Optical anti-turbulence device and method for polarization multiplexing space optical communication

Abstract

The application discloses a kind of optical anti-turbulence devices of polarization multiplexing space optical communication method, it is characterized in that: it further includes mode demultiplexer connected with optical fiber, single-mode fiber array respectively coupled with each spatial eigenmode after mode demultiplexer decomposition, polarization CBC chip connected with the other end of single-mode fiber array, drive control module connected with polarization CBC chip and polarization multiplexing optical communication digital coherent receiver (Rx) connected with polarization CBC through single-mode fiber;The application is realized by the setting of polarization CBC chip, the compatibility of polarization multiplexing technology and mode multiplexing coherent beam combination technology, breaks down the polarization dimension information loss or strong crosstalk problem caused by polarization state rotator (PSR) and polarization maintaining optical fiber in the prior art, retains the modulation information of two orthogonal polarization dimensions completely, improves communication bandwidth, and greatly improves communication efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of space optical communication, in particular to an optical anti-turbulence device and method for polarization multiplexing space optical communication. BACKGROUND

[0002] In space optical communication applications, atmospheric turbulence is one of the key factors affecting the performance of communication links. Atmospheric turbulence can cause beam intensity scintillation, drift and wavefront distortion, significantly reducing the bit error rate, communication capacity and availability of optical communication systems. In order to overcome these effects, various wavefront distortion correction techniques have been proposed, mainly including the following categories:

[0003] 1. Adaptive optical correction technology: As the most mainstream wavefront distortion correction technology, it can effectively compensate for the effects of atmospheric turbulence by monitoring and correcting the wavefront distortion of the optical signal in real time. The core components of the system include a wavefront sensor (such as a Shack-Hartmann wavefront sensor), a wavefront corrector (such as a MEMS deformable mirror, a digital micromirror or a liquid crystal spatial light modulator) and a control algorithm. However, it has the problems of complex system, high cost and relatively slow response speed (the fastest MEMS device can usually only reach tens of kHz level), and its correction ability is still difficult to fully meet the needs of high-speed communication under strong turbulence conditions.

[0004] 2. Optical phase conjugation compensation correction technology: By introducing a phase conjugate wavefront to compensate for turbulence distortion, the principle is to transmit reference light at the receiving end without carrying modulation information, use a wavefront detector to detect the phase disturbance of the turbulence, and then use a spatial light modulator to pre-load the conjugate phase information of the turbulence disturbance to the transmitted light signal. However, this technology requires complex optical path design and synchronous control, increasing the complexity and cost of the system, and has poor adaptability to the environment, making it difficult to maintain stable compensation effect under dynamically changing atmospheric turbulence.

[0005] 3. Correction technology combining mode multiplexing and coherent beam combining: The distorted light signal is received by a large field angle optical lens group and coupled into a few-mode or multi-mode optical fiber, and the modes are separated by a mode demultiplexer and then phase-synchronized by coherent beam combining technology. However, in existing technology, the coherent beam combining device is sensitive to the polarization of light. In order to reduce the interference of polarization state changes, a polarization state rotator (PSR) and a polarization maintaining optical fiber are usually integrated into the system, resulting in poor compatibility with polarization multiplexing optical communication technology, which can only save information in a single polarization dimension or cause strong crosstalk between two polarization dimensions, wasting polarization dimension information modulation resources and limiting the improvement of communication bandwidth. Therefore, an optical anti-turbulence device and method for polarization multiplexing space optical communication are proposed. SUMMARY

[0006] The application aims to provide an optical anti-turbulence device and method for polarization multiplexing space optical communication.

[0007] To achieve the above-mentioned purpose, the application provides the following technical scheme: an optical anti-turbulence device and method for polarization multiplexing space optical communication, comprising an optical signal receiving system for receiving a polarization multiplexing optical signal transmitted through atmospheric turbulence, and an optical fiber connected with the optical signal receiving system for collecting the optical signal; characterized in that: further comprising a mode demultiplexer connected with the optical fiber for decomposing the optical signal in the optical fiber into a plurality of spatial eigenmodes, a single-mode fiber array coupled with each spatial eigenmode decomposed by the mode demultiplexer, a polarization CBC chip connected with the other end of the single-mode fiber array for coherently combining the fundamental mode optical signals output by the single-mode fiber array and keeping the modulation information of two orthogonal polarization dimensions from being lost, a driving control module connected with the polarization CBC chip for adjusting the polarization CBC chip to realize phase synchronization of the optical signal, and a polarization multiplexing optical communication digital coherent receiver (Rx) connected with the polarization CBC through a single-mode fiber for receiving and demodulating the optical signal after coherent combination; the polarization CBC chip is composed of a polarization beam splitter, a CBC unit, a phase delay line device and a polarization beam combiner from left to right; wherein the polarization CBC chip is configured to coherently combine and keep the modulation information of two orthogonal polarization dimensions from being lost by the following steps:

[0008] a. decomposing the optical signal into a plurality of TE fundamental modes and TM fundamental modes through the polarization beam splitter;

[0009] b. coherently combining the TE fundamental modes and the TM fundamental modes through the CBC unit respectively;

[0010] c. eliminating the phase difference between the TE fundamental modes and the TM fundamental modes through the phase delay line device;

[0011] d. polarization combining the coherently combined TE fundamental modes and TM fundamental modes through the polarization beam combiner.

[0012] As a preferred, the polarization CBC chip further comprises a mode converter.

[0013] As a preferred, the CBC unit comprises a plurality of phase shifters for realizing phase synchronization of two input optical signals, and a beam splitter connected with the phase shifters at intervals for coherent combination; and the non-output port of the beam splitter is integrated with a photodetector (PD) for monitoring the real-time coherent combination state.

[0014] As a preferred, the optical signal receiving system comprises a large field angle lens, a collimating lens group, a beam expanding lens group and a converging lens group.

[0015] As preferred, the mode demultiplexer is a multi-plane light converter, a photonic lantern multiplexer, a cascaded spatial light modulator, a digital micromirror device, and a metasurface device with beam wavefront phase control function.

[0016] As preferred, the optical fiber is a single-core few-mode fiber, a single-core multi-mode fiber, a multi-core few-mode fiber, a multi-core multi-mode fiber, and an orbital angular momentum (OAM) fiber; the single-mode fiber array includes a single-core single-mode fiber array or a multi-core single-mode fiber array.

[0017] As preferred, the photodetector (PD) transmits the detected optical power information to the driving control module through an electrical signal link 1, the driving control module generates a phase modulation signal according to the optical power information fed back by the PD and adjusts the phase shifter through an electrical signal link 2, realizing phase synchronization control of the optical signal.

[0018] A method for an optical anti-turbulence device of polarization multiplexing spatial optical communication, characterized in that the method is as follows:

[0019] 1) receiving the polarization multiplexing optical signal transmitted through the atmospheric turbulence by the optical signal receiving system, and coupling it to at least a few-mode or multi-mode optical fiber;

[0020] 2) decomposing the optical signal in the few-mode or multi-mode optical fiber into a plurality of spatial eigenmodes by a mode demultiplexer;

[0021] 3) coupling each spatial eigenmode after decomposition to a single-mode fiber array and converting it to a single-mode fiber base mode;

[0022] 4) inputting the optical signal output by the single-mode fiber array into a polarization CBC chip, and performing coherent beam combining by the polarization CBC chip, the beam combining process including:

[0023] a. decomposing the optical signal into a plurality of TE base modes and TM base modes by a polarization beam splitter;

[0024] b. performing coherent beam combining on the TE base modes and TM base modes respectively by a CBC unit;

[0025] c. eliminating the phase difference between the TE base modes and the TM base modes by a phase delay line device;

[0026] d. performing polarization beam combining on the TE base modes and TM base modes after beam combining by a polarization beam combiner;

[0027] 5) connecting a polarization multiplexing optical communication digital coherent receiver (Rx) to the base mode optical signal after beam combining by a single-mode fiber to receive the base mode optical signal, and performing polarization diversity digital coherent reception and demodulation on the two orthogonal polarization dimensions carrying modulation information in the optical signal.

[0028] As preferred, in step 4, the TM mode can also be converted into TE mode by the mode converter before inputting into the CBC unit, and part of the TE mode can be converted into TM mode by the mode converter after beam combination.

[0029] As preferred, in step 4, the light power information detected by the photodetector is transmitted to the driving control module by using the electrical signal link 1 during the beam combination process, and the phase modulation signal generated by the driving control module is transmitted to the phase shifter by using the electrical signal link 2, so that the phase of the optical signal is synchronously modulated by the phase shifter.

[0030] The beneficial effects of the present application are as follows: through the arrangement of the polarization CBC chip, the compatibility of polarization multiplexing technology and mode multiplexing coherent beam combination technology is realized, the polarization dimension information loss or strong crosstalk problem caused by the polarization state rotator (PSR) and polarization maintaining fiber in the prior art is broken through, the modulation information of two orthogonal polarization dimensions is completely reserved, the communication bandwidth is improved, and the communication efficiency is greatly improved; through the combination of mode demultiplexing and polarization coherent beam combination, the wavefront distortion caused by atmospheric turbulence is effectively resisted, the optical signal receiving power and the phase disturbance resistance are improved, and the stability and availability of the communication link are improved; the driving control module realizes the real-time closed-loop control of the photodetector (PD) light power monitoring and the phase shifter phase modulation through the double electrical signal link, accurately adjusts the phase shifter in the CBC unit, ensures the phase synchronization accuracy of the two optical signals, and guarantees the efficiency and stability of the coherent beam combination.

[0031] The core components such as the optical signal receiving system, the mode demultiplexer and the optical fiber type can be flexibly selected according to the actual requirements such as turbulence intensity and communication rate, and are suitable for turbulence environments of different levels from weak to strong, and have a wide range of application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall structure of the optical anti-turbulence device of the polarization multiplexing space optical communication of the present application.

[0033] Figure 2 It is a schematic diagram of the structure of the polarization CBC chip of the present application.

[0034] Figure 3 It is a schematic diagram of the structure of the polarization CBC chip with a mode converter of the present application.

[0035] Figure 4 It is a schematic diagram of the structure and working principle of the CBC unit of the present application.

[0036] Figure 5 It is a schematic diagram of the structure and working principle of the mode converter of the present application. DETAILED DESCRIPTION

[0037] In the following, we will combine Figures 1-5The application further discloses a polarization multiplexing spatial optical communication optical anti-turbulence device and method.

[0038] It should be noted that all directionality indications such as up, down, left, right, front, back, and the like in the embodiments of the application are only used to explain the relative positional relationship and movement condition between components in a certain specific posture, as shown in the drawings, and if the specific posture changes, the directionality indications also change accordingly.

[0039] Referring to Figures 1-5 The application further discloses a polarization multiplexing spatial optical communication optical anti-turbulence device and method, which is based on a 4-mode demultiplexing combined with a polarization CBC beam splitter. Embodiment one:

[0040] The polarization multiplexing optical signal emitted by the transmitting end and having no wavefront distortion passes through the atmospheric turbulence, and a polarization multiplexing optical signal with wavefront distortion is formed, and the turbulence causes the beam intensity to flicker and the phase to be disturbed;

[0041] The distorted optical signal is received by an optical signal receiving system, is converged and coupled into the few-mode optical fiber, and the spatial collection of the optical signal is completed; the optical signal receiving system is composed of a large field angle lens, a collimating lens and a converging lens;

[0042] The polarization multiplexing optical signal carrying the turbulence disturbance is transmitted to a mode demultiplexer (such as a multi-plane light converter MPLC) by the few-mode optical fiber, the spatial mode decomposition of the optical signal is performed by using the coupling mode theory, and the optical signal is decomposed into four orthogonal complete spatial eigenmodes such as LG01, LG02, LG12 and LG22; the specific mode type changes dynamically with the turbulence, and the linear superposition of the four modes can approximately restore the field distribution of the original optical signal;

[0043] The four decomposed eigenmodes are coupled into a single-mode optical fiber array respectively, the single-mode optical fiber array is composed of four single-mode optical fibers, and a multi-type fiber taper device is integrated in the spatial mode incident section of the single-mode optical fiber, so that each spatial mode is converted into a fundamental mode in the single-mode optical fiber, and preparation is made for subsequent coherent beam combining;

[0044] The four paths of fundamental mode optical signals output by the single-mode optical fiber array are input into a polarization CBC chip, and first polarization separation is performed by a polarization beam splitter on the left side of the chip: each path of the fundamental mode optical signals is decomposed into a TE fundamental mode and a TM fundamental mode in a waveguide, and a total of eight paths of signals are decomposed by the polarization beam splitter 1, the polarization beam splitter 2, the polarization beam splitter 3 and the polarization beam splitter 4 from the four paths of the TE fundamental mode and the four paths of the TM fundamental mode, and are output from different ports;

[0045] Based on the binary tree topology network structure of the polarization CBC chip, two-stage beam combining is performed on the eight paths of signals.

[0046] First stage of beam combining: 4 TE base modes are divided into 2 groups, each group of 2 signals is input into a TE dedicated CBC unit, which are CBC unit 1 and CBC unit 2 respectively; 4 TM base modes are also divided into 2 groups, each group of 2 signals is input into a TM dedicated CBC unit, which are CBC unit 3 and CBC unit 4 respectively;

[0047] During the working process of the CBC unit, the two input signals are assumed to be A1exp(iφ1) and A2exp(iφ2). The base mode light signal A1exp(iφ1) passes through the phase shifter 1 and generates a phase shift of Δφ1, becoming A1*exp[i(φ1+Δφ1)], and the light signal after passing through the beam splitter 1 (50:50 splitting ratio) is A3exp(iφ3). One of the signals passes through the phase shifter 2, generates a phase shift of Δφ2, and then passes through the beam splitter 2, and the light signal is only output from the port without a photoelectric detector (PD);

[0048] The photoelectric detector (PD) transmits the light power information of the non-output port of the beam splitter 2 to the driving control module in real time through the electrical signal link 1. If the photoelectric detector (PD) detects that the power of A1exp(iφ1) is higher than the threshold of -30dBm, the driving control module sends a phase modulation signal to the phase shifter 1 through the electrical signal link 2, so that Δφ1=φ2-φ1+(2m-1)π / 2 (m is a positive integer), and the light intensity ratio of the two outputs of the beam splitter 1 is stabilized at 1:1;

[0049] The driving control module continues to adjust the phase shifter 2 through the feedback of the photoelectric detector (PD), so that Δφ2=(2m-1)π (m is a positive integer), ensuring that the output signal of the beam splitter 2 is only output from the port without a PD, and the photoelectric detector (PD) detects the power <-30dBm, realizing the phase synchronization of the two signals;

[0050] Second stage of beam combining: After the first stage of beam combining, 2 TE base modes and 2 TM base modes are obtained, the TE base modes are input into CBC unit 5, and the TM base modes are input into CBC unit 6, respectively for secondary beam combining, finally obtaining 1 TE base mode after beam combining and 1 TM base mode after beam combining;

[0051] The TE base mode and the TM base mode after beam combining pass through a phase delay line device respectively to eliminate the phase difference caused by the transmission distance of the waveguide in the chip and the difference of the effective refractive index of the mode, ensuring the phase matching of the two;

[0052] The TE base mode and the TM base mode after phase compensation are input into a polarization beam combiner to combine into 1 base mode light signal that preserves the dual polarization information;

[0053] The stable mode light signal after beam combination is transmitted to a polarization multiplexing optical communication digital coherent receiver (Rx) through a single mode optical fiber. The receiver separates the TE and TM two orthogonal polarization states through polarization diversity technology. The original modulation information is recovered by digital coherent demodulation of the two polarization states, and the polarization multiplexing optical communication process against turbulence interference is completed.

[0054] Embodiment two: polarization CBC chip containing mode converter

[0055] The 4-path base mode light signal is input into the polarization CBC chip, and is first separated into 4-path TE base mode and 4-path TM base mode through a polarization beam splitter;

[0056] The mode converter includes a TM→TE mode converter and a TE→TM mode converter. The 4-path TM base mode enters the TM→TE mode converter. The TM→TE mode converter is composed of a mode converter TM0→TE1 and a mode converter TE1→TE0. The mode converter TM0→TE1 adopts a Taper structure, and the Taper length and the width of the two ends are adjusted to realize the matching and high-efficiency conversion of the mode refractive index from TM0 to TE1. The mode converter TE1→TE0 is a waveguide coupling structure, and the width of the two unequal-width waveguides, the gap between the waveguides and the length of the waveguide coupling region are adjusted to realize the conversion from TE1 to TE0. According to the symmetry principle, the TE0 mode is output from the output end of the TM→TE mode converter, so that the high-efficiency conversion from TM0 to TE0 is realized at the output end of the TM→TE mode converter, and the conversion efficiency is > 95%. At this time, the light signals to be combined in the chip are all TE base modes, a total of 8 paths: original 4-path TE base mode + converted 4-path TE base mode;

[0057] First-stage beam combination: the 8-path TE base mode is divided into 4 groups, and each group of 2-path TE base mode is input into a CBC unit. The driving control module receives the optical power information of the photodetector (PD) in each CBC unit in real time through the electrical signal link 1 (monitoring threshold <-40dBm), and outputs a phase modulation signal to the phase shifter 1 through the electrical signal link 2, so that the output light intensity ratio of the beam splitter 1 is stabilized to 1:1. Then, the phase shifter 2 is adjusted to ensure that the output signal of the beam splitter 2 is only output from the photodetector (PD) port (the power of the photodetector (PD) is <-40dBm), and the 4-path beam combination is completed.

[0058] Second-stage beam combination: the 4-path beam combination signal is divided into 2 groups, and the CBC units are controlled by the driving control module in the same way, and is combined into 2-path TE base mode.

[0059] One of the TE base modes after the beam combination enters a TE→TM mode converter, which is composed of a mode converter TE0→TE1 and a mode converter TE1→TM0, and is symmetrical with the TM→TE converter structure. Through the symmetry, efficient conversion from TE0 to TM0 is realized at the output end of the TE→TM mode converter, and the conversion efficiency is >95%. The conversion is into a TM base mode;

[0060] The other TE base mode and the converted TM base mode are respectively adjusted by a phase delay line device of a driving control module to compensate for the phase difference caused by the conversion process and the waveguide transmission difference, and are input into a polarization beam combiner to be combined into one dual-polarization base mode optical signal, which is delivered to a polarization multiplexing optical communication digital coherent receiver (Rx) through a single-mode optical fiber.

[0061] The above examples are descriptions of the present application and are not limitations of the present application. Any simple transformation of the present application also belongs to the protection scope of the present application.

Claims

1. An optical anti-turbulence device for polarization multiplexed spatial optical communication, comprising an optical signal receiving system for receiving a polarization multiplexed optical signal transmitted after atmospheric turbulence, and an optical fiber connected with the optical signal receiving system for collecting the optical signal; characterized in that: Also included are a mode demultiplexer connected with the optical fiber for decomposing the optical signal in the optical fiber into a plurality of spatial eigenmodes, a single-mode fiber array respectively coupled with each spatial eigenmode decomposed by the mode demultiplexer, a polarization CBC chip connected with the other end of the single-mode fiber array for coherently combining the fundamental mode optical signals output by the single-mode fiber array and maintaining the modulation information of two orthogonal polarization dimensions without loss, a driving control module connected with the polarization CBC chip for adjusting the polarization CBC chip to achieve phase synchronization of the optical signal, and a polarization multiplexed optical communication digital coherent receiver (Rx) connected with the polarization CBC through a single-mode fiber for receiving and demodulating the optical signal after coherent combination; the polarization CBC chip is sequentially composed of a polarization beam splitter, a CBC unit, a phase delay line device, and a polarization beam combiner from left to right; wherein the polarization CBC chip is configured to coherently combine and maintain the modulation information of two orthogonal polarization dimensions without loss by the following steps: a. decomposing the optical signal into a plurality of TE and TM modes by the polarization beam splitter; b. coherently combining the TE and TM modes by the CBC unit respectively; c. eliminating the phase difference between the TE and TM modes by the phase delay line device; d. polarization combining the combined TE and TM modes by the polarization beam combiner.

2. The optical anti-turbulence device for polarization multiplexed space optical communication according to claim 1, characterized in that: The polarization CBC chip further includes a mode converter.

3. The optical anti-turbulence device for polarization multiplexed space optical communication according to claim 1, characterized in that: The CBC unit includes a plurality of phase shifters for achieving phase synchronization of two input optical signals and a beam splitter connected with the phase shifters for coherent combination; and the non-output port of the beam splitter is integrated with a photodetector (PD) for monitoring the real-time coherent combination state.

4. The optical anti-turbulence device for polarization multiplexed space optical communication of claim 1, wherein: The optical signal receiving system includes a large field angle lens, a collimating lens group, a beam expanding lens group, and a converging lens group.

5. The optical anti-turbulence device for polarization multiplexed space optical communication according to claim 1, wherein: The mode demultiplexer is a multi-plane optical converter, a photonic lantern multiplexer, a cascaded spatial light modulator, a digital micromirror device, and a metasurface device with beam wavefront phase control function.

6. The optical anti-turbulence device for polarization multiplexed space optical communication according to claim 1, wherein: The optical fiber is a single-core few-mode fiber, a single-core multi-mode fiber, a multi-core few-mode fiber, a multi-core multi-mode fiber, and an orbital angular momentum (OAM) fiber; the single-mode fiber array includes a single-core single-mode fiber array or a multi-core single-mode fiber array.

7. The optical anti-turbulence device for polarization multiplexed space optical communication according to claim 3, characterized in that: The photodetector (PD) transmits the detected optical power information to the driving control module through an electrical signal link 1, and the driving control module generates a phase modulation signal according to the optical power information fed back by the PD and adjusts the phase shifter through an electrical signal link 2 to achieve phase synchronization control of the optical signal.

8. A method of using the optical turbulence resistant device for polarization multiplexed space optical communication according to any one of claims 1-7, characterized in that, The method is as follows: 1) receiving the polarization multiplexed optical signal after atmospheric turbulence transmission through the optical signal receiving system, and coupling it into a few-mode or multi-mode fiber; 2) decomposing the optical signal in the few-mode or multi-mode fiber into a plurality of spatial eigenmodes by the mode demultiplexer; 3) respectively coupling each spatial eigenmode after decomposition into a single-mode fiber array and converting it into a single-mode fiber fundamental mode; 4) inputting the optical signal output by the single-mode fiber array into the polarization CBC chip and coherently combining it by the polarization CBC chip, the combination process including: a. splitting the optical signal into TE and TM modes by a polarization beam splitter; b. coherently combining the TE and TM modes by a CBC unit respectively; c. eliminating the phase difference between the TE and TM modes by a phase delay line device; d. polarization combining the combined TE and TM modes by a polarization beam combiner; 5) connecting a polarization multiplexed optical communication digital coherent receiver (Rx) by a single mode fiber to receive the combined mode optical signal, and performing polarization diversity digital coherent reception and demodulation on the two orthogonal polarization dimensions in the optical signal carrying modulation information.

9. The method of claim 8, wherein the optical turbulence is caused by atmospheric turbulence. In step 4, the TM mode can also be converted into the TE mode by a mode converter before inputting into the CBC unit, and part of the TE mode is converted into the TM mode by a mode converter after the combination.

10. The method of claim 9, wherein the optical turbulence is caused by atmospheric turbulence. In step 4, the optical power information detected by the photodetector is transmitted to the driving control module by the electrical signal link 1 during the combination process, and the phase modulation signal generated by the driving control module is transmitted to the phase shifter by the electrical signal link 2, so that the phase of the optical signal is modulated synchronously by the phase shifter.

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