Multi-channel transceiver based on PIC

Abstract

An optoelectronic device (100, 500) includes a dual fold mirror (114, 510) mounted on a carrier substrate (112, 524), the first and second reflective surfaces (520, 522) of the dual fold mirror being disposed diagonally. A plurality of identical photonic integrated circuits (PICs 108, 110, 320, 502, 504, 506, 508) are disposed on a carrier substrate. Each PIC comprises: an array of optical transceiver units (314, 400) on a planar substrate, the array of optical transceiver units having respective edge couplers (406) along an edge of the planar substrate; and an optical distribution tree (320) coupled to transmit the coherent radiation to the optical transceiver units. The first PIC is disposed on the carrier substrate such that an edge of the first PIC is proximate to the first reflective surface, and the second PIC is rotated 180 DEG relative to the first PIC such that an edge of the second PIC is proximate to the second reflective surface.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 342,176 filed on May 16, 2022, the disclosure of which is incorporated herein by reference. Field of the Invention

[0003] The present invention relates generally to devices and methods for optical sensing and imaging, and more particularly to integrated photonic devices and systems incorporating such devices.

[0004] background

[0005] In many optical sensing applications, multiple points on a target are irradiated by one or more light beams, and the reflected radiation from each point is processed to analyze the properties of the target. In some applications, such as optical coherence tomography (OCT) and CW LiDAR, a coherent light beam is emitted toward the target, and the reflected radiation is sensed and processed coherently with the emitted radiation. In order to sense the properties of the target with high resolution, the area should be densely probed by scanning the emitted light beam in the region of interest or by simultaneously emitting and sensing an array of multiple light beams. However, scanning solutions generally suffer from low throughput. Arrays of transmitters and receivers can increase the throughput, but their resolution is limited by the spacing of the array, which in turn is limited by the size of the transmitters and receivers themselves.

[0006] As used in this specification and claims, the terms "optical", "light" and "optical radiation" refer to electromagnetic radiation in any of the visible, infrared and ultraviolet spectral ranges.

[0007] Overview

[0008] Embodiments of the invention described below provide improved systems, devices, and methods for optical sensing.

[0009] Therefore, according to an embodiment of the present invention, there is provided an optoelectronic device, comprising: a carrier substrate and a double-folded reflector, the double-folded reflector being mounted on the carrier substrate and comprising a first reflective surface and a second reflective surface being arranged diagonally relative to a normal of the carrier substrate. A plurality of identical photonic integrated circuits (PICs) each comprises: a planar substrate; an array of optical transceiver units, the array of optical transceiver units being arranged on the planar substrate and comprising corresponding edge couplers arranged along an edge of the planar substrate; and an optical distribution tree, the optical distribution tree being coupled to transmit coherent radiation from a radiation source to the optical transceiver units. The plurality of identical PICs comprises a first PIC and a second PIC, the first PIC being arranged on the carrier substrate so that an edge of the first PIC is close to the first reflective surface, the second PIC being rotated 180° relative to the first PIC and being arranged on the carrier substrate so that an edge of the second PIC is close to the second reflective surface.

[0010] In a disclosed embodiment, the bi-fold mirror has a triangular profile, wherein the first and second reflective surfaces are oriented at +45° and -45°, respectively, relative to the normal.

[0011] Additionally or alternatively, the edge couplers in each PIC are arranged along the edge with a predefined spacing between the edge couplers, and the first PIC and the second PIC are arranged on the carrier substrate so that the edge couplers on the first PIC are shifted by half of the predefined spacing relative to the edge couplers on the second PIC.

[0012] In some embodiments, each PIC includes: a central region in which edge couplers are arranged along the edge with a first spacing between the edge couplers; a first peripheral region at a first side of the central region in which no edge couplers are arranged along the edge; and a second peripheral region at a second side of the central region opposite to the first side in which the edge couplers are arranged at a second spacing, the second spacing being finer than the first spacing. In disclosed embodiments, the second spacing is half of the first spacing.

[0013] Additionally or alternatively, the plurality of identical PICs include: a third PIC disposed side by side with the first PIC on the carrier substrate such that an edge of the third PIC is close to the first reflective surface; and a fourth PIC rotated 180° relative to the first PIC and disposed side by side with the second PIC on the carrier substrate such that an edge of the fourth PIC is close to the second reflective surface.

[0014] Typically, an optical distribution tree comprises a network of waveguides and switches arranged on a planar substrate.

[0015] In some embodiments, the optical transceiver unit is configured to: direct coherent radiation through a respective edge coupler, via a bifold mirror, toward a target; receive optical radiation from the target through the respective edge coupler via the bifold mirror; mix a portion of the coherent radiation with the optical radiation received through the edge coupler; and output an electrical signal in response to the mixed radiation. Typically, the edge coupler defines a respective optical aperture of the optical transceiver unit, and the apparatus includes one or more optical elements configured to image the optical aperture onto the target, thereby defining a respective field of view of the optical transceiver unit. In disclosed embodiments, the apparatus includes a scanner configured to scan the field of view of the optical transceiver unit over the target.

[0016] According to an embodiment of the present invention, there is also provided an optoelectronic device, which includes: a planar substrate and an array of optical transceiver units, the array of optical transceiver units being arranged on the substrate. Each transceiver unit includes an optical transducer, which is configured to couple optical radiation between the transceiver unit and a target outside the substrate. The optical distribution tree includes a hierarchical network of switches interconnected by waveguides, arranged on the substrate, and coupled to transmit coherent radiation from a radiation source to the optical transceiver units. The hierarchical network includes at least a first layer of first switches having a first switching time and a second layer of second switches having a second switching time different from the first switching time. The controller is configured to actuate the switches so as to select different subsets of the optical transceiver units to receive coherent radiation from the radiation source at different times.

[0017] In some embodiments, each first switch in the first layer has at least two first outputs, the at least two first outputs are respectively coupled to at least two second switches in the second layer, and each second switch in the second layer has at least two second outputs coupled to the transceiver units, and the first switching time is shorter than the second switching time. In the disclosed embodiment, the optical transceiver units and the second switches are arranged in different respective first and second regions of the substrate in first and second groups, and the waveguides interconnect the first switches and the second switches so that one of the first outputs of each first switch is coupled to the first group of the transceiver units and the second switch, and the other of the first outputs of each first switch is coupled to the second group of the transceiver units and the second switch.

[0018] In some embodiments, the apparatus includes a scanner configured to scan respective fields of view of optical transceiver units over a target, wherein the controller is configured to actuate a switch to select different subsets of the optical transceiver units to transmit coherent radiation toward the target during different sweeps of the scanner over the target. In one embodiment, scanning the respective fields of view of the optical transceiver units over the target defines a plurality of respective scan lines over the target, wherein a first switching time is shorter than a second switching time, and wherein the controller is configured to actuate the first switch to activate different groups of scan lines in each sweep over the target. Additionally or alternatively, the controller is configured to actuate the switch to selectively activate scan lines in a region of interest over the target.

[0019] In a disclosed embodiment, a controller is configured to process signals output by the transceiver unit to generate a three-dimensional (3D) map of the target.

[0020] Switches include thermo-optical switches.

[0021] According to an embodiment of the present invention, a thermo-optical switch is provided, which includes: an interferometer, the interferometer including a first waveguide and a second waveguide having corresponding input ends and output ends; and a first heater and a second heater, the first heater and the second heater being configured to heat the first waveguide and the second waveguide, respectively. An optical splitter is coupled to receive a coherent optical signal and input the optical signal to the input ends of both the first waveguide and the second waveguide. A mixer is coupled to receive and mix optical signals from the output ends of the first waveguide and the second waveguide, and guides the mixed optical signal to a first output or a second output of the switch according to a phase shift between the first waveguide and the second waveguide. A controller is coupled to control the first heater and the second heater so as to exchange the mixed optical signal between the first output and the second output.

[0022] In some embodiments, the controller is configured to alternately drive the first heater and the second heater to toggle the mixed optical signal between the first output and the second output. In a disclosed embodiment, the controller is configured to drive the first heater and the second heater with a voltage waveform including a pre-emphasis pulse each time the output is switched. Additionally or alternatively, the controller is configured to drive the first heater and the second heater with respective voltages that cause respective temperatures of the first waveguide and the second waveguide to increase continuously over multiple cycles of switching between the first output and the second output.

[0023] In a disclosed embodiment, the controller includes a first digital / analog converter (DAC) and a second digital / analog converter, which are configured to apply corresponding voltages to the first heater and the second heater in response to corresponding digital inputs.

[0024] According to an embodiment of the present invention, there is also provided a beam shifter, which includes a first microlens array and a second microlens array, wherein the first microlens array and the second microlens array include microlenses arranged in corresponding first and second planes and having a common predefined spacing. One or more layers of birefringent material are included between the first microlens array and the second microlens array. The thickness and birefringence of each layer are selected so that light of a first polarization entering the layer through one of the microlenses is laterally displaced a distance equal to the spacing of the microlens array, while light of a second polarization orthogonal to the first polarization passes through the layer without being displaced.

[0025] In some embodiments, the beam shifter includes a directional polarization rotator between the first microlens array and the second microlens array, together with a birefringent material, and the directional polarization rotator is configured to rotate the polarization of light passing through the directional polarization rotator in a given direction by 90° without rotating the polarization of light passing through the directional polarization rotator in the opposite direction. In a disclosed embodiment, the polarization rotator includes a Faraday rotator and a half-wave plate.

[0026] Additionally or alternatively, the one or more layers of birefringent material include a first layer adjacent to the first microlens array and a second layer adjacent to the second microlens array, wherein the directional polarization rotator is contained between the first and second layers of birefringent material. In one embodiment, the first and second layers of birefringent material are oriented such that both the first and second layers laterally displace light of the first polarization in the same direction. In an alternative embodiment, the first and second layers of birefringent material are oriented such that the first and second layers laterally displace light of the first polarization in opposite directions.

[0027] According to an embodiment of the present invention, an optical device is further provided, the device comprising: a beam shifter as described above; and a photonic integrated circuit (PIC), the photonic integrated circuit comprising at least one row of optical couplers, the at least one row of optical couplers being spaced apart at a predefined pitch and aligned with a first microlens array so as to couple corresponding beams of light between the optical couplers and corresponding microlenses in the first array. Therefore, the first polarized beam coupled into and coupled out from the adjacent optical couplers in the at least one row and the second polarized beam coupled into and coupled out from the adjacent optical couplers in the at least one row are combined at the second microlens array.

[0028] In some embodiments, the optical coupler comprises an edge coupler. In one embodiment, the turning mirror is disposed between the edge coupler and the device.

[0029] Alternatively, the optical coupler comprises a vertical coupler disposed on the surface of the PIC. In a disclosed embodiment, the vertical coupler is disposed in a two-dimensional matrix of positions on the surface of the PIC, and the first microlens array and the second microlens array comprise a two-dimensional array of microlenses aligned with the two-dimensional matrix of the vertical coupler.

[0030] According to an embodiment of the present invention, an optical device is also provided, which includes a photonic integrated circuit (PIC), the photonic integrated circuit including at least one row of vertical couplers, the at least one row of vertical couplers being arranged on the surface of the PIC and spaced apart at a predefined spacing, and being configured to couple corresponding beams of light into and out of the PIC while collimating the corresponding beams. A beam shifter is arranged above the PIC and includes: a microlens array, the microlens array including microlenses arranged in a plane, spaced apart at a predefined spacing and aligned with the vertical couplers; and one or more layers of birefringent material contained between the PIC and the microlens array. The thickness and birefringence of each layer are selected so that light of a first polarization entering the layer through one of the microlenses or the vertical coupler is laterally displaced a distance equal to the spacing, while light of a second polarization orthogonal to the first polarization passes through the layer without being displaced.

[0031] In some embodiments, the beam displacer includes a directional polarization rotator between the microlens array and the PIC, together with a birefringent material, and the directional polarization rotator is configured to rotate the polarization of light passing through the directional polarization rotator in a given direction by 90° without rotating the polarization of light passing through the directional polarization rotator in an opposite direction. In disclosed embodiments, the one or more layers of birefringent material include a first layer adjacent to the first microlens array and a second layer adjacent to the PIC, wherein the directional polarization rotator is contained between the first layer and the second layer of birefringent material.

[0032] According to an embodiment of the present invention, an optical device is also provided, which includes a photonic integrated circuit (PIC), the photonic integrated circuit including at least one row of optical couplers, which are spaced apart at a predefined spacing and are configured to couple corresponding beams of light into and out of the PIC. A prism includes a birefringent material, which is arranged close to the row of optical couplers. The birefringence and prism angle of the prism are selected so that light of a first polarization passing through the prism to or from one of the optical couplers is deflected by a first angle, while light of a second polarization orthogonal to the first polarization is deflected by a second angle different from the first angle when passing through the prism. The first angle and the second angle are selected so that the light beams of the first polarization coupled into and out of the adjacent optical couplers in the at least one row and the light beams of the second polarization coupled out are combined by the prism.

[0033] According to an embodiment of the present invention, an optical device is further provided, the optical device comprising: a substrate and a polarization beam splitter disposed on the substrate. The polarization beam splitter comprises a first waveguide having a first end, a second end and a first tapered section, the first end being configured to receive an input light beam including both a TE polarization component and a TM polarization component, the second end being configured to output the TE polarization component, and the first tapered section having a first width that decreases in a direction from the first end toward the second end. The second waveguide has a second tapered section close to the first tapered section, the second tapered section having a second width that increases in a direction from the first end toward the second end, so that the TM polarization component is coupled from the first tapered section to the second tapered section.

[0034] In a disclosed embodiment, the device includes a polarization rotator disposed on the substrate and coupled to receive a TM polarization component from the second waveguide and convert the TM polarization component to a TE polarization.

[0035] According to an embodiment of the present invention, a signal processing device is also provided, which includes an array of coherent detection units. Each unit includes: a detector configured to output a corresponding beat signal in response to radiation received by the unit; and a mixer coupled to mix the corresponding beat signal with a carrier at a corresponding modulation frequency, whereby the coherent detection unit outputs a corresponding modulated signal at a different corresponding modulation frequency. An analog adder is coupled to sum the modulated signals output by the array of coherent detection units to output a summed signal. An analog-to-digital converter (ADC) is coupled to digitize the summed signal to output a digital data stream. The processing circuit is configured to demultiplex the digital data stream into a plurality of frequency channels at corresponding modulation frequencies and extract a corresponding beat frequency from each of these frequency channels.

[0036] In a disclosed embodiment, the processing circuit is configured to demultiplex a digital data stream into multiple frequency channels by transforming the digital data stream into the frequency domain and identifying a corresponding pair of peaks in the transformed data stream, the corresponding pair of peaks being separated by twice the corresponding modulation frequency of each unit.

[0037] In some embodiments, each of the coherent detection units includes a corresponding first mixer and a second mixer, the first mixer and the second mixer being configured to mix the corresponding beat frequency signal with the corresponding first carrier and the second carrier at different corresponding first modulation frequencies and second modulation frequencies, so that the coherent detection unit outputs a corresponding first modulated signal and a second modulated signal, wherein there is a different corresponding frequency difference between the first modulated signal and the second modulated signal output by each of the coherent detection units. The processing circuit demultiplexes the digital data stream into a plurality of frequency channels in response to the corresponding frequency difference. In a disclosed embodiment, the analog adder includes a first adder and a second adder, the first adder and the second adder are respectively coupled to sum the first modulated signal and the second modulated signal output by the first mixer and the second mixer in the coherent detection unit, and the ADC includes a first ADC and a second ADC, the first ADC and the second ADC are coupled to receive and digitize the corresponding first summed signal and the second summed signal output by the first adder and the second adder, respectively, so as to generate a first data stream and a second data stream for input to the processing circuit.

[0038] According to an embodiment of the present invention, an optical device is further provided, which includes: a first substrate and a first array of photonic integrated circuits (PICs) disposed on the first substrate. Each PIC includes one or more optical edge couplers adjacent to an upper surface of the first substrate. A second substrate includes a second array of steering mirrors and is mounted on the upper surface of the first substrate so that each steering mirror in the second array is aligned with one or more optical edge couplers on a corresponding one of the PICs, whereby light is coupled into and out of the optical edge couplers via the steering mirrors.

[0039] In a disclosed embodiment, the turning mirrors have respective reflective surfaces that are inclined 45° relative to a lower surface of a second substrate mounted on an upper surface of the first substrate.

[0040] In some embodiments, the first substrate and the second substrate include semiconductor material that is patterned and etched to produce the PICs and the turning mirror. Additionally or alternatively, the first substrate is patterned to define a cavity between the PICs, wherein the edge coupler is adjacent to a corresponding cavity in the cavity, and the second substrate is patterned such that when the second substrate is mounted on the upper surface of the first substrate, the turning mirror protrudes into the cavity adjacent to the edge coupler.

[0041] According to an embodiment of the present invention, there is also provided a method for producing an optoelectronic device, the method comprising mounting a double-folded reflector on a carrier substrate, the double-folded reflector comprising a first reflective surface and a second reflective surface arranged diagonally relative to a normal of the carrier substrate. A plurality of identical photonic integrated circuits (PICs) are mounted on the carrier substrate, each PIC comprising: a planar substrate; an array of optical transceiver units, which are arranged on the planar substrate and include corresponding edge couplers arranged along the edge of the planar substrate; and an optical distribution tree, which is coupled to transmit coherent radiation from a radiation source to the optical transceiver units. The plurality of identical PICs comprises a first PIC and a second PIC, the first PIC being mounted on the carrier substrate so that an edge of the first PIC is close to the first reflective surface, the second PIC being rotated 180° relative to the first PIC and mounted on the carrier substrate so that an edge of the second PIC is close to the second reflective surface.

[0042] According to an embodiment of the present invention, there is also provided a method for producing an optoelectronic device, the method comprising forming an array of optical transceiver units on a planar substrate, each transceiver unit comprising an optical transducer configured to couple optical radiation between the transceiver unit and a target external to the substrate. An optical distribution tree is coupled to transmit coherent radiation from a radiation source to the optical transceiver units, the optical distribution tree comprising a hierarchical network of switches interconnected by waveguides and disposed on the substrate. The hierarchical network comprises at least a first layer of first switches having a first switching time and a second layer of second switches having a second switching time different from the first switching time. A controller is coupled to actuate the switches so as to select different subsets of the optical transceiver units to receive coherent radiation from the radiation source at different times.

[0043] According to an embodiment of the present invention, a method for switching is further provided, the method comprising: providing a thermo-optical switch, the thermo-optical switch comprising: an interferometer, the interferometer comprising a first waveguide and a second waveguide having respective input ends and output ends; a first heater and a second heater, the first heater and the second heater being configured to heat the first waveguide and the second waveguide, respectively; an optical splitter, the optical splitter being coupled to receive a coherent optical signal and input the optical signal to both the input ends of the first waveguide and the second waveguide; and a mixer, the mixer being coupled to receive and mix optical signals from the output ends of the first waveguide and the second waveguide, and directing the mixed optical signal to a first output or a second output of the switch according to a phase shift between the first waveguide and the second waveguide. The first heater and the second heater are controlled so as to exchange the mixed optical signal between the first output and the second output.

[0044] According to an embodiment of the present invention, a method for beam displacement is also provided. The method includes providing a first microlens array and a second microlens array, the first microlens array and the second microlens array including microlenses arranged in corresponding first and second planes and having a common predefined spacing. One or more layers of birefringent material are inserted between the first microlens array and the second microlens array. The thickness and birefringence of each layer are selected so that light of a first polarization entering the layer through one of the microlenses is laterally displaced a distance equal to the spacing of the microlens array, while light of a second polarization orthogonal to the first polarization passes through the layer without being displaced.

[0045] According to an embodiment of the present invention, there is further provided a method for beam shifting, the method comprising providing a photonic integrated circuit (PIC), the PIC comprising at least one row of vertical couplers, the at least one row of vertical couplers being arranged on a surface of the PIC and spaced apart at a predefined spacing, and being configured to couple corresponding beams of light into and out of the PIC while collimating the corresponding beams. A beam shifter is provided, the beam shifter comprising: a microlens array, the microlens array comprising microlenses arranged in a plane and spaced apart at the predefined spacing; and one or more layers of birefringent material contained between the PIC and the microlens array. The thickness and birefringence of each layer are selected so that light of a first polarization entering the layer through one of the microlenses or the vertical coupler is laterally shifted a distance equal to the spacing, while light of a second polarization orthogonal to the first polarization passes through the layer without being shifted. The beam shifter is positioned above the PIC so that the microlenses are aligned with the vertical couplers accordingly.

[0046] According to an embodiment of the present invention, there is also provided a method for beam shifting, the method comprising: providing a photonic integrated circuit (PIC), the PIC comprising at least one row of optical couplers, the at least one row of optical couplers being spaced apart at a predefined spacing and configured to couple corresponding beams of light into and out of the PIC. Positioning a prism comprising a birefringent material close to the row of optical couplers. The birefringence and prism angle of the prism are selected so that light of a first polarization passing through the prism to or from one of the optical couplers is deflected by a first angle, while light of a second polarization orthogonal to the first polarization is deflected by a second angle different from the first angle when passing through the prism, and the first angle and the second angle are selected so that the light beams of the first polarization coupled into and out of the adjacent optical couplers in the at least one row and the light beams of the second polarization coupled out are combined by the prism.

[0047] According to an embodiment of the present invention, a method for beam control is also provided, the method comprising forming a first waveguide on a substrate, the first waveguide having a first end, a second end and a first tapered section, the first end being configured to receive an input beam including both a TE polarization component and a TM polarization component, the second end being configured to output the TE polarization component, and the first tapered section having a first width that decreases in a direction from the first end toward the second end. A second waveguide is formed on the substrate, the second waveguide having a second tapered section close to the first tapered section, the second tapered section having a second width that increases in a direction from the first end toward the second end, so that the TM polarization component is coupled from the first tapered section to the second tapered section.

[0048] According to an embodiment of the present invention, there is further provided a method for signal processing, the method comprising: providing an array of coherent detection units, each unit comprising a detector configured to output a corresponding beat frequency signal in response to radiation received by the unit. The corresponding beat frequency signal output by each unit is mixed with a carrier at a corresponding modulation frequency, whereby the coherent detection unit outputs a corresponding modulated signal at a different corresponding modulation frequency. The modulated signals output by the array of coherent detection units are summed to produce a summed analog signal. The summed analog signal is digitized to produce a digital data stream. The digital data stream is demultiplexed into a plurality of frequency channels at corresponding modulation frequencies. The corresponding beat frequency is extracted from each of the frequency channels.

[0049] According to an embodiment of the present invention, there is also provided a method for optical manufacturing, the method comprising forming a first array of photonic integrated circuits (PICs) on a first substrate. Each PIC comprises one or more optical edge couplers adjacent to an upper surface of the first substrate. A second array of steering mirrors is formed on a second substrate. The second substrate is mounted on an upper surface of the first substrate such that each steering mirror in the second array is aligned with one or more optical edge couplers on a corresponding one of the PICs, whereby light is coupled into and out of the optical edge couplers via the steering mirrors.

[0050] The present invention will be more fully understood from the following detailed description of embodiments of the present invention in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a schematic illustration of a scanning transceiver array device according to an embodiment of the present invention;

[0053] Figure 2 According to an embodiment of the present invention, Figure 1 A block diagram of the details of the transceiver array;

[0054] Figure 3 is a schematic top view of a photonic integrated circuit (PIC) including a hierarchical optical switching network according to an embodiment of the present invention;

[0055] Figure 4 According to an embodiment of the present invention, Figure 3 Schematic detail view of a transceiver cell (TC) used in a PIC;

[0056] Figure 5 is a schematic front view of a transceiver device including four PICs and a central turning mirror according to an embodiment of the present invention;

[0057] Fig. 6A , Figure 6B , Figure 6C and Fig.6D is a schematic front view of a continuous scanning pattern applied on a scene by a switch-type optical sensing system according to an embodiment of the present invention;

[0058] Fig. 7A is a block diagram schematically illustrating an optical switching tree on a PIC according to an embodiment of the present invention;

[0059] Figure 7B Two graphs are shown schematically illustrating the response of a thermo-optical switch to a voltage applied to a resistive heater of the switch according to an embodiment of the present invention;

[0060] Fig. 8A , Figure 8B and Figure 8C shows graphs schematically illustrating a voltage control scheme for a thermo-optical switch and the response of the switch to an applied voltage according to an alternative embodiment of the present invention;

[0061] Fig.9A is a block diagram schematically illustrating an optical switching tree including a fast thermal optical switch on a PIC according to another embodiment of the present invention;

[0062] Fig. 9B shows three graphs schematically illustrating a voltage control scheme for a thermo-optical switch and the response of the switch to an applied voltage according to another embodiment of the present invention;

[0063] Figures 10 to 13 is a schematic top view of a micro-optical beam displacer according to various embodiments of the present invention;

[0064] Fig.14 and Fig.15 Schematic side view and top view of a transceiver array device with a micro-optical beam shifter according to an embodiment of the present invention;

[0065] Fig.16 and Fig.17 Schematic side view and top view of a transceiver array device with a micro-optical beam shifter according to another embodiment of the present invention;

[0066] Fig.18 and Fig.19 Schematic side view and top view of a transceiver array device with a micro-optical beam shifter according to another embodiment of the present invention;

[0067] Figure 20 to Figure 22 is a schematic side view of a transceiver array device with a micro-optical beam shifter according to other embodiments of the present invention;

[0068] Fig.23A and Fig. 23B is a schematic side view of a birefringent prism according to an embodiment of the present invention;

[0069] Fig.23C is a schematic side view of a birefringent prism-based beam displacer according to an embodiment of the present invention;

[0070] Fig.24A is a block diagram schematically illustrating a polarization beam splitter rotator (PBSR) implemented on a PIC according to an embodiment of the present invention;

[0071] Fig. 24B is a schematic top view of a polarization beam splitter according to an embodiment of the present invention;

[0072] Fig.24C According to another embodiment of the present invention Fig.24A Schematic top view of PBSR;

[0073] Fig.25A is a block diagram schematically illustrating a signal processing scheme for use with a transceiver array according to an embodiment of the present invention;

[0074] Fig.25B According to an embodiment of the present invention, Fig.25A A schematic graph of signal outputs of some channels of a transceiver array;

[0075] Fig.26 and Fig. 27 is a block diagram schematically illustrating a signal processing scheme for use with a transceiver array according to an alternative embodiment of the present invention; and

[0076] Fig.28A is a schematic diagram showing an array of edge-emitting PICs and turning mirrors according to an embodiment of the present invention; and

[0077] Fig.28B It is shown Fig.28ASchematic cross-sectional view of a detail of an array. DETAILED DESCRIPTION

[0078] Overview

[0079] PCT International Publication WO 2023 / 023106 (the disclosure of which is incorporated herein by reference) describes a transceiver array and scanning system capable of scanning targets with high resolution and high throughput. The embodiments described in the disclosure use photonic transceiver chips. Each chip includes optical components for emitting and sensing radiation beams, as well as supporting electronic devices. In order to reduce the size and power requirements of the transceiver chip, the beam to be emitted can be centrally generated by the core transceiver engine and then multiplexed between the various transceivers (also referred to herein as transceiver units). A scanner (such as an optical mechanical scanning device) scans the beams of all transceivers in the area of ​​interest so that the area is densely covered-with a resolution finer than the spacing of the array-and with high throughput. Multiplexing and scanning can be controlled to adapt the scanning area and resolution to the application requirements.

[0080] The above PCT publications describe a variety of array geometries and scanning patterns that can be used for these purposes. Other transceiver arrays and scanning systems are described in PCT International Publications WO 2023 / 023105 and WO 2023 / 034465 and in PCT Patent Application PCT / US2022 / 47516 filed on October 24, 2022. All of the above PCT publications and applications are assigned to the assignee of this patent application, and their disclosures are incorporated herein by reference.

[0081] The photonic transceiver chips themselves are typically produced using photonic integrated circuit (PIC) technology. These chips are designed to meet application requirements such as sensing mode (e.g., coherent or incoherent, and sensitivity), mode of input / output coupling (e.g., vertical or across the chip edge, via gratings or via mirrors), and wavelength characteristics (spectral range, and single wavelength sensing or multi-wavelength sensing).

[0082] PIC technology does not yet enable high-density and high-yield electronic integrated circuits (EICs), such as CMOS chips. Therefore, for practical reasons, it may be advantageous to use several PICs arranged together on a common carrier substrate when creating a complete transceiver array. In addition, it may also be useful to separate the functions of electronic control, logic, and signal processing onto an EIC, which is tightly coupled to the PIC on which the transceiver array itself is formed. The above-mentioned PCT publications and patent applications describe embodiments using tightly coupled PICs and EICs. In one of these embodiments described in PCT / US2022 / 47516, the EIC is mounted on the PIC and performs control and / or signal processing functions in conjunction with the optoelectronic components of the PIC.

[0083] The embodiments described below extend the concepts and implementations set forth in the above-mentioned publications and patent applications. The present embodiments are directed to improving the optical quality and density of scanning coverage, as well as enabling efficient production and compact assembly, low-cost transceiver array devices. Although the disclosed embodiments relate to optical sensing in the visible, infrared, or ultraviolet ranges, the principles of the invention may alternatively be applied, with appropriate modifications, to other spectral ranges, such as microwave and millimeter wave radiation.

[0084] System architecture

[0085] Figure 1 A scanning transceiver array device 100 is schematically shown in accordance with an embodiment of the present invention. The device 100 includes a transceiver array 102, optics 104, and a scanner 106. The transceiver array 102 includes a pair of edge emitting PICs 108 and 110 mounted on a common carrier substrate 112. The PICs 108 and 110 transmit respective sets of beams toward a central triangular (knife-edge) mirror 114, which steers the beams away from the substrate 112. Some transceiver arrays and mirrors of this type are shown in the following figures, and other types of transceiver arrays and mirrors are described in the above-mentioned PCT publications and patent applications.

[0086] The scanner 106 includes a galvanometer 116 and a galvanometer mirror 118. The optics 104 collimates and directs the beams emitted by the PICs 108 and 110 and reflected by the mirror 114 toward the galvanometer mirror 118. The mirror rotates about the vertical (Y) axis at positive angles +θ and negative angles -θ, as indicated by the double arrow 120, thereby scanning each beam output from the PICs 108 and 110 along the horizontal (XZ) plane. In addition, the optics 104 can be displaced along the vertical axis, thereby moving each beam in small increments in the vertical direction. The transceiver array 102 can be "sparse", meaning that the pitch of the array is large compared to the desired sensing resolution. The optics 104 includes a projection lens 122 that maps the sparse array into angular space in the vertical direction; and fine vertical movement of the optics can be used to fill in gaps in the angular space, thereby enhancing the sensing resolution.

[0087] Figure 2 According to an embodiment of the present invention, Figure 1 1 is a block diagram of details of the transceiver array 102. Each of the two PICs 108 and 110 generates an array of light beams 202, which are emitted through the edge of the PIC towards the central turning mirror 114. Each PIC 108 and 110 also receives return radiation reflected from the turning mirror 114 back to the edge of the PIC, where the return radiation is shown as light beam 204.

[0088] In the illustrated example, each PIC 108 and 110 is fed by a pair of lasers, with lasers 206 and 208 feeding PIC 108 and lasers 210 and 212 feeding PIC 110. Light beams 214 and 216 emitted by lasers 206 and 208 and light beams 218 and 220 emitted by lasers 210 and 212 are modulated (e.g., by respective I / Q modulators 222, 224, 226, and 228, or by DC modulation). The light beams are amplified by respective arrays of semiconductor optical amplifiers (SOAs) 230 and 232, which may also include beam splitters to generate a plurality of output light beams 234, 236. The amplified and split sets of light beams 234 and 236 are distributed as a plurality of individual output light beams 202 by a hierarchical network of switches within the respective PICs 108 and 110. As follows Figure 5 As shown, the two PICs 108 and 110 may advantageously be shifted vertically relative to each other by half the beam spacing, effectively doubling the vertical resolution of the system.

[0089] Figure 33 is a block diagram schematically illustrating details of a hierarchical optical switching network 320 used as an optical distribution tree in a PIC 300 according to an embodiment of the present invention. The illustrated network includes two layers 302 and 304 of 1:2 switches 310 and 312 (each having one input and two outputs), labeled SW1 and SW2, interconnected by waveguides 316, all formed on a planar substrate such as a silicon-on-insulator (SOI) substrate. Alternatively, switches 310 and / or 312 may switch between a greater number of outputs.

[0090] The switches 310 and 312 distribute the output beams on the PIC 300 via waveguides 316 for transmission by an array 306 of transceiver units (TC) 314. Alternatively, a network hierarchy with a greater number of layers can be used to generate a greater number of output beams. The switches 310 and 312 are typically controlled by a controller 318, which includes suitable electronic logic and interface circuits, which can be implemented as a tightly coupled EIC (not shown in the figure). Therefore, the controller 318 selects different subsets of optical transceiver units to receive coherent radiation from the radiation source at different times. Each beam is input to a corresponding transceiver unit 314 including a transmission circuit and a detection circuit, which transmits an outgoing (Tx) beam toward a target and receives and detects a return (Rx) beam.

[0091] exist Figure 3 In the embodiment of the present invention, the optical transceiver units 314 and switches 312 are arranged in two groups in different corresponding areas of the PIC 300. The waveguide 316 interconnects the switches 310 and 312 so that one output of each switch 310 is coupled to a first group of transceiver units 314 and switches 312, and another output of each switch 310 is coupled to another group of transceiver units and switches of the second layer. Thus, each switch (SW1) 310 in the first layer 302 provides a plurality of optical transceiver units 314 and switches 312 to the upper portion of the transceiver array 306 (channels CH1 to CH2). N / 2 ) and the lower portion of the transceiver array 306 (channel CH N / 2+1 To CH N) are exchanged between the second waveguide 316 fed by the first branch and the second waveguide 316 fed by the switch. As shown, the waveguides from the SW1 switch 310 to the corresponding SW2 switch 312 can cross each other in the same layer or different layers of the PIC 300. This arrangement of the SW1 switch and the waveguides facilitates the ability to exchange the active area of ​​the transceiver array between the upper window and the lower window served by the first branch and the second branch connected by the switch, respectively. (In this specification, for convenience, the terms "upper", "lower", "vertical" and "horizontal" are used with respect to the orientation of the drawings and do not necessarily have any relationship to the orientation of the transceiver device itself.) This exchange between windows helps enable the controller 318 to select specific areas or windows of interest for measurement and processing.

[0092] In some embodiments, switches in different layers 302, 304 may have different characteristics, such as different switching speeds (or equivalently, different switching times). Slower switches are generally less expensive to implement in terms of chip footprint and power consumption, but fast switches are desirable to enable fast switching between different regions of interest or different scan lines. Various types of switches may be used for these purposes. As further described below, some embodiments described below use thermo-optical switches with drive circuits and waveforms that support fast switching rates.

[0093] In one embodiment, the SW1 switches 310 in the first layer 302 have fast switching times, while the SW2 switches 312 in the second layer 304 have slower switching times. For example, when the SW1 switches are set to pass output beams to the upper window, the slower SW2 switches can be set to select a specific subset of transceiver units in the lower window. Once the SW2 switches have stabilized, the SW1 switches can be quickly switched to pass beams to the selected transceiver units in the lower window.

[0094] In an alternative embodiment, the SW1 switch is slow, while the SW2 switch or another mid-layer switch is fast.

[0095] At the bottom of the array 306, groups 322 of transceiver units 314 and corresponding waveguides 316 are intentionally packed more densely than the rest of the array. For example, the spacing of the groups 322 may be half the spacing of the center portion of the array 306. This arrangement facilitates stitching together the sensing areas of two PICs 300 on opposite sides of the steering mirror 114, as further explained below. Alternatively or additionally, local variations in the density of transceiver units may be used for other purposes, such as different stitching schemes and producing variations in local sensing density.

[0096] Figure 4According to an embodiment of the present invention, Figure 3 Detailed schematic view of a transceiver cell (TC) 400 used in an array 306 of FIG. 1 . In this example, the transceiver cell is assumed to be a coherent sensing cell that directs coherent radiation through a corresponding edge coupler 406 and toward a target via a bifold mirror 114, receives optical radiation from the target via the bifold mirror and through a corresponding edge coupler, mixes a portion of the coherent radiation with the optical radiation received via the edge coupler, and outputs an electrical signal in response to the mixed radiation. The edge coupler 406 defines a corresponding optical aperture of the optical transceiver cell. Optical elements, such as lens 122 ( Figure 1 ), imaging the optical aperture onto the target, thereby defining the field of view of the optical transceiver unit. The scanner 106 scans the field of view of the optical transceiver unit over the target.

[0097] For the purpose of coherent sensing, the TC 400 includes a 2x2 coupler 412 and a balanced photodiode pair (BPD) 414. The outgoing beam for transmission passes through the waveguide 402 at the upper side of the unit 400 and exits through the polarization beam splitter rotator (PBSR) 404 and the edge coupler 406 to reach the steering mirror 114. A portion of the outgoing beam is split into the waveguide 408 within the transceiver unit to be used as a local oscillator (LO) beam. The incident beam reflected from the target is guided by the PBSR 404 into the receiving waveguide 410 and mixed with the LO beam in the 2x2 coupler 412. The BPD pair 414 senses the output of the 2x2 coupler and outputs an electrical signal 416 for EIC processing.

[0098] Various other kinds of sensing and transceiver units that may be used in embodiments are described in the above-mentioned PCT publications and patent applications.Alternatively, other types of transceiver units may be used.

[0099] Figure 5 5 is a schematic front view of a transceiver device 500 according to an embodiment of the present invention, the transceiver device 500 comprising four PICs 502, 504, 506 and 508 and a central turning mirror 510, all of which are mounted on a carrier substrate 524. The turning mirror 510 comprises reflective surfaces 520 and 522, which are arranged at diagonals relative to a normal to the carrier substrate, for example, at +45° and -45° relative to the normal. The PICs 502, 504, 506 and 508 are substantially similar to the PIC 300 ( Figure 3 ) and for simplicity, Figure 5Details of the PICs are omitted in FIG. 4. Four PICs 502, 504, 506 and 508 are positioned in pairs on opposite sides of a turning mirror 510, near reflective surfaces 520 and 522, wherein PICs 506 and 508 are rotated 180° relative to PICs 502 and 504.

[0100] The PICs on opposite sides of the turning mirror 510 are laterally shifted relative to each other on the carrier substrate 524 so that the edge couplers of the transceiver cells 512 of the PICs 506 and 508 are shifted relative to the PICs 502 and 504 by an offset equal to half the pitch of the transceiver cells 512. Thus, the output beams reflected from the turning mirror 510 are staggered in a closely spaced array along the vertical direction.

[0101] However, due to practical limitations in the manufacture of PICs 502, 504, 506, and 508, such as the need to leave space for electrical connection pads in the edge of the PIC die, there are gaps in the peripheral region 526 of the transceiver array. To avoid corresponding gaps in the array of output beams, the groupings 514 of transceiver cells in the peripheral region 528 at the other end of the array in each PIC are packed more densely together, as described above with respect to FIG. Figure 3 The PICs on opposite sides of the turning mirror are offset relative to each other so that the dense grouping 514 of transceiver units in one PIC is positioned opposite to the peripheral region 528 in the edge of the PIC on the other side of the turning mirror. For example, the grouping 514 in PIC 502 is positioned opposite to the lower edge of PIC 506. Thus, the transceiver devices generate an array of uniform, densely spaced output beams along the entire length of the turning mirror 510.

[0102] Although transceiver device 500 includes two PICs with corresponding transceiver arrays on each side of turning mirror 510, the principles of the present embodiments may alternatively be applied to devices including only a single PIC on each side of a turning mirror or including three or more PICs on each side.

[0103] Fig. 6A , Figure 6B , Figure 6C and Fig.6D 6 is a schematic front view of a continuous scanning pattern applied by a switch-type optical sensing system on a scene 600 according to an embodiment of the present invention. In this example, the sensing system includes two sensing devices 602 and 604 with staggered scanning lines. The sensing devices 602 and 604 can be similar to Figure 1. For simplicity of illustration, each sensing device 602, 604 includes a respective laser source 606 and an optical switching network 608 that distributes the laser radiation to transceiver units 610. When specific transceiver units are actuated through the switching network 608, these specific transceiver units generate corresponding scan lines 612 labeled AD and A'-D', respectively.

[0104] FIG. 6A to FIG. 6D 6 shows the use of switching and application of optical power in regions of interest (i.e., regions believed to contain valuable information) in scene 600, while reducing resource usage in regions of less interest. Figure 1 The scanner 106 in the array scans the corresponding fields of view of the optical transceiver units in the array over the target. A controller (such as Figure 3 The controller 318 in the optical distribution tree actuates switches in the optical distribution tree to select different subsets of units to transmit coherent radiation toward the target during different sweeps of the scanner over the target. The field of view of the optical transceiver unit is scanned over the target with a plurality of corresponding scan lines over the target, and the controller actuates the switches to selectively activate the scan lines in regions of interest over the target. As described above, different switching times of switches in different layers of the network can be used to activate different groups of scan lines in each sweep over the target.

[0105] In this example, the optical switching network 608 in devices 602 and 604 includes switches 609 that rapidly switch between transceiver units 610 to actuate different scan lines, such as switching between lines A and B, between lines C and D, between lines A' and B', and between lines C' and D'. Galvanometer mirrors, such as mirror 118 ( Figure 1 ), from left to right (as in Fig. 6A ) and then from right to left (in Figure 6B After each pair of galvanometer scans, the scan line is moved vertically, such as by piezoelectric actuation of an optical device or a sensing device (as described above), thereby moving the scan line vertically by a small increment, such as by moving a single pixel in the output depth map.

[0106] Therefore, in the frames labeled Step: 1, Step: 2, and Step: 3 ( Fig. 6A , Figure 6B and Figure 6C ), different switches 609 in the optical switching network 608 are activated for different parts of each scan. The switches 609 are switched in the middle of each scan line 612 so that the corresponding transceiver unit is turned on when the scan passes through the area of ​​interest, and off otherwise. At the end of the process (at Fig.6D ), each region of interest has been covered by a scan line.

[0107] In summary, the combination of mechanical and optical control in devices according to embodiments of the present invention provides several capabilities that can focus on a region of interest with high resolution and sensitivity:

[0108] The galvanometer mirror can be controlled to select the angular scan range and scan speed in the horizontal direction. The scan speed can be reduced in areas of interest to increase sensitivity and resolution in these areas. The optics can also be moved vertically to select areas of interest and control the vertical scan density.

[0109] A switching network in the transceiver PIC enables the outgoing beam to be selectively multiplexed on a scan line across the region of interest. Fast switching on the PIC can be used to change the scan line within each sweep of the galvanometer mirror.

[0110] The integration time and gain of the processing electronics that receive the signals from each transceiver unit can be increased to enhance sensitivity in areas of the scene where the signals are weak, or can be reduced to support higher scanning speeds and avoid saturation in other areas.

[0111] For example, using these capabilities, a galvanometer mirror can be scanned at a higher speed at the edge of a scene than at the center. For portions of the scene at short range, the transceiver unit can be operated with lower integration times and gains. Integration times and gains can be increased in long range portions of the scene. These increases can be implemented over the entire scan line, or only over one or more specific portions of a scan line as it passes through an area of ​​interest, such as a window containing an object of interest that is relatively far from the device. Further details and examples of these capabilities are presented in the above-mentioned PCT publication.

[0112] Fast thermal optical switching

[0113] Fig. 7A 700 is a block diagram schematically showing an optical switching tree on a PIC 700 according to an embodiment of the present invention. The PIC 700 uses a thermal optical switch 702 (labeled as TO SW). The fast variants of the switches 702 and 703 are described in detail below.

[0114] The switch 703 includes a Mach-Zehnder interferometer 704 including two branches 706 and 708 with resistive heaters 710 and 712 on the respective branches. A multi-mode interference (MMI) unit 714 is used as a beam splitter to split the coherent optical signal from an input waveguide 718 between the input ends of the two branches 706 and 708. Another MMI unit 716 is used as a mixer to mix the optical signals from the output ends of the branches 706 and 708 into one of the two output waveguides 720 or 722 according to the optical phase difference between the branches. Digital controllers 724 and 726 set the voltage applied to the respective resistive heaters 710 and 712, thereby switching the setting of the switch between the two output waveguides 720 and 722. The controller 726 is shown in a dashed box to indicate that in some embodiments, a single controller with a switched output can be used to drive both heaters 710 and 712. Controllers 724 and 726 may advantageously be implemented using digital / analog converters to generate waveforms for driving heaters 710 and 712, and are therefore labeled I-DAC 1 and I-DAC 2, respectively.

[0115] Switch 702 is similar to switch 703, but may use a simpler drive scheme in order to reduce the size and complexity of the circuitry on PIC 700. Switch 703 implements a push-pull scheme in which heaters 710 and 712 are alternately driven to provide faster switching than switch 702 and to switch the mixed optical signal between the outputs of switch 703. FIG. 8A to FIG. 8C and Fig.9A As described in detail in FIG. 9C , switch 703 may be further accelerated by using a pre-emphasis voltage pulse as part of the push-pull scheme each time the output is switched.

[0116] like Fig. 7A As shown, switch 703 is only used in the first layer of switches in PIC 700. Therefore, fast switch 703 is only used where needed, while switch 702 is used elsewhere in the switching tree of PIC 700. Fig. 7A The illustrated examples in the figures below show enhanced switch 703 in only a single location in the first layer, but in other embodiments, similar fast thermal optical switches may be deployed in other layers in addition to or instead of the first layer.

[0117] Figure 7BGraphs 728 and 730 are shown, which schematically illustrate the response of switch 703 to voltage applied to resistive heaters 710 and 712 in a basic implementation according to an embodiment of the present invention. Graphs 728 and 730 show the response of switch 703 to voltage applied to resistive heaters 710 and 712 over time. Fig. 7A 734 for the respective resistive heaters 710 and 712 in the switch 703, and the output optical powers 736 and 738 in the waveguides 720 and 722. (In this embodiment, the voltage 734 is zero.) A voltage is applied to one of the two heaters (applied to Figure 7B The heater 710 in the first example achieves a fast switch-on, but thereafter the switching speed is controlled by the cooling rate of the branch of the waveguide, which is inherently slow. The switching speed of the optical power between the two exit waveguides 720 and 722 is limited by the same token. In this example, the switching time is about 10 μs.

[0118] Fig. 8A , Figure 8B and Figure 8C Graphs are shown, which schematically show that in an implementation using a pre-emphasis voltage, the switch 703 ( Fig. 7A ) in response to the voltage applied to the resistive heaters 710 and 712 over time.

[0119] In these embodiments, when the switch 703 is turned on, the pre-emphasis voltage is applied for a short period of time. In this embodiment, the pre-emphasis voltage is added to one of the resistive heaters 710 or 712 for a short period of time, which reduces the turn-on time of the switch 703 to about 1 μs. For comparison, in the following FIG. 8A to FIG. 8C Three different durations of the pre-emphasis voltage pulse are shown in FIG. However, the off time is still limited by the cooling rate. In this embodiment, the pre-emphasis voltage is applied by I-DAC1. Alternatively, the pre-emphasis voltage can be applied to either heater 710 or 712 by a controller connected in parallel with I-DAC 1 or I-DAC 2, which will be described below. Fig.9A Shown in.

[0120] Fig. 8A Graphs 802, 804, and 806 are shown. In graph 802, curve 808 shows the input voltage to heater 710, and curve 810 shows the power in waveguide 720, both expressed in arbitrary units (AU). The pre-emphasis voltage includes a spike 812 at each rising edge of curve 808, with a peak amplitude of 3 AU and a width of 0.6 μs. In graph 804, curve 814 shows the input voltage to heater 712 (zero in this embodiment), and curve 816 shows the power in waveguide 722. Curve 816 and curve 816 are shown in FIG. Figure 7B A comparison of curve 738 in FIG. 806 shows that the turn-on time shown in curve 816 is faster than the turn-on time in curve 738. In graph 806, curves 818 and 820 show the optical phase shift under the respective resistive heaters 710 and 712.

[0121] Figure 8B Graphs 822, 824, and 826 are shown, and Figure 8C Graphs 828, 830, and 832 are shown, similar to Fig. 8A Graphs 802, 804 and 806 of FIG.

[0122] exist Figure 8B In graph 822 of FIG. 8A , curve 834 shows the input voltage to heater 710, and curve 836 shows the power in waveguide 720. The pre-emphasis voltage includes a spike 838 with a width of 0.8 μs. In graph 824, curve 840 shows the zero input voltage to heater 712, and curve 842 shows the power in waveguide 722. The turn-on time of curve 842 is even faster than the turn-on time of curve 816. In graph 826, curves 844 and 846 show the optical phase shift at the respective resistive heaters 710 and 712.

[0123] exist Figure 8C In graph 828 of FIG. 848 , curve 848 shows the input voltage to heater 710, and curve 850 shows the power in waveguide 720. The pre-emphasis voltage includes a spike 852 with a width of 1.0 μs. In graph 830 , curve 854 shows the zero input voltage to heater 712, and curve 856 shows the power in waveguide 722. The on-time of curve 856 is similar to the on-time of curve 842, but shows some distortion immediately after the power reaches its maximum value. In graph 832 , curves 858 and 860 show the phase shift at the respective resistive heaters 710 and 712.

[0124] Fig.9A is a block diagram schematically illustrating a thermo-optical switching tree on a PIC 900 according to an embodiment of the present invention. In this embodiment, a pre-emphasis voltage is applied to two resistive heaters 710 and 712 on two branches 706 and 708 of a Mach-Zehnder interferometer 704. In the illustrated example, this push-pull pre-emphasis scheme is applied only to the first layer of the switching tree to achieve fast switching between the upper and lower subtrees in the network. Alternatively or additionally, switches in other layers can be driven in this manner to achieve fast switching.

[0125] The PIC 900 includes features similar to the PIC 700 ( Fig. 7A) in which separate pre-emphasis voltage controllers 904 and 906 are added to the first layer switch 903, which will be described in detail below. Switch 903 is similar to switch 703 ( Fig. 7A ). Items in switch 903 that are similar or identical to those in switch 703 are indicated by the same labels. For conceptual clarity, pre-emphasis voltage controllers 904 and 906, labeled PreEmp 1 and PreEmp 2, are shown as separate functional blocks. However, in practice, the pre-emphasis function can be integrated into digital controllers 724 and 726, representing a portion of the voltage waveform applied to resistive heaters 710 and 712. Monitoring photodiodes 908 and 910, labeled PMON, can be used to verify the current state of switch 903 and adjust the voltage if necessary to achieve more accurate switching.

[0126] Fig. 9B Three graphs 912 , 914 , and 916 are shown that schematically illustrate the response of switch 903 to voltages applied by digital controllers 724 and 726 , according to an embodiment of the present invention.

[0127] In the graph 912, curve 918 shows the input voltage of the heater 710, where the input voltage is the sum of the basic switching voltage and the pre-emphasis voltage. The pre-emphasis voltage includes peaks 920 located at the rising edge of the input voltage waveform. In this example, the width of each peak 920 is 0.8 μs. Curve 920 shows the output power from the switch 903 into the waveguide 720.

[0128] In graph 914, curve 922 shows that only pre-emphasis voltage peaks 924 are applied to heater 712. Peaks 924 are located at the falling edge of the input voltage waveform (curve 918) of heater 710. The width of each peak 924 is 0.75 μs.

[0129] In graph 916 , curves 926 and 928 illustrate the respective optical phase shifts applied to branches 706 and 708 by heaters 710 and 712 .

[0130] When the heaters 710 and 712 are driven using the respective voltages shown in the graphs 912 and 914, the temperature of the two branches of the switch increases continuously in multiple cycles of alternating steps. Thus, at each step, the optical output of the switch switches rapidly between the exit waveguides 720 and 722. In other words, in the first step, the upper branch 706 is rapidly heated by an increment ΔT (for example) using a pre-emphasis voltage, followed by the rapid heating of the lower branch 708 by ΔT in the next step, and then the upper branch 706 is rapidly heated to 2ΔT, and so on. Thus, the switching speed is controlled by the rapid heating time and is not limited by the slower cooling time of the heaters.

[0131] After a specified number of fast switching cycles, the switch is allowed to cool, after which fast switching operations can be resumed. Fig.9A As shown, a monitoring photodiode (PMON) can be used to verify the current state of the switch.

[0132] Beam Shifters and Circulators

[0133] Figure 4 The transceiver unit 400 shown in FIG. 4 is a monostatic cell because the transmit axis and the receive axis are collinear at the edge of the unit. (The PBSR 404 within the unit 400 separates the receive beam from the transmit beam.)

[0134] In a bistatic unit, on the other hand, the receive axis is laterally displaced relative to the transmit axis at the edge of the unit. However, the reflection of a given transmit beam from a target scene is collinear with the transmit beam (assuming the speed of the scanning mirror is slow enough so that the scanning deviation is not significant). Therefore, it is necessary to displace the axis of the receive beam relative to the axis of the transmit beam in order to match the displacement between the transmit and receive axes of the transceiver unit. The embodiments shown in the following figures and described below provide optical components that can be used for this purpose.

[0135] Fig.10 1 is a schematic top view of a micro-optical beam shifter 1000 according to an embodiment of the present invention, which is used for this purpose together with an array of transceiver units 1002 in a PIC 1004. The beam shifter 1000 includes a layer of birefringent material, such as a birefringent crystal 1006, sandwiched between a pair of microlens arrays 1008 and 1010. The microlens arrays have a pitch P equal to the spacing between adjacent transmit axes 1012 and receive axes 1014 of each transceiver unit 1002. This pitch P is half the pitch (2P) of the transceiver units themselves. Alternatively, the microlens array 1010 can have a pitch of 2P, matching the pitch of the combined transmit and receive axes at the outside of the beam shifter 1000.

[0136] In this embodiment, axes 1012 and 1014 are defined by the locations of corresponding waveguides and edge couplers at the edge of PIC 1004 adjacent to beam shifter 1000, and microlens array 1008 is aligned with these axes. The thickness and birefringence of crystal 1006 are selected so that light of one polarization entering the crystal through one of the microlenses in array 1008 or 1010 is deflected and thus laterally displaced a distance equal to the pitch of the microlens array, while light of the orthogonal polarization passes through the layer without being deflected.

[0137] Therefore, in this example, each transceiver unit 1002 transmits a TE polarized transmission beam 1016, which is denoted as TX TE , is collimated by the corresponding microlens 1018 and passes through the birefringent crystal 1006 toward the target. TM 1010) is laterally displaced by a birefringent crystal 1006 by an amount equal to the pitch P of the microlens array 1008 and is thus focused by the next microlens 1022 in the array 1008 along the appropriate receive axis 1014. The axes of the TX beam and the RX beam are combined at the microlens array 1010. In this embodiment, the TE component of the reflected beam 1020 is discarded.

[0138] The notation TX for the transmitted light beam and RX for the reflected light beam is also followed in the description below, with the subscripts TE and TM for the respective polarization components of the electric field.

[0139] although Fig.10 1 and subsequent figures show a one-dimensional (linear) array of transceiver units and microlenses, but the principles of these embodiments can be similarly implemented in a two-dimensional array.

[0140] Fig.11 1 is a schematic top view of a micro-optical beam displacer 1100 according to another embodiment of the present invention, wherein both the TM component and the TE component of a reflected light beam 1102 are coupled into a transceiver cell array 1104. In this embodiment, the PIC 1106 includes separate input waveguides 1108 and 1110 for each respective TE component and TM component of the reflected light beam 1102. In this case, the pitch of the transceiver cells is three times the pitch of the waveguides in the PIC 1106.

[0141] The beam shifter 1100 includes two birefringent layers, such as birefringent crystals 1112 and 1114, on opposite sides of a directional polarization rotator 1116 that rotates the polarization of light passing through it in one direction by 90° without rotating the polarization of light passing through it in the opposite direction. In this embodiment, the polarization rotator 1116 includes a Faraday rotator 1118 (e.g., a latchable garnet rotator) and a half-wave plate 1120. Similar to the beam shifter 1000 ( Fig.10 ), the assembly of birefringent crystals 1112 and 1114 and directional polarization rotator 1116 is sandwiched between a pair of microlens arrays 1115 and 1117. (Although both microlens arrays 1115 and 1117 are Fig.11 1106, but the pitch of the microlens array 1117 may alternatively be three times the waveguide pitch.) The directional polarization rotator 1116 converts the TE polarized transmitted beam 1122 to TM so that it is shifted onto the axis of the TE polarization component of the reflected beam 1102. The TM polarization component of the reflected beam 1102 remains TM polarized by the directional polarization rotator 1116 and is therefore shifted into the waveguide 1110 by both the birefringent crystals 1114 and 1116.

[0142] Fig.12 1 is a schematic top view of a micro-optical beam shifter 1200 according to an alternative embodiment of the present invention, in which both the TM component and the TE component of the reflected beam 1202 are coupled into the transceiver unit 1204. In this embodiment, the same input waveguide 1206 receives both the TE component and the TM component of each reflected beam 1202. Fig.11 ), the beam shifter 1200 here also includes two birefringent crystals 1208 and 1210 on opposite sides of a directional polarization rotator 1212, the directional polarization rotator 1212 includes a Faraday rotator 1214 and a half-wave plate 1216, and the directional polarization rotator 1212 and the two birefringent crystals 1208 and 1210 are sandwiched between a pair of microlens arrays 1218 and 1220. However, in this case, the axis of the second crystal 1210 is flipped 180° relative to the first crystal 1208, so that the two crystals deflect the TM component in opposite directions. Therefore, the TE component and the TM component are output from the beam shifter 1200 along the same axis 1222.

[0143] Fig.131 is a schematic top view of a micro-optical beam shifter 1300 according to another embodiment of the present invention, wherein both the TM component and the TE component of the reflected beam 1302 are coupled to a transceiver unit 1304. In this embodiment, the beam shifter 1300 includes a single birefringent crystal 1306 and a directional polarization rotator 1308, which is similar to the polarization rotator 1212 ( Fig.12 ), including a Faraday rotator 1310 and a half-wave plate 1312. The birefringent crystal 1306 and the directional polarization rotator 1308 are sandwiched between a pair of microlens arrays 1314 and 1316. Therefore, the beam shifter 1300 guides the TM component of the reflected beam 1302 into the transmission waveguide 1318. The polarization beam splitter rotator (PBSR, not shown in the figure) on the PIC 1320 separates the TM component 1322 of the reflected beam 1302 from the TE polarized transmission beam 1324.

[0144] Fig.14 and Fig.15 14 and 14, respectively, are schematic side and top views of a transceiver array device 1400 with micro-optical beam shifters 1408 and 1410 according to an embodiment of the present invention. Figure 2 In the embodiment of the present invention, the device shown includes a pair of PICs 1402 and 1404 having a central turning mirror 1406. Each PIC 1402, 1404 has a central turning mirror 1406. Fig.11 Corresponding micro-optical beam shifters 1408, 1410 of the type described. Alternatively, in this embodiment, Fig.12 Micro-optical beam shifters of the type shown, as well as other types of beam shifters according to the principles described herein. The beam shifters shown in the following figures may similarly be replaced by variations of these types.

[0145] Fig.16 and Fig.17 1 and 2 are schematic side and top views of a transceiver array device 1600 having a micro-optical beam shifter unit 1602 according to another embodiment of the present invention. Fig.14 and Fig.15 As in the embodiment of FIG. 1 , the device 1600 also includes a pair of PICs 1604 and 1606 having a central turning mirror 1608; and each PIC 1604, 1606 has a respective one of the above reference Fig.111604 and 1606 and the beam shifters 1610 and 1612. However, in this embodiment, the micro-optical beam shifters 1610 and 1612 are mounted above the turning mirror 1608, rather than being mounted between the PICs 1604 and 1606 and the turning mirror as in the previous embodiment. In other words, the turning mirror 1608 is disposed between the PICs 1604, 1606 and the beam shifters 1610 and 1612.

[0146] Fig.18 1 is a schematic side view of a transceiver array device 1800 with a micro-optical beam shifter 1802 according to an alternative embodiment of the present invention. In this embodiment, the PIC 1804 includes vertical couplers 1806a, 1808a, 1810a, 1812a, 1814a, and 1816a on the surface of the PIC (as will be described below). Fig.19 1804) such as gratings or micromirrors. The vertical couplers deflect the transmitted beam upward, away from the PIC, and deflect the reflected beam back into the waveguide in the plane of the PIC. The vertical couplers 1806a, 1808a, 1810a, 1812a, 1814a, and 1816a are aligned with corresponding microlenses 1806b, 1808b, 1810b, 1812b, 1814b, and 1816b. The micro-optical beam shifter 1802 mounted above the PIC 1804 is the same as the one shown in the figure above. Fig.11 The type of description.

[0147] exist Fig.18 Two transceiver units 1818 and 1820 are shown in side view, with further details of the units described below. Fig.19 Shown in.

[0148] Fig.19 18 is a schematic top view of a PIC 1804 in a transceiver array device 1800 according to an embodiment of the present invention. For simplicity, only units 1818 and 1820 and their components are labeled. Each transceiver unit 1818, 1820, ... has three vertical couplers: one vertical coupler for transmitting a light beam (e.g., couplers 1808a and 1814a), and two other vertical couplers for receiving the TE component and the TM component of the light beam, respectively (couplers 1806b and 1810b in unit 1818 and couplers 1812b and 1816b in unit 1820). The vertical couplers are formed at a two-dimensional matrix of positions on the surface of the PIC 1804. The microlenses in arrays 1115 and 1117 form a two-dimensional array that is aligned with the two-dimensional matrix of vertical couplers.

[0149] Fig. 202 is a schematic side view of a transceiver array device 2000 according to yet another embodiment of the present invention, the transceiver array device 2000 having a micro-optical beam shifter 2002 mounted directly on a PIC 2004. In this embodiment, the micro-optical beam shifter 2002 is Fig.11 , but without the lower microlens array. As in the previous embodiments, the micro-optical beam displacer 2002 includes an upper microlens array 1117 and one or more layers of birefringent material (in this case two layers including birefringent crystals 1112 and 1114). A directional polarization rotator 1116 including a Faraday rotator 1118 and a half-wave plate 1120 is included between the two birefringent layers.

[0150] In place of a lower microlens array, PIC 2004 includes vertical couplers 2006, 2008, 2010, 2012, 2014, and 2016, which have a large mode field diameter (MFD) and a small numerical aperture (NA), and have the same spacing as the microlenses in array 1117. Vertical couplers 2006, 2008, 2010, 2012, 2014, and 2016 deflect the transmit beam into the micro-optical beam shifter 2002 and collimate the beam sufficiently to eliminate the need for the lower microlens, and focus and deflect the receive beam 2018 into the receive waveguide of PIC 2004.

[0151] Fig.21 2 is a schematic side view of a transceiver array device 2100 with a micro-optical beam shifter 2102 according to another alternative embodiment of the present invention. Fig. 20 , except that the micro-optical beam displacer 2102 does not include a lower birefringent layer. In this embodiment, vertical couplers 2104, 2106, 2108, and 2110 with large MFD also serve as collimating and collecting optics.

[0152] Fig. 22 2 is a schematic side view of a transceiver array device 2200 with a micro-optical beam shifter 2202 according to another embodiment of the present invention. In this embodiment, in order to reduce the thickness of the optical stack, the microlens 2204 is formed directly on the beam shifter 2202 instead of being formed on a separate substrate. In other respects, this embodiment is similar to Fig.21 Embodiment of the invention.

[0153] exist Figures 10 to 22In the illustrated embodiment, there may be issues with back reflections of the transmit beam from the interface between the layers of the beam shifter into the receive waveguide. Such back reflections may be detrimental to device performance. To reduce back reflections, the interface may have an anti-reflection coating. Additionally or alternatively, the interface may be angled relative to the optical axes of the transmit and receive beams so that the back reflections are directed out of the plane of the PIC. A small tilt angle of the order of one or a few degrees may be sufficient for this purpose.

[0154] Fig.23A , Fig. 23B and Fig.23C A transceiver array device 2300 according to an embodiment of the present invention is schematically shown, and the transceiver array device 2300 includes a beam shifter 2320 based on a birefringent prism 2302. Fig.23A and Fig. 23B shows the geometric and optical characteristics of the prism itself, and Fig.23C is a side view of device 2300.

[0155] like Fig.23A As shown, this birefringent prism 2303 (similar to prism 2302, but with a larger prism angle α) will deflect the two polarization components of the incident light ray 2304, but the deflection angles β1 and β2 are different. Fig. 23B The total deflection of an incident light ray by a prism 2306 of refractive index n is shown and is determined by the following formula:

[0156]

[0157] By replacing the two polarizations (n o and n e ), the deflection angle difference δ between the two polarizations can be calculated.

[0158] As in the previous embodiments, the PIC 2312 includes at least one row of optical couplers that are spaced apart at a predefined pitch and couple respective beams of light into and out of the PIC. Fig.23CIt is shown how the differential deflection properties of a birefringent prism 2302 can be used to align the transmit axis 2308 and receive axis 2310 of one of the transceiver units on a PIC 2312, respectively. The prism 2302 is aligned near a row of optical couplers. The birefringence and prism angles are selected so that light of one polarization (e.g., TE light emitted along the transmit axis 2308) passing through the prism from one of the optical couplers is deflected by a specific angle, while light of an orthogonal polarization (e.g., TM light returning to the receive axis 2310) is deflected by a different angle when passing through the prism. The deflection angles are selected using the above criteria so that beams of TE polarization and TM polarization coupled into and out of adjacent optical couplers in the PIC 2312 are combined by the prism 2302.

[0159] PIC-based polarization beam splitter rotator

[0160] Fig.24A 2 is a block diagram schematically illustrating a polarization beam splitter rotator (PBSR) 2400 implemented on a PIC 2402 according to an embodiment of the present invention. Fig.13 In the illustrated embodiment, the PBSR 2400 transmits a TE beam from the PIC 2402 and receives a reflected TM beam from the target, thereby separating the incoming receive beam from the outgoing transmit beam to and from each transceiver unit. Alternatively, the PBSR 2400 can be configured to transmit a TM beam and receive a reflected TE beam. A polarization beam splitter (PS) 2404 separates the TE component from the TM component, and a polarization rotator (PR) 2406 converts the received TM beam to TE, or alternatively, converts the transmitted TE beam to TM. The PBSR 2400 can be efficiently and compactly manufactured on a PIC, and is therefore particularly suitable for use in PIC-based transceiver arrays.

[0161] Fig. 24B 24 is a schematic top view of a PS2404 according to an embodiment of the present invention. PS2404 includes a pair of waveguides 2420 and 2422, such as SiN waveguides on a silicon or SiO2 substrate, which are formed close to each other on a substrate 2424. A first end 2426 of the waveguide 2420 is coupled to receive an input beam or emit an output beam, which includes both a TE polarization component and a TM polarization component. The TE polarization component propagates through the waveguide 2420 and is output to or input from a second end 2428. The TM polarization component propagates in the waveguide 2422 and is received in or emitted from an end 2430 that is parallel to the end 2428 of the waveguide 2420.

[0162] The waveguides 2420 and 2422 are tapered to facilitate adiabatic coupling of TM waves between the waveguides, while the TE waves remain confined within the waveguide 2420. To this end, the waveguide 2420 has a tapered section whose width decreases in a direction from the first end 2426 toward the second end 2428 (at Fig. 24B The width of the corresponding segment in waveguide 2422 increases from width w3 to width w4 in the direction from the first end toward the second end. The opposite tapers allow the TM polarization components to couple between the tapered segments. For efficient coupling, the dimensions are ideally selected such that w5>w4, while w2 may or may not be equal to w4. This design is advantageous in supporting broadband coupling and is relatively insensitive to manufacturing tolerances.

[0163] Fig.24C is a schematic top view of a PBSR 2400 according to another embodiment of the present invention. PBSR 2400 may be fabricated in whole or in part on PIC 2402, including waveguides 2408, 2410, and 2412 in a non-silicon layer such as SiN to support a high power transmit beam.

[0164] The PS 2404 in this embodiment includes a TE waveguide 2408 and a TM waveguide 2412, with an intermediate transition waveguide 2410 being wider than both waveguides 2408 and 2412. The TE component remains well contained in the waveguide 2408. However, coupling through higher order modes of the transition waveguide 2410 transfers most of the energy in the TM component to the waveguide 2412.

[0165] PR 2406 is implemented in a silicon layer located below the SiN layer. A double taper 2434 couples TM waves between a waveguide 2412 in the SiN layer and a waveguide 2432 in the underlying silicon layer. A pair of wings 2434 having a thickness less than that of the waveguide 2432 facilitates polarization rotation of the guided waves between TM and TE.

[0166] Multi-channel signal processing

[0167] Fig.25A 25 is a block diagram schematically illustrating a signal processing scheme for use with a transceiver array 2500 according to an embodiment of the present invention. In this embodiment, a single signal processing chain 2501 processes output signals from multiple transceiver channels simultaneously. This scheme reduces the cost, size, and power consumption of the electronic IC used to perform the processing, although it may be at the expense of reduced signal-to-noise ratio (SNR) and overlap between channels. It is particularly useful (although not exclusive) for identifying regions of interest in a scene in a coarse wide-area scan. Once a region of interest is identified, it can be scanned at a finer resolution and higher SNR.

[0168] exist Fig.25A In the embodiment of FIG. 2 , it is assumed that the N transceiver units 2502 in the array 2500 are configured for coherent sensing of reflected light, for example, Figure 4 As shown. A frequency chirp is applied to the transmitted light beam, and the balanced photodiode 412 in each unit outputs a beat signal that indicates the distance of the target from which the light is reflected and may indicate the speed of the target. These signals are amplified by corresponding transimpedance amplifiers (TIA). The amplified signals are mixed with carriers of different modulation frequencies by corresponding analog mixers 2504, so that unit 2502 outputs corresponding modulated signals of different corresponding modulation frequencies. Analog adder 2505 sums the modulated signals (still in the analog domain). In the illustrated example, the modulation frequency is assumed to be an integer multiple of 1 MHz.

[0169] The summed analog signal is digitized by an analog-to-digital converter (ADC) 2506, transformed to the frequency domain by a frequency analyzer 2508 (e.g., by a fast Fourier transform (FFT)), and then digitally processed in a digital signal processor (DSP) 2510 to extract the modulated beat frequency.

[0170] Fig.25B 25 is a schematic diagram of signal outputs from some channels of array 2500 according to an embodiment of the present invention. Each channel (corresponding to one of transceiver units 2502) outputs a pair of frequency peaks separated by twice the modulation frequency applied to the channel. Thus, in the illustrated example, the two peaks 2512 and 2514 from channel 7 are separated by 14 MHz, the two peaks 2516 and 2518 from channel 4 are separated by 8 MHz, and so on. DSP 2510 is thus able to demultiplex the beat signal frequencies and identify the channels to which these frequencies belong based on the peak spacing.

[0171] Fig.26 2600 is a block diagram schematically illustrating a signal processing scheme for use with a transceiver array 2600 according to an alternative embodiment of the present invention. In this case, the output from each channel 2602 is mixed with carriers at two different modulation frequencies in two mixers 2604 and 2606, and the modulated signals are all added together. The summing and processing of the signals is achieved as in the previous embodiments. The summed signal will contain pairs of frequency peaks, where each pair of frequency peaks is separated by the difference between the modulation frequencies applied to the corresponding channels.

[0172] Fig. 27 2 is a block diagram schematically illustrating a signal processing scheme used with a transceiver array 2700 according to yet another embodiment of the present invention. Fig.26As in the embodiment of FIG. 2 , the output from each channel 2702 is mixed with modulated waves at two different frequencies in two mixers 2704 and 2706. However, in this case, the modulated signals are summed in two separate groups, with the signal from mixer 2704 for each channel in one group and the signal from mixer 2706 in another group. After being digitized by the corresponding ADCs 2708 and 2710 and transformed to the frequency domain by frequency analyzers 2712 and 2714, the DSP 2716 compares the distribution of peaks in the two groups to identify the beat frequency output by each channel.

[0173] Wafer Level Vertical Coupler

[0174] Fig.28A and Fig.28B An array of edge-emitting PICs 2800 is schematically shown, with turning mirrors 2802 aligned to couple a beam from each PIC into a vertical direction, according to an embodiment of the invention. Fig.28A is a diagram, and Fig.28B is a cross-sectional detail view. This embodiment solves the problem of aligning the turning mirror 2802 with the edge coupler 2804. In this embodiment, an array of PICs 2800 is formed on a substrate (such as a silicon wafer 2808). Each PIC includes one or more optical edge couplers 2808 adjacent to the upper surface of the substrate. An array 2806 of turning mirrors 2802 is formed on a reflector substrate (e.g., another silicon wafer 2820). The reflector substrate is mounted on the upper surface of the PIC substrate so that each turning mirror 2802 in the array 2806 is aligned with an optical edge coupler 2804 on a corresponding PIC 2800. Therefore, light is coupled into and out of the optical edge coupler via the turning mirrors.

[0175] This embodiment provides a mirror array 2806 that is mounted on a finished PIC wafer 2808 and captures light emitted from one or more edge couplers 2804 in each PIC 2800. The mirror array 2806 and PIC 2800 are patterned and etched by wafer-level processing using semiconductor processing techniques. The mirror array structure includes a "leg" 2810 at the front edge of each mirror 2802 that protrudes into a corresponding cavity 2812 etched into the upper surface 2814 of the corresponding PIC 2800, as shown in FIG. Fig.28BAs shown. Cavity 2812 can be etched using standard PIC processing, such as wet etching or deep reactive ion etching (DRIE) processes. Adding legs 2810 in cavity 2812 enables mirror 2802 to capture and reflect substantially all of the light emitted from edge coupler 2804 of PIC 2800, and provides a large collection angle for directing the reflected light into the edge of the PIC.

[0176] The reflector 2802 is placed together on the PIC wafer 2808 in a simple, precise alignment step. The method uses the upper surface 2814 of the PIC wafer 2808 as a height reference. Because both the PIC 2800 and the reflector 2802 on the wafer 2808 are photolithographically defined, the reflector can be aligned with the PIC with high precision. The reflector 2802 can be produced from a silicon wafer, for example using a wet etching process on a wafer formed with an offset of 9.7° relative to the <0,0,0> silicon crystal plane. Thus, the etching process will produce a reflective surface that is precisely tilted 45° relative to the lower surface of the wafer. (The other crystal plane will be 54.7°+9.7°=64.4°.)

[0177] It should be understood that the above embodiments are cited by way of example, and the present invention is not limited to what has been specifically shown and described above. More specifically, the scope of the present invention includes combinations and sub-combinations of the various features described above, as well as variations and modifications of these features that would occur to a person skilled in the art after reading the foregoing description and that are not disclosed in the prior art.

Claims

1. A photoelectric device comprising: - a carrier substrate; - a bifolding mirror mounted on the carrier substrate and comprising a first reflecting surface and a second reflecting surface arranged diagonally with respect to a normal to the carrier substrate; - a plurality of identical photonic integrated circuits (PICs), each PIC comprising: -- Planar substrate; an array of optical transceiver units arranged on the planar substrate and comprising respective edge couplers arranged along an edge of the planar substrate; and an optical distribution tree coupled to transmit coherent radiation from a radiation source to the optical transceiver unit, -Wherein, the plurality of identical PICs include a first PIC and a second PIC, the first PIC being arranged on the carrier substrate such that an edge of the first PIC is close to the first reflective surface, and the second PIC being rotated 180° relative to the first PIC and arranged on the carrier substrate such that an edge of the second PIC is close to the second reflective surface.

2. The device according to claim 1, wherein: The bi-fold mirror has a triangular profile, wherein the first and second reflecting surfaces are oriented at +45° and -45°, respectively, relative to the normal.

3. The device according to claim 1, wherein: The edge couplers in each PIC are arranged along the edge with a predefined spacing between the edge couplers, and wherein the first PIC and the second PIC are arranged on the carrier substrate so that the edge couplers on the first PIC are shifted by half of the predefined spacing relative to the edge couplers on the second PIC.

4. The device according to claim 1, wherein: Each PIC includes: a central region in which edge couplers are arranged along an edge with a first spacing between the edge couplers; a first peripheral region at a first side of the central region, in which no edge couplers are disposed along an edge; and In a second peripheral region at a second side of the central region opposite to the first side, in the second peripheral region, edge couplers are arranged at a second pitch, the second pitch being finer than the first pitch.

5. The device according to claim 4, wherein: The second spacing is half of the first spacing.

6. The device according to claim 1, wherein: The plurality of identical PICs include: a third PIC disposed side by side with the first PIC on the carrier substrate such that an edge of the third PIC is close to the first reflective surface; and A fourth PIC is rotated 180° relative to the first PIC and disposed on the carrier substrate side by side with the second PIC such that an edge of the fourth PIC is close to the second reflective surface.

7. The device according to any one of claims 1 to 6, wherein: The optical distribution tree comprises a network of waveguides and switches disposed on the planar substrate.

8. The device according to any one of claims 1 to 6, wherein: The optical transceiver unit is configured to: direct coherent radiation through the corresponding edge coupler, via the double-folded reflector, toward a target; receive optical radiation from the target through the corresponding edge coupler, via the double-folded reflector; mixing a portion of the coherent radiation with the optical radiation received through the edge coupler; And outputting an electrical signal in response to the mixed radiation.

9. The device according to claim 8, wherein: The edge coupler defines a respective optical aperture of the optical transceiver unit, and wherein the apparatus comprises one or more optical elements configured to image the optical aperture onto the target, thereby defining a respective field of view of the optical transceiver unit.

10. Apparatus according to claim 9, and comprising a scanner configured to scan a field of view of the optical transceiver unit over the target.

11. An optoelectronic device comprising: Planar substrate; an array of optical transceiver units disposed on the substrate, each transceiver unit comprising an optical transducer configured to couple optical radiation between the transceiver unit and a target external to the substrate; an optical distribution tree comprising a hierarchical network of switches interconnected by waveguides, disposed on the substrate, and coupled to transmit coherent radiation from a radiation source to the optical transceiver unit, the hierarchical network comprising at least a first layer of first switches having a first switching time and a second layer of second switches having a second switching time different from the first switching time; as well as A controller is configured to actuate the switch so as to select different subsets of the optical transceiver units to receive the coherent radiation from the radiation source at different times.

12. The device according to claim 11, wherein Each first switch in the first layer has at least two first outputs, the at least two first outputs are respectively coupled to at least two second switches of the second switches in the second layer, and each second switch in the second layer has at least two second outputs coupled to the transceiver unit, and wherein the first switching time is shorter than the second switching time.

13. The device according to claim 12, wherein: The optical transceiver units and the second switches are arranged in different respective first and second regions of the substrate in first and second groups, and wherein the waveguide interconnects the first switches and the second switches such that one of the first outputs of each first switch is coupled to the first group of the transceiver units and the second switch, and the other of the first outputs of each first switch is coupled to the second group of the transceiver units and the second switch.

14. Apparatus according to any one of claims 11 to 13, and comprising a scanner configured to scan a respective field of view of the optical transceiver unit over the target, wherein The controller is configured to actuate the switch to select different subsets of the optical transceiver units to transmit the coherent radiation toward the target during different sweeps of the scanner over the target.

15. The device according to claim 14, wherein: Scanning respective fields of view of the optical transceiver units over the target defines a plurality of respective scan lines over the target, wherein the first switching time is shorter than the second switching time, and wherein the controller is configured to actuate the first switch so as to activate a different grouping of the scan lines in each sweep over the target.

16. The apparatus according to claim 14, wherein: Scanning respective fields of view of the optical transceiver units over the target defines a plurality of respective scan lines over the target, and wherein the controller is configured to actuate the switch to selectively activate the scan lines in regions of interest over the target.

17. The apparatus according to any one of claims 11 to 13, wherein: The controller is configured to process signals output by the transceiver unit to generate a three-dimensional (3D) map of the target.

18. The apparatus according to any one of claims 11 to 13, wherein: The switch comprises a thermo-optical switch.

19. A thermo-optical switch, comprising: an interferometer comprising a first waveguide and a second waveguide having respective input and output ends; a first heater and a second heater, the first heater and the second heater being configured to heat the first waveguide and the second waveguide, respectively; an optical splitter coupled to receive a coherent optical signal and input the optical signal to input ends of both the first waveguide and the second waveguide; a mixer coupled to receive and mix the optical signal from an output end of the first waveguide and an output end of the second waveguide, and direct the mixed optical signal to a first output or a second output of the switch according to a phase shift between the first waveguide and the second waveguide; as well as A controller is coupled to control the first heater and the second heater to exchange the mixed optical signal between the first output and the second output.

20. The switch according to claim 19, wherein: The controller is configured to alternately drive the first heater and the second heater to switch the mixed light signal between the first output and the second output.

21. The switch according to claim 20, wherein: The controller is configured to drive the first heater and the second heater with a voltage waveform including a pre-emphasis pulse every time the output is switched.

22. The switch according to claim 20, wherein: The controller is configured to drive the first and second heaters with respective voltages that cause respective temperatures of the first and second waveguides to increase continuously over a plurality of cycles of switching between the first and second outputs.

23. The switch according to any one of claims 19 to 22, wherein: The controller includes a first digital / analog converter (DAC) and a second digital / analog converter, and the first and second digital / analog converters are configured to apply corresponding voltages to the first and second heaters in response to corresponding digital inputs.

24. A beam shifter, comprising: a first microlens array and a second microlens array, the first microlens array and the second microlens array comprising microlenses arranged in respective first and second planes and having a common predefined pitch; as well as One or more layers of birefringent material, the one or more layers of birefringent material being contained between the first microlens array and the second microlens array, the thickness and birefringence of each layer being selected so that light of a first polarization entering the layer through one of the microlenses is laterally displaced a distance equal to the pitch of the microlens array, while light of a second polarization orthogonal to the first polarization passes through the layer without being displaced.

25. A beam shifter according to claim 24, and including a directional polarization rotator, which is between the first microlens array and the second microlens array, and together with the birefringent material, the directional polarization rotator is configured to rotate the polarization of light passing through the directional polarization rotator in a given direction by 90° without rotating the polarization of light passing through the directional polarization rotator in an opposite direction.

26. The beam shifter of claim 25, wherein: The polarization rotator includes a Faraday rotator and a half-wave plate.

27. The beam shifter of claim 25, wherein: The one or more layers of birefringent material include a first layer adjacent to the first microlens array and a second layer adjacent to the second microlens array, Therein, the directional polarization rotator is contained between the first layer and the second layer of birefringent material.

28. The beam shifter of claim 27, wherein: The first and second layers of the birefringent material are oriented such that both the first and second layers laterally displace light of the first polarization in the same direction.

29. The beam shifter of claim 27, wherein: The first and second layers of the birefringent material are oriented such that the first and second layers laterally displace light of the first polarization in opposite directions.

30. An optical device comprising: A beam displacer according to any one of claims 24 to 29; as well as a photonic integrated circuit (PIC) comprising at least one row of optical couplers spaced apart at a predefined pitch and aligned with the first array of microlenses so as to couple respective beams of light between the optical couplers and respective microlenses in the first array, Thus, the light beams of the first polarization and the light beams of the second polarization coupled into and out from the adjacent optical couplers in the at least one row are combined at the second microlens array.

31. The device according to claim 30, wherein The optical coupler includes an edge coupler.

32. An apparatus according to claim 31 and comprising a turning mirror disposed between the edge coupler and the device.

33. The device according to claim 30, wherein: The optical coupler includes a vertical coupler disposed on a surface of the PIC.

34. The device according to claim 33, wherein The vertical couplers are arranged in a two-dimensional matrix of locations on the surface of the PIC, and wherein the first and second microlens arrays comprise two-dimensional arrays of microlenses aligned with the two-dimensional matrix of vertical couplers.

35. An optical device comprising: a photonic integrated circuit (PIC) comprising at least one row of vertical couplers disposed on a surface of the PIC and spaced apart at a predefined pitch and configured to couple respective beams of light into and out of the PIC while collimating the respective beams; as well as - a beam shifter, said beam shifter being arranged above said PIC and comprising: a microlens array comprising microlenses arranged in a plane, spaced apart at the predefined pitch and aligned with the vertical coupler; as well as one or more layers of birefringent material contained between the PIC and the microlens array, the thickness and birefringence of each layer being selected such that light of a first polarization entering the layer through one of the microlenses or the vertical couplers is laterally displaced a distance equal to the spacing, while light of a second polarization orthogonal to the first polarization passes through the layer without being displaced.

36. A beam shifter according to claim 35, and including a directional polarization rotator, which is between the microlens array and the PIC, and together with the birefringent material, the directional polarization rotator is configured to rotate the polarization of light passing through the directional polarization rotator in a given direction by 90° without rotating the polarization of light passing through the directional polarization rotator in the opposite direction.

37. The beam shifter of claim 36, wherein: The polarization rotator includes a Faraday rotator and a half-wave plate.

38. A beam displacer according to claim 36 or 37, wherein: The one or more layers of birefringent material include a first layer adjacent to the first microlens array and a second layer adjacent to the PIC, Therein, the directional polarization rotator is contained between the first layer and the second layer of birefringent material.

39. Optical device, comprising: a photonic integrated circuit (PIC) comprising at least one row of optical couplers spaced apart at a predefined pitch and configured to couple respective beams of light into and out of the PIC; as well as A prism comprising a birefringent material, the birefringent material being arranged close to the row of optical couplers and the birefringence index and prism angle of the prism being selected so that light of a first polarization passing through the prism to or from one of the optical couplers is deflected by a first angle, while light of a second polarization orthogonal to the first polarization is deflected by a second angle different from the first angle when passing through the prism, and the first angle and the second angle being selected so that the light beams of the first polarization and the light beams of the second polarization coupled into and coupled out from the adjacent optical couplers in the at least one row are combined by the prism.

40. An optical device comprising: - substrate; - a polarization beam splitter, the polarization beam splitter being arranged on the substrate, comprising: a first waveguide having a first end, a second end, and a first tapered section, the first end being configured to receive an input light beam including both a TE polarization component and a TM polarization component, the second end being configured to output the TE polarization component, the first tapered section having a first width that decreases in a direction from the first end toward the second end; as well as a second waveguide having a second tapered section adjacent to the first tapered section, the second tapered section having a second width increasing in the direction from the first end toward the second end, such that the TM polarization component is coupled from the first tapered section into the second tapered section.

41. The apparatus of claim 40, and comprising a polarization rotator disposed on the substrate and coupled to receive the TM polarization component from the second waveguide and convert the TM polarization component to TE polarization.

42. A signal processing device, comprising: - an array of coherent detection units, each unit comprising: a detector configured to output a corresponding beat signal in response to radiation received by the unit; and a mixer coupled to mix the respective beat frequency signals with carrier waves at respective modulation frequencies, whereby the coherent detection unit outputs respective modulated signals at different respective modulation frequencies; - an analog adder coupled to sum the modulated signals output by the array of coherent detection units to output a summed signal; - an analog-to-digital converter (ADC) coupled to digitize the summed signal to output a digital data stream; and - a processing circuit configured to demultiplex the digital data stream into a plurality of frequency channels at the respective modulation frequencies and to extract the respective beat frequency from each of the frequency channels.

43. The device according to claim 42, wherein: The processing circuit is configured to demultiplex the digital data stream into the plurality of frequency channels by transforming the digital data stream into the frequency domain and identifying a corresponding pair of peaks in the transformed data stream, the corresponding pair of peaks being separated by twice the corresponding modulation frequency of each cell.

44. The device according to claim 42, wherein: Each of the coherent detection units includes a respective first mixer and a second mixer, the first mixer and the second mixer being configured to mix the respective beat frequency signal with respective first carrier waves and second carrier waves, the respective first carrier waves and second carrier waves being at different respective first modulation frequencies and second modulation frequencies, so that the coherent detection unit outputs respective first modulated signals and second modulated signals, wherein there are different respective frequency differences between the first modulated signals and the second modulated signals output by each of the coherent detection units, and Wherein the processing circuit demultiplexes the digital data stream into the plurality of frequency channels in response to the corresponding frequency differences.

45. The device according to claim 44, wherein The analog adder includes a first adder and a second adder, the first adder and the second adder are respectively coupled to sum the first modulated signal and the second modulated signal respectively output by the first mixer and the second mixer in the coherent detection unit, and The ADC includes a first ADC and a second ADC, and the first ADC and the second ADC are coupled to receive and digitize the corresponding first summation signal and the second summation signal output by the first adder and the second adder respectively, so as to generate a first data stream and a second data stream for inputting into the processing circuit.

46. ​​An optical device comprising: a first substrate; a first array of photonic integrated circuits (PICs) disposed on the first substrate, each PIC comprising one or more optical edge couplers adjacent to an upper surface of the first substrate; as well as a second substrate comprising a second array of turning mirrors and mounted on an upper surface of the first substrate such that each turning mirror in the second array is aligned with one or more optical edge couplers on a corresponding one of the PICs, whereby light is coupled into and out of the optical edge couplers via the turning mirrors.

47. The device according to claim 46, wherein The turning mirrors have respective reflecting surfaces that are inclined at 45° relative to a lower surface of the second substrate mounted on the upper surface of the first substrate.

48. The apparatus of claim 46, wherein: The first substrate and the second substrate include semiconductor material that is patterned and etched to produce the PIC and the turning mirror.

49. The device according to any one of claims 46 to 48, wherein The first substrate is patterned to define cavities between the PICs, wherein the edge couplers are adjacent to corresponding ones of the cavities, and wherein the second substrate is patterned such that when the second substrate is mounted on the upper surface of the first substrate, the turning mirror protrudes into the cavity proximate to the edge coupler.

50. A method for producing an optoelectronic device, the method comprising: - mounting a bifold mirror on a carrier substrate, the bifold mirror comprising a first reflective surface and a second reflective surface arranged at a diagonal angle relative to a normal to the carrier substrate; - mounting a plurality of identical photonic integrated circuits (PICs) on said carrier substrate, each PIC comprising: -- Planar substrate; an array of optical transceiver units arranged on the planar substrate and comprising respective edge couplers arranged along an edge of the planar substrate; and an optical distribution tree coupled to transmit coherent radiation from a radiation source to the optical transceiver unit, - wherein the plurality of identical PICs include a first PIC and a second PIC, the first PIC being mounted on the carrier substrate such that an edge of the first PIC is close to the first reflective surface, and the second PIC being rotated 180° relative to the first PIC and mounted on the carrier substrate such that an edge of the second PIC is close to the second reflective surface.

51. The method of claim 50, wherein: The bi-fold mirror has a triangular profile, wherein the first and second reflecting surfaces are oriented at +45° and -45°, respectively, relative to the normal.

52. The method of claim 50, wherein: The edge couplers in each PIC are arranged along an edge with a predefined spacing between the edge couplers, and wherein mounting the plurality of identical PICs comprises mounting the first PIC and the second PIC on the carrier substrate such that the edge couplers on the first PIC are shifted relative to the edge couplers on the second PIC by half of the predefined spacing.

53. The method of claim 50, wherein: Each PIC includes: a central region in which edge couplers are arranged along an edge with a first spacing between the edge couplers; a first peripheral region at a first side of the central region, in which no edge couplers are disposed along an edge; and In a second peripheral region at a second side of the central region opposite to the first side, in the second peripheral region, edge couplers are arranged at a second pitch, the second pitch being finer than the first pitch.

54. The method of claim 53, wherein: The second spacing is half of the first spacing.

55. The method of claim 50, wherein: Installing the multiple identical PICs includes: mounting a third PIC on the carrier substrate side by side with the first PIC so that an edge of the third PIC is adjacent to the first reflective surface; and A fourth PIC rotated 180° relative to the first PIC is mounted on the carrier substrate side by side with the second PIC so that an edge of the fourth PIC is close to the second reflective surface.

56. The method of claim 50, wherein: The optical distribution tree comprises a network of waveguides and switches disposed on the planar substrate.

57. The method according to any one of claims 50 to 56, wherein: The optical transceiver unit is configured to: direct coherent radiation through the corresponding edge coupler, via the double-folded reflector, toward a target; receive optical radiation from the target through the corresponding edge coupler, via the double-folded reflector; mixing a portion of the coherent radiation with the optical radiation received through the edge coupler; And outputting an electrical signal in response to the mixed radiation.

58. The method of claim 57, wherein: The edge couplers define respective optical apertures of the optical transceiver units, and wherein the method comprises positioning one or more optical elements to image the optical apertures onto the target, thereby defining respective fields of view of the optical transceiver units.

59. A method as claimed in claim 58 and comprising positioning a scanner to scan the field of view of the optical transceiver unit over the target.

60. A method for producing an optoelectronic device, the method comprising: forming an array of optical transceiver units on a planar substrate, each transceiver unit comprising an optical transducer configured to couple optical radiation between the transceiver unit and a target external to the substrate; a coupled optical distribution tree comprising a hierarchical network of switches interconnected by waveguides and arranged on the substrate to transmit coherent radiation from a radiation source to the optical transceiver unit, the hierarchical network comprising at least a first layer of first switches having a first switching time and a second layer of second switches having a second switching time different from the first switching time; as well as A controller is coupled to actuate the switch to select different subsets of the optical transceiver units to receive the coherent radiation from the radiation source at different times.

61. The method of claim 60, wherein: Each first switch in the first layer has at least two first outputs, the at least two first outputs are respectively coupled to at least two second switches of the second switches in the second layer, and each second switch in the second layer has at least two second outputs coupled to the transceiver unit, and wherein the first switching time is shorter than the second switching time.

62. The method of claim 61, wherein: The optical transceiver units and the second switches are arranged in different respective first and second regions of the substrate in first and second groups, and wherein coupling the optical distribution tree comprises interconnecting the first switches and the second switches such that one of the first outputs of each first switch is coupled to the first group of the transceiver units and the second switch, and another of the first outputs of each first switch is coupled to the second group of the transceiver units and the second switch.

63. A method according to claim 60 and comprising positioning a scanner to scan a respective field of view of said optical transceiver unit over said target, wherein: Coupling the controller includes actuating the switch to select different subsets of the optical transceiver units to transmit the coherent radiation toward the target during different sweeps of the scanner over the target.

64. The method of claim 63, wherein: Scanning respective fields of view of the optical transceiver units over the target defines a plurality of respective scan lines over the target, wherein the first switching time is shorter than the second switching time, and wherein actuating the switch comprises actuating the first switch to activate a different grouping of the scan lines in each sweep over the target.

65. The method of claim 63, wherein: Scanning respective fields of view of the optical transceiver units over the target defines a plurality of respective scan lines over the target, and wherein actuating the switch comprises selectively activating the scan lines in regions of interest over the target.

66. A method according to claim 60 and comprising processing signals output by the transceiver unit to produce a three-dimensional (3D) map of the target.

67. The method according to any one of claims 60 to 66, wherein: The switch comprises a thermo-optical switch.

68. A method for exchanging, comprising: - Provided is a thermo-optical switch, the thermo-optical switch comprising: an interferometer comprising a first waveguide and a second waveguide having respective input and output ends; a first heater and a second heater, the first heater and the second heater being configured to heat the first waveguide and the second waveguide, respectively; a beam splitter coupled to receive a coherent optical signal and input the optical signal to input ends of both the first waveguide and the second waveguide; and a mixer coupled to receive and mix the optical signals from output ends of the first waveguide and the second waveguide, and to direct the mixed optical signals to a first output or a second output of the switch according to a phase shift between the first waveguide and the second waveguide; and - controlling the first heater and the second heater so as to exchange the mixed optical signal between the first output and the second output.

69. The method of claim 68, wherein: Controlling the first heater and the second heater includes alternately driving the first heater and the second heater to switch the mixed light signal between the first output and the second output.

70. The method of claim 69, wherein: Driving the first heater and the second heater includes applying a voltage waveform including a pre-emphasis pulse to at least one of the heaters each time the output is switched.

71. The method of claim 69, wherein: Driving the first heater and the second heater includes applying respective voltages such that respective temperatures of the first waveguide and the second waveguide increase continuously over a plurality of cycles of switching between the first output and the second output.

72. The method of any one of claims 68 to 71, wherein: Controlling the first heater and the second heater includes applying a digital input to a first digital / analog converter (DAC) and a second digital / analog converter, and the first digital / analog converter and the second digital / analog converter are configured to apply corresponding voltages to the first heater and the second heater in response to the digital input.

73. A method for beam shifting, the method comprising: providing a first microlens array and a second microlens array, the first microlens array and the second microlens array comprising microlenses arranged in respective first and second planes and having a common predefined pitch; and One or more layers of birefringent material are inserted between the first microlens array and the second microlens array, and the thickness and birefringence of each layer are selected so that light of a first polarization entering the layer through one of the microlenses is laterally displaced a distance equal to the pitch of the microlens array, while light of a second polarization orthogonal to the first polarization passes through the layer without being displaced.

74. The method of claim 73, and comprising inserting a directional polarization rotator between the first microlens array and the second microlens array, together with the birefringent material, the directional polarization rotator being configured to rotate the polarization of light passing through the directional polarization rotator in a given direction by 90° without rotating the polarization of light passing through the directional polarization rotator in an opposite direction.

75. The method of claim 74, wherein: The polarization rotator includes a Faraday rotator and a half-wave plate.

76. The method of claim 74, wherein: inserting one or more layers of birefringent material comprises inserting a first layer of birefringent material adjacent to the first microlens array and a second layer of birefringent material adjacent to the second microlens array, Therein, the directional polarization rotator is contained between the first layer and the second layer of birefringent material.

77. The method of claim 76, wherein: The first and second layers of the birefringent material are oriented such that both the first and second layers laterally displace light of the first polarization in the same direction.

78. The method of claim 76, wherein: The first and second layers of the birefringent material are oriented such that the first and second layers laterally shift light of the first polarization in opposite directions.

79. A method according to any one of claims 73 to 78, and comprising positioning a photonic integrated circuit (PIC) comprising at least one row of optical couplers spaced apart at a predefined pitch such that the optical couplers are aligned with the first array of microlenses so as to couple corresponding beams of light between the optical couplers and corresponding microlenses in the first array, Thus, the light beams of the first polarization and the light beams of the second polarization coupled into and out from the adjacent optical couplers in the at least one row are combined at the second microlens array.

80. The method of claim 79, wherein: The optical coupler includes an edge coupler.

81. The method of claim 80 and comprising positioning a turning mirror between the edge coupler and the first microlens array.

82. The method of claim 79, wherein: The optical coupler includes a vertical coupler disposed on a surface of the PIC.

83. The method of claim 82, wherein: The vertical couplers are arranged in a two-dimensional matrix of locations on the surface of the PIC, and wherein the first and second microlens arrays comprise two-dimensional arrays of microlenses aligned with the two-dimensional matrix of vertical couplers.

84. A method for beam shifting, comprising: - providing a photonic integrated circuit (PIC), the PIC comprising at least one row of vertical couplers, the at least one row of vertical couplers being arranged on a surface of the PIC and spaced apart at a predefined pitch and configured to couple respective beams of light into and out of the PIC while collimating the respective beams of light; and - providing a beam shifter, the beam shifter comprising: a microlens array comprising microlenses arranged in a plane and spaced apart at said predefined pitch; and one or more layers of birefringent material, the one or more layers of birefringent material being included between the PIC and the microlens array, the thickness and birefringence of each layer being selected so that light of a first polarization entering the layer through one of the microlenses or the vertical couplers is laterally displaced a distance equal to the pitch, while light of a second polarization orthogonal to the first polarization passes through the layer without being displaced; and - Positioning the beam shifter above the PIC such that the micro lenses are aligned with the vertical couplers, respectively.

85. The method of claim 84, wherein: The beam displacer includes a directional polarization rotator between the microlens array and the PIC, and together with the birefringent material, the directional polarization rotator is configured to rotate the polarization of light passing through the directional polarization rotator in a given direction by 90° without rotating the polarization of light passing through the directional polarization rotator in the opposite direction.

86. The method of claim 85, wherein: The polarization rotator includes a Faraday rotator and a half-wave plate.

87. The method of claim 85 or 86, wherein: The one or more layers of birefringent material include a first layer adjacent to the first microlens array and a second layer adjacent to the PIC, Therein, the directional polarization rotator is contained between the first layer and the second layer of birefringent material.

88. A method for beam shifting, comprising: providing a photonic integrated circuit (PIC) comprising at least one row of optical couplers spaced apart at a predefined pitch and configured to couple respective beams of light into and out of the PIC; as well as A prism is positioned, the prism including a birefringent material, the birefringent material being proximate to the row of optical couplers, the birefringence index and prism angle of the prism being selected such that light of a first polarization passing through the prism to or from one of the optical couplers is deflected by a first angle, while light of a second polarization orthogonal to the first polarization is deflected by a second angle different from the first angle when passing through the prism, and the first angle and the second angle being selected such that the light beams of the first polarization and the light beams of the second polarization coupled into and out of adjacent optical couplers in the at least one row are combined by the prism.

89. A method for beam steering, comprising: forming a first waveguide on a substrate, the first waveguide having a first end, a second end, and a first tapered section, the first end being configured to receive an input light beam including both a TE polarization component and a TM polarization component, the second end being configured to output the TE polarization component, and the first tapered section having a first width that decreases in a direction from the first end toward the second end; as well as A second waveguide is formed on the substrate, the second waveguide having a second tapered section adjacent to the first tapered section, the second tapered section having a second width increasing in the direction from the first end toward the second end, so that the TM polarization component is coupled from the first tapered section into the second tapered section.

90. The method of claim 89, and comprising coupling a polarization rotator on the substrate to receive the TM polarization component from the second waveguide and convert the TM polarization component to TE polarization.

91. A method for signal processing, comprising: providing an array of coherent detection cells, each cell comprising a detector configured to output a respective beat frequency signal in response to radiation received by the cell; mixing the respective beat frequency signals output by each unit with a carrier wave at a respective modulation frequency, whereby the coherent detection units output respective modulated signals at different respective modulation frequencies; summing the modulated signals output by the array of coherent detection elements to produce a summed analog signal; digitizing the summed analog signal to produce a digital data stream; demultiplexing the digital data stream into a plurality of frequency channels at the corresponding modulation frequencies; as well as The corresponding beat frequency is extracted from each of the frequency channels.

92. The method of claim 91, wherein: Demultiplexing the digital data stream includes transforming the digital data stream into the frequency domain, and wherein extracting the corresponding beat frequency includes identifying a corresponding pair of peaks in the transformed data stream, the corresponding pair of peaks separated by twice the corresponding modulation frequency of each cell.

93. The method of claim 91, wherein: mixing the respective beat frequency signals comprises mixing each beat frequency signal with a respective first carrier and a second carrier, the respective first carrier and the second carrier being at different respective first modulation frequencies and second modulation frequencies, so that the coherent detection units output respective first modulated signals and second modulated signals, wherein there are different respective frequency differences between the first modulated signals and the second modulated signals output by each of the coherent detection units, and Wherein, demultiplexing the digital data stream comprises demultiplexing the digital data stream into the plurality of frequency channels in response to the corresponding frequency differences.

94. The method of claim 93, wherein: Summing the modulated signals comprises summing the first modulated signal in a first analog adder and summing the second modulated signal in a second analog adder, and Wherein, digitizing the summed analog signal includes digitizing the corresponding first summed signal and second summed signal outputted by the first analog adder and the second analog adder, respectively, so as to generate a first digital data stream and a second digital data stream.

95. A method for optical manufacturing, comprising: forming a first array of photonic integrated circuits (PICs) on a first substrate, each PIC comprising one or more optical edge couplers adjacent to an upper surface of the first substrate; as well as forming a second array of turning mirrors on a second substrate; as well as The second substrate is mounted on the upper surface of the first substrate so that each turning mirror in the second array is aligned with one or more optical edge couplers on a corresponding one of the PICs, whereby light is coupled into and out of the optical edge coupler via the turning mirror.

96. The method of claim 95, wherein: The turning mirrors have respective reflecting surfaces inclined at 45° relative to a lower surface of the second substrate mounted on the upper surface of the first substrate.

97. The method of claim 95, wherein: The first substrate and the second substrate include semiconductor material that is patterned and etched to produce the PIC and the turning mirror.

98. The method according to any one of claims 95 to 97, wherein: forming the first array comprises patterning a first substrate to define cavities between the PICs, wherein the edge couplers are adjacent to respective ones of the cavities, and Wherein forming the second array includes patterning the second substrate so that when the second substrate is mounted on the upper surface of the first substrate, the turning mirror protrudes into the cavity proximate the edge coupler.

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