Optical phased array equipment

Abstract

The apparatus may include an optical phased array (e.g., on a photonic integrated circuit), a focusing element, and a steering element, where the focusing element may be at a fixed position relative to the optical phased array and configured to receive an optical beam from the optical phased array, and the steering element may be at a fixed position relative to the focusing element and configured to transmit the optical beam received from the focusing element. In some implementations, at least one of the focusing element or the steering element is externally coupled to the photonic integrated circuit.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims priority and benefit of U.S. Provisional Application No. 63 / 112,301, titled "Optical Steering of an Optical Phased Array," filed on November 11, 2020, and U.S. Provisional Application No. 63 / 203,468, titled "Optical Steering of an Optical Phased Array," filed on July 23, 2021.

[0002] This application relates to optical steering of an optical phased array.

Background Art

[0003] There is an Optical Phased Array (OPA) having a linear distribution of emitter elements (also referred to as emitters or antennas). By changing the relative phase shift in a plurality of phase shifters that supply light to each emitter element, steering can be performed about a first axis perpendicular to the linear distribution. Other techniques can also be used to steer about a second axis orthogonal to the first axis.

Summary of the Invention

[0004] In one aspect, generally, a device includes a photonic integrated circuit including an optical phased array, a focusing element at a fixed position with respect to the optical phased array and configured to receive an optical beam from the optical phased array, and a steering element at a fixed position with respect to the focusing element and configured to transmit the optical beam received from the focusing element. At least one of the focusing element or the steering element is externally coupled to the photonic integrated circuit.

[0005] The plurality of aspects may include one or more of the following features.

[0006] The steering element includes a dispersive element.

[0007] The dispersive element includes a diffractive element.

[0008] Dispersive elements include reflective elements.

[0009] Reflecting elements include prisms.

[0010] The focusing element includes a lens.

[0011] The focusing element includes a reflective surface.

[0012] The photonic integrated circuit, focusing element, and steering element are included in at least a portion of the LiDAR system.

[0013] Photonic integrated circuits, focusing elements, and steering elements are included in the free-space optical link of the communication system.

[0014] In other aspects, the apparatus generally includes an optical phased array, a reflective surface fixed to the optical phased array and configured to redirect optical beams received from the optical phased array, and a steering element fixed to the reflective surface and configured to transmit the optical beams redirected from the reflective surface.

[0015] Multiple aspects may include one or more of the following characteristics:

[0016] The reflective surface is shaped to collimate the light beam in at least the first plane.

[0017] The device further includes a light source configured to supply light waves to multiple antenna elements of an optical phased array.

[0018] The relative phase shift between multiple antenna elements steers the light beam emitted from the optical phased array in a second plane perpendicular to the first plane.

[0019] The steering element includes a diffraction element, and the light source includes a tunable light source configured to tune the wavelength of the light wave applied to the plurality of antenna elements of the optical phased array. By the tuned wavelength, the light beam emitted from the diffraction element is steered in the first plane.

[0020] The steering element includes a diffraction element configured to be tuned to electronically manipulate the beam in the first plane.

[0021] The optical phased array, the reflecting surface, and the steering element are included in at least a part of the LiDAR system.

[0022] The optical phased array, the reflecting surface, and the steering element are included in at least a part of the free space optical link of the communication system.

[0023] On the other side, generally, the device includes an optical phased array, a lens at a fixed position with respect to the optical phased array, the lens being configured to receive a light beam from the optical phased array, and a steering element at a fixed position with respect to the lens, the steering element being configured to transmit the light beam received from the lens.

[0024] The plurality of sides may include one or more of the following features.

[0025] The lens is substantially shaped to collimate the light beam at least in the first plane.

[0026] The device further includes a light source configured to apply light waves to the plurality of antenna elements of the optical phased array.

[0027] By the relative phase shift between the plurality of antenna elements, the light beam emitted from the optical phased array is steered in the second plane perpendicular to the first plane.

[0028] The steering element includes a diffraction element, and the light source includes a tunable light source configured to tune the wavelength of the light wave applied to the plurality of antenna elements of the optical phased array. The light beam emitted from the diffraction element is steered in the first plane by the tuned wavelength.

[0029] The steering element includes a diffraction element configured to be tuned to electronically manipulate the beam in the first plane.

[0030] The optical phased array includes a plurality of antenna elements coupled to respective optical waveguides formed in a photonic integrated circuit.

[0031] The optical phased array, the lens, and the steering element are included in at least a part of the LiDAR system.

[0032] The optical phased array, the lens, and the steering element are included in at least a part of the free space optical link of the communication system.

[0033] On the other hand, generally, the apparatus includes a plurality of optical phased arrays and a single focusing element at a fixed position with respect to the plurality of optical phased arrays, the single focusing element being configured to receive light beams from the plurality of optical phased arrays. The focusing element is arranged and configured to substantially collimate the light beam at least in the first plane.

[0034] The plurality of aspects may include one or more of the following features.

[0035] The plurality of optical phased arrays and the single focusing element are included in at least a part of the LiDAR system.

[0036] The plurality of optical phased arrays and the single focusing element are included in at least a part of the free space optical link of the communication system.

[0037] Multiple optical phased arrays are arranged on a pedestal, each optical phased array containing radiating elements of a linear array along a first axis, the radiating elements of each linear array being offset along the first axis relative to other linear arrays and offset along a second axis perpendicular to the first axis relative to other linear arrays.

[0038] In other aspects, the apparatus generally includes an optical phased array and a focusing steering element fixed to the optical phased array, which is configured to receive an optical beam from the optical phased array, and the focusing steering element is configured to substantially collimate the optical beam in at least a first plane and to steer the optical beam in the first plane.

[0039] Multiple aspects may include one or more of the following characteristics:

[0040] The focusing steering element includes a focusing diffraction element.

[0041] A single optical phased array and a single focusing steering element are included in at least part of the LiDAR system.

[0042] A phased optical array and a focusing element are included in at least a portion of the free-space optical link of the communication system.

[0043] In other aspects, the apparatus generally includes an optical phased array and a reflective focusing element fixed to the optical phased array, which is configured to receive and transmit an optical beam from the optical phased array.

[0044] Multiple aspects may include one or more of the following characteristics:

[0045] The reflective focusing element includes a reflective surface.

[0046] The apparatus further includes a diffraction element fixed in position relative to a reflective focusing element, which is configured to transmit a light beam redirected from a reflective surface.

[0047] The diffracting element includes a curved diffracting element, which transmits a light beam through the curved diffracting element.

[0048] One optical phased array and one reflective focusing element are included in at least part of the LiDAR system.

[0049] A phased optical array and a reflective focusing element are included in at least a portion of the free-space optical link of the communication system.

[0050] Multiple aspects may possess one or more of the following advantages:

[0051] The techniques described herein can be used to provide various steering and / or focusing mechanisms for OPA-based transceivers including one or more POAs. The transceiver can be used to transmit and / or receive a light beam at a desired transmit and / or receive angle. In some implementations of the OPA-based transceiver, one or more photonic integrated circuits (or chips) include a linear array of OPA antennas that emit coherently interfering light to provide a beam steered around a first axis using OPA phase shift. The OPA-based transceiver can be configured to include, in a compact and efficient manner, any of the various other mechanisms for steering around a second axis perpendicular to the first axis. Beam collimation can also be provided by various techniques detailed below. These techniques can be used, for example, for OPA-based LiDAR sensor systems and for telecommunications terminals such as nodes in communication systems using free-space optical links between nodes. For such an optical system, the waves forming the beam have a spectrum with peak wavelengths that fall within a specific range of optical wavelengths (e.g., from about 10 nm to about 1 mm or a portion thereof), also known as optical waves, light waves, or simply light.

[0052] Other features and advantages will become apparent from the following description, as well as from the drawings and claims. [Brief explanation of the drawing]

[0053] This disclosure is best understood in conjunction with the attached drawings, as detailed below. It is emphasized that, by common practice, various features of the drawings are not to scale. Conversely, dimensions of various features have been arbitrarily enlarged or reduced for clarity.

[0054] [Figure 1] Figure 1 is a schematic diagram of an exemplary OPA-based transceiver. [Figure 2A-2B] Figures 2A and 2B are schematic diagrams of exemplary OPA chips. [Figure 3A-3C]Figures 3A, 3B, and 3C are schematic diagrams of OPA beam extension. [Figure 4A-4B] Figures 4A and 4B are schematic diagrams of the structure that limits beam expansion. [Figure 5] Figure 5 is a schematic diagram of an array of lattice emitters that limit beam expansion. [Figure 6] Figure 6 is a schematic diagram of an OPA equipped with a collimating lens. [Figure 7] Figure 6 is a schematic diagram of an OPA equipped with a collimating lens and a secondary steering mechanism. [Figure 8] Figure 8 is a schematic diagram of an OPA equipped with a focusing steering element. [Figure 9] Figure 9 is a schematic diagram of an element configured to flatten and tilt the beam phase front. [Figure 10] Figure 10 is a schematic diagram of an element configured to flatten the beam phase front. [Figure 11] Figure 11 is a schematic diagram of an element configured to flatten and tilt the beam phase front. [Figure 12] Figure 12 is a schematic diagram of the phase plate structure. [Figures 13A-13B] Figures 13A and 13B are schematic diagrams of exemplary lens arrangements. [Figures 14A-14B] Figures 14A and 14B are schematic diagrams of exemplary lens arrangements. [Figure 15] Figure 15 is a schematic diagram of a curved mirror used as a focusing element. [Figure 16A] Figures 16A, 16B, and 16C are schematic diagrams of light rays for a curved mirror used as a focusing element. [Figure 16B-16C] Figures 16A, 16B, and 16C are schematic diagrams of light rays for a curved mirror used as a focusing element. [Figures 17A-17B] Figures 17A and 17B are sketches of beam extension. [Figures 18A-18C] Figures 18A, 18B, and 18C are schematic diagrams illustrating the characteristics of an end-fire waveguide example. [Figure 19] Figure 19 is a schematic diagram of a half-mirror example. [Figure 20] Figure 20 is a sketch of the light rays associated with an example of a half-mirror. [Figure 21] Figure 21 is a schematic diagram of a plane wave focused by a cylindrical mirror. [Figure 22] Figure 22 is a schematic diagram of the wave vector associated with the example in Figure 21. [Figure 23] Figure 23 is a schematic diagram of the focal point of a downward-shining beam. [Figure 24] Figure 24 is a schematic diagram of the focal plane curve for the example in Figure 23. [Figure 25] Figure 25 is a schematic diagram of beam rotation corresponding to OPA position shift. [Figure 26A] Figures 26A and 26B are schematic diagrams of exemplary OPA chip arrangements in a pedestal. [Figure 26B] Figures 26A and 26B are schematic diagrams of exemplary OPA chip arrangements in a pedestal. [Figure 27] Figure 27 is a schematic diagram of an OPA steering array using mirrors and secondary steering elements. [Figure 28] Figures 28 and 29 are schematic diagrams of exemplary LiDAR sensor systems. [Figure 29] Figures 28 and 29 are schematic diagrams of exemplary LiDAR sensor systems. [Figure 30A] Figures 30A and 30B are schematic diagrams of an OPA steering array equipped with multiple OPA chips. [Figure 30B] Figures 30A and 30B are schematic diagrams of an OPA steering array equipped with multiple OPA chips. [Figure 31] Figure 31 is a schematic diagram of the communication system. [Figure 32A] Figures 32A, 32B, and 32C are schematic diagrams of exemplary secondary steering configurations. [Figure 32B] Figures 32A, 32B, and 32C are schematic diagrams of exemplary secondary steering configurations. [Figure 32C] Figures 32A, 32B, and 32C are schematic diagrams of exemplary secondary steering configurations. [Figure 33A] Figures 33A and 33B are schematic diagrams of exemplary lattice reflections used for wavelength-based steering. [Figure 33B] Figures 33A and 33B are schematic diagrams of exemplary lattice reflections used for wavelength-based steering. [Figure 34] Figure 34 is a schematic diagram of an exemplary refraction steering mechanism using a prism or wedge. [Figure 35A] Figures 35A, 35B, and 35C are schematic diagrams of the wavelength dependence of different refractive steering arrays. [Figure 35B] Figures 35A, 35B, and 35C are schematic diagrams of the wavelength dependence of different refractive steering arrays. [Figure 35C] Figures 35A, 35B, and 35C are schematic diagrams of the wavelength dependence of different refractive steering arrays. [Figure 36] Figure 36 is a schematic diagram of an exemplary steering mechanism using a curved diffractometer. [Modes for carrying out the invention]

[0055] In an OPA-based transceiver, the optical beam radiated from the optical phased array can be steered using, for example, reflective structures, dispersive structures, and / or refractive structures. The same "steer" mechanism can be used to configure the receiving angle of the incident optical beam received into the optical phased array. Some implementations utilize secondary collimating or focusing devices to modify the beam divergence. An example of such a configuration is shown in Figure 1. In this implementation, the OPA-based transceiver 100 includes a set of OPAs 102, which may be configured to utilize optical antennas, such as end-fire antennas or short grid antennas (or other short antennas), that radiate / receive beams formed by interference across a linear antenna array. In this example, each OPA 102 resides on a separate chip. The radiation angle of the outgoing beam 106A and the (same) receiving angle of the incident beam 106B are steered in the XZ plane (or the equivalent plane around the Y axis) by phase control (i.e., controlling the relative phase shift applied by a phase shifter coupled to each antenna). The beam from such an end-fire (or short-grid) antenna expands to fill the concave mirror 104. Since the end of the OPA 102 is placed at a focal length 105 relative to the mirror 104, the outgoing beam 106A emanating from the mirror is collimated rather than diverging in the YZ plane. As shown in the figure, the collimated beam 107 is redirected from the illumination spot 109 on the mirror 104. In this example, steering in the YZ plane is performed by a steering element. This steering element is implemented by changing the incident wavelength via laser tuning using a dispersion element 110 such as a diffraction element (e.g., a diffraction surface element such as a diffraction grating). For example, separate lasers (not shown) or a single laser (not shown) may be used in each of the multiple OPA102s to supply light to all of them. Alternatively, the steering element may use alternative mechanisms such as liquid crystals, metasurfaces, polarizing gratings, acousto-optics, refractive elements (e.g., prisms), and / or other types of dispersion elements.By combining an OPA102 for steering in the XZ plane and a steering element for steering in the YZ plane, a non-mechanical beam steering system can be created to cover the optical cone in front of the transceiver 100 (the central axis of the optical cone is in the Z direction). The field of view in the XZ plane is determined by the single beam steering range of a single OPA102. For example, a range of phase steering angles 108 is shown. Multiple OPA102s can be distributed at different locations on a set of pedestals 112 to extend the field of view (FOV) beyond the range possible with a single OPA102. This is described below with respect to Figures 26A and 26B.

[0056] When an OPA-based transceiver 100 is used in a LiDAR sensor system, the backscattered light travels in the reverse direction along the same path and is collected by the same OPA 102, an adjacent receiving (Rx) OPA, or an adjacent transceiver (as detailed below for Figures 30A and 30B). In this example, a concave (e.g., cylindrical) mirror 104 is selected as the focusing optical element because the concave mirror 104 can be configured not to introduce aberrations into the emitted outgoing beam 106A. However, the same is not true for cylindrical lenses. An exemplary analysis using Maxwell's equations demonstrates this point and is given below. Multiple optical phased arrays that rely on a large surface-emitting aperture may suffer from aberrations caused by manufacturing imperfections that can limit the aperture size. Such imperfections can be caused, for example, by surface distortion (bow), non-uniformity of layer thickness, or uneven phase accumulation along an imperfect waveguide.

[0057] Furthermore, when surface emission is achieved by long gratings, the direction of radiation becomes highly wavelength-dependent, which can be useful (e.g., in the case of intentional steering by wavelength sweeping) or detrimental (e.g., in the case of WDM data communication systems). In this exemplary implementation, an end-fire (or short-grating) antenna optical phased array coupled to an external one-dimensional (1D) focusing / collimating optical system is introduced to achieve a large effective aperture without requiring long antenna elements.

[0058] Referring to Figure 2A, the OPA chip 200 includes a distribution network 201 (e.g., a waveguide tree or star coupler) that delivers an optical field of equal distribution (or a predetermined distribution such as a Gaussian distribution) from the optical input 202 to the array of waveguides 204. Individual phase shifters 206 (e.g., electro-optic, thermal, liquid crystal, pn junction-based, etc.) can be coupled to each waveguide 204 to control the phase of the light emitted from the end-fire radiators 208 at the ends of the array of waveguides 204.

[0059] This light can be coupled from a laser located in or outside the OPA chip 200 to the optical input section 202 located in the OPA chip 200. Light from the radiators 208 passes through the phase shifter 206 and the radiators 208 and is emitted into the optical cone 210. Each radiator 208 generates its own elemental factor in the lateral and vertical directions. If the phase shifter 206 imparts a linear phase progression (which can be contained within 0–2π) to the light emitted from the radiators 208, the light from all the radiators is coupled to form a radiated beam 212 with a substantially flat phase front 214 (e.g., plane wave radiation) on the plane of the OPA chip 200, as shown in Figure 2B. As can be seen in Figure 2B, which shows a top view of the optical phased array portion of the OPA chip 200 in operation, the beam 212 emitted from the optical phased array is diffracted to have a pattern determined by the width (and observation angle) of the optical phased array. Therefore, even though the light 216 emitted from each radiator expands rapidly, the overall array beam diffraction 218 behaves like a slowly expanding semi-Gaussian beam. Nevertheless, in the vertical direction, the behavior of this flat array cannot be compared to the in-plane view shown in Figure 2B.

[0060] As seen in Figure 3A, which shows a cross-section of the optical phased array viewed from the side, the waveguide mode 300 corresponds to the core layer (e.g., silicon) in the cladding 302 (e.g., silicon dioxide) located at the top of the substrate 304 (e.g., the embedded oxide (BOX) layer of a silicon-on-insulator (SOI) platform). The beam 306 emitted from the waveguide mode 300 expands rapidly in the illustrated plane perpendicular to the linear array of radiators, in response to the expansion of a single radiator. The expansion rate depends on the mode size. The expansion rate is also measured by the mode cone angle. Beam expansion in the perpendicular (longitudinal) direction of the illustrated plane depends on the effective aperture size of the end-fire radiator. Figure 3B shows a small mode section 310 that results in rapid beam expansion 312. Figure 3C shows a large mode section 314 that results in slow beam expansion 316.

[0061] Mode and associated beam expansion can be controlled by any of the following techniques. Figure 4A shows an example of coupling light to a loose waveguide structure 400 (e.g., a layer of polymer, silicon oxynitride, silicon nitride, etc.) with a low refractive index to limit the expansion of beam 402, and Figure 4B shows an example of stepwise coupling to multiple waveguide layers 410 to prevent the expansion of beam 412. Another method for reducing beam divergence despite increasing beam size is to utilize grating radiators. Figure 5 shows an example of an array of grating radiators 500. These grating radiators are configured to radiate the output beam 502 in a direction away from the plane of the grating radiator. The intensity of this grating coupler can be adjusted such that the total length of the radiator and the corresponding effective aperture size 504 match the desired beam divergence angle.

[0062] The techniques described above allow for increasing the effective aperture size from the submicron scale to several micrometers. Nevertheless, the beam's transverse mode size still expands much faster in the longitudinal direction (orthogonal to the array) than in the transverse direction (within the array's plane). One way to overcome this beam over-expansion is to utilize a focusing element that has collimating power only within the desired plane.

[0063] As can be seen in Figure 6, the light emitted from the edge of the end-face radiator of the OPA600 expands rapidly, and the expanded beam 602 fills the cylindrical lens 604. The lens 604 has translational symmetry along the edge of the OPA600. As a result, the lens 604 has low focusing power along that edge, which is appropriate because the beam 602 expands slowly in the XZ plane. Since the beam 602 expands rapidly in the longitudinal direction, the lens 604 has a focal length f selected to collimate the beam 602 in the longitudinal direction. Observers from distances greater than the Fraunhofer distance see the electric field distribution, which is the Fourier transform of the near-field. The angular range of the beam 602 in the far-field in each direction depends on the aperture size in that direction. The effective aperture size in the lateral direction (X) depends on the size of the optical phased array, and the effective aperture size in the vertical direction (Y) depends on the size of the lens aperture and the percentage of the aperture filled by the extended beam 602 from the end-face radiator of the OPA600. This configuration can steer only light having phase in one direction (i.e., "lateral steering" in the XZ plane). Steering in a second direction (around the X axis) can be achieved by a secondary steering mechanism. Figure 7 shows an example of such a secondary steering mechanism. In this example, the secondary steering mechanism is provided by a dispersion element 700 which can be implemented as a liquid crystal, a polarizing grating, an acousto-optic beam steerer, or other high-speed steering electrical control mechanism capable of steering light vertically (around the X axis or in the YZ plane).

[0064] Referring to Figure 8, in several implementation examples, the same diffraction / dispersion element can be configured as a focusing steering element 800 that performs steering in the longitudinal direction (YZ plane) and also provides focusing capability. Given an arbitrary phase function in the Y direction, the effective phase function of the focusing steering element 800 can be adjusted to collimate and steer the light in a desired direction (for example, in the Y direction in this example). As can be seen in Figure 9, the element 900 is configured to adjust the (e.g., flattened and tilted) phase front of the beam 904 by applying an adjustable phase function acting on the extended beam 902, thereby generating a plane wave with the necessary phase gradient to direct the beam in a predetermined direction in the YZ plane. This can be done, for example, by an element 900 equipped with a lens whose shape changes (only in the YZ plane) or a plate with a programmed phase.

[0065] Referring to Figure 10, element 1000 may be configured to apply an adjustable phase function acting on the expanded beam 1002 as a tunable 3D cylindrical lens of any shape. For example, the phase function may be wrapped in the range of 0 to 2π to implement a Fresnel lens that gives a flattened phase front to the beam 1004. Element 1000 may be a diffraction / focusing element such as a Fresnel lens with an adjustable phase front that can simultaneously change both the expansion and direction of the beam.

[0066] Referring to Figure 11, one example of a method for controlling the phase function at each point of element 1100 is by providing a microstructure that electronically changes the effective refractive index. Element 1100 acting on the extended beam 1102 provides a flattened and tilted phase front to beam 1104. As an example of such a refractive index changing structure, a 2D pattern of phase can be provided that allows for simultaneous collimation and steering of beam 1104 by pumping carriers into a pn junction-based resonant structure on a phase plate. Referring to Figure 12, the phase plate structure 1200 includes a 2D array of voltage-controlled refractive index changing elements that apply voltage-controlled effective refractive indexes that vary at different points across the received phase front of the input beam 1202. The phase plate structure 1200 may be coated with liquid crystal to enhance the effect of the refractive index change.

[0067] Referring to Figure 13A, in an example of a thick cylindrical lens 1300, the associated lens function may depend on the angle of incidence. As can be seen in Figure 13A, when the focal length of the lens for orthogonal incidence for collimation in the YZ plane is f, and the optical phased array output is positioned at the focal point, the situation of a phase-steered beam steered at an angle θ along the Z axis from the center of the OPA 600 (indicated by θ=z) is different from the situation of a phase-steered beam steered at an angle θ off the Z axis (indicated by θ>z). Referring to Figure 13B, at a non-zero angle θ (relative to the YZ plane), the effective focal length of the lens (f(θ)) is different from f, and furthermore, the distance (d) the extended beam travels to the lens is longer than f. In this case, it is predicted that f(θ) and d do not match, and the OPA will not be positioned at the effective focal length of the lens. This results in a beam that rapidly diverges without being collimated before reaching the target at that distance. While the amount of beam divergence may be acceptable when the target is at a short distance, such systems may not be suitable for long-range applications such as automotive Lidar sensors or long-range free-space optical links.

[0068] Referring to Figure 14A, one way to mitigate the divergence at non-zero angles θ (as shown in Figure 13B) is to modify the lens design to a complex shape that compensates for the angular beam extension problem. For example, as seen in Figure 14A, the center of the lens can be placed on a curve in the XZ plane to adjust for changes in distance. This ensures that the distance d remains equal to the focal length f. Alternatively, referring to Figure 14B, the intensity of the lens, expressed by the effective focal length f(θ), can be modified for different angles of incidence. This ensures that f(θ) and d remain substantially equal even as θ and d change. For example, as seen in Figure 14B, the focal curvature of the lens at the center can differ (e.g., be smaller) from the focal curvature at the two ends that vary the effective focal length, which is a function of angle. In other implementations, the two approaches described above can be combined in lenses where both intensity and center point vary with angle.

[0069] Referring to Figure 15, another method for achieving collimation for a beam extending in the YZ plane is to utilize a curved mirror 1500 as a focusing element for the beam from OPA 1502. Mirror 1500 has a concave profile in the YZ plane and is uniform over its length along the X direction. As seen in Figure 16A, by placing the OPA tip 1600 in front of (i.e., inside) the concave mirror 1602, the radiator can be approximately positioned at the focal point of the mirror 1602. The relative phase applied to the OPA tip 1600 can steer the beam along the X direction (i.e., in the XZ plane around the Y axis), while the beam exits the tip and extends in the Y direction (i.e., in the YZ plane). The mirror is parabolic (z=4fy) with focal length f 2 ) may be used. The entire beam portion (also referred to as a ray or simply "beam") emanating from the OPA chip 1600 is collimated so as to be aligned with the Z direction. In this example, the OPA chip 1600 is positioned at the center of the mirror 1602 and illuminates downward toward the center of the mirror 1602, so that a portion of the back-reflected light is blocked by the OPA chip 1600, resulting in loss.

[0070] One solution to the optical loss caused by blocking by the OPA chip 1600 is to have the OPA chip 1600 illuminate the mirror 1602 at a fixed angle. For example, as can be seen in Figure 16B, if the orientation of the OPA chip 1600 changes so that only the right side of the mirror 1602 is illuminated, while the surface of the OPA chip 1600 remains at the focal point, then no optical blocking occurs. The size of the collimated beam emanating from the system depends on the focal length, the beam divergence from the OPA chip 1600, and the orientation of the OPA chip 1600. For example, referring to Figure 16C, if the range of the optical cone emanating from the OPA chip 1600 is θ1 and θ2, then the orientation angle (θ0) of the optical phased array must be greater than θ1, and the beam size depends on f, θ0, θ1, and θ2.

[0071] The size of the curved mirror used as the focusing element must be large enough to accommodate the steered beam (in the X direction, also referred to here as length) and the beam expansion in the YZ direction (mirror width). As an example, Figures 17A and 17B show representations of beam expansion where the mirror width is four times its focal length (W>4f) (shown in Figure 17A) and beam expansion where the mirror length is ten times its focal length (L>10f) (shown in Figure 17B). This example covers approximately ±60 degrees in both directions in addition to the steering angle. The exact minimum size depends on the beam divergence and the required steering range.

[0072] Figures 18A to 18C show an example of beam divergence from an end-fire waveguide that may be used in an OPA. Figure 18A shows different measurements of beam divergence in each direction. This can be defined as the full beam angle between points where the beam intensity drops below -10 dB from the peak beam intensity. As seen in Figure 18A, α and β are the 10 dB cone angles of the beam in the transverse (X) and longitudinal (Y) directions, respectively. Referring to Figure 18B, the waveguide width (W) and height (H) are shown for the full width portion and the tapered end face portion. In this example, the waveguide is tapered from a wide cross-section to a narrow cross-section (with the width W reduced while the height H remains the same). If the waveguide height remains smaller than the width at the end face, the output beam diverges faster in the Y direction. As shown in Figure 18C, the small waveguide height results in β being larger than α.

[0073] Figure 19 shows an example of an OPA chip 1900 that beams onto a half-mirror 1902. In this example, the beam angle 1904 is greater than β / 2. This limits the intensity of any beam-blocking events by the OPA chip 1900 to less than -10 dB. The beam angle 1904 can be further increased as the beam blocking decreases, but the right mirror width needs to be increased as the optical cone moves to the right of the half-mirror 1902. In other words, there is a trade-off between a large beam size and a compact device size.

[0074] Figure 20 shows the trace of a beam array emerging from an OPA tip with a ±60° optical cone, compared to the half-mirror configuration in Figure 19. The OPA tip is tilted up to 65°. As can be seen from the beam, the right half of the beam spreads out due to this tilt and occupies a considerable area of ​​the mirror. Therefore, the beam emerging from the half-mirror system is asymmetrical, with the right side of the beam spreading out in the Y direction.

[0075] Another consideration is the collimation (spread in the Y direction) of the beam when the optical phased array steers the optical beam along the X (length) direction. As shown in Figures 13A and 13B, when a conventional cylindrical lens is used to collimate the beam in the Y direction, steering along the X direction causes the outgoing beam to blur and diverge. It can be illustrated that a beam steered and collimated along the X direction by a parabolic mirror does not suffer from this aberration (blurring) problem.

[0076] Figure 21 shows an example of a cylindrical mirror that focuses on an incident plane wave. Possible defocusing problems can be investigated by comparing the focal length (f1) of the plane wave incident directly below with the focal length (f2) of the mirror, which is tilted along the length of the mirror, in this example along Y. The associated wave vector k for the plane wave corresponding to point A in Figure 21 is shown in Figure 22. The associated components of the wave vector are related as follows.

number

number

number

number

number

number

[0077] The following is an example of the wave vector component relationship for a cylindrical lens.

number

[0078] Therefore, the angle of refraction with respect to the x-axis is a function of the angle of incidence with respect to the y-axis. Hence, the focal position along the x-axis is a function of the angle of incidence.

number

[0079] As can be seen in Figure 23, when the beam is directed straight down along the z-axis, the beam focuses at the center of the mirror, forming a parabolic focal point. As shown in Figure 24, when the beam is tilted with respect to the x-axis, the beam's focal point moves in both the x and z directions along the focal plane curve 2400.

[0080] This characteristic can be utilized when the system's output beam rotates in the XZ plane (rotates around the Y axis). For example, as shown in Figure 25, when the OPA tip 2500 moves along the focal trajectory to three different positions shown, the collimated output beam rotates in the XZ plane along each of the three different output angles shown.

[0081] This characteristic can be used to cover a large angular range. For example, such variations in angular coverage around different central beam angles can be seen in Figure 26A for several OPA chips stacked side by side on a stepped structure of pedestal 2600 along mirror 2602. The only difference between OPA chips is the position of the output waveguide and radiator of the OPA chip in the YZ plane, near the focal length in the Z direction. Each OPA chip contains radiator elements in a linear array arranged along the Y axis. The radiator elements of each linear array are offset along the Y axis relative to other linear arrays (for example, in this example the OPA chips are arranged so as not to overlap along the Y axis). The radiator elements of each linear array are also offset along the Z axis relative to other linear arrays. These linear arrays are substantially in the same position along the X axis.

[0082] This characteristic allows for a set of beams where the static center of the beam covers a certain angular range in the XZ plane. Nevertheless, in such a configuration shown in Figure 26A, phase control is only possible for steering along the Y axis (in the XY plane). Referring to Figure 26B, the beam can be steered in the X direction (i.e., within the XZ plane) in response to changes in wavelength by adding a diffraction / dispersion plate 2604 before the mirror 2602 to add steering capability in the XZ plane, similar to the example shown in Figure 7, to the lens-based system. A cross-sectional view of this system is shown in Figure 27. Steering along the Y direction of the OPA 2700 (into / out of the plane of the paper) is performed using the phase applied by the phase shifter in the OPA 2700, while lateral steering is performed by using a secondary steering element 2702 (e.g., a diffraction / dispersion plate) after reflection from the mirror 2704.

[0083] The two-dimensional steering capability described herein can be used for LiDAR sensor systems. For example, referring to Figure 28, two mirror-based OPA systems can be arranged side by side. Both of these systems steer in the same direction using both OPA phase control and diffracting / dispersing plates used as secondary steering elements. In this example, the Tx phased array system 2800 acts as a transmitter of the light energy of the outgoing beam, and the Rx phased array system 2802 collects the backscattered light in the collected beam. For example, an FMCW (Frequency Continuous Modulation) scheme or a time-of-flight detection scheme can be used to measure the object 2804 and its velocity (by Doppler shift detection).

[0084] As can be seen in Figure 29, the LiDAR sensor system may also be configured to include at least one transmitter (Tx) unit 2900 and a number of receiver (Rx) units 2902. These can be used to increase the light collection capability and range of the LiDAR sensor system.

[0085] Alternatively, for a more compact system, as seen in Figure 30A, a single concave collimating mirror 3000 may be used with an array of several TxOPA and RxOPA chips 3002. In this example, the OPA chips 3002 are stacked along the X direction, and only one diffractive optical element 3004 is used to steer Y for all OPA chips 3002. It is also possible, for example, if a WDM or circulator component is used, the same OPA chip may be configured to perform both transmitting and receiving. Alternatively, Figure 30B shows an example in which the mirrors and diffractive optical systems at each terminal can be simplified by arranging a pair of TXOPA and RXOPA chips 3006 side by side in front of the same mirror 3000.

[0086] Figure 31 shows two OPA-based Tx / Rx transceiver systems. These systems include a local terminal 3100 and a remote terminal 3102 at each end of an optical link that can be used to implement a WDM high data rate communication system using a free-space optical beam.

[0087] Secondary steering using diffraction / dispersion elements or other secondary steering elements can be performed in various different ways. For example, some secondary steering techniques depend on the polarization state of light. Referring to Figure 32A, the polarization state of light from the OPA chip 3200 is transverse electric field (TE) type (E x If we consider E as the x-component of the electric field, then x If dominant, the light hitting the concave mirror 3202 is S-polarized (E x ) and the same applies to light striking the diffracting element 3204 (or other secondary steering elements such as other forms of dispersion elements). Depending on the efficiency of optical steering in the YZ plane by the diffracting element 3204, the polarization of the light can be rotated either at the OPA chip 3200 (for example, by converting to transverse magnetic field (TM) polarization) or before / after the diffracting element. Figure 32B shows an example in which the polarization rotator 3206 is positioned between the concave mirror 3202 and the diffracting element 3204. Alternatively, the diffracting element 3204 (or other forms of dispersion elements) may be designed to be polarization insensitive.

[0088] After determining the optimal polarization for the diffracting / dispersive element used for secondary steering, steering range, speed, required continuous vs. discrete steering, and / or insertion loss can be used to determine the choice of secondary steering mechanism. One method of steering using relatively simple diffracting / dispersive elements and potentially complex laser and photonics chips utilizes wavelength variation to implement the secondary steering mechanism. For example, Figure 32C includes a tunable laser 3208 that provides light to the OPA chip 3200. The wavelength of the light provided by the tunable laser 3208 can be tuned over a predetermined wavelength range (e.g., 1400-1600 nm). The wavelength variation results in dispersion-based beam steering after the reflecting diffracting element 3210. For example, the reflecting diffracting element 3210 may be a grating. Figure 33A shows an example where the beam of incident light 3300 is reflected from the grating 3302, and the direction of the diffracted beam is wavelength-dependent. To enhance this effect, multiple gratings, including an additional grating 3304, can be used, as shown in Figure 33B. When used for LIDAR purposes, unwanted reflections / spurious reflections (e.g., unused diffraction orders) may be blocked by baffles or other forms of optical mechanical assemblies to prevent them from propagating back into the LIDAR system.

[0089] As an alternative, instead of, or in conjunction with, wavelength tuning, a tunable lattice structure incorporating electro-optics, liquid crystal, or metasurface diffraction can be used.

[0090] A dispersive element can provide steering based on the angular dispersion of the dispersive element. For example, a beam steering device may include a phase-shifter optical phased array having a phase shifter that provides steering in the first dimension. The phase shifter provides light incident on a focusing element that produces a collimated beam. The collimated beam is supplied to one or more subsequent beam steering elements. One or more subsequent beam steering elements provide secondary steering in a second dimension in addition to the dimension of the phase shifter. One or more beam steering elements may be dispersive elements that provide steering based on the wavelength of the input light. If a tunable laser source coupled to the optical phased array has an optical bandwidth of Δλ (nm), a dispersive element with an angular dispersion value of ∂θ / ∂λ can provide an angular change of Δθ = (∂θ / ∂λ) × Δλ (degrees) as a function of wavelength change to achieve wavelength-based steering.

[0091] The dispersion element may be, for example, a diffraction element such as a grating, a refractive element such as a prism, a combination of both, or some other dispersion element. In some implementation examples, optical wedges may also be used to increase the angular dispersion of the system.

[0092] Figures 34, 35A to 35C, and 36 show examples of refractive elements used as steering elements.

[0093] Figure 34 shows a 3D perspective view of a collimated input beam 3400 supplied to a prism / wedge refractive element 3402 used to provide wavelength-based steering. The input beam 3400 can be collimated, for example, by using a beam coming after an optical phased array and a cylindrical mirror, as in the various implementation examples described herein. In this example, since the angle of refraction is wavelength-dependent, if the input beam 3400 is tuned to three different wavelengths, the input beam 3400 will be dispersed at three different angles.

[0094] Figure 35A shows a 2D side view of the collimated input beam 3500 supplied to the prism / wedge refractive element 3502, which is used to provide wavelength-based steering, similar to the example shown in Figure 34. Here, wavelength tuning is used to provide steering in the plane of this side view.

[0095] Figure 35B shows a 2D side view in which the collimated input beam 3500 is dispersed using a prism / wedge 3502 and a trailing prism / wedge 3504, which is used to further increase the wavelength-based field of view, when wavelength tuning is used for steering purposes.

[0096] Figure 35C shows a 2D side view of a collimated input beam 3500 being dispersed using a diffraction grating 3506 (used in the case of transmission) followed by a prism / wedge refractive element 3508 to further increase angular dispersion. The diffraction grating 3506 generates a highly efficient diffracted beam to a specific diffraction order, as shown, for example, in Figure 33A, unless transmitted instead of reflected. However, a certain amount of light can still be directed to other unwanted diffraction orders. When used for LIDAR purposes, light from these unwanted diffraction orders can propagate to several distant targets, be reflected back into the LIDAR system, and overwhelm the operational return signal from the specific diffraction order used for measurement. This can be mitigated by blocking these unwanted diffraction orders using an optical baffle or optics-mechanical assembly.

[0097] Figure 36 shows an exemplary system including an OPA chip 3600 followed by a cylindrical mirror 3602. A curved diffraction element 3604 (e.g., a diffraction grating used in the case of transmission) follows the cylindrical mirror 3602.

[0098] Various alternatives can be used for these examples. Referring again to the examples in Figure 34 (3D view) and Figure 35A (2D view for the same configuration), the prism / wedges 3402 and 3502 must be sufficiently long in the dimension orthogonal to the 2D view (i.e., in the x-direction outward from the plane of the paper). This allows light coming from the upstream optical phased array and / or collimator element to be captured by steering using a phase-based steering mechanism for a full horizontal (phase-based) angular field of view. Additionally, to further increase angular dispersion, any number of prisms may be cascaded, as shown in the example in Figure 35B (which features two prisms). For a given steering angle range, the dispersion of a two-prism system is twice that of a single prism, and this can further correspond to the number of prisms. Prisms can be designed to maximize angular dispersion. Diffraction gratings can also be used as dispersion elements. The amount of angular dispersion is controlled by the refractive index as well as the apex angle of the prism / wedge. Diffraction gratings can be used in transmission or reflection applications. A configuration with an appropriate balance of diffraction efficiency, angular dispersion, polarization insensitivity, and overall size can be selected. Multiple diffraction gratings may be stacked in succession to increase the angular dispersion of the system, and thus increase the angular field of view (FOV) in that dimension. Figure 35C shows an example in which an optical prism / wedge 3508 follows a transmission diffraction grating 3506. While the transmission diffraction grating 3506 gives the system an initial wavelength-based FOV, the optical prism / wedge 3508 further increases the beam divergence. If a diverging beam is incident on the optical prism / wedge, the angular divergence of the beam may increase further.

[0099] To maintain high diffraction efficiency by allowing light to pass through the horizontal field of view provided by the phase shifter, the angle of incidence on the transmission diffraction grating may be configured to be the normal angle of incidence. This can be achieved by having a curved diffraction element (e.g., a diffraction grating). An example of such a configuration is shown in Figure 36. This configuration can mitigate the otherwise potentially large angle of incidence (steering based on the phase shifter) on the diffraction element.

[0100] Although this disclosure has been described in relation to certain embodiments, it should be understood that this disclosure is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included in the appended claims, and the scope should be given the broadest possible interpretation to include all modifications and equivalent structures permitted under the law.

Claims

1. It is a device, A photonic integrated circuit including an optically phased array configured to form a light beam, A focusing element located at a fixed position relative to the optical phased array, configured to receive the optical beam from the optical phased array, A steering element located in a fixed position relative to the focusing element and Includes, The relative phase shift between the multiple antenna elements of the optical phased array provides steering in the first plane of the light beam emitted from the optical phased array. The focusing element intersects the path of the light beam between the optical phased array and the steering element. The focusing element is shaped to substantially collimate the light beam in the second plane so as to limit the expansion of the light beam in the second plane perpendicular to the first plane when the light beam is coupled from the optical phased array. The steering element is configured to receive the light beam substantially collimated in the second plane by the focusing element and to steer the light beam in the second plane. An apparatus in which at least one of the focusing element or the steering element is externally coupled to the photonic integrated circuit.

2. The apparatus according to claim 1, wherein the steering element includes a dispersion element.

3. The apparatus according to claim 2, wherein the dispersion element includes a diffraction element.

4. The apparatus according to claim 2, wherein the dispersion element includes a refractive element.

5. The apparatus according to claim 4, wherein the refractive element includes a prism.

6. The apparatus according to claim 1, wherein the focusing element includes a lens.

7. The apparatus according to claim 1, wherein the focusing element includes a reflective surface.

8. The apparatus according to claim 1, wherein the photonic integrated circuit, the focusing element, and the steering element are included in at least a portion of the LiDAR system.

9. The apparatus according to claim 1, wherein the photonic integrated circuit, the focusing element, and the steering element are included in at least a portion of the free-space optical link of the communication system.

10. It is a device, A phased optical array configured to form a light beam, A reflective surface located at a fixed position relative to the optical phased array, configured to redirect the optical beam received from the optical phased array, A steering element located in a fixed position relative to the reflective surface and Includes, The relative phase shift between the multiple antenna elements of the optical phased array provides steering in the first plane of the light beam emitted from the optical phased array. The reflective surface intersects the path of the light beam between the optical phased array and the steering element, The reflective surface is shaped to substantially collimate the light beam in the second plane so as to limit the expansion of the light beam in the second plane perpendicular to the first plane when the light beam is redirected from the optical phased array. The steering element is configured to receive the light beam, which has been redirected from the reflective surface and substantially collimated in the second plane, and to steer the light beam in the second plane.

11. The apparatus of claim 10, further comprising a light source configured to supply light waves to the plurality of antenna elements of the optical phased array.

12. The steering element includes a diffraction element, The light source includes a tunable light source configured to tune the wavelength of the light waves supplied to the plurality of antenna elements of the optical phased array, The apparatus of claim 11, wherein the light beam emitted from the diffracting element is steered in the second plane by the tuned wavelength.

13. The apparatus of claim 10, wherein the steering element includes a diffraction element configured to be tuned to electronically manipulate the light beam in the second plane.

14. The apparatus of claim 10, wherein the optical phased array, the reflective surface, and the steering element are included in at least a portion of the LiDAR system.

15. The apparatus of claim 10, wherein the optical phased array, the reflective surface, and the steering element are included in at least a portion of the free-space optical link of the communication system.

16. It is a device, A phased optical array configured to form a light beam, A lens located at a fixed position relative to the optical phased array, configured to receive the light beam from the optical phased array, A steering element located in a fixed position relative to the lens and Includes, The relative phase shift between the multiple antenna elements of the optical phased array provides steering in the first plane of the light beam emitted from the optical phased array. The lens intersects the path of the light beam between the optical phased array and the steering element, The lens is shaped to substantially collimate the light beam in the second plane so as to limit the expansion of the light beam in the second plane perpendicular to the first plane when the light beam is received from the optical phased array. The steering element is configured to receive the light beam substantially collimated in the second plane by the lens, and to steer the light beam in the second plane.

17. The apparatus of claim 16, further comprising a light source configured to supply light waves to the plurality of antenna elements of the optical phased array.

18. The steering element includes a diffraction element, The light source includes a tunable light source configured to tune the wavelength of the light waves supplied to the plurality of antenna elements of the optical phased array, The apparatus of claim 17, wherein the light beam emitted from the diffracting element is steered in the second plane by the tuned wavelength.

19. The apparatus of claim 16, wherein the steering element includes a diffraction element configured to be tuned to electronically manipulate the light beam in the second plane.

20. The apparatus of claim 16, wherein the optical phased array includes a plurality of antenna elements coupled to each optical waveguide formed in a photonic integrated circuit.

21. The apparatus of claim 16, wherein the optical phased array, the lens, and the steering element are included in at least a portion of the LiDAR system.

22. The apparatus of claim 16, wherein the optical phased array, the lens, and the steering element are included in at least a portion of the free-space optical link of the communication system.

23. The apparatus according to claim 1, further comprising a light source configured to supply light waves to the plurality of antenna elements of the optical phased array.

24. The steering element includes a dispersion element, The light source includes a tunable light source configured to tune the wavelength of the light waves supplied to the plurality of antenna elements of the optical phased array, The apparatus of claim 23, wherein the tuned wavelength provides steering in the second plane of the light beam emitted from the dispersive element.

25. The apparatus according to claim 1, wherein the relative phase shift between the plurality of antenna elements is applied through each of the phase shifters coupled to each of the plurality of antenna elements.

26. The apparatus according to claim 2, wherein the dispersion element includes at least two prisms.

27. The apparatus according to claim 2, wherein the dispersion element includes at least one diffraction grating and at least one prism.

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