WO2018202132A1 - 基于激光器的无线频率传输系统及其传输装置和传输方法 - Google Patents

基于激光器的无线频率传输系统及其传输装置和传输方法 Download PDF

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Publication number
WO2018202132A1
WO2018202132A1 PCT/CN2018/085609 CN2018085609W WO2018202132A1 WO 2018202132 A1 WO2018202132 A1 WO 2018202132A1 CN 2018085609 W CN2018085609 W CN 2018085609W WO 2018202132 A1 WO2018202132 A1 WO 2018202132A1
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Prior art keywords
laser
signal
phase
based wireless
frequency transmission
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PCT/CN2018/085609
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English (en)
French (fr)
Inventor
陈诗军
侯冬
龚翠玲
陈大伟
陈强
王园园
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中兴通讯股份有限公司
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Publication of WO2018202132A1 publication Critical patent/WO2018202132A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/501—Structural aspects
    • H04B10/503—Laser transmitters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/548—Phase or frequency modulation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/66—Non-coherent receivers, e.g. using direct detection
    • H04B10/67—Optical arrangements in the receiver
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/66—Non-coherent receivers, e.g. using direct detection
    • H04B10/69—Electrical arrangements in the receiver
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/66—Non-coherent receivers, e.g. using direct detection
    • H04B10/69—Electrical arrangements in the receiver
    • H04B10/697—Arrangements for reducing noise and distortion

Definitions

  • the present invention relates to the field of frequency synchronization technologies, and in particular, to a laser-based wireless frequency transmission system, and a transmission device and a transmission method thereof.
  • High-precision time-frequency synchronization plays an important role in the practical application of modern scientific experiments and engineering. Its purpose is to synchronize the reference frequency signal sources of two or more points at a certain distance in phase and time. High-precision synchronization technology has a wide range of applications in communications, radar detection, telemetry, navigation systems, astronomical observation and basic scientific research.
  • Fiber-optic frequency transmission technology requires the construction of a dedicated fiber channel. Fiber-optic frequency transmission technology cannot be used in some cases where there is no existing fiber link or it is not convenient to build a fiber link.
  • FIG. 1 is a schematic block diagram showing a dual-station wireless frequency transmission system according to the related art.
  • the receiving end 10 modulates the microwave frequency signal or the time signal to be transmitted to the laser 102 by the microwave source 101, and then transmits the laser signal to the free space through the optical space first beam expanding mirror 103. In space.
  • the receiving end 20 focuses the laser signal onto the second photodetector 202 through the second beam expander 201 to recover the microwave frequency signal or the time signal.
  • the laser-based wireless frequency transmission technology provides a simple synchronization method, and in this mode, the synchronization accuracy can be close to the method of fiber frequency transmission.
  • the invention provides a laser-based wireless frequency transmission system, a transmission device thereof and a transmission method.
  • a laser-based wireless frequency transmission apparatus comprising at least a pair of third beam expanders and a phase compensation unit, wherein: the third beam expander The mirror is configured to couple the laser signal reflected back by the receiving end to the phase compensation unit; and the phase compensation unit is configured to perform phase comparison on the reference frequency signal and the microwave signal modulated in the laser signal reflected back by the receiving end in real time. And adjusting the phase of the laser signal modulated with the reference frequency signal according to the phase error.
  • a laser-based wireless frequency transmission device applied to a receiving end and comprising: a beam returning unit for receiving a received laser signal Part of it is reflected back to the sender.
  • a laser-based wireless frequency transmission system comprising a transmitting end and at least one receiving end, wherein the transmitting end comprises according to the first aspect A laser-based wireless frequency transmission device, the receiving end comprising the laser-based wireless frequency transmission device according to the second aspect.
  • a laser-based wireless frequency transmission method is provided, the method being applied to a transmitting end, and comprising: loading a reference frequency signal onto a laser; generating a continuous laser modulated with the reference frequency signal a signal; coupling the modulated laser signal to free space for transmission; receiving a laser signal reflected back by the receiving end; and performing phase comparison of the reference frequency signal and the microwave signal modulated in the reflected laser signal in real time, according to the phase error Adjusting the phase of the modulated laser signal.
  • a laser-based wireless frequency transmission method is provided, the method being applied to a receiving end, and comprising: decomposing the received laser signal into a transmitted light and a reflected light having a preset light intensity ratio. And transmitting the transmitted light to a second beam expander in the receiving end to return the reflected light to the transmitting end.
  • FIG. 1 is a schematic block diagram of a laser-based dual-station wireless frequency transmission system in accordance with the related art of the present invention.
  • FIG. 2 is a schematic structural diagram of a laser-based wireless frequency transmission apparatus applied to a transmitting end according to Embodiment 1 of the present invention.
  • FIG. 3 is a schematic structural diagram and a phase compensation principle diagram of a phase compensation unit according to Embodiment 2 of the present invention.
  • FIG. 4 is a schematic structural diagram of a laser-based wireless frequency transmission apparatus according to Embodiment 3 of the present invention.
  • FIG. 5 is a schematic structural diagram of a beam stabilizing unit according to Embodiment 3 of the present invention.
  • FIG. 6 is a schematic structural diagram of a laser-based wireless frequency transmission apparatus applied to a receiving end according to Embodiment 4 of the present invention.
  • FIG. 7 is a schematic diagram of the original structure of another laser-based wireless frequency transmission device according to Embodiment 4 of the present invention.
  • FIG. 8 is a schematic structural diagram of a laser-based wireless dual-station frequency transmission system according to Embodiment 5 of the present invention.
  • FIG. 9 is a block diagram showing the structure of a laser-based wireless multi-station frequency transmission system in accordance with the related art of the present invention.
  • FIG. 10 is a schematic structural diagram of a laser-based wireless multi-station frequency transmission system according to Embodiment 6 of the present invention.
  • FIG. 11 is a flowchart of a laser-based wireless frequency transmission method according to Embodiment 7 of the present invention.
  • FIG. 12 is a flowchart of another laser-based wireless frequency transmission method according to Embodiment 8 of the present invention.
  • a laser-based radio frequency transmission apparatus is applied to a transmitting end 10, including a microwave source 101, a laser 102, a first beam expander 103, a third beam expander 104, and Phase compensation unit 105.
  • the microwave source 101 is used to load a reference frequency signal onto the laser 102 and provide the reference frequency signal to the phase compensation unit 105.
  • the microwave source 101 is generally a voltage controlled controlled source that can generate a single frequency radio frequency signal with extremely low phase noise as a reference frequency signal of the transmitting end 10 and modulate the reference frequency signal onto the laser 102.
  • the laser 102 is for generating a laser signal modulated with a reference frequency signal, and supplies the laser signal modulated with the reference frequency signal to the phase compensating unit 105.
  • the laser 102 can generate a wavelength-tunable single-frequency continuous laser. Since the microwave source 101 modulates the reference frequency signal to the laser 102, the laser 102 can provide a continuous laser signal modulated with a reference frequency signal, and the laser signal can be Has very good monochromaticity and very high side touch suppression ratio. For example, a 1.5 micron wavelength laser can be used as the local light source, and the microwave signal can be loaded into the laser signal of the laser by current modulation.
  • a first beam expander 103 is used to couple the modulated laser signal from phase compensation unit 105 to free space.
  • the first beam expander 103 couples the laser signal into the free space by expanding the diameter of the laser beam and reducing the divergence angle of the laser beam.
  • the function of the antireflection film of the lens of the first beam expander 103 can be achieved according to different wavelengths.
  • the laser signal coupled to the free space is received by the receiving end 20 and a portion of the laser signal is reflected back to the transmitting end 10 by the receiving end 20.
  • the third beam expander 104 is configured to couple the laser signal reflected back by the received receiving end 20 to the phase compensation unit 105.
  • the phase compensation unit 105 is configured to perform phase comparison on the reference frequency signal and the microwave signal modulated in the laser signal reflected back from the receiving end 20 in real time, and adjust the laser signal modulated with the reference frequency signal according to the phase error obtained by phase comparison. The phase.
  • the phase of the laser signal modulated with the reference frequency signal is adjusted by introducing the phase compensation unit 105 at the transmitting end in real time according to the phase error of the reference frequency signal of the transmitting end and the microwave signal modulated by the laser signal reflected by the receiving end. (ie, the phase of the laser signal to be coupled to the free space to be received by the receiving end), which can effectively suppress phase fluctuations in the wireless channel due to atmospheric turbulence, vibration, temperature fluctuations, etc., greatly improving the free-space frequency transmission system. Synchronization accuracy and reliability.
  • a phase compensation unit 105 provided by an embodiment of the present invention can be implemented by a phase shifter 1051, a first photodetector 1052, a phase detector 1053, a processor 1054, and a fiber stretcher 1055.
  • the phase shifter 1051 is for adjusting the phase of the reference frequency signal and outputting the reference frequency signal to the phase detector 1053.
  • phase of the reference frequency signal input to the phase detector 1053 and the phase of the reference frequency signal modulated in the laser signal entering the fiber tensioner from the laser 102 generally have an inherent deviation, and the phase shifter 1051 adjusts the phase of the reference frequency signal. Mainly to compensate for this inherent deviation. In the case where the deviation of the two phases is negligible, or the processor 1054 is capable of calculating the inherent deviation, the phase shifter 1051 may not be provided.
  • the first photodetector 1052 is configured to demodulate the microwave signal modulated in the laser signal reflected back from the receiving end 20, and output it to the phase detector 1053.
  • the phase detector 1053 is for phase comparison of the reference frequency signal input by the phase shifter 1051 and the microwave signal (which is also a frequency signal) input by the first photodetector 1052, and outputs the phase error to the processor 1054.
  • the phase detector 1053 functions to extract the phase difference of the round-trip signal.
  • the phase detector 1053 can perform phase comparison between the input reference frequency signal and the frequency signal fed back by the receiving end 20, and the comparison is obtained.
  • the phase difference i.e., phase error
  • the phase detector 1053 can be integrated with the phase shifter 1051, that is, the phase shifter 1053 can implement the function of the phase shifter 1051.
  • the processor 1054 is configured to calculate a phase error, obtain a feedback driving signal, and output the feedback driving signal to the fiber tensioner 1055, thereby driving the fiber tensioner 1055 by the feedback control signal, thereby adjusting the input to the fiber tensioner.
  • the phase of the laser signal is configured to calculate a phase error, obtain a feedback driving signal, and output the feedback driving signal to the fiber tensioner 1055, thereby driving the fiber tensioner 1055 by the feedback control signal, thereby adjusting the input to the fiber tensioner.
  • the processor 1054 may perform a calculation process on the phase error of the signal form to obtain a feedback drive signal.
  • the processor 1054 can be a computer, a single chip system, a DSP system, or an FPGA system.
  • a fiber stretcher 1055 is used to adjust the phase of the laser 102 based on the feedback drive signal.
  • the fiber tensioner 1055 can receive a feedback driving signal from the processor 1054, change an optical path on the laser transmission path (fiber path) according to the feedback driving signal, and change the phase movement caused by the optical path change. By compensating for the phase fluctuations caused by the wireless channel, it is also possible to stabilize the laser phase.
  • the transmitting end 10 uses a laser 102 (such as a wavelength of 1.5 micrometers) as a local light source, and simultaneously applies a microwave signal as a reference frequency signal to the laser 102 by current modulation. Assume that the initial phase of the microwave signal is ⁇ 0 .
  • the laser signal passes through the fiber tensioner 1055, and the phase produced by the fiber tensioner 1055 is moved to ⁇ c .
  • the laser beam signal is sent to the free space through the first beam expander 103. Due to environmental factors such as air turbulence, vibration and temperature drift, the signal is introduced into the noise ⁇ p during the free space transmission, and the signal arrives at the receiving end 20
  • the phase is ⁇ 0 + ⁇ c + ⁇ p .
  • a part of the laser signal is transmitted from the receiving end 20 to the third beam expander 104 through the same free space path, and converted into a microwave electric signal by the first photodetector 1051, and noise ⁇ is introduced in the process. p , then the phase of the local laser signal returned by the receiving end is ⁇ 0 + ⁇ c + 2 ⁇ p .
  • the laser signal is sent to the phase detector 1053 for phase discrimination with the reference frequency signal, and the phase detection result is sent to the processor 1054 as an error signal for calculation processing, and the phase drive algorithm is used to obtain the feedback drive signal and send it.
  • the phase compensation algorithm adjusts the phase shift ⁇ c of the fiber tensioner 1055, and cancels the phase fluctuation ⁇ p generated in the free space transmission with the adjusted ⁇ c , so that the signal at the receiving end is completely synchronized with the local reference frequency signal, This achieves high precision free space frequency transmission.
  • the phase compensation scheme is limited by the tensile capability of the fiber stretcher 1055, the compensation scheme is effective as long as the free-space phase fluctuation does not exceed the stretch range of the fiber stretcher 1055.
  • the first beam stabilizing unit 106 is added at the transmitting end 10 to directly cancel the beam fluctuation.
  • the first beam stabilizing unit 106 is disposed between the third beam expander 104 and the phase compensating unit 105, and the first beam stabilizing unit 106 is configured to adjust the return from the receiving end 20 (and through the third beam expander).
  • the beam direction of the laser signal is expanded to focus the modulated laser signal to the photocell of the first photodetector 1052 of the phase compensation unit 105.
  • the first beam stabilizing unit 106 includes a first high speed turning mirror 1061, a first beam splitting mirror 1062, a first beam position sensor 1063, and a first proportional integral derivative ( Proportional integral derivat ive, PTD) controller 1064 and first high speed steering mirror driver 1065.
  • a first high speed turning mirror 1061 a first beam splitting mirror 1062
  • a first beam position sensor 1063 a first beam position sensor 1063
  • PTD Proportional integral derivat ive
  • the first high speed turning mirror 1061 is for deflecting the input laser signal and transmitting it to the first beam splitter 1062.
  • the first beam splitter 1062 is configured to decompose the laser signal to obtain a beam of the target laser signal and a laser beam focused to the photocell of the first photodetector 1052. There is no special requirement for the light intensity ratio of the two laser signals obtained by the decomposition.
  • the first beam position sensor 1063 is configured to detect the position of the target laser signal, obtain a position error signal, and transmit the position error signal to the first PTD controller 1064.
  • the first PTD controller 1064 is configured to obtain a position adjustment voltage according to the position error signal, and output the position adjustment voltage to the first high speed steering mirror driver 1065.
  • the first high speed steering mirror driver 1065 is for controlling the rotation of the first high speed steering mirror 1061 in accordance with the position adjustment voltage.
  • the laser signal received by the third beam expander 104 passes through the first high speed turning mirror 1061 and the first beam splitting mirror 1062 to obtain a target laser signal, and the first beam position sensor 1063 targets the target laser signal.
  • the position is detected, the position error signal is obtained, and the position error signal is transmitted to the first PTD controller 1064.
  • the first PTD controller (1064) obtains the position adjustment voltage according to the position error signal, and feeds the position adjustment voltage to the first high speed.
  • the steering mirror driver 1065 controls the deflection of the first high-speed steering mirror (1061) in the two dimensions of the X-axis and the Y-axis according to the position adjustment voltage by the first high-speed steering mirror driver 1065, thereby rapidly adjusting the beam direction to achieve a stable beam. purpose.
  • a first high speed turning mirror 1061 is introduced.
  • the high speed turning mirror 1061 can perform high speed deflection in two dimensions (ie, X and Y directions), and the laser beam passes through the turning mirror.
  • the first beam splitter 1062 is split into two beams, and the first beam position sensor 1063 is used to detect one of the laser beams (one splitting signal) to generate a position error signal in two dimensions, and the error signal can be Output in the form of voltage. It is assumed that the output error signal in the X direction is ⁇ x, and the output error signal in the Y direction is ⁇ y.
  • the first beam position sensor 1063 inputs the obtained voltage error signals in two dimensions to the first PTD controller 1064, respectively, and the first PTD controller 1064 will output - ⁇ x and - ⁇ y to the first high speed steering mirror driver 1065.
  • the feedback signal (position adjustment voltage) is further driven by the first high speed steering mirror driver 1065 to drive the first high speed steering mirror 1061 to ensure that the light beam is always illuminated to the center point of the first beam position sensor 1063. Therefore, the entire beam can be stabilized at a fixed position by the PTD loop, thereby ensuring the stabilization of the beam output from the first beam splitter 1062 to the first photodetector 1052.
  • the beam fluctuation frequency is low (about KHz level), and the speed of the high-speed steering mirror driven by the first PTD controller (about MHz level) can be fully compensated, so that it can be finally achieved. Eliminate the purpose of beam fluctuations.
  • the beam stabilization scheme is limited by the area of the beam position sensor, the beam stabilization scheme is effective as long as the beam fluctuation does not exceed the sensing area of the beam position sensor.
  • the inventor Based on the above algorithm and control scheme, the inventor implemented a frequency transmission experiment of outdoor wireless free space with a reference frequency of 100 MHz and a transmission distance of more than 120 meters. During the transmission, the phase fluctuation and the unstable transmission frequency of the Allan variance were measured.
  • the 100MHz microwave signal is transmitted in 5000 seconds, and the rms phase fluctuation is determined to be about 22 picoseconds.
  • the frequency instability is 3 ⁇ 10 -12 in 1 s, and the frequency instability is in a thousand seconds. It is 4 ⁇ 10 -14 .
  • the achieved frequency stability is superior to that of the commercial helium atomic clock 5071A and the helium atomic clock, so the radio frequency transmission scheme can be used for the transmission of helium atom and helium atomic clock signals.
  • the present invention solves the problem of beam fluctuation caused by the vibration of the optical platform and the mirror by increasing the beam stabilizing unit, and reduces the phase noise caused by the fluctuation of the beam with the environment, thereby further improving the freedom. Synchronization accuracy and reliability of spatial frequency transmission systems.
  • a laser-based wireless frequency transmission device is applied to a receiving end 20, and includes a beam returning unit 203, a second beam expander 201, and a second photodetector 202.
  • the beam return unit 203 is for reflecting a portion of the received laser signal back to the transmitting end 10.
  • the beam return unit 203 is also used to transfer the remainder of the received laser signal to the second beam expander 201.
  • the second beam expander 201 is used to focus the laser signal received from the beam return unit 203 (i.e., the remainder of the laser signal received by the beam return unit 203) to the second photodetector 202.
  • the second beam expander 201 can couple the laser signal to the phototube of the second photodetector 202 by expanding the diameter of the laser beam and reducing the divergence angle of the laser beam.
  • the second photodetector 202 is configured to demodulate the microwave signal modulated from the laser signal received by the second beam expander 201.
  • the second photodetector 202 can convert the modulated microwave signal into an electrical signal output by photoelectric conversion, and generally has a frequency response ranging from direct current to upper GHz, and the gain is adjustable.
  • the beam return unit 203 can be realized by a combination of the beam splitter 2031 and the mirror 2032.
  • the beam splitting mirror 2031 is for decomposing the laser signal into transmitted light and reflected light having a preset light intensity ratio, and the reflected light (which is the part of the laser light signal received by the light beam returning unit 203) is transmitted to the mirror 2032. Transmitting the transmitted light (the remaining portion of the laser signal received as the beam return unit 203) to the second beam expander 201,
  • the mirror 2032 is configured to return the decomposed reflected light to the transmitting end 10.
  • the second beam expander 201 and the A second beam stabilizing unit 204 is added between the two photodetectors 20. In this way, the effect of beam fluctuations is suppressed.
  • the second beam stabilizing unit 204 is for adjusting the beam direction of the laser signal from the second beam expander to stably focus the laser signal from the second beam expander 201 to the phototube of the second photodetector 20.
  • the second beam stabilizing unit 204 is also a photocell that focuses the laser light from the beam expander to the photodetector.
  • the specific implementation of the second beam stabilizing unit 204 is substantially similar to that of the first beam stabilizing unit 106. For details, refer to the description of the first beam stabilizing unit 106, which will not be repeated here.
  • the radio frequency transmission apparatus provided by the embodiment of the present invention returns a part of the received laser signal to the transmitting end 10 by adding the beam returning unit 203, so that the transmitting end 10 can perform real-time compensation according to the phase difference.
  • the second beam stabilizing unit is synchronously increased to reduce the phase noise caused by the fluctuation of the beam with the influence of the environment, thereby further improving the synchronization precision and reliability of the free-space frequency transmission.
  • the embodiment of the present invention takes a dual-station frequency synchronous transmission system as an example for description.
  • phase jitter occurs due to deformation of the signal waveform due to factors such as atmospheric turbulence, vibration, and temperature fluctuation.
  • the phase compensation unit 105 is added to the transmitting end 10 of FIG. 1 to actively compensate the phase.
  • a laser-based wireless frequency transmission system includes a transmitting end 10 and at least one receiving end 20.
  • the transmitting end 10 can be a laser-based wireless frequency transmitting device as provided in any of the first embodiment to the third embodiment.
  • the receiving end 20 can be a laser-based wireless frequency transmitting device as provided in Embodiment 4 or Embodiment 5.
  • the specific implementation and configuration of the transmitting end 10 and the receiving end 20 are as described above with reference to FIG. 2 to FIG. 7, and details are not described herein again.
  • the laser-based wireless frequency transmission system of the embodiment of the present invention introduces a portion of the received laser signal by adding a beam returning device 203 at the receiving end 20, and introduces a phase compensating unit 105 at the transmitting end to reflect the reference frequency signal and the receiving end in real time.
  • the phase error of the microwave signal modulated in the back laser signal adjusts the phase of the laser signal, which can effectively suppress the phase fluctuation caused by atmospheric turbulence, vibration and temperature fluctuation, and greatly improve the synchronization accuracy and reliability of the free space frequency transmission system.
  • FIG. 9 is a basic system block diagram of a laser-based multi-station frequency transmission system according to the related art of the present invention.
  • the system includes a transmitting end 10 and n receiving ends 20-i, where n is a natural number greater than 1, i is a natural number, and 1 ⁇ i ⁇ n.
  • the transmitting end 10 modulates the microwave frequency signal or the time signal to be transmitted to the laser 102 by the microwave source 101, and then the n first beam expanding mirrors 103-i respectively emit the laser signals into the free space.
  • the receiving end 20 focuses the laser signal on the n corresponding second photodetectors 202-i through the n second beam expanders 201-i to recover the microwave frequency signal or the time signal.
  • the n base station firstly modulates the transmitted unique microwave frequency signal or time signal into the laser 102 in an over-modulated manner, and then divides the laser signal generated by the laser 102 into n at a ratio of 1/n.
  • the beam, n-beam laser signals are emitted into the space through n identical optical spatial beam expanders.
  • the n receiving ends e.g., base stations respectively receive the laser signal with the second beam expander 201-i and focus the received laser signal to the second photodetector 202-i for recovering the microwave frequency signal or the time signal.
  • i is a natural number and 1 ⁇ i ⁇ n.
  • a laser-based wireless multi-station frequency transmission system is similar to the first embodiment to the fifth embodiment, in order to solve the problems of low synchronization precision, short transmission distance, and high signal noise.
  • n phase compensation units 105-i and n third beam expanders 104-i are designed, where i is a natural number and 1 ⁇ i ⁇ n.
  • the second beam expander 201-i and the second photodetector 202-i at each receiving end 20-i.
  • a second beam stabilizing unit (not shown in Fig. 10) is added to suppress the influence of the beam fluctuation.
  • a first beam stabilizing unit 106-i may be provided between each pair of third beam expanding mirrors 104-i and phase compensating unit 105-i of the transmitting end 10 to suppress the influence of beam fluctuations.
  • the phase compensating unit 105-i is introduced at the transmitting end 10 to calculate the reference frequency signal in real time.
  • the phase error of the microwave signal modulated in the laser signal reflected by the receiving end 20-i adjusts the phase of the laser signal, which can effectively suppress phase fluctuation caused by atmospheric turbulence, vibration and temperature fluctuation, and greatly improve the free space frequency transmission system. Synchronization accuracy and reliability.
  • the fluctuation of the beam position can be suppressed, the phase noise caused by the fluctuation of the beam with the environment is avoided, and the free-space frequency transmission system is further improved. Synchronization accuracy and reliability.
  • a laser-based wireless multi-station frequency transmission method is applied to a transmitting end, and the method includes:
  • the laser generates a continuous laser signal modulated with a reference frequency signal.
  • S106 Perform phase comparison on the reference frequency signal and the microwave signal modulated in the reflected laser signal in real time, and adjust the phase of the modulated laser signal according to the phase error.
  • the microwave source 101 loads the reference frequency signal onto the continuous laser 102 by, for example, current modulation or external modulation, and the output of the laser 102 is modulated (ie, modulated After the laser signal of the reference frequency signal passes through the fiber tensioner 1055, the modulated laser signal is transmitted by the first beam expander 103. At the receiving end 20, a portion of the received laser signal is returned to the transmitting end 10 by the beam return unit 203. After the returned laser beam passes through the third beam expander 104, the concentrated beam is sent to the first beam stabilizing unit 106 for beam position stabilization. Referring to FIG.
  • the stabilization mode is: the first beam position sensor 1063 detects the beam direction, thereby generating a position error signal, and the position error signal is sent to the first PTD controller 1064 to obtain a driving signal, using the first
  • the high speed steering mirror driver 1065 adjusts the first high speed turning mirror 1066 to stabilize the beam in a fixed position.
  • the laser light passing through the first beam stabilizing unit 106 is coupled into the first photodetector 1052 to obtain a microwave signal, which is then filtered and amplified to obtain an electrical signal of a single frequency.
  • the electric signal and the local reference signal are sent to the phase detector 1053 to realize high-precision phase discrimination, and the phase error of the output is calculated by the processor 1054 to obtain phase fluctuation of the reciprocating laser, and then the compensation algorithm is used to obtain the unidirectional laser.
  • the phase-fluctuated voltage signal is fed back to the fiber tensioner 1055 for phase shifting operation.
  • the laser phase of this wireless path is stabilized, thereby achieving high-precision phase compensation of the link.
  • the vibration of the transmitting and receiving optical platform, the beam expander, and the mirror causes amplitude fluctuation caused by the change of the beam direction, and the fluctuation of the beam position causes relative intensity noise generated when the beam is coupled, and the method further include:
  • the third beam expander sends the concentrated beam of the reflected laser signal to the first beam stabilizing unit to stabilize the beam position.
  • first beam stabilizing unit in the present embodiment are the same as those described in connection with FIG. 5 in the third embodiment, and will not be repeated here.
  • another laser-based wireless multi-station frequency transmission method provided in Embodiment 6 of the present invention is applied to a receiving end, and the method includes:
  • the method further includes:
  • the condensed beam of the laser signal is sent to the second beam stabilizing unit by the second beam expander to stabilize the beam position.
  • the second beam expander sends the concentrated beam of the laser signal to the second beam stabilizing unit to perform the beam position stabilization principle and the step and the third beam expander sends the concentrated beam of the laser signal into the first beam to stabilize
  • the principle and steps of the unit for beam position stabilization are similar and will not be repeated here.
  • the laser-based wireless frequency transmission system, the transmission device and the transmission method thereof suppress the turbulence and vibration due to the atmosphere by returning a part of the received laser signal at the receiving end and introducing an active phase compensation link at the transmitting end.
  • the phase fluctuation caused by temperature fluctuations greatly improves the synchronization accuracy and reliability of the free-space frequency transmission system.
  • a beam stabilizing unit at the transmitting end and/or the receiving end to adjust the high-speed steering mirror, the fluctuation of the beam position can be suppressed, the phase noise caused by the fluctuation of the beam with the environment is avoided, and the free-space frequency transmission system is further improved. Synchronization accuracy and reliability.

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Abstract

本发明公开了一种基于激光器的无线频率传输系统及其传输装置和传输方法。该系统包括发送端(10)和至少一个接收端(20)。接收端(20)包括光束返回单元(203)，光束返回单元(203)用于将接收到的激光信号的一部分反射回发送端(10)。发送端(10)包括至少一对第三扩束镜(104)和相位补偿单元(105)，第三扩束镜(104)用于将接收端反射回的激光信号耦合到相位补偿单元(105)，相位补偿单元(105)用于实时对基准频率信号和接收端反射回的激光信号中调制的微波信号进行相位比较，根据相位误差调整调制有所述基准频率信号的激光信号的相位。

Description

基于激光器的无线频率传输系统及其传输装置和传输方法 技术领域
本发明涉及频率同步技术领域，尤其涉及一种基于激光器的无线频率传输系统及及其传输装置和传输方法。
背景技术
高精度时频同步在现代科学实验与工程实际应用中扮演着十分重要的作用，其目的是使相距一定距离的两个点或多个点的基准频率信号源在相位与时间上达到同步。高精度同步技术在通信、雷达探测、遥测技术、导航系统、天文观测和基础科学研究等领域有着广泛的应用。
目前常用的频率信号传输方式包括无线射频传输、全球定位系统(GPS)和光纤频率传输技术。无线射频传输和GPS同步方式很容易受到环境的干扰，障碍物阻挡和大气波动等问题的影响，其同步精度受到很大的限制。光纤频率传输技术需要构建专用的光纤信道，在某些没有现成的光纤链路或者不方便搭建光纤链路的场合无法使用光纤频率传输技术。
已存在基于自由空间信道的无线频率传输方式。图1为示出根据相关技术的双站间无线频率传输系统的原理框图。如图1所示，接收端10通过微波源101将所要传递的微波频率信号或者时间信号以过调幅的方式调制到激光器102上，然后通过光学空间第一扩束镜103将激光信号发射到自由空间中。接收端20通过第二扩束镜201将激光信号聚焦到第二光电探测器202上，用以恢复微波频率信号或者时间信号。在可视距离的情况(小于十千米)下，基于激光的无线频率传输技术提供了简便的同步方式，并且在该方式下其同步精度可以接近光纤频率传输的方法。
然而，采用激光实现自由空间无线频率传输中会面临如下问题：1)无线激光在空气传输中，由于大气湍流、振动以及温度波动等因素导致信号波形变形而产生相位抖动；2)诸如光学平台、准直镜和反射镜等光学元件的振动会导致 光束发生波动，进而增加了接收信号的相对强度噪声。如此，降低了自由空间无线频率传输的同步精度和可靠性。
发明内容
本发明提供了一种基于激光器的无线频率传输系统及其传输装置和传输方法。
根据本发明的第一方面，提供一种基于激光器的无线频率传输装置，所述基于激光器的无线频率传输装置包括至少一对第三扩束镜和相位补偿单元，其中：所述第三扩束镜用于将接收端反射回的激光信号耦合到所述相位补偿单元；并且所述相位补偿单元用于实时对基准频率信号和所述接收端反射回的激光信号中调制的微波信号进行相位比较，根据相位误差调整调制有所述基准频率信号的激光信号的相位。
根据本发明的第二方面，提供一种基于激光器的无线频率传输装置，所述基于激光器的无线频率传输装置，应用于接收端，并且包括：光束返回单元，其用于将接收到的激光信号的一部分反射回发送端。
根据本发明的第三方面，提供一种基于激光器的无线频率传输系统，所述基于激光器的无线频率传输系统包括发送端和至少一个接收端，其中，所述发送端包括根据所述第一方面的基于激光器的无线频率传输装置，所述接收端包括根据所述第二方面的基于激光器的无线频率传输装置。
根据本发明的第四方面，提供一种基于激光器的无线频率传输方法，该方法应用于发送端，并且包括：将基准频率信号加载到激光器上；产生调制有所述基准频率信号的连续的激光信号；将已调制激光信号耦合到自由空间传递出去；接收接收端反射回的激光信号；以及，实时对所述基准频率信号和反射回的激光信号中调制的微波信号进行相位比较，根据相位误差调整所述已调制激光信号的相位。
根据本发明的第五方面，提供一种基于激光器的无线频率传输方法，该方法应用于接收端，并且包括：将接收到的激光信号分解成具有预设的光强比的透射光与反射光；以及，将所述透射光传递给接收端中的第二扩束镜，将所述反射光返回至发送端。
附图说明
图1为根据本发明相关技术的一种基于激光器的双站间无线频率传输系统的原理框图。
图2为本发明实施例一提供的应用于发送端的基于激光器的无线频率传输装置的结构示意图。
图3为本发明实施例二提供的相位补偿单元的结构示意图及相位补偿原理图。
图4为本发明实施例三提供的一种基于激光器的无线频率传输装置的结构示意图。
图5为本发明实施例三提供的光束稳定单元结构示意图。
图6为本发明实施例四提供的应用于接收端的基于激光器的无线频率传输装置的结构示意图。
图7为本发明实施例四提供的另一种基于激光器的无线频率传输装置的原结构示意图。
图8为本发明实施例五提供的一种基于激光器的无线双站频率传输系统的结构示意图。
图9为根据本发明相关技术的基于激光器的无线多站频率传输系统的结构示意图。
图10为本发明实施例六提供的一种基于激光器的无线多站频率传输系统的结构示意图。
图11为本发明实施例七提供的一种基于激光器的无线频率传输方法的流程图。
图12为本发明实施例八提供的另一种基于激光器的无线频率传输方法的流程图。
本发明目的的实现、功能特点及优点将结合实施例，参照附图做进一步说明。
具体实施方式
为了使本发明所要解决的技术问题、技术方案及有益效果更加清楚、明白，以下结合附图和实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
除非另有定义，本文所使用的所有技术和科学术语与属于本发明的技术领域的技术人员通常理解的含义相同。此外，除非上下文明确指示，否则本文所使用的“第一”、“第二”、“第三”等序数用语不代表次序或顺序，而仅仅是为了表述的方便或概念之间的区分。
实施例一
如图2所示，本发明实施例提供的一种基于激光器的无线频率传输装置，应用于发送端10，包括微波源101、激光器102、第一扩束镜103，第三扩束镜104以及相位补偿单元105。
微波源101用于将基准频率信号加载到激光器102上，并将该基准频率信号提供给相位补偿单元105。
具体的，微波源101一般为压控受控源，其可以产生极低相位噪声的单频射频信号，作为发送端10的基准频率信号，并将基准频率信号调制加载到激光器102上。
激光器102用于产生调制有基准频率信号的激光信号，并该将调制有基准频率信号的激光信号提供给相位补偿单元105。
具体的，激光器102可以产生波长可调谐的单频连续激光，由于微波源101将基准频率信号调制加载到激光器102，因此激光器102可提供调制有基准频率信号的连续的激光信号，该激光信号可具有非常好的单色性和非常高的边摸抑制比。比如，可采用一个1.5微米波长的激光器作为本地光源，同时可将微波信号通过电流调制方式加载到激光器的激光信号上。
第一扩束镜103，用于将来自相位补偿单元105的已调制的激光信号耦合到自由空间。
具体的，第一扩束镜103通过扩展激光光束的直径和减小激光光束的发散角，将激光信号耦合到自由空间。可以根据不同波长在第一扩束镜103的镜头镀增透膜来实现其功能。如下文所述，耦合到自由空间的激光信号被接收端20 接收，且激光信号的一部分被接收端20反射回发送端10。
第三扩束镜104用于将接收到的接收端20反射回的激光信号耦合到相位补偿单元105。
相位补偿单元105用于实时对基准频率信号和接收端20反射回的激光信号中调制的微波信号进行相位比较，根据(相位比较得到的)相位误差来调整所述调制有基准频率信号的激光信号的相位。
本发明实施例中，通过在发送端引入相位补偿单元105以实时根据发送端的基准频率信号和接收端反射回的激光信号中调制的微波信号的相位误差调整调制有基准频率信号的激光信号的相位(即，要耦合到自由空间以被接收端接收的激光信号的相位)，能够有效抑制由于大气湍流、振动以及温度波动等造成的无线信道中的相位波动，极大提高了自由空间频率传输系统的同步精度和可靠性。
实施例二
如图3所示，本发明实施例提供的一种相位补偿单元105可通过移相器1051、第一光电探测器1052、鉴相器1053、处理器1054和光纤拉伸器1055来实现。
移相器1051用于调整基准频率信号的相位，并将基准频率信号输出给鉴相器1053。
输入到鉴相器1053的基准频率信号的相位与从激光器102进入光纤拉伸器的激光信号中调制的基准频率信号的相位一般存在一固有偏差，移相器1051对基准频率信号的相位的调整主要是为了补偿该固有偏差。在这两个相位的偏差可忽略，或处理器1054能够计算该固有偏差的情况下，也可以不设置移相器1051。第一光电探测器1052用于将接收端20反射回的激光信号中调制的微波信号解调出来，输出给鉴相器1053。
鉴相器1053用于对移相器1051输入的基准频率信号和第一光电探测器1052输入的微波信号(其也是一频率信号)进行相位比较，并将相位误差输出给处理器1054。
具体的，鉴相器1053的作用在于提取往返信号的相位差，在本实施例中，鉴相器1053可以对输入的基准频率信号与接收端20反馈回来的频率信号进行 相位比较，将比较得到的相位差(即相位误差)输出到处理器1054进行计算。另外，在一实施方式中，可以鉴相器1053可以与移相器1051为一体，即可由鉴相器1053实现移相器1051的功能。
处理器1054用于对相位误差进行计算，得到反馈驱动信号，并将反馈驱动信号输出给光纤拉伸器1055，从而由该反馈控制信号驱动光纤拉伸器1055，进而调整输入到光纤拉伸器的激光信号的相位。
具体的，处理器1054可以对信号形式的相位误差进行计算处理以得到反馈驱动信号。该处理器1054可采用计算机、单片机系统、DSP系统、或FPGA系统等。
光纤拉伸器1055用于根据反馈驱动信号调整激光器102的相位。
具体的，光纤拉伸器1055可接收来自处理器1054的反馈驱动信号，根据该反馈驱动信号改变激光器传输路径(光纤路径)上的光程，并通过该光程改变所带来的相位移动来补偿无线信道带来的相位波动，还可以实现对激光相位进行稳定。
下面结合图3对本发明实施例的主动补偿相位原理和过程进行说明：
1、发送端10采用一个激光器102(比如波长为1.5微米)作为本地光源，同时将作为基准频率信号的微波信号通过电流调制方式加载到该激光器102上。假设该微波信号的初始相位为φ 0。
2、激光信号经入光纤拉伸器1055，由光纤拉伸器1055产生的相位移动为φ c。
3、通过第一扩束镜103将激光信号送入自由空间，由于受空气湍流、震动和温漂等环境因素影响，信号在自由空间传输过程中被引入噪声φ p，到达接收端20后信号相位为φ 0+φ c+φ p。
4、将该激光信号的一部分从接收端20通过同一自由空间路径传回第三扩束镜104，并通过第一光电探测器1051将其转换为微波电信号，在此过程中又引入噪声φ p，于是由接收端传回本地的激光信号相位为φ 0+φ c+2φ p。
5、该激光信号被送到鉴相器1053中与基准频率信号进行鉴相，并将鉴相结果作为误差信号送到处理器1054进行计算处理，利用相位补偿算法得到反馈驱动信号，将其送入光纤拉伸器1055以实现相位的预补偿，即使得：φ c+φ 0-(φ 0+φ c+2φ p)＝0，因此可得φ c＝-φ p。该相位补偿算法调整光纤拉伸器1055的相移 φ c，用调整后的φ c抵消了自由空间传输中产生的相位波动φ p，使得接收端的信号与本地的基准频率信号达到完全同步，由此实现高精度的自由空间频率传输。该相位补偿方案虽然受限于光纤拉伸器1055的拉伸能力，但只要自由空间相位波动不超过光纤拉伸器1055的拉伸范围，补偿方案均有效。
实施例三
如图4所示，本发明实施例提供的一种基于激光器的无线频率传输装置中，存在由于光束位置的波动导致光束耦合时产生相对强度噪声，由于收发光学平台、扩束镜、反射镜的振动导致光束方向变化，带来幅度波动的问题。为了抑制光束波动带来的影响，在发送端10增加了第一光束稳定单元106直接消除光束波动。
如图4所示，第一光束稳定单元106设置在第三扩束镜104与相位补偿单元105之间，第一光束稳定单元106用于调节从接收端20返回(并经第三扩束镜104扩束)的激光信号的光束方向，以将经调节的激光信号聚焦到相位补偿单元105的第一光电探测器1052的光电管。
作为本实施例的一种实施方式，如图5所示，第一光束稳定单元106包括第一高速转向镜1061、第一分束镜1062、第一波束位置传感器1063、第一比例积分微分(proportion integral derivat ive，PTD)控制器1064以及第一高速转向镜驱动器1065。
第一高速转向镜1061用于将输入的激光信号偏转后传递给第一分束镜1062。
第一分束镜1062用于将激光信号进行分解，得到一束目标激光信号和一束向第一光电探测器1052的光电管聚焦的激光信号。对分解得到的两束激光信号的光强比没有特殊要求。
第一波束位置传感器1063用于对目标激光信号的位置进行探测，得到位置误差信号，并将位置误差信号传递给第一PTD控制器1064。
第一PTD控制器1064用于根据位置误差信号得到位置调整电压，并将位置调整电压输出给第一高速转向镜驱动器1065。
第一高速转向镜驱动器1065用于根据位置调整电压控制第一高速转向镜1061的转动。
具体来说，第三扩束镜104接收到的激光信号依此通过第一高速转向镜1061和第一分束镜1062，得到一束目标激光信号，第一波束位置传感器1063对目标激光信号的位置进行探测，得到位置误差信号并将该位置误差信号传递给第一PTD控制器1064，第一PTD控制器(1064)根据位置误差信号得到位置调整电压，并将位置调整电压反馈给第一高速转向镜驱动器1065，由第一高速转向镜驱动器1065根据位置调整电压在X轴和Y轴两个维度上控制第一高速转向镜(1061)的偏转，从而快速调整光束方向，以达到稳定光束的目的。
下面结合图5说明第一光束稳定单元106的原理和工作过程：
1、沿光路方向，在第三扩束镜103后引入了第一高速转向镜1061，该高速转向镜1061可以在两个维度(即X和Y方向)上进行高速偏转，激光光束经过转向镜反射后被第一分束镜1062分成两束，利用第一波束位置传感器1063去探测其中的一束激光光束(一路分光信号)，产生出两个维度上的位置误差信号，该误差信号可以以电压的形式输出。假设X方向上输出误差信号为Δx，Y方向上输出误差信号为Δy。
2、第一波束位置传感器1063将所获得的两个维度上的电压误差信号分别输入第一PTD控制器1064，第一PTD控制器1064将向第一高速转向镜驱动器1065输出-Δx和-Δy的反馈信号(位置调整电压)，进而由第一高速转向镜驱动器1065去驱动第一高速转向镜1061，以保证光束一直照射到第一波束位置传感器1063的中心点。因此通过该PTD环路可以将整个光束稳定在一个固定的位置，从而确保从第一分束镜1062向第一光电探测器1052输出的光束的稳定。由于传输系统的震动因素导致的光束波动频率较低(约为KHz级)，而通过第一PTD控制器驱动的高速转向镜的速度(约为MHz级)完全能够予以补偿，这样便可最终达到消除光束波动的目的。该光束稳定方案虽然受限于波束位置传感器的面积，但只要光束波动不超过波束位置传感器的感应面积，该光束稳定方案均有效。
发明人基于以上算法和控制方案，实施了基准频率为100MHz，传输距离超过120米的户外无线自由空间的频率传输实验。在传输过程中，测量了相位波动和艾伦方差的不稳定性传输频率。在5000秒内传输该100MHz的微波信号，均方根值(RMS)相位波动经测定为22皮秒左右，在1s内频率不稳定度是3×10 -12，在千秒内频率不稳定度是4×10 -14。所实现的频率稳定度要优于商用铯原子钟5071A以及铷原子钟，因此该无线频率传输方案可以用于铯原子和铷原子 钟信号的传输。
本实施例在上述实施例一和二的基础上，通过增加光束稳定单元解决由于光学平台、反射镜的振动会导致的光束波动，减少光束随环境影响波动带来的相位噪声，进一步提高了自由空间频率传输系统的同步精度和可靠性。
实施例四
如图6所示，本发明实施例提供的一种基于激光器的无线频率传输装置，应用于接收端20，该装置包括光束返回单元203、第二扩束镜201和第二光电探测器202。
光束返回单元203用于将接收到的激光信号的一部分反射回发送端10。光束返回单元203还用于将接收到的激光信号的其余部分传递给第二扩束镜201。
第二扩束镜201用于将从光束返回单元203接收到的激光信号(即，光束返回单元203接收到的激光信号的其余部分)聚焦到第二光电探测器202。
具体的，第二扩束镜201可通过扩展激光光束的直径和减小激光光束的发散角，将激光信号耦合第二光电探测器202的光电管。
第二光电探测器202，用于将从第二扩束镜201接收的激光信号中调制的微波信号解调出来。
具体的，第二光电探测器202可以通过光电转换将已调制微波的激光信号转换成电信号输出，通常其频响范围从直流到上GHz，且增益可调。
如图7所示，作为本实施例的一种实施方式，光束返回单元203可以通过分束镜2031和反射镜2032组合来实现。
分束镜2031用于将激光信号分解成具有预设的光强比的透射光与反射光，反射光(作为光束返回单元203接收到的激光信号的所述一部分)传递给反射镜2032。将透射光(作为光束返回单元203接收到的激光信号的所述其余部分)传递给第二扩束镜201，
反射镜2032，用于将分解出的反射光返回发送端10。
如图7所示，作为本实施例的另一种实施方式，为了消除接收端光束位置的波动导致光束耦合时产生的相对强度噪声，还可以在接收端20的第二扩束镜201和第二光电探测器20之间增加第二光束稳定单元204。以这种方式，抑制 了光束波动带来的影响。
第二光束稳定单元204用于调节来自第二扩束镜的激光信号的光束方向，以使来自第二扩束镜201的激光信号稳定地聚焦到第二光电探测器20的光电管。
与第一光束稳定单元106类似，第二光束稳定单元204也是将来自扩束镜的激光聚焦到光电探测器的光电管。第二光束稳定单元204的具体实现方式与第一光束稳定单元106基本类似，具体参见对第一光束稳定单元106的说明，这里不再重述。
本发明实施例提供的无线频率传输装置，通过增加光束返回单元203将接收到的激光信号的一部分返回给发送端10，从而使得发送端10能根据相位差进行实时补偿。此外，同步增加第二光束稳定单元减少光束随环境影响而波动带来的相位噪声，进一步提高了自由空间频率传输的同步精度和可靠性。
实施例五
本发明实施例以双站频率同步传输系统为例进行说明。如前面基于图1所说明的，当激光信号在空气中传输中，由于大气湍流、振动以及温度波动等因素会导致信号波形变形而产生相位抖动。为了抑制由于大气湍流、振动以及温度波动造成的相位波动，在图1的发送端10中增加相位补偿单元105进行主动补偿相位。
如图8所示，本发明实施例提供的一种基于激光器的无线频率传输系统包括发送端10和至少一个接收端20。发送端10可为如实施例一至实施例三中任一实施例所提供的基于激光器的无线频率传输装置。接收端20可为如实施例四或实施例五所提供的基于激光器的无线频率传输装置。发送端10和接收端20的具体实现方式和构成如前面参考附图2至附图7所描述，在此不再赘述。
本发明实施例的基于激光器的无线频率传输系统，通过在接收端20增加光束返回装置203以返回接收到激光信号的一部分，在发送端引入相位补偿单元105以实时根据基准频率信号和接收端反射回的激光信号中调制的微波信号的相位误差调整激光信号的相位，能够有效抑制由于大气湍流、振动以及温度波动造成的相位波动，极大提高了自由空间频率传输系统的同步精度和可靠性。
实施例六
本发明实施例以多站频率同步传输为例进行说明，图9示出了根据本发明相关技术的基于激光器的多站频率传输系统的基本系统框图。该系统包括一个发送端10和n个接收端20-i，其中，n为大于1的自然数，i为自然数，且1≤i≤n。发送端10通过微波源101将所要传递的微波频率信号或者时间信号以过调幅的方式调制到激光器102上，然后n个第一扩束镜103-i分别将激光信号发射到自由空间中。接收端20通过n个第二扩束镜201-i将激光信号聚焦到n个对应的第二光电探测器202-i上，用以恢复微波频率信号或者时间信号。
具体的，以n基站举例来说，首先是要将传递的唯一微波频率信号或者时间信号以过调幅的方式调制到激光器102上，然后以1/n的比例将激光器102产生的激光信号分成n束，n束激光信号通过n个相同的光学空间扩束镜发射到空间中。n个接收端(例如，基站)分别用第二扩束镜201-i接收激光信号并将接收到的激光信号聚焦到第二光电探测器202-i，用以恢复微波频率信号或者时间信号。其中i为自然数，且1≤i≤n。
如图10所示，本发明实施例提供的一种基于激光器的无线多站频率传输系统，与上述实施例一到实施例五类似，为了解决同步精度低，传输距离近、信号噪声高等问题，在多站频率传输系统的发送端10中，设计了完全相同的n个相位补偿单元105-i以及n第三扩束镜104-i，其中i为自然数，且1≤i≤n。通过以上系统可以实现多站间的高精度无线频率传输，其多站间无线频率传输指标不低于实施例五的双站频率的传输指标。此外，为了消除接收端20光束位置的波动导致光束耦合时产生的相对强度噪声，还可以在每个接收端20-i的第二扩束镜201-i和第二光电探测器202-i之间，增加第二光束稳定单元(图10中未示出)来抑制光束波动带来的影响。类似地，可以在发送端10的每对第三扩束镜104-i与相位补偿单元105-i之间，设置第一光束稳定单元106-i来抑制光束波动带来的影响。
本发明实施例中，通过在每个接收端20-i增加光束返回单元203-i以返回接收到的激光信号的一部分，在发送端10引入相位补偿单元105-i以实时根据基准频率信号和接收端20-i反射回的激光信号中调制的微波信号的相位误差调整激光信号的相位，能够有效抑制由于大气湍流、振动以及温度波动造成的相位波动，极大提高了自由空间频率传输系统的同步精度和可靠性。此外，通过在 发送端和/或接收端引入光束稳定单元来调节高速转向镜，能够抑制光束位置的波动，避免了光束随环境影响波动带来的相位噪声，进一步提高了自由空间频率传输系统的同步精度和可靠性。
实施例七
如图11所示，本发明实施例提供的一种基于激光器的无线多站频率传输方法，应用于发送端，该方法包括：
S101、将基准频率信号加载到激光器上。
S102、激光器产生调制有基准频率信号的连续的激光信号。
S103、将已调制激光信号耦合到自由空间传递出去。
S104、接收接收端反射回的激光信号。
S106、实时对基准频率信号和反射回的激光信号中调制的微波信号进行相位比较，根据相位误差调整已调制激光信号的相位。
具体的，以图4和图6所示的结构为例，微波源101通过例如电流调制或者外调制的方式将基准频率信号加载到连续激光器102上，激光器102输出的已调制(即，调制有基准频率信号的)激光信号通过光纤拉伸器1055后，利用第一扩束镜103将已调制激光信号传递出去。在接收端20处，利用光束返回单元203，将接收到的激光信号的一部分返回至发送端10。返回的激光光束通过第三扩束镜104后，聚集波束被送入第一光束稳定单元106进行光束位置稳定。参考图5，稳定方式为：由第一波束位置传感器1063去探测光束方向，以此产生出位置误差信号，将该位置误差信号送入第一PTD控制器1064后得到驱动信号，利用第一个高速转向镜驱动器1065调整第一高速转向镜1066，使光束被稳定在一个固定的位置。将通过第一光束稳定单元106的激光耦合入第一光电探测器1052，得到微波信号，再对其滤波和放大，得到单一频率的电信号。将该电信号与本地参考信号送入鉴相器1053实现高精度的鉴相，输出的相位误差经过处理器1054计算，得到往返激光的相位波动，再利用补偿算法，得到用于补偿单向激光相位波动的电压信号，将该电压信号反馈到光纤拉伸器1055上进行移相操作。使得这一无线路径的激光相位得到稳定，从而实现了链路的高精度相位补偿。
关于本实施例中的主动补偿相位的原理和过程，与在实施例二中结合图3 所描述的原理和过程相同，这里不再重述。
作为本实施例的一种实施方式，针对收发光学平台、扩束镜、反射镜的振动导致光束方向变化带来的幅度波动，光束位置的波动导致光束耦合时产生的相对强度噪声，该方法还包括：
S105、第三扩束镜将反射回的激光信号的聚集波束送入第一光束稳定单元进行光束位置稳定。
关于本实施方式中的第一光束稳定单元的原理和工作过程，与在实施例三中结合图5所描述的原理和过程相同，这里不再重述。
实施例八
如图12所示，本发明实施例六提供的另一种基于激光器的无线多站频率传输方法，应用于接收端，该方法包括：
S201、将接收到的激光信号分解成具有预设的光强比的透射光与反射光。
S202、将透射光传递给接收端中的第二扩束镜，将反射光返回至发送端。
作为本实施例的一种实施方式，该方法还包括：
S203、由第二扩束镜将激光信号的聚集波束送入第二光束稳定单元进行光束位置稳定。
本发明实施例中，第二扩束镜将激光信号的聚集波束送入第二光束稳定单元进行光束位置稳定的原理及步骤与第三扩束镜将激光信号的聚集波束送入第一光束稳定单元进行光束位置稳定的原理和步骤类似，这里不再重述。
本发明实施例的基于激光器的无线频率传输系统及其传输装置和传输方法，通过在接收端返回接收到的激光信号的一部分，在发送端引入主动相位补偿环节，抑制了由于大气湍流、振动以及温度波动造成的相位波动，从而极大提高了自由空间频率传输系统的同步精度和可靠性。此外，通过在发送端和/或接收端引入光束稳定单元来调节高速转向镜，能够抑制光束位置的波动，避免了光束随环境影响波动带来的相位噪声，进一步提高了自由空间频率传输系统的同步精度和可靠性。
以上参照附图说明了本发明的优选实施例，并非因此局限本发明的权利范围。本领域技术人员不脱离本发明的范围和实质，可以有多种变型方案实现本 发明，比如作为一个实施例的特征可用于另一实施例而得到又一实施例。凡在运用本发明的技术构思之内所作的任何修改、等同替换和改进，均应在本发明的权利范围之内。

Claims (15)

  1. 一种基于激光器的无线频率传输装置，包括至少一对第三扩束镜(104)和相位补偿单元(105)，其中：
    所述第三扩束镜(104)用于将接收端(20)反射回的激光信号耦合到所述相位补偿单元(105)；并且
    所述相位补偿单元(105)用于实时对基准频率信号和所述接收端(20)反射回的激光信号中调制的微波信号进行相位比较，根据相位误差调整调制有所述基准频率信号的激光信号的相位。
  2. 根据权利要求1所述的基于激光器的无线频率传输装置，其中，所述相位补偿单元(105)包括移相器(1051)、第一光电探测器(1052)、鉴相器(1053)、处理器(1054)和光纤拉伸器(1055)，其中：
    所述移相器(1051)用于调整所述基准频率信号的相位，并将所述基准频率信号输出给所述鉴相器(1053)；
    所述第一光电探测器(1052)用于通过光电转换将所述接收端(20)反射回的激光信号中调制的微波信号解调出来，并输出给所述鉴相器(1053)；
    所述鉴相器(1053)用于对从所述移相器(1051)输入的基准频率信号和从所述第一光电探测器(1052)输入的微波信号的相位进行比较，并将相位误差输出给所述处理器(1054)；
    所述处理器(1054)用于对所述相位误差进行计算，得到反馈驱动信号，并将所述反馈驱动信号输出给所述光纤拉伸器(1055)；并且
    所述光纤拉伸器(1055)用于根据所述反馈驱动信号调整所述调制有所述基准频率信号的激光信号的相位。
  3. 根据权利要求2所述的基于激光器的无线频率传输装置，还包括：
    第一光束稳定单元(106)，其设置在所述第三扩束镜(104)与所述相位补偿单元(105)之间，用于调节从所述接收端(20)反射回的激光信号的光束方向，以将经调节的激光信号聚焦到所述第一光电探测器(1052)的光电管。
  4. 根据权利要求3所述的基于激光器的无线频率传输装置，其中，所述第一光束稳定单元(106)包括第一高速转向镜(1061)、第一分束镜(1062)、 第一波束位置传感器(1063)、第一比例积分微分PID控制器(1064)以及第一高速转向镜驱动器(1065)，其中：
    所述第一高速转向镜(1061)用于将输入到所述第一光束稳定单元(106)的激光信号偏转后传递给所述第一分束镜(1062)；
    所述第一分束镜(1062)用于将来自所述第一高速转向镜(1061)的激光信号进行分解，得到一束目标激光信号；
    所述第一波束位置传感器(1063)用于对所述目标激光信号的位置进行探测，得到位置误差信号，并将所述位置误差信号传递给所述第一PID控制器(1064)；
    所述第一PID控制器(1064)用于根据所述位置误差信号得到位置调整电压，并将所述位置调整电压输出给所述第一高速转向镜驱动器(1065)；并且
    所述第一高速转向镜驱动器(1065)用于根据所述位置调整电压控制所述第一高速转向镜(1061)的转动。
  5. 根据权利要求4所述的基于激光器的无线频率传输装置，其中，所述第一高速转向镜驱动器(1065)用于根据所述位置调整电压在X轴和Y轴两个维度上控制所述第一高速转向镜(1061)的偏转。
  6. 根据权利要求1所述的基于激光器的无线频率传输装置，还包括微波源(101)、激光器(102)和第一扩束镜(103)，其中：
    所述微波源(101)用于将所述基准频率信号加载到所述激光器(102)上以及将所述基准频率信号提供给所述相位补偿单元(105)；
    所述激光器(102)用于产生所述调制有所述基准频率信号的激光信号，并将所述调制有所述基准频率信号的激光信号提供给所述相位补偿单元(105)；并且
    所述第一扩束镜(103)用于将经所述相位补偿单元(105)调整的激光信号耦合到自由空间。
  7. 一种基于激光器的无线频率传输装置，应用于接收端(20)，其中，所述基于激光器的无线频率传输装置包括：
    光束返回单元(203)，用于将接收到的激光信号的一部分反射回发送端 (10)。
  8. 根据权利要求7所述的基于激光器的无线频率传输装置，其中，所述光束返回单元(203)包括：
    分束镜(2031)，用于将所述激光信号分解成具有预设的光强比的透射光与反射光，并将作为所述激光信号的所述一部分的所述反射光传递给所述反射镜(2032)；以及
    反射镜(2032)，用于将所述反射光反射回发送端(10)。
  9. 根据权利要求7所述的基于激光器的无线频率传输装置，还包括第二扩束镜(201)和第二光电探测器(202)，其中：
    所述光束返回单元(203)还用于将接收到的激光信号的其余部分传递给所述第二扩束镜(201)；
    所述第二扩束镜(201)用于将来自所述光束返回单元(203)的激光信号聚焦到所述第二光电探测器(202)；并且
    所述第二光电探测器(202)用于将来自所述第二扩束镜(201)的激光信号中调制的微波信号解调出来。
  10. 根据权利要求9所述的基于激光器的无线频率传输装置，还包括：
    第二光束稳定单元(204)，其设置在所述第二扩束镜(201)与所述第二光电探测器(202)之间，用于调节来自所述第二扩束镜(201)的激光信号的光束方向，以将经调节的激光信号聚焦到所述第二光电探测器(20)的光电管。
  11. 一种基于激光器的无线频率传输系统，包括发送端(10)和至少一个接收端(20)，其中，所述发送端(10)包括根据权利要求1-6中任意一项权利要求所述的基于激光器的无线频率传输装置，所述接收端(20)包括根据权利要求7-10中任意一项权利要求所述的基于激光器的无线频率传输装置。
  12. 一种基于激光器的无线频率传输方法，应用于发送端，其中，该方法包括：
    将基准频率信号加载到激光器(102)上；
    产生调制有所述基准频率信号的连续的激光信号；
    将已调制激光信号耦合到自由空间传递出去；
    接收接收端反射回的激光信号；以及
    实时对所述基准频率信号和反射回的激光信号中调制的微波信号进行相位比较，根据相位误差调整所述已调制激光信号的相位。
  13. 根据权利要求12所述的基于激光器的无线频率传输方法，还包括：将反射回的激光信号的聚集波束送入第一光束稳定单元(106)进行光束位置稳定。
  14. 一种基于激光器的无线频率传输方法，应用于接收端(20)，其中，该方法包括：
    将接收到的激光信号分解成具有预设的光强比的透射光与反射光；以及
    将所述透射光传递给接收端中的第二扩束镜(201)，将所述反射光返回至发送端(10)。
  15. 根据权利要求14所述的基于激光器的无线频率传输方法，还包括：由第二扩束镜(201)将接收到的激光信号的聚集波束送入第二光束稳定单元(204)进行光束位置稳定。
PCT/CN2018/085609 2017-05-05 2018-05-04 基于激光器的无线频率传输系统及其传输装置和传输方法 WO2018202132A1 (zh)

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