Optical phased array architecture for wavefront sensing

Abstract

This paper provides an optical phased array (OPA) architecture for wireless optical communication terminals implementing wavefront sensing. SOLUTION: An optical phased array (OPA) photonic integrated chip (114) includes a plurality of array elements (120), a plurality of phase shifters (121), a plurality of combiners (230-234), and an edge coupler (236) configured to couple to a single mode waveguide. The plurality of phase shifters includes a layer of phase shifters having a phase shifter connected to each array element in the plurality of array elements. The plurality of combiners is configured to connect the plurality of phase shifters to the edge coupler. The plurality of combiners includes a first combiner having a first output connected to a second combiner or the edge coupler, and a second output of the first combiner is connected to a photodetector (240). An in-phase optical portion in the first combiner is output through a first output, and an out-of-phase optical portion in the first combiner is output through a second output.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to and benefit of the filing dates of U.S. Patent Application No. 17 / 897,410, filed August 29, 2022, and U.S. Provisional Patent Application No. 63 / 246,605, filed September 21, 2021, the entire disclosures of which are incorporated herein by reference. [Background technology]

[0002] Wireless optical communications enable high-throughput and long-distance communications, in part due to the high gain provided by the narrow angular width of the transmitted beam. However, the narrow beam also requires that it must be accurately and actively pointed to remain aligned with the terminal aperture at the remote end. This pointing can be achieved by small mirrors (e.g., MEMS or voice coil-based fast steering mirror mechanisms) that are actuated to steer the beam. In other implementations, electro-optical steering of the beam with no moving parts is used to steer the beam, which offers cost, lifetime, and performance advantages. Optical phased arrays (OPAs) are a key technology building block with additional advantages for adaptive optics, point-to-multipoint support, and mesh network topologies. Each active element within an OPA requires electro-optical phase shifting capabilities. Summary of the Invention

[0003] An aspect of the present disclosure provides an optical phased array (OPA) photonic integrated chip, the OPA chip including: a plurality of array elements; a plurality of phase shifters including a layer of phase shifters with a phase shifter connected to each array element in the plurality of array elements; a plurality of combiners configured to connect the plurality of phase shifters to an edge coupler for a single-mode waveguide, the plurality of combiners including a first combiner having a first output connected to a second combiner or the edge coupler, the second output of the first combiner being connected to a photodetector, an in-phase optical portion of the first combiner being output through the first output, and an out-of-phase optical portion of the first combiner being output through the second output; and the edge coupler configured to couple to the single-mode waveguide.

[0004] In one example, the plurality of array elements includes grating emitters. In another example, the plurality of array elements are arranged in a 32x32 grating of array elements. In a further example, the plurality of combiners includes at least one 2x2 multimode interferometer (MMI). In yet another example, the plurality of combiners includes at least one directional coupler. In yet another example, the plurality of combiners are arranged in an H-tree configuration. In another example, the plurality of combiners includes two or more combiners having outputs connected to photodetectors.

[0005] In a further example, the array elements and phase shifters are disposed in silicon and the edge couplers are disposed in silicon nitride. In this example, a first set of combiners is disposed in silicon and a second set of combiners is disposed in silicon nitride. In yet another example, the OPA chip also includes a microlens array disposed between the array elements and an edge of the OPA chip.

[0006] In yet another example, an optical communication system includes an OPA chip. In this example, the optical communication system also includes one or more processors configured to transmit a first optical signal through the OPA chip and receive a second optical signal through the OPA chip. Also in this example, the one or more processors are configured to receive a signal from the photodetector, determine an adjustment to at least one phase shifter of the plurality of phase shifters to increase an amount of incident light coupled into the OPA chip, and send instructions to the at least one phase shifter to make the adjustment. Additionally or alternatively, in this example, the first optical signal and the second optical signal have a wavelength separation of 100 GHz or greater.

[0007] Another aspect of the present disclosure provides a method for performing wavefront correction for optical communications, the method including receiving an incident optical communications beam at an optical phased array on a photonic integrated chip in a communications system, receiving a first beam portion of the incident optical communications beam and a second beam portion of the incident optical communications beam at a combiner of the photonic integrated chip, combining the first beam portion and the second beam portion into an output beam at the combiner, outputting a first output beam portion from the combiner toward an edge coupler of the photonic integrated chip, where the first output beam portion is an in-phase portion of the output beam, outputting a second output beam portion from the combiner to a photodetector, where the second output beam portion is an out-of-phase portion of the output beam, detecting, by one or more processors of the communications system, a measurement of the second output beam portion from the photodetector, determining, by the one or more processors, a wavefront error of the incident optical communications beam based on the measurement, and adjusting, by the one or more processors, at least one phase shifter of the communications system based on the determined wavefront error.

[0008] In one example, determining the wavefront error includes determining a relative phase difference based on the measurement. In another example, the method also includes transmitting an output optical communications beam using the photonic integrated chip and adjusted at least one phase shifter by one or more processors. In this example, detecting the measurement, determining the wavefront error, and adjusting the at least one phase shifter include a feedback loop. In yet another example, the method also includes tracking changes in the input optical communications beam using the feedback loop. In a further example, adjusting the at least one phase shifter includes increasing an in-phase portion of the output beam and decreasing an out-of-phase portion of the output beam at the combiner. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a block diagram of a first communication device and a second communication device according to an aspect of the present disclosure. [Figure 2A] FIG. 1 is a pictorial diagram of a phase shifter architecture according to an aspect of the present disclosure. [Figure 2B] FIG. 1 is a pictorial diagram of an optical phased array architecture according to an aspect of the present disclosure. [Figure 3] FIG. 1 is a pictorial diagram of a network according to an aspect of the present disclosure. [Figure 4] FIG. 1 is a flow diagram according to an aspect of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] overview The present technology relates to an optical phased array (OPA) architecture for a wireless optical communication terminal that performs wavefront sensing. The architecture design can enable real-time wavefront measurement, angle-of-arrival measurement, and high transmit power with low-power received signals. The wavefront measurement can be lossless. Furthermore, the architecture design for a single OPA can perform simultaneous transmit and receive functions.

[0011] The OPA architecture may include a microlens array, an emitter associated with each microlens, multiple phase shifters, and waveguides connecting the components within the OPA. The OPA architecture may be located on a single chip, the OPA chip. The waveguides gradually merge between the emitters and edge couplers that connect to other transmitter and / or receiver components. In particular, the waveguide configuration may combine two waveguides at each stage, meaning that the number of waveguides is reduced by a factor of two for each successive stage closer to the edge coupler. The coupling points may be nodes, and a combiner may be located at each node. The combiner may be a 2x2 multimode interference (MMI) or directional coupler.

[0012] The microlens array may be composed of convex lenses that focus light onto the emitter to increase the effective fill factor. In some implementations, the emitter may be a grating emitter. Each microlens in the array is shaped to eliminate side lobes in the signal due to the counter-passing beam as well as the receiver angular acceptance. Each microlens is typically tens to hundreds of micrometers in diameter and height. Furthermore, each microlens may be fabricated by molding, printing, or etching the lens directly onto a wafer. Integrating a microlens array allows for a reduction in grating emitter size and an increase in the pitch between emitters. In this way, two-dimensional waveguide routing in this architecture may be better suited to single-layer optical phased arrays.

[0013] The emitters may be configured to produce specific phase and intensity profiles to further increase the effective fill factor and improve the wavefront. The phase and intensity profiles can be determined using inverse design or other techniques to describe how the transmitted signal changes as it propagates through and passes through the microlens array. The phase profile can differ from the flat profile of conventional grating emitters, and the intensity profile can differ from the Gaussian-shaped intensity profile of conventional grating emitters.

[0014] At least some components of the OPA architecture can be located in silicon nitride (SiN) to support higher power in the transmit signal. SiN has a higher optical power nonlinearity threshold than traditional silicon-on-insulator (SOI) materials. SiN is compatible with standard casting processes and provides low attenuation for wavelengths between the visible and infrared. Because of its large bandgap, SiN is immune to the two-photon absorption that limits the maximum output power of silicon. This architecture allows multi-watt transmit power to be injected into the OPA chip, which is then concentrated through the waveguide configuration. As the transmit signal branches within the waveguide configuration toward the emitter, the power in each branch in the stage closest to the emitter can be reduced below the two-photon absorption limit of the SOI. The branches of the transmit signal can be adiabatically coupled to the emitter within the SOI layer. In some implementations, portions of the waveguide configuration can be located within the SOI layer.

[0015] In some of the nodes, a combiner is present at each node in the receive path for the incoming optical beam, so that each node has two input ports and two output ports. The first output may be directed to a photodetector, and the second output may be directed to the next node in the receive path or another receiver component. The number of combiners with photodetectors can be selected based on an algorithm to any number between a single photodetector at the final combined signal at the edge coupler and a photodetector at each node along the waveguide tree. The first output can transmit an out-of-phase portion of the incoming optical beam, i.e., the first portion, and the second output can transmit an in-phase portion of the incoming optical beam, i.e., the second portion. Thus, if there is no light exiting one port, it can be determined that all light from the incoming beam is exiting the other port.

[0016] The photodetector may be configured to measure the amount of light of the first portion of the incident light beam received from the first output. The amount of light in the first output port may include the portion from the first input port and the portion from the second input port. For example, the amount of light may include a first light beam that is a scaled value of the signal at the first input port and a second light beam that is a scaled and 90-degree phase-shifted value of the signal at the second input port. Measuring the amount of light may include generating a first signal along a first axis of the photodetector and generating a second signal along a second axis of the photodetector with a 90-degree phase shift from the first axis. For example, the first signal may be generated based on the first light beam, and the second signal may be generated based on the second light beam. The amplitude of the generated first signal and the amplitude of the generated second signal may be summed to determine the magnitude or intensity of the first portion. For example, the amplitude squared of the sum of the first and second signals may be measured by the photodetector.

[0017] The measured amplitude or intensity may be output from the photodetector to determine the relative phase difference between the two input optical signals, which is then used to calculate the wavefront and input angle of arrival. This measurement and calculation introduces little or no additional loss. Based on the determined relative phase difference, the phase shifter may be adjusted to reduce the measured light in the first portion of the input beam at the first output. The less light at the first output port, the more light will couple into the second output port, which is connected to the next node in the receive path or other receiver component.

[0018] The transmit and receive signals used by the terminal may be configured to have a frequency separation. The frequency separation improves the isolation between the transmit and receive signals that may simultaneously pass through the terminal and through free space. Because the waveguides for the transmit and receive signals may be identical and the path lengths within the waveguide tree may be designed to be approximately identical, the frequency separation may be selected to be as large as possible while ensuring that the terminal components have the same effect on both signals. In some examples, optical isolation may be provided by a circulator. In some further examples, optical isolation may also be provided by using one waveguide for the transmit path and another waveguide for the receive path along a portion of the terminal, such as between the circulator and the light source or sensor. There may also be a filter at or near the circulator that further increases the isolation between the transmit and receive signals. In one example, the frequency separation may be approximately 100 GHz or greater.

[0019] Overall, this OPA design for an optical communications terminal can enable faster and more accurate alignment adjustments, which can increase the amount of light transmitted along the optical link. The OPA materials and design can also be configured to transmit at high power and detect low-power received signals. The OPA architecture can also reduce the complexity, components, and cost of manufacturing an optical communications terminal. The reduced complexity and components can also reduce errors or wear and increase the system's lifespan.

[0020] System Example FIG. 1 is a block diagram 100 of a first communication device of a first communication terminal configured to form one or more links with a second communication device of a second communication terminal, for example, as part of a system such as a free-space optical communications (FSOC) system. FIGS. 2A-2B are pictorial diagrams of an example system architecture of the first communication device of FIG. 1. For example, the first communication device 102 includes one or more processors 104, memory 106, a transceiver 112, and an optical phased array (OPA) photonic integrated chip 114. In some implementations, the transceiver 112 may be a photonic integrated chip. The first communication device 102 may include two or more transceiver chips and / or two or more OPA chips.

[0021] The one or more processors 104 may be any conventional processor(s), such as a commercially available CPU. Alternatively, the one or more processors may be dedicated devices, such as application specific integrated circuits (ASICs), or other hardware-based processors, such as field programmable gate arrays (FPGAs). While FIG. 1 functionally depicts the one or more processors 104 and memory 106 as being within the same block, such as modem 202 for digital signal processing shown in FIG. 2A, the one or more processors 104 and memory 106 may actually comprise multiple processors and memories that may or may not be housed within the same physical housing, such as both modem 202 and a separate processing unit 203. Thus, reference to a processor or computer will be understood to include reference to a collection of processors or computers or memories that may or may not operate in parallel.

[0022] The memory 106 may store information accessible by one or more processors 104, including data 108 and instructions 110 that may be executed by the one or more processors 104. The memory may be any type of memory capable of storing information accessible by a processor, including computer-readable media such as hard drives, memory cards, ROM, RAM, DVDs, or other optical disks, as well as other writable and read-only memory. Systems and methods may include various combinations of the above, whereby various portions of the data 108 and instructions 110 are stored on various types of media. The memory of each communication device, such as the memory 106, may store calibration information, such as one or more offsets determined for tracking signals.

[0023] Data 108 may be retrieved, stored, or modified by one or more processors 104 according to instructions 110. For example, although the system and method are not limited by any particular data structure, data 108 may be stored in computer registers in a relational database, as a table with multiple distinct fields and records, an XML document, or a flat file. Data 108 may be formatted in any computer-readable format, such as, but not limited to, binary values ​​or Unicode. By way of further example only, image data may be stored as a bitmap, which consists of a grid of pixels stored according to a format that is compressed or uncompressed, lossless (e.g., BMP) or lossy (e.g., JPEG), and bitmap or vector-based (e.g., SVG), as well as computer instructions for drawing graphics. Data 108 may include any information sufficient to identify related information, such as numbers, descriptive text, dedicated codes, references to data stored in other areas of the same or different memory (including other network locations), or information used by a function to calculate related data.

[0024] The instructions 110 may be any set of instructions (e.g., machine code) or instructions (e.g., script) that are executed directly or indirectly by one or more processors 104. For example, the instructions 110 may be stored as computer code on a computer-readable medium. In this regard, the terms “instructions” and “program” may be used interchangeably herein. The instructions 110 may be stored in object code format for direct processing by one or more processors 104, or may be stored in any other computer language, including a script or collection of separate source code modules that are interpreted on demand or pre-compiled. The functions, methods, and routines of the instructions 110 are described in more detail below.

[0025] The one or more processors 104 may be in communication with the transceiver 112. The transceiver 112 may comprise transmitter and receiver components on one or more photonic integrated chips. As shown in FIG. 2A, one or more processors in the modem 202 may be in communication with the transceiver chip 112 and configured to receive and process incoming optical signals and transmit optical signals. The transceiver chip 112 may include one or more transmitter components and one or more receiver components. Thus, the one or more processors 104 may be configured to transmit data in signals via the transmitter components and receive communications and data in signals via the receiver components. The received signals may be processed by the one or more processors 104 to extract communications and data.

[0026] The transmitter components can include at least a light source such as a seed laser 116. Other transmitter components may include an amplifier such as a high-power semiconductor optical amplifier 204. In some implementations, the amplifier is on a separate photonic chip. The seed laser 116 may be a distributed feedback laser (DFB), a light-emitting diode (LED), a laser diode, a fiber laser, or a solid-state laser. The optical output or optical signal of the seed laser 116 can be controlled by a current or an electrical signal applied directly to the seed laser, such as from a modulator that modulates a received electrical signal. The light transmitted from the seed laser 116 is received by the OPA chip 114.

[0027] The receiver components may include at least a sensor 118, such as a photodiode. The sensor may convert the received light or optical signal into an electrical signal that can be processed by one or more processors. Other receiver components may include an attenuator, such as variable optical attenuator 206, an amplifier, such as semiconductor optical amplifier 208, or a filter.

[0028] The one or more processors 104 may be in communication with an optical phased array chip 114. The OPA chip 114 receives light from a transmitter component and outputs light as a coherent communication beam that is received by a remote communication device, such as a second communication device 122. The OPA chip 114 also receives light from free space, such as a communication beam from the second communication device 122, and provides it to a receiver component.

[0029] The OPA chip 114 may include multiple array elements 120 or emitters and multiple phase shifters 121. Multiple microlenses may be arranged on the multiple array elements 120 to focus incoming light and collimate outgoing light. Each microlens in the array may be a convex lens that focuses light onto a corresponding emitter. Additionally, each microlens may be shaped to eliminate side lobes in the transmitted or received light beam. Each microlens has a diameter and height on the order of tens or hundreds of micrometers. The multiple array elements 120 may be arranged in a grid pattern with a consistent pitch or distance between adjacent elements. In some examples, the multiple array elements 120 may be grid emitters with a grid pattern. By way of example, the grid pattern may be a 32x32 grid with a 100 micron pitch. In other examples, the array elements 120 may be arranged differently with different numbers of rows and columns, different shapes, and / or different pitches (consistent or inconsistent). The phase shifters 121 alter the incoming and outgoing light at the array elements 120. The incoming light is provided to a receiver component, and the outgoing light is provided to the array elements 120. As shown in FIG. 2B , the architecture of the multiple phase shifters 121 includes at least one layer of phase shifters. The first layer of phase shifters can include one phase shifter connected to each array element in the multiple array elements 120. For a 32×32 grid of array elements, there are 1024 phase shifters. In some examples, the phase shifter architecture includes multiple layers of phase shifters, and the phase shifters in the first layer can be connected in series with one or more phase shifters in the second layer.

[0030] The OPA chip may also include one or more combiners that narrow the incoming light beam and direct the outgoing light beam to each array element, and edge couplers that couple the incoming light beam between the OPA chip and a single-mode waveguide. The single-mode waveguide then directs the beam to the transceiver 112. If the grid pattern of the multiple array elements 120 is a 32x32 grid, there are 1024 incoming beam portions that are merged into a single output beam. The incoming beam portions may be combined in a 2x, H-tree, or higher order until a single output beam is formed. When using an H-tree configuration, there are 10 layers of combiners, with the layers containing the following numbers of combiners, starting closest to the array elements and ending closest to the edge couplers: 512, 256, 128, 64, 32, 16, 8, 4, 2, and 1.

[0031] One or more of the combiners may be a 2x2 MMI or directional coupler. A given combiner may receive two incident beam portions at a first input and a second input, merge the beams into an output beam, and direct a portion of the output beam from the output to an input of another combiner or edge coupler. For at least some of the one or more combiners, a portion of the output beam may be directed from a separate output of such combiner to a photodetector or redirected from the output beam. The photodetector may include a photodiode, photoresistor, phototransistor, or other type of light intensity sensor.

[0032] FIG. 2B illustrates a sample portion of an OPA architecture according to features described herein. For example, OPA chip 114 may include emitters 120A, 120B, 120C, and 120D, phase shifters 121A, 121B, 121C, and 121D, 2×2 MMIs 230, 232, and 234, and an edge coupler 236. Emitter 120A is connected to phase shifter 121A. Emitter 120B is connected to phase shifter 121B. Emitter 120C is connected to phase shifter 121C, and emitter 120D is connected to phase shifter 121D. The architecture illustrated in FIG. 2B may be extrapolated or extended for architectures with more emitters, phase shifters, and combiners. For example, the OPA chip may include an additional layer of nodes that may also include combiners, the last layer of which may be connected to multiple phase shifters 121.

[0033] 2B, a first input of combiner 230 may be connected to phase shifter 121A. A second input of combiner 230 may be connected to phase shifter 121B. A third input of combiner 232 may be connected to phase shifter 121C, and a fourth input of combiner 232 may be connected to phase shifter 121D. Combiner 230 may include a first output to photodetector 240 and a second output to combiner 234, and combiner 232 may include a third output to photodetector 242 and a fourth output to combiner 234. Combiner 234 may include a fifth input connected to the second output of combiner 230, a sixth input connected to the fourth output of combiner 232, a fifth output connected to photodetector 246, and a sixth output connected to edge coupler 236. In other implementations, only the combiner 234 may have two outputs, one of which is connected to a photodetector, and the combiners 230, 232 have only one output connected to the combiner 234. The edge coupler 236 can direct the combined incoming light beam into a single-mode waveguide that leads to other receiver components. In some examples, the single-mode waveguide leads to a circulator that provides separation of the incoming light from any outgoing light.

[0034] For a combiner connected to a photodetector, a first portion of the output beam that is out of phase may be directed from the first output toward the photodetector, and a second portion of the output beam that is in phase may be directed from the second output toward another combiner or edge coupler. The photodetector may be configured to sense a magnitude of received light, such as the first portion of the output beam, and provide a signal indicative of the magnitude of the received light to one or more processors 104 of the communications device 102. In this manner, the sensed magnitude may be used by the one or more processors to generate and provide an angle-of-arrival estimate to one or more processors 104, such as one in the processing unit 203.

[0035] Components within an OPA chip may be disposed on a combination of silicon (Si) and silicon nitride (SiN), such as silicon-on-insulator (SOI). A first set of components, including the edge coupler and closer to the edge coupler, may be disposed on the SiN, and a second set of components, including the array elements and closer to the array elements, may be disposed on the SiN. As shown in FIG. 2B , the edge coupler 236 and combiners 230, 232, and 234 may be disposed on the SiN, as indicated by the stippled shading. The array elements 120 and phase shifters 121 may be disposed on the Si, as indicated by the non-stippled solid fill.

[0036] The system may include additional components that support the functionality of the communications terminal. For example, the system may include one or more lenses and / or mirrors forming a telescope. The telescope may receive collimated light and output collimated light. The telescope may include an objective portion, an eyepiece portion, or a relay portion. As shown in FIG. 2A , the system may include an objective lens 210, an eyepiece lens 212, and relay lenses 214 and 216. The system may also include a circulator, such as a single-mode circulator 218, that routes the incoming and outgoing light while keeping them at least partially on separate paths. The system may also include one or more sensors 220 for detecting environmental characteristics and / or measurements of system components. The system may also include one or more steering mechanisms, such as one or more biasing means for controlling one or more phase shifters, which may be part of the OPA chip 114, and / or an actuated / steering mirror 222, such as a fast / fine pointing mirror. In some examples, the actuated mirror may be a MEMS two-axis mirror, a two-axis voice coil mirror, or a piezoelectric two-axis mirror. One or more processors 104, such as those in processing unit 203, may be configured to receive and process signals from one or more sensors 220, transceiver 112, and / or OPA chip 114 and control one or more steering mechanisms to adjust the pointing direction and / or wavefront shape, as described in more detail below. The system also includes optical fibers or waveguides connecting the optical components and creating a path between seed laser 116 and OPA chip 114 and between OPA chip 114 and photodiode 118.

[0037] As shown in FIG. 1, the first communication device 102 may output a light beam 20 a directed to the second communication device 122 .

[0038] Similarly, the second communication device 122 includes one or more processors 124, memory 126, a transceiver 132, and an OPA chip 134. The one or more processors 124 may be similar to the one or more processors 104 described above. The memory 126 may store information accessible by the one or more processors 124, including data 128 and instructions 130 that may be executed by the processor 124. The memory 126, data 128, and instructions 130 may be configured similar to the memory 106, data 108, and instructions 110 described above. Additionally, the transceiver 132 and OPA chip 134 of the second communication device 122 may be similar to the transceiver 112 and OPA chip 114. The transceiver 132 may include both transmitter and receiver components. The transmitter component may include a light source, such as a seed laser 136 configured similar to the seed laser 116. Other transmitter components may include an amplifier, such as a high-power semiconductor optical amplifier. The receiver components may include a sensor 138 configured similarly to sensor 118. Other receiver components may include an attenuator, such as a variable optical attenuator, an amplifier, such as a semiconductor optical amplifier, or a filter. OPA chip 114 may include a plurality of array elements 140 and a plurality of phase shifters 141, which may be similar to array element 120 and phase shifter 121, respectively. Similar to the additional components described above, additional components may be included to support the functionality of communication device 122. Communication device 122 may have a system architecture that is the same as or similar to the system architecture shown in FIG. 2.

[0039] As shown in FIG. 1, the second communication device 122 can output a light beam 20b directed towards the first communication device 102, which receives the light beam 20b.

[0040] As shown in FIG. 1 , a communication link 22 may be formed between the first communication device 102 and the second communication device 122 when the transceivers of the first and second communication devices are aligned. Alignment may be determined by determining when a line of sight is established between the communication devices 102, 122 using optical beams 20 a, 20 b. Using the communication link 22, one or more processors 104 may transmit communication signals to the second communication device 122 through free space using optical beam 20 a, and one or more processors 124 may transmit communication signals to the first communication device 102 through free space using optical beam 20 b. The communication link 22 between the first communication device 102 and the second communication device 122 allows for bidirectional transmission of data between the two devices. Notably, the communication link 22 in these examples may be a free-space optical communication (FSOC) link. In other implementations, one or more of the communication links 22 may be radio frequency communication links or other types of communication links capable of traveling through free space.

[0041] As shown in FIG. 3, multiple communication devices, such as a first communication device 102 and a second communication device 122, may be configured to form multiple communication links (shown as arrows) between multiple communication terminals, thereby forming a network 200. The network 300 may include client devices 310 and 312, a server device 314, and communication devices 102, 122, 320, 322, and 324. Each of the client devices 310, 312, the server device 314, and the communication devices 320, 322, and 324 may include one or more processors, memory, transceivers, and OPA chips similar to those described above. Using transmitters and receivers, each communication device in the network 300 can form at least one communication link with another communication device, as shown by the arrows. The communication link may be for optical frequencies, radio frequencies, other frequencies, or a combination of different frequency bands. In FIG. 3, the communication device 102 is shown having communication links with the client device 310 and the communication devices 122, 320, and 322. Communication device 122 is shown having communication links with communication devices 102 , 320 , 322 , and 324 .

[0042] The network 300 shown in FIG. 3 is merely exemplary, and in some implementations, the network 300 may include additional or different communication terminals. The network 300 may be a terrestrial network with multiple communication devices on multiple terrestrial communication terminals. In other implementations, the network 300 may include one or more high altitude platforms (HAPs), which may be balloons, blimps, or other airships, airplanes, unmanned aerial vehicles (UAVs), satellites, or any other form of high altitude platform or other type of mobile or fixed communication terminal. In some implementations, the network 300 may serve as an access network for client devices, such as mobile phones, laptop computers, desktop computers, wearable devices, or tablet computers. The network 300 may also be connected to a larger network, such as the Internet, and may be configured to provide client devices with access to resources stored on or provided through the larger computer network.

[0043] Example of how to During operation, the one or more processors 104 may perform wavefront sensing and / or correction for optical communication. Figure 4 illustrates a flow diagram 400 according to some of the aspects described above, which may be performed by one or more processors 104 of the first communication device 102. Additionally or alternatively, one or more processors 124 of the second communication device 122 may perform one or more steps of the flow diagram 400. While Figure 4 illustrates blocks in a particular order, the order may be changed, multiple operations may be performed simultaneously, and operations may be added or omitted.

[0044] In block 402, an incident optical communication beam may be received at an optical phased array on a photonic integrated chip in a communication system. The incident optical communication beam may carry data from a telecommunications system or a client device. The incident optical communication beam may be received at multiple array elements of the optical phased array. Each beam portion received at a given array element may be directed through a phase shifter of multiple phase shifters. The beam portions are coupled to a waveguide, which directs the collected beam portions to a receiver component of the communication system for processing. The data may be processed and / or transmitted to the next hop in the network. For example, optical beam 20b may be received at array element 120 in OPA chip 114 of communication device 102. Optical beam 20b may be directed through phase shifter 121 in OPA chip 114 toward a single-mode waveguide, which directs the optical beam to a receiver component, such as sensor 118.

[0045] In block 404, a first beam portion of the incident optical communication beam and a second beam portion of the incident optical communication beam may be received at a combiner of the photonic integrated chip. The combiner may have two inputs and two outputs. For example, the combiner may be a 2×2 MMI, such as one or more of combiners 230, 232, and 234 of OPA 114. The first beam portion may be received at a first input of the combiner, and the second beam portion may be received at a second input of the combiner. Using combiner 230 of FIG. 2B as an example, the first beam portion may be received from array element 120A via phase shifter 121A, and the second beam portion may be received from array element 120B via phase shifter 121B. In block 406, the first beam portion and the second beam portion may be combined into an output beam at the combiner.

[0046] In block 408, a first output beam portion may be output from the combiner toward an edge coupler of the photonic integrated chip. The first output beam portion may be an in-phase portion of the output beam. In block 410, a second output beam portion may be output from the combiner to a photodetector. The second output beam portion may be an out-of-phase portion of the output beam. For example, the out-of-phase portion may include a scaled value of the first beam portion from the first input and a scaled and 90-degree phase-shifted value of the second beam portion from the second input. In an example using the combiner 230, the first output beam portion may be sent from the first output to the combiner 234, and the second output beam may be sent from the second output to the photodetector 240.

[0047] At block 412, a measurement of the second output beam portion from the photodetector may be detected by one or more processors of the communication system. The photodetector may be configured to detect the magnitude or intensity by generating a first signal along a first axis of the photodetector and a second signal along a second axis of the photodetector with a 90-degree phase shift from the first axis. For example, the first signal may be based on a scaled value of the first beam portion, and the second signal may be based on a scaled and 90-degree phase-shifted value of the second beam portion. The amplitude of the generated first signal and the amplitude of the generated second signal may be summed to determine the magnitude or intensity of the first portion. For example, the measurement of the second output beam portion from the photodetector may be the amplitude squared of the sum of the first and second signals. The measurement may be output from the photodetector to determine a relative phase difference, which is then used to calculate the wavefront and input angle of arrival. For example, one or more processors 104 of the communication device 102 may detect the magnitude or intensity measurement of the second output beam portion from the photodetector 240.

[0048] At block 414, a wavefront error of the incident optical communication beam may be determined by one or more processors based on the magnitude or intensity measurements. In some implementations, determining the wavefront error may include determining a relative phase difference and / or an input arrival angle based on the magnitude or intensity measurements. The determined terms for the input arrival angle may include a combination of tip, tilt, or higher order terms. The one or more processors may determine the wavefront error based on the relative phase difference and / or the input arrival angle. For example, the one or more processors 104 may determine the wavefront error of the optical beam 20b based on a magnitude or intensity measurement from the optical detector 240.

[0049] In block 416, at least one phase shifter of the communication system may be adjusted by one or more processors based on the determined wavefront error. Adjustment of the at least one phase shifter may be performed to achieve improved coupling of the incoming optical communication beam at the OPA chip, which may also improve coupling of the outgoing optical communication beam at the telecommunications system. Improved coupling at the OPA chip may increase the in-phase portion of the output beam at a given combiner while decreasing the out-of-phase portion of the output beam at a given combiner. Blocks 412, 414, and 416 may be part of a feedback loop executed by one or more processors that iterates to minimize the measured power in the out-of-phase portion of the output beam. The feedback loop may include making a phase shifter adjustment in each cycle. The closer the out-of-phase portion of the output beam is to zero intensity, the better the coupling to the in-phase portion of the output beam and, therefore, to the remainder of the receive path.

[0050] In other implementations, the one or more processors may additionally or alternatively adjust the wavefront or pointing direction based on the determined wavefront error. The wavefront and / or pointing direction may be adjusted mechanically and / or electronically. Mechanical steering may include controlling the angle of a secondary steering element, such as an actuated mirror. Electronic steering may include controlling multiple phase shifters, such as by setting a phase shift setting for each phase shifter. In some implementations, steering a secondary steering element may be used for larger low-frequency adjustments, while steering using multiple phase shifters may be for smaller high-frequency adjustments. For example, the one or more processors 104 may adjust the wavefront and / or pointing direction of the communication device 102 based on the determined wavefront error. Mechanical steering may include controlling the steering mirror 222. Electronic steering may include controlling multiple phase shifters 121.

[0051] Once the at least one phase shifter is adjusted, an outgoing optical communications beam can be transmitted using the photonic integrated chip and the at least one adjusted phase shifter. For example, one or more processors 104 can transmit the optical beam 20a using the array elements 120 and phase shifters 121 of the OPA chip 114. In some implementations, a first set of processors can perform the detection of magnitude or intensity measurements, the determination of wavefront error, and the adjustment of the at least one phase shifter, and a second set of processors can perform the transmission of the outgoing optical communications beam. The first set of processors can perform steps in a feedback loop that can be used to track changes in the incoming optical communications beam. The changes can include position changes, such as drift, fading, or scintillation, or other types of changes.

[0052] The features described herein can be implemented on an integrated photonic chip to provide a more cost-effective and accurate communication system. The single-path transmit-receive design of this system-mode system allows for the use of less complex and less expensive components. Furthermore, this design reduces alignment errors between communication devices. This design can also reduce errors by replacing the boresight requirement between the tracking beam and the communication beam with a feedback loop connected directly to the communication beam rather than to the branching beam.

[0053] Unless otherwise specified, the foregoing alternatives are not mutually exclusive and can be implemented in various combinations to achieve unique advantages. These and other variations and combinations of the above features can be utilized without departing from the subject matter defined by the claims, and the foregoing description of embodiments should be construed as illustrative, not limiting, of the subject matter defined by the claims. Furthermore, the provision of examples described herein, as well as terms such as "such as," "including," and the like, should not be construed as limiting the subject matter of the claims to any particular examples; rather, these examples are intended to illustrate only one of many possible embodiments. Furthermore, the same reference symbols on different drawings may identify the same or similar elements.

Claims

1. 1. An optical phased array (OPA) photonic integrated chip, comprising: a plurality of array elements; a plurality of phase shifters including a layer of phase shifters having a phase shifter connected to each array element in the plurality of array elements; a plurality of combiners configured to connect the plurality of phase shifters to an edge coupler for a single mode waveguide, the plurality of combiners comprising: a first combiner having a first output connected to the second combiner or the edge coupler; a second output of the first combiner connected to a photodetector; a plurality of combiners, each of which outputs an in-phase light portion of the first combiner through the first output and an out-of-phase light portion of the first combiner through the second output; the edge coupler configured to couple to the single mode waveguide; 1. An optical phased array (OPA) photonic integrated chip comprising:

2. The OPA photonic integrated chip of claim 1 , wherein the plurality of array elements comprises grating emitters.

3. The OPA photonic integrated chip of claim 1 , wherein the plurality of array elements are arranged in a 32×32 grid of array elements.

4. The OPA photonic integrated chip of claim 1 , wherein the plurality of combiners includes at least one 2×2 multimode interferometer (MMI).

5. The OPA photonic integrated chip of claim 1 , wherein the plurality of combiners includes at least one directional coupler.

6. The OPA photonic integrated chip of claim 1 , wherein the plurality of combiners are arranged in an H-tree configuration.

7. The OPA photonic integrated chip of claim 1 , wherein the plurality of combiners comprises two or more combiners having outputs connected to photodetectors.

8. The OPA photonic integrated chip of claim 1 , wherein the plurality of array elements and the plurality of phase shifters are disposed in silicon, and the edge coupler is disposed in silicon nitride.

9. The OPA photonic integrated chip of claim 8 , wherein the first set of combiners is disposed in silicon and the second set of combiners is disposed in silicon nitride.

10. The OPA photonic integrated chip of claim 1 , further comprising a microlens array disposed between the plurality of array elements and an edge of the OPA photonic integrated chip.

11. An optical communication system comprising the OPA photonic integrated chip of claim 1.

12. 12. The system of claim 11, further comprising one or more processors configured to transmit a first optical signal through the OPA photonic integrated chip and receive a second optical signal through the OPA photonic integrated chip.

13. the one or more processors: receiving a signal from the photodetector; determining an adjustment to at least one phase shifter of the plurality of phase shifters to increase an amount of incident light coupled into the OPA photonic integrated chip; 13. The system of claim 12, configured to send instructions to the at least one phase shifter to perform the adjustment.

14. 13. The system of claim 12, wherein the first optical signal and the second optical signal have a wavelength separation of 100 GHz or greater.

15. 1. A method for performing wavefront correction for optical communications, the method comprising: receiving an incident optical communications beam at an optical phased array on a photonic integrated chip in a communications system; receiving a first beam portion of the incident optical communication beam and a second beam portion of the incident optical communication beam at a combiner of the photonic integrated chip; combining the first beam portion and the second beam portion at the combiner into an output beam; outputting a first output beam portion from the combiner toward an edge coupler of the photonic integrated chip, the first output beam portion being an in-phase portion of the output beam; outputting a second output beam portion from the combiner to a photodetector, the second output beam portion being an out-of-phase portion of the output beam; detecting, by one or more processors of the communication system, a measurement of the second output beam portion from the photodetector; determining, by the one or more processors, a wavefront error of the incident optical communications beam based on the measurements; and adjusting, by the one or more processors, at least one phase shifter of the communication system based on the determined wavefront error; A method comprising:

16. The method of claim 15 , wherein the determining the wavefront error comprises determining a relative phase difference based on the measurement.

17. 16. The method of claim 15, further comprising transmitting, by the one or more processors, an outgoing optical communication beam using the photonic integrated chip and the tuned at least one phase shifter.

18. 18. The method of claim 17, wherein the detecting of the measurement, the determining of the wavefront error, and the adjusting of the at least one phase shifter comprise a feedback loop.

19. 20. The method of claim 18, further comprising using the feedback loop to track changes in the incident optical communication beam.

20. 16. The method of claim 15, wherein the adjusting of the at least one phase shifter comprises increasing the in-phase portion of the output beam and decreasing the out-of-phase portion of the output beam at the combiner.

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