Frequency transmission system and method

Abstract

The application provides a frequency transmission system and method, and relates to the technical field of frequency synchronization, the system comprises a transmitting device, at least one receiving device and at least one relay amplification filtering device; each receiving device is connected to the transmitting device through a corresponding optical fiber link, and at least one relay amplification filtering device is arranged on the optical fiber link; the receiving device modulates a generated probe frequency signal onto a second optical signal and then transmits the second optical signal to the transmitting device through the corresponding optical fiber link; the transmitting device modulates a generated reference frequency signal onto a first optical signal and a generated probe frequency signal onto a third optical signal, and the wavelengths of the three optical signals are different, so that the relay amplification filtering device can suppress non-ideal scattering of corresponding transmission signals and suppress ASE noise generated when the relay amplification filtering device amplifies the optical power of the transmission signals, thereby improving the signal-to-noise ratio of the transmission signals, and effectively establishing long-distance frequency transmission from one transmitting device to multiple receiving devices.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of frequency synchronization technology, and particularly relates to a frequency transmission system and method. BACKGROUND

[0002] Optical carrier radio frequency refers to modulating a radio frequency signal onto an optical signal by a transmitting device, and then transmitting the optical signal to a receiving device through an optical fiber link. Frequency synchronization based on optical carrier radio frequency refers to that the receiving device can reproduce a frequency signal generated by a reference frequency source of the transmitting device, that is, a frequency signal output by a frequency source generation device of the receiving device is synchronized in frequency with the frequency signal generated by the reference frequency source, and a phase difference between the two is kept constant.

[0003] When a phase-locked loop is used in the receiving device to realize frequency synchronization, a signal-to-noise ratio of an input signal of the phase-locked loop needs to meet certain requirements. If the signal-to-noise ratio of the input signal of the phase-locked loop is lower than a required signal-to-noise ratio threshold, the locking error of the phase-locked loop will increase, the deviation between a frequency of an output signal of the phase-locked loop and an expected frequency will be large, and even the phase-locked loop will lose lock, and the frequency transmission will be interrupted.

[0004] However, when one transmitting device needs to simultaneously perform frequency synchronization based on optical carrier radio frequency with multiple receiving devices that are far away from the transmitting device, the existing scheme has a problem of low signal-to-noise ratio of a transmission signal, which makes it difficult for the existing scheme to effectively establish long-distance frequency transmission from the transmitting device to the multiple receiving devices. SUMMARY

[0005] In order to solve the problem of low signal-to-noise ratio of a transmission signal existing in the existing scheme and to effectively establish long-distance frequency transmission from one transmitting device to multiple receiving devices, the present application provides a frequency transmission system and method.

[0006] The technical scheme of the present application is as follows:

[0007] The present application provides a frequency transmission system, comprising: a transmitting device, at least one receiving device, and at least one relay amplification and filtering device.

[0008] Each receiving device is connected to the transmitting device through a corresponding optical fiber link, and at least one relay amplification and filtering device is arranged on the optical fiber link.

[0009] The transmitting device is configured to generate a reference frequency signal, modulate the reference frequency signal onto a first optical signal to obtain a first modulated optical signal, demodulate a second modulated optical signal carrying a probe frequency signal to obtain the probe frequency signal when receiving the second modulated optical signal from a target receiving device, modulate the probe frequency signal onto a third optical signal to obtain a third modulated optical signal, and output a coupled optical signal obtained by coupling the first modulated optical signal and the third modulated optical signal to the optical fiber link of the target receiving device; wherein the reference frequency signal is a frequency signal obtained by performing first frequency multiplication on a first frequency signal generated by a reference frequency source.

[0010] The relay amplification and filtering device is configured to perform optical power amplification on the second modulated optical signal when receiving the second modulated optical signal from the receiving device, perform noise suppression on the second modulated optical signal by using a first optical filter unit of the relay amplification and filtering device, and perform non-ideal scattering suppression on the second modulated optical signal by using a second optical filter unit of the relay amplification and filtering device, and perform optical power amplification on the coupled optical signal when receiving the coupled optical signal from the transmitting device, perform noise suppression on the coupled optical signal by using the second optical filter unit, and perform non-ideal scattering suppression on the coupled optical signal by using the first optical filter unit, wherein the carrier wavelengths of the first modulated optical signal, the second modulated optical signal, and the third modulated optical signal are different.

[0011] The receiving device is configured to generate a probe frequency signal, modulate the probe frequency signal onto a second optical signal to obtain a second modulated optical signal, output the second modulated optical signal to an optical fiber link of the receiving device, and control the output of a voltage-controlled crystal oscillator of the receiving device based on the coupled optical signal when receiving the coupled optical signal from the transmitting device, so that a second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and the phase difference remains constant; wherein the probe frequency signal is a frequency signal obtained by performing second frequency multiplication on the second frequency signal.

[0012] Optionally, the transmitting device comprises a signal generation module, an optical fiber coupler, and at least one signal processing module.

[0013] The output end of the signal generation module is connected to the first port of each signal processing module through the optical fiber coupler, and the second port of each signal processing module is connected to the receiving device through a corresponding optical fiber link.

[0014] The signal generating module is configured to generate the reference frequency signal and modulate the reference frequency signal onto the first optical signal to obtain the first modulated optical signal.

[0015] The optical fiber coupler is configured to split the first modulated optical signal and provide the first modulated optical signal for each signal processing module.

[0016] The signal processing module is configured to, when receiving a second modulated optical signal carrying a probe frequency signal from a corresponding receiving device, demodulate the second modulated optical signal to obtain the probe frequency signal, modulate the probe frequency signal onto a third optical signal to obtain a third modulated optical signal, and output a coupled optical signal obtained by coupling the first modulated optical signal and the third modulated optical signal to an optical fiber link corresponding to the receiving device.

[0017] Optionally, the signal processing module comprises:

[0018] An optical signal conditioning unit is configured to perform noise suppression and optical power amplification on the second modulated optical signal when receiving the second modulated optical signal.

[0019] A first photodetector is configured to demodulate the second modulated optical signal output by the optical signal conditioning unit to obtain the probe frequency signal.

[0020] A radio frequency signal conditioning unit is configured to perform noise suppression and power amplification on the probe frequency signal.

[0021] A first optical transmitting unit is configured to modulate the probe frequency signal output by the radio frequency signal conditioning unit onto the third optical signal to obtain the third modulated optical signal.

[0022] A first wavelength division multiplexer is configured to couple the first modulated optical signal from the optical fiber coupler and the third modulated optical signal from the first optical transmitting unit to obtain the coupled optical signal.

[0023] A first circulator is configured to output the coupled optical signal from the first wavelength division multiplexer to an optical fiber link corresponding to the receiving device and send the second modulated optical signal from the optical fiber link to the optical signal conditioning unit.

[0024] Optionally, the relay amplification filter device comprises a second circulator, the first optical filter unit, the second optical filter unit, an optical power amplification unit, and a third circulator.

[0025] The first optical filter unit comprises a third optical filter and a sixth optical filter, an input end of the third optical filter is connected to the first side of the optical power amplification unit, an output end of the third optical filter is connected to the first port of the second optical circulator, an input end of the sixth optical filter is connected to the third port of the third optical circulator, and an output end of the sixth optical filter is connected to the second side of the optical power amplification unit.

[0026] The second optical filter unit comprises a first optical filter subunit and a second optical filter subunit, an input end of the first optical filter subunit is connected to the third port of the second optical circulator, an output end of the first optical filter subunit is connected to the first side of the optical power amplification unit, an input end of the second optical filter subunit is connected to the second side of the optical power amplification unit, and an output end of the second optical filter subunit is connected to the first port of the third optical circulator.

[0027] The second optical circulator is used for transmitting an optical signal from the second port thereof to the third port thereof and transmitting an optical signal from the first port thereof to the second port thereof, and the second port of the second optical circulator is connected to the transmitting device or the third optical circulator of the relay amplification filter device adjacent to the second optical circulator.

[0028] The third optical circulator is used for transmitting an optical signal from the first port thereof to the second port thereof and transmitting an optical signal from the second port thereof to the third port thereof, and the second port of the third optical circulator is connected to the receiving device or the second optical circulator of the relay amplification filter device adjacent to the third optical circulator.

[0029] Optionally, the first optical filter subunit comprises a second wavelength division multiplexer, a third wavelength division multiplexer, a first optical filter and a second optical filter, and the second optical filter subunit comprises a fourth wavelength division multiplexer, a fifth wavelength division multiplexer, a fourth optical filter and a fifth optical filter.

[0030] An input end of the second wavelength division multiplexer is connected to the third port of the second optical circulator, two output ends of the second wavelength division multiplexer are respectively connected to input ends of the first optical filter and the second optical filter, output ends of the first optical filter and the second optical filter are respectively connected to two input ends of the third wavelength division multiplexer, an output end of the third wavelength division multiplexer is connected to the first side of the optical power amplification unit, an input end of the fourth wavelength division multiplexer is connected to the second side of the optical power amplification unit, two output ends of the fourth wavelength division multiplexer are respectively connected to input ends of the fourth optical filter and the fifth optical filter, output ends of the fourth optical filter and the fifth optical filter are respectively connected to two input ends of the fifth wavelength division multiplexer, and an output end of the fifth wavelength division multiplexer is connected to the first port of the third optical circulator.

[0031] Optionally, the first optical filtering subunit comprises a seventh wavelength division multiplexer and an eighth wavelength division multiplexer, and the second optical filtering subunit comprises a ninth wavelength division multiplexer and a tenth wavelength division multiplexer;

[0032] The input end of the seventh wavelength division multiplexer is connected to the third port of the second circulator, the output end of the seventh wavelength division multiplexer is connected to the input end of the eighth wavelength division multiplexer, the output end of the eighth wavelength division multiplexer is connected to the first side of the optical power amplification unit, the input end of the ninth wavelength division multiplexer is connected to the second side of the optical power amplification unit, the output end of the ninth wavelength division multiplexer is connected to the input end of the tenth wavelength division multiplexer, and the output end of the tenth wavelength division multiplexer is connected to the first port of the third circulator.

[0033] Optionally, the optical power amplification unit comprises a fourth circulator, a bidirectional optical power amplifier, and a fifth circulator.

[0034] The first port of the fourth circulator is connected to the output end of the first optical filtering subunit, the second port of the fourth circulator is connected to the first end of the bidirectional optical power amplifier, and the third port of the fourth circulator is connected to the input end of the third optical filter.

[0035] The third port of the fifth circulator is connected to the input end of the second optical filtering subunit, the first port of the fifth circulator is connected to the output end of the sixth optical filter, and the second port of the fifth circulator is connected to the second end of the bidirectional optical power amplifier.

[0036] Optionally, the optical power amplification unit comprises a first optical power amplifier and a second optical power amplifier.

[0037] The input end of the first optical power amplifier is connected to the output end of the first optical filtering subunit, and the output end of the first optical power amplifier is connected to the input end of the second optical filtering subunit.

[0038] The input end of the second optical power amplifier is connected to the output end of the sixth optical filter, and the output end of the second optical power amplifier is connected to the input end of the third optical filter.

[0039] Optionally, the receiving device specifically comprises a sixth circulator, a third optical power amplifier, a sixth wavelength division multiplexer, a second photodetector, a third photodetector, a loop locking unit, and a second optical transmitting unit.

[0040] The sixth circulator is used to transmit the coupled optical signal from the transmitting device to the third optical power amplifier and transmit a second modulated optical signal from the second optical transmitting unit to the optical fiber link of the receiving device.

[0041] the third optical power amplifier, configured to perform optical power amplification on the coupled optical signal;

[0042] the sixth wavelength division multiplexer, configured to perform channel separation on the coupled optical signal from the third optical power amplifier to obtain the first modulated optical signal and the third modulated optical signal;

[0043] the second photodetector, configured to demodulate the first modulated optical signal from the sixth wavelength division multiplexer to obtain the reference frequency signal;

[0044] the third photodetector, configured to demodulate the third modulated optical signal from the sixth wavelength division multiplexer to obtain the probe frequency signal;

[0045] the loop locking unit, configured to generate the probe frequency signal, and mix the reference frequency signal from the second photodetector and the probe frequency signal from the third photodetector to obtain a mixed signal, and phase demodulate the mixed signal and the probe frequency signal to obtain an error signal of the second frequency signal relative to the first frequency signal, and control an output of a voltage-controlled crystal oscillator of the loop locking unit by using the error signal, so that the second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and a phase difference between them remains constant; wherein a signal frequency of the reference frequency signal is twice a signal frequency of the probe frequency signal, so that a phase disturbance introduced by the reference frequency signal in a single-pass transmission process between the transmitting device and the receiving device and a phase disturbance introduced by the probe frequency signal in a round-trip transmission process between the transmitting device and the receiving device can be common-mode cancelled;

[0046] the second optical transmitting unit, configured to modulate the probe frequency signal from the loop locking unit onto a second optical signal to obtain the second modulated optical signal.

[0047] Optionally, the loop locking unit comprises:

[0048] a mixer, configured to mix the reference frequency signal from the second photodetector and the probe frequency signal from the third photodetector to obtain the mixed signal;

[0049] a first radio frequency filter, configured to perform noise suppression on the mixed signal from the mixer; the first radio frequency filter is a low-pass filter;

[0050] a phase detector for phase detecting the mixed signal from the first radio frequency filter with the probe frequency signal to obtain an error signal of the second frequency signal relative to the first frequency signal;

[0051] a loop controller for controlling the output of a voltage controlled crystal oscillator of the loop locking unit by using the error signal, so that the second frequency signal output by the voltage controlled crystal oscillator is frequency synchronized with the first frequency signal and the phase difference is kept constant;

[0052] a voltage controlled crystal oscillator for generating the second frequency signal;

[0053] a first dielectrically locked oscillator for performing second frequency multiplication on the second frequency signal to obtain the probe frequency signal.

[0054] The application further provides a frequency transmission method, comprising:

[0055] The receiving device generates a probe frequency signal, modulates the probe frequency signal onto a second optical signal to obtain a second modulated optical signal, and outputs the second modulated optical signal to an optical fiber link of the receiving device, wherein the optical fiber link is provided with at least one relay amplification filter device; the probe frequency signal is a frequency signal obtained by performing second frequency multiplication on a second frequency signal output by a voltage controlled crystal oscillator of the receiving device.

[0056] Each relay amplification filter device in the optical fiber link sequentially performs a preset signal conditioning operation on the second modulated optical signal and then outputs the second modulated optical signal to the transmitting device; the preset signal conditioning operation comprises optical power amplification operation, noise suppression operation and non-ideal scattering suppression operation.

[0057] The transmitting device demodulates the second modulated optical signal to obtain the probe frequency signal, modulates the probe frequency signal onto a third optical signal to obtain a third modulated optical signal, and then couples the first modulated optical signal and the third modulated optical signal to output the obtained coupled optical signal to the optical fiber link; the first modulated optical signal is a modulated optical signal obtained by modulating a reference frequency signal generated by the transmitting device onto a first optical signal, and the reference frequency signal is a frequency signal obtained by performing first frequency multiplication on a first frequency signal generated by a reference frequency source.

[0058] Each relay amplification filter device in the optical fiber link sequentially performs the preset signal conditioning operation on the coupled optical signal and then outputs the coupled optical signal to the receiving device.

[0059] The receiving device controls the output of a voltage-controlled crystal oscillator of the receiving device based on the coupled optical signal, so that a second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and a phase difference remains constant.

[0060] The present application has the following beneficial effects:

[0061] A frequency transmission system, by setting a first optical filter unit and a second optical filter unit in a relay amplification filtering device, a receiving device modulates a probe frequency signal generated by the receiving device to a second optical signal to obtain a second modulated optical signal, a transmitting device modulates a reference frequency signal generated by the transmitting device to a first optical signal to obtain a first modulated optical signal, and modulates a probe frequency signal obtained by demodulation to a third optical signal to obtain a third modulated optical signal, wherein the carrier wavelengths of the first modulated optical signal, the second modulated optical signal and the third modulated optical signal are different, so that when the second modulated optical signal from the receiving device passes through the relay amplification filtering device, noise (including ASE noise generated by the relay amplification filtering device when amplifying the optical power of the transmission signal) suppression of the second modulated optical signal can be realized by controlling the transmission of the second modulated optical signal to the first optical filter unit, and non-ideal scattering suppression of the second modulated optical signal can be realized by controlling the transmission of the non-ideal scattered light signal of the second modulated optical signal to the second optical filter unit. The same applies when the coupled optical signals corresponding to the first modulated optical signal and the third modulated optical signal are transported to the relay amplification filtering device. Therefore, the present application can realize non-ideal scattering suppression of the transmission signal, and suppress the ASE noise generated by the relay amplification filtering device when amplifying the optical power of the transmission signal, thereby improving the signal-to-noise ratio of the transmission signal, and further enabling the present application to effectively establish long-distance frequency transmission from one transmitting device to multiple receiving devices. BRIEF DESCRIPTION OF DRAWINGS

[0062] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor based on the provided drawings.

[0063] Figure 1 is a structural schematic diagram of a frequency transmission system provided by an embodiment of the present application;

[0064] Figure 2 is a structural schematic diagram of a transmitting device provided by an embodiment of the present application;

[0065] Figure 3is a structural schematic diagram of a relay amplification filtering device provided by an embodiment of the present application;

[0066] Figure 4 is a structural schematic diagram of a second optical filtering unit provided by an embodiment of the present application;

[0067] Figure 5 is a structural schematic diagram of an optical power amplification unit provided by an embodiment of the present application;

[0068] Figure 6 is a structural schematic diagram of another optical power amplification unit provided by an embodiment of the present application;

[0069] Figure 7 is a structural schematic diagram of a receiving device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0070] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work, fall within the protection scope of the present application.

[0071] Radio over fiber refers to modulating a radio frequency signal onto an optical signal by a transmitting device, and then transmitting the optical signal to a receiving device through an optical fiber link. Frequency synchronization based on radio over fiber refers to that the receiving device can reproduce a frequency signal generated by a reference frequency source of the transmitting device, that is, the frequency signal output by a frequency source generation device of the receiving device is frequency-synchronized with the frequency signal generated by the reference frequency source, and the phase difference remains constant. When the receiving device uses a phase-locked loop to realize frequency synchronization, the signal-to-noise ratio of the input signal of the phase-locked loop needs to meet certain requirements. If the signal-to-noise ratio of the input signal of the phase-locked loop is lower than the required signal-to-noise ratio threshold, the locking error of the phase-locked loop will often increase, the deviation between the frequency of the output signal of the phase-locked loop and the expected frequency will be large, and even the phase-locked loop will lose lock, and the frequency transmission will be interrupted.

[0072] In a case that one transmitting device needs to perform optical carrier frequency-based frequency synchronization with multiple receiving devices which are far away from the transmitting device, due to the long distance of signal transmission, there is a large fiber loss and non-ideal scattering in the transmission signal, wherein the fiber loss can be compensated by optical power amplification through an EDFA (Erbium-Doped Fiber Amplifier) in time, but the ASE noise (Amplifier Spontaneousemission Noise) of the EDFA will deteriorate the signal-to-noise ratio of the transmission signal, and the non-ideal scattering will also deteriorate the signal-to-noise ratio of the transmission signal. It should be noted that in the field of long-distance frequency transmission, the main non-ideal scattering considered is backscattering Rayleigh scattering, especially first-order Rayleigh scattering and second-order Rayleigh scattering.

[0073] Therefore, in order to improve the signal-to-noise ratio of the transmission signal and effectively establish long-distance frequency transmission from one transmitting device to multiple receiving devices, the present application provides a frequency transmission system and method. The technical solutions of the present application will be described in detail below with reference to the accompanying drawings.

[0074] Figure 1 is a structural schematic diagram of a frequency transmission system provided by an embodiment of the present application. As shown in Figure 1 the frequency transmission system comprises a transmitting device 11, at least one receiving device 12 and at least one relay amplification and filtering device 13. Figure 1 N represents the number of receiving devices 12, and N is a positive integer greater than or equal to 1.

[0075] Each receiving device 12 is connected to the transmitting device 11 through a corresponding optical fiber link, and at least one relay amplification and filtering device 13 is arranged on the optical fiber link. Figure 1 M1, M2,..., and M N respectively represent the number of relay amplification and filtering devices 13 on the optical fiber link of each receiving device 12, and the number of relay amplification and filtering devices 13 on different optical fiber links can be the same or different. A person skilled in the art can reasonably determine the number of relay amplification and filtering devices 13 on the optical fiber link according to the length of the optical fiber link.

[0076] The transmitting device 11 is configured to generate a reference frequency signal, modulate the reference frequency signal onto a first optical signal to obtain a first modulated optical signal, demodulate a second modulated optical signal carrying a probe frequency signal to obtain the probe frequency signal when receiving the second modulated optical signal from a target receiving device, modulate the probe frequency signal onto a third optical signal to obtain a third modulated optical signal, and output a coupled optical signal obtained by coupling the first modulated optical signal and the third modulated optical signal to the optical fiber link of the target receiving device. In the present application, the reference frequency signal is a frequency signal obtained by performing first frequency multiplication on a first frequency signal generated by a reference frequency source.

[0077] The relay amplification filtering device 13 is configured to perform optical power amplification on the second modulated optical signal when receiving the second modulated optical signal from the corresponding receiving device, perform noise suppression on the second modulated optical signal by using a first optical filter unit of the relay amplification filtering device, and perform non-ideal scattering suppression on the second modulated optical signal by using a second optical filter unit of the relay amplification filtering device, and perform optical power amplification on the coupled optical signal when receiving the coupled optical signal from the transmitting device, perform noise suppression on the coupled optical signal by using the second optical filter unit, and perform non-ideal scattering suppression on the coupled optical signal by using the first optical filter unit, wherein the carrier wavelengths of the first modulated optical signal, the second modulated optical signal and the third modulated optical signal are different. It should be noted that the noise herein includes ASE noise generated by the relay amplification filtering device when performing optical power amplification on the transmission signals (the first modulated optical signal, the second modulated optical signal and the third modulated optical signal).

[0078] The receiving device 12 is configured to generate a probe frequency signal, modulate the probe frequency signal onto a second optical signal to obtain a second modulated optical signal, output the second modulated optical signal to the optical fiber link of the receiving device, and control the output of a voltage-controlled crystal oscillator of the receiving device based on the coupled optical signal when receiving the coupled optical signal from the transmitting device, so that the second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and the phase difference remains constant. In the present application, the probe frequency signal is a frequency signal obtained by performing second frequency multiplication on the second frequency signal.

[0079] In actual application, the transmitting device 11 can simultaneously receive probe frequency signals from different receiving devices 12 and simultaneously establish effective long-distance radio frequency signal frequency transmission with the different receiving devices 12.

[0080] The components of the frequency transmission system of the present application will be described in further detail below.

[0081] Figure 2 is a structural schematic diagram of a transmitting device provided by an embodiment of the present application. As shown in Figure 2As shown, the transmitting device 11 comprises a signal generating module 21, an optical coupler 22 and at least one signal processing module 23.

[0082] The output of the signal generating module 21 is connected to the first port of each signal processing module 23 through the optical coupler 22, and the second port of each signal processing module 23 is connected to the receiving device 12 through a corresponding optical fiber link.

[0083] The signal generating module 21 is configured to generate a reference frequency signal, and modulate the reference frequency signal onto a first optical signal to obtain a first modulated optical signal.

[0084] Specifically, the signal generating module 21 can comprise a second dielectrically locked phase oscillator, a first laser and a first modulator. The second dielectrically locked phase oscillator is configured to perform first frequency multiplication on a first frequency signal generated by a reference frequency source to obtain the reference frequency signal. The first laser is configured to generate the first optical signal, and the first modulator is configured to modulate the reference frequency signal from the second dielectrically locked phase oscillator onto the first optical signal generated by the first laser to obtain the first modulated optical signal. The first modulator can be integrated inside the first laser, or the first modulator can be independent of the first laser.

[0085] The optical coupler 22 is configured to split the first modulated optical signal and simultaneously provide the first modulated optical signal to each signal processing module 23.

[0086] The signal processing module 23 is configured to, when receiving a second modulated optical signal carrying a probe frequency signal from the corresponding receiving device 12, demodulate the second modulated optical signal to obtain the probe frequency signal, modulate the probe frequency signal onto a third optical signal to obtain a third modulated optical signal, and output the coupled optical signal obtained by coupling the first modulated optical signal and the third modulated optical signal to the optical fiber link of the corresponding receiving device 12.

[0087] Specifically, the signal processing module 23 can comprise:

[0088] The optical signal conditioning unit 201 is configured to, when receiving the second modulated optical signal, perform noise suppression and optical power amplification on the second modulated optical signal. Specifically, the optical signal conditioning unit 201 can comprise a seventh optical filter and a fourth optical power amplifier. When receiving the second modulated optical signal, the optical signal conditioning unit 201 uses the seventh optical filter to perform noise suppression on the second modulated optical signal, and uses the fourth optical power amplifier to perform optical power amplification on the second modulated optical signal.

[0089] The first photodetector 202 is configured to demodulate the second modulated optical signal output by the optical signal conditioning unit 201 to obtain the probe frequency signal.

[0090] The radio frequency signal conditioning unit 203 is configured to perform noise suppression and power amplification on the probe frequency signal. Specifically, the radio frequency signal conditioning unit 203 can include a second radio frequency filter and a radio frequency low noise power amplifier. The second radio frequency filter is configured to perform noise suppression on the probe frequency signal, and the radio frequency low noise power amplifier is configured to perform power amplification on the probe frequency signal.

[0091] The first optical transmitting unit 204 is configured to modulate the probe frequency signal output by the radio frequency signal conditioning unit onto a third optical signal to obtain a third modulated optical signal. Specifically, the first optical transmitting unit 204 can include a second laser and a second modulator. The second laser is configured to generate the third optical signal, and the second modulator is configured to modulate the probe frequency signal output by the radio frequency signal conditioning unit onto the third optical signal to obtain the third modulated optical signal. The second modulator can be integrated inside the second laser, or the second modulator can be independent of the second laser.

[0092] The first wavelength division multiplexer 205 is configured to couple the first modulated optical signal from the optical fiber coupler with the third modulated optical signal from the first optical transmitting unit to obtain a coupled optical signal.

[0093] The first circulator 206 is configured to output the coupled optical signal from the first wavelength division multiplexer to an optical fiber link of a corresponding receiving device, and send a second modulated optical signal from the optical fiber link to the optical signal conditioning unit. It should be noted that each circulator in the present application is configured to realize bidirectional optical signal transmission on a single optical fiber, and the signal transmission direction of the circulator is irreversible, i.e., the optical signal can only be guided from one port to another port of the circulator in one direction at a time.

[0094] Figure 3 is a structural schematic diagram of a relay amplification filtering device provided by an embodiment of the present application. As shown in Figure 3 The relay amplification filtering device 13 includes a second circulator 31, a first optical filtering unit 32, a second optical filtering unit 33, an optical power amplification unit 34, and a third circulator 35.

[0095] The first optical filter unit 32 comprises a third optical filter 321 and a sixth optical filter 322. The input end of the third optical filter 321 is connected to the first side of the optical power amplification unit 34, and the output end of the third optical filter 321 is connected to the first port of the second circulator 31. The input end of the sixth optical filter 322 is connected to the third port of the third circulator 35, and the output end of the sixth optical filter 322 is connected to the second side of the optical power amplification unit 34. It should be noted that the center wavelengths of the third optical filter 321 and the sixth optical filter 322 are the same as the carrier wavelength of the second modulated optical signal, so that the third optical filter 321 and the sixth optical filter 322 can pass the second modulated optical signal and filter out optical signals of other wavelengths.

[0096] The second optical filter unit 33 comprises a first optical filter subunit 331 and a second optical filter subunit 332. The input end of the first optical filter subunit 331 is connected to the third port of the second circulator 31, and the output end of the first optical filter subunit 331 is connected to the first side of the optical power amplification unit 34. The input end of the second optical filter subunit 332 is connected to the second side of the optical power amplification unit 34, and the output end of the second optical filter subunit 332 is connected to the first port of the third circulator 35. It should be noted that the first optical filter subunit 331 and the second optical filter subunit 332 can pass the first modulated optical signal and the third modulated optical signal and filter out optical signals of other wavelengths.

[0097] The second circulator 31 is used to transmit the optical signal from the second port thereof to the third port thereof and transmit the optical signal from the first port thereof to the second port thereof. The second port of the second circulator 31 is connected to the transmitting device or the third circulator of the relay amplification and filtering device adjacent to the second circulator.

[0098] The third circulator 35 is used to transmit the optical signal from the first port thereof to the second port thereof and transmit the optical signal from the second port thereof to the third port thereof. The second port of the third circulator 35 is connected to the receiving device or the second circulator of the relay amplification and filtering device adjacent to the third circulator.

[0099] In actual application, when the third circulator 35 receives the second modulated optical signal from the receiving device, the third circulator 35 outputs the second modulated optical signal to the sixth optical filter 322, the sixth optical filter 322 performs noise suppression on the second modulated optical signal and then outputs the second modulated optical signal to the optical power amplification unit 34, the optical power amplification unit 34 performs optical power amplification compensation on the second modulated optical signal and then outputs the second modulated optical signal to the third optical filter 321, the third optical filter 321 performs ASE noise suppression on the second modulated optical signal and then outputs the second modulated optical signal to the second circulator 31, and the process realizes power amplification and noise suppression on the second modulated optical signal. The second circulator 31 outputs the second modulated optical signal to the next relay amplification filtering device or the transmitting device, and meanwhile, the second circulator 31 outputs the non-ideal scattered optical signal of the second modulated optical signal to the first optical filtering subunit 331. Since the first optical filtering subunit 331 filters out optical signals of other wavelengths except the carrier wavelength of the first modulated optical signal and the third modulated optical signal, the carrier wavelengths of the first modulated optical signal, the second modulated optical signal and the third modulated optical signal are different, and the wavelength of the non-ideal scattered optical signal of the second modulated optical signal is equal to the carrier wavelength of the second modulated optical signal, which makes the non-ideal scattered optical signal of the second modulated optical signal unable to pass through the first optical filtering subunit 331, and therefore, the first optical filtering subunit 331 can realize non-ideal scattering suppression on the second modulated optical signal.

[0100] It should be noted that when the second port of the third circulator 35 is directly connected to the receiving device, the third circulator 35 directly receives the second modulated optical signal from the receiving device, and when the second port of the third circulator 35 is indirectly connected to the receiving device through other relay amplification filtering devices, the third circulator 35 indirectly receives the second modulated optical signal from the receiving device through the other relay amplification filtering devices. The structure and working principle of each relay amplification filtering device are the same.

[0101] Similarly, when the second circulator 31 receives the coupled light signal from the transmitting device, the second circulator 31 outputs the coupled light signal to the first optical filtering subunit 331, the first optical filtering subunit 331 performs noise suppression on the coupled light signal, and then outputs the coupled light signal to the optical power amplification unit 34, the optical power amplification unit 34 performs optical power amplification compensation on the coupled light signal, and then outputs the coupled light signal to the second optical filtering subunit 332, the second optical filtering subunit 332 performs ASE noise suppression on the coupled light signal again, and then outputs the coupled light signal to the third circulator 35, the third circulator 35 outputs the coupled light signal to the next relay amplification filtering device or the receiving device, and at the same time, the third circulator 35 outputs the non-ideal scattered light signal of the coupled light signal to the sixth optical filter 322. Since the center wavelengths of the sixth optical filter 322 are all the same as the carrier wavelength of the second modulated light signal, the carrier wavelengths of the first modulated light signal, the second modulated light signal and the third modulated light signal are different, the coupled light signal is composed of the first modulated light signal and the third modulated light signal, the wavelength of the non-ideal scattered light signal of the first modulated light signal is equal to the carrier wavelength of the first modulated light signal, and the wavelength of the non-ideal scattered light signal of the third modulated light signal is the same, the non-ideal scattered light signal of the coupled light signal cannot pass through the sixth optical filter 322, and thus the non-ideal scattering suppression on the coupled light signal is realized.

[0102] It should be noted that in the above non-ideal scattering suppression process, the first-order Rayleigh scattering in the non-ideal scattering is mainly suppressed, so as to avoid useless signal from stealing the gain of the related optical power amplifier and improve the signal-to-noise ratio of the transmission signal. At the same time, by suppressing the first-order Rayleigh scattering, the formation process of the corresponding second-order Rayleigh scattering is destroyed, and thus the effect of suppressing the second-order Rayleigh scattering is achieved.

[0103] Figure 4 is a structural schematic diagram of a second optical filtering unit provided by an embodiment of the present application. As shown in Figure 4 In the second optical filtering unit 33, the first optical filtering subunit 331 includes a second wavelength division multiplexer 3311, a third wavelength division multiplexer 3314, a first optical filter 3312 and a second optical filter 3313, and the second optical filtering subunit 332 includes a fourth wavelength division multiplexer 3321, a fifth wavelength division multiplexer 3324, a fourth optical filter 3322 and a fifth optical filter 3323.

[0104] The input end of the second wavelength division multiplexer 3311 is connected to the third port of the second circulator 31, the two output ends of the second wavelength division multiplexer 3311 are respectively connected to the input ends of the first optical filter 3312 and the second optical filter 3313, the output ends of the first optical filter 3312 and the second optical filter 3313 are respectively connected to the two input ends of the third wavelength division multiplexer 3314, the output end of the third wavelength division multiplexer 3314 is connected to the first side of the optical power amplification unit 34, the input end of the fourth wavelength division multiplexer 3321 is connected to the second side of the optical power amplification unit 34, the two output ends of the fourth wavelength division multiplexer 3321 are respectively connected to the input ends of the fourth optical filter 3322 and the fifth optical filter 3323, the output ends of the fourth optical filter 3322 and the fifth optical filter 3323 are respectively connected to the two input ends of the fifth wavelength division multiplexer 3324, and the output end of the fifth wavelength division multiplexer 3324 is connected to the first port of the third circulator 35.

[0105] Here, the center wavelengths of the first optical filter 3312 and the fourth optical filter 3322 are the same as the carrier wavelength of the first modulated optical signal, so that the first optical filter 3312 and the fourth optical filter 3322 can pass the first modulated optical signal and filter out optical signals of other wavelengths, and the center wavelengths of the second optical filter 3313 and the fifth optical filter 3323 are the same as the carrier wavelength of the third modulated optical signal, so that the second optical filter 3313 and the fifth optical filter 3323 can pass the third modulated optical signal and filter out optical signals of other wavelengths. Based on this, when the second circulator 31 outputs the non-ideal scattered optical signal of the second modulated optical signal to the first optical filtering subunit 331, if the non-ideal scattered optical signal passes through the second wavelength division multiplexer 3311, since only the optical signal with the wavelength equal to the carrier wavelength of the first modulated optical signal can pass through the first optical filter 3312, and the wavelength of the non-ideal scattered optical signal of the second modulated optical signal is different from the carrier wavelength of the first modulated optical signal, the non-ideal scattered optical signal cannot pass through the first optical filter 3312, and for the same reason, the non-ideal scattered optical signal also cannot pass through the second optical filter 3313. Therefore, the first optical filtering subunit 331 can realize non-ideal scattering suppression of the second modulated optical signal. Furthermore, when the second circulator 31 outputs the coupled optical signal from the transmitting device to the first optical filtering subunit 331, the second wavelength division multiplexer 3311 performs channel separation on the coupled optical signal to obtain the first modulated optical signal and the third modulated optical signal, the first optical filter 3312 and the second optical filter 3313 perform noise suppression on the first modulated optical signal and the third modulated optical signal respectively and then output to the third wavelength division multiplexer 3314, the third wavelength division multiplexer 3314 performs channel coupling on the first modulated optical signal and the third modulated optical signal to obtain the coupled optical signal, and the processing principle of the coupled optical signal in the second optical filtering subunit 332 is the same, which will not be described here.

[0106] In addition, considering that the wavelength division multiplexer itself has a filtering function, therefore, for the first optical filter subunit 331 and / or the second optical filter subunit 332, a suitable wavelength division multiplexer can be selected to realize the omission of the internal optical filter.

[0107] Based on this, in another second optical filter implementation, the first optical filter subunit includes a seventh wavelength division multiplexer and an eighth wavelength division multiplexer, and the second optical filter subunit includes a ninth wavelength division multiplexer and a tenth wavelength division multiplexer.

[0108] The input end of the seventh wavelength division multiplexer is connected to the third port of the second circulator 31, the output end of the seventh wavelength division multiplexer is connected to the input end of the eighth wavelength division multiplexer, the output end of the eighth wavelength division multiplexer is connected to the first side of the optical power amplification unit 34, the input end of the ninth wavelength division multiplexer is connected to the second side of the optical power amplification unit 34, the output end of the ninth wavelength division multiplexer is connected to the input end of the tenth wavelength division multiplexer, and the output end of the tenth wavelength division multiplexer is connected to the first port of the third circulator 35.

[0109] Here, the seventh wavelength division multiplexer can replace the first optical filter 3312 described above to filter out the non-ideal scattered light signal of the second modulated light signal in the first modulated light signal, and the seventh wavelength division multiplexer can also replace the second optical filter 3313 to filter out the non-ideal scattered light signal of the second modulated light signal in the third modulated light signal.

[0110] Similarly, the ninth wavelength division multiplexer can replace the fourth optical filter 3322 to realize ASE noise suppression of the first modulated light signal, and replace the fifth optical filter 3323 to realize ASE noise suppression of the third modulated light signal.

[0111] It should be noted that when the bandwidth of one channel of the wavelength division multiplexer is less than or equal to the bandwidth of a certain optical filter, the wavelength division multiplexer can realize the filtering function of the optical filter through the channel, for example, when the bandwidth of the channel of the second wavelength division multiplexer 3311 connected to the first optical filter 3312 is less than or equal to the bandwidth of the first optical filter 3312, the second wavelength division multiplexer 3311 can realize filtering out the non-ideal scattered light signal of the second modulated light signal in the first modulated light signal through the channel, and when the bandwidth of the channel of the fourth wavelength division multiplexer 3321 connected to the fourth optical filter 3322 is less than or equal to the bandwidth of the fourth optical filter 3322, the fourth wavelength division multiplexer 3321 can realize ASE noise suppression of the first modulated light signal through the channel.

[0112] Figure 5 is a structural schematic diagram of an optical power amplification unit provided by an embodiment of the present application. As shown in the figure, the optical power amplification unit includes a first circulator 31, a second circulator 35, an optical power amplification unit 34, a first optical filter subunit 331, and a second optical filter subunit 332.Figure 5 As shown in the figure, the optical power amplification unit 34 comprises a fourth circulator 341, a bidirectional optical power amplifier 342 and a fifth circulator 343.

[0113] The first port of the fourth circulator 341 is connected to the output end of the first optical filtering subunit 331, the second port of the fourth circulator 341 is connected to the first end of the bidirectional optical power amplifier 342, and the third port of the fourth circulator 341 is connected to the input end of the third optical filter 321.

[0114] The third port of the fifth circulator 343 is connected to the input end of the second optical filtering subunit 332, the first port of the fifth circulator 343 is connected to the output end of the sixth optical filter 322, and the second port of the fifth circulator 343 is connected to the second end of the bidirectional optical power amplifier 342.

[0115] In actual application, when the fifth circulator 343 receives the second modulated optical signal from the sixth optical filter 322, it outputs the second modulated optical signal to the bidirectional optical power amplifier 342, and outputs the non-ideal scattered light signal of the second modulated optical signal to the second optical filtering subunit 332, which will suppress the non-ideal scattered light signal of the second modulated optical signal. After the bidirectional optical power amplifier 342 performs optical power amplification compensation on the second modulated optical signal, it is output to the fourth circulator 341, which outputs the second modulated optical signal from the bidirectional optical power amplifier 342 to the third optical filter 321. When the fourth circulator 341 receives the coupled light signal from the third wavelength division multiplexer 3314, the same applies here and will not be repeated here.

[0116] Figure 6 is another structure diagram of an optical power amplification unit provided by an embodiment of the present application. As shown in the figure, Figure 6 The optical power amplification unit 34 comprises a first optical power amplifier 344 and a second optical power amplifier 345.

[0117] The input end of the first optical power amplifier 344 is connected to the output end of the first optical filtering subunit 331, and the output end of the first optical power amplifier 344 is connected to the input end of the second optical filtering subunit 332.

[0118] The input end of the second optical power amplifier 345 is connected to the output end of the sixth optical filter 322, and the output end of the second optical power amplifier 345 is connected to the input end of the third optical filter 321.

[0119] In actual application, the first optical power amplifier 344, after receiving the coupled optical signal from the first optical filter subunit 331, performs optical power amplification compensation on the coupled optical signal and outputs to the second optical filter subunit 332. The second optical power amplifier 345, after receiving the second modulated optical signal from the sixth optical filter 322, performs the same operation, which will not be described herein.

[0120] Figure 7 is a structural schematic diagram of a receiving device provided by an embodiment of the present application. As shown in Figure 7 the receiving device can specifically include a sixth circulator 71, a third optical power amplifier 72, a sixth wavelength division multiplexer 73, a second photodetector 74, a third photodetector 75, a loop lock unit 76, and a second optical transmitting unit 77.

[0121] The sixth circulator 71 is configured to transmit the coupled optical signal from the transmitting device to the third optical power amplifier 72 and transmit the second modulated optical signal from the second optical transmitting unit 77 to the optical fiber link of the receiving device.

[0122] The third optical power amplifier 72 is configured to perform optical power amplification on the coupled optical signal.

[0123] The sixth wavelength division multiplexer 73 is configured to perform channel separation on the coupled optical signal from the third optical power amplifier 72 to obtain a first modulated optical signal and a third modulated optical signal.

[0124] The second photodetector 74 is configured to demodulate the first modulated optical signal from the sixth wavelength division multiplexer 73 to obtain a reference frequency signal.

[0125] The third photodetector 75 is configured to demodulate the third modulated optical signal from the sixth wavelength division multiplexer 73 to obtain a detection frequency signal. The present application can further be provided with a radio frequency filter at the output end of the second photodetector 74 and the third photodetector 75 respectively, to filter the reference frequency signal output by the second photodetector 74 and the detection frequency signal output by the third photodetector 75, so as to realize noise suppression on the two radio frequency signals.

[0126] The loop locking unit 76 is configured to generate a probe frequency signal, and mix the reference frequency signal from the second photodetector 74 and the probe frequency signal from the third photodetector 75, and phase demodulate the mixed signal with the probe frequency signal to obtain an error signal of the second frequency signal relative to the first frequency signal, and control the output of the voltage-controlled crystal oscillator of the loop locking unit 76 by using the error signal, so that the second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and the phase difference is kept constant; wherein the signal frequency of the reference frequency signal is twice the signal frequency of the probe frequency signal, so that the phase disturbance introduced by the reference frequency signal in the single-pass transmission between the transmitting device and the receiving device and the phase disturbance introduced by the probe frequency signal in the round-trip transmission between the transmitting device and the receiving device can be common-mode cancelled.

[0127] The second light emitting unit 77 is configured to modulate the probe frequency signal from the loop locking unit 76 onto the second optical signal to obtain a second modulated optical signal. Specifically, the second light emitting unit 77 can include a third laser and a third modulator. The third laser is configured to generate the second optical signal, and the third modulator is configured to modulate the probe frequency signal from the loop locking unit 76 onto the second optical signal to obtain the second modulated optical signal. The third modulator can be integrated inside the third laser, or can be independent of the third laser.

[0128] In the embodiment of the present application, the loop locking unit 76 can specifically include:

[0129] The mixer 761 is configured to mix the reference frequency signal from the second photodetector and the probe frequency signal from the third photodetector to obtain a mixed signal.

[0130] In the optical signal transmission process, due to the changes of temperature and stress and other factors in the laying environment of the optical fiber link, the optical path experienced by the optical signal changes, causing the phase of the transmitted optical signal to fluctuate, i.e., introducing phase disturbance in the optical signal. As known from the foregoing, the probe frequency signal is transmitted from the receiving device to the transmitting device and then transmitted back to the receiving device, while the reference frequency signal is transmitted from the transmitting device to the receiving device, i.e., in the entire signal transmission process, the optical path experienced by the probe frequency signal is twice the optical path experienced by the reference frequency signal, and since the signal frequency of the reference frequency signal is twice the signal frequency of the probe frequency signal, the phase disturbance introduced in the probe frequency signal and the phase disturbance introduced in the reference frequency signal are equal in the entire signal transmission process, so that when the reference frequency signal and the probe frequency signal are mixed, the phase disturbances introduced in the two frequency signals can be common-mode cancelled.

[0131] The first radio frequency filter 762 is used for noise suppression of the mixed signal from the mixer. Here, the first radio frequency filter 762 can be a band-pass filter.

[0132] In addition, a radio frequency filter can be additionally arranged between the second photodetector 74 and the mixer 761, and used for radio frequency filtering of the reference frequency signal output by the second photodetector 74. A radio frequency filter can also be additionally arranged between the third photodetector 75 and the mixer 761, and used for radio frequency filtering of the detection frequency signal output by the third photodetector 75.

[0133] The phase detector 763 is used for phase detection of the mixed signal from the first radio frequency filter 762 and the detection frequency signal, and obtaining an error signal of the second frequency signal relative to the first frequency signal.

[0134] The loop controller 764 is used for generating a control signal by using the error signal, and sending the control signal to the voltage-controlled crystal oscillator 765. The control signal is used for adjusting the frequency and phase of the second frequency signal output by the voltage-controlled crystal oscillator 765, so that the second frequency signal output by the voltage-controlled crystal oscillator 765 can be frequency-synchronized with the first frequency signal, and the phase difference remains constant.

[0135] The voltage-controlled crystal oscillator 765 is used for generating the second frequency signal.

[0136] The first dielectric resonator oscillator 766 is used for second frequency multiplication processing of the second frequency signal, and obtaining the detection frequency signal.

[0137] In the present application, the frequency of the reference frequency signal is twice the frequency of the detection frequency signal by the first dielectric resonator oscillator for first frequency multiplication processing of the first frequency signal, and the first dielectric resonator oscillator for second frequency multiplication processing of the second frequency signal. In a specific example, the frequency of the first frequency signal generated by the reference frequency source of the transmitting device can be 100MHz, the frequency of the reference frequency signal obtained by the first dielectric resonator oscillator after first frequency multiplication processing of the first frequency signal is 2GHz, and the frequency of the detection frequency signal obtained by the first dielectric resonator oscillator 766 after second frequency multiplication processing of the second frequency signal is 1GHz.

[0138] In summary, the application adopts the technical scheme, and the optical path experienced by the probe frequency signal in the whole signal transmission process is twice that of the reference frequency signal, and the signal frequency of the reference frequency signal is twice that of the probe frequency signal, so that the phase disturbance introduced in the probe frequency signal is equal to that introduced in the reference frequency signal in the whole signal transmission process, and then the phase disturbances introduced in the two radio frequency signals can be common-mode canceled when the reference frequency signal and the probe frequency signal are mixed. The application uses a phase-locked loop, has stronger compensation capability and compensation bandwidth. It should be noted that the phase-locked loop includes a phase discriminator 763, a loop controller 764 and a voltage-controlled crystal oscillator 765.

[0139] And the probe frequency signal generated by the receiving device is modulated onto the second optical signal, the reference frequency signal generated by the transmitting device is modulated onto the first optical signal, and the probe frequency signal obtained by demodulation is modulated onto the third optical signal, and the wavelengths of the first optical signal, the second optical signal and the third optical signal are different, so that the relay amplification filter device proposed in the application can suppress the non-ideal scattering of the corresponding transmission signal, and the relay amplification filter device can also suppress the ASE noise of the optical power amplifier, which enables the application to ensure the signal-to-noise ratio of the transmission signal by reasonably arranging multiple relay amplification filter devices between the transmitting device and any receiving device, so that the application can realize effective long-distance frequency transmission.

[0140] And the application sets a fiber coupler and at least one signal processing module in the transmitting device, so that the transmitting device can simultaneously establish stable phase transmission of radio frequency signals with at least one receiving device, and since the stable phase transmission of radio frequency signals between each receiving device and the transmitting device is independent, the frequency transmission system of the application is not limited by space, can realize a star-shaped topology, and has high signal transmission efficiency. In addition, since multiple receiving devices can share one transmitting device, the application can also reduce hardware costs.

[0141] Based on a general inventive concept, the application also provides a frequency transmission method implemented by the above-mentioned frequency transmission system.

[0142] The frequency transmission method of the application comprises:

[0143] The receiving device 12 generates a probe frequency signal, modulates the probe frequency signal onto a second optical signal to obtain a second modulated optical signal, and outputs the second modulated optical signal to the optical fiber link of the receiving device, and at least one relay amplification filter device 13 is arranged in the optical fiber link. The probe frequency signal is a frequency signal obtained by performing second frequency doubling on a second frequency signal output by a voltage-controlled crystal oscillator of the receiving device.

[0144] The relay amplification filter devices 13 in the optical fiber link perform preset signal conditioning operations on the second modulated optical signal in turn, and output the second modulated optical signal to the transmitting device 11; the preset signal conditioning operations include optical power amplification operation, noise suppression operation and non-ideal scattering suppression operation.

[0145] The transmitting device 11 demodulates the second modulated optical signal to obtain a probe frequency signal, modulates the probe frequency signal to a third optical signal to obtain a third modulated optical signal, and outputs the obtained coupled optical signal to the optical fiber link after coupling the first modulated optical signal and the third modulated optical signal; wherein the first modulated optical signal is a modulated light obtained by modulating a reference frequency signal generated by the transmitting device to a first optical signal, and the reference frequency signal is a frequency signal obtained by performing first frequency multiplication on a first frequency signal generated by a reference frequency source.

[0146] The relay amplification filter devices 13 in the optical fiber link perform preset signal conditioning operations on the coupled optical signal in turn, and output the coupled optical signal to the receiving device.

[0147] The receiving device 12 controls the output of the voltage-controlled crystal oscillator of the receiving device based on the coupled optical signal, so that the second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and the phase difference is kept constant.

[0148] It should be noted that the specific execution process and beneficial effects of the embodiments of the present application are described in the foregoing embodiments, and will not be described here.

[0149] For the foregoing method embodiments, in order to simply describe, they are all expressed as a series of action combinations, but those skilled in the art should know that the present application is not limited to the action sequence described, because according to the present application, certain steps can be performed in other sequences or at the same time. Secondly, those skilled in the art should know that the embodiments described in the specification all belong to preferred embodiments, and the actions and modules involved are not necessarily necessary for the present application.

[0150] It should be noted that each embodiment in the specification is described in a progressive manner, and each embodiment mainly describes the difference from other embodiments, and the same and similar parts between the embodiments can be referred to each other.

[0151] The steps in the method of each embodiment of the present application can be adjusted, combined and reduced in sequence according to actual needs, and the technical features described in each embodiment can be replaced or combined.

[0152] Finally, it should be noted that, in this document, the term "only" is used simply to set off from another element, and not to necessarily require or imply that only that element is present. Also, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0153] The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A frequency transmission system, characterized by, The application relates to a transmission device, a plurality of receiving devices and a plurality of relay amplification filtering devices. Each receiving device is connected to the transmission device through a corresponding optical fiber link, and at least one relay amplification filtering device is arranged on the optical fiber link. The transmission device is used for generating a reference frequency signal, modulating the reference frequency signal onto a first optical signal to obtain a first modulated optical signal, demodulating a second modulated optical signal carrying a probe frequency signal to obtain the probe frequency signal when the second modulated optical signal is received from a target receiving device, modulating the probe frequency signal onto a third optical signal to obtain a third modulated optical signal, coupling the first modulated optical signal and the third modulated optical signal, and outputting the obtained coupled optical signal to the optical fiber link of the target receiving device; wherein the reference frequency signal is a frequency signal obtained by first frequency multiplication of a first frequency signal generated by a reference frequency source. The relay amplification filtering device is used for performing optical power amplification on the second modulated optical signal when the second modulated optical signal is received from the corresponding receiving device, performing noise suppression on the second modulated optical signal by using a first optical filter unit of the relay amplification filtering device, performing non-ideal scattering suppression on the second modulated optical signal by using a second optical filter unit of the relay amplification filtering device, performing optical power amplification on the coupled optical signal when the coupled optical signal is received from the transmission device, performing noise suppression on the coupled optical signal by using the second optical filter unit, and performing non-ideal scattering suppression on the coupled optical signal by using the first optical filter unit; wherein the carrier wavelengths of the first modulated optical signal, the second modulated optical signal and the third modulated optical signal are different. The receiving device is used for generating a probe frequency signal, modulating the probe frequency signal onto a second optical signal to obtain a second modulated optical signal, outputting the second modulated optical signal to the optical fiber link of the receiving device, and controlling the output of a voltage-controlled crystal oscillator of the receiving device based on the coupled optical signal when the coupled optical signal is received from the transmission device, so that a second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and the phase difference remains constant; wherein the probe frequency signal is a frequency signal obtained by second frequency multiplication of the second frequency signal. The transmission device comprises a signal generation module, an optical fiber coupler and at least one signal processing module.

2. The frequency transmission system of claim 1, wherein, The output end of the signal generation module is connected to the first port of each signal processing module through the optical fiber coupler, and the second port of each signal processing module is connected to the receiving device through a corresponding optical fiber link. The signal generation module is used for generating the reference frequency signal and modulating the reference frequency signal onto the first optical signal to obtain the first modulated optical signal. ​ The optical fiber coupler is used for splitting the first modulated optical signal and simultaneously providing the first modulated optical signal for each signal processing module; The signal processing module is used for, when receiving a second modulated optical signal carrying a probe frequency signal from the corresponding receiving device, demodulating the second modulated optical signal to obtain the probe frequency signal, modulating the probe frequency signal onto a third optical signal to obtain a third modulated optical signal, coupling the first modulated optical signal and the third modulated optical signal, and outputting a coupled optical signal obtained by the coupling to an optical fiber link corresponding to the receiving device.

3. The frequency transmission system of claim 2, wherein, The signal processing module comprises: An optical signal conditioning unit is used for, when receiving the second modulated optical signal, performing noise suppression and optical power amplification on the second modulated optical signal; A first photodetector is used for demodulating the second modulated optical signal output by the optical signal conditioning unit to obtain the probe frequency signal; An RF signal conditioning unit is used for performing noise suppression and power amplification on the probe frequency signal; A first optical transmitting unit is used for modulating the probe frequency signal output by the RF signal conditioning unit onto the third optical signal to obtain the third modulated optical signal; A first wavelength division multiplexer is used for coupling the first modulated optical signal from the optical fiber coupler and the third modulated optical signal from the first optical transmitting unit to obtain the coupled optical signal; A first circulator is used for outputting the coupled optical signal from the first wavelength division multiplexer to an optical fiber link corresponding to the receiving device and sending the second modulated optical signal from the optical fiber link to the optical signal conditioning unit.

4. The frequency transmission system of claim 1, wherein, The relay amplification filter device comprises a second circulator, the first optical filter unit, the second optical filter unit, an optical power amplification unit, and a third circulator; The first optical filter unit comprises a third optical filter and a sixth optical filter, an input end of the third optical filter is connected to a first side of the optical power amplification unit, an output end of the third optical filter is connected to a first port of the second circulator, an input end of the sixth optical filter is connected to a third port of the third circulator, and an output end of the sixth optical filter is connected to a second side of the optical power amplification unit; The second optical filter unit comprises a first optical filter subunit and a second optical filter subunit, an input end of the first optical filter subunit is connected to a third port of the second circulator, an output end of the first optical filter subunit is connected to the first side of the optical power amplification unit, an input side of the second optical filter subunit is connected to the second side of the optical power amplification unit, and an output end of the second optical filter subunit is connected to the first port of the third circulator; The second circulator is used for transmitting an optical signal from a second port thereof to a third port thereof and transmitting an optical signal from a first port thereof to the second port thereof, and the second port of the second circulator is connected to the transmitting device or a third circulator of the relay amplification filter device adjacent to the second circulator. The third circulator is configured to transmit an optical signal from a first port thereof to a second port thereof and transmit an optical signal from the second port thereof to a third port thereof, and the second port of the third circulator is connected to the receiving device or a second circulator of the relay amplification and filtering device adjacent to the third circulator.

5. The frequency transmission system of claim 4, wherein, The first optical filtering subunit comprises a second wavelength division multiplexer, a third wavelength division multiplexer, a first optical filter and a second optical filter, and the second optical filtering subunit comprises a fourth wavelength division multiplexer, a fifth wavelength division multiplexer, a fourth optical filter and a fifth optical filter. An input end of the second wavelength division multiplexer is connected to a third port of the second circulator, two output ends of the second wavelength division multiplexer are respectively connected to input ends of the first optical filter and the second optical filter, output ends of the first optical filter and the second optical filter are respectively connected to two input ends of the third wavelength division multiplexer, an output end of the third wavelength division multiplexer is connected to a first side of the optical power amplification unit, an input end of the fourth wavelength division multiplexer is connected to a second side of the optical power amplification unit, two output ends of the fourth wavelength division multiplexer are respectively connected to input ends of the fourth optical filter and the fifth optical filter, output ends of the fourth optical filter and the fifth optical filter are respectively connected to two input ends of the fifth wavelength division multiplexer, and an output end of the fifth wavelength division multiplexer is connected to a first port of the third circulator.

6. The frequency transmission system of claim 4, wherein, The first optical filtering subunit comprises a seventh wavelength division multiplexer and an eighth wavelength division multiplexer, and the second optical filtering subunit comprises a ninth wavelength division multiplexer and a tenth wavelength division multiplexer. An input end of the seventh wavelength division multiplexer is connected to a third port of the second circulator, an output end of the seventh wavelength division multiplexer is connected to an input end of the eighth wavelength division multiplexer, an output end of the eighth wavelength division multiplexer is connected to a first side of the optical power amplification unit, an input end of the ninth wavelength division multiplexer is connected to a second side of the optical power amplification unit, an output end of the ninth wavelength division multiplexer is connected to an input end of the tenth wavelength division multiplexer, and an output end of the tenth wavelength division multiplexer is connected to a first port of the third circulator.

7. The frequency transmission system of claim 4, wherein, The optical power amplification unit comprises a fourth circulator, a bidirectional optical power amplifier and a fifth circulator. A first port of the fourth circulator is connected to an output end of the first optical filtering subunit, a second port of the fourth circulator is connected to a first end of the bidirectional optical power amplifier, and a third port of the fourth circulator is connected to an input end of the third optical filter. A third port of the fifth circulator is connected to an input end of the second optical filtering subunit, a first port of the fifth circulator is connected to an output end of the sixth optical filter, and a second port of the fifth circulator is connected to a second end of the bidirectional optical power amplifier.

8. The frequency transmission system of claim 4, wherein, The optical power amplification unit comprises a first optical power amplifier and a second optical power amplifier. An input end of the first optical power amplifier is connected to an output end of the first optical filtering subunit, and an output end of the first optical power amplifier is connected to an input end of the second optical filtering subunit. An input end of the second optical power amplifier is connected to an output end of the sixth optical filter, and an output end of the second optical power amplifier is connected to an input end of the third optical filter.

9. The frequency transmission system of claim 1, wherein, The receiving device specifically comprises a sixth circulator, a third optical power amplifier, a sixth wavelength division multiplexer, a second photodetector, a third photodetector, a loop lock unit and a second optical transmitting unit. The sixth circulator is configured to transmit the coupled optical signal from the transmitting device to the third optical power amplifier, and transmit a second modulated optical signal from the second optical transmitting unit to an optical fiber link of the receiving device. The third optical power amplifier is configured to perform optical power amplification on the coupled optical signal. The sixth wavelength division multiplexer is configured to perform channel separation on the coupled optical signal from the third optical power amplifier to obtain the first modulated optical signal and the third modulated optical signal. The second photodetector is configured to demodulate the first modulated optical signal from the sixth wavelength division multiplexer to obtain the reference frequency signal. The third photodetector is configured to demodulate the third modulated optical signal from the sixth wavelength division multiplexer to obtain the probe frequency signal. The loop lock unit is configured to generate the probe frequency signal, mix the reference frequency signal from the second photodetector and the probe frequency signal from the third photodetector, phase demodulate the mixed signal and the probe frequency signal to obtain an error signal of the second frequency signal relative to the first frequency signal, and control an output of a voltage-controlled crystal oscillator of the loop lock unit by using the error signal, so that the second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and a phase difference between them is kept constant; wherein a signal frequency of the reference frequency signal is twice a signal frequency of the probe frequency signal, so that a phase disturbance introduced by the reference frequency signal in a single-pass transmission process between the transmitting device and the receiving device and a phase disturbance introduced by the probe frequency signal in a round-trip transmission process between the transmitting device and the receiving device can be common-mode cancelled. The second optical transmitting unit is configured to modulate the probe frequency signal from the loop lock unit onto a second optical signal to obtain the second modulated optical signal.

10. A frequency transmission method, characterized by, A frequency transmission method for establishing a frequency transmission between one transmitting device and multiple receiving devices, the frequency transmission method being applied to the frequency transmission system of any one of claims 1 to 9, and the frequency transmission method comprising: The receiving device generates a probe frequency signal, modulates the probe frequency signal onto a second optical signal to obtain a second modulated optical signal, and outputs the second modulated optical signal to an optical fiber link of the receiving device, wherein the optical fiber link is provided with at least one relay amplification filter device; and wherein the probe frequency signal is a frequency signal obtained by performing second frequency multiplication on a second frequency signal output by a voltage-controlled crystal oscillator of the receiving device. The relay amplification filter devices in the optical fiber link perform preset signal conditioning operations on the second modulated optical signal in turn, and output the second modulated optical signal to the transmitting device; the preset signal conditioning operations include optical power amplification operation, noise suppression operation and non-ideal scattering suppression operation; The transmitting device demodulates the second modulated optical signal to obtain the probe frequency signal, modulates the probe frequency signal to a third optical signal to obtain a third modulated optical signal, couples the first modulated optical signal and the third modulated optical signal, and outputs the obtained coupled optical signal to the optical fiber link; wherein the first modulated optical signal is obtained by modulating a reference frequency signal generated by the transmitting device to a first optical signal, and the reference frequency signal is a frequency signal obtained by performing first frequency multiplication on a first frequency signal generated by a reference frequency source; The relay amplification filter devices in the optical fiber link perform the preset signal conditioning operations on the coupled optical signal in turn, and output the coupled optical signal to the receiving device; The receiving device controls the output of a voltage-controlled crystal oscillator of the receiving device based on the coupled optical signal, so that the second frequency signal output by the voltage-controlled crystal oscillator is frequency-synchronized with the first frequency signal, and the phase difference remains constant.

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