Integrated optical diversity receiving device

Abstract

The invention discloses an integrated optical diversity receiving device, 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 method comprises the steps that free space light focused by a lens is received by a multimode / few-mode optical fiber; the multi-mode light beams received by the multimode / few-mode optical fiber enter the photon lantern; the photon lantern is coupled to the single-mode fiber array after mode demultiplexing; each light beam in the single-mode fiber array enters a polarization beam splitting rotary combiner through an edge coupler; the polarization beam splitting rotation combiner performs transverse electric wave (TE) and transverse magnetic wave (TM) mode separation on the entered light beam, then rotates the separated TM polarization state light to a TE polarization state, combines the rotated TE polarization state light and the separated TE polarization state light, and then enters the MZI network; the MZI network is used for realizing optical coherent beam combination; a control circuit controls the merging of the light beams in the MZI network.

Description

Technical Field

[0001] The invention relates to an integrated optical diversity receiving device based on a photon lantern and an integrated optical chip, and belongs to the fields of optoelectronics, integrated optics and optical communications. 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 very difficult to configure and the system is bulky. Subsequent signal processing often requires high-power digital signal processing. Summary of the invention

[0004] In view of 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 an integrated optical diversity receiving device based on a photon lantern and an integrated optical chip.

[0005] An integrated optical diversity receiving device of the present invention comprises a multi-mode / few-mode optical fiber, a photon lantern, a single-mode optical fiber array, an MZI network, a control circuit, N groups of edge couplers and a polarization beam splitter rotation combiner, wherein N is the number of light beams in the single-mode optical fiber array;

[0006] The free-space light focused by the lens is received by the multimode / few-mode fiber;

[0007] The beams of multiple modes received by the multimode / fewmode fiber enter the photon lantern;

[0008] The photon lanterns are mode demultiplexed and coupled into a single-mode fiber array;

[0009] Each beam in the single-mode fiber array enters a polarization splitter and rotation combiner through an edge coupler;

[0010] The polarization beam splitter and rotation combiner is used to separate the incoming light beam into transverse electric wave TE and transverse magnetic wave TM modes, and then rotate the separated transverse magnetic wave TM polarization state light to the transverse electric wave TE polarization state. The rotated transverse electric wave TE polarization state light is combined with the separated TE polarization state light and then enters the MZI network;

[0011] MZI networks are used to achieve optical coherent beam combining;

[0012] The control circuit controls the merging of the light beams in the MZI network.

[0013] Preferably, the polarization beam splitter, rotator and combiner comprises a polarization beam splitter, a polarization rotator and an MZI unit;

[0014] Polarization beam splitter, used to separate the incoming light beam into transverse electric wave TE and transverse magnetic wave TM modes;

[0015] A polarization rotator, used for rotating the separated transverse magnetic wave TM polarization state light into a transverse electric wave TE polarization state;

[0016] The rotated transverse electric wave TE polarization state light and the separated TE polarization state light enter the MZI unit, and the MZI unit is used to perform optical coherence combination on the two incoming light beams and then enter the MZI network.

[0017] Preferably, the MZI network comprises a plurality of MZI units, each of which comprises two 50:50 beam splitters and two phase shifters;

[0018] Each 50:50 beam splitter has two inputs and two outputs;

[0019] 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.

[0020] 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.

[0021] Preferably, the 50:50 beam splitter is a directional coupler or a multimode interferometer.

[0022] 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.

[0023] 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.

[0024] Preferably, the voltage applied to each phase shifter in the MZI network is determined by a gradient descent method or a hill climbing method.

[0025] This embodiment 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.

[0026] 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.

[0027] Beneficial effects of the present invention:

[0028] High integration and miniaturization: Compared with traditional multi-aperture receivers, the present invention integrates edge couplers, polarization beam splitter rotation combiners, MZI networks and transmission waveguides 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.

[0029] 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.

[0030] 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.

[0031] Low power consumption design: While achieving efficient reception, the present invention realizes low power consumption integrated optoelectronic device design by optimizing optical chip and phase shifter control.

[0032] High coupling efficiency: Multi-mode / few-mode optical fiber is used as the spatial light receiving end, which has a large receiving area and high coupling efficiency, thereby increasing the receiving sensitivity of the laser communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the principle of the present invention;

[0034] Figure 2 It is a schematic diagram of the principle of the input part of the present invention;

[0035] Figure 3 It is a schematic diagram of the principle of the polarization beam splitter and rotation combiner of the present invention;

[0036] Figure 4 It is a schematic diagram of the working principle of the polarization beam splitter of the present invention;

[0037] Figure 5 It is a schematic diagram of the working principle of the polarization rotator of the present invention;

[0038] Figure 6 It is the principle schematic diagram of the MZI unit;

[0039] Figure 7 It is the principle diagram of MZI network;

[0040] Figure 8 It is a structural schematic diagram of the MZI unit;

[0041] Fig. 9 It is a structural schematic diagram of a multi-mode interferometer MMI;

[0042] Fig.10 It is a structural diagram of the MZI network;

[0043] Fig.11 A schematic diagram of another MZI network. DETAILED DESCRIPTION

[0044] 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.

[0045] 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.

[0046] 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.

[0047] An integrated optical diversity receiving device of this embodiment is as follows Figure 1 As shown, it includes an input part and a photonic chip, wherein the input part includes a multi-mode / few-mode optical fiber for receiving a light source, a photon lantern and a single-mode optical fiber array for realizing mode demultiplexing; wherein, the free-space light focused by the lens is received by the multi-mode or few-mode optical fiber, and excites a high-order mode, and the light beam coupled to the multi-mode or few-mode optical fiber will evolve into multiple modes in this part due to the influence of atmospheric turbulence, and will be mode-demultiplexed by subsequent photon lanterns, and the modes in the multi-mode / few-mode optical fiber will be coupled to the single-mode optical fiber array, and then enter the photonic chip through the edge coupler for coherent beam combining function.

[0048] Few-mode optical fiber, photon lantern, and single-mode optical fiber array are independent of the photonic chip. Through chip packaging technology, the single-mode optical fiber array is connected to the photonic chip.

[0049] The photonic chip includes an MZI network, a control circuit, N groups of edge couplers and a polarization beam splitter and rotation combiner; the single-mode fiber array is connected to the edge coupler. For each optical path input by the edge coupler, since there are two polarizations in the optical fiber and the edge coupler does not have polarization selectivity, this embodiment deploys a polarization beam splitter and rotation combiner in the chip to decompose the TE and TM modes and convert the TM mode into the TE mode. The processed optical signal is then first polarization-merged through the MZI and then connected to the MZI processing network. The overall structure of the polarization rotation beam splitter and combination is shown in the figure. Figure 3 As shown, the polarization beam splitter, rotator and combiner includes a polarization beam splitter, a polarization rotator and an MZI unit;

[0050] For polarization beam splitters, it mainly uses the different properties of materials with different polarizations from the input light, and uses a special waveguide structure to achieve spatial separation of light with different polarization states, thereby realizing the manipulation and application of light. The schematic diagram of its working principle is shown in Figure 4As shown, the polarization beam splitter of this embodiment separates the incoming light beam into transverse electric wave TE and transverse magnetic wave TM modes, thereby realizing the separate output of TE and TM light;

[0051] After the TE and TM polarized light are split by the polarization beam splitter, in order to achieve efficient use of the received optical power, it is also necessary to merge the generated light of different polarization states. This embodiment mainly rotates the electric field direction of the TM polarized light through the waveguide structure of the polarization rotator, thereby achieving the effect of converting TM polarization into TE polarization. The schematic diagram of its working principle is shown in Figure 5 As shown. The polarization rotator of this embodiment realizes the conversion from TM polarization state to TE polarization state through a unique waveguide structure design. At this time, due to the phase difference between the polarization rotator and the two polarizations themselves, this embodiment uses the MZI unit to coherently merge the two beams after polarization beam splitting rotation, and outputs the TE polarized light to enter the subsequent MZI network for processing.

[0052] The MZI network of this embodiment includes several MZI units, such as Figure 6 As shown, each MZI unit includes two 50:50 beam splitters and two phase shifters;

[0053] Each 50:50 beam splitter has two inputs and two outputs;

[0054] 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.

[0055] 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.

[0056] 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 7 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.

[0057] Specific design:

[0058] Given the MZI unit structure, Figure 8 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.

[0059] Specifically, after the light inputted by input_1 passes through the No. 1 electrically controlled thermal phase shifter 312, it is 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 enters 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 of light is π, the light intensity at its 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 of light 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 of light 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.

[0060] 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. Fig. 9As 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.

[0061] 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 Fig.10 As 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.

[0062] 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. Fig.10 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.

[0063] This embodiment also provides an MZI network, such as Fig.11As 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.

[0064] The optical signal received in this embodiment adopts optical coherent beam combining to avoid photoelectric conversion and digital signal processing to circumvent the efficiency and frequency problems caused by them. 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. This embodiment uses multi-mode or few-mode optical fiber for spatial light reception, with high coupling efficiency and low alignment difficulty. This embodiment coherently combines the two polarizations in the optical fiber in real time and dynamically to improve signal processing efficiency.

[0065] 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. An integrated optical diversity receiving device, characterized in that: It includes a multi-mode / few-mode optical fiber, a photon lantern, a single-mode optical fiber array, an MZI network, a control circuit, N groups of edge couplers and a polarization beam splitter and rotation combiner, where N is the number of light beams in the single-mode optical fiber array; The free-space light focused by the lens is received by the multimode / few-mode fiber; The beams of multiple modes received by the multimode / fewmode fiber enter the photon lantern; The photon lanterns are mode demultiplexed and coupled into a single-mode fiber array; Each beam in the single-mode fiber array enters a polarization splitter and rotation combiner through an edge coupler; The polarization beam splitter and rotation combiner is used to separate the incoming light beam into transverse electric wave TE and transverse magnetic wave TM modes, and then rotate the separated transverse magnetic wave TM polarization state light to the transverse electric wave TE polarization state. The rotated transverse electric wave TE polarization state light is combined with the separated TE polarization state light and then enters the MZI network; MZI networks are used to achieve optical coherent beam combining; The control circuit controls the merging of the light beams in the MZI network.

2. The integrated optical diversity receiving device according to claim 1, characterized in that: The polarization beam splitter, rotator and combiner comprises a polarization beam splitter, a polarization rotator and an MZI unit; Polarization beam splitter, used to separate the incoming light beam into transverse electric wave TE and transverse magnetic wave TM modes; A polarization rotator, used for rotating the separated transverse magnetic wave TM polarization state light into a transverse electric wave TE polarization state; The rotated transverse electric wave TE polarization state light and the separated TE polarization state light enter the MZI unit, and the MZI unit is used to perform optical coherence combination on the two incoming light beams and then enter the MZI network.

3. An integrated optical diversity receiving device according to claim 1 or 2, 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.

4. The integrated optical diversity receiving device according to claim 3, characterized in that: The 50:50 beam splitter is a directional coupler or a multimode interferometer.

5. The integrated optical diversity receiving device according to claim 3, 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.

6. The integrated optical diversity receiving device according to claim 5, 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.

7. The integrated optical diversity receiving device according to claim 6, 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.

8. The integrated optical diversity receiving device according to claim 3, 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.

9. The integrated optical diversity receiving device according to claim 8, 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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