CN116015465A - Underwater wireless optical communication device and method based on single photon detector - Google Patents
Underwater wireless optical communication device and method based on single photon detector Download PDFInfo
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Abstract
The invention discloses an underwater wireless optical communication device based on a single photon detector, which comprises a first single photon communication device and a second single photon communication device which are in two-way communication, wherein the first single photon communication device and the second single photon communication device respectively comprise a laser emitting unit, a signal receiving unit, a signal comprehensive processing unit and a power supply module; the laser transmitting unit loads the received modulated electric signals into optical signals and outputs the optical signals, and simultaneously transmits auxiliary alignment laser to align the communication device; the signal receiving unit converts the received optical signals into electric signals through the single photon detector and transmits the electric signals to the outside, and meanwhile, the signal receiving unit receives auxiliary alignment laser to finish alignment of the communication device; the signal comprehensive processing unit receives the communication information of the upper computer, converts the communication information into a modulated electric signal, transmits the modulated electric signal to the laser transmitting unit, demodulates and restores the electric signal transmitted by the signal receiving unit into the communication information, and transmits the communication information to the upper computer. The invention can improve the underwater communication distance and meet the requirements of long-distance wireless optical communication under different water quality environments.
Description
Technical Field
The invention relates to the technical field of underwater wireless optical communication, in particular to an underwater wireless optical communication device and method based on a single photon detector.
Background
With the gradual deep cognition and development of ocean characteristics, unmanned submarines, underwater robots and submarine preset systems are increasingly widely applied, and the number of nodes is gradually increased, so that the unmanned submarines, the underwater robots and the submarine preset systems become an important component of an ocean information network. Meanwhile, the bandwidth requirements for information transmission among underwater platforms are greatly increased, and how to hinge dynamic and static nodes scattered in each water area quickly unloads data of each network node, so that the information transmission capacity is improved, the communication requirements of high bandwidth, instantaneity and concealment are met, and the problem to be solved in the field of underwater communication is urgent.
In recent years, low-loss underwater wireless optical communication technology (Underwater optical wireless communication, UOWC) has been widely focused, and has a higher transmission rate, a lower transmission link delay, i.e. lower energy consumption of a transceiver system, and the transmission rate and the communication distance of a typical UOWC system can reach the order of magnitude of Gbps/tens of meters and magnitude of Mbps/hundred meters, which is an important technical means for future deep-sea underwater information transmission. However, in long-distance underwater wireless optical communication, the transmission of an optical link is affected by the combined action of underwater channel complexity, water attenuation, scattering caused by macromolecular particles and flat fading caused by underwater turbulence, the energy of an optical signal reaching a receiving end after long-distance transmission is very weak, and the conventional underwater wireless optical communication technology is difficult to meet the long-distance communication requirement. In recent years, with the development of single photon detection devices, the detection sensitivity of a receiver is improved from the device end, and the detection sensitivity is a key for breaking through the action distance of underwater wireless optical communication in the future. However, while the introduction of single photon detectors helps to increase the range of the underwater wireless optical communication system in terms of sensitivity, it is limited by the partial single photon detector target surface size (such as about 200 μm in Si-GMAPD mature product), the optical field angle of the system is small, and alignment of the link during underwater communication is a great challenge. Meanwhile, the high-sensitivity signal detection also brings the problems of background noise sensitivity and the like, and under the interference of different water quality conditions and different background noise, the robust demodulation of the information is difficult to complete through single parameter setting, and the high requirements on the environmental adaptability and the communication error rate of the underwater single-photon wireless optical communication are also put forward. Therefore, the invention provides an underwater wireless optical communication device and a method based on single photon detection, which are used for solving or partially solving the technical problem of the current underwater high-sensitivity wireless optical communication.
Disclosure of Invention
The invention aims to design an underwater bidirectional wireless optical communication device and method based on a single photon detector according to the defects of the prior art, so that the underwater communication distance is increased, and the requirements of long-distance wireless optical communication under different water quality environments are met.
The technical scheme adopted by the invention is as follows:
there is provided an underwater wireless optical communication device based on a single photon detector, characterized in that,
the system comprises a first single-photon communication device and a second single-photon communication device which are in two-way communication, wherein the first single-photon communication device and the second single-photon communication device both comprise a laser emitting unit, a signal receiving unit, a signal comprehensive processing unit and a power module;
the laser transmitting unit loads the received modulated electric signals into optical signals and outputs the optical signals, and simultaneously transmits auxiliary alignment laser to align the communication device;
the signal receiving unit converts the received optical signal into an electric signal through the single photon detector and transmits the electric signal to the outside, and simultaneously receives auxiliary alignment laser to finish alignment of the communication device;
the signal comprehensive processing unit receives the communication information of the upper computer, converts the communication information into a modulated electric signal, transmits the modulated electric signal to the laser transmitting unit, demodulates and restores the electric signal transmitted by the signal receiving unit into the communication information, and transmits the communication information to the upper computer.
The technical scheme is that the laser emission unit comprises two light paths, wherein one light path comprises a beacon laser and a first collimator; the other light path comprises a plurality of information source lasers, a beam combiner, a second collimator, a dichroic mirror and a beam expanding optical system; the beam combiner is used for combining the laser output by the plurality of information source lasers into one path and outputting the laser; the first collimator is used for collimating the beacon laser and outputting the collimated beacon laser; the second collimator is used for collimating the information source laser and outputting the collimated information source laser; the dichroic mirror is connected with the first collimator and the second collimator, and is used for combining the collimated information source laser and the beacon laser and outputting the combined information source laser and the combined beacon laser to the beam expanding optical system.
With the technical proposal, the wavelength of the source laser of one laser emitting unit is the same as that of the beacon laser of the other laser emitting unit.
The signal receiving unit comprises two paths of light paths, wherein one path of light path comprises a receiving optical system, a dichroic mirror, an optical filter assembly, a first converging optical system and a single photon detector which are connected in sequence; the receiving optical system receives the laser emitted by the laser emitting unit, the dichroic mirror is used for separating the information source laser from the beacon laser, the information source laser is filtered by the optical filter assembly and then is output to the first converging optical system so as to converge the information source laser energy to the target surface of the single photon detector, and the single photon detector is used for receiving the information source laser energy and converting the information source laser energy into a digital pulse signal and outputting the digital pulse signal to the signal comprehensive processing unit;
the other path comprises a second converging optical system and a camera, the second converging optical system is connected with the dichroic mirror, and the camera is connected with an external computer; the second converging optical system is used for converging the beacon laser energy to the target surface of the camera, and the camera receives the beacon laser light spot and finishes the alignment of the transmitting and receiving optical axes according to the light spot position.
The above technical solution is adopted, wherein the band-pass center wavelength range of the filter component of the signal receiving unit of the first single photon communication device covers the wavelengths of the plurality of source lasers of the laser transmitting unit of the second single photon communication device, and the cut-off wavelength range covers the wavelengths of the plurality of source lasers of the first laser transmitting unit.
According to the technical scheme, the band-pass center wavelength range of the optical filter component of the receiving unit of the second single-photon communication device covers the wavelengths of the plurality of source lasers of the laser emitting unit of the first single-photon communication device, and the cut-off wavelength range covers the wavelengths of the plurality of source lasers of the laser emitting unit of the second single-photon communication device.
By adopting the technical scheme, the single photon detector is a Geiger mode APD single photon detector, a photon counting PMT single photon detector or a superconductive nanowire single photon detector.
The camera is a CCD camera or a CMOS camera.
The signal comprehensive processing unit comprises an information transmission module, a level conversion module, a modulation function module, a demodulation function module and a system initialization module.
The invention also provides an underwater wireless optical communication method based on the single photon detector, which is based on the underwater wireless optical communication device based on the single photon detector and comprises the following steps:
the method comprises the steps of firstly, completing the alignment of the transmitting and receiving optical axes of a first single photon communication device and a second single photon communication device;
the second step, the laser emission unit emits low-energy, medium-energy and high-energy lasers, the scattered echo count collected by the signal receiving unit is used for evaluating the absorption coefficient and the scattering coefficient of the water quality environment, and the average value of the three measurements is used as the absorption coefficient and the scattering coefficient of the current water quality environment;
thirdly, determining the current water quality condition according to the sum value of the absorption coefficient and the scattering coefficient, and setting low-energy and high-repetition frequency modulation to realize the output of the information source laser when the current water quality condition is lower than the clean seawater attenuation coefficient; when the attenuation coefficient is higher than the attenuation coefficient of clean seawater, high energy and low repetition frequency modulation are set to realize the output of the information source laser;
and fourthly, counting the background noise photon counting rate and the maximum information photon counting rate of the single symbol period environment by the signal receiving unit through the single photon detector, setting a minimum pulse interval threshold value and a signal recovery judgment threshold value of on-line signal demodulation so as to adapt to communication under different background environments and transmission distances, and repeating the third and fourth steps to realize continuous communication transmission. The first step comprises: and the beacon laser and the camera of the two single photon communication devices are used for completing auxiliary alignment, so that the centers of the converging light spots of the source lasers at the two ends fall at the alignment center position of the camera.
The second step comprises:
1) The beacon laser is set to a fixed frequency output, first emitting N with low single pulse energy L Pulse, trigger detector and data acquisition device to obtain T L Performing exponential fitting on the long-duration backward scattering signal according to the scattering waveform to obtain a water body absorption coefficient A under low pulse energy L Scattering coefficient B L
2) Sequentially adopting the same method to transmit medium energy N M Pulse and high energy N H Pulse to obtain the absorption coefficient A of the corresponding medium energy water body M Scattering coefficient B M And a high energy water absorption coefficient A H Scattering coefficient B H . And averaging the three measurement results to obtain an absorption coefficient A and a scattering coefficient B of the current water quality environment:
the third step comprises:
when the sum of the absorption coefficient A and the scattering coefficient B is lower than 0.151m -1 (clean seawater attenuation coefficient) shows that the current water quality condition is better, and the low-energy and high-repetition-frequency modulation is set to realize the output of the information source laser; when the sum of the absorption coefficient A and the scattering coefficient B is higher than 0.151m -1 The current water quality condition is worse, and the high-energy and low-repetition-frequency modulation is set to realize the output of the information source laser.
The source laser energy output is set by the laser's single pulse out light duration. At low energy output, the duration T of light emission s Short; at high energy output, the duration T of light emission s Long.
Modulation frequency and communication frequency R of information source laser b Direct correlation, due to the discrete pulse output characteristics of single photon detection and dead time constraints, 1/R in a single symbol period of communication b The source laser does not always keep high level, and adopts a spread spectrum output mode, namely 1/R in a single symbol period b N pulses are transmitted, wherein N is the spread spectrum number, and the capacity loss caused by the dead time of the single photon detector is avoided.
The fourth step includes:
a) Under the condition that the information source laser and the beacon laser are closed, the single photon detector is turned on, and the single photon detector can output discrete pulses outwards due to factors such as environmental noise, dark counting and the like. Counting single symbol period 1/R by signal integrated processing unit b Maximum count rate N of internal noise DCR 。
b) The information source laser works normally, the single photon detector outputs pulse outwards after receiving the laser signal, and the maximum counting rate N of the single photon detector is counted in the single symbol period 1/R of communication SIG ；
c) To ensure low error rate of communication, the noise count rate N is required to be used DCR And maximum signal count rate N SIG Comprehensively setting a minimum pulse interval threshold T inter Signal recovery decision threshold N RECOVER The value is as follows:
i.e. when the signal is demodulated, the time interval between the first pulse signal and the second pulse signal of the single photon detector is longer than T inter When the current pulse is considered as a noise photon, the subsequent counting statistics is not carried out, and the signal photon is waited again; when the interval time between the first pulse signal and the second pulse signal of the single photon detector is less than or equal to T inter When the pulse is considered a signal photon, counting statistics of a subsequent single symbol period begin. When the count statistic value is greater than or equal to N RECOVER When the count statistics is smaller than N, the symbol is "1 RECOVER When this symbol is considered to be "0".
d) Repeating the steps b) to c) to complete the demodulation of one frame of communication data.
The invention has the beneficial effects that: the invention adopts the single photon detector as the receiver to realize the signal detection with higher sensitivity, thereby improving the system action distance.
Secondly, aiming at the high sensitivity characteristic of the single photon detector, an optical isolation method is adopted to inhibit the back scattering influence of the same side source laser, thereby ensuring the bidirectional full duplex communication capability.
Thirdly, the water quality condition is evaluated according to the back scattering echo count value of the beacon laser under different low, medium and high energies, the output energy and the modulation frequency of the information source laser are adaptively modulated, the communication requirements of different water quality environments are met, and the system robustness is improved.
Finally, according to the background noise photon count and the maximum information photon count of the single symbol period environment obtained by the single photon detector, the on-line signal demodulation threshold setting is completed, the requirements of different background environments and transmission distances can be met, the communication error rate is reduced, and the environmental adaptability of single photon communication is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following description will briefly explain the drawings used in the embodiments or the description of the prior art, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of two-way communication of a single photon communication device according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a laser emitting unit of a single photon communication device according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a signal receiving unit of a single photon communication device according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a signal integrated processing unit of a single photon communication device according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As shown in fig. 1, the underwater bidirectional wireless optical communication device based on the single photon detector in the embodiment of the invention specifically comprises a single photon communication device 1 and a single photon communication device 2, wherein the two devices are independent communication modules and can realize bidirectional communication for transmitting and receiving ends.
The single photon communication device 1 includes a laser emitting unit 11, a signal receiving unit 12, a signal integrated processing unit 13, and a power module 14. The single photon communication device 2 includes a laser emitting unit 21, a signal receiving unit 22, a signal integrated processing unit 23, and a power module 24.
The function of the laser emitting units 11, 22 is the same as the optical path arrangement. The laser transmitting unit can load the received modulated electric signals into the optical signals to realize the transmission of communication information, and can transmit auxiliary alignment laser to complete the alignment of the communication device. As shown in fig. 2, the laser emission unit specifically includes two light paths, one of which includes a beacon laser and a collimator b1, and the other includes source lasers a1 to aN, a beam combiner, a collimator b2, a dichroic mirror c, and a beam expanding optical system. The beacon laser is a high power, continuous laser, and is an auxiliary alignment light source. The information source lasers a 1-aN are high-modulation-frequency and high-extinction-ratio lasers and are used for completing optical transmission of communication information, and light and closing are realized through external modulation pulses. The source lasers 1a to 1N of the laser emitting unit 11 have the same wavelength as the beacon lasers of the laser emitting unit 22, and the source lasers 1a to 1N of the laser emitting unit 22 have the same wavelength as the beacon lasers of the laser emitting unit 11. The beam combiner is used for combining the laser output by the plurality of information source lasers into one path and outputting the laser, and the optical fiber beam combiner can be selected. The collimator b1 is used for collimating and outputting the beacon laser; the collimator b2 is used for collimating the source laser and outputting the collimated source laser. The dichroic mirror c is used for combining the collimated information source laser and the beacon laser and outputting the combined information source laser and the combined beacon laser to the beam expanding optical system. The beam expanding optical system is used for outputting the beam-expanded laser beam after expanding the beam, reducing the emergent divergence angle and improving the communication distance.
The function of the signal receiving units 12, 21 is the same as the optical path arrangement. The signal receiving unit can convert the received optical signal into an electrical signal and transmit the electrical signal to the outside, and can receive auxiliary alignment laser to complete alignment of the communication device. As shown in fig. 3, the signal receiving unit includes two paths, one path specifically includes a receiving optical system, a dichroic mirror, an optical filter assembly, a converging optical system d1, and a single photon detector, which are sequentially connected, the receiving optical system receives the laser emitted by the laser emitting unit, and outputs the laser to the signal comprehensive processing unit through the single photon detector; the other path comprises a converging optical system d2 and a camera which are connected, the converging optical system d2 is connected with a dichroic mirror, and the camera is connected with an external computer (used for transmitting user data to a signal comprehensive processing unit). The receiving optical system is used for receiving the laser energy and transmitting the laser energy to the dichroic mirror. The dichroic mirror is used for separating the source laser from the beacon laser, and one is used for completing communication and the other is used for completing alignment. The filter set is a bandpass filter set, and the bandpass center wavelength range of the filter set of the signal receiving unit 12 covers the plurality of source lasers of the laser emitting unit 22, and the cutoff wavelength range covers the plurality of source lasers of the laser emitting unit 11. The band-pass center wavelength range of the filter assembly of the signal receiving unit 21 covers the plurality of source lasers of the laser emitting unit 11, and the cut-off wavelength range covers the plurality of source lasers of the laser emitting unit 22. The converging optical system d1 is used for converging the source laser energy to the target surface of a single photon detector, and the single photon detector is used for receiving the source laser energy and converting the source laser energy into a digital pulse signal, such as a geiger mode APD single photon detector, a photon counting PMT single photon detector, a superconducting nanowire single photon detector or the like. The converging optical system d2 is used for converging the beacon laser energy to the camera target surface. The camera is used for receiving the beacon laser light spot and aligning the transmitting and receiving optical axes according to the position of the light spot, such as a CCD camera, a CMOS camera and the like.
The signal synthesis processing units 13, 23 are identical. The signal comprehensive processing unit receives the communication information of the upper computer (namely the computer), converts the communication information into a modulated electric signal and transmits the modulated electric signal to the laser transmitting unit, demodulates and restores the electric signal transmitted by the signal receiving unit into the communication information, and transmits the communication information to the upper computer. Meanwhile, the on-off of the beacon laser and the on-off of the camera can be controlled according to the requirements. As shown in fig. 4, the signal comprehensive processing unit includes an information transmission module, a level conversion module, a modulation function module, a demodulation function module, and a system initialization module.
The information transmission module is used for receiving information transmitted by the upper computer and converting the information into data to be transmitted to the modulation function module; the modulation energy-passing module encodes the data to be transmitted and then transmits the encoded data to the level conversion module in a high (representing a symbol of '1') and low (representing a symbol of '0') level form; the level conversion module loads high and low levels onto the laser according to the laser driving power supply, and the high level emits light and the low level does not emit light. Meanwhile, discrete pulses output by the single photon detector are converted into level signals which can be detected by the demodulation functional module; the demodulation function module demodulates the discrete pulse output by the single photon detector, and then transmits the demodulation information to a computer through the information transmission module; the system initialization module is used for completing initialization setting of other modules.
The laser transmitting units and the signal receiving units in the two single photon communication devices are symmetrically arranged, and the alignment of the short-distance transmitting ends and the receiving ends is ensured.
The underwater wireless optical communication method based on the single photon detector comprises the following steps:
in a first step, alignment of the emission and reception optical axes of the single photon communication device 1 and the single photon communication device 2 is accomplished by a beacon laser and a camera.
And secondly, according to the low-energy, medium-energy and high-energy laser emitted by the beacon laser, the absorption coefficient and the scattering coefficient of the water quality environment are evaluated by using the scattered echo count acquired by the single photon detector.
And thirdly, adaptively adjusting the single pulse energy and the modulation frequency of the source laser according to the estimated absorption coefficient and the estimated scattering coefficient, and transmitting a frame of communication information.
And fourthly, converting the received optical signals into output discrete pulse digital signals by a single photon detector in the signal receiving unit, demodulating the discrete pulse digital signals by a signal comprehensive processing unit to recover one frame of communication information, and repeating the third and fourth steps to realize continuous communication transmission. In the two-way communication, the single photon communication device 1 and the communication device 2 are mutually information transmitting and receiving ends.
The first step comprises:
(1) The beacon laser in the single photon communication device 1 continuously outputs, and the camera 2 in the single photon communication device 2 adjusts the angle and the height of the device 2 according to the position of the converging light spot, so that the center of the converging light spot of the laser falls at the center of the camera;
(2) Closing the beacon laser in the single photon communication device 1, continuously outputting the beacon laser in the single photon communication device 2, observing whether the converging light spot position is at the center of the camera of the single photon communication device 1, and if so, completing alignment of the transmitting and receiving optical axes of the single photon communication devices 1 and 2; when the condensed light spot deviates greatly from the camera center of the single photon communication device 1, the internal optical axes of the single photon communication devices 1 and 2 deviate, and bidirectional communication is impossible.
The second step comprises:
1) The beacon laser is set to a fixed frequency output, first emitting N with low single pulse energy L Pulse triggering detector and data acquisitionDevice acquisition T L Performing exponential fitting on the long-duration backward scattering signal according to the scattering waveform to obtain a water body absorption coefficient A under low pulse energy L Scattering coefficient B L ；
2) Sequentially adopting the same method to transmit medium energy N M Pulse and high energy N H Pulse to obtain the absorption coefficient A of the corresponding medium energy water body M Scattering coefficient B M And a high energy water absorption coefficient A H Scattering coefficient B H . And averaging the three measurement results to obtain an absorption coefficient A and a scattering coefficient B of the current water quality environment:
the third step comprises:
when the sum of the absorption coefficient A and the scattering coefficient B is lower than 0.151m -1 (clean seawater attenuation coefficient) shows that the current water quality condition is better, and the low-energy and high-repetition-frequency modulation is set to realize the output of the information source laser; when the sum of the absorption coefficient A and the scattering coefficient B is higher than 0.151m -1 The current water quality condition is worse, and the high-energy and low-repetition-frequency modulation is set to realize the output of the information source laser.
The source laser energy output is set by the laser's single pulse out light duration. At low energy output, the duration T of light emission s Short; at high energy output, the duration T of light emission s Long.
Modulation frequency and communication frequency R of information source laser b Direct correlation, due to the discrete pulse output characteristics of single photon detection and dead time constraints, 1/R in a single symbol period of communication b The source laser does not always keep high level, and adopts a spread spectrum output mode, namely 1/R in a single symbol period b N pulses are transmitted, wherein N is the spread spectrum number, and the capacity loss caused by the dead time of the single photon detector is avoided.
The fourth step comprises:
a) Under the condition that the information source laser and the beacon laser are closed, the single photon detector is turned on, and the single photon detector can output discrete pulses outwards due to factors such as environmental noise, dark counting and the like. Counting single symbol period 1/R by signal integrated processing unit b Maximum count rate N of internal noise DCR 。
b) The information source laser works normally, the single photon detector outputs pulse outwards after receiving the laser signal, and the maximum counting rate N of the single photon detector is counted in the single symbol period 1/R of communication SIG ；
c) To ensure low error rate of communication, the noise count rate N is required to be used DCR And maximum signal count rate N SIG Comprehensively setting a minimum pulse interval threshold T inter Signal recovery decision threshold N RECOVER The value is as follows:
i.e. when the signal is demodulated, the time interval between the first pulse signal and the second pulse signal of the single photon detector is longer than T inter When the current pulse is considered as a noise photon, the subsequent counting statistics is not carried out, and the signal photon is waited again; when the interval time between the first pulse signal and the second pulse signal of the single photon detector is less than or equal to T inter When the pulse is considered a signal photon, counting statistics of a subsequent single symbol period begin. When the count statistic value is greater than or equal to N RECOVER When the count statistics is smaller than N, the symbol is "1 RECOVER When this symbol is considered to be "0".
d) Repeating the steps b) to c) to complete the demodulation of one frame of communication data.
In conclusion, the single photon detector is adopted as the receiver, so that the signal detection with higher sensitivity can be realized, and the system acting distance is increased. Secondly, aiming at the high sensitivity characteristic of the single photon detector, an optical isolation method is adopted to inhibit the back scattering influence of the same side source laser, thereby ensuring the bidirectional full duplex communication capability. Thirdly, the water quality condition is evaluated according to the back scattering echo count value of the beacon laser under different low, medium and high energies, the output energy and the modulation frequency of the information source laser are adaptively modulated, the communication requirements of different water quality environments are met, and the system robustness is improved. Finally, according to the background noise photon count and the maximum information photon count of the single symbol period environment obtained by the single photon detector, the on-line signal demodulation threshold setting is completed, the requirements of different background environments and transmission distances can be met, the communication error rate is reduced, and the environmental adaptability of single photon communication is improved.
It will be understood that modifications and variations will be apparent to those skilled in the art from the foregoing description, and it is intended that all such modifications and variations be included within the scope of the following claims.
Claims (10)
1. An underwater wireless optical communication device based on a single photon detector is characterized in that,
the system comprises a first single-photon communication device and a second single-photon communication device which are in two-way communication, wherein the first single-photon communication device and the second single-photon communication device both comprise a laser emitting unit, a signal receiving unit, a signal comprehensive processing unit and a power module;
the laser transmitting unit loads the received modulated electric signals into optical signals and outputs the optical signals, and simultaneously transmits auxiliary alignment laser to align the communication device;
the signal receiving unit converts the received optical signals into electric signals through the single photon detector and transmits the electric signals to the outside, and meanwhile, the signal receiving unit receives auxiliary alignment laser to finish alignment of the communication device;
the signal comprehensive processing unit receives the communication information of the upper computer, converts the communication information into a modulated electric signal, transmits the modulated electric signal to the laser transmitting unit, demodulates and restores the electric signal transmitted by the signal receiving unit into the communication information, and transmits the communication information to the upper computer.
2. The single photon detector based underwater wireless optical communication device of claim 1, wherein the laser emitting unit comprises two optical paths, one of which comprises a beacon laser and a first collimator; the other light path comprises a plurality of information source lasers, a beam combiner, a second collimator, a dichroic mirror and a beam expanding optical system; the beam combiner is used for combining the laser output by the plurality of information source lasers into one path and outputting the laser; the first collimator is used for collimating the beacon laser and outputting the collimated beacon laser; the second collimator is used for collimating the information source laser and outputting the collimated information source laser; the dichroic mirror is connected with the first collimator and the second collimator, and is used for combining the collimated information source laser and the beacon laser and outputting the combined information source laser and the combined beacon laser to the beam expanding optical system.
3. The single photon detector based underwater wireless optical communication device as in claim 2 wherein the source laser of one laser emitting unit is the same wavelength as the beacon laser of the other laser emitting unit.
4. The underwater wireless optical communication device based on the single photon detector as claimed in claim 1, wherein the signal receiving unit comprises two paths, wherein one path specifically comprises a receiving optical system, a dichroic mirror, an optical filter assembly, a first converging optical system and a single photon detector which are connected in sequence; the receiving optical system receives the laser emitted by the laser emitting unit, the dichroic mirror is used for separating the information source laser from the beacon laser, the information source laser is filtered by the optical filter assembly and then is output to the first converging optical system so as to converge the information source laser energy to the target surface of the single photon detector, and the single photon detector is used for receiving the information source laser energy and converting the information source laser energy into a digital pulse signal and outputting the digital pulse signal to the signal comprehensive processing unit;
the other path comprises a second converging optical system and a camera, the second converging optical system is connected with the dichroic mirror, and the camera is connected with an external computer; the second converging optical system is used for converging the beacon laser energy to the target surface of the camera, and the camera receives the beacon laser light spot and finishes the alignment of the transmitting and receiving optical axes according to the light spot position.
5. The single photon detector based underwater wireless optical communication device of claim 4, wherein the band pass center wavelength range of the filter assembly of the signal receiving unit of the first single photon communication device covers the wavelength of the plurality of source lasers of the laser emitting unit of the second single photon communication device and the cut-off wavelength range covers the wavelength of the plurality of source lasers of the first laser emitting unit.
6. The single photon detector based underwater wireless optical communication device of claim 4, wherein the band pass center wavelength range of the filter assembly of the receiving unit of the second single photon communication device covers the wavelength of the plurality of source lasers of the laser emitting unit of the first single photon communication device and the cut-off wavelength range covers the wavelength of the plurality of source lasers of the laser emitting unit of the second single photon communication device.
7. The underwater wireless optical communication device based on the single-photon detector as in claim 4, wherein the single-photon detector is a geiger-mode APD single-photon detector, a photon counting PMT single-photon detector, or a superconducting nanowire single-photon detector.
8. The underwater wireless light communication device based on the single photon detector as claimed in claim 4, wherein the camera is a CCD camera or a CMOS camera.
9. The underwater wireless optical communication device based on the single photon detector as claimed in claim 1 wherein the signal integrated processing unit comprises an information transmission module, a level conversion module, a modulation function module, a demodulation function module, and a system initialization module.
10. An underwater wireless optical communication method based on a single photon detector, which is characterized by comprising the following steps of:
the method comprises the steps of firstly, completing the alignment of the transmitting and receiving optical axes of a first single photon communication device and a second single photon communication device;
the second step, the laser emission unit emits low-energy, medium-energy and high-energy lasers, the scattered echo count collected by the signal receiving unit is used for evaluating the absorption coefficient and the scattering coefficient of the water quality environment, and the average value of the three measurements is used as the absorption coefficient and the scattering coefficient of the current water quality environment;
thirdly, determining the current water quality condition according to the sum value of the absorption coefficient and the scattering coefficient, and setting low-energy and high-repetition frequency modulation to realize the output of the information source laser when the current water quality condition is lower than the clean seawater attenuation coefficient; when the attenuation coefficient is higher than the attenuation coefficient of clean seawater, high energy and low repetition frequency modulation are set to realize the output of the information source laser;
and fourthly, counting the background noise photon counting rate and the maximum information photon counting rate of the single symbol period environment by the signal receiving unit through the single photon detector, setting a minimum pulse interval threshold value and a signal recovery judgment threshold value of on-line signal demodulation so as to adapt to communication under different background environments and transmission distances, and repeating the third and fourth steps to realize continuous communication transmission.
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