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

Abstract

The invention discloses a method of an optical anti-turbulence device for polarization multiplexing spatial optical communication. The mode demultiplexer is connected with the optical fiber; the single-mode optical fiber array is respectively coupled with each spatial intrinsic mode decomposed by the mode demultiplexer; the polarization CBC chip is connected with the other end of the single-mode optical fiber array; the driving control module is connected with the polarization CBC chip; the polarization multiplexing optical communication digital coherent receiver (Rx) is connected with the polarization CBC chip through a single-mode optical fiber; through the arrangement of the polarization CBC chip, the compatibility of a polarization multiplexing technology and a mode multiplexing coherent beam combination technology is realized, the problem of polarization dimension information loss or strong crosstalk caused by the use of a polarization state rotator (PSR) and a polarization maintaining optical fiber in the prior art is solved, modulation information of two orthogonal polarization dimensions is completely reserved, the communication bandwidth is improved, and the communication efficiency is improved. And the communication efficiency is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of space optical communication technology, specifically to an optical anti-turbulence device and method for polarization multiplexing space optical communication. Background Technology

[0002] In space optical communication applications, atmospheric turbulence is one of the key factors affecting communication link performance. Atmospheric turbulence can cause beam intensity flicker, drift, and wavefront distortion, significantly reducing the bit error rate, communication capacity, and availability of optical communication systems. To overcome these effects, various wavefront distortion correction techniques have been proposed, mainly including the following categories: 1. Adaptive Optical Correction Technology: As the most mainstream wavefront distortion correction technology, it effectively compensates for the effects of atmospheric turbulence by monitoring and correcting the wavefront distortion of optical signals in real time. The core components of this system include wavefront sensors (such as Shaker-Hartmann wavefront sensors), wavefront correctors (such as MEMS deformable mirrors, digital galvanometers, or liquid crystal spatial light modulators), and control algorithms. However, it suffers from system complexity, high cost, and relatively slow response speed (the fastest MEMS devices currently available typically only reach tens of kHz levels). Under strong turbulence conditions, its correction capability still cannot fully meet the requirements of high-speed communication.

[0003] 2. Optical Phase Conjugate Compensation Correction Technology: This technology compensates for turbulence distortion by introducing a phase conjugate wavefront. The principle involves emitting reference light without modulation information at the receiver, using a wavefront detector to detect phase disturbances in the turbulence, and then preloading the wavefront of the emitted light signal with the conjugate phase information of the turbulence disturbance using a spatial light modulator. However, this technology requires complex optical path design and synchronization control, increasing system complexity and cost. Furthermore, it has poor environmental adaptability and struggles to maintain stable compensation effects under dynamically changing atmospheric turbulence.

[0004] 3. Combining mode multiplexing and coherent beam combining correction techniques: Distorted light signals are received via a large field-of-view optical lens group and coupled into few-mode or multimode optical fibers. Modes are separated using a mode demultiplexer, and phase synchronization is achieved through coherent beam combining technology. However, in existing technologies, coherent beam combining devices are sensitive to light polarization. To reduce interference from polarization state changes, polarization state rotators (PSRs) and polarization-maintaining fibers are typically integrated into the system. This results in poor compatibility with polarization-multiplexed optical communication technology, allowing only the preservation of information in a single polarization dimension or leading to strong crosstalk between two polarization dimensions. This wastes polarization dimension modulation resources and limits the improvement of communication bandwidth. Therefore, an optical anti-turbulence device and method for polarization-multiplexed spatial optical communication is proposed. Summary of the Invention

[0005] The purpose of this invention is to solve the above problems by proposing an optical anti-turbulence device and method for polarization multiplexing space optical communication.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an optical anti-turbulence device and method for polarization-multiplexed space optical communication, comprising an optical signal receiving system for receiving polarization-multiplexed optical signals transmitted through atmospheric turbulence, and an optical fiber connected to the optical signal receiving system for acquiring optical signals; characterized in that: it further comprises a mode demultiplexer connected to the optical fiber for decomposing the optical signal in the optical fiber into multiple spatial eigenmodes, a single-mode fiber array coupled to each spatial eigenmode decomposed by the mode demultiplexer, a polarization CBC chip connected to the other end of the single-mode fiber array for coherently combining the fundamental mode optical signal output by the single-mode fiber array and maintaining the modulation information of the two orthogonal polarization dimensions without loss, a drive control module connected to 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 to the polarization CBC via a single-mode fiber for receiving and demodulating the optical signal after coherent combining; the polarization CBC chip is composed of a polarization beamsplitter, a CBC unit, a phase delay line device, and a polarization beam combiner from left to right.

[0007] Preferably, the polarization CBC chip also includes a mode converter.

[0008] Preferably, the CBC unit includes several phase shifters for achieving phase synchronization of the two input optical signals and a beam splitter connected at intervals to the phase shifters for coherent beam combining; and the non-output port of the beam splitter integrates a photodetector (PD) for monitoring the real-time coherent beam combining status.

[0009] Preferably, the optical signal receiving system includes a wide field-of-view lens, a collimating lens group, a beam expander lens group, and a converging lens group.

[0010] Preferably, the mode demultiplexer is a multiplane optical converter, a photonic lantern multiplexer, a cascaded spatial light modulator, a digital micromirror device, or a metasurface device with beam wavefront phase modulation function.

[0011] Preferably, 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, or 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.

[0012] Preferably, the photodetector (PD) transmits the detected optical power information to the drive control module through electrical signal link 1. The drive control module generates a phase modulation signal based on the optical power information fed back by the PD and adjusts the phase shifter through electrical signal link 2 to achieve phase synchronization control of the optical signal.

[0013] A method for an optical anti-turbulence device for polarization multiplexing space optical communication, characterized by the following steps: 1) Receive polarization-multiplexed optical signals transmitted through atmospheric turbulence through an optical signal receiving system and couple them to at least-mode or multi-mode optical fibers; 2) The optical signal in a few-mode or multimode fiber is decomposed into multiple spatial eigenmodes by a mode demultiplexer; 3) The decomposed spatial intrinsic modes are coupled into a single-mode fiber array and converted into single-mode fiber fundamental modes; 4) The optical signal output from the single-mode fiber array is input into the polarization CBC chip, and coherent beam combining is performed by the polarization CBC chip. The beam combining process includes: a. The optical signal is decomposed into multiple TE fundamental modes and TM fundamental modes using a polarization beam splitter; b. Coherently combine the TE fundamental mode and the TM fundamental mode using the CBC unit; c. Eliminate the phase difference between the TE fundamental mode and the TM fundamental mode using a phase delay line device; d. The combined TE and TM fundamental modes are polarized and combined using a polarization combiner; 5) Connect a polarization-multiplexed optical communication digital coherent receiver (Rx) through a single-mode fiber to receive the combined fundamental mode optical signal, and perform digital coherent reception and demodulation of the two orthogonal polarization dimensions carrying modulation information in the optical signal for polarization diversity.

[0014] Preferably, in step 4, the TM fundamental mode can be converted to the TE fundamental mode by a mode converter and then input into the CBC unit. After beam combining, some of the TE fundamental modes can be converted to the TM fundamental mode by a mode converter.

[0015] Preferably, in step 4, during the beam combining process, the optical power information detected by the photodetector is transmitted to the drive control module via electrical signal link 1, and the phase modulation signal generated by the drive control module is transmitted to the phase shifter via electrical signal link 2, so that the phase shifter synchronously modulates the phase of the optical signal.

[0016] The beneficial effects of this invention are as follows: By setting up a polarization CBC chip, the compatibility of polarization multiplexing technology and mode multiplexing coherent beam combining technology is achieved, overcoming the problems of polarization dimension information loss or strong crosstalk caused by the use of polarization state rotators (PSRs) and polarization-maintaining fibers in the prior art. The modulation information of the two orthogonal polarization dimensions is completely preserved, improving communication bandwidth and significantly increasing communication efficiency. By combining mode demultiplexing with polarization coherent beam combining, wavefront distortion caused by atmospheric turbulence is effectively resisted, improving optical signal receiving power and anti-phase disturbance capability, and enhancing the stability and availability of the communication link. The drive control module realizes real-time closed-loop control of photodetector (PD) optical power monitoring and phase shifter phase modulation through dual electrical signal links, accurately adjusting the phase shifter in the CBC unit to ensure the phase synchronization accuracy of the two optical signals, ensuring the high efficiency and stability of coherent beam combining. The core components, such as the optical signal receiving system, mode demultiplexer, and fiber type, can be flexibly selected according to actual needs such as turbulence intensity and communication rate, adapting to different levels of turbulence environments from weak to strong, and have a wide range of application scenarios. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the optical anti-turbulence device for polarization multiplexing space optical communication of the present invention; Figure 2 This is a schematic diagram of the polarization CBC chip of the present invention; Figure 3 This is a schematic diagram of the polarization CBC chip structure containing a mode converter according to the present invention; Figure 4 This is a schematic diagram illustrating the structure and working principle of the CBC unit of the present invention; Figure 5 This is a schematic diagram illustrating the structure and working principle of the mode converter of the present invention. Detailed Implementation

[0018] Below we combine Figures 1-5 The present invention provides a further description of an optical anti-turbulence device and method for polarization multiplexing spatial optical communication.

[0019] It should be noted that all directional indications in the embodiments of the present invention, such as up, down, left, right, front, back, etc., are only used to explain the relative positional relationship and movement of the components in a specific posture as shown in the attached figure. If the specific posture changes, the directional indication will also change accordingly.

[0020] See Figures 1-5 As shown, an optical anti-turbulence device and method for polarization multiplexing space optical communication is presented, taking four-mode demultiplexing combined with polarization CBC beam splitting as an example.

[0021] Example 1: When a polarization-multiplexed optical signal without wavefront distortion is emitted from the transmitter passes through atmospheric turbulence, it becomes a polarization-multiplexed optical signal with wavefront distortion. Turbulence causes beam intensity flicker and phase perturbation. The optical signal receiving system receives distorted optical signals, converges and couples them into a minimum-mode fiber to complete the spatial acquisition of optical signals; the optical signal receiving system consists of a wide field-of-view lens, a collimating lens group, and a converging lens. Few-mode fiber transmits polarization-multiplexed optical signals carrying turbulence disturbances to a mode demultiplexer (such as a multiplane optical converter MPLC). The optical signal is spatially decomposed into four orthogonal and complete spatial eigenmodes, such as LG01, LG02, LG12, and LG22, using coupled-mode theory. 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. The four intrinsic modes after decomposition are coupled to a single-mode fiber array, which consists of four single-mode fibers. The single-mode fibers integrate multiple fiber-type taper devices in the spatial mode incident section to convert each spatial mode into the fundamental mode in the single-mode fiber, in preparation for subsequent coherent bundle combining. The four fundamental mode optical signals output from the single-mode fiber array are input to the polarization CBC chip. First, polarization separation is performed by the polarization beam splitter on the left side of the chip: each fundamental mode optical signal is decomposed into TE fundamental mode and TM fundamental mode in the waveguide. A total of four fundamental mode optical signals are decomposed into eight signals by polarization beam splitter 1, polarization beam splitter 2, polarization beam splitter 3 and polarization beam splitter 4 respectively. Among them, four TE fundamental modes and four TM fundamental modes are output from different ports. A binary tree topology network structure based on a polarization CBC chip is used to combine eight signals in two stages. First-stage beam combining: The 4-channel TE fundamental mode is divided into 2 groups, with each group of 2 signals input into a dedicated TE CBC unit, namely CBC unit 1 and CBC unit 2; at the same time, the 4-channel TM fundamental mode is divided into 2 groups, with each group of 2 signals input into a dedicated TM CBC unit, namely CBC unit 3 and CBC unit 4. During the operation of the CBC unit, the two input signals are assumed to be A1exp(iφ1) and A2exp(iφ2). The fundamental mode optical signal A1exp(iφ1) undergoes a phase shift of Δφ1 after passing through phase shifter 1, becoming A1*exp[i(φ1+Δφ1)]. The optical signals after passing through beam splitter 1 (50:50 splitting ratio) are all A3exp(iφ3). One of the signals undergoes a phase shift of Δφ2 after passing through phase shifter 2. After passing through beam splitter 2, the optical signal is only output from the port without a photodetector (PD). Without a photodetector (PD), the optical power information of the non-output port of the beam splitter 2 is transmitted to the drive control module in real time through the electrical signal link 1. If the power of A1exp(iφ1) detected by the photodetector (PD) is higher than the threshold of -30dBm, the drive control module sends a phase modulation signal to the deflector 1 through the electrical signal link 2, so that Δφ1=φ2-φ1+(2m-1)π / 2 (m is a positive integer), so that the intensity ratio of the two optical paths output by the beam splitter 1 is stabilized at 1:1. The drive control module continues to adjust the phase shifter 2 through feedback from the photodetector (PD) to make Δφ2=(2m-1)π (m is a positive integer), ensuring that the output signal of the beam splitter 2 is only output from the PD-less port and that the detection power of the photodetector (PD) is <-30dBm, thereby achieving phase synchronization of the two signals; Second-stage beam combining: After the first-stage beam combining, two TE fundamental modes and two TM fundamental modes are obtained. The TE fundamental mode is input to CBC unit 5 and the TM fundamental mode is input to CBC unit 6. They are then beam combined twice to finally obtain one beam combined TE fundamental mode and one beam combined TM fundamental mode. After beam combining, the TE fundamental mode and TM fundamental mode are respectively passed through phase delay line devices to eliminate the phase difference caused by the waveguide transmission distance and the difference in the effective refractive index of the mode within the chip, ensuring phase matching between the two. The phase-compensated TE and TM fundamental modes are input to a polarization combiner and combined into a single fundamental mode optical signal that retains dual polarization information. The combined stable fundamental mode optical signal is transmitted through a single-mode optical fiber to a polarization-multiplexed optical communication digital coherent receiver (Rx). The receiver separates the two orthogonal polarization states, TE and TM, using polarization diversity technology. The two polarization states are then digitally coherently demodulated to recover the original modulation information, thus completing the polarization-multiplexed optical communication process that is resistant to turbulence interference.

[0022] Example 2: Polarization CBC chip with mode converter Four fundamental mode optical signals are input to the polarization CBC chip, and are first separated into four TE fundamental modes and four TM fundamental modes by a polarization beam splitter. The mode converter includes a TM→TE mode converter and a TE→TM mode converter. Four TM fundamental modes enter the TM→TE mode converter. The TM→TE mode converter consists of a TM0→TE1 mode converter and a TE1→TE0 mode converter. The TM0→TE1 mode converter adopts a Taper-type structure. By adjusting the length of the Taper and the width at both ends, the refractive index matching and efficient conversion of the TM0 to TE1 modes are achieved. The TE1→TE0 mode converter is a waveguide-coupled structure. By adjusting the width of the two unequal-width waveguides, the gap between the waveguides, and the length of the waveguide coupling region, the conversion of TE1 to TE0 is achieved. According to the principle of symmetry, the TE0 mode is output from the output end of the TM→TE mode converter, thus achieving efficient conversion of TM0 to TE0 at the output end of the TM→TE mode converter, with a conversion efficiency >95%. At this time, the optical signals to be combined in the chip are all TE fundamental modes, totaling 8 channels: the original 4 TE fundamental modes + the converted 4 TE fundamental modes. First-stage beam combining: The 8-channel TE fundamental mode is divided into 4 groups, with 2 input channels to the dedicated TE CBC unit in each group; the drive control module receives the optical power information of the photodetectors (PD) in each CBC unit in real time through electrical signal link 1 (monitoring threshold <-40dBm), and outputs the phase modulation signal to the phase shifter 1 through electrical signal link 2 to stabilize the output light intensity ratio of the beam splitter 1 at 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 port without photodetectors (PD) (photodetector (PD) power <-40dBm), thus completing the 4-channel beam combining; Second-stage beam combining: The four beam combining signals are further divided into two groups, and the CBC unit is controlled by the drive control module in the same way to synthesize two TE fundamental modes. One of the TE fundamental modes after beam combining enters the TE→TM mode converter. This converter consists of mode converters TE0→TE1 and TE1→TM0, and is structurally symmetrical with the TM→TE converter. Through symmetry, it achieves efficient conversion from TE0 to TM0 from the output of the TE→TM mode converter, with a conversion efficiency of >95%, and converts it to the TM fundamental mode. The other TE fundamental mode and the converted TM fundamental mode are respectively controlled by phase delay line devices adjusted by the drive control module to compensate for the phase difference caused by the conversion process and waveguide transmission differences. They are then input into a polarization combiner to synthesize a dual-polarization fundamental mode optical signal, which is transmitted to a polarization multiplexed optical communication digital coherent receiver (Rx) through a single-mode optical fiber.

[0023] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. An optical anti-turbulence device for polarization-multiplexed space optical communication, comprising an optical signal receiving system for receiving polarization-multiplexed optical signals transmitted through atmospheric turbulence, and an optical fiber connected to the optical signal receiving system for acquiring the optical signals; characterized in that: It also includes a mode demultiplexer connected to an optical fiber for decomposing the optical signal in the optical fiber into multiple spatial eigenmodes; a single-mode fiber array coupled to each spatial eigenmode decomposed by the mode demultiplexer; a polarization CBC chip connected to the other end of the single-mode fiber array for coherently combining the fundamental mode optical signal output by the single-mode fiber array and maintaining the modulation information of the two orthogonal polarization dimensions; a drive control module connected to 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 to the polarization CBC via a single-mode fiber for receiving and demodulating the optical signal after coherent combining; the polarization CBC chip is composed of a polarization beamsplitter, a CBC unit, a phase delay line device, and a polarization beam combiner from left to right.

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

3. The optical anti-turbulence device for polarization multiplexing space optical communication according to claim 1, characterized in that: The CBC unit includes several phase shifters for phase synchronization of two input optical signals and beam splitters connected at intervals to the phase shifters for coherent beam combining; and the non-output port of the beam splitter integrates a photodetector (PD) for monitoring the real-time coherent beam combining status.

4. The optical anti-turbulence device for polarization multiplexing space optical communication according to claim 1, characterized in that: The optical signal receiving system includes a wide field-of-view lens, a collimating lens group, a beam expander lens group, and a converging lens group.

5. The optical anti-turbulence device for polarization multiplexing space optical communication according to claim 1, characterized in that: 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 modulation function.

6. The optical anti-turbulence device for polarization multiplexing space optical communication according to claim 1, characterized in that: The optical fiber is a single-core few-mode fiber, a single-core multimode fiber, a multi-core few-mode fiber, a multi-core multimode 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 multiplexing space optical communication according to claim 1, characterized in that: The photodetector (PD) transmits the detected optical power information to the drive control module through electrical signal link 1. The drive control module generates a phase modulation signal based on the optical power information fed back by the PD and adjusts the phase shifter through electrical signal link 2 to achieve phase synchronization control of the optical signal.

8. A method for an optical anti-turbulence device for polarization multiplexing space optical communication according to claims 1-7, characterized in that, The method is as follows: 1) Receive polarization-multiplexed optical signals transmitted through atmospheric turbulence through an optical signal receiving system and couple them to at least-mode or multi-mode optical fibers; 2) The optical signal in a few-mode or multimode fiber is decomposed into multiple spatial eigenmodes by a mode demultiplexer; 3) The decomposed spatial intrinsic modes are coupled into a single-mode fiber array and converted into a single-mode fiber fundamental mode; 4) The optical signal output from the single-mode fiber array is input into the polarization CBC chip, and coherent beam combining is performed by the polarization CBC chip. The beam combining process includes: a. The optical signal is decomposed into multiple TE fundamental modes and TM fundamental modes using a polarization beam splitter; b. Coherently combine the TE fundamental mode and the TM fundamental mode using the CBC unit; c. Eliminate the phase difference between the TE fundamental mode and the TM fundamental mode using a phase delay line device; d. The combined TE and TM fundamental modes are polarized and combined using a polarization combiner; 5) Connect a polarization-multiplexed optical communication digital coherent receiver (Rx) through a single-mode fiber to receive the combined fundamental mode optical signal, and perform digital coherent reception and demodulation of the two orthogonal polarization dimensions carrying modulation information in the optical signal for polarization diversity.

9. A method for an optical anti-turbulence device for polarization multiplexing space optical communication according to claim 8, characterized in that: In step 4, the TM fundamental mode can be converted to the TE fundamental mode by a mode converter and then input into the CBC unit. After beam combining, some of the TE fundamental modes can be converted to the TM fundamental mode by a mode converter.

10. A method for an optical anti-turbulence device for polarization multiplexing space optical communication according to claim 9, characterized in that: In step 4, during the beam combining process, the optical power information detected by the photodetector is transmitted to the drive control module via electrical signal link 1, and the phase modulation signal generated by the drive control module is transmitted to the phase shifter via electrical signal link 2, so that the phase shifter synchronously modulates the phase of the optical signal.

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