A fiber optic frequency relay transmission system and method without phase-locked loop

Abstract

The application relates to the technical field of optical fiber communication, and discloses a kind of optical fiber optical frequency relay transmission system and method without phase-locked loop.The optical fiber optical frequency relay transmission system includes: multiple stages of relay stations cascaded in turn through optical fiber transmission link, for each stage of relay station, the optical frequency signal of the stage emitted by the regenerative cavity stable laser of the stage and the optical frequency signal received from the relay station of the upper stage are frequency mixing processed by the first photoelectric detector, the frequency mixing signal of the stage is obtained, and the optical frequency signal transmitted by the relay station of the upper stage and the frequency mixing signal of the stage are mixed and summed by the data interaction unit, the noise accumulation generated in the signal transmission process in the conventional phase-locked loop scheme can be completely eliminated, so that the noise term in the optical frequency signal output to the user end is completely cancelled, i.e. high-precision original optical frequency signal is provided for the user end, and long-distance, high-precision optical frequency transmission can be realized on the basis of reducing the complexity of system design.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber communication, in particular to an optical fiber optical frequency relay transmission system and method without phase-locked loop. BACKGROUND

[0002] With the rapid development of atomic cooling technology, the stability and uncertainty of optical clock system have reached 10 -18 orders of magnitude, which plays a crucial role in the development of gravitational wave detection, precision physical measurement and geodesy. The stability of traditional satellite-based time-frequency comparison is limited to 10 -15 / day, which cannot meet the transmission comparison requirements of optical clock signals. Due to the characteristics of low loss, high bandwidth and anti-interference of optical fiber, optical frequency transmission technology based on optical fiber is an important means to realize long-distance transmission of high-precision optical clock signals.

[0003] In the process of optical frequency signal transmission along the optical fiber signal, the detection and elimination of the additional phase noise of the optical fiber are realized by using the Doppler noise elimination technology. In order to further improve the noise suppression capability, the segmented detection and control of the link noise are realized by using the optical fiber optical frequency regenerative relay system. The principle is to use the phase locking of the narrow linewidth laser in the system on the transmission optical frequency signal to realize the amplification and regeneration of the transmission optical frequency signal. However, this scheme will cause the noise of the regenerative laser in the relay system to accumulate with the increase of the cascade number, resulting in further broadening of the laser linewidth. When the noise level of the regenerative laser is higher than that of the optical fiber link, it will cause errors in the measurement of the optical fiber noise and limit the transmissible distance of the relay system. SUMMARY

[0004] In order to solve the above problems of the prior art, the present application provides an optical fiber optical frequency relay transmission system and method without phase-locked loop, which aims to completely eliminate the noise accumulation generated in the signal transmission process in the traditional phase-locked loop scheme, so as to realize that the noise term in the optical frequency signal output from each relay station to the user end is completely cancelled, i.e. to provide the user end with high-precision original optical frequency signal.

[0005] In one aspect, the present application provides an optical fiber optical frequency relay transmission system without phase-locked loop, comprising: a plurality of relay stations cascaded in sequence through an optical fiber transmission link, each relay station comprising:

[0006] a wave division system for splitting the signal transmitted by the previous relay station to obtain an optical signal transmitted by the previous relay station to a data interaction unit, and an optical frequency signal transmitted by the previous relay station to a first photodetector; wherein the optical signal comprises: noise signals of the previous optical fiber transmission link, and signals of frequency difference information between optical frequency signals emitted by regenerative cavity stable lasers in each two adjacent relay stations.

[0007] The regenerative cavity stabilized laser of the current stage is used to emit the optical frequency signal of the current stage and transmit the optical frequency signal of the current stage to the next stage relay station through the sum and difference wavelength system; wherein, the frequency of the optical frequency signal of the current stage is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the relay station of the previous stage;

[0008] The first photodetector is used to beat the optical frequency signal of the current stage and the optical frequency signal transmitted by the relay station of the previous stage to obtain the beat frequency signal of the current stage;

[0009] The data interaction unit is used to mix and sum the beat frequency signal of the current stage and the optical signal transmitted by the relay station of the previous stage to obtain the mixed beat frequency signal, and transmit the mixed beat frequency signal and the optical signal transmitted by the relay station of the previous stage to the next stage relay station through the sum and difference wavelength system;

[0010] The first acousto-optic modulator is used to shift the frequency of the optical frequency signal of the current stage based on the mixed beat frequency signal to obtain the optical frequency signal of the current stage which is the same as the original optical frequency signal of the optical fiber optical frequency relay transmission system, and transmit the optical frequency signal of the current stage to the user end.

[0011] Optionally, each stage relay station further comprises: a first optical fiber coupler, a second optical fiber coupler, a third optical fiber coupler and a fourth optical fiber coupler, and a transmitting end acousto-optic modulator;

[0012] The regenerative cavity stabilized laser of the current stage is further used to transmit the optical frequency signal of the current stage to the first photodetector through the fourth optical fiber coupler, the second optical fiber coupler and the first optical fiber coupler in turn, and transmit the optical frequency signal of the current stage to the transmitting end acousto-optic modulator through the fourth optical fiber coupler, the second optical fiber coupler and the third optical fiber coupler in turn;

[0013] The transmitting end acousto-optic modulator is used to positively shift the frequency of the optical frequency signal of the current stage, and transmit the positively shifted optical frequency signal of the current stage to the optical fiber transmission link between the relay station and the next stage relay station through the sum and difference wavelength system.

[0014] Optionally, each stage relay station further comprises: a second photodetector and a frequency division processor;

[0015] The third optical fiber coupler is used to reflect the optical frequency signal of the current stage transmitted through the fourth optical fiber coupler and the second optical fiber coupler to the second photodetector by using the connected second 45-degree Faraday rotator, and reflect the feedback optical signal of the current stage transmitted through the sum and difference wavelength system and the transmitting end acousto-optic modulator to the second photodetector; wherein, the feedback optical signal of the current stage is the feedback optical signal transmitted between the relay station and the next stage relay station;

[0016] a second photodetector configured to perform beat frequency processing on the local optical frequency signal and the local feedback optical signal to obtain a feedback beat frequency signal, and transmit the feedback beat frequency signal to the frequency halving processor;

[0017] a frequency halving processor configured to process the feedback beat frequency signal to obtain a noise signal of an optical fiber transmission link between the relay station and a next-level relay station, and transmit the noise signal of the optical fiber transmission link between the relay station and the next-level relay station to the data interaction unit for storage through a frequency counting unit;

[0018] The data interaction unit is further configured to transmit the noise signal of the optical fiber transmission link between the relay station and the next-level relay station to the next-level relay station through a wavelength division system.

[0019] Optionally, each level of the relay station further comprises a receiving end acousto-optic modulator;

[0020] The wavelength division system is specifically configured to split the signal transmitted by the previous-level relay station to obtain an optical signal transmitted to the data interaction unit and a to-be-shifted optical frequency signal transmitted to the receiving end acousto-optic modulator.

[0021] The receiving end acousto-optic modulator is configured to perform positive frequency shift on the to-be-shifted optical frequency signal transmitted by the previous-level relay station to obtain an optical frequency signal transmitted by the previous-level relay station to the first optical fiber coupler.

[0022] The first optical fiber coupler is configured to reflect the optical frequency signal transmitted by the previous-level relay station to the first photodetector by using a connected first 45-degree Faraday rotator, and transmit the optical frequency signal transmitted by the previous-level relay station to a transmission link between the previous-level relay station and the relay station through the receiving end acousto-optic modulator and the wavelength division system.

[0023] Optionally, the relay station is an Nth-level relay station, the optical signal transmitted by the previous-level relay station is an optical signal transmitted by an (N-1) th-level relay station, and N is an integer greater than 2.

[0024] The noise signal of the preceding optical fiber transmission link included in the optical signal transmitted by the (N-1) th-level relay station is:

[0025] ;

[0026] wherein, is an optical fiber transmission link between a sending device in the optical fiber optical frequency relay transmission system and the first-level relay station; is additional noise signal on the optical fiber optical frequency relay transmission system; and are an angular frequency and a phase of an acoustic wave modulation signal of the receiving end acousto-optic modulator, respectively; and respectively, are the angular frequency and phase of the acoustic wave modulation signal of the transmitting acousto-optic modulator; is a time variable; is an optical fiber transmission link between the first level relay station and the second level relay station; is an additional noise signal on the optical fiber transmission link; is an optical fiber transmission link between the N-1 level relay station and the N level relay station; is an additional noise signal on the optical fiber transmission link; a receiving acousto-optic modulator and a transmitting acousto-optic modulator are arranged in each level relay station; is an optical fiber transmission link between the transmitting device and the first level relay station; is an additional phase noise on the optical fiber transmission link; is an optical fiber transmission link between the first level relay station and the second level relay station; is an additional phase noise on the optical fiber transmission link; is an optical fiber transmission link between the N-1 level relay station and the N level relay station; is an additional phase noise on the optical fiber transmission link.

[0027] Optionally, the optical signal transmitted by the N-1 level relay station includes a signal of frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in each two adjacent relay stations in the front sequence:

[0028] ;

[0029] wherein, is a first level beat frequency signal output by a first photodetector in the first level relay station; and respectively, are the angular frequency and phase of the optical frequency signal output by the regenerative cavity stabilized laser in the first level relay station; and respectively, are the angular frequency and phase of the original optical frequency signal; is a second level beat frequency signal output by a first photodetector in the second level relay station; and respectively, are the angular frequency and phase of the optical frequency signal output by the regenerative cavity stabilized laser in the second level relay station; is an N-1 level beat frequency signal output by a first photodetector in the N-1 level relay station; and respectively, are the angular frequency and phase of the optical frequency signal output by the regenerative cavity stabilized laser in the N-1 level relay station; and respectively, are the angular frequency and the phase of the optical frequency signal output by the regenerative cavity stabilized laser in the N-2th relay station; is the optical fiber transmission link between the N-2th relay station and the N-1th relay station; is the optical fiber transmission link between the N-2th relay station and the N-1th relay station; is the additional phase noise on the optical fiber transmission link between the N-2th relay station and the N-1th relay station.

[0030] Optionally, the first photoelectric detector outputs a beat frequency signal of the current level is:

[0031] ;

[0032] wherein, and respectively, are the angular frequency and the phase of the optical frequency signal output by the regenerative cavity stabilized laser in the Nth relay station; and respectively, are the angular frequency and the phase of the optical frequency signal output by the regenerative cavity stabilized laser in the N-1th relay station.

[0033] Optionally, the optical fiber optical frequency relay transmission system further comprises a sending device, the sending device being connected with the first level relay station, the sending device corresponding to the upper level relay station of the first level relay station, an original cavity stabilized laser in the sending device emitting an original optical frequency signal; the sending device comprises:

[0034] the original cavity stabilized laser for emitting the original optical frequency signal :

[0035] ;

[0036] wherein, and respectively, are the angular frequency and the phase of the original optical frequency signal; is a time variable;

[0037] an original photoelectric detector for beating the original optical frequency signal and a feedback optical signal between the sending device and the first level relay station to obtain an original beat frequency signal :

[0038] ;

[0039] wherein, and respectively, are the angular frequency and the phase of the sound wave modulation signal of the receiving end acousto-optic modulator in the first level relay station; and respectively, are the angular frequency and the phase of the sound wave modulation signal of the sending end acousto-optic modulator in the sending device; is a time variable; for a fiber transmission link between the transmitting device and the first level relay station; for additional phase noise on the

[0040] a raw frequency division processor for processing the raw beat signal to obtain a noise signal of the fiber transmission link between the transmitting device and the first level relay station;

[0041] a raw data interaction unit for receiving and storing the noise signal of the fiber transmission link between the transmitting device and the first level relay station through the raw frequency counting unit, and transmitting the noise signal of the fiber transmission link between the transmitting device and the first level relay station to the first level relay station through the raw and wave division system.

[0042] Optionally, each level relay station further comprises:

[0043] a global positioning system (GPS) servo rubidium clock for controlling the synchronization of the transmitted signal and the second pulse between the relay station and the next level relay station.

[0044] In another aspect, the embodiments of the present application also provide a fiber optical frequency relay transmission method without phase-locked loop, which is applied to the fiber optical frequency relay transmission system as described above, and the method comprises:

[0045] for each level relay station, the signal transmitted by the previous level relay station is split by using the de-wave division system to obtain the optical signal transmitted by the previous level relay station and transmitted to the data interaction unit, and the optical frequency signal transmitted by the previous level relay station and transmitted to the first photoelectric detector; wherein the optical signal comprises the noise signal of the previous fiber transmission link, and the signal of the frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in each two adjacent relay stations;

[0046] the optical frequency signal of the current level is emitted by using the regenerative cavity stabilized laser of the current level, and the optical frequency signal of the current level is transmitted to the next level relay station by using the and wave division system; wherein the frequency of the optical frequency signal of the current level is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the previous level relay station;

[0047] the beat signal of the current level is obtained by using the first photoelectric detector to beat the optical frequency signal of the current level and the optical frequency signal transmitted by the previous level relay station;

[0048] the mixed beat signal is obtained by using the data interaction unit to mix and sum the beat signal of the current level and the optical signal transmitted by the previous level relay station, and the mixed beat signal and the optical signal transmitted by the previous level relay station are transmitted to the next level relay station by using the and wave division system;

[0049] The first acousto-optic modulator is used to shift the frequency of the light frequency signal in the current stage based on the mixed beat frequency signal, so as to obtain the same optical frequency signal in the current stage as the original optical frequency signal of the optical fiber optical frequency relay transmission system, and the optical frequency signal in the current stage is transmitted to the user end.

[0050] The technical scheme provided in the application can at least achieve the following beneficial effects:

[0051] The application provides a fiber-optic frequency relay transmission system and method without a phase-locked loop. The fiber-optic frequency relay transmission system comprises: a plurality of relay stations connected in sequence through a fiber transmission link, each relay station comprising: a demultiplexing system configured to split a signal transmitted by a previous relay station to obtain an optical signal transmitted by the previous relay station to a data interaction unit and an optical frequency signal transmitted by the previous relay station to a first photodetector; wherein the optical signal comprises: a noise signal of a previous optical fiber transmission link, and a signal of frequency difference information between optical frequency signals emitted by regenerative cavity stabilized lasers in each two adjacent relay stations in the previous optical fiber transmission link; a current regenerative cavity stabilized laser configured to emit a current optical frequency signal and transmit the current optical frequency signal to a next relay station through a multiplexing system; wherein the frequency of the current optical frequency signal is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the previous relay station; the first photodetector is configured to beat the current optical frequency signal and the optical frequency signal transmitted by the previous relay station to obtain a current beat signal; the data interaction unit is configured to mix and sum the current beat signal and the optical signal transmitted by the previous relay station to obtain a mixed beat signal, and transmit the mixed beat signal and the optical signal transmitted by the previous relay station to the next relay station through the multiplexing system; and a first acousto-optic modulator is configured to shift the frequency of the current optical frequency signal based on the mixed beat signal to obtain a current optical frequency signal that is the same as an original optical frequency signal of the fiber-optic frequency relay transmission system, and transmit the current optical frequency signal to a user end. In each relay station, first, the first photodetector in the relay station beats the current optical frequency signal emitted by the current regenerative cavity stabilized laser and the optical frequency signal transmitted by the previous relay station to obtain a signal of frequency difference information between the optical frequency signal emitted by the current regenerative cavity stabilized laser and the optical frequency signal emitted by the regenerative cavity stabilized laser in the previous relay station; then, the data interaction unit in the relay station mixes and sums the received noise signal of the previous optical fiber transmission link, the signal of frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in each two adjacent relay stations in the previous optical fiber transmission link, and the signal of frequency difference information between the optical frequency signal emitted by the current regenerative cavity stabilized laser and the optical frequency signal emitted by the regenerative cavity stabilized laser in the previous relay station to obtain a mixed beat signal; finally, the first acousto-optic modulator is driven to shift the frequency based on the mixed beat signal. In this way, the noise accumulation in the signal transmission process in the conventional phase-locked loop scheme can be completely eliminated, so that the noise term in the optical frequency signal output by each relay station to the user end is completely cancelled, that is, the original optical frequency signal with high precision is provided for the user end, and long-distance and high-precision optical frequency transmission can be realized on the basis of reducing the complexity of system design.

[0052] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory, rather than limiting the technical solutions provided by the embodiments of the application. BRIEF DESCRIPTION OF DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of 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 some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0054] Figure 1 A structure schematic diagram of a fiber optical frequency relay transmission system without phase-locked loop provided by the embodiment of the present application;

[0055] Figure 2 A specific structure schematic diagram of a relay station in actual application included in the fiber optical frequency relay transmission system without phase-locked loop provided by the embodiment of the present application;

[0056] Figure 3 A specific structure schematic diagram of a sending device in actual application in the fiber optical frequency relay transmission system without phase-locked loop provided by the embodiment of the present application;

[0057] Figure 4 A flowchart of a fiber optical frequency relay transmission method without phase-locked loop provided by the embodiment of the present application. DETAILED DESCRIPTION

[0058] The embodiments of the present application will be described below with reference to the drawings and preferred embodiments, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in the present description. The present application can also be implemented or applied by other different specific embodiments, and each detail in the present description can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be understood that the preferred embodiments are only for illustrating the present application, but not for limiting the protection scope of the present application.

[0059] In the following description, "some embodiments" are described, which describe a subset of all possible embodiments, but it can be understood that "some embodiments" can be the same subset or different subset of all possible embodiments, and can be combined with each other without conflict.

[0060] In the following description, the terms "first\second\third" are only to distinguish similar objects, and do not represent the specific order of the objects. It can be understood that "first\second\third" can be interchanged with specific order or sequence as allowed, so that the embodiments of the present application described here can be implemented in an order other than that illustrated or described here.

[0061] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the application belong. The terminology used herein is for the purpose of describing embodiments of the application only and is not intended to be limiting of embodiments of the application.

[0062] Embodiment 1

[0063] Referring to Figure 1 As shown in the figure, a structure schematic diagram of a fiber-optical frequency relay transmission system without phase-locked loop provided by the present application is shown, the fiber-optical frequency relay transmission system 10 comprises: a plurality of relay stations cascaded in sequence through a fiber transmission link, referring to Figure 1 The upper-level relay station 200 and the lower-level relay station 300 of the relay station 100 are shown, here taking Figure 1 The relay station 100 shown in the figure is taken as an example for description, wherein each relay station 100 comprises:

[0064] The demultiplexing system 101 is configured to split the signal transmitted by the upper-level relay station 200 to obtain an optical signal transmitted by the upper-level relay station 200 and transmitted to the data interaction unit 104, and an optical frequency signal transmitted by the upper-level relay station 200 and transmitted to the first photodetector 103.

[0065] The optical signal comprises: a noise signal of a preceding optical fiber transmission link, and a signal of a frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in each two adjacent relay stations.

[0066] The regenerative cavity stabilized laser 102 is configured to emit a current-level optical frequency signal and transmit the current-level optical frequency signal to the lower-level relay station 300 through the multiplexing system 106.

[0067] The frequency of the current-level optical frequency signal is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the upper-level relay station 200.

[0068] The first photodetector 103 is configured to beat the current-level optical frequency signal and the optical frequency signal transmitted by the upper-level relay station 200 to obtain a current-level beat signal.

[0069] The data interaction unit 104 is configured to mix and sum the current-level beat signal and the optical signal transmitted by the upper-level relay station 200 to obtain a mixed beat signal, and transmit the mixed beat signal and the optical signal transmitted by the upper-level relay station 200 to the lower-level relay station 300 through the multiplexing system 106.

[0070] The first acousto-optic modulator 105 is used for frequency shifting the optical frequency signal of the current stage based on the mixed beat frequency signal, so as to obtain the optical frequency signal of the current stage which is the same as the original optical frequency signal of the optical fiber optical frequency relay transmission system 10, and transmit the optical frequency signal of the current stage to the user end 400.

[0071] In some embodiments of the present application, the relay station 200, the relay station 100 and the relay station 300 in the optical fiber optical frequency relay transmission system 10 are cascaded through the optical fiber transmission links in sequence; wherein, after the signal transmitted by the relay station 200 through the optical fiber transmission link enters the relay station 100, the signal is split by the demultiplexing system 101, a part of the signal is transmitted to the data interaction unit 104 for storage and subsequent processing, and a part of the signal is transmitted to the first photodetector 103, and the optical frequency signal transmitted to the first photodetector 103 is the optical frequency signal transmitted by the relay station 200.

[0072] In some embodiments of the present application, the optical signal transmitted to the data interaction unit 104 includes the noise signal of the previous optical fiber transmission link and the signal of the frequency difference information between the optical frequency signals emitted by the regenerative cavity stable lasers in each two adjacent relay stations in sequence. In other words, if the relay station 100 is the third-level relay station in the optical fiber optical frequency relay transmission system 10, the optical signal received by the relay station 100 is the optical signal transmitted by the second-level relay station in the optical fiber optical frequency relay transmission system 10, and the noise signal of the previous optical fiber transmission link included in the optical signal includes the noise signal of the optical fiber transmission link between the sending device and the first-level relay station in the optical fiber optical frequency relay transmission system 10, the noise signal of the optical fiber transmission link between the first-level relay station and the second-level relay station, and the noise signal of the optical fiber transmission link between the second-level relay station and the third-level relay station. Here, for the third-level relay station, the previous optical fiber transmission link includes the optical fiber transmission link between the sending device and the first-level relay station in the optical fiber optical frequency relay transmission system 10, the optical fiber transmission link between the first-level relay station and the second-level relay station, and the optical fiber transmission link between the second-level relay station and the third-level relay station; correspondingly, the signal of the frequency difference information between the optical frequency signals emitted by the regenerative cavity stable lasers in each two adjacent relay stations in sequence includes the signal of the frequency difference information between the optical frequency signals emitted by the regenerative cavity stable lasers in the sending device and the first-level relay station, and the signal of the frequency difference information between the optical frequency signals emitted by the regenerative cavity stable lasers in the first-level relay station and the second-level relay station.

[0073] It should be noted that the optical fiber optical frequency relay transmission system 10 further includes a sending device (not shown) connected to the first-level relay station in the optical fiber optical frequency relay transmission system 10 through the optical fiber transmission link, i.e., the sending device is the upper-level relay station corresponding to the first-level relay station. Figure 1 The sending device is connected to the first-level relay station in the optical fiber optical frequency relay transmission system 10 through the optical fiber transmission link, i.e., the sending device is the upper-level relay station corresponding to the first-level relay station.

[0074] In some embodiments of the present application, the relay station 100 can not only include the above-mentioned: wavelength division multiplexing (WDM) 101, the current regenerative cavity stabilized laser 102, the first photo detector (PD) 103, the data interaction unit 104, the first acousto-optic modulator 105, and the wavelength division system 106; it can further include: a plurality of optical couplers (OC), a frequency division by two processor (f / 2), a plurality of 45-degree Faraday rotation mirrors (FM), a frequency counting unit, etc., to specifically implement the transmission of related signals.

[0075] In some embodiments of the present application, taking the N-level regenerative cavity stabilized laser (Laser N) in the N-level relay station in the optical fiber optical frequency relay transmission system 10 as an example, the current regenerative cavity stabilized laser 102 can emit the current optical frequency signal which can be shown by formula (1):

[0076] Formula (1);

[0077] wherein, and the angular frequency and the phase of the optical frequency signal emitted by the N-level regenerative cavity stabilized laser; is a time variable.

[0078] In some embodiments of the present application, the frequency of the optical frequency signal emitted by the current regenerative cavity stabilized laser in each level relay station in the optical fiber optical frequency relay transmission system 10 is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the upper level relay station. And for the optical fiber optical frequency relay transmission system 10, the frequency range of the optical frequency signal emitted by the regenerative cavity stabilized laser involved in the system can be (5MHz-50MHz).

[0079] In some embodiments of the present application, the data interaction unit 104 can further include: an optical receiver, a data processor, and an optical transmitter.

[0080] In some embodiments of the present application, each level relay station 100 further includes: a first optical fiber coupler, a second optical fiber coupler, a third optical fiber coupler, and a fourth optical fiber coupler, and a transmitting end acousto-optic modulator (not shown): Figure 1

[0081] ​The current regenerative cavity stable laser 102 is also configured to transmit the current optical frequency signal to the first photodetector 103 through the fourth fiber coupler, the second fiber coupler and the first fiber coupler in sequence, and transmit the current optical frequency signal to the transmitting end acousto-optic modulator through the fourth fiber coupler, the second fiber coupler and the third fiber coupler in sequence.

[0082] The transmitting end acousto-optic modulator is configured to positively frequency shift the current optical frequency signal, and transmit the positively frequency shifted current optical frequency signal to the optical fiber transmission link between the relay station 100 and the next level relay station 300 through the wavelength division system 106.

[0083] In some embodiments of the present application, each level relay station 100 further comprises a second photodetector, a two-frequency division processor (not shown) and a data interaction unit 104. Figure 1

[0084] The third fiber coupler is configured to reflect the current optical frequency signal transmitted by the fourth fiber coupler and the second fiber coupler to the second photodetector by the connected second 45-degree Faraday rotator, and reflect the current feedback optical signal transmitted by the wavelength division system 106 and the transmitting end acousto-optic modulator to the second photodetector.

[0085] The current feedback optical signal is the feedback optical signal transmitted between the relay station 100 and the next level relay station 300.

[0086] The second photodetector is configured to beat the current optical frequency signal and the current feedback optical signal to obtain a feedback beat frequency signal, and transmit the feedback beat frequency signal to the two-frequency division processor.

[0087] The two-frequency division processor is configured to process the feedback beat frequency signal to obtain a noise signal of the optical fiber transmission link between the relay station 100 and the next level relay station 300, and transmit the noise signal of the optical fiber transmission link between the relay station 100 and the next level relay station 300 to the data interaction unit 104 for storage through the frequency counting unit.

[0088] The data interaction unit 104 is also configured to transmit the noise signal of the optical fiber transmission link between the relay station 100 and the next level relay station 300 to the next level relay station 300 through the wavelength division system 106.

[0089] Correspondingly, each level relay station 100 further comprises a receiving end acousto-optic modulator (not shown) and a two-frequency division processor. Figure 1

[0090] ​​The de-wavelength subsystem 101 is specifically used to decompose the signal transmitted by the previous relay station 200 to obtain the optical signal transmitted by the previous relay station 200 and transmitted to the data interaction unit 104, as well as the frequency-shiftable optical frequency signal transmitted by the previous relay station 200 and transmitted to the acousto-optic modulator at the receiving end.

[0091] The receiving end acousto-optic modulator is used to perform positive frequency shifting on the optical frequency signal to be shifted transmitted by the previous level relay station 200, so as to obtain the optical frequency signal transmitted by the previous level relay station 200 to the first fiber coupler.

[0092] The first fiber optic coupler is used to reflect the optical frequency signal transmitted by the previous relay station 200 to the first photodetector 103 using the connected first 45-degree Faraday rotator, and to transmit the optical frequency signal transmitted by the previous relay station 200 to the transmission link between the previous relay station 200 and the relay station 100 through the receiving end acousto-optic modulator and the de-wavelength subsystem 101.

[0093] In some embodiments of this application, each relay station 100 further includes:

[0094] Global Positioning System (GPS) servo rubidium clock Figure 1 (Not shown in the image), used to control the transmission of signals and second pulse synchronization between relay station 100 and the next-level relay station 300.

[0095] Here you can refer to Figure 2 The diagram shown is a schematic representation of the specific structure of the relay stations in the phase-locked loop-free fiber optic frequency relay system provided in this application embodiment, as shown in practical applications. In this phase-locked loop-free fiber optic frequency relay system, relay stations N-1 (the (N-1)th level relay station), N (the Nth level relay station), and N+1 (the N+1th level relay station) are shown, sequentially cascaded through fiber optic transmission links. In relay station N:

[0096] Using WDM1 (i.e., corresponding Figure 1 The de-wave subsystem shown divides the signal transmitted by relay station N-1 into two channels (the first channel and the second channel); the first channel is connected to the data interaction unit N, and the second channel is used to transmit the optical frequency signal transmitted by relay station N-1.

[0097] Here, the optical frequency signal transmitted by relay station N-1 passes through Figure 2The AOMR (receiving end acousto-optic modulator) shown in the middle carries out positive frequency shift, and transmits the signal after positive frequency shift to OC1 (first optical fiber coupler); wherein the right end of the OC1 is connected with FM1 (first 45-degree Faraday rotator), which transmits the signal after positive frequency shift to PD1 (first photodetector) for processing.

[0098] Meanwhile, the Laser N (i.e. the regenerative cavity stable laser in the relay station N) transmits light frequency signals with a frequency greater than that of the regenerative cavity stable laser in the relay station N-1. Here, the N-level light frequency signal transmitted by the Laser N is divided into three parts by the OC4 (fourth optical fiber coupler), i.e. transmitted through three transmission channels, wherein:

[0099] The first transmission channel: through the OC2 (second optical fiber coupler) and the OC1, into the PD1; in this way, the PD1 carries out beat frequency processing on the light frequency signal and the transmitted signal after positive frequency shift mentioned above.

[0100] The second transmission channel: through the OC3 (i.e. an optical fiber coupler), the AOML (sending end acousto-optic modulator) and the WDM2 (corresponding Figure 1 to the wavelength division system shown in the middle); wherein the OC3 is connected with the FM2 (second 45-degree Faraday rotator).

[0101] The third transmission channel: transmitted to the AOM3 (first acousto-optic modulator), which carries out negative frequency shift on the received signal.

[0102] Here, the data interaction unit N can further include an optical receiver, a data processor and an optical transmitter.

[0103] Here, the PD1 transmits the beat frequency signal through the transmission path as shown in Figure 2 Band-Pass Filter (BPF) 1→ Line Amplifier (LA) 1→ frequency counting unit→ data interaction unit N); at the same time, the data interaction unit N can also drive the AOM3 to carry out negative frequency shift on the received signal (the signal transmitted by the Laser N through the OC4) through the Data Distribution Service (DDS) as shown in Figure 2

[0104] ​Further, the internal hardware structure of the relay station N+1 is completely consistent with that of the relay station N, and the relay station N+1 will also feed back the signal transmitted by the relay station N to the relay station N through the OC1 connected with the FM1 inside the relay station N+1, i.e., the relay station N will receive the feedback signal through the WDM2, and transmit the feedback signal to the PD2 through the AOML (which will perform positive frequency shift on the received signal) and the OC3 connected with the FM2. Figure 2 The PD2 will beat the received feedback signal and the optical frequency signal to obtain a beat signal, and transmit the beat signal through the transmission channel as shown in

[0105] Referring to Figure 2 , the relay station N further includes a GPS servo rubidium clock for synchronizing the transmission signal and the second pulse between the relay station N and the relay station N+1.

[0106] In some embodiments of the present application, the output corresponding to the GPS servo rubidium clock includes: 1 signal with a frequency of 10 MHz, a second pulse signal (1PPS as shown in Figure 2

[0107] In some embodiments of the present application, the optical fiber optical frequency relay transmission system further includes: a sending device, the sending device is connected with the first level relay station, the upper level relay station corresponding to the first level relay station is the sending device, and the original cavity stabilized laser in the sending device emits an original optical frequency signal; for details, refer to Figure 3 , which is a specific structure diagram of the sending device in the optical fiber optical frequency relay transmission system without a phase-locked loop provided by the embodiments of the present application in actual application; wherein the sending device includes:

[0108] The original cavity stabilized laser (Laser as shown in Figure 3 ) is used to emit an original optical frequency signal .

[0109] Formula (2);

[0110] Wherein, and are the angular frequency and phase of the original optical frequency signal, respectively; is a time variable.

[0111] The original photoelectric detector (PD as shown in Figure 3 ) is used to beat the original optical frequency signal and the feedback optical signal between the sending device and the first level relay station to obtain an original beat signal .

[0112] Formula (3);​

[0113] wherein, and are the angular frequency and phase of the acoustic wave modulation signal of the receiving end acousto-optic modulator in the first stage relay station, respectively; and are the angular frequency and phase of the acoustic wave modulation signal of the transmitting end acousto-optic modulator in the transmitting device, respectively; is a time variable; is the optical fiber transmission link between the transmitting device and the first stage relay station; is additional phase noise on

[0114] the original frequency division processor (f / 2) shown in FIG. 1, is used to process the original beat frequency signal to obtain the noise signal of the optical fiber transmission link between the transmitting device and the first stage relay station. Figure 3 the original data interaction unit (D) shown in FIG. 1, is used to receive and store the noise signal of the optical fiber transmission link between the transmitting device and the first stage relay station through the original frequency counting unit, and transmit the noise signal of the optical fiber transmission link between the transmitting device and the first stage relay station to the first stage relay station through the original and wave division system.

[0115] Figure 3 In some embodiments of the present application, the original frequency division processor (f / 2) shown in FIG. 1 transmits to the data interaction unit: the noise signal of the optical fiber transmission link between the transmitting device and the first stage relay station :

[0116] Figure 3

[0117] Equation (4).

[0118] Here, the noise signal of the optical fiber transmission link between the transmitting device and the first stage relay station will be recorded in real time by the frequency counter in the transmitting device and transmitted to the next stage relay system (the first stage relay station) through the data interaction unit.

[0119] In other words, in the first stage relay station in the optical fiber optical frequency relay transmission system, the optical frequency signal (1st optical frequency signal) output by the regenerative cavity stabilized laser inside it is:

[0120] Equation (5);

[0121] wherein, and are the angular frequency and phase of the optical frequency signal output by the regenerative cavity stabilized laser in the first stage relay station, respectively.​​​ is a time variable.

[0122] Correspondingly, the first photodetector in the first relay station, corresponding beat processing of the above-mentioned optical frequency signal (1st optical frequency signal) of the current stage and the optical signal fed back by the second relay station, obtains the beat signal (1st beat signal) of the current stage is:

[0123] Formula (6).

[0124] Thus, the data processing unit inside the first relay station mixes and subtracts and the optical signal sent from the sending device to the inside of the first relay station, to obtain the mixed beat signal of the current stage :

[0125] Formula (7).

[0126] Here, the optical signal sent from the sending device to the inside of the first relay station can be shown by the following formula (8) only including the noise signal of the optical fiber transmission link between the sending device and the first relay station (the signal does not store the frequency difference information between the optical frequency signals emitted by the regenerative cavity stable laser in each two adjacent relay stations in the previous sequence for the first relay station), that is, as shown in the above formula (4).

[0127] Correspondingly, the mixed beat signal of the current stage is driven by the optical transmitter and DDS inside the first relay station and AOM3 (negative frequency shift operation is performed) so that the user terminal connected with the first relay station receives the 1st optical frequency signal :

[0128] Formula (8).

[0129] In some embodiments of the application, taking the relay station as the Nth relay station, the optical signal transmitted by the previous stage relay station is the optical signal transmitted by the N-1th relay station, and N is an integer greater than 2. The noise signal of the optical fiber transmission link in the previous sequence included in the optical signal transmitted by the N-1th relay station can be represented by the following formula (9):

[0130] Formula (9);

[0131] wherein, is the optical fiber transmission link between the sending device and the first relay station in the optical fiber optical frequency relay transmission system; is the additional noise signal on ; and These are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the receiving end, respectively; and These are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the transmitting end, respectively; It is a time variable; For the fiber optic transmission link between the first-level relay station and the second-level relay station; for Additional noise signals on; For the fiber optic transmission link between the (N-1)th level relay station and the Nth level relay station; for Additional noise signals on the signal; each relay station is equipped with a receiver-end acousto-optic modulator and a transmitter-end acousto-optic modulator. For the fiber optic transmission link between the transmitting device and the first-level relay station; for Additional phase noise; For the fiber optic transmission link between the first-level relay station and the second-level relay station; for Additional phase noise; For the fiber optic transmission link between the (N-1)th level relay station and the Nth level relay station; for Additional phase noise on the surface.

[0132] Correspondingly, the following formula (10) can be used to represent the signal that includes the frequency difference information between the optical frequency signals emitted by the regenerated cavity stabilized lasers in every two adjacent preceding relay stations:

[0133] Formula (10);

[0134] in, The first-level beat frequency signal output by the first photodetector in the first-level relay station; and These represent the angular frequency and phase of the optical signal output from the regenerated cavity stabilized laser in the first-level relay station, respectively. and These are the angular frequency and phase of the original optical frequency signal, respectively. and These are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the receiving end, respectively; and These are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the transmitting end, respectively; It is a time variable; For the fiber optic transmission link between the transmitting device and the first-level relay station; for additional phase noise on ω0; a second-order beat signal output by a first photodetector in the second-order repeater station; and respectively an angular frequency and a phase of an optical frequency signal output by a regenerative cavity stabilized laser in the second-order repeater station; a fiber transmission link between the first-order repeater station and the second-order repeater station; a first-order beat signal output by a first photodetector in the first-order repeater station; and respectively an angular frequency and a phase of an optical frequency signal output by a regenerative cavity stabilized laser in the first-order repeater station; and respectively an angular frequency and a phase of an optical frequency signal output by a regenerative cavity stabilized laser in the N-2 order repeater station; and respectively an angular frequency and a phase of an optical frequency signal output by a regenerative cavity stabilized laser in the N-2 order repeater station; a fiber transmission link between the N-2 order repeater station and the N-1 order repeater station; a first-order beat signal output by a first photodetector in the first-order repeater station; additional phase noise on ω0.

[0135] Continuing the above description, taking the case where the optical signal transmitted by the above order repeater station is the optical signal transmitted by the N-1 order repeater station, and taking the case where N is an integer greater than 2, the present order repeater station is the N order repeater station, and the present order beat signal output by the first photodetector in the N order repeater station is which can be expressed by formula (11):

[0136] formula (11);

[0137] wherein, and respectively an angular frequency and a phase of an optical frequency signal output by a regenerative cavity stabilized laser in the N order repeater station; and respectively an angular frequency and a phase of an optical frequency signal output by a regenerative cavity stabilized laser in the N-1 order repeater station; a fiber transmission link between the N-1 order repeater station and the N order repeater station; additional phase noise on ω0; and respectively an angular frequency and a phase of an acoustic wave modulation signal of the receiving end acousto-optic modulator; and respectively an angular frequency and a phase of an acoustic wave modulation signal of the transmitting end acousto-optic modulator.

[0138] ​Thus, in the current relay station (Nth relay station), the internal data interaction unit receives the signals described in the above equations (9) to (11), and mixes and sums the above signals to obtain the mixed beat frequency signal shown in the following equation (12) :

[0139] Equation (12).

[0140] Here, continuing the above description, equation (1) shows the current optical frequency signal emitted by the current regenerative cavity stabilized laser in the current relay station (Nth relay station) . Here, the obtained mixed beat frequency signal is used to drive the first acousto-optic modulator in the current relay station to perform frequency shift processing on the current optical frequency signal , thereby obtaining the current optical frequency signal :

[0141] Equation (13).

[0142] and transmitting the current optical frequency signal to the user end, which is the same as the original optical frequency signal .

[0143] The optical fiber optical frequency relay transmission system without a phase-locked loop provided by the embodiments of the present application comprises: a plurality of relay stations cascaded in sequence through optical fiber transmission links; in each relay station, first, the current optical frequency signal emitted by the current regenerative cavity stabilized laser and the optical frequency signal transmitted by the previous relay station are beat through the internal first photodetector to obtain a signal of frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in the current relay station and the previous relay station; then, the data interaction unit in the internal part mixes and sums the received noise signal added by the previous optical fiber transmission link, the signal of frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in each two adjacent relay stations, and the signal of frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in the current relay station and the previous relay station to obtain a mixed beat frequency signal; finally, the first acousto-optic modulator is driven based on the mixed beat frequency signal to perform frequency shift compensation; in this way, not only can the noise accumulation in the signal transmission process in the conventional phase-locked loop scheme be completely eliminated, so that the noise term in the optical frequency signal output by each relay station to the user end is completely cancelled, that is, the user end is provided with a high-precision original optical frequency signal, but also the long-distance and high-precision optical frequency transmission can be realized on the basis of reducing the complexity of system design.

[0144] Embodiment 2

[0145] Referring to Figure 4 As shown in the figure, it is a flowchart of a method for optical fiber optical frequency relay transmission without phase-locked loop provided by an embodiment of the present application; the method is applied to any of the above-mentioned optical fiber optical frequency relay transmission systems, and the method comprises the following steps:

[0146] Step 401, for each relay station, the signal transmitted by the upper-level relay station is split by the demultiplexing system to obtain the optical signal transmitted by the upper-level relay station and transmitted to the data interaction unit, and the optical frequency signal transmitted by the upper-level relay station and transmitted to the first photodetector.

[0147] The optical signal comprises the noise signal of the preceding optical fiber transmission link, and the signal of the frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized laser in each two adjacent relay stations.

[0148] Step 402, the regenerative cavity stabilized laser in the current level emits a current-level optical frequency signal, and the current-level optical frequency signal is transmitted to the next-level relay station through the multiplexing system.

[0149] The frequency of the current-level optical frequency signal is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the upper-level relay station.

[0150] Step 403, the first photodetector is used to beat the current-level optical frequency signal and the optical frequency signal transmitted by the upper-level relay station to obtain a current-level beat signal.

[0151] Step 404, the data interaction unit is used to mix and sum the current-level beat signal and the optical signal transmitted by the upper-level relay station to obtain a mixed beat signal, and the mixed beat signal and the optical signal transmitted by the upper-level relay station are transmitted to the next-level relay station through the multiplexing system.

[0152] Step 405, the first acousto-optic modulator is used to shift the frequency of the current-level optical frequency signal based on the mixed beat signal to obtain a current-level optical frequency signal which is the same as the original optical frequency signal of the optical fiber optical frequency relay transmission system, and the current-level optical frequency signal is transmitted to the user end.

[0153] It should be noted that the description of the method embodiment is similar to the description of the above-mentioned system embodiment, and has similar beneficial effects as the system embodiment. For technical details not disclosed in the system and method embodiments of the present application, please refer to the description of the system embodiment of the present application for understanding.

[0154] Those skilled in the art will appreciate that embodiments of the application can be devised for a method, a system, or a computer program product. Accordingly, the present application can be embodied in the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application can take the form of a computer program product on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROMs, optical storage devices, etc.) embodying computer readable program code.

[0155] The present application is described in reference to the flowchart and / or block diagrams of the method, apparatus (system) and computer program product according to embodiments of the application. It will be understood that each block of the flowchart and / or block diagrams, and combinations of blocks in the flowchart and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer, special purpose computer, embedded processing device or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0156] These computer program instructions can also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the function specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0157] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks. Figure 1 one or more functions specified in the flowchart and / or block diagram block or blocks.

[0158] Finally, it should be noted that the above-mentioned embodiments are merely intended for describing the technical solutions of the present application, but not for limiting it. Although the present application is described in detail with reference to the above embodiments, those skilled in the field should understand that the specific embodiments of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and any modification or equivalent replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. An optical fiber optic frequency relay transmission system without a phase-locked loop, characterized in that, The application relates to a multi-stage relay station cascaded through optical fiber transmission links in sequence, wherein each stage of the relay station comprises: an and wave division system for splitting the signal transmitted by the previous stage of the relay station to obtain an optical signal transmitted by the previous stage of the relay station to a data interaction unit and an optical frequency signal transmitted by the previous stage of the relay station to a first photoelectric detector; wherein the optical signal comprises a noise signal of a previous optical fiber transmission link and a signal of a frequency difference between optical frequency signals emitted by regenerative cavity stabilized lasers in every two adjacent relay stations of the previous optical fiber transmission link; a current regenerative cavity stabilized laser for emitting a current optical frequency signal and transmitting the current optical frequency signal to a next stage of the relay station through the and wave division system; wherein the frequency of the current optical frequency signal is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the previous stage of the relay station; the first photoelectric detector for beating the current optical frequency signal and the optical frequency signal transmitted by the previous stage of the relay station to obtain a current beat frequency signal; the data interaction unit for mixing and summing the current beat frequency signal and the optical signal transmitted by the previous stage of the relay station to obtain a mixed beat frequency signal and transmitting the mixed beat frequency signal and the optical signal transmitted by the previous stage of the relay station to the next stage of the relay station through the and wave division system; the first acousto-optic modulator for frequency shifting the current optical frequency signal based on the mixed beat frequency signal to obtain a current optical frequency signal identical to the original optical frequency signal of the optical fiber optical frequency relay transmission system and transmitting the current optical frequency signal to a user end. Each stage of the relay station further comprises a first optical fiber coupler, a second optical fiber coupler, a third optical fiber coupler, a fourth optical fiber coupler and a sending end acousto-optic modulator; 2. The optical fiber optic frequency relay transfer system of claim 1, wherein, the current regenerative cavity stabilized laser is further configured to transmit the current optical frequency signal to the first photoelectric detector through the fourth optical fiber coupler, the second optical fiber coupler and the first optical fiber coupler in sequence and transmit the current optical frequency signal to the sending end acousto-optic modulator through the fourth optical fiber coupler, the second optical fiber coupler and the third optical fiber coupler in sequence; the sending end acousto-optic modulator is configured to positively frequency shift the current optical frequency signal and transmit the positively frequency shifted current optical frequency signal to an optical fiber transmission link between the relay station and the next stage of the relay station through the and wave division system. Each stage of the relay station further comprises a second photoelectric detector and a two-frequency division processor; 3. The optical fiber optic frequency relay transfer system of claim 2, wherein, the third optical fiber coupler is configured to reflect the current optical frequency signal transmitted through the fourth optical fiber coupler and the second optical fiber coupler to the second photoelectric detector and reflect a current feedback optical signal transmitted through the and wave division system and the sending end acousto-optic modulator to the second photoelectric detector by using the connected second 45-degree Faraday rotator; wherein the current feedback optical signal is a feedback optical signal transmitted between the relay station and the next stage of the relay station; the second photoelectric detector is configured to beat the current optical frequency signal and the current feedback optical signal to obtain a feedback beat frequency signal and transmit the feedback beat frequency signal to the two-frequency division processor; ​ The frequency division processor is configured to process the feedback beat frequency signal to obtain a noise signal of the optical fiber transmission link between the relay station and a next-level relay station, and transmit the noise signal of the optical fiber transmission link between the relay station and the next-level relay station to the data interaction unit for storage through the frequency counting unit. The data interaction unit is further configured to transmit the noise signal of the optical fiber transmission link between the relay station and the next-level relay station to the next-level relay station through the wavelength division system.

4. The optical fiber optic frequency relay transfer system of claim 3, wherein, Each level of the relay station further comprises a receiving end acousto-optic modulator. The wavelength division demodulation system is configured to split the signal transmitted by the previous-level relay station to obtain an optical signal transmitted by the previous-level relay station to the data interaction unit, and a to-be-shifted optical frequency signal transmitted by the previous-level relay station to the receiving end acousto-optic modulator. The receiving end acousto-optic modulator is configured to perform positive frequency shift on the to-be-shifted optical frequency signal transmitted by the previous-level relay station to obtain an optical frequency signal transmitted by the previous-level relay station to the first optical fiber coupler. The first optical fiber coupler is configured to reflect the optical frequency signal transmitted by the previous-level relay station to the first photoelectric detector through the connected first 45-degree Faraday rotator, and transmit the optical frequency signal transmitted by the previous-level relay station to the transmission link between the previous-level relay station and the relay station through the receiving end acousto-optic modulator and the wavelength division demodulation system.

5. The fiber optic frequency relay transfer system of claim 1, wherein, The relay station is an Nth-level relay station, the optical signal transmitted by the previous-level relay station is an optical signal transmitted by an (N-1) th-level relay station, and N is an integer greater than 2. The noise signal of the preceding optical fiber transmission link included in the optical signal transmitted by the (N-1) th-level relay station is: ； in, For fiber optic transmission links between transmitting equipment and the first-level relay station in a fiber optic frequency relay system; for Additional noise signals on; and These are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the receiving end, respectively; and These are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the transmitting end, respectively; It is a time variable; For the fiber optic transmission link between the first-level relay station and the second-level relay station; for Additional noise signals on; For the fiber optic transmission link between the (N-1)th level relay station and the Nth level relay station; for Additional noise signals on the signal; each relay station is equipped with a receiver-end acousto-optic modulator and a transmitter-end acousto-optic modulator. For the fiber optic transmission link between the transmitting device and the first-level relay station; for Additional phase noise; For the fiber optic transmission link between the first-level relay station and the second-level relay station; for Additional phase noise; For the fiber optic transmission link between the (N-1)th level relay station and the Nth level relay station; for Additional phase noise on the surface.

6. The fiber optic frequency relay transfer system of claim 5, wherein, The signal of the frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in each two adjacent relay stations included in the optical signal transmitted by the (N-1) th-level relay station is: ； wherein is a first order beat frequency signal output by a first photodetector within the first repeater station; and are the angular frequency and phase, respectively, of the optical frequency signal output by the regenerative cavity stabilized laser within the first repeater station; and are the angular frequency and phase, respectively, of the original optical frequency signal; is a second order beat frequency signal output by a first photodetector within the second repeater station; and are the angular frequency and phase, respectively, of the optical frequency signal output by the regenerative cavity stabilized laser within the second repeater station; is an N-1 order beat frequency signal output by a first photodetector within the N-1 repeater station; and are the angular frequency and phase, respectively, of the optical frequency signal output by the regenerative cavity stabilized laser within the N-1 repeater station; and are the angular frequency and phase, respectively, of the optical frequency signal output by the regenerative cavity stabilized laser within the N-2 repeater station; is an optical fiber transmission link between the N-2 repeater station and the N-1 repeater station; is additional phase noise on 7. The optical fiber optic frequency relay transfer system of claim 5 or 6, wherein, The first photodetector outputs a beat signal of this stage Is: ； wherein, and ωNand φNare the angular frequency and phase of the optical frequency signal output by the regenerative cavity stabilized laser in the Nth relay station, respectively; and ωN-1and φN-1are the angular frequency and phase of the optical frequency signal output by the regenerative cavity stabilized laser in the Nth-1 relay station, respectively.

8. The optical fiber optic frequency relay transfer system of claim 1, wherein, The optical fiber optical frequency relay transmission system further comprises a sending device, the sending device is connected with the first-level relay station, the previous-level relay station corresponding to the first-level relay station is the sending device, and an original cavity stabilized laser in the sending device emits an original optical frequency signal; the sending device comprises: Primary cavity stabilized laser for emitting a primary optical frequency signal : ； wherein and are the angular frequency and phase of the original optical frequency signal, respectively; is the time variable; a primary photodetector for frequency mixing the primary optical frequency signal and the feedback optical signal between the transmitting device and the first stage relay station to obtain a primary beat frequency signal : ； wherein and are the angular frequency and phase of the acoustic modulation signal of the receiving end acousto-optic modulator in the first stage relay, respectively; and are the angular frequency and phase of the acoustic modulation signal of the transmitting end acousto-optic modulator in the transmitting device, respectively; is a time variable; is an optical fiber transmission link between the transmitting device and the first stage relay; is additional phase noise on The original frequency division processor is configured to process the original beat frequency signal to obtain a noise signal of an optical fiber transmission link between the sending device and the first-level relay station. The original data interaction unit is configured to receive and store the noise signal of the optical fiber transmission link between the sending device and the first-level relay station through the original frequency counting unit, and transmit the noise signal of the optical fiber transmission link between the sending device and the first-level relay station to the first-level relay station through the original wavelength division system.

9. The optical fiber optic frequency relay transfer system of claim 1, wherein, Each level of the relay station further comprises a global positioning system (GPS) servo rubidium clock configured to control synchronization of the transmission signal between the relay station and the next-level relay station with a second pulse. The optical fiber optical frequency relay transmission method is applied to the optical fiber optical frequency relay transmission system as claimed in any one of claims 1 to 9, and the method comprises:

10. A method of optical fiber-optical frequency relay transfer without a phase-locked loop, characterized by, ​ For each level of relay station, the signal transmitted by the upper level relay station is split by the demultiplexing system to obtain the optical signal transmitted by the upper level relay station to the data interaction unit, and the optical frequency signal transmitted by the upper level relay station to the first photodetector; wherein the optical signal includes: the noise signal of the pre-order optical fiber transmission link, the frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized laser in each two adjacent relay stations; The regenerative cavity stabilized laser in the current level emits a current level optical frequency signal, and the current level optical frequency signal is transmitted to the next level relay station through the wavelength division system; wherein the frequency of the current level optical frequency signal is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the upper level relay station; The first photodetector is used to beat the current level optical frequency signal and the optical frequency signal transmitted by the upper level relay station to obtain a current level beat frequency signal; The data interaction unit is used to mix and sum the current level beat frequency signal and the optical signal transmitted by the upper level relay station to obtain a mixed beat frequency signal, and the mixed beat frequency signal and the optical signal transmitted by the upper level relay station are transmitted to the next level relay station through the wavelength division system; The first acousto-optic modulator is used to shift the frequency of the current level optical frequency signal based on the mixed beat frequency signal to obtain a current level optical frequency signal which is the same as the original optical frequency signal of the optical fiber optical frequency relay transmission system, and the current level optical frequency signal is transmitted to the user end.

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