High-speed low-cost laser optical communication method for near sea surface long distance

Abstract

The invention relates to the field of laser communication, in particular to a near sea surface-oriented low-altitude long-distance laser communication system and a near sea surface-oriented low-altitude long-distance laser communication scheme. A transmitting end uses an optical module to perform multi-path multi-wavelength optical OOK signal transmission, and each path of optical signal is subjected to independent transmission power control and independent transmission optical aperture transmission; a receiving end uses a large-aperture receiving optical unit for receiving, uses a large-core-diameter multimode optical fiber to replace a single-mode optical fiber to realize signal receiving with higher optical power, and uses a multimode wavelength division multiplexing demultiplexer to separate received multiple paths of optical signals. Each path of separated signals is subjected to signal detection and information recovery through a receiving optical module, and finally, the information transmission quality is judged according to the bit error rate.

Description

Technical Field

[0001] The present invention relates to the field of laser optical communication technology, and in particular to a high-speed and low-cost laser optical communication method for long distances near sea surfaces. Background Art

[0002] With the development of 5G communication technology, high-speed broadband Internet is rapidly spreading around the world. However, it is still difficult to popularize high-speed Internet communication in remote mountainous areas and islands far from the land. Although some wireless communication technologies can cover these areas, the corresponding communication rate is still limited by the frequency of electromagnetic waves. Free space optical communication, as another alternative to fiber optic communication, uses light beams as carriers for communication and has the characteristics of high bandwidth. In addition, its spectrum resources are not limited, its size is small, and its cost is low. It can be deployed flexibly and quickly, providing a potential solution for Internet access in these areas.

[0003] Compared with short distance, long-distance laser communication faces more severe challenges, especially long-distance laser communication links in the near-ground horizontal direction. On the one hand, with the increase of transmission distance, link attenuation increases greatly, and weather factors such as rain, snow, and dense fog will also cause the attenuation of ground links to increase. In order to compensate for the high attenuation of the link, increasing the average generated power has become the main countermeasure. On the other hand, ground laser links will be affected by atmospheric turbulence effects. Atmospheric turbulence will cause the wavefront distortion of the transmission beam, resulting in beam expansion, arrival angle fluctuations, light intensity flickering, coherence degradation and other phenomena, and the turbulence effect continues to accumulate with the increase of transmission distance. The strength of atmospheric turbulence is different at different altitudes. As a typical atmospheric turbulence refractive index structure constant model, the Hufnagel-Valley model describes the turbulence strength distribution of atmospheric turbulence in the vertical direction. According to the model, the atmospheric turbulence refractive index structure constant at high altitudes is significantly weaker than that at low altitudes, and the atmospheric turbulence effect on longer-distance ground horizontal links is more serious.

[0004] If adaptive optics technology is used to compensate for atmospheric turbulence, the system cost will increase greatly with the use of adaptive optics technology. If adaptive optics technology is not used, in a long-distance, low-altitude environment, strong turbulence will cause the coherence of the carrier beam to degenerate, and the beam mode will diffuse from the Gaussian base mode to the high-order Laguerre-Gaussian mode, which will seriously reduce the coherent mixing efficiency and limit the coherent communication system. The intensity modulation / direct detection communication method is not subject to this limitation. Therefore, in a long-distance, highly turbulent horizontal laser communication link, the basic OOK (on-off keying, abbreviated as OOK) signal SFP+ optical module communication method can be used as a feasible solution. Combined with WDM (Wavelength Division Multiplexing, abbreviated as WDM) wavelength division multiplexing technology, high-speed information transmission can be achieved. Summary of the invention

[0005] In view of the shortcomings of the existing technology, in order to achieve high-speed laser communication between low-altitude islands, the present invention proposes a high-speed and low-cost laser optical communication method for long distances near the sea. This method uses low-cost commercial general SFP+ packaged optical modules with different wavelengths and the same information rate as signal sources, uses high-power optical amplifiers for power control and transmission, and uses large-aperture optical receiving units and large-core multimode optical fibers as receivers at the receiving end. Without using adaptive optics, high-speed laser communication can be achieved between two low-altitude and long-distance islands.

[0006] A high-speed and low-cost laser optical communication method for long distance near the sea surface, the method comprising the following steps:

[0007] Step S1, transmitting the data information to be transmitted to the multi-channel optical module through the cable and selecting the corresponding number of WDM wavelength transmitting optical modules according to the rate requirement, and converting the data information into OOK optical signals through the multi-channel optical module;

[0008] Step S2, each wavelength of the OOK optical signal passes through a single-mode optical fiber to an optical amplifier, and the optical amplifier independently controls the output optical power of each optical signal;

[0009] Step S3, the amplified optical signals of each wavelength are transmitted through a single-mode optical fiber to an optical transmitting unit of the corresponding wavelength, and are converted into multi-channel Gaussian beams with a divergence angle less than 0.5 mrad. The Gaussian beams are transmitted through an atmospheric space link and transmitted to a receiving end;

[0010] Step S4, the receiving end uses a large-aperture optical receiving unit with a diameter greater than 200 mm and a large-core multimode optical fiber with a diameter greater than 50 microns to couple and receive each Gaussian beam, and transmit it to a wavelength division multiplexing demultiplexer;

[0011] Step S5, the multiple OOK optical signals are wavelength demultiplexed and separated by a wavelength division multiplexing demultiplexer, and the separated optical signals are respectively transmitted through multimode optical fibers into receiving optical modules of corresponding wavelengths;

[0012] Step S6, the receiving optical modules respectively detect and perform photoelectric conversion on the respective received optical signals, convert the OOK optical signals into electrical signals, and restore the transmitted data information.

[0013] The technical solution is further optimized in that the number of the multi-channel optical modules corresponds to the number of the receiving optical modules, and the number of the multi-channel optical modules is not less than 1.

[0014] The technical solution is further optimized in that the optical amplifier controls the output optical power of the input optical signal, and the output power range can be continuously controlled by adjusting the pump current of the amplifier by a control knob, and the output power range is 100mW to 7W.

[0015] The technical solution is further optimized, the multimode optical fiber is of FC-FC and FC-LC connector type, and the core diameter is 105 microns.

[0016] The technical solution is further optimized in that the optical emission unit is a high-precision light beam collimation emission unit, and its light beam divergence angle is less than 0.5 mrad.

[0017] The technical solution is further optimized in that the optical receiving unit is a large-aperture Cassegrain telescope, and the diameter of its receiving aperture is greater than 200 mm.

[0018] The technical solution is further optimized, and the optical module can be not only an SFP+ packaged optical module, but also an optical module of other package types, such as XFP, QSFP package, etc.

[0019] Further optimization of the technical solution also includes step S7. If the transmitted data information is the audio and video information collected by the camera, the corresponding data information will be displayed in real time through the display, and the information transmission quality will be judged by the audio and video quality; if the transmitted data information is the PRBS code sequence of the bit error meter, the receiving optical module will be directly placed in the receiving bit error meter, the communication rate of the bit error meter setting interface will be set to 10Gbps, the PRBS sequence and the transmitted sequence will be set to be the same, the received information will be judged and compared, and the transmission bit error rate of the information will be calculated.

[0020] Compared with the traditional laser communication system, the present invention has the following technical advantages:

[0021] 1) Low system cost. The signal transmission system adopts a relatively simple direct modulation / direct detection method. Compared with the coherent communication method, it has a simpler signal transmission and reception structure, a simple system structure, and a lower cost. In order to combat the interference of atmospheric turbulence effects, high-power transmission and large-aperture reception, multi-mode fiber coupling are adopted, which can greatly reduce the system cost requirements compared with the use of adaptive optical technology.

[0022] 2) High bandwidth and high speed. The invention inherits the high bandwidth advantage of optical fiber communication. By adopting wavelength division multiplexing technology, it can support full-band communication in the field of optical communication, has extremely high bandwidth advantages, and supports high-speed communication.

[0023] 3) High flexibility. The transmitter uses a single-channel independent transmission method. Each channel does not interfere with each other and is independent of each other. The number of transmission channels can be adjusted according to actual needs, which has high flexibility. The receiving and transmitting optical modules use commercial general optical modules, and the transmission rate of the optical modules can also be adjusted according to actual needs to meet the needs of different communication density scenarios.

[0024] 4) Wide scope of application: The solution of the present invention is not only applicable to optical communication interconnection between low altitude areas near the sea, but also to long-distance optical communication interconnection on land and relatively remote areas, and has a wide range of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the architecture of the low-altitude and long-distance laser communication system for near-sea surfaces described in the present invention;

[0026] Figure 2 This is a schematic diagram of the laser communication link described in the present invention;

[0027] Figure 3 This is a flow chart of the method for transmitting information in the laser communication system described in the present invention.

[0028] Description of reference numerals:

[0029] 101 transmits data signal, 102 transmits optical module, 103 optical amplifier, 104 optical transmitting unit, 105 near sea surface atmospheric link, 106 receives optical unit, 107 wavelength division multiplexing demultiplexer, 108 receives optical module, 109 receives data signal, 110 calculates bit error rate. DETAILED DESCRIPTION

[0030] In order to explain the technical content, structural features, achieved objectives and effects of the technical solution in detail, the following is a detailed description in conjunction with specific embodiments and accompanying drawings.

[0031] See also Figure 1As shown in the figure, it is a schematic diagram of the architecture of the low-altitude and long-distance laser communication system for the near-sea surface proposed by the present invention. The low-altitude and long-distance laser communication system for the near-sea surface includes 10 parts, namely: a transmitting data signal 101, which refers to the data information to be transmitted; a transmitting optical module 102, which refers to an optical module packaged by the SFP+ process, which can convert the data information into an optical OOK signal; an optical amplifier 103, which refers to an erbium-doped fiber amplifier, and its transmitting power is continuously adjustable; an optical transmitting unit 104, which refers to a Gaussian beam transmitting device, which can convert the optical signal in the optical fiber into a collimated Gaussian beam for long-distance space transmission; a near-sea surface large The air link 105 refers to the laser beam transmission environment at a low altitude near the sea surface; the receiving optical unit 106 refers to the Cassegrain telescope, which can receive the laser beam transmitted in space and couple the optical signal into the optical fiber; the wavelength division multiplexing demultiplexer 107 is a fiber passive component that can separate the mixed multi-wavelength signals; the receiving optical module 108 refers to the optical module packaged using the SFP+ process, which can convert the optical OOK signal into data information; the received data signal 109 refers to the received data information; the bit error rate calculation 110 refers to the data transmission error rate in the received data information corresponding to the transmitted data information.

[0032] Take the bidirectional information transmission experiment between two islands at a dual wavelength of 20Gbps at 29 kilometers off the sea as an example. Figure 2 As shown, it is a schematic diagram of the laser communication link of this embodiment. Figure 3 This is a flow chart of the method for transmitting information in the laser communication system of this example. The following specific steps refer to Figure 3 Proceed as shown in the step flow.

[0033] Step 1: Start information communication from position A to position B.

[0034] Step 2: Prepare the information to be transmitted, such as video data collected by the camera or random PRBS sequence codes generated by the bit error meter. If there is no information to be transmitted, you need to continue waiting.

[0035] Step 3: Transmit the information to be transmitted to the commercial optical module in SFP+ package through the cable. If a bit error meter is used, the multi-channel optical module needs to be directly inserted into the bit error meter device, and the information transmission rate of the PRBS code is set to 10Gbps. The wavelengths selected by the two transmitting optical modules are 1556.55nm and 1558.98nm respectively, and their maximum optical OOK signal transmission rates are both 10Gbps, the output optical signal power is about 0dBm, and the output port is an LC fiber port. The two transmitting optical modules convert the transmission information into a high-speed optical OOK signal.

[0036] Step 4: The converted two optical OOK signals are transmitted to two optical amplifiers through two LC-APC single-mode optical fibers. The optical amplifier can control the output optical power of each input optical signal separately. The output power range can be continuously controlled by adjusting the pump current of the amplifier through the control knob. The output power range is 100mW to 7W. In order to cope with the 29km transmission link, the output power of the two optical signals is controlled at 36dBm, that is, 4W output power.

[0037] Step 5, transmit the amplified two high-power optical OOK signals to two optical transmitting units through single-mode optical fiber. The optical transmitting unit is a two-way high-precision beam collimation transmitting unit. It converts the optical signal in the optical fiber into a collimated Gaussian beam that can be transmitted in space, thereby transmitting the signal. The divergence angles of the beams are 0.498mrad and 0.472mrad respectively, and can withstand high-power transmission, with transmission efficiencies of 92% and 90% respectively.

[0038] Step 6: This step is the process of transmitting the Gaussian beam signal through the atmospheric space link to the receiving end. Figure 3As shown in . The transmission distance is 29km. The altitude of position A is 250 meters, and the altitude of position B is 150m. To ensure accurate reception, the optical axes of both ends of the transmitter and receiver need to be calibrated in advance. The calibration procedure includes two steps. Both ends of the transmitter and receiver need CCD image detectors of corresponding wavelengths to facilitate the observation of the calibration process of the optical axis and make accurate judgments. 1. Rough calibration of the optical axis: The rough calibration process uses beacon light with a wavelength of 850nm. The emission and reception of the beacon light are parallel to the emission and reception of the signal light, respectively, to ensure that the optical axis of the transceiver is unique. The beacon light emission aperture is 60mm, and the divergence angle of the emission beam is about 1mrad. The larger divergence angle can ensure rapid coverage in the direction of the alignment light, so as to quickly find the approximate direction of the optical axis. The receiving aperture of the beacon light at the receiving end is about 100mm. The beacon light does not transmit information, but only serves for the rough alignment of the optical axis. The detection surface is a highly sensitive CCD detector. The output spot image is transmitted to the display screen through the VGA (HDMI) line, and the transceiver optical device unit is controlled by twisting the azimuth and pitch angle adjustment controller of the transceiver device to achieve coarse alignment of the transceiver optical axis. Second, fine alignment of the optical axis: After the coarse alignment of the optical axis is achieved, the fine alignment of the optical axis of the transceiver optical device is required. Fine alignment is performed using the transceiver unit of the signal light. The emission is the emission aperture of the signal light, and the reception is the receiving aperture of the signal light. The difference is that the receiving end will perform a 1:9 spatial beam splitting before coupling the received signal light into the optical fiber. 10% of the light is sent to the 1550nm wide-band CCD image sensor, and the spot image of the signal light is transmitted to the display interface through the VGA (HDMI) line, and the transceiver optical device unit is controlled by twisting the azimuth and pitch angle adjustment controller of the transceiver device to achieve fine alignment of the transceiver optical axis. There is a reference center in the image display interface of the coarse / fine alignment. When the center of the light spot is aligned with the reference center, the coarse / fine optical axis alignment process is completed. Once the optical axis alignment process is completed, the transmission step of the atmospheric link is completed.

[0039] Step 7: Use the optical unit at the receiving end to uniformly receive the two transmitted light beam signals, and its aperture size is 250 mm. The receiving optical unit combines and receives the two optical signals of different wavelengths with equal gain, and couples them together into a multimode optical fiber with a core diameter of 105 μm.

[0040] Step 8, after the 1:1 power splitting, the multimode optical fiber with a core diameter of 105μm is sent to the optical power detector to detect the optical power of the received optical signal. If there is no optical power, wait, if there is, proceed to the next step. The other way is transmitted to the wavelength division multiplexing demultiplexer through the 105μm multimode optical fiber.

[0041] Step 9: The optical signal is demultiplexed and separated by a multimode wavelength division multiplexing / demultiplexing device with a core diameter of 105 μm, and the two optical signals with wavelengths of 1556.55 nm and 1558.98 nm are separated.

[0042] Step 10: The separated two optical signals of different wavelengths are transmitted through two multimode optical fibers respectively and enter two corresponding receiving optical modules. The multimode optical fibers are of FC-LC connector type to adapt to the type of receiving port of the receiving optical module.

[0043] Step 11, the two receiving optical modules respectively detect and perform photoelectric conversion on their respective received optical signals, convert the two OOK optical signals into electrical signals, and restore the two 10 Gbps data information transmitted.

[0044] Step 12, if the transmission is the audio and video information collected by the camera, the corresponding data information will be displayed in real time through the display, and the information transmission quality will be judged by the audio and video quality; if the transmission is the PRBS code sequence of the bit error meter, the optical module will be directly placed in the receiving bit error meter, and the communication rate of the bit error meter setting interface will be set to 10Gbps, and the PRBS sequence will be set to be the same as the transmitted sequence. The received information is judged and compared, and the transmission bit error rate of the information is calculated. The bit error rate results of the forward transmission are shown in Table 1. Appendix 1 is the test results of the 29 km near-sea surface laser communication of the present invention, which are as follows:

[0045] Table 1

[0046]

[0047] The average received optical powers of the two wavelength signals obtained in the forward transmission test are -13.9dBm and -11.7dBm. The bit error rates of the two wavelength signals in the forward transmission are 1.1×10 -8 and 5.9×10 -9 , which is much smaller than the bit error rate requirement of 3.8×10 -3 (7% forward error correction code threshold), so accurate information transmission can be achieved.

[0048] The above steps are the information communication operation steps for the forward dual-wavelength 20Gbps rate from position A to position B. The steps of reverse communication (position B to position A) are the same as those of forward communication (position A to position B). Steps 1 to 12 need to be repeated. The wavelengths of the two optical signals of reverse communication are replaced by 1537.40nm and 1539.77nm. The test results of reverse communication are shown in Table 1. The average received optical power of the two wavelength signals obtained by the reverse transmission test is -9.1dBm and -11.2dBm. The bit error rates of the two wavelength signals in reverse transmission are 4.5×10 -9 and 3.7×10 -8, which is much smaller than the bit error rate requirement of 3.8×10 -3 (7% forward error correction code threshold), so accurate information transmission can be achieved.

[0049] The above can realize two-way information transmission between two islands at a dual wavelength of 20Gbps information rate 29 kilometers near the sea.

[0050] It should be added that the example uses two-way wavelength optical signal transmission and reception, but the present invention does not limit the number of transmissions and receptions. For example, two-way transmission can achieve information transmission at a maximum rate of 20Gbps, while three-way transmission can achieve information transmission at a maximum rate of 30Gbps. The more transmissions and receptions there are, the higher the information transmission rate that can be achieved.

[0051] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or terminal device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of further restrictions, the elements defined by the sentence "include..." or "comprise..." do not exclude the existence of other elements in the process, method, article or terminal device including the elements. In addition, in this article, "greater than", "less than", "exceed" and the like are understood to exclude the number itself; "above", "below", "within" and the like are understood to include the number itself.

[0052] Although the above embodiments have been described, once those skilled in the art know the basic creative concepts, they can make additional changes and modifications to these embodiments. Therefore, the above description is only an embodiment of the present invention and does not limit the patent protection scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the specification and drawings of the present invention, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A high-speed and low-cost laser optical communication method for long distance near the sea surface, characterized in that: The method comprises the following steps: Step S1, transmitting the data information to be transmitted to the multi-channel optical module through the cable and selecting the corresponding number of WDM wavelength transmitting optical modules according to the rate requirement, and converting the data information into OOK optical signals through the multi-channel optical module; Step S2, each wavelength of the OOK optical signal passes through a single-mode optical fiber to an optical amplifier, and the optical amplifier independently controls the output optical power of each optical signal; Step S3, the amplified optical signals of each wavelength are transmitted through a single-mode optical fiber to an optical transmitting unit of the corresponding wavelength, and are converted into multi-channel Gaussian beams with a divergence angle less than 0.5 mrad. The Gaussian beams are transmitted through an atmospheric space link and transmitted to a receiving end; Step S4, the receiving end uses a large-aperture optical receiving unit with a diameter greater than 200 mm and a large-core multimode optical fiber with a diameter greater than 50 microns to couple and receive each Gaussian beam, and transmit it to a wavelength division multiplexing demultiplexer; Step S5, the multiple OOK optical signals are wavelength demultiplexed and separated by a wavelength division multiplexing demultiplexer, and the separated optical signals are respectively transmitted through multimode optical fibers into receiving optical modules of corresponding wavelengths; Step S6, the receiving optical modules respectively detect and perform photoelectric conversion on the respective received optical signals, convert the OOK optical signals into electrical signals, and restore the transmitted data information.

2. The high-speed, low-cost laser optical communication method for long distance near the sea surface as claimed in claim 1, characterized in that: The number of the multi-channel optical modules corresponds to the number of the receiving optical modules, and the number of the multi-channel optical modules is not less than 1.

3. The high-speed, low-cost laser optical communication method for long distance near the sea surface as claimed in claim 2, characterized in that: The number of the multi-channel optical modules and the number of the receiving optical modules are both 2.

4. The high-speed, low-cost laser optical communication method for long distance near the sea surface as claimed in claim 1, characterized in that: The optical amplifier controls the output optical power of the input optical signal, and the output power range can be continuously controlled by adjusting the pump current of the amplifier through a control knob, and the output power range is 100mW to 7W.

5. The high-speed, low-cost laser optical communication method for long distance near the sea surface as claimed in claim 1, characterized in that: In step S4, after the multimode optical fiber undergoes 1:1 power splitting, one path is sent to an optical power detector to detect the optical power of the received optical signal. If there is no optical power, wait; if there is, proceed to the next step; the other path is transmitted to the wavelength division multiplexing demultiplexer through the multimode optical fiber.

6. The high-speed, low-cost laser optical communication method for long distance near the sea surface as claimed in claim 1, characterized in that: The multimode optical fiber is of FC-LC connector type, and has a core diameter of 105 μm.

7. The high-speed, low-cost laser optical communication method for long distance near the sea surface as claimed in claim 1, characterized in that: The optical emission unit is a high-precision light beam collimation emission unit.

8. The high-speed, low-cost laser optical communication method for long distance near the sea surface as claimed in claim 1, characterized in that: It also includes step S7. If the transmitted data information is the audio and video information collected by the camera, the corresponding data information will be displayed in real time through the display, and the information transmission quality will be judged by the audio and video quality; if the transmitted data information is the PRBS code sequence of the bit error meter, the receiving optical module will be directly placed in the receiving bit error meter, the communication rate of the bit error meter setting interface will be set to 10Gbps, the PRBS sequence and the transmitted sequence will be set to be the same, the received information will be judged and compared, and the transmission bit error rate of the information will be calculated.

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