Diversity receiving photon chip for space optical communication

Abstract

The invention discloses a diversity receiving photon chip for space optical communication, solves the problem of high power consumption when the influence caused by phase distortion and light beam pointing error is corrected in the existing free space optical communication, and belongs to the field of optical communication. The system comprises a grating array, an MZI network and a control circuit. The grating array is a combination of a plurality of densely-arranged gratings, and the input light source adopts a lens to converge input spatial light which enters the grating array at a set angle; according to the grating design, the high duty ratio can be achieved, and meanwhile optical signal coupling between gratings, between the grating and the transmission waveguide and between the transmission waveguides is avoided, so that the receiving efficiency and the receiving signal quality are prevented from being reduced. The grating array transmits the received light to the waveguides connected with the gratings and accesses the MZI network through the waveguides, the MZI network is used for realizing optical coherent beam combination, and the control circuit controls the combination of light beams in the MZI network.

Description

Technical Field

[0001] The invention relates to a diversity receiving photon chip for space optical communication, belonging to the fields of optoelectronics, integrated optics and optical communication. Background Art

[0002] Free Space Optical Communication (FSOC) is considered as one of the alternative technologies to meet the growing demand for high data transmission. FSOC uses optical signals as carriers to transmit information. When light propagates in the atmosphere, the air is affected by wind and solar heat, resulting in uneven temperature and pressure distribution of the air, causing random refractive index fluctuations. Changes in the refractive index and propagation path of the light beam in the air may cause random fluctuations in the amplitude and phase of the received signal, resulting in wavefront phase distortion and reduced beam coherence. Under the influence of atmospheric turbulence, the laser will produce light intensity flicker and beam drift after passing through the atmosphere, thereby reducing the optical power that can be detected on the receiving detector. This directly affects the quality and communication distance of communication. In addition, the errors in beam aiming and tracking, combined with the pointing errors caused by the optical adjustment accuracy and the arrival angle fluctuations caused by turbulence, will also cause fluctuations in the received optical power. Therefore, how to compensate for the effects of atmospheric turbulence and pointing errors has become an important issue in free space optical communication.

[0003] In order to correct the effects of phase distortion and beam pointing errors, existing methods include multi-aperture reception or multi-mode reception followed by mode decomposition. The above process is generally completed through multiple receiving antennas and multiple detectors, which is difficult to deploy and the system is bulky; and subsequent signal processing often requires high-power digital signal processing. The above factors are not conducive to the lightweight, integrated and low-power realization of the receiving system. Summary of the invention

[0004] Aiming at the problem of high power consumption when correcting the effects of phase distortion and beam pointing error in existing free-space optical communications, the present invention provides a diversity receiving photonic chip for space optical communications.

[0005] A diversity receiving photonic chip for space optical communication of the present invention comprises a grating array, an MZI network and a control circuit;

[0006] The grating array is a combination of several densely arranged gratings. The input light source uses a lens to converge the input spatial light and enter the grating array at a set angle.

[0007] The grating array transmits the received light to the waveguide connected to each grating, and accesses the MZI network through the waveguide. The MZI network is used to realize optical coherent beam combining, and the control circuit controls the merging of light beams in the MZI network.

[0008] Preferably, the grating array is a two-layer grating array, wherein the first layer of grating is made of silicon nitride material, the second layer of grating is made of silicon material, and the waveguide of the first layer of grating is coupled into the waveguide of the second layer of grating through a mode converter.

[0009] Preferably, each layer of the grating array includes three levels, and the number of gratings in the three levels are 3, 4, and 3 respectively.

[0010] Preferably, the MZI network comprises a plurality of MZI units, each of which comprises two 50:50 beam splitters and two phase shifters;

[0011] Each 50:50 beam splitter has two inputs and two outputs;

[0012] Each MZI unit has two inputs and two outputs. The input of phase shifter No. 1 and one input of 50:50 beam splitter No. 1 serve as the two inputs of the MZI unit. The output of phase shifter No. 1 enters the other input of 50:50 beam splitter No. 1. The two outputs of 50:50 beam splitter No. 1 enter the input of phase shifter No. 2 and one input of 50:50 beam splitter No. 2 respectively. The output of phase shifter No. 2 enters the other input of 50:50 beam splitter No. 2. The two outputs of 50:50 beam splitter No. 2 serve as the two outputs of the MZI unit.

[0013] Several MZI units are combined for input and output so that multiple beam inputs can be combined into one or more outputs to form an MZI network.

[0014] Preferably, the 50:50 beam splitter is a directional coupler or a multimode interferometer.

[0015] Preferably, the MZI network comprises several stages, the number of MZI units in the latter stage is half of the MZI units in the previous stage, one output of each of the two MZI units in the previous stage is respectively connected to the two inputs of an MZI unit in the latter stage, the other output of the MZI unit in the previous stage is connected to a photodetector, and the last stage is one MZI unit.

[0016] Preferably, the control circuit changes the voltage applied to the phase shifter in the MZI network, and when the signal detected by the photodetector in each stage reaches a minimum value, it is determined that the coherent combination of the light beams in each stage has been completed.

[0017] Preferably, the voltage applied to each phase shifter in the MZI network is determined by a gradient descent method or a hill climbing method.

[0018] The present application also provides an MZI network, which includes several stages, the number of MZI units in the odd-numbered stages is the same, and the number of MZI units in the even-numbered stages is one less than the number of MZI units in the odd-numbered stages; one output of each of the two MZI units in the odd-numbered stages is respectively connected to two inputs of an MZI unit in the next even-numbered stage, and the output of the MZI unit in the odd-numbered stage that is not connected to the next even-numbered stage is connected to the input of the MZI unit in the next odd-numbered stage.

[0019] Preferably, a training set is constructed, including the input and output of the MZI network, and the MZI network is trained using the training set to determine the voltage magnitude of each phase shifter in the MZI network.

[0020] Beneficial effects of the present invention:

[0021] High integration and miniaturization: Compared with traditional multi-aperture receivers, the present invention integrates the MZI network and grating array into a single chip through integrated optical technology. This highly integrated chip structure can greatly reduce the size and complexity of the system and is suitable for portable, lightweight free-space optical communication equipment.

[0022] All-optical coherent combining: Traditional free-space optical communications are limited by phase and amplitude fluctuations caused by atmospheric turbulence. This invention uses phase shifters in the MZI network to achieve coherent combining of multipath optical signals, effectively reducing the impact of atmospheric turbulence on the signal, thereby improving the system's anti-interference ability. At the same time, due to the all-optical design, the use of multiple detectors and high-power digital signal processing is avoided, thereby improving the processing efficiency of optical signals.

[0023] High stability and reliability: Based on the physical properties of photonic integrated circuits, the chip design of the present invention has excellent temperature stability and mechanical stability, is suitable for working in a complex and changeable external environment, and is not easily affected by environmental changes.

[0024] Low power consumption design: While achieving efficient reception, the present invention realizes low power consumption integrated optoelectronic device design by optimizing waveguide design and phase shifter control.

[0025] High coupling efficiency: Compared with the existing grating array design, the present invention improves the coupling efficiency of the grating array by optimizing the grating structure, arrangement, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the principle of the present invention;

[0027] Figure 2 The double-layer grating array structure of the present invention;

[0028] Figure 3is a plan view schematic diagram of a grating array of the present invention;

[0029] Figure 4 It is the principle schematic diagram of the MZI unit;

[0030] Figure 5 It is the principle diagram of MZI network;

[0031] Figure 6 It is a structural schematic diagram of the MZI unit;

[0032] Figure 7 It is a structural schematic diagram of a multi-mode interferometer MMI;

[0033] Figure 8 It is a structural diagram of the MZI network;

[0034] Fig. 9 A schematic diagram of another MZI network. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0038] The diversity receiving photonic chip for space optical communication of this embodiment is as follows: Figure 1 As shown, it includes a grating array, an MZI network, a control circuit and an output module;

[0039] The grating array is a combination of several densely arranged gratings, which are used to receive input light sources. The input light sources use lenses to converge the input spatial light and enter the grating array at a set angle. The grating design should be able to achieve a high duty cycle, and at the same time, optical signal coupling between gratings, between gratings and transmission waveguides, and between transmission waveguides should be avoided to avoid reducing the receiving efficiency and the quality of the received signal.

[0040] The grating array transmits the received light to the waveguide connected to each grating, and accesses the MZI network through the waveguide. The MZI network is used to realize optical coherent beam combining, and the control circuit controls the merging of light beams in the MZI network.

[0041] The MZI network dynamically combines the multi-path light with randomly changing intensities and phases through multiple interferences. In this way, the optical signals received by multi-mode / few-mode come from the same light source, they carry the same information, but have different amplitudes and phases. The function of the MZI network is to adjust the amplitude and phase of these input signals to achieve the function of coherent beam combining.

[0042] like Figure 2 As shown, the grating array of this embodiment is two-layer, the first layer of grating is made of silicon nitride material, and the second layer of grating is made of silicon material. The duty cycle of the single-layer grating is about 70%, while the total duty cycle of the double-layer grating can reach more than 90%, which significantly increases the light receiving area, realizes distributed coupling, and improves the receiving efficiency. In addition, silicon waveguides are prone to fluctuations in optical performance due to thermo-optical effects under high power or temperature changes. SiN has a low thermo-optical coefficient, so adding a SiN layer to the grating array can enhance the stability to ambient temperature changes. At the same time, Si may experience a two-photon absorption effect at the communication wavelength (1550nm), resulting in nonlinear losses. SiN is suitable for high-power applications because it has no two-photon absorption effect. Therefore, under high-power input, the SiN grating serves as the first-layer receiving surface to protect the Si grating from nonlinear effects.

[0043] Each layer of the grating array in this embodiment consists of three levels, such as Figure 3 As shown, the number of gratings is 3, 4, and 3, respectively, with a total of 10 gratings. Taking the silicon material grating array as an example, the grating lateral spacing is 2μm and the longitudinal spacing is 16μm. The grating array size is 63μm (lateral) × 53μm (longitudinal), and the array duty cycle is about 70%. Figure 3 The oblique line area is the waveguide layer 1, which has a thickness of 220nm. The thickness of the grating groove 2 is 150nm, and the two together form a grating network structure. After the light received by the grating array is transmitted through a waveguide that is 220nm thick, 400nm wide and 500nm long, ports 3 to 12 are output to the MZI network. Due to SOI process limitations, the grating etching depth is 70nm, the spacing between a single silicon structure should not be less than 200nm, and the width should not be less than 200nm. The grating period used here is 631nm, the duty cycle is 53.5%, and its coupling efficiency is about 30%. It is worth noting that any grating array that can achieve a tight arrangement can achieve the functions of this module without coupling between grating signals.

[0044] It is worth noting that the waveguide connected to the SiN grating needs to be coupled into the Si waveguide through a mode converter so that the subsequent MZI network can perform optical processing.

[0045] The MZI network of this embodiment includes several MZI units, such as Figure 4As shown, each MZI unit includes two 50:50 beam splitters and two phase shifters;

[0046] Each 50:50 beam splitter has two inputs and two outputs;

[0047] Each MZI unit has two inputs and two outputs. The input of phase shifter No. 1 and one input of 50:50 beam splitter No. 1 serve as the two inputs of the MZI unit. The output of phase shifter No. 1 enters the other input of 50:50 beam splitter No. 1. The two outputs of 50:50 beam splitter No. 1 enter the input of phase shifter No. 2 and one input of 50:50 beam splitter No. 2 respectively. The output of phase shifter No. 2 enters the other input of 50:50 beam splitter No. 2. The two outputs of 50:50 beam splitter No. 2 serve as the two outputs of the MZI unit.

[0048] The above-mentioned photonic chips can be based on any mature material system, including but not limited to SOI, SiN, GaAs, lithium niobate, etc. The 50:50 beam splitter can be based on a directional coupler (DC) or a multimode interferometer (MMI) coupler, and the phase shifter can utilize the thermo-optical effect, electro-optical effect or carrier injection of the material. The PD can be integrated on the chip, or the photonic chip can be connected to the off-chip PD using optical fiber. And the MZI network design is by no means limited to these two types.

[0049] By utilizing the processing characteristics of the MZI unit for light beams and cooperating with a photonic detector (PD), a corresponding MZI network can be designed so that multiple light beam inputs can be combined into one output, such as Figure 5 As shown, the MZI network includes several stages, the number of MZI units in the latter stage is half of that in the former stage, one output of each of the two MZI units in the former stage is respectively connected to the two inputs of one MZI unit in the latter stage, the other output of the MZI unit in the former stage is connected to the photodetector, and the last stage is one MZI unit. The control circuit changes the voltage applied to the phase shifter in the MZI network, and when the signal detected by the photodetector in each stage reaches the minimum value, it is determined that the coherent merging of the light beams in each stage has been completed.

[0050] Specific design:

[0051] Here is the MZI unit structure, such as Figure 6 The MZI unit is a 2-input 2-output structure, where two beams of input light are input into the MZI unit through input_1 and input_2, and the two output ends are output_1 and output_2, one of which should be connected to a PD to confirm the coherent combination.

[0052] Specifically, after the light inputted by input_1 passes through the No. 1 electrically controlled thermal phase shifter 312, it will be adjusted to be the same as input_2, or to have a phase difference of π (depending on the structure of different MMIs, this phase difference will also change accordingly), and then enter the No. 1 multi-mode interferometer 313 (Multi-Mode Interferometer, MMI) with two inputs and two outputs. This MMI is designed so that when the phase difference between the two beams is π, the light intensity at the output end is equal, and when the phase difference is an integer multiple of π / 2, the output is mainly from one end of the two arms. Therefore, when the phase difference between the two beams entering the No. 1 multi-mode interferometer 313 is an integer multiple of π, the No. 1 multi-mode interferometer 313 will divide the two beams into two outputs with the same intensity. After that, one of the optical signals enters the No. 2 electrically controlled thermal phase shifter 314, and the phase difference between it and the other arm is adjusted to an integer multiple of π / 2, and then enters the MMI of the No. 2 multi-mode interferometer for coherent merging. As mentioned above, when the output of the external PD on the output reaches the minimum value, it is considered that the coherent combining has been successfully achieved.

[0053] Specifically speaking of structural parameters, the length of thermal control phase shifter No. 1 312 is 260 μm, TiN material is used as the heating electrode, power is supplied through copper electrodes at both ends, and the vertical distance from the waveguide is 2000 nm. The structures of multi-mode interferometer No. 1 313 and multi-mode interferometer No. 2 315 are the same, as shown in FIG. Figure 7 As shown in the figure, the four arms of the multimode interferometer have the same structural parameters, with an input / output length of 30μm, a thinner end width of 500nm, and a thicker end width of 1500nm. The multimode interference region in the middle is 42.7μm long and 6μm wide. The entire MMI is etched on a silicon material with a thickness of 220nm.

[0054] The MZI network is composed of the above MZI units through a specific topological structure. Here we provide a binary tree network structure, such as Figure 8As shown. Specifically, the input optical signals 111 and 211, 311 and 411, 511 and 611, 711 and 811 enter the first-stage multimode interferometer MZI shown by number 911 respectively, and the phase is adjusted by adjusting the two phase shifters in the MZI unit to realize the function of coherent merging of the light beams in pairs, and through the electrical signal intensity output by the four integrated photodetectors (PD), this embodiment can know whether the coherent merging of the light beams is completed. Specifically, when the PD output reaches the minimum value, this embodiment considers that the light beam is output to the other output end of the MZI unit, realizing the coherent merging function of this level, and at the same time, the output of the MZI network of this level exists as the input of the MZI network of the next level. Through the three-level MZI network of the first level 911, the second level 112, and the third level 132, and the PD detection output of the first layer 101, the second layer 122, and the third layer 142, this embodiment can realize the function of coherently merging 8 input signals into one output signal.

[0055] The combined effect of the MZI network is identified and controlled by the control circuit of this embodiment. Specifically, the phase shift size is adjusted by adjusting the voltage applied by the thermally controlled phase shifter of the MZI. Figure 8 For the MZI network shown, a power of 60mW can achieve a phase shift of 0 to 2π. As for the judgment of the MZI effect, this embodiment is achieved by monitoring the output voltage of the PD. When the PD output voltage reaches the minimum value, the coherent combining effect is achieved. Specifically, by changing the voltage applied to the phase shifter, the corresponding PD output is obtained, and through a specific algorithm, such as the gradient descent method or the hill climbing method, the function of finding the minimum value of the PD output can be realized.

[0056] This embodiment also provides an MZI network, such as Fig. 9 As shown, the MZI network includes several stages, the number of MZI units in the odd-numbered stages is the same, and the number of MZI units in the even-numbered stages is one less than the number of MZI units in the odd-numbered stages; one output of each of the two MZI units in the odd-numbered stages is respectively connected to the two inputs of an MZI unit in the next even-numbered stage, and the output of the MZI unit in the odd-numbered stage that is not connected to the next even-numbered stage is connected to the input of the MZI unit in the next odd-numbered stage. This MZI network can be used as an optical neural network, and the light output by the grating array and the light output by the diversity receiving photonic chip for space optical communication are used to form a training set. The optical neural network is trained using the training set to determine the voltage size of each phase shifter in each MZI network, and the optical neural network finally obtained can realize optical coherent beam combining.

[0057] This embodiment is based on the design of a spatial light combining chip with grating array input. The received light signal adopts optical coherence combining to avoid photoelectric conversion and digital signal processing to circumvent the efficiency and frequency problems caused by them. In order to solve the problem of low coupling efficiency of traditional grating arrays, this embodiment improves the grating design, reduces the area of ​​a single grating, adopts a special grating shape, and adopts a double-layer grating structure to increase the light receiving area and improve the coupling efficiency. This embodiment adopts an integrated design, and all optical devices are integrated on an optical chip through micro-nano technology, which greatly reduces the required space. In addition, thanks to the existing packaging technology, the input and output of the chip do not require a complicated assembly process, which improves the stability and reliability of the system.

[0058] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that features described in conjunction with individual embodiments may be used in other described embodiments.

Claims

1. A diversity receiving photonic chip for space optical communication, characterized in that: Includes grating array, MZI network and control circuit; The grating array is a combination of several densely arranged gratings. The input light source uses a lens to converge the input spatial light and enter the grating array at a set angle. The grating array transmits the received light to the waveguide connected to each grating, and accesses the MZI network through the waveguide. The MZI network is used to realize optical coherent beam combining, and the control circuit controls the merging of light beams in the MZI network.

2. The diversity receiving photonic chip for spatial optical communication according to claim 1, characterized in that: The grating array is a two-layer grating array, wherein the first layer of grating is made of silicon nitride material, the second layer of grating is made of silicon material, and the waveguide of the first layer of grating is coupled into the waveguide of the second layer of grating through a mode converter.

3. The diversity receiving photonic chip for spatial optical communication according to claim 2, characterized in that: Each layer of the grating array includes three levels, and the number of gratings in the three levels are 3, 4, and 3 respectively.

4. The diversity receiving photonic chip for spatial optical communication according to claim 1, characterized in that: The MZI network includes several MZI units, each of which includes two 50:50 beam splitters and two phase shifters; Each 50:50 beam splitter has two inputs and two outputs; Each MZI unit has two inputs and two outputs. The input of phase shifter No. 1 and one input of 50:50 beam splitter No. 1 serve as the two inputs of the MZI unit. The output of phase shifter No. 1 enters the other input of 50:50 beam splitter No.

1. The two outputs of 50:50 beam splitter No. 1 enter the input of phase shifter No. 2 and one input of 50:50 beam splitter No. 2 respectively. The output of phase shifter No. 2 enters the other input of 50:50 beam splitter No.

2. The two outputs of 50:50 beam splitter No. 2 serve as the two outputs of the MZI unit. Several MZI units are combined for input and output so that multiple beam inputs can be combined into one or more outputs to form an MZI network.

5. The diversity receiving photonic chip for spatial optical communication according to claim 4, characterized in that: The 50:50 beam splitter is a directional coupler or a multimode interferometer.

6. The diversity receiving photonic chip for spatial optical communication according to claim 4, characterized in that: The MZI network includes several stages. The number of MZI units in the latter stage is half of that in the former stage. One output of each of the two MZI units in the former stage is connected to two inputs of an MZI unit in the latter stage respectively. The other output of the MZI unit in the former stage is connected to a photodetector. The last stage is one MZI unit.

7. The diversity receiving photonic chip for spatial optical communication according to claim 6, characterized in that: The control circuit changes the voltage applied to the phase shifter in the MZI network. When the signal detected by the photodetector in each stage reaches a minimum value, it is determined that the coherent combination of the light beams in each stage has been completed.

8. The diversity receiving photonic chip for spatial optical communication according to claim 7, characterized in that: The voltage applied to each phase shifter in the MZI network is determined by a gradient descent method or a hill climbing method.

9. The diversity receiving photonic chip for spatial optical communication according to claim 4, characterized in that: The MZI network includes several stages, the number of MZI units in the odd-numbered stages is the same, and the number of MZI units in the even-numbered stages is one less than the number of MZI units in the odd-numbered stages; one output of each of the two MZI units in the odd-numbered stages is respectively connected to two inputs of an MZI unit in the next even-numbered stage, and the output of the MZI unit in the odd-numbered stage that is not connected to the next even-numbered stage is connected to the input of the MZI unit in the next odd-numbered stage.

10. The diversity receiving photonic chip for spatial optical communication according to claim 9, characterized in that: A training set is constructed, including the input and output of the MZI network, and the MZI network is trained using the training set to determine the voltage magnitude of each phase shifter in the MZI network.

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