaging method using polarization diversification that enables a shared path for transmitting and receiving optical signals, according to one embodiment of the present disclosure.

[0239] In step 2301, the light source is generated from the light source.

[0240] In step 2303, light from a light source is guided through a waveguide circuit to one or more polarization-diversified free-space paired waveguide couplers in the coherent photosensor of the optical coherent imager. According to some embodiments, the guidance of light from a light source through the waveguide circuit may be achieved by controlling electro-optical or thermo-optical switches in the waveguide circuit using a control system. More specifically, each target scene position corresponds to a field of view position of the optical coherent imager, which corresponds to a polarization-diversified free-space paired waveguide coupler in the coherent photosensor of the optical coherent imager.

[0241] In step 2305, for each of the selected polarization-diversified free-space versus waveguide couplers (which we will call "couplers" for simplicity) into which the light source is directed, the light source is output-coupled from the coupler to free space, producing output light having a first polarization. Here, free space refers to a vacuum, air, a region on the surface of the coupler, or any homogeneous medium with a boundary scale that is much longer (e.g., at least 10 times) than the wavelength of the light signal propagating through it. According to some embodiments, the polarization-diversifying free-space paired waveguide coupler may be realized by the coupler 101 illustrated and described with respect to Figure 1B, by the coupler 200 illustrated and described with respect to Figure 2, by the coupler 300 illustrated and described with respect to Figure 3, by the coupler 1000 illustrated and described with respect to Figure 10A, by the coupler 1100 illustrated and described with respect to Figure 11A, by the coupler 1300 illustrated and described with respect to Figure 13A, by the coupler 1500 illustrated and described with respect to Figure 15A, by the coupler 1600 illustrated and described with respect to Figure 16A, or by the coupler 1700 illustrated and described with respect to Figure 17A.

[0242] In step 2307, for the output light emitted by each of the selected polarization-diversified free-space versus waveguide couplers, the first polarization of the output light may be converted to a second polarization by a polarization conversion structure. The second polarization may be the same as or different from the first polarization. The second polarization may be linearly polarized, circularly polarized, or elliptically polarized. According to some embodiments, the polarization conversion may be achieved by one or a combination of optical components, including but not limited to a Faraday rotor, a polarizing rotor, and a quarter-wave plate.

[0243] In step 2307, according to some embodiments, the optical path of the output light may be further displaced laterally or angularly, or both laterally and angularly. This displacement may be realized by at least one of optical path displacement components, such as a polarization-dependent beam separator, but is not limited to these. According to some embodiments, the polarization conversion and optical path displacement operations may be realized by a combination of optical components, including but not limited to a Faraday rotator, a polarizing rotator, a quarter-wave plate, and a polarization-dependent beam separator. According to some embodiments, such operations may be realized by at least one of the configurations shown in Figures 4C, 5A, 5C, 6A, 6C, 10C, 11B, 12A, 13C, 15C, 16C, and 17B, but is not limited to these. According to some embodiments, the configuration for such operations may or may not be arranged together with other optical components of the imaging optical system. For example, referring to Figure 22A, the polarization conversion configuration with optical path displacement includes components 2241, 2242, 2251, 2252, and 2261, which are arranged together with the optical components (lenses) of the imaging optical system 2203.

[0244] In step 2309, the converted output light is directed to one or more targets located in the field of view of an optical coherent imager corresponding to a polarization-diversified free-space versus waveguide coupler selected according to step 2303. According to some embodiments, the converted output light can be directed to the target using an additional imaging optical system placed between the selected coupler and the target.

[0245] In step 2311, the targets may reflect or scatter the converted output light that illuminates them. The reflected or scattered light from the targets may be received by an optical coherent imager at the field of view of the imaging device corresponding to the selected polarization-diversified free-space versus waveguide coupler described in step 2309. According to some embodiments, the reflected or scattered light may be received by an additional imaging optical system positioned between the selected coupler and the targets. According to some embodiments, the optical imaging system may be the same as the imaging optical system in step 2309.

[0246] In step 2313, the received light reflected or scattered from the target may be transformed by the same polarization transformation structure as described in step 2307. At each of the field of view positions of the imaging device described in step 2311, the received light may include one or both of a component having a third polarization which is the same as the second polarization of the transformed output light, and a component having a fourth polarization which is orthogonal to the third polarization component. At each of the field of view positions, the polarization transformation configuration can transform the third polarization of the received light into a fifth polarization which is orthogonal to the first polarization of the output light at that position. Similarly, the polarization transformation configuration can transform the fourth polarization of the received light into a sixth polarization which is orthogonal to the fifth polarization of the transformed received light. According to some embodiments, at each of the field of view positions, the optical path of at least one polarization component of the received light may be further displaced by the same optical path displacement component as described in step 2307. According to some embodiments, the displaced polarization component of the received light may be one or both of the third and fourth polarizations.

[0247] In step 2315, the converted received light may be coupled from free space to an internally coupled waveguide using one or more polarization-diversified free-space paired waveguide couplers. According to some embodiments, these polarization-diversified free-space paired waveguide couplers may be the same set of polarization-diversified free-space paired waveguide couplers used to radiate the output polarization in step 2305. For each of the polarization-diversified free-space waveguide couplers, at least one of the internally coupled waveguides that receive some or all of the received light converted through the polarization-diversified free-space paired waveguide coupler is different from the waveguide that leads the light source light to the coupler according to step 2303 (i.e., the output coupled waveguide).

[0248] On the other hand, more specifically, according to some embodiments, a polarization-diversified free-space paired waveguide coupler can input couple a fifth polarization of the converted received light, which is orthogonal to the first polarization of the output light emitted from the coupler, to at least one waveguide different from the output coupling waveguide. This is preferably achieved by designing a polarization-diversified free-space paired waveguide coupler that couples the fifth polarization of the converted received light to an input coupling waveguide different from the output coupling waveguide. According to some embodiments, this is preferably achieved by the optical path displacement of the third polarization of the received light. As a result, the fifth polarization of the converted received light can reach a coupler located at a spatial position different from the spatial position from which the output light is emitted from the coupler.

[0249] On the other hand, according to some embodiments, the polarization-diversifying free-space paired waveguide coupler may be orthogonal to the fifth polarization of the converted received light and input couple the sixth polarization of the converted received light to at least one waveguide different from the output coupling waveguide. This may be achieved by the optical path displacement of the fourth polarization of the received light. As a result, the sixth polarization of the converted received light may reach a coupler at a spatial position different from the spatial position from which the output light is emitted from the coupler. According to some embodiments, the optical path displacements of the third and fourth polarizations of the received light can be realized through the same optical path displacement components described in step 2313.

[0250] In step 2317, the received light internally coupled in the internally coupled waveguide may be detected by a detector positioned in close proximity to a polarization-diversified free-space paired waveguide coupler that internally couples the converted received light. The detector may be positioned as a heterodyne detector to perform heterodyne detection using local oscillator light supplied to the heterodyne detector.

[0251] In step 2319, the detected signal can be processed to extract information about the target. The signal processing may be performed by a signal processing unit which may or may not be part of the optical coherent imager. According to some embodiments, the target information includes, but is not limited to, the coordinates of the target and the reflectance of the target surface. According to some embodiments, the target information may include the distance from the optical coherent imager to the target. According to some embodiments, the target information may include the velocity information of the target. According to some embodiments, the distance and velocity information may be obtained by modulating the light source in step 2301 according to the FMCW LIDAR technique and extracted by the Fourier transform of the detected signal.

[0252] For the purpose of describing and defining this disclosure, it should be noted that the term "degree" (e.g., "substantially," "slightly," "about," "equivalent," etc.) may be used herein to express the degree of inherent uncertainty that may arise from quantitative comparisons, values, measurements, or other expressions. Such terms of degree may be used herein to express the extent to which a quantitative expression may deviate from a stated standard (e.g., about 10% or less) without altering the fundamental function of the subject matter in question. Unless otherwise stated herein, numerical values ​​described herein are deemed to be modified by terms of degree (e.g., "about"), thereby reflecting their inherent uncertainty. While various embodiments of this disclosure are described in detail herein, those skilled in the art will readily understand modifications and other embodiments without departing from the spirit and scope of this disclosure as set forth in the appended claims.

Claims

1. An optical coherent sensor comprising multiple coherent sensing units, Each of the aforementioned coherent sensing units is: A polarization-diversifying optical coupler that can guide an optical signal having a first polarization state into and from a first waveguide, and a optical signal having a second polarization state into and from a second waveguide, A 2x2 optical coupler optically coupled to the polarization-diversifying optical coupler via at least one of the first and second waveguides, It has, The polarization-diversifying optical coupler has a first subcoupler and a second subcoupler. The first sub-coupler guides an optical signal having the first polarization state to and from the first waveguide. The second subcoupler guides an optical signal having the second polarization state to and from the second waveguide. An optical coherent sensor characterized in that one of the first and second subcouplers has polarization dependence that allows it to appropriately couple with an optical signal in a predetermined polarization state, and the other of the first and second subcouplers has polarization independence that allows it to appropriately couple with an optical signal in any polarization state.

2. The optical coherent sensor according to claim 1, characterized in that the second subcoupler is arranged vertically and separately on the first subcoupler.

3. An optical coherent sensor comprising multiple coherent sensing units, Each of the aforementioned coherent sensing units is: A polarization-diversifying optical coupler that can guide an optical signal having a first polarization state into and from a first waveguide, and a optical signal having a second polarization state into and from a second waveguide, A 2x2 optical coupler optically coupled to the polarization-diversifying optical coupler via at least one of the first and second waveguides, It has, The polarization-diversifying optical coupler has a first subcoupler and a second subcoupler. The first sub-coupler guides an optical signal having the first polarization state to and from the first waveguide. The second subcoupler guides an optical signal having the second polarization state to and from the second waveguide. The first and second subcouplers are arranged on a photonic substrate and are separated from each other laterally. Furthermore, it includes a polarization converter positioned on the coherent sensing unit, The polarization converter guides the optical signal output from one of the first and second subcouplers into an optical path in free space, and separates the optical signal input from the optical path into a first optical signal having a first polarization state and a second optical signal having a second polarization state. An optical coherent sensor characterized in that at least one of the first and second optical signals is spatially displaced by the polarization converter such that the first and second optical signals are input to the first and second subcouplers, respectively.

4. An optical coherent sensor comprising a plurality of coherent sensing units and a polarization converter disposed on the coherent sensing units, Each of the aforementioned coherent sensing units is: A polarization-diversifying optical coupler that can guide an optical signal having a first polarization state into and from a first waveguide, and a optical signal having a second polarization state into and from a second waveguide, A 2x2 optical coupler optically coupled to the polarization-diversifying optical coupler via at least one of the first and second waveguides, It has, The polarization-diversifying optical coupler has a first subcoupler and a second subcoupler. The first sub-coupler guides an optical signal having the first polarization state to and from the first waveguide. The second subcoupler guides an optical signal having the second polarization state to and from the second waveguide. The polarization converter is characterized by having at least one polarization-dependent beam separator, making it an optical coherent sensor.

5. The optical coherent sensor according to claim 4, characterized in that the polarization converter has a polarization converter that rotates a linearly polarized optical signal by a predetermined angle.

6. The optical coherent sensor according to claim 5, characterized in that the polarization converter is a Faraday rotor.

7. The optical coherent sensor according to claim 4, characterized in that the polarization converter has a quarter-wave plate.

8. An optical coherent sensor comprising multiple coherent sensing units, Each of the aforementioned coherent sensing units is: A polarization-diversifying optical coupler that can guide an optical signal having a first polarization state to and from a first waveguide, a optical signal having a second polarization state to and from a second waveguide, and an optical signal having a third polarization state to and from a third waveguide, A 2x2 optical coupler optically coupled to the polarization-diversifying optical coupler via at least one of the first waveguide, the second waveguide, and the third waveguide, It has, The polarization-diversifying optical coupler has a first subcoupler, a second subcoupler, and a third subcoupler. The first sub-coupler guides an optical signal having the first polarization state from the first waveguide. The second subcoupler guides the optical signal having the second polarization state into the second waveguide. The optical coherent sensor is characterized in that the third subcoupler guides an optical signal having the third polarization state into the third waveguide.

9. The optical coherent sensor according to claim 8, characterized in that the first, second, and third subcouplers are arranged on a photonic substrate and are separated from each other laterally.

10. Furthermore, it includes a polarization converter positioned on the coherent sensing unit, The polarization converter guides the optical signal output from the first subcoupler into an optical path in free space, and separates the optical signal input from the optical path into a first optical signal having the second polarization state and a second optical signal having the third polarization state. The optical coherent sensor according to claim 8, characterized in that at least one of the first and second optical signals is spatially displaced by the polarization converter such that the first and second optical signals are input to the second and third subcouplers, respectively.

11. The polarization-diversifying optical coupler can further guide optical signals having a fourth polarization state into and from the fourth waveguide. The polarization-diversifying optical coupler further comprises a fourth subcoupler, The optical coherent sensor according to claim 8, characterized in that the fourth subcoupler guides the optical signal having the fourth polarization state from the fourth waveguide.

12. An optical coherent imager having an optical coherent sensor according to any one of claims 1, 3, and 4 and an imaging optical system including a plurality of lenses, The imaging optical system is characterized in that the optical coherent sensor is positioned in close proximity to the image plane of the imaging optical system, thereby providing an optical coherent imager.

13. The steps include: emitting an output optical signal from an optical coherent imager to a target along an optical path corresponding to the field of view of the optical coherent imager; The steps include receiving the input optical signal reflected from the target, which was emitted by the output optical signal, by the optical coherent imager along the optical path, The steps include converting the input optical signal using the polarization converter of the optical coherent imager into a first optical component having a first polarization state and a second optical component having a second polarization state orthogonal to the first polarization state, The steps of guiding the first and second optical components to one or more photodetectors of the optical coherent sensor of the optical coherent imager by a polarization-diversifying optical coupler on the optical coherent sensor, It has, The polarization-diversifying optical coupler can guide an optical signal having the first polarization state to and from the first waveguide, and can guide an optical signal having the second polarization state to and from the second waveguide. The step of emitting the output optical signal is: A step of generating a light source signal from a light source, The steps include converting the light source light signal into an output light signal having a first radiant polarization state using the polarization-diversifying optical coupler, The steps include: emitting the output optical signal from the polarization-diversifying optical coupler; It has, The step of converting the input optical signal includes spatially displacing at least one of the first and second optical components according to the first and second polarization states, such that each of the first and second optical components is input to the first and second subcouplers of the polarization-diversifying optical coupler. The first sub-coupler guides an optical signal having the first polarization state to and from the first waveguide. The second subcoupler guides an optical signal having the second polarization state to and from the second waveguide. The first and second subcouplers are arranged on a photonic substrate and are separated from each other laterally. A light coherent imaging method characterized by the following.

14. The optical coherent imaging method according to claim 13, further comprising the step of outputting an output optical signal from the polarization-diversifying optical coupler, and then converting the output optical signal from a first output polarization state to a second output polarization state using the polarization converter of the optical coherent imager.

15. The optical coherent imaging method according to claim 13, characterized in that the step of converting the input optical signal includes rotating the first polarization state of the input optical signal by a first predetermined polarization angle and rotating the second polarization state of the input optical signal by a second predetermined polarization angle.

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