Planar optical elements for optical coupling

Abstract

A system for free-space optical coupling between a two-dimensional optical transmitter array and a two-dimensional optical receiver array using planar optical elements includes a transmitter array configured to emit one or more optical beams, a first planar optical element configured to receive the optical beams from the transmitter array and generate one or more intermediate optical beams, a first spacer disposed between the optical transmitter array and the first planar optical element, a receiver array, a second planar optical element configured to receive the intermediate optical beams and generate one or more output optical beams directed to the receiver array, and a second spacer disposed between the second planar optical element and the optical receiver array. The TX and RX portions of the optical coupling system can be used in a LiDAR system as a light emitting element (beam steerer) and a detector, respectively. The planar optical element is configured to provide a wide field of view for the LiDAR.

Description

[Technical Field]

[0001] Background of the Invention The present invention relates to optical elements and optical systems, and in particular to planar optical elements and their applications in optical and photonic systems. [Background technology]

[0002] Free-space optical coupling between two-dimensional optical transmitter arrays and two-dimensional optical receiver arrays offers significant advantages in realizing high-bandwidth-density optical channels, which are essential for applications such as optical interconnects, photonic packaging, sensing, imaging, and computing. However, conventional free-space optical systems based on refractive and reflective optics typically require many precisely aligned optical components to optimize the link and meet requirements such as coupling efficiency, mode matching, channel density, field of view, and link distance. These requirements make the optical assemblies very complex, bulky, and costly, and also limit their performance.

[0003] Edge coupling and surface-normal coupling are the two main configurations for on- and off-chip coupling to PICs. Edge coupling is limited to accessing only the periphery of the chip and is also constrained by the large optical fiber pitch. As a result, edge coupling is fundamentally limited in terms of bandwidth density. Furthermore, edge coupling is only applicable to die-level characterization and is not compatible with wafer-level testing. Surface-normal coupling typically utilizes 2D grating arrays, which achieve much higher bandwidth density and compatibility with wafer-level testing. To date, grating couplers have almost always been designed for coupling to optical fibers, whose mode field diameter is approximately 10 μm, matching that of a standard single-mode fiber.

[0004] Coupling to large-area, freely propagating beams (emission or reception modes) has been little investigated to date, despite its importance for many space missions. Recently, surface-enlarged diffraction grating couplers for coupling to high-power lasers or multimode fibers have been investigated. However, these devices only provide high-quality (small M near unity) coupling. 2 They are not suitable for coupling with free-space beams (characterized by optical parameters) (e.g., multimode couplers cannot form high-quality beams due to multimode interference). In addition, even these "large-area" diffraction gratings are only smaller than 100 μm in size. Optical phased arrays (OPAs) combine a large number of individual light-emitting elements, each with tunable output phase, to achieve wavefront control and beamforming. However, high-quality large-area beamforming using OPAs requires a small light-emitting element pitch and a large number of phase-modulating elements. For example, a 1 mm 2 In OPAs with an area of ​​1000 nm, the number of individually addressed light-emitting elements can reach the order of one million, let alone larger arrays. Alternative methods involve using discrete optical elements, such as lenses or mirrors, to convert the output from a point source (e.g., a miniature diffraction grating coupler) into a collimated beam. This approach has been adopted to enable high-throughput inspection of on-chip device arrays, matable expanded-beam optical connectors with relaxed alignment tolerances, and lens-assisted beam steering. These examples use traditional bulky refractive or reflective optical elements, which significantly increase the module footprint and require sequential die- or chip-level assembly with low throughput and yield.

[0005] LiDAR is an exemplary application where such a PIC-to-free-space optical coupling mechanism plays a transformative role. LiDAR is a laser-based ranging technology for 3D depth (distance) measurement, characterized by much higher accuracy compared to radar (the radio-wave counterpart of LiDAR). It has been widely deployed in metrology, robotics, environmental monitoring, meteorology, remote sensing, autonomous driving, and other fields. Traditional LiDAR uses a mechanically rotating light source and detector to cover the surrounding scene, but this limits the speed, resolution, robustness, compactness, and cost-effectiveness of LiDAR systems. To address these limitations, solid-state LiDAR based on nanophotonic technologies, exemplified by PIC-based OPAs and active metasurfaces, has been widely investigated in recent years. However, these solutions still face scaling challenges toward high-density, large-scale arrays, which are crucial for practical deployment. First, aliasing-free operation over a wide field of view (FOV) requires a subwavelength (ideally, ≤λ / 2 or half-wavelength) pitch, which introduces significant crosstalk and fabrication difficulties. Second, achieving high-quality beamforming requires large-aperture (millimeter-scale) arrays with precisely controlled optical phase profiles. However, large arrays with subwavelength pitch imply a huge number (millions) of individually addressed, densely packed optical antennas, posing integration and packaging challenges. In PIC-based OPAs, this challenge is typically mitigated by introducing wavelength tuning for beam steering along one direction, but they nevertheless suffer from a rather small steering angular range. Finally, the frame rate of these scanning LiDARs is essentially limited by the beam scanning speed, resulting in motion artifacts. Summary of the Invention [Means for solving the problem]

[0006] Summary of the Invention Embodiments of the present invention provide an optical coupling and beam shaping architecture based on planar optical elements that offers high performance, small form factor, and structural simplicity compared to traditional optical approaches. This architecture can be used in a variety of optical systems, including optical interconnects, photonic packaging, sensing, imaging, computing, etc.

[0007] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof, as well as the appended drawings.

[0008] To achieve the above object, the present invention provides an optical coupling system including a transmitter array including one or more optical transmitters configured to emit one or more optical beams, a first planar optical element configured to receive the optical beams from the transmitter array and generate one or more intermediate optical beams, a first spacer disposed between the optical transmitter array and the first planar optical element, a receiver array including one or more optical receivers, a second planar optical element configured to receive the intermediate optical beams and generate one or more output optical beams to be directed to the receiver array, and a second spacer disposed between the second planar optical element and the optical receiver array.

[0009] In a preferred embodiment, the first and second planar optical elements are configured to provide optical relay or mode matching between the transmitter array and the receiver array. Each of the multiple optical transmitters is a light source or an optical channel coupled to an external light source, and each of the multiple optical receivers is an optical sensor or an optical channel coupled to an external optical sensor. The optical transmitter array and / or the optical receiver array may be a photonic integrated circuit.

[0010] In another aspect, the present invention provides an optical beam steering system including: a two-dimensional light-emitting element array including a number of light-emitting elements configured to emit a number of light beams; a first metasurface configured to receive a light beam from each light-emitting element of the light-emitting element array and generate one or more corresponding output light beams or light distribution patterns, wherein the output light beams or patterns have at least one beam characteristic that depends on the two-dimensional position of the corresponding light-emitting element, the at least one beam characteristic including direction, collimation, divergence, or intensity distribution, the first metasurface configured to generate the output light beam over a field of view greater than 60 degrees relative to a normal direction of the first metasurface; and a first control circuit coupled to the light-emitting element array for modulating or selectively turning on or off individual light-emitting elements in the light-emitting element array.

[0011] In another aspect, the present invention provides a LiDAR (light detection and ranging) system including a light emitting element and a light detector, wherein the light emitting element includes the light beam steering system described above. The light detector of the LiDAR system includes a two-dimensional light detector array including a number of light detectors, a second metasurface configured to receive a light beam reflected from a target scene and focus the light beam on the light detector array, the second metasurface configured to receive the light beam reflected from the target scene over a field of view greater than 60 degrees relative to a normal direction of the second metasurface, and a second control circuit coupled to the light detector array for processing signals generated by the light detector array.

[0012] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. [Brief explanation of the drawings]

[0013] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1]1 illustrates a schematic diagram of an optical coupling and interconnection system employing planar optical elements, according to an embodiment of the present invention. [Figure 2] 1 illustrates a schematic diagram of an exemplary optical coupling and interconnection system employing planar optical elements, in accordance with an embodiment of the present invention. [Figure 3] 10A and 10B illustrate schematic diagrams of optical coupling and interconnection systems employing planar optical elements with folded optical paths, in accordance with another embodiment of the present invention. [Figure 4] 10A and 10B illustrate schematic diagrams of optical coupling and interconnection systems employing planar optical elements, where one or both planar optical elements provide a microlens function, according to another embodiment of the present invention. [Figure 5] 10 illustrates a schematic diagram of an optical coupling and interconnection system employing a planar optical element used as an image inverter, according to another embodiment of the present invention. [Figure 6] 1 illustrates a schematic diagram of an optical transmitter or detector of a LiDAR (Light Detection and Ranging) system, according to an embodiment of the present invention; [Figure 7] 10 illustrates a schematic diagram of an optical transmitter of a LiDAR system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Detailed Description of the Invention Embodiments of the present invention provide optical coupling and interconnection architectures and designs based on planar optical elements. In embodiments of the present invention, metasurface optics, which employ subwavelength arrays of optical antennas or "meta-atoms," each designed to impart a specific phase delay, offer a new method for on-demand wavefront shaping. Unlike traditional refractive or reflective optics, which are customarily fabricated from bulk materials, metasurface optics boast a flat, low-profile form factor that is amenable to mass manufacturing via standard CMOS microfabrication and wafer-level assembly, making them ideally suited for scalable integration with PICs. Furthermore, while traditional optical systems face the fundamental challenge of typically requiring a series of lenses to correct aberrations, the metasurface-based coupling approach according to embodiments of the present invention enables compact systems with low-aberration wavefront control at large optical input / output angles.

[0015] As schematically depicted in FIG. 1 , an optical coupling system according to an embodiment of the present invention includes a first planar optical element 11 (planar optical element 1) coupled to an optical transmitter (TX) array 13 having a number of optical transmitters and a second planar optical element 12 (planar optical element 2) coupled to an optical receiver (RX) array 14 having a number of optical receivers. The coupling between the TX array and the first planar optical element is performed via a spacer 15, which may be any optically transparent medium, such as an air gap, a solid or liquid material, a porous material, a metamaterial, etc. Similarly, the coupling between the second planar optical element and the RX array, and the coupling between the first planar optical element and the second planar optical element are also performed via respective spacers 16 and 17, which may be an air gap, a solid or liquid material, a porous material, a metamaterial, etc. It should be emphasized that the optical coupling between the planar optical elements 11 and 12 and the corresponding optical transmitters 13 and optical receivers 14 involves three-dimensional free-space light propagation, e.g., the coupling of light between the PIC and the space outside the PIC. In other words, the planar optical element 11 or 12 and the corresponding optical transmitter 13 or optical receiver 14 are not integrated together in the same PIC.

[0016] The first planar optical element 11 receives the light beams emitted by the TX array 13 and generates multiple intermediate light beams, and the second planar optical element 12 receives the intermediate light beams and generates multiple output light beams that are directed to the RX array 14. The first and second planar optical elements are configured to provide optical relay and / or mode matching between the TX array and the RX array. In one example, the first planar optical element collimates the light emitted from the TX array and steers the beams toward the second planar optical element, which then focuses the beams onto the corresponding RX array. The optical system can be configured to achieve normal, oblique, or any other type of beam combination at the object and image planes. The image height or light intensity pattern generated by the optical system can be further designed to control the position or distribution of the TX and / or RX spot arrays. To further improve performance, additional optical elements (e.g., planar optical elements, refractive and / or reflective optics, microlens arrays, etc.) can be incorporated into the optical combination system.

[0017] In this disclosure, planar optical elements may include, but are not limited to, subwavelength optics, metasurfaces, multilayer metasurfaces, metamaterials, diffractive optical elements (DOEs, such as binary, multilevel, or grayscale DOEs), holographic optical elements (HOEs), wafer-level optics (WLOs), micro-optics, etc. One example of a planar optical element is an optical metasurface. An optical metasurface, also known as a subwavelength diffractive optic, is an artificial medium that typically includes a two-dimensional (2D) array of subwavelength optical structures (commonly referred to as meta-atoms) arranged on a substrate. The meta-atoms and the substrate may be made of the same optical material or different optical materials. The meta-atoms are designed to change the phase, amplitude, and / or polarization of incident light. The meta-atoms may have the same geometry, dimensions, and orientation, or different geometries, dimensions, and orientations. Exemplary geometries may include rectangular, cylindrical, freeform, or any other suitable shape, or a combination of different shapes. The lattice of meta-atoms can have any suitable shape and periodicity (e.g., square, rectangular, or hexagonal). The lattice can also be aperiodic, where the distance between adjacent meta-atoms is varied or random. In some examples, the gaps between adjacent meta-atoms can be designed to have a constant gap distance.

[0018] The metasurface can be flat, curved, or conformally integrated with a substrate. One or both sides of the substrate can be flat or curved. Both the metasurface and the substrate can be rigid, flexible, or stretchable. The geometry, dimensions, and layout of the meta-atoms and substrate are designed to provide a target optical function. The metasurface can be designed to operate at a single wavelength, multiple wavelengths, or over a continuous spectral range.

[0019] The optical transmitter may include a light source (e.g., a laser, a light-emitting diode (LED)) and / or an optical channel (e.g., an optical fiber, an optical waveguide, an optical coupler, etc.) that transmits light from an external light source. The optical receiver may include an optical sensor such as a photodetector and / or an optical channel (e.g., a fiber, an optical waveguide, an optical coupler, etc.) that transmits light to an external light sensor. The optical transmitter array and / or the optical receiver array may be a PIC device. In addition to physical objects, the transmitter and receiver, respectively, may be non-physical, such as an image or light pattern generated by an external light source or an image or light pattern received by another optical component or system. The optical transmitter and receiver may have different physical sizes and / or orientations.

[0020] The light emitted by each optical transmitter of the TX array (i.e., the light incident on the first planar optical element) has defined optical characteristics, such as a divergence angle, an incident angle with respect to the surface of the first planar optical element, a wavefront shape (possibly aspherical), a wavelength, and / or a polarization. The first planar optical element is designed based not only on these optical characteristics of the incident light but also on the required characteristics of the intermediate light beam output by the first planar optical element, such as a divergence angle, an output direction, a wavefront shape, a polarization, and a wavelength. On the RX side, the light output by the second planar optical element must have defined optical characteristics, such as a divergence angle, an output direction, a wavefront shape, a polarization, and a wavelength, suitable for the RX array. The second planar optical element is designed based on the optical characteristics of the intermediate light beam (i.e., the light incident on the second planar optical element) and the required optical characteristics of the output light from the second planar optical element. With this design, the first and second planar optical elements can provide optical relay and / or mode matching between the TX array and the RX array. As mentioned above, in one example, the first planar optical element is configured to collimate light emitted from each optical transmitter of the TX array and output a beam at a defined angle toward the second planar optical element, which is configured to focus each beam onto a corresponding receiver of the RX array.

[0021] 1 has a telecentric configuration on both the TX and RX sides. That is, the chief ray of the light emitted from each transmitter is normal to the first planar optical element, and the chief ray of the output light beam toward each receiver is normal to the second planar optical element. In other examples, the optical system may be near-telecentric (the chief ray is within about 20 degrees of the normal to the respective planar optical element), non-telecentric, telecentric or near-telecentric only on the TX or RX side, etc.

[0022] 1, all of the intermediate light beams overlap at a common area on the plane between the two planar optical elements, but it should be noted that this is not required, and the first and second planar optical elements do not have to be parallel to each other.

[0023] FIG. 2 shows an exemplary optical coupling system in which a first planar optical element 11 and a second planar optical element 12 (planar optical element 1 and planar optical element 2) are configured to relay a 1.6 mm-wide light source array (numerical aperture NA of approximately 0.05) as a transmit (TX) array 13 to a 0.4 mm-wide fiber array (numerical aperture NA of approximately 0.22) as a receive (RX) array 14. This ultra-compact design employs only two layers of planar optical elements separated by a spacer 15. Optical simulations (ray tracing simulations, FIG. 2) demonstrated high-density, diffraction-limited coupling and precise mode matching between the TX and RX arrays. The total track length of the optical system is 8.8 mm and is further adjustable. In some examples, the spacer can be formed of air, glass, polymer, semiconductor, or other suitable optical material. Other aspects of this embodiment are similar to those of the embodiment of FIG. 1.

[0024] FIG. 3 schematically illustrates another optical coupling architecture using planar optical elements with a folded optical path. This system includes a metasurface 39, a spacer 37, and a reflector 38, with the metasurface 39 and the reflector 38 positioned at two locations across the spacer 37. The metasurface 39 includes one or more regions, such as a first planar optical element region 31 (planar optical element 1) and a second planar optical element region 32 (planar optical element 2). The first planar optical element region is coupled to an optical transmitter (TX) array 33 via a spacer 35, and the second planar optical element region is coupled to an optical receiver (RX) array 34 via a spacer 36. The spacers 35 and 36 may be formed on the same physical layer. The optical beams emitted from the TX array 33 are coupled by the first planar optical element region 31 and redirected toward the reflector 38. The reflector reflects, reshapes and / or redirects the beam towards the second planar optical element region 31 , where the beam is further coupled into the RX array 34 .

[0025] The first and second planar optical element regions and the reflector are configured to provide optical relay and / or mode matching between the transmitter array and the receiver array. In one example, the first planar optical element region 31 collimates light emitted from the transmitter array 33 and directs the beam toward the planar mirror 38, where it is reflected toward the second planar optical element region 32 and then focused by the second planar optical element region onto the corresponding receiver array 34. The optical system can be configured to achieve normal, oblique, or any other type of optical coupling at the object and image planes. The reflector 38 can be flat, curved, or of any other geometry to redirect and / or reshape the light. Reflection can be based on reflective coatings or structures, diffraction, metasurfaces, and / or total internal reflection. To further improve performance, additional optical elements (e.g., planar optical elements, refractive and / or reflective optics, microlens arrays, etc.) can be incorporated into the system. Other aspects of this embodiment are similar to those of the embodiment of FIG. 1.

[0026] 4, one or both of the first planar optical element 41 and the second planar optical element 42 are configured to provide the functionality of a microlens array, with different non-overlapping regions of the first planar optical element 41 designated to couple to different TX channels 43 and / or different non-overlapping regions of the second planar optical element 42 designated to couple to different RX channels 44. For example, in the example shown in FIG. 4, the first planar optical element 41 directs intermediate beams corresponding to individual optical transmitters of the TX array 43 to separate non-overlapping regions of the second planar optical element 42, with each region producing only an output optical beam corresponding to one optical receiver. Other aspects of this embodiment are similar to those of the embodiment of FIG. 1.

[0027] FIG. 5 schematically illustrates an optical coupling system used as a metasurface-based image inverter (metanverter), which inverts the image to significantly improve compactness, e.g., achieve an aspect ratio of approximately 2:1 or less compared to an aspect ratio of 4:1 or more using conventional optical systems. To form the image inverter, both the first planar optical element 11 and the second planar optical element 12 are collimating lenses, and the chief rays of all intermediate beams pass through a common point. In some embodiments, the first planar optical element and the second planar optical element have the same size and generate an inverted image having the same size as the original image on the TX side. In some embodiments, the structures of the first planar optical element and the second planar optical element are symmetrical to each other with respect to the center of the planar optical element. As previously mentioned, the TX array and the RX array can each be non-physical, such as an image or light pattern (or intermediate image) generated by an external light source or an image or light pattern received by another optical component or system. Other aspects of this embodiment are similar to those of the embodiment of FIG. 1.

[0028] Another embodiment of the present invention provides a hybrid PIC metasurface-based LiDAR system. It uses a chip-scale packaging platform to enable efficient coupling between photonic integrated circuits (PICs) and free space, generating high-quality (e.g., diffraction-limited), large-area (e.g., diameters ranging from tens of microns to several millimeters or more), dense array beams. This technology can be utilized to realize chip-scale optical engines for unprecedented ultra-wide field-of-view (FOV), low-loss, and high-frame-rate light detection and ranging (LiDAR). This optical coupling interface greatly facilitates the implementation of PIC technology in various applications, such as navigation, communications, and sensing. The coupling of PICs with large-area free-space beams offers many advantages, including light weight, compactness, and high performance. Additionally, LiDAR technology will have a broad impact on other applications, such as robotics control, unmanned aerial vehicle (UAV) navigation, automotive sensing, and consumer electronics.

[0029] This LiDAR system uses metasurface-based beam steering to project a light beam or pattern toward a target scene with a wide field of view (FOV). The light sources behind the metasurface can be individually controlled to direct, steer, toggle, or adjust the beam over a large area. To collect signals over a large area, the same wide-field metalens used to project the light can also be employed in the LiDAR device's receiver.

[0030] The overall structure and operating principles of LiDAR systems are generally known, so the following discussion will focus on the metasurface-based light emitter and metasurface-based light detector of LiDAR systems.

[0031] FIG. 6 illustrates the structure of a metasurface-based light-emitting element or photodetector in a LiDAR system according to an embodiment of the present invention. In the case of a light-emitting element, component 63 is an optical transmitter (TX) array, and in the case of a photodetector, component 63 is an optical receiver (RX) array. As shown in FIG. 6 , the metasurface-based light-emitting element or photodetector includes a planar optical element 61 optically coupled to a TX or RX array 63 via a spacer 65. In the case of a light-emitting element, the TX array 63 includes a 2D array of light-emitting elements, such as a light source (e.g., a VCSEL (vertical cavity surface-emitting laser), an LED (light-emitting diode), etc.) or a PIC (photonic integrated circuit) coupler, waveguide, optical fiber, etc., that transmits light from an external light source. In the case of a photodetector, the RX array 63 includes a light sensor, such as a photodetector, and / or an optical channel (e.g., a fiber, a waveguide, an optical coupler, etc.) that transmits light to the external light sensor.

[0032] In the case of a light-emitting element, the planar optical element 61 can be a metasurface formed from an array of meta-atoms (light-emitting element metasurface), where each meta-atom can be individually configured to emit light with a different phase, amplitude, and polarization state. The light-emitting element metasurface is configured to receive diverging incident light beams emitted by each light-emitting element and collimate the beams to generate corresponding collimated output beams. The output direction of the corresponding output beams depends on the 2D position of the incident light beam, i.e., the physical location of the particular light-emitting element within the 2D light-emitting element array. The light-emitting elements within the array are individually controlled by the control circuitry 60 to turn them on / off and / or modulate the phase of their emitted light. As a result, the direction of the output light beam generated by the metasurface is controlled by the control circuitry 60. In this way, the metasurface light-emitting element array achieves light beam shaping and steering over a wide range of angles without mechanical movement.

[0033] More generally, the light-emitting element metasurface is configured such that at least one optical property of the output beam, such as direction, collimation, divergence, or intensity distribution, depends on the two-dimensional position of the corresponding light-emitting element.

[0034] Light-emitting element metasurfaces can be configured to generate one-to-one emission (i.e., one light-emitting element produces one output beam), one-to-N emission (i.e., one light-emitting element produces multiple output beams), or patterned emission (i.e., one light-emitting element produces an output beam pattern).

[0035] The light emitting element array 63 may be implemented with an optical waveguide, a light emitting element array for coupling light from the waveguide into free space, a switch network for routing the light to the individual light emitting elements, and a modulator array for modulating the output light. Such switched light emitting element arrays are known in the art and will not be described in further detail here.

[0036] In preferred embodiments, the light-emitting element metasurface is configured to have a wide FOV, e.g., at least ±30 degrees relative to the metasurface normal, and preferably ±90 degrees relative to the normal (i.e., a 180-degree FOV). This wide FOV is achieved by the design of the light-emitting element metasurface and associated optical structures, as described in more detail below.

[0037] The metasurface for the photodetector (photodetector metasurface) can have a structure and properties similar to the light-emitting element metasurface described above. The photodetector metasurface is configured to receive light beams reflected from a target scene over a wide FOV and focus or redirect the beams onto the optical receiver array 63.

[0038] A specific example of a light-emitting element (or photodetector) for a LiDAR system according to one embodiment of the present invention is shown in FIG. 7 . Component 72 is a light source or an optical transmitter array, such as a PIC coupler, in the case of a light-emitting element, and a photodetector or an optical receiver array, such as a PIC coupler, in the case of a photodetector. This system operates in the 1550 nm band, which is considered eye-safe, but can easily be adapted to other wavelengths. Metasurface 71 is formed of a-Si nanopillars immersed in an epoxy layer and sandwiched between two glass spacers 73 and 74. An aperture 75 is formed on the top surface of upper spacer 73 facing the target. The aperture and metasurface 71, separated by spacer 73, together form a wide-FOV metalens. In this example, the metalens has an aperture size of 1 mm and a numerical aperture (NA) of 0.20 (f / #=2.5). The NA can be tuned to match the divergence angle of the optical transmitters in TX array 72 (or the spot size of the optical receivers in the receiver array) to maximize coupling efficiency. In a preferred embodiment, the metalens has a telecentric configuration, which contributes to aberration suppression. Additionally, this configuration ensures that the chief ray angle of the light beam emitted by the optical transmitter toward the metasurface (or generated by the metasurface toward the optical receiver) is close to zero relative to the normal to the metasurface, regardless of the light beam exit (or entrance) angle of the LiDAR device. This is an important advantage for LiDAR because it avoids the angle-dependent spectral drift of LiDAR integrated filters and enables the use of a single bandpass filter that efficiently removes background ambient light from the entire FOV. The metalens (fisheye lens) maintains diffraction-limited focusing quality at all beam exit (or entrance) angles (up to a 180° FOV). At extreme beam exit (or entrance) angles (greater than 80° relative to the normal), efficiency may decrease due to Fresnel reflection losses, but this can be mitigated by appropriate surface texturing or angle-dependent metasurface design. The angular resolution of LiDAR is determined by the pitch of the emission or detection coupler array, with a coupler pitch of 10 μm resulting in a resolution of about 0.2°, which meets the requirements of most practical applications.Additional metasurfaces can be used to further improve performance, such as compensating for barrel distortion at large AOIs (angle of incidence or exit). Further resolution improvements are possible using couplers and waveguide arrays with pitches below 10 μm.

[0039] The metasurface detector array shown in Figure 7 can provide directional information about incident light, facilitating the reconstruction of a three-dimensional image of the environment. Additionally, metasurfaces can provide angular, spectral, and / or polarization modulation functionality (e.g., filtering). As a result, information within specific angular, spectral, and / or polarization ranges can be extracted, removed, and / or modulated.

[0040] In one example, to fabricate the metasurface, an a-Si film is deposited by plasma-enhanced chemical vapor deposition and then patterned using electron beam lithography and plasma etching. After patterning the metasurface, a layer of SU-8 epoxy is spin-coated to enhance the robustness of the nanopost meta-atoms. SU-8 can completely fill the gaps between the meta-atoms without leaving any air pockets and also produce a flat, fully planarized top surface suitable for subsequent junction integration.

[0041] In a practical implementation, the light-emitting element and the photodetector metasurface may share the same portion of the metasurface.

[0042] Note that the LiDAR emitter or photodetector system shown in FIG. 6 does not include an aperture, while the emitter or photodetector system shown in FIG. 7 has an aperture 75. In embodiments of the present invention, LiDAR emitters typically do not use apertures but may, and LiDAR detectors typically use apertures but do not require them. In the case of emitters, the optical transmitter typically has a defined divergence angle (NA) that is within the control of the system designer, so the phase profile of the emitter metasurface can be designed to provide wide FOV output light and high imaging performance without the use of an aperture. If the optical transmitter has a large NA, a physical aperture may be used to reduce aberrations.

[0043] On the receiving side, because incident light can arrive from any incident direction, apertures are typically employed to achieve a wide FOV. In some examples, physical apertures are provided, such as the example in Figure 7, so that light from different AOIs is directed to designated regions on the metasurface. Alternatively, the system may employ virtual or self-forming apertures defined by the metasurface to differentially modulate light depending on the AOI. For example, a metasurface may be designed to have localized angular-dependent responses, thereby providing different angular filtering effects in different regions and thus forming virtual apertures for different AOIs. These angular-dependent responses may be enabled by meta-atom designs that exhibit different phase and / or amplitude responses in different AOIs. The system may also include pixelated or non-pixelated angular-dependent filters, such as DBR filters, to provide such spatially varying angular selectivity.

[0044] In optical interconnection systems that include both TX and RX with predefined optical paths (such as the systems shown in Figures 1-5), for example, where the light beam from the TX planar optical element is directed toward a small overlap region between the first and second planar optical elements, no apertures are required on the TX or RX side.

[0045] The LiDAR system further includes a modulation and processing unit (e.g., a processor or computer) that controls the light emission pattern, performs frequency modulation for distance measurement, and optionally performs phase modulation for improved resolution. It also processes the optical signal returned from the target to calculate the distance and reflectivity of the target object in the environment. The LiDAR system also preferably includes integrated electronics and circuitry for rapid light modulation, data acquisition, and initial processing. The LiDAR system may employ AI (artificial intelligence) components for real-time data processing and object recognition. These processing units and circuitry are schematically represented by components 60 and 70 in FIGS. 6 and 7. The processing unit and circuitry may be a distributed system with multiple units communicating and cooperating with each other to perform all necessary control and data processing functions of the LiDAR system. The control and data processing methods of LiDAR systems are generally known and will not be described in further detail here.

[0046] In the LiDAR system of this embodiment, various desirable functions in addition to beam steering can be achieved through the specific design of the light-emitting element metasurface and the control of the light emission of the light-emitting element array, some examples of which are described below.

[0047] High-resolution imaging: Precise control of light emission and detection enables detailed images and accurate depth measurements. This allows for the detection of small features that may be missed by conventional LiDAR systems. For example, specific portions of a light-emitting element metasurface can be designed to generate beams with different characteristics, such as beams with different collimation, divergence, or focusing properties. Light-emitting elements located at locations corresponding to such metasurface portions can be selectively turned on to generate beams with desired properties to achieve required imaging and / or sensing functions. For example, specific portions of a light-emitting element metasurface can be designed to generate focused light beams with smaller spot sizes, and light-emitting elements located at locations corresponding to such metasurface portions can be selectively turned on to generate focused light beams to achieve higher-resolution imaging.

[0048] Adaptive illumination: The system can be controlled to dynamically adjust the illumination pattern based on the environment. For example, the system can be controlled to focus light on an area of ​​interest for more detailed scanning. More specifically, certain portions of the light-emitting element metasurface can be designed to generate a focused light beam, while other certain portions of the light-emitting element metasurface can be designed to generate a diverging light beam. Light-emitting elements located at locations corresponding to different metasurface portions can be selectively turned on to generate a focused light beam, a diverging light beam, or a light beam with any other desired illumination pattern, for example, based on the illumination needs. Light beams emitted from different light-emitting elements can be combined coherently or incoherently to generate desired amplitude and / or phase patterns and achieve desired interference effects.

[0049] Versatile: The system can be controlled to switch between different LiDAR modes, such as switching between multiple operating states, such as short-range and long-range probing and / or narrow-FOV and wide-FOV scanning. More specifically, certain portions of the light-emitting element metasurface can be designed to generate a collimated beam, while other certain portions of the light-emitting element metasurface can be designed to generate a diverging beam. Light-emitting elements located at locations corresponding to different metasurface regions can be selectively turned on to achieve different spot sizes for short-range wide-angle scanning or long-range narrow-field-of-view probing.

[0050] In summary, light-emitting element metasurfaces can be designed so that different portions of the metasurface are configured to generate light beams with different characteristics, such as divergence angle and beam direction, and light-emitting elements located at corresponding locations can be selectively turned on to generate illumination beams with desired characteristics to achieve a desired function. Such light-emitting elements can also be applied as lighting devices outside the LiDAR field.

[0051] Light-emitting element metasurfaces can also be designed so that overlapping or partially overlapping portions of the metasurface are configured to generate light beams with different characteristics, such as divergence angle and beam direction, and so that light-emitting elements located at corresponding locations can be selectively turned on to generate illumination beams with desired characteristics to achieve a desired function. Furthermore, metasurfaces can provide angle-, spectral-, and / or polarization-dependent responses such that light with different characteristics or light emitted from light sources with different characteristics is modulated differently (e.g., polarized in different directions). Light-emitting element arrays can include light-emitting elements with different wavelengths or polarization states. Light-emitting element arrays can include filters with different spectral or polarization filtering characteristics.

[0052] The LiDAR system according to this embodiment can achieve a compact and robust design: the lack of moving parts reduces mechanical complexity, size, weight, and wear, resulting in a more durable and portable system.

[0053] The metasurface-based LiDAR systems described herein are useful in fields where precise mapping and sensing are important, including autonomous vehicles, robotics, aerospace, and various forms of remote sensing. Advances in metasurface technology may enable further miniaturization of the systems, potentially leading to their integration into smartphones and other personal electronic devices for augmented reality applications and spatial computing.

[0054] Embodiments of the present invention provide a chip-scale platform that enables efficient coupling from single-mode PICs into large-area, diffraction-limited beams, and further utilize this technology to realize unprecedented ultra-wide FOV, low-loss, high-frame-rate chip-scale LiDAR systems.

[0055] In some embodiments, the coupling scheme uses a planar fisheye metalens to convert the optical output from the PIC into a collimated beam with high quality (or any other desired beam intensity / phase distribution). PIC processing can leverage standard photonic foundry fabrication. Metalens integration is also amenable to wafer-scale processing, resulting in thin, chip-scale packages. In addition to its compatibility with scalable fabrication and integration techniques, this scheme is also unique in its ability to couple large-area (over several millimeters in diameter) free-space beams while maintaining near-diffraction-limited beam quality. This capability allows for small beam divergence (0.001-0.01 degrees) and excellent beam directionality from chip-scale modules, making them highly useful for applications such as LiDAR and free-space laser communications.

[0056] In some embodiments, the coupling optical system employs a flat fisheye metalens with a structure similar to that shown in FIG. 7 . It includes a single flat transparent substrate 73 with an optional aperture 75 located on the front side and a metasurface 71 located on the back side (facing the optical transmitter array or optical receiver array). Light beams entering or exiting the optical structure at different angles of incidence or exit (AOI) are modulated (e.g., focused) by the metasurface. When the metasurface phase function φ satisfies a closed-form solution, all focal points across the entire FOV fall on the same image plane while minimizing coma.

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[0057] The above equation shows that a flat substrate decorated with a single-layer metasurface can be transformed into a fisheye lens with a diffraction-limited FOV close to 180°. Furthermore, the flat focal plane can greatly simplify the optical system architecture.

[0058] While the metasurface phase function φ for a fisheye lens with an FOV close to 180° is given above, more generally, wide FOV metalenses (e.g., those with FOVs of 60° or more relative to the normal direction) can be achieved using numerical optimization methods. For light-emitting elements, a near-telecentric architecture is preferred to achieve a wide FOV, and the divergence (numerical aperture) of the metalens is preferably designed to match that of the light-emitting element array. More generally, metalenses are designed to achieve wavefront or mode matching between the light-emitting element and the far-field beam via metasurface modulation.

[0059] Unlike conventional approaches that require manual alignment of discrete lenses to light sources or PICs, architectures according to embodiments of the present invention allow for lithographically accurate, wafer-scale bonding of metalenses (including optional aperture stops, optical filters, and spacers, as needed) to PICs, followed by dicing and die singulation into individual chip-scale modules. This process facilitates the parallel assembly of large numbers of modules at the wafer level, avoiding the laborious and costly optical alignment and packaging steps for each and every device. While this is based on the same rationale that drove the emergence of wafer-level optics (WLO) as an alternative to discretely assembled optics, metasurfaces overcome several long-standing challenges plaguing WLO, including precise optical surface shape control (especially for aspheric and freeform surfaces), wafer-to-wafer variations, and yield. Furthermore, metasurfaces enable efficient light bending, even at large angles, which is essential for designing compact optical systems with large fields of view (FOVs).

[0060] In one embodiment, a PIC for a LiDAR engine includes a modulator array for modulating output light, a switch network for routing the light, a light-emitting element array for coupling light from the waveguide to the metalens, and a receiver for collecting the reflected signal (e.g., an on-chip coherent receiver for frequency-modulated continuous wave (FMCW) LiDAR). The laser light source can be integrated on an active interposer. PIC components include, but are not limited to, low-loss waveguides, waveguide couplers / light-emitting elements, high-speed modulators, 2x2 optical switches, and analog / digital photodetectors. The main requirements for the coupler include: 1) a spot size that matches the focal point of the metalens; 2) a beam divergence angle specified by the effective numerical aperture (NA) of the metalens; 3) minimal insertion loss and back reflection; and 4) a compact footprint compatible with high-density array integration. Photonic inverse design protocols can be employed to design the coupler.

[0061] As a result, the described LiDAR platform avoids limitations such as scalability, FOV, beam quality, and speed faced by current nanophotonic LiDAR technology.

[0062] In terms of scalability, unlike OPA and active metasurface based LiDARs, systems according to embodiments of the present invention are essentially aliasing-free and not subject to λ / 2 pitch constraints. Furthermore, N 2 Unlike an OPA, which requires N individually phase-modulated light-emitting elements, the LiDAR system described above requires log2(N 2 ) = 2log2(N) switches are required. The logarithmic network topology dramatically reduces the complexity of the electronic control.

[0063] In terms of FOV and beam quality, by leveraging the design principles of a flat fisheye lens, the LiDAR system described above uniquely combines a record-breaking FOV of close to 180°, diffraction-limited beam quality, and high optical efficiency. This design is also easily scalable to large metalens aperture sizes (from a few millimeters to several centimeters) while maintaining diffraction-limited performance, enabling high-quality beamforming with minimal divergence and high pointing accuracy, features particularly useful in long-range LiDAR applications.

[0064] In terms of speed, unlike OPAs or active metasurfaces, which require sequential beam scanning, the LiDAR system described above allows multiple light-emitting elements to transmit and receive signals simultaneously, thereby achieving simultaneous multi-channel operation. These light-emitting elements share the same metalens aperture, each addressing one channel in the point cloud. The parallel interrogation scheme improves overall speed and frame rate. In addition, different modulation formats can be employed between different groups of simultaneously operating light-emitting elements, dramatically reducing optical crosstalk and sensitivity to background ambient light.

[0065] It will be apparent to those skilled in the art that various modifications and variations can be made in the metasurface-based optical coupling and interconnection system of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.

Claims

1. a transmitter array including one or more optical transmitters configured to emit one or more optical beams; a first planar optical element configured to receive the light beams from the transmitter array and generate one or multiple intermediate light beams; a first spacer disposed between the optical transmitter array and the first planar optical element; a receiver array including one or many optical receivers; a second planar optical element configured to receive the intermediate light beam and generate one or more output light beams that are directed to the receiver array; a second spacer disposed between the second planar optical element and the optical receiver array; and an optical coupling system comprising:

2. The optical coupling system of claim 1 , wherein the first and second planar optical elements are configured to provide optical relay or mode matching between the transmitter array and the receiver array.

3. 2. The optical coupling system of claim 1, wherein a chief ray of the light beam emitted by the transmitter array is within 20 degrees of a normal direction of the first planar optical element, and a chief ray of the output light beam generated by the second planar optical element is within 20 degrees of a normal direction of the second planar optical element.

4. The optical coupling system of claim 1 , wherein the intermediate beam produced by the first planar optical element is a collimated beam.

5. 10. The optical coupling system of claim 1, wherein each of the first spacer and the second spacer comprises one or more of an air gap, an optically transparent solid or liquid material, a porous material, and a metamaterial.

6. 10. The optical coupling system of claim 1, wherein each of the first and second planar optical elements comprises one or more of a subwavelength optic, a metasurface, a multilayer metasurface, a metamaterial, a diffractive optical element, a holographic optical element, a wafer-level optic, and a micro-optic.

7. 2. The optical coupling system of claim 1, wherein each of the multiple optical transmitters is an optical channel coupled to a light source or an external light source, and each of the multiple optical receivers is an optical sensor or an optical channel coupled to an external light sensor.

8. The optical coupling system of claim 1 , wherein the optical transmitter array is a photonic integrated circuit and / or the optical receiver array is a photonic integrated circuit.

9. The optical coupling system of claim 1 , wherein the transmitter array and the receiver array have different physical sizes and / or orientations.

10. The optical coupling system of claim 1 , further comprising one or more optical elements configured to transmit the intermediate light beam from the first planar optical element to the second planar optical element.

11. The optical coupling system of claim 10 , wherein the one or more optical elements include a third spacer disposed between the first planar optical element and the second planar optical element.

12. The optical coupling system of claim 10 , wherein the one or more optical elements include a reflector.

13. 13. The optical coupling system of claim 12, wherein the one or more optical elements further include a third spacer, the first and second planar optical elements being regions of a metasurface formed on one surface of the third spacer, and the reflector being formed on the other, opposite surface of the third spacer.

14. 2. The optical coupling system of claim 1, wherein different non-overlapping or partial overlapping regions of the first planar optical element are designated to couple to different ones of the multiple optical transmitters, or different non-overlapping or partial overlapping regions of the second planar optical element are designated to couple to different ones of the multiple optical receivers.

15. The optical coupling system of claim 1 , wherein the first planar optical element and the second planar optical element are configured to form an image inverter.

16. a two-dimensional light emitting element array including one or more light emitting elements configured to emit one or more light beams; a first metasurface configured to receive the light beam from each light-emitting element of the light-emitting element array and generate one or more corresponding output light beams or light distribution patterns, the output light beams or patterns having at least one beam characteristic that depends on a two-dimensional position of the corresponding light-emitting element, the at least one beam characteristic including direction, collimation, divergence, or phase or intensity distribution; a first metasurface configured to generate an output light beam over a field of view greater than 60 degrees relative to a normal to the first metasurface; a first control circuit coupled to the light-emitting element array for modulating or selectively turning on or off individual light-emitting elements within the light-emitting element array; 1. A light beam steering system comprising:

17. the first metasurface has a phase function φ; [Equation 1] where r, λ, n, L, and f denote the radial position from the center of the first metasurface, the wavelength of the light beam, the refractive index of the substrate, the thickness of the substrate, and the effective focal length, respectively; h is the focal position corresponding to the field of view; and h is the differential form with respect to the angle of incidence θ, i.e., [Equation 2] 17. The optical beam steering system of claim 16, wherein:

18. 17. A LiDAR (Light Detection and Ranging) system including a light emitting element and a light detector, wherein the light emitting element comprises the optical beam steering system of claim 16.

19. The photodetector a two-dimensional photodetector array including one or many photodetectors; a second metasurface configured to receive a light beam reflected from a target scene and focus the light beam onto the photodetector array; a second metasurface configured to receive a light beam reflected from the target scene over a field of view greater than 60 degrees relative to a normal to the second metasurface; and a second control circuit coupled to the photodetector array for processing signals generated by the photodetector array; 20. The LiDAR system of claim 18, comprising:

20. 20. The LiDAR system of claim 19, wherein the light emitting element further comprises an aperture located a defined distance from the first metasurface.

21. 20. The LiDAR system of claim 19, wherein the photodetector further comprises an aperture located a defined distance from the second metasurface.

22. 22. The LiDAR system of claim 21 , wherein the second metasurface forms a virtual aperture, the second metasurface having a local angle-dependent response and providing different angular filtering effects in different regions, thereby forming the virtual aperture for different angles of incidence.

23. 20. The LiDAR system of claim 19, wherein the first or second metasurface is configured to provide an angle-, spectral-, and / or polarization-dependent response.

24. 24. The LiDAR system of claim 23, wherein the array of light emitting elements includes light emitting elements having different wavelengths or polarization states.

25. 20. The LiDAR system of claim 19, wherein the first metasurface has different portions configured to generate light beams with different divergence angles, and the first control circuit is configured to modulate or selectively turn on or off light emitting elements located at locations corresponding to the different portions of the metasurface to generate an illumination beam of defined characteristics.

26. a two-dimensional light emitting element array including one or more light emitting elements configured to emit one or more light beams; a metasurface configured to receive the light beam from the light-emitting element or each light-emitting element of the light-emitting element array and generate one or more corresponding output light beams or light distribution patterns, the output light beams or patterns having at least one beam characteristic that depends on a two-dimensional position of the corresponding light-emitting element, the at least one beam characteristic including direction, collimation, divergence, or phase and / or intensity distribution; a control circuit coupled to the light emitting elements or the light emitting element array for modulating or selectively turning on or off individual light emitting elements within the light emitting element array; 1. A light illumination device comprising:

27. 27. The optical illumination of claim 26, wherein the metasurface has different portions configured to generate an optical beam with different divergence angles, and the control circuit is configured to modulate or selectively turn on or off light-emitting elements located at locations corresponding to the different portions of the metasurface to generate an illumination beam with defined characteristics.

28. 27. The optical illumination of claim 26, wherein the metasurface is configured to provide an angle-, spectrum-, and / or polarization-dependent response, and the array of light-emitting elements includes light-emitting elements having different wavelengths or polarization states.

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