High-speed underwater wireless coherent optical communication system and method compatible with multiple modulation formats

Abstract

The invention relates to underwater wireless communication, in particular to a high-speed underwater wireless coherent optical communication system and method compatible with multiple modulation formats, and solves the problem that high-speed long-distance underwater wireless optical communication cannot be realized due to fewer modulation formats caused by immature blue-green optical devices in the existing underwater optical communication. The IQ modulator can load signals in multiple dimensions of an infrared light signal, supports multiple modulation formats, converts an infrared light carrier signal into a blue-green light carrier signal suitable for underwater transmission by introducing the light wavelength conversion module, solves the problem that an existing high-order modulator is limited to an infrared band, and is suitable for underwater transmission. The underwater long-distance high-efficiency stable optical signal transmission is realized by combining the light beam shaping module and the like, and compared with direct detection, the digital coherent detection module is adopted, so that the amplitude and phase information of the signal can be obtained at the same time, and the spectrum analysis capability is improved, and the digital coherent detection module is combined with the high-speed signal generation module. And the spectrum efficiency and the data transmission rate of the system are improved.

Description

Technical Field

[0001] The invention relates to underwater wireless optical communication, and in particular to a high-speed underwater wireless coherent optical communication system and method compatible with multiple modulation formats. Background Art

[0002] With the continuous development of marine resources, ocean detection systems and underwater communication technologies have developed rapidly during the development process. Underwater communication technology is mainly divided into wired communication and wireless communication. Wireless communication is the transmission of signals in seawater through sound waves, electromagnetic waves or light waves. Compared with other underwater communication methods, underwater wireless optical communication has attracted widespread attention for its high transmission rate, strong anti-interference ability, good confidentiality and high flexibility. Since 1963, when researchers discovered that blue-green light with a wavelength between 450nm and 550nm is the "light-transmitting window" of seawater, underwater wireless optical communication technology has gradually been verified as a feasible technology.

[0003] At present, the research on blue-green optical communication is mostly focused on the fields of high-speed short-distance and low-speed long-distance, which makes it difficult to meet the communication needs of long distance and high speed at the same time. In order to effectively solve the contradiction between communication distance and rate, researchers introduced coherent optical communication technology, which brought breakthroughs to underwater optical communication. After experiments, coherent optical communication can significantly improve the sensitivity of the receiving end and effectively extend the communication distance. However, the existing research on coherent optical communication technology is mostly concentrated in the infrared band, and the modulator used to load high-speed signals is also mainly used in the infrared band. This modulator supports high-order modulation and can realize many adjustment formats. However, there are currently few modulators used in the blue-green light band, and the achievable modulation formats are relatively few. How to break through the performance limitations of the existing blue-green optical devices in underwater optical communication in terms of bandwidth and the few achievable modulation formats, improve the communication rate and communication distance, and realize high-speed and long-distance underwater wireless optical communication has become an important research topic. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the existing underwater wireless optical communication has few achievable modulation formats due to the immaturity of blue-green optical devices, thus limiting the development of underwater wireless optical communication, and to provide a high-speed underwater wireless coherent optical communication system and method that is compatible with multiple modulation formats.

[0005] In order to achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0006] A high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats, which is special in that: it comprises a transmitting end and a receiving end, the transmitting end and the receiving end communicate through a seawater channel; the transmitting end comprises a high-speed signal generating module, an optical amplifier, an optical wavelength conversion module, a beam shaping module and a beam emission alignment module connected in sequence; the receiving end comprises an optical signal collecting module and a digital coherent detection module connected in sequence;

[0007] The high-speed signal generating module is used to generate an infrared optical carrier signal, and includes an infrared laser, an IQ modulator, a high-speed signal generator, and a driver, wherein the output end of the infrared laser is connected to the first input end of the IQ modulator, the output end of the high-speed signal generator is connected to the input end of the driver, and the output end of the driver is connected to the second input end of the IQ modulator;

[0008] The input end of the optical amplifier is connected to the output end of the IQ modulator;

[0009] The optical wavelength conversion module includes a frequency doubling crystal, the input end of which is connected to the output end of the optical amplifier, and is used to convert the infrared optical carrier signal into a blue-green optical carrier signal;

[0010] The beam shaping module comprises a beam splitter and a spatial light modulator connected in sequence, and the output end of the frequency doubling crystal is connected to the input end of the beam splitter;

[0011] The input end of the beam emission alignment module is connected to the output end of the spatial light modulator, which is used to adjust the beam angle and direction of the blue-green light carrier signal and emit the blue-green light carrier signal into the seawater channel in the form of spatial light;

[0012] The optical signal collection module is used to collect blue-green optical carrier signals transmitted from the seawater channel;

[0013] The digital coherent detection module comprises a coherent receiving module and a digital signal processing module connected in sequence;

[0014] The coherent receiving module is used to convert the blue-green optical carrier signal transmitted from the optical signal collecting module into an analog electrical signal;

[0015] The digital signal processing module is used to convert the analog electrical signal into a digital electrical signal and process the digital electrical signal to recover its information data.

[0016] Further, the coherent receiving module includes a local oscillator laser, a 90° optical mixer and a balanced detector, the output end of the optical signal collection module is connected to the first input end of the 90° optical mixer, and the output end of the local oscillator laser is connected to the second input end of the 90° optical mixer; there are two balanced detectors, the two input ends of one balanced detector are respectively connected to the two output ends of the 90° optical mixer, and the phase differences of the optical signals output from the two output ends of the 90° optical mixer are 0° and 180° respectively; the two input ends of the other balanced detector are respectively connected to the other two output ends of the 90° optical mixer, and the phase differences of the optical signals output from the other two output ends of the 90° optical mixer are 90° and 270° respectively, and the balanced detector is used to convert the received optical signal into an analog electrical signal;

[0017] The digital signal processing module includes an analog-to-digital converter and an FPGA module. There are two analog-to-digital converters for converting analog electrical signals into digital electrical signals, and the input ends of the two analog-to-digital converters are respectively connected to the output ends of the two balanced detectors, and the output ends of the two analog-to-digital converters are connected to the FPGA module. The FPGA module is used to process the digital electrical signals to recover their information data.

[0018] Furthermore, the coherent receiving module also includes a low-pass filter. There are two low-pass filters, and the input ends of the two low-pass filters are respectively connected to the output ends of the two balanced detectors, and the output ends are respectively connected to the input ends of the two analog-to-digital converters.

[0019] Furthermore, the optical wavelength conversion module also includes a collimator and a filter, the output end of the frequency doubling crystal is connected to the input end of the collimator, the output end of the collimator is connected to the input end of the filter, and the output end of the filter is connected to the input end of the beam splitter.

[0020] Furthermore, the optical wavelength conversion module also includes a temperature control system, and the temperature control system is used to adjust the working temperature of the frequency doubling crystal.

[0021] At the same time, the present invention also provides a high-speed underwater wireless coherent optical communication method compatible with multiple modulation formats, which adopts the above-mentioned high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats, and its special feature is that it includes the following steps:

[0022] S1, start the infrared laser, high-speed signal generator and driver, the infrared laser transmits an infrared light signal to the IQ modulator, the high-speed signal generator transmits a high-speed signal and inputs it into the IQ modulator through the driver, and the IQ modulator loads the received high-speed signal onto the received infrared light signal to form an infrared light carrier signal;

[0023] S2, the infrared optical carrier signal is transmitted to the optical amplifier to amplify its power;

[0024] S3, the infrared optical carrier signal after power amplification is transmitted to the frequency doubling crystal of the optical wavelength conversion module, and the frequency doubling crystal converts the infrared optical carrier signal into a blue-green optical carrier signal by using the nonlinear optical effect;

[0025] S4, the blue-green optical carrier signal is transmitted to the beam splitter in the beam shaping module for beam splitting, and then enters the spatial light modulator to optimize its beam shape and energy distribution, thereby improving the stability during underwater transmission;

[0026] S5. The optimized blue-green light carrier signal is transmitted to the light beam emission alignment module to adjust the light beam angle and direction. After the adjustment, the blue-green light carrier signal is emitted into the seawater channel in the form of spatial free light for transmission;

[0027] S6. The blue-green optical carrier signal transmitted through the seawater channel is transmitted to the optical signal collection module for collection;

[0028] S7, the collected blue-green optical carrier signal is transmitted to the coherent receiving module of the digital coherent detection module for processing, and the blue-green optical carrier signal is converted into an analog electrical signal;

[0029] S8. The analog electrical signal is transmitted to the digital signal processing module for processing, the analog electrical signal is converted into a digital electrical signal and processed to recover its information data, thereby completing high-speed underwater wireless coherent optical communication compatible with multiple modulation formats.

[0030] Furthermore, step S3 is specifically as follows: the infrared light carrier signal after power amplification is transmitted to the frequency doubling crystal of the optical wavelength conversion module, the frequency doubling crystal uses the nonlinear optical effect to convert the infrared light carrier signal into a blue-green light carrier signal, the blue-green light carrier signal is transmitted to the collimator for collimation, and the collimated blue-green light carrier signal is transmitted to the filter to filter out the residual light signal outside the blue-green light band.

[0031] Further, step S7 includes:

[0032] S7.1. The collected blue-green optical carrier signal is transmitted to a 90° optical mixer in a coherent receiving module of a digital coherent detection module. In the 90° optical mixer, the blue-green optical carrier signal is mixed with a local oscillator light generated by a local oscillator laser to form four optical signals with phase differences of 0°, 90°, 180° and 270° respectively.

[0033] S7.2, two optical signals with phase differences of 0° and 180° are transmitted to one balanced detector, and two optical signals with phase differences of 90° and 270° are transmitted to another balanced detector;

[0034] S7.3. The optical signal is converted into an electrical signal in the balanced detector, and an analog in-phase component I electrical signal and an analog orthogonal component Q electrical signal are output from two balanced detectors respectively. The analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal are respectively transmitted to two low-pass filters to eliminate high-frequency noise and useless frequency components.

[0035] Further, step S8 includes:

[0036] S8.1, the analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal are respectively transmitted to two analog-to-digital converters, which respectively convert the analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal into discrete digital in-phase component I electrical signal and digital orthogonal component Q electrical signal;

[0037] S8.2. The electrical signal after analog-to-digital conversion is transmitted to the FPGA module for processing, and frequency offset compensation, clock recovery and phase recovery are performed on it to extract the amplitude and phase information in the signal. The channel is further estimated, noise reduced and compensated, and the signal distortion is corrected to recover its information data, completing high-speed underwater wireless coherent optical communication compatible with multiple modulation formats.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) In the high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats provided by the present invention, the IQ modulator of the high-speed signal generation module can load signals in multiple dimensions of the infrared optical signal to achieve high-order modulation, and support multiple modulation formats, such as OOK, PPM, PAM, BPSK, QPSK and m-QAM modulation formats. By introducing an optical wavelength conversion module to achieve band conversion, the infrared optical carrier signal is converted into a blue-green optical carrier signal that is more suitable for underwater transmission. The modulation is first completed using the mature modulation device in the existing infrared band, and then the optical wavelength conversion module is used to achieve band conversion. The IQ modulator used in the infrared band has a wider bandwidth, which can achieve high-speed communication, and the modulation format that can be achieved More, a variety of modulation formats are flexible and adjustable, which solves the problem that the existing devices that can realize high-order modulation are limited to the infrared band; combined with the beam shaping module and the beam emission alignment module, long-distance, efficient and stable optical signal transmission can be achieved under complex ocean water conditions; the receiving end uses an optical signal collection module to collect the blue-green optical carrier signal in the seawater channel, and the collected blue-green optical carrier signal is converted into a digital signal in the analog-to-digital converter. The digital signal is transmitted to the FPGA module for frequency offset compensation, clock recovery and phase recovery processing, and the amplitude and phase information in the signal are extracted. The channel is further estimated, denoised and compensated, and the signal distortion is corrected to recover its information data, realizing high-speed and long-distance underwater wireless optical communication.

[0040] (2) The frequency doubling crystal used in the optical wavelength conversion module of the high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats provided by the present invention is a nonlinear optical crystal that can complete the conversion of optical bands, and then convert the infrared optical carrier signal modulated by the IQ modulator into a blue-green optical carrier signal that is more suitable for transmission in seawater.

[0041] (3) The optical wavelength conversion module of the multi-modulation format compatible high-speed underwater wireless coherent optical communication system provided by the present invention also includes a collimator and a filter. The collimator can ensure the directionality and quality of the light beam, and the filter can filter out the residual optical signal of the non-blue-green light band, thereby obtaining a high-performance blue-green light carrier signal suitable for transmission in the seawater channel.

[0042] (4) The multi-modulation format compatible high-speed underwater wireless coherent optical communication system provided by the present invention adopts a digital coherent detection module. Compared with direct detection, the digital coherent detection technology it uses can simultaneously obtain the amplitude and phase information of the signal, greatly improving the ability to analyze the spectrum. At the same time, the high sensitivity of digital coherent detection enables it to effectively process low-power optical signals, significantly improving the detection capability and transmission reliability, and providing an implementation solution for large-capacity, long-distance, and high-sensitivity underwater wireless optical communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A schematic structural diagram of an embodiment of a high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats of the present invention;

[0044] Figure 2 A schematic structural diagram of a transmitting end in an embodiment of a high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats of the present invention;

[0045] Figure 3 This is a simplified structural diagram of the receiving end in an embodiment of a high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats of the present invention.

[0046] The following are the descriptions of the reference numerals:

[0047] 1-transmitter, 11-high-speed signal generation module, 111-infrared laser, 112-IQ modulator, 113-high-speed signal generator, 114-driver; 12-optical amplifier, 13-optical wavelength conversion module, 131-frequency doubling crystal, 132-collimator, 133-filter, 134-temperature control system; 14-beam shaping module, 15-beam emission alignment module;

[0048] 2-receiving end, 21-optical signal collection module, 22-digital coherent detection module, 221-coherent receiving module, 2211-local oscillator laser, 2212-90° optical mixer, 2213-balanced detector, 2214-low-pass filter; 222-digital signal processing module, 2221-analog-to-digital converter, 2222-FPGA module;

[0049] 3- Seawater channel. DETAILED DESCRIPTION

[0050] The present invention will be further described below in conjunction with the accompanying drawings and exemplary embodiments.

[0051] Reference Figure 1-Figure 3 The multi-modulation format compatible high-speed underwater wireless coherent optical communication system provided by the present invention includes a transmitter 1 and a receiver 2. The transmitter 1 communicates with the receiver 2 through a seawater channel 3. In practical applications, the seawater channel 3 is seawater.

[0052] The structure of the transmitter 1 is as follows Figure 2 As shown, it includes a high-speed signal generating module 11, an optical amplifier 12, an optical wavelength conversion module 13, a beam shaping module 14 and a beam emission alignment module 15 which are connected in sequence.

[0053] The high-speed signal generating module 11 includes an infrared laser 111, an IQ modulator 112, a high-speed signal generator 113 and a driver 114, wherein the infrared laser 111 can emit an infrared light signal with a wavelength of 1550nm, and the output end of the infrared laser 111 is connected to the first input end of the IQ modulator 112, the output end of the high-speed signal generator 113 is connected to the input end of the driver 114, and the output end of the driver 114 is connected to the second input end of the IQ modulator 112. The IQ modulator 112 loads the high-speed signal onto the received infrared light signal to form an infrared light carrier signal to complete high-order modulation, and the IQ modulator 112 is a mature infrared band modulation device, which can realize various modulation formats such as OOK, PPM, PAM, BPSK, QPSK and m-QAM, and can be flexibly modulated according to actual applications.

[0054] In order to ensure the stability of the optical signal in subsequent transmission, its power needs to be amplified, so an optical amplifier 12 is provided, and the input end of the optical amplifier 12 is connected to the output end of the IQ modulator 112 for amplifying the power of the infrared optical carrier signal.

[0055] The optical wavelength conversion module 13 includes a frequency doubling crystal 131, a collimator 132, a filter 133 and a temperature control system 134. The input end of the frequency doubling crystal 131 is connected to the output end of the optical amplifier 12, the output end of the frequency doubling crystal 131 is connected to the input end of the collimator 132, and the output end of the collimator 132 is connected to the input end of the filter 133. Because the frequency doubling crystal 131 is a nonlinear optical crystal, if it is used directly, it needs to adjust its angle continuously. Therefore, the frequency doubling crystal 131 is generally encapsulated in the module, and its input and output ends are both optical fibers. In actual use, it can be directly connected to the input and output ends for use, saving adjustment time, and a coupling mirror can be added to the input and output ends to improve the conversion efficiency. In this embodiment, the infrared laser 111 emits infrared light with a wavelength of 1550nm, so the frequency doubling crystal 131 uses a triple frequency doubling crystal in this embodiment, which can convert an infrared light carrier signal with a wavelength of 1550nm into a blue-green light carrier signal with a wavelength of about 517nm.

[0056] The collimator 132 can collimate the blue-green light carrier signal to ensure the directionality and quality of its light beam, and the filter 133 is a blue light filter, which only allows the blue-green light carrier signal with a wavelength of about 517nm to pass through, thereby filtering out the residual light signal outside the blue-green light band, and then obtaining a high-performance blue-green light carrier signal suitable for transmission in the seawater channel 3.

[0057] The temperature control system 134 is used to adjust the working temperature of the frequency doubling crystal 131 so that it is always at the optimal working temperature, thereby ensuring the nonlinear conversion efficiency and working stability of the crystal and avoiding the influence of ambient temperature fluctuations on the conversion process.

[0058] The beam shaping module 14 includes a beam splitter and a spatial light modulator connected in sequence. The output end of the filter 133 is connected to the input end of the beam splitter. The blue-green light carrier signal is transmitted to the beam splitter for beam splitting, and then enters the spatial light modulator to optimize its beam shape and energy distribution. The optimized blue-green light carrier signal has a better beam shape and energy distribution, and can reduce energy loss caused by scattering and diffraction, providing high-quality optical signal input for subsequent modules, ensuring the reliability and stability of long-distance transmission.

[0059] The input end of the beam emission alignment module 15 is connected to the output end of the spatial light modulator, which is used to adjust the angle and direction of the beam so that the blue-green light carrier signal can be aligned with the receiving end 2, thereby realizing an efficient and stable communication link. Therefore, the beam emission angle and direction of the blue-green light carrier signal must be adjusted so that more blue-green light carrier signals can reach the receiving end 2. As a mature optical device, the galvanometer can adjust the angle and direction of the beam through directional vibration. The role of the galvanometer in the optical field is to adjust the angle and direction of the beam. Here, the beam emission alignment module 15 can be implemented by a galvanometer, etc.

[0060] The structure of receiving end 2 is as follows Figure 3 As shown, it includes an optical signal collection module 21 and a digital coherent detection module 22 which are connected in sequence.

[0061] Because the blue-green optical carrier signal emitted from the beam emission alignment module 15 is transmitted in the seawater channel 3 in the form of spatial free light, it is necessary to set up an optical signal collection module 21 to efficiently collect the blue-green optical carrier signal in the seawater channel 3 to provide sufficient signal input for subsequent modules.

[0062] The digital coherent detection module 22 includes a coherent receiving module 221 and a digital signal processing module 222 connected in sequence. Compared with direct detection, the digital coherent detection technology it adopts can simultaneously obtain the amplitude and phase information of the signal, greatly improving the ability to analyze the spectrum. At the same time, the high sensitivity of coherent detection enables it to effectively process low-power optical signals, significantly improving the detection capability and transmission reliability of weak optical signals, and providing an implementation solution for large-capacity, long-distance, and high-sensitivity underwater wireless optical communications.

[0063] The coherent receiving module 221 includes a local oscillator laser 2211, a 90° optical mixer 2212, a balanced detector 2213 and a low-pass filter 2214. The output end of the optical signal collecting module 21 is connected to the first input end of the 90° optical mixer 2212, the output end of the local oscillator laser 2211 is connected to the second input end of the 90° optical mixer 2212, and there are two balanced detectors 2213. The blue-green optical carrier signal is transmitted to the 90° optical mixer. In the frequency mixer 2212, the local oscillator laser 2211 emits the local oscillator light to the 90° optical mixer 2212, and the blue-green light carrier signal is mixed with the local oscillator light in the 90° optical mixer 2212 to form four optical signals with phase differences of 0°, 90°, 180° and 270° respectively; and the 90° optical mixer 2212 has four output ends, and the two input ends of one of the balanced detectors 2213 are respectively connected to the two output ends of the 90° optical mixer 2212. The output ends of the two balanced detectors 2213 are connected, and the phase differences of the optical signals outputted from the two output ends of the 90° optical mixer 2212 are 0° and 180° respectively; the two input ends of another balanced detector 2213 are connected to the other two output ends of the 90° optical mixer 2212, and the phase differences of the optical signals outputted from the other two output ends of the 90° optical mixer 2212 are 90° and 270° respectively, the balanced detector 2213 converts the received optical signal into an analog electrical signal, and outputs an analog in-phase component I electrical signal and an analog orthogonal component Q electrical signal from the two balanced detectors 2213 respectively, there are two low-pass filters 2214, the input ends of the two low-pass filters 2214 are connected to the output ends of the two balanced detectors 2213 respectively, and the output ends are connected to the input ends of the two analog-to-digital converters 2221 respectively, the analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal are transmitted to the two low-pass filters 2214 respectively to eliminate high-frequency noise and useless frequency components.

[0064] The digital signal processing module 222 includes an analog-to-digital converter 2221 and an FPGA module 2222. There are two analog-to-digital converters 2221, and the input ends of the two analog-to-digital converters are respectively connected to the output ends of the two low-pass filters 2214, and the output ends are connected to the FPGA module 2222. The analog in-phase component I electrical signal and the analog quadrature component Q electrical signal are respectively transmitted to the two analog-to-digital converters 2221, which respectively convert the analog in-phase component I electrical signal and the analog quadrature component Q electrical signal into discrete digital in-phase component I electrical signal and digital quadrature component Q electrical signal. The electrical signals after analog-to-digital conversion are transmitted to the FPGA module 2222 for processing, and frequency offset compensation, clock recovery and phase recovery are performed on them, and the amplitude and phase information in the signal are extracted. The paired channels are further estimated, noise reduced and compensated, and the signal distortion is corrected to recover its information data.

[0065] At the same time, the present invention also provides a high-speed underwater wireless coherent optical communication method compatible with multiple modulation formats, using the above-mentioned high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats, comprising the following steps:

[0066] S1, start the infrared laser 111, the high-speed signal generator 113 and the driver 114, the infrared laser 111 transmits an infrared light signal to the IQ modulator 112, the high-speed signal generator 113 transmits a high-speed signal and inputs it into the IQ modulator 112 through the driver 114, and the IQ modulator 112 loads the received high-speed signal onto the received infrared light signal to form an infrared light carrier signal;

[0067] S2, the infrared optical carrier signal is transmitted to the optical amplifier 12 to amplify its power;

[0068] S3, the infrared light carrier signal after power amplification is transmitted to the frequency doubling crystal 131 of the optical wavelength conversion module 13, the frequency doubling crystal 131 uses the nonlinear optical effect to convert the infrared light carrier signal into a blue-green light carrier signal, the blue-green light carrier signal is transmitted to the collimator 132 for collimation, and the collimated blue-green light carrier signal is transmitted to the filter 133 to filter out the residual light signal of the non-blue-green light band;

[0069] S4, the blue-green optical carrier signal is transmitted to the beam splitter in the beam shaping module 14 for beam splitting, and then enters the spatial light modulator to optimize its beam shape and energy distribution, thereby improving the stability during underwater transmission;

[0070] S5, the optimized blue-green light carrier signal is transmitted to the light beam emission alignment module 15 to adjust its light beam angle and direction, and the adjusted blue-green light carrier signal is emitted into the seawater channel 3 in the form of spatial free light for transmission;

[0071] S6, the blue-green optical carrier signal transmitted through the seawater channel 3 is transmitted to the optical signal collection module 21 for collection;

[0072] S7.1. The collected blue-green optical carrier signal is transmitted to the 90° optical mixer 2212 in the coherent receiving module 221 of the digital coherent detection module 22. The blue-green optical carrier signal is mixed with the local oscillator light generated by the local oscillator laser 2211 in the 90° optical mixer 2212 to form four optical signals with phase differences of 0°, 90°, 180° and 270° respectively.

[0073] S7.2, two optical signals with phase differences of 0° and 180° are transmitted to one balanced detector 2213, and two optical signals with phase differences of 90° and 270° are transmitted to another balanced detector 2213;

[0074] S7.3. The optical signal is converted into an electrical signal in the balanced detector 2213, and the analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal are output from the two balanced detectors 2213 respectively. The analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal are respectively transmitted to two low-pass filters 2214 to eliminate high-frequency noise and useless frequency components.

[0075] S8.1, the analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal are respectively transmitted to two analog-to-digital converters 2221, which respectively convert the analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal into discrete digital in-phase component I electrical signal and digital orthogonal component Q electrical signal;

[0076] S8.2. The electrical signal after analog-to-digital conversion is transmitted to FPGA module 2222 for processing, and frequency offset compensation, clock recovery and phase recovery are performed on it to extract the amplitude and phase information in the signal. The channel is further estimated, noise reduced and compensated, and the signal distortion is corrected to recover its information data, thereby completing high-speed underwater wireless coherent optical communication compatible with multiple modulation formats.

[0077] The embodiments described above are merely descriptions of specific implementation methods of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats, characterized in that: The invention comprises a transmitting end (1) and a receiving end (2), wherein the transmitting end (1) communicates with the receiving end (2) through a seawater channel (3); the transmitting end (1) comprises a high-speed signal generating module (11), an optical amplifier (12), an optical wavelength conversion module (13), a beam shaping module (14) and a beam emission alignment module (15) which are connected in sequence; the receiving end (2) comprises an optical signal collecting module (21) and a digital coherent detection module (22) which are connected in sequence; The high-speed signal generating module (11) is used to generate an infrared optical carrier signal, and comprises an infrared laser (111), an IQ modulator (112), a high-speed signal generator (113) and a driver (114); the output end of the infrared laser (111) is connected to a first input end of the IQ modulator (112); the output end of the high-speed signal generator (113) is connected to an input end of the driver (114); and the output end of the driver (114) is connected to a second input end of the IQ modulator (112); The input end of the optical amplifier (12) is connected to the output end of the IQ modulator (112); The optical wavelength conversion module (13) comprises a frequency doubling crystal (131), the input end of the frequency doubling crystal (131) being connected to the output end of the optical amplifier (12) and being used for converting the infrared optical carrier signal into a blue-green optical carrier signal; The beam shaping module (14) comprises a beam splitter and a spatial light modulator connected in sequence, and the output end of the frequency doubling crystal (131) is connected to the input end of the beam splitter; The input end of the light beam emission alignment module (15) is connected to the output end of the spatial light modulator, and is used to adjust the light beam angle and direction of the blue-green light carrier signal, and emit the blue-green light carrier signal into the seawater channel (3) in the form of spatial light; The optical signal collection module (21) is used to collect blue-green optical carrier signals transmitted from the seawater channel (3); The digital coherent detection module (22) comprises a coherent receiving module (221) and a digital signal processing module (222) which are connected in sequence; The coherent receiving module (221) is used to convert the blue-green optical carrier signal transmitted by the optical signal collecting module (21) into an analog electrical signal; The digital signal processing module (222) is used to convert the analog electrical signal into a digital electrical signal and process the digital electrical signal to recover its information data.

2. The multi-modulation format compatible high-speed underwater wireless coherent optical communication system according to claim 1, characterized in that: The coherent receiving module (221) comprises a local oscillator laser (2211), a 90° optical mixer (2212) and a balanced detector (2213); the output end of the optical signal collecting module (21) is connected to the first input end of the 90° optical mixer (2212); the output end of the local oscillator laser (2211) is connected to the second input end of the 90° optical mixer (2212); there are two balanced detectors (2213), two input ends of one balanced detector (2213) are connected to the 90° optical mixer (2212) and two input ends of the other balanced detector (2213) are connected to the 90° optical mixer (2212). The balanced detector (2213) is connected to two output ends of a 90° optical mixer (2212), and the phase differences of the optical signals outputted from the two output ends of the 90° optical mixer (2212) are 0° and 180° respectively; the two input ends of another balanced detector (2213) are connected to the other two output ends of the 90° optical mixer (2212), and the phase differences of the optical signals outputted from the other two output ends of the 90° optical mixer (2212) are 90° and 270° respectively, and the balanced detector (2213) is used to convert the received optical signal into an analog electrical signal; The digital signal processing module (222) comprises an analog-to-digital converter (2221) and an FPGA module (2222); there are two analog-to-digital converters (2221) for converting analog electrical signals into digital electrical signals; the input ends of the two analog-to-digital converters (2221) are respectively connected to the output ends of two balanced detectors (2213); the output ends of the two analog-to-digital converters (2221) are connected to the FPGA module (2222); and the FPGA module (2222) is used to process the digital electrical signals to recover their information data.

3. The multi-modulation format compatible high-speed underwater wireless coherent optical communication system according to claim 2, characterized in that: The coherent receiving module (221) further comprises a low-pass filter (2214), wherein there are two low-pass filters (2214), the input ends of the two low-pass filters (2214) are respectively connected to the output ends of the two balanced detectors (2213), and the output ends are respectively connected to the input ends of the two analog-to-digital converters (2221).

4. The multi-modulation format compatible high-speed underwater wireless coherent optical communication system according to claim 3, characterized in that: The optical wavelength conversion module (13) further comprises a collimator (132) and an optical filter (133); the output end of the frequency doubling crystal (131) is connected to the input end of the collimator (132); the output end of the collimator (132) is connected to the input end of the optical filter (133); and the output end of the optical filter (133) is connected to the input end of the beam splitter.

5. The multi-modulation format compatible high-speed underwater wireless coherent optical communication system according to claim 4, characterized in that: The optical wavelength conversion module (13) further comprises a temperature control system (134), wherein the temperature control system (134) is used to adjust the operating temperature of the frequency doubling crystal (131).

6. A high-speed underwater wireless coherent optical communication method compatible with multiple modulation formats, using the high-speed underwater wireless coherent optical communication system compatible with multiple modulation formats as described in any one of claims 1 to 5, characterized in that: The following steps are involved: S1, starting the infrared laser (111), the high-speed signal generator (113) and the driver (114), the infrared laser (111) emits an infrared light signal to the IQ modulator (112), the high-speed signal generator (113) emits a high-speed signal and inputs the high-speed signal into the IQ modulator (112) through the driver (114), and the IQ modulator (112) loads the received high-speed signal onto the received infrared light signal to form an infrared light carrier signal; S2, the infrared optical carrier signal is transmitted to the optical amplifier (12) to amplify its power; S3, the infrared optical carrier signal after power amplification is transmitted to the frequency doubling crystal (131) of the optical wavelength conversion module (13), and the frequency doubling crystal (131) converts the infrared optical carrier signal into a blue-green optical carrier signal by using the nonlinear optical effect; S4, the blue-green optical carrier signal is transmitted to the beam splitter in the beam shaping module (14) for beam splitting, and then enters the spatial light modulator to optimize its beam shape and energy distribution, thereby improving the stability during underwater transmission; S5, the optimized blue-green light carrier signal is transmitted to the light beam emission alignment module (15) to adjust the light beam angle and direction, and the adjusted blue-green light carrier signal is emitted into the seawater channel (3) in the form of spatial free light for transmission; S6, the blue-green optical carrier signal transmitted through the seawater channel (3) is transmitted to the optical signal collection module (21) for collection; S7, the collected blue-green optical carrier signal is transmitted to the coherent receiving module (221) of the digital coherent detection module (22) for processing, and the blue-green optical carrier signal is converted into an analog electrical signal; S8. The analog electrical signal is transmitted to the digital signal processing module (222) for processing, the analog electrical signal is converted into a digital electrical signal and processed to recover its information data, thereby completing high-speed underwater wireless coherent optical communication compatible with multiple modulation formats.

7. The multi-modulation format compatible high-speed underwater wireless coherent optical communication method according to claim 6, characterized in that: Step S3 specifically comprises: transmitting the infrared light carrier signal after power amplification to the frequency doubling crystal (131) of the optical wavelength conversion module (13); the frequency doubling crystal (131) converts the infrared light carrier signal into a blue-green light carrier signal by using the nonlinear optical effect; the blue-green light carrier signal is transmitted to the collimator (132) for collimation; the collimated blue-green light carrier signal is transmitted to the filter (133) to filter out residual light signals in non-blue-green light bands.

8. The multi-modulation format compatible high-speed underwater wireless coherent optical communication method according to claim 7, characterized in that: Step S7 includes: S7.1, the collected blue-green optical carrier signal is transmitted to the 90° optical mixer (2212) in the coherent receiving module (221) of the digital coherent detection module (22), and the blue-green optical carrier signal is mixed with the local oscillator light generated by the local oscillator laser (2211) in the 90° optical mixer (2212) to form four optical signals with phase differences of 0°, 90°, 180° and 270° respectively; S7.2, two optical signals with phase differences of 0° and 180° are transmitted to a balanced detector (2213), and two optical signals with phase differences of 90° and 270° are transmitted to another balanced detector (2213); S7.

3. The optical signal is converted into an electrical signal in the balanced detector (2213), and an analog in-phase component I electrical signal and an analog orthogonal component Q electrical signal are outputted from the two balanced detectors (2213) respectively. The analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal are respectively transmitted to two low-pass filters (2214) to eliminate high-frequency noise and useless frequency components.

9. The multi-modulation format compatible high-speed underwater wireless coherent optical communication method according to claim 8, characterized in that: Step S8 includes: S8.1, the analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal are respectively transmitted to two analog-to-digital converters (2221), which respectively convert the analog in-phase component I electrical signal and the analog orthogonal component Q electrical signal into discrete digital in-phase component I electrical signal and digital orthogonal component Q electrical signal; S8.

2. The electrical signal after analog-to-digital conversion is transmitted to the FPGA module (2222) for processing, and frequency offset compensation, clock recovery and phase recovery are performed on it to extract the amplitude and phase information in the signal. The channel is further estimated, noise reduced and compensated, and the signal distortion is corrected to recover its information data, thereby completing high-speed underwater wireless coherent optical communication compatible with multiple modulation formats.

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