A laser communication mode diversity receiving device and method

Abstract

This invention relates to the field of laser communication mode diversity technology, specifically to a laser communication mode diversity receiving device and method. The laser communication mode diversity receiving device includes: a capture and receiving module, a mode demultiplexing module, and an optical reconstruction module; an electronically controlled feedback unit acquires the power signals of each mode output by the optical power detection unit, calculates the power fluctuation of each channel in real time, and generates a phase adjustment control command which is sent to a silicon-based photonic integrated chip; inside the silicon-based photonic integrated chip: each cascaded Mach-Zehnder interferometer integrates a phase shifter for real-time phase compensation of each mode; the multi-stage Mach-Zehnder interferometer sequentially coherently combines all mode signals pairwise to output a single-mode optical signal. This invention, based on a static compensation + dynamic control dual-stage mechanism, reduces the power fluctuation amplitude between modes from the traditional 15%-20% to below 3%.

Description

Technical Field

[0001] This invention relates to the field of laser communication mode diversity technology, and specifically to a laser communication mode diversity receiving device and method. Background Technology

[0002] Free-space laser communication has become a core technology for applications such as space-to-ground communication and aerospace communication due to its advantages such as high transmission rate and strong security. However, when optical signals pass through atmospheric channels, they are prone to optical field distortion and intensity flicker due to turbulence, which leads to increased signal coupling loss and decreased transmission reliability.

[0003] In the existing technology, the single-mode fiber direct receiving scheme has limited ability to capture distorted light fields due to the fiber core diameter of only about 9μm, making it difficult to meet the requirements of weak signal reception. Especially when the signal scintillation index is greater than 0.1, even if a fast-turning mirror is introduced for closed-loop correction, it is difficult to achieve effective optical communication. While adaptive optics systems can correct wavefront distortion to adapt to single-mode fiber devices, they are complex, costly, and consume a lot of power. Some solutions use few-mode or multi-mode fibers to collect distorted light fields, amplify them through a few-mode erbium-doped fiber amplifier (EDFA), and then receive them with a multi-mode detector. This leverages the multi-mode acquisition characteristics to improve turbulence resistance, but this approach has low sensitivity, relies on matching multi-mode devices, has complex component design, and requires high signal uniformity across modes. Other mode diversity solutions use a single PD detector combined with Kramers-Kroning (KK) light field recovery technology to receive signals, but this approach has high digital processing complexity, large time delay, and does not solve the problem of mode power fluctuation suppression. Spatial diversity reception technology uses multiple independent optical antennas to construct parallel channels, which can alleviate turbulent multipath fading, but it requires multiple optical terminals and signal processing components, resulting in large space requirements, high costs, and complex multi-channel synchronous combining algorithms.

[0004] In summary, existing technologies struggle to balance high coupling efficiency with low modal power fluctuations, exhibiting problems such as weak acquisition capabilities, system complexity, high cost, reliance on dedicated components, large processing delays, and high synchronization difficulties. Consequently, they fail to guarantee both the stability and reliability of laser communication. Therefore, how to improve coupling efficiency while suppressing modal power fluctuations to ensure communication stability has become a pressing technical bottleneck that needs to be addressed. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects existing in the prior art, thereby providing a laser communication mode diversity receiving device and method.

[0006] A laser communication mode diversity receiving device includes: a capture receiving module consisting of a coupling mirror group and a multimode fiber; a mode demultiplexing module using an MPLC multiplane optical conversion device; and an optical recombination module that is signal-connected to the mode demultiplexing module and receives several mode optical signals. The optical reconstruction module uses a silicon-based photonic integrated chip and integrates a cascaded Mach-Zehnder interferometer, an electronically controlled feedback unit, and an optical power detection unit. Among them, the optical power detection unit captures the power changes of each mode of optical signal; The electronic control feedback unit calculates the power fluctuations captured by the optical power detection unit and outputs corresponding phase adjustment commands. The Mach-Zehnder interferometer and the electronically controlled feedback unit are connected by signal. Based on the phase adjustment command, the state of the phase shifter inside the Mach-Zehnder interferometer is controlled to perform real-time phase compensation motion on each mode optical signal. In this way, all mode optical signals are coherently synthesized in pairs, and finally all mode optical signals are synthesized into a single-channel single-mode optical signal.

[0007] Preferably, the polarization purity of each mode of optical signal input to the silicon-based photonic integrated chip is ≥95%.

[0008] Preferably, the optical power detection unit uses an InGaAs array photodetector to capture the power changes of each mode of optical signal.

[0009] Preferably, the MPLC multiplane optical conversion device uses a quartz substrate with a 1550nm antireflection coating on its surface.

[0010] Preferably, the MPLC multi-plane optical conversion device has four built-in microstructured reflective phase plates with an adjacent spacing of 3cm.

[0011] A laser communication mode diversity receiving method, implemented using a laser communication mode diversity receiving device, includes: The laser signal in free space, distorted by atmospheric turbulence, is captured using a capture and receiver module. The mode demultiplexing module distributes the energy of the distorted optical field to each single-mode fiber channel; The optical recombination module is used to perform real-time coherent recombination and dynamic control of several modal optical signals output from each single-mode fiber channel; Specifically, the optical power detection unit in the optical reconstruction module captures the power changes of each mode of optical signal; the electronic control feedback unit calculates the power fluctuations captured by the optical power detection unit and outputs corresponding phase adjustment commands; and several phase shifters perform real-time phase compensation motion on each mode of optical signal based on the phase adjustment commands. The cascaded Mach-Zehnder interferometer coherently synthesizes all phase-compensated modal optical signals pairwise, ultimately combining all modal optical signals into a single-channel single-mode optical signal.

[0012] The technical solution of this invention has the following advantages: This invention relies on multimode fiber large core capture and 10-mode MPLC demultiplexing technology, which reduces coupling loss by 3~10dB compared with traditional single-mode fiber receiving schemes. By capturing the multimode of distorted light field through MPLC multi-plane optical conversion device, it effectively avoids energy loss caused by the high alignment accuracy requirements of single-mode fiber, and provides sufficient power margin for high-speed transmission. Attached Figure Description

[0013] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0014] Figure 1 This is an overall block diagram of a laser communication mode diversity receiving device according to the present invention. Detailed Implementation

[0015] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0017] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0018] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0019] Example 1 like Figure 1 This embodiment discloses a high-speed laser communication technology applicable to atmospheric turbulence interference scenarios such as star-to-ground and air-to-ground communication. Specifically, it discloses a laser communication mode diversity receiving device, including: a capture and receiving module composed of a coupling mirror group and a multimode fiber; a mode demultiplexing module using an MPLC multiplane optical conversion device; and an optical recombination module connected to the mode demultiplexing module for receiving several mode optical signals. The acquisition and receiving module consists of a coupling mirror assembly and a multimode fiber, used to capture laser signals distorted by atmospheric turbulence in free space. The coupling mirror assembly uses a Cassegrain telescope with an aperture ≥ 50cm, equipped with a fast-steering mirror for coarse target localization. Its focusing spot diameter is adapted to the multimode fiber core size. The multimode fiber is OM3 type step-index fiber with a core diameter of 50μm and a length of 4m. The acquisition and receiving module utilizes the large core size of the multimode fiber to ensure that the diffused light field energy after turbulence distortion is coupled to the multimode fiber to the maximum extent, providing a sufficient energy basis for subsequent mode decomposition.

[0020] The core component of the mode demultiplexing module is the MPLC multiplane optical converter, which uses a quartz substrate coated with a 1550nm antireflection film and incorporates four microstructured reflective phase plates with a 3cm spacing between adjacent plates. The quartz substrate measures 50mm × 50mm × 5mm, the antireflection film has a transmittance of ≥99.5%, and the microstructured reflective phase plates have a pixel size of 20μm. As a passive spatial demultiplexer, the MPLC multiplane optical converter accurately decomposes the composite optical field input from the multimode fiber into 10 spatially separated Gaussian mode signals. Each mode corresponds to an independent single-mode fiber output, with a mode separation of ≥95%, decomposition loss ≤1.5dB, intermode crosstalk ≤-25dB, single-mode fiber insertion loss ≤0.1dB, and a length of 1m. The MPLC multiplane optical converter achieves mode conversion through multiple reflections and Fourier transforms, distributing the energy of the distorted optical field to each single-mode fiber channel.

[0021] The optical reconstruction module uses a silicon-based photonic integrated chip and integrates a cascaded Mach-Zehnder interferometer, an electronically controlled feedback unit, and an optical power detection unit; the phase modulation depth is 0~2π, the synthesis insertion loss is ≤0.8dB, and the operating temperature is -40~85℃.

[0022] The optical power detection unit captures the power changes of each mode of optical signal. Specifically, the optical power detection unit uses an InGaAs array photodetector to capture the power changes of each mode of optical signal. It should be noted that the sampling rate of the optical power detection unit must meet the requirements of real-time monitoring. The InGaAs array photodetector has a responsivity ≥ 0.9 A / W and a noise equivalent power ≤ 10. -12 W / √Hz.

[0023] The electronic control feedback unit is connected to several phase shifters and optical power monitoring units built into the silicon-based photonic integrated chip via a high-speed bus. During initial configuration: connect the power management unit of the device to each module, start the power supply and check for abnormal heating; load the control program and complete the parameter initialization configuration.

[0024] The electronic control feedback unit calculates the power fluctuations captured by the optical power detection unit and outputs corresponding phase adjustment commands; The silicon-based photonic integrated chip has several built-in phase shifters and an electronically controlled feedback unit that are signal-connected. Based on phase adjustment commands, it performs real-time phase compensation for each mode of optical signal. Specifically, in this embodiment, the silicon-based photonic integrated chip has a total of 9 built-in Mach-Zehnder interferometers. Inside the silicon-based photonic integrated chip, each cascaded Mach-Zehnder interferometer is equipped with a phase shifter for real-time phase compensation of each mode of optical signal. The cascaded Mach-Zehnder interferometer coherently synthesizes all the phase-compensated modal optical signals pairwise, ultimately combining all the modal optical signals into a single-channel single-mode optical signal.

[0025] Example 2 A laser communication mode diversity receiving method, implemented using a laser communication mode diversity receiving device according to Embodiment 1, includes: The laser signal in free space, distorted by atmospheric turbulence, is captured using a capture and receiver module. The mode demultiplexing module distributes the energy of the distorted optical field to each single-mode fiber channel; The optical recombination module is used to perform real-time coherent recombination and dynamic control of several modal optical signals output from each single-mode fiber channel; Among them, the power changes of each mode optical signal are captured by the optical power detection unit in the optical reconstruction module; The electronic control feedback unit calculates the power fluctuations captured by the optical power detection unit and outputs corresponding phase adjustment commands. Several phase shifters perform real-time phase compensation motion on each mode of optical signal based on phase adjustment commands; The cascaded Mach-Zehnder interferometer coherently synthesizes all the phase-compensated modal optical signals pairwise, ultimately combining all the modal optical signals into a single-channel single-mode optical signal.

[0026] Specifically: Capture and receive: Adjust the azimuth and elevation angles of the Cassegrain telescope to align it with the target signal source, and use a fast-turning mirror to correct coarse positioning errors caused by satellite orbital deviation or equipment vibration. The Cassegrain telescope focuses the distorted light field onto the core of a multimode fiber, taking advantage of the large aperture of the multimode fiber to fully capture diffused energy, achieving a coupling efficiency of ≥80%, and transmits the optical signal to the input of the mode demultiplexing module.

[0027] It should be noted that in practical applications, the Cassegrain telescope is fixed to the optical ground station observation platform; the multimode fiber input end is fixed to the Cassegrain telescope focusing point through a three-dimensional fine-tuning bracket, and the coupling efficiency is monitored by an optical power detection unit; during installation: the mode demultiplexing module and the optical reconstruction module are fixed to the rack in sequence, and a heat dissipation gap of ≥10cm is reserved.

[0028] When connecting the optical path: the multimode fiber output is coupled to the mode demultiplexing module input via an FC / PC flange, with an insertion loss ≤0.1dB; the 10 single-mode fiber outputs of the mode demultiplexing module are coupled to the PIC chip input via an array of optical fibers to ensure polarization alignment; the silicon-based photonic integrated chip output is connected to an external receiver via single-mode fiber, with all single-mode fibers having a bending radius ≥30mm to avoid high-order mode leakage.

[0029] Pattern demultiplexing: The composite optical field output from the multimode fiber enters the mode demultiplexing module. After multiple reflections and spatial transformations on a microstructured reflective phase plate, it is decomposed into 10 independent Gaussian mode signals. Each mode signal is transmitted to the optical recombination module through a single-mode fiber. During the decomposition process, the mode demultiplexing module maintains the polarization consistency of each mode, ensuring that the polarization purity of the optical signal input to the silicon-based photonic integrated chip is ≥95%, laying the foundation for coherent recombination.

[0030] Phase and power modulation and coherent recombination: The optical power monitoring unit of the optical recombination module collects power data of each mode signal in real time. The electronic control feedback unit calculates power fluctuations using a preset algorithm. When a power fluctuation of a certain mode signal exceeds a threshold, a phase adjustment command is automatically generated to drive the phase shifter for real-time phase compensation, dynamically offsetting phase distortion and power imbalance caused by turbulence. Simultaneously, a static phase compensation mechanism offsets the static phase difference introduced by fiber transmission and inherent device defects. The 10 modulated signals are then combined pairwise using a cascaded Mach-Zehnder interferometer on a silicon-based photonic integrated chip, ensuring phase matching and uniform power distribution of each mode signal, ultimately synthesizing a single-mode optical signal.

[0031] It should be noted that each Mach-Zehnder interferometer carries two phase shifters: a first phase shifter and a second phase shifter. During operation, the first-stage phase shifter is first adjusted to ensure that the upper and lower waveguide arms split the optical power equally, each accounting for 50%. Then, the second-stage phase shifter is adjusted to switch all the optical power to one output port.

[0032] In this embodiment, there are a total of 9 Mach-Zehnder interferometers.

[0033] Signal output and processing The synthesized single-channel single-mode optical signal is transmitted to an external receiver, such as a digital coherent receiver (DCR), which supports demodulation of both coherent and incoherent modulation methods and is suitable for high-speed data transmission of 10~100Gbps. Simultaneously, relevant system cached operating data is configured to facilitate subsequent operation, maintenance, and parameter optimization.

[0034] This embodiment also includes a calibration step: A 1550nm analog signal was injected into the target signal source to test the response characteristics of each phase shifter to ensure that the dynamic control requirements are met; a turbulent environment with D / r0=7 was simulated, and the fluctuation threshold and control algorithm parameters of the electronic control feedback unit were adjusted to make the power fluctuation ≤3%; the optical power monitoring unit was calibrated and the reference power was set. D represents the effective aperture of the Cassegrain telescope. r0 is Fried's constant, used to represent the atmospheric coherence length, in meters (m).

[0035] Maintenance Instructions Regular maintenance: Clean the end face of the fiber optic flange used to connect the multimode fiber and the mode demultiplexing module monthly; check the heat dissipation status of the silicon-based photonic integrated chip quarterly to ensure that the operating temperature is ≤85℃; calibrate the phase shifter accuracy and the algorithm parameters of the electronic control feedback unit every six months; when the satellite orbit deviates, adjust the positioning only through the fast-turning mirror without changing the optical path connection.

[0036] Troubleshooting: If coupling efficiency decreases, check the alignment and end-face cleanliness of each fiber; if power fluctuations are too large, recalibrate the parameters of the electronic control feedback unit; if synthesis efficiency decreases, verify the parameters of the cascaded Mach-Zehnder interferometer of the silicon-based photonic integrated chip to ensure phase matching.

[0037] Summarize: In terms of significantly improving coupling efficiency, this embodiment relies on multimode fiber large core capture and 10-mode MPLC demultiplexing technology, which reduces coupling loss by 3~10dB compared to the traditional single-mode fiber receiving scheme. By capturing the multimode of the distorted light field through the MPLC multi-plane optical conversion device, the energy loss caused by the high alignment accuracy requirements of single-mode fiber is effectively avoided, providing sufficient power margin for high-speed transmission.

[0038] In terms of power fluctuation suppression, by leveraging the dual-level mechanism of "static compensation + dynamic control" of the mode demultiplexing module and optical reconstruction module, the inter-mode power fluctuation amplitude is reduced from 15%~20% in existing solutions to below 3%, significantly improving communication stability. The fast response characteristics of the electronic control feedback unit and phase shifter ensure that the device can track turbulence changes in real time, effectively suppressing light intensity flicker and phase distortion.

[0039] In terms of superior system characteristics, the overall device architecture has no moving parts, significantly improving reliability; the MPLC multi-plane optical conversion device is a passive device, and the silicon-based photonic integrated chip has low power consumption. The overall device power consumption is reduced by more than 60% compared to traditional spatial diversity solutions, and the hardware cost is only 1 / 5 to 1 / 3 of that of traditional adaptive optics systems. The equipment has a compact structure and can be directly integrated into existing optical ground stations without significant layout modifications.

[0040] In terms of compatibility and adaptability, the system supports mainstream communication wavelengths in the 1550nm band, and the output signal is compatible with various single-mode fiber components, such as erbium-doped fiber amplifiers and high-speed detectors, without the need to replace existing terminal equipment; it can adapt to atmospheric turbulence scenarios of weak to strong levels: D / r0=1~18, and has strong robustness to input power fluctuations and turbulence velocity changes, and can be widely used in various laser communication scenarios such as space-to-ground and air-to-ground communication.

[0041] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A laser communication mode diversity receiving device, comprising: The acquisition and receiving module, consisting of a coupling mirror group and a multimode fiber, and the mode demultiplexing module using an MPLC multiplane optical conversion device, are characterized in that they further include an optical recombination module that is signal-connected to the mode demultiplexing module and receives several mode optical signals. The optical reconstruction module uses a silicon-based photonic integrated chip and integrates a cascaded Mach-Zehnder interferometer, an electronically controlled feedback unit, and an optical power detection unit. Among them, the optical power detection unit captures the power changes of each mode of optical signal; The electronic control feedback unit calculates the power fluctuations captured by the optical power detection unit and outputs corresponding phase adjustment commands. The Mach-Zehnder interferometer and the electronically controlled feedback unit are connected by a signal. Based on the phase adjustment command, the phase shifter state inside the Mach-Zehnder interferometer is controlled to perform real-time phase compensation motion on each mode optical signal, and all mode optical signals are coherently synthesized in pairs, and finally all mode optical signals are synthesized into a single-channel single-mode optical signal.

2. The laser communication mode diversity receiving device according to claim 1, characterized in that, The polarization purity of each mode of optical signal input to the silicon-based photonic integrated chip is ≥95%.

3. The laser communication mode diversity receiving device according to claim 2, characterized in that, The optical power detection unit uses an InGaAs array photodetector to capture the power changes of each mode of optical signal.

4. The laser communication mode diversity receiving device according to claim 3, characterized in that, The MPLC multiplane optical conversion device uses a quartz substrate with a 1550nm anti-reflection coating on its surface.

5. A laser communication mode diversity receiving device according to claim 4, characterized in that, The MPLC multi-plane optical conversion device incorporates four microstructured reflective phase plates with an adjacent spacing of 3 cm.

6. A laser communication mode diversity reception method, characterized in that, The laser communication mode diversity receiving device according to claim 5 is implemented, comprising: The laser signal in free space, distorted by atmospheric turbulence, is captured using a capture and receiver module. The mode demultiplexing module distributes the energy of the distorted optical field to each single-mode fiber channel; The optical recombination module is used to perform real-time coherent recombination and dynamic control of several modal optical signals output from each single-mode fiber channel; Specifically, the optical power detection unit in the optical reconstruction module captures the power changes of each mode of optical signal; the electronic control feedback unit calculates the power fluctuations captured by the optical power detection unit and outputs corresponding phase adjustment commands; and several phase shifters perform real-time phase compensation motion on each mode of optical signal based on the phase adjustment commands. The cascaded Mach-Zehnder interferometer coherently synthesizes all phase-compensated modal optical signals pairwise, ultimately combining all modal optical signals into a single-channel single-mode optical signal.

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