Optical phased array architecture for wavefront sensing

Abstract

The objective is to provide an optical phased array (OPA) architecture for wireless optical communication terminals that perform wavefront sensing. [Solution] The 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, each having a phase shifter connected to each array element in the plurality of array elements. The plurality of combiners are configured to connect the plurality of phase shifters to the edge coupler. The plurality of combiners include 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 (240). The in-phase portion of the first combiner is output through the first output, and the out-of-phase portion of the first combiner is output through the second output.

Description

Technical Field

[0001] (Cross - Reference to Related Applications) This application claims the benefit and priority of the filing dates of U.S. Patent Application No. 17 / 897,410, filed on August 29, 2022, and U.S. Provisional Patent Application No. 63 / 246,605, filed on September 21, 2021, the entire disclosures of which are incorporated herein by reference.

Background Art

[0002] Wireless optical communication enables high - throughput and long - distance communication, partly due to the high gain provided by the narrow angular width of the transmission beam. However, the narrow beam also requires being accurately and actively directed in order to remain aligned with the terminal aperture at the remote end. This pointing can be achieved by a small mirror (e.g., a MEMS or voice - coil - based fast - steering mirror mechanism) actuated to steer the beam. In other implementations, electro - optical steering of the beam without moving parts is used, which offers cost, lifetime, and performance advantages. An optical phased array (OPA) is an important technical component with additional advantages for adaptive optics, point - to - multi - point support, and mesh network topologies. Each active element within an OPA requires electro - optical phase - shifting capabilities.

Summary of the Invention

[0003] Aspects of the present disclosure provide an optically phased array (OPA) photonic integrated chip. The OPA chip includes 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 including a first combiner having a first output connected to a second combiner or an edge coupler, the second output of the first combiner being connected to a photodetector, the in-phase portion of light in the first combiner being output through the first output, and the out-of-phase portion of light in the first combiner being output through the second output, and an edge coupler configured to couple to a single-mode waveguide.

[0004] In one example, the array elements include a grid emitter. In another example, the array elements are arranged in a 32x32 grid. In yet another example, the combiners include at least one 2x2 multimode interferometer (MMI). In yet another example, the combiners include at least one directional coupler. In yet another example, the combiners are arranged in an H-tree configuration. In yet another example, the combiners include two or more combiners with outputs connected to a photodetector.

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

[0006] In yet another example, the 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 via the OPA chip and to receive a second optical signal via the OPA chip. In this example, one or more processors are also configured to receive a signal from a photodetector, determine to adjust at least one of a plurality of phase shifters to increase the amount of incident light coupled to the OPA chip, and send an instruction to at least one phase shifter to perform the adjustment. As an addition or alternative, in this example, the first and second optical signals have a wavelength separation of 100 GHz or higher.

[0007] Other aspects of the present disclosure provide a method for performing wavefront correction for optical communication. The method includes receiving an incident optical communication beam in an optical phased array on a photonic integrated chip in a communication system; receiving a first beam portion and a second beam portion of the incident optical communication beam in a combiner of the photonic integrated chip; coupling the first beam portion and the second beam portion into an output beam in the combiner; outputting a first output beam portion from the combiner toward an edge coupler of the photonic integrated chip, wherein 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, wherein the second output beam portion is an out-of-phase portion of the output beam; detecting a measurement of the second output beam portion from the photodetector by one or more processors of the communication system; determining a wavefront error of the incident optical communication beam based on the measurement by one or more processors; and adjusting at least one phase shifter of the communication system based on the determined wavefront error by one or more processors.

[0008] In one example, determining the wavefront error includes determining the relative phase difference based on measurements. In another example, the method also includes transmitting an outgoing optical communication beam using a photonic integrated chip and at least one tuned phase shifter by one or more processors. In this example, the detection of measurements, determination of the wavefront error, and tuning of at least one phase shifter include a feedback loop. Further in this example, the method also includes tracking changes in the incident optical communication beam using the feedback loop. In yet another example, tuning of at least one phase shifter includes increasing the in-phase portion of the output beam and decreasing the out-of-phase portion of the output beam in a combiner. [Brief explanation of the drawing]

[0009] [Figure 1] This is a block diagram of a first communication device and a second communication device according to an aspect of the present disclosure. [Figure 2A] This is a diagram of a phase shifter architecture according to an aspect of the present disclosure. [Figure 2B] This is a diagram of an optical phased array architecture according to an aspect of the present disclosure. [Figure 3] This is a diagram of the network according to the manner of disclosure. [Figure 4] This is a flowchart according to the aspects of this disclosure. [Modes for carrying out the invention]

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

[0011] An 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, an OPA chip. The waveguides gradually merge between the emitters and edge couplers connecting to other transmitter and / or receiver components. In particular, the waveguide configuration can combine two waveguides at each stage, meaning that the number of waveguides is reduced by half for each consecutive stage closer to the edge coupler. The merging points may be nodes, and combiners may be present at each node. The combiners may be 2x2 multimode interference (MMI) or directional couplers.

[0012] The microlens array may consist 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 remove side lobes in the signal for the back-pass beam as well as receiver angle reception. Each microlens typically has a diameter and height of tens to hundreds of micrometers. Furthermore, each microlens may be manufactured by directly molding, printing, or etching the lens onto the wafer. Integrating the microlens array allows for a reduction in the grating emitter size and an increase in the pitch between emitters. In this way, two-dimensional waveguide routing in this architecture can be better suited to a single-layer optical phased array.

[0013] The emitter may be configured to generate 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 the microlens array. The phase profile may differ from the flat profile of a conventional grating emitter, and the intensity profile may differ from the Gaussian-shaped intensity profile of a conventional grating emitter.

[0014] At least some components of the OPA architecture may be placed within silicon nitride (SiN) to support higher power in the transmitted signal. SiN has a higher optical power nonlinear threshold than conventionally used silicon-on-insulator (SOI). SiN fits into standard casting processes and provides low attenuation for wavelengths between visible and infrared. Due to its large bandgap, SiN is unaffected by two-photon absorption, which limits the maximum power of silicon. This architecture allows multi-watt transmit power to be injected into the OPA chip, which is then focused through the waveguide configuration. As the transmitted signal branches toward the emitter within the waveguide configuration, the power in each branch of the stage closest to the emitter can be reduced to below the two-photon absorption limit of the SOI. The branches of the transmitted signal can be adiabatically coupled to the emitter in the SOI layer. In some implementations, part of the waveguide configuration may be placed within the SOI layer.

[0015] In some of the nodes, combiners are located at each node in the receiving path for the incident light beam, such 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 receiving path or to other receiver components. The number of combiners with photodetectors can be selected based on an algorithm for any number between a single photodetector in the final combined signal at the edge coupler and photodetectors at each node along the waveguide tree. The first output can transmit the out-of-phase portion, i.e., the first portion, of the incident light beam, and the second output can transmit the in-phase portion, i.e., the second portion, of the incident light beam. Therefore, if no light is emitted from one port, it can be determined that all the light from the incident beam is being output from the other port.

[0016] A photodetector may be configured to measure the amount of light in a first portion of an incident light beam received from a first output. The amount of light in the first output port may include a portion of light from a first input port and a portion of light from a second input port. For example, the amount of light may include a first light beam, which is a scaled value of the signal at the first input port, and a second light beam, which 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 of 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 amplitudes of the generated first signal and the generated second signal may be summed to determine the magnitude or intensity of the first portion. For example, the square of the amplitude of the sum of the first and second signals can be measured by the photodetector.

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

[0018] The transmit and receive signals used by the terminal may be configured to have frequency separation. Frequency separation improves the separation between the transmit and receive signals, which may pass through the terminal simultaneously and potentially through free space. Since the waveguides for the transmit and receive signals may be identical and the path lengths in the waveguide tree may be designed to be approximately identical, the frequency separation can be chosen to be as large as possible while ensuring that the terminal components have the same effect on both signals. In some examples, optical separation may be provided by a circulator. In some further examples, optical separation may also be provided by using one waveguide for the transmit path and another waveguide for the receive path along parts of the terminal, such as between a circulator and a light source or sensor. Filters may be present in or near the circulator to further increase the separation between the transmit and receive signals. In one example, the frequency separation may be about 100 GHz or higher.

[0019] Overall, this OPA design for optical communication terminals can enable faster and more precise alignment adjustments, which can increase the amount of light transmitted along the optical link. The materials and design of the OPA 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 optical communication terminals. The reduction in complexity and components can also reduce errors or wear and increase the lifespan of the system.

[0020] System example Figure 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 communication (FSOC) system. Figures 2A and 2B are illustrative system architecture diagrams of the first communication device of Figure 1. For example, the first communication device 102 includes one or more processors 104, a 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] One or more processors 104 may be any conventional processor(s), such as a commercially available CPU. Alternatively, 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). Figure 1 functionally shows one or more processors 104 and memory 106 in the same block, such as the modem 202 for digital signal processing shown in Figure 2A; however, one or more processors 104 and memory 106 may actually comprise multiple processors and memory, which may or may not be housed in the same physical housing, such as both the modem 202 and a separate processing unit 203. Thus, references to processors or computers should be understood to include references to a collection of processors or computers or memories, which may or may not operate in parallel.

[0022] Memory 106 may store information accessible by one or more processors 104, including data 108 and instructions 110 that may be executed by one or more processors 104. The memory may be any type of memory capable of storing information accessible by a processor, including a hard drive, memory card, ROM, RAM, DVD, or other optical disk, as well as other writable and read-only memories. The system and method may include any of the above combinations, whereby various portions of data 108 and instructions 110 are stored on various types of media. The memory of each communication device, such as memory 106, may store calibration information, such as one or more offsets determined to track signals.

[0023] Data 108 may be retrieved, stored, or modified by one or more processors 104 according to instructions 11Q. For example, although the system and method are not limited by any particular data structure, data 108 may be stored in a computer register of a relational database as a table having a plurality of different 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. As a further mere example, 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 rendering the graphics. Data 108 may include any information sufficient to identify related information, such as numbers, descriptive text, proprietary codes, references to other data stored in the same or different memory (including other network locations), or information used by a function to calculate related data.

[0024] Command 110 can be any set of instructions (such as machine code) directly executed by one or more processors 104 or instructions (such as scripts) indirectly executed. For example, command 110 may be stored as computer code on a computer-readable medium. In this regard, the terms "instruction" and "program" may be used interchangeably herein. Command 110 may be stored in object code form for direct processing by one or more processors 104, or may include a script or collection of independent source code modules that are interpreted on demand or pre-compiled, and may be stored in any other computer language. The functions, methods, and routines of command 110 will be described in more detail below.

[0025] One or more processors 104 may communicate with transceiver 112. Transceiver 112 can include a transmitter component and a receiver component on one or more photonic integrated chips. As shown in FIG. 2A, one or more processors within modem 202 may communicate with transceiver chip 112 and are configured to receive and process an incident optical signal and transmit an optical signal. Transceiver chip 112 may include one or more transmitter components and one or more receiver components. Thus, one or more processors 104 may be configured to transmit data with a signal via the transmitter component and may also be configured to receive communication and data with a signal via the receiver component. The received signal may be processed by one or more processors 104 to extract communication and data.

[0026] The transmitter components may 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 resides 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 electrical signal applied directly to the seed laser 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 can 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 attenuators such as a variable optical attenuator 206, amplifiers such as a semiconductor optical amplifier 208, or filters.

[0028] One or more processors 104 may communicate with an optical phased array chip 114. The OPA chip 114 receives light from the transmitter components and outputs the light as a coherent communication beam that is received by a telecommunication 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 the receiver components.

[0029] The OPA chip 114 may include a plurality of array elements 120 or emitters and a plurality of phase shifters 121. Multiple microlenses can be arranged on the plurality of array elements 120 to focus incident light and collimate outgoing light. Each microlens in the array may be a convex lens that focuses light onto the corresponding emitter. In addition, each microlens may be shaped to remove 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 plurality of array elements 120 may be arranged in a grid pattern with a consistent pitch or distance between adjacent elements. In some examples, the plurality of array elements 120 may be grid emitters having a grid pattern. For example, the grid pattern may be a 32×32 grid with a pitch of 100 microns. In other examples, the array elements 120 may be different arrangements having different numbers of rows and columns, different shapes, and / or different pitches (consistent or inconsistent). The phase shifter 121 changes the incident and outgoing light in the array element 120. The incident light is supplied to the receiver component, and the outgoing light is supplied to the array element 120. As shown in Figure 2B, the architecture of multiple phase shifters 121 includes at least one layer of phase shifters. The first layer of phase shifters may include one phase shifter connected to each array element in the multiple array elements 120. For a 32×32 grid array element, 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 may 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 incident light beam and direct the outgoing light beam to each array element, and an edge coupler that couples the incident light beam between the OPA chip and a single-mode waveguide. The single-mode waveguide can then direct the beam to the transceiver 112. If the grid pattern of the multiple array elements 120 is a 32×32 grid, there are 1024 incident beam portions that are merged into a single output beam. The incident beam portions may be joined in a number of 2, or an H-tree, or more, until a single output beam is formed. When using an H-tree configuration, there are 10 layers of combiners, and the layers include the following numbers of combiners, starting closest to the array elements and ending closest to the edge coupler: 512, 256, 128, 64, 32, 16, 8, 4, 2, and 1.

[0031] One or more combiners may be 2x2 MMIs or directional couplers. 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 the input of another combiner or edge coupler. With respect to 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] Figure 2B shows a sample portion of an OPA architecture with features described herein. For example, the 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 shown in Figure 2B can 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 which may also include combiners, and its final layer may be connected to a plurality of phase shifters 121.

[0033] In the portion shown in Figure 2B, the first input of combiner 230 may be connected to phase shifter 121A. The second input of combiner 230 may be connected to phase shifter 121B. The third input of combiner 232 may be connected to phase shifter 121C, and the 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 combiner 234 may have two outputs, one of which may be connected to a photodetector, while combiners 230 and 232 have only one output connected to combiner 234. The edge coupler 236 can direct the coupled incident light beam to a single-mode waveguide leading to other receiver components. In some examples, the single-mode waveguide leads to a circulator that provides separation of the incident light from any outgoing light.

[0034] With respect to 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 the magnitude of the received light, such as the first portion of the output beam, and to provide a signal indicating the magnitude of the received light to one or more processors 104 of the communication device 102. In this way, the sensed magnitude may be used by one or more processors to generate an estimated angle of arrival and provide it to one or more processors 104, such as one in the processing unit 203.

[0035] The components within the OPA chip may be arranged on a combination of silicon (Si) and silicon nitride (SiN), such as a silicon-on-insulator (SOI). A first set of components, including an edge coupler and closer to the edge coupler, may be arranged on SiN, while a second set of components, including multiple array elements and closer to the multiple array elements, may be arranged on Si. As shown in Figure 2B, the edge coupler 236 and combiners 230, 232, and 234 may be arranged on SiN, as indicated by the stippling shading. Multiple array elements 120 and multiple phase shifters 121 may be arranged on Si, as indicated by the unstippled fills.

[0036] The system may include additional components to support the functionality of a communication 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 section, an eyepiece section, or a relay section. As shown in Figure 2A, the system may include an objective lens 210, an eyepiece lens 212, and relay lenses 214, 216. The system may include a circulator, such as a single-mode circulator 218, which routes the incident and outgoing light while keeping them on at least partially separate paths. The system may include one or more sensors 220 for detecting environmental features and / or measurements of system components. The system may include one or more steering mechanisms, such as one or more bias means for controlling one or more phase shifters, which may be part of the OPA chip 114, and / or actuated / steering mirrors 222, such as high-speed / fine pointing mirrors. 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 one in the processing unit 203, may be configured to receive and process signals from one or more sensors 220, a transceiver 112, and / or an OPA chip 114, and to control one or more steering mechanisms to adjust the pointing direction and / or wavefront shape, which will be described in more detail below. The system also includes optical fibers or waveguides that connect the optical components and create paths between the seed laser 116 and the OPA chip 114 and between the OPA chip 114 and the photodiode 118.

[0037] As shown in Figure 1, the first communication device 102 can output an optical beam 20a directed towards the second communication device 122.

[0038] Similarly, the second communication device 122 includes one or more processors 124, a memory 126, a transceiver 132, and an OPA chip 134. The one or more processors 124 may be the same as 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 processors 124. The memory 126, data 128, and instructions 130 may be configured similarly to the memory 106, data 108, and instructions 110 described above. In addition, 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 similarly 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 attenuators such as variable optical attenuators, amplifiers such as semiconductor optical amplifiers, or filters. The OPA chip 114 may include a plurality of array elements 140 and a plurality of phase shifters 141, which may be similar to array elements 120 and phase shifter 121, respectively. Similar to the additional components described above, additional components to support the functionality of the communication device 122 may be included. The communication device 122 may have the same or a similar system architecture as the system architecture shown in Figure 2.

[0039] As shown in Figure 1, the second communication device 122 can output an optical beam 20b directed towards the first communication device 102 that receives the optical beam 20b.

[0040] As shown in Figure 1, when the transceivers of the first and second communication devices are aligned, a communication link 22 can be formed between the first communication device 102 and the second communication device 122. Alignment can be determined by using optical beams 20a and 20b to determine when a line of sight is established between the communication devices 102 and 122. Using the communication link 22, one or more processors 104 can transmit communication signals to the second communication device 122 via free space using optical beam 20a, and one or more processors 124 can transmit communication signals to the first communication device 102 via free space using optical beam 20b. The communication link 22 between the first communication device 102 and the second communication device 122 enables bidirectional transmission of data between the two devices. In particular, 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 that can travel through free space.

[0041] As shown in Figure 3, the network 300 may be configured to form a network 200 by forming multiple communication links (indicated by arrows) between multiple communication devices, such as a first communication device 102 and a second communication device 122, and multiple communication terminals. 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 may form at least one communication link with another communication device, as indicated by the arrows. The communication links may be for optical frequencies, radio frequencies, other frequencies, or combinations of different frequency bands. In Figure 3, communication device 102 is shown having communication links with client device 310 and communication devices 122, 320, and 322. Communication device 122 is shown to have communication links with communication devices 102, 320, 322, and 324.

[0042] The network 300 shown in Figure 3 is merely illustrative, and in some implementations, the network 300 may include additional or different communication terminals. The network 300 may be a ground network where multiple communication devices rest on multiple ground communication terminals. In other implementations, the network 300 may include one or more high-altitude platforms (HAPs), which may be balloons, small airships, or other airships, airplanes, unmanned aerial vehicles (UAVs), satellites, or any other form of high-altitude platform or other types of mobile or fixed communication terminals. In some implementations, the network 300 may function 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 a larger computer network.

[0043] Example of a method During operation, one or more processors 104 can perform wavefront sensing and / or correction for optical communication. Figure 4 shows a flow chart 400 according to some of the embodiments described above, which may be performed by one or more processors 104 of the first communication device 102. In addition or alternatively, one or more processors 124 of the second communication device 122 may perform one or more steps of the flow chart 400. Figure 4 shows the blocks in a specific order, but the order may be changed, and multiple operations may be performed simultaneously. Operations may also be added or omitted.

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

[0045] In block 404, the first beam portion and the second beam portion of the incident optical communication beam may be received by a combiner of the photonic integrated chip. The combiner may have two inputs and two outputs. For example, the combiner may be a 2×2MMI such as one or more of the combiners 230, 232, and 234 of OPA114. The first beam portion may be received at the first input of the combiner, and the second beam portion may be received at the second input of the combiner. Using combiner 230 in Figure 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 coupled to an output beam in the combiner.

[0046] In block 408, a first output beam portion may be output from the combiner toward the edge coupler of the photonic integrated chip. The first output beam portion may be the in-phase portion of the output beam. In block 410, a second output beam portion may be output from the combiner toward the photodetector. The second output beam portion may be the 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 the example using combiner 230, the first output beam portion may be transmitted from the first output to combiner 234, and the second output beam may be transmitted from the second output to the photodetector 240.

[0047] In block 412, a measurement of a second output beam portion from a photodetector may be detected by one or more processors of the communication system. The photodetector may be configured to detect 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 of 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 amplitudes of the generated first signal and 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 square of the amplitude 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 for calculating the wavefront and input angle of arrival. For example, one or more processors 104 of the communication device 102 may detect a magnitude or intensity measurement of the second output beam portion from the photodetector 240.

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

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

[0050] In other implementations, one or more processors may, additionally or alternatively, adjust the wavefront or Poynting direction based on the determined wavefront error. The wavefront and / or Poynting 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-scale low-frequency adjustments, while steering using multiple phase shifters may be for smaller-scale high-frequency adjustments. For example, one or more processors 104 may adjust the wavefront and / or Poynting direction of the communication device 102 based on the determined wavefront error. Mechanical steering may include controlling a steering mirror 222. Electronic steering may include controlling multiple phase shifters 121.

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

[0052] The features described herein, by implementing integrated photonic chips, can provide a more cost-effective and accurate communication system. The single-path transceiver design of this system-mode system allows for less complexity and the use of less expensive components. Furthermore, this design also 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 directly connected to the communication beam, rather than a branched beam.

[0053] Unless otherwise specified, the aforementioned alternatives are not mutually exclusive and can be implemented in various combinations to achieve their own advantages. These and other variations and combinations of the above features can be used without departing from the subject matter defined by the claims, and the foregoing description of embodiments should be interpreted as illustrative rather than as an limitation of the subject matter defined by the claims. Furthermore, the provision of examples described herein, and expressions such as “etc.” and “including,” should not be interpreted as limiting the subject matter of the claims to specific examples, but rather these examples are intended to illustrate only one of many possible embodiments. Furthermore, the same reference numerals in different drawings may identify identical or similar elements.

Claims

1. Optical phased array (OPA) photonic integrated chip, Multiple array elements, A plurality of phase shifters including a layer of phase shifters having a phase shifter connected to each array element within 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, wherein the plurality of combiners are Includes a second combiner or a first combiner having a first output connected to the edge coupler, The second output of the first combiner is connected to a photodetector. A plurality of combiners, wherein the in-phase light portion of the first combiner is output through the first output, and the out-of-phase light portion of the first combiner is output through the second output, The edge coupler configured to couple to the single-mode waveguide, A photonic phased array (OPA) photonic integrated chip equipped with this technology.

2. The OPA chip according to claim 1, wherein the plurality of array elements include a lattice emitter.

3. The OPA chip according to claim 1, wherein the plurality of array elements are arranged in a 32 x 32 grid array.

4. The OPA chip according to claim 1, wherein the plurality of combiners include at least one 2x2 multimode interferometer (MMI).

5. The OPA chip according to claim 1, wherein the plurality of combiners include at least one directional coupler.

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

7. The OPA chip according to claim 1, wherein the plurality of combiners include two or more combiners having outputs connected to a photodetector.

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

9. The OPA chip according to claim 8, wherein a first set of the plurality of combiners is arranged in silicon, and a second set of the plurality of combiners is arranged in silicon nitride.

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

11. An optical communication system comprising the OPA chip described in claim 1.

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

13. The one or more processors described above A signal is received from the aforementioned photodetector, In order to increase the amount of incident light coupled to the OPA chip, an adjustment is determined for at least one of the multiple phase shifters. The system according to claim 12, configured to transmit a command to the at least one phase shifter to perform the adjustment.

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

15. A method for performing wavefront correction for optical communication, wherein the method is In a photonic integrated chip within a communication system, the process involves receiving an incident optical communication beam in an optical phased array. In the combiner of the photonic integrated chip, the first beam portion and the second beam portion of the incident optical communication beam are received, In the combiner, the first beam portion and the second beam portion are coupled to the output beam, The combiner outputs a first output beam portion toward the edge coupler of the photonic integrated chip, wherein the first output beam portion is the in-phase portion of the output beam. The combiner outputs a second output beam portion to a photodetector, wherein the second output beam portion is a phase-different portion of the output beam. One or more processors of the communication system detect the measurement of the second output beam portion from the photodetector, The one or more processors determine the wavefront error of the incident optical communication beam based on the measurement, The one or more processors adjust at least one phase shifter of the communication system based on the determined wavefront error, Methods that include...

16. The method according to claim 15, wherein the determination of the wavefront error includes determining the relative phase difference based on the measurement.

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

18. The method according to claim 17, wherein the detection of the measurement, the determination of the wavefront error, and the adjustment of the at least one phase shifter include a feedback loop.

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

20. The method according to claim 15, wherein the adjustment of the at least one phase shifter includes increasing the in-phase portion of the output beam and decreasing the out-of-phase portion of the output beam in the combiner.

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