Optical fiber optical frequency relay transmission system and method without phase-locked loop

Abstract

The invention relates to the technical field of optical fiber communication, and discloses an optical fiber optical frequency relay transmission system and method without a phase-locked loop. The optical fiber optical frequency relay transmission system comprises multiple stages of relay stations which are sequentially cascaded through an optical fiber transmission link, and for each stage of relay station, a first photoelectric detector is used for carrying out beat frequency processing on a current-stage optical frequency signal sent by a current-stage regeneration cavity-stabilized laser and an optical frequency signal received from a previous-stage relay station; frequency mixing and summation are carried out on the current-level beat frequency signal and an optical frequency signal transmitted by an upper-level relay station through the data interaction unit, so that noise accumulation generated in a signal transmission process in a traditional phase-locked loop scheme can be thoroughly eliminated; therefore, the noise item in the optical frequency signal output to the user side is completely counteracted, that is, the high-precision original optical frequency signal is provided for the user side, and long-distance and 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 field of optical fiber communication technology, and in particular to an optical fiber optical frequency relay transmission system and method that does not require a phase-locked loop. Background Art

[0002] With the rapid development of atomic cooling technology, the stability and uncertainty of optical clock systems have reached 10 -18 The magnitude of the time-frequency comparison is very important in the development of gravitational wave detection, precision physical measurement and geodesy. -15 / day, which is no longer enough to meet the transmission and comparison requirements of optical clock signals. Due to the low loss, high bandwidth, and anti-interference characteristics of optical fiber, optical frequency transmission technology based on optical fiber is an important means to achieve long-distance transmission of high-precision optical clock signals.

[0003] During the transmission of optical signals along optical fibers, Doppler noise cancellation techniques are used to detect and eliminate the additive phase noise of the fiber. To further improve noise suppression, a fiber-optic regeneration relay system is used to achieve segmented detection and control of link noise. This approach utilizes a narrow-linewidth laser in the system to phase-lock the transmitted optical signal, amplifying and regenerating the transmitted optical signal. However, this solution causes the noise of the regenerated laser in the relay system to accumulate as the number of cascaded stages increases, further broadening the laser linewidth. When the noise level of the regenerated laser exceeds the additive phase noise of the optical fiber link, errors in fiber noise measurement can occur and limit the transmission distance of the relay system. Summary of the Invention

[0004] In order to solve the above-mentioned problems of the prior art, the embodiments of the present application provide a fiber optic optical frequency relay transmission system and method that does not require a phase-locked loop, aiming to completely eliminate the noise accumulation generated during the signal transmission process in the traditional phase-locked loop solution, thereby achieving the complete cancellation of the noise terms in the optical frequency signal output by each level of relay station to the user end, that is, providing the user end with a high-precision original optical frequency signal.

[0005] On the one hand, the present application provides a fiber optical frequency relay transmission system without a phase-locked loop, comprising: a plurality of relay stations cascaded sequentially through an optical fiber transmission link, each relay station comprising: A wavelength division multiplexing system is configured to split the signal transmitted by the previous relay station to obtain an optical signal transmitted by the previous relay station and transmitted to the data exchange unit, and an optical frequency signal transmitted by the previous relay station and transmitted to the first photodetector; wherein the optical signal includes: a noise signal of the preceding optical fiber transmission link, and a signal indicating the frequency difference between the optical frequency signals emitted by the regenerative cavity-stabilized lasers in each of two adjacent relay stations; The regenerative cavity-stabilized laser of this stage is used to emit the optical frequency signal of this stage and transmit the optical frequency signal of this stage to the next stage relay station through the sum wavelength division system; wherein the frequency of the optical frequency signal of this stage is greater than the frequency of the optical frequency signal emitted by the regenerative cavity-stabilized laser in the previous stage relay station; The first photoelectric detector is used to beat the optical frequency signal of the current stage and the optical frequency signal transmitted by the previous stage relay station to obtain the beat frequency signal of the current stage; A data exchange unit is used to mix and sum the beat signal of this stage and the optical signal transmitted by the previous stage relay station to obtain a mixed beat signal, and transmit the mixed beat signal and the optical signal transmitted by the previous stage relay station to the next stage relay station through the sum wavelength division system; The first acousto-optic modulator is used to frequency-shift the current-stage optical frequency signal based on the mixed beat frequency signal to obtain the current-stage optical frequency signal that is identical to the original optical frequency signal of the optical fiber optical frequency relay transmission system, and transmit the current-stage optical frequency signal to the user end.

[0006] Optionally, each relay station further includes: a first optical fiber coupler, a second optical fiber coupler, a third optical fiber coupler, a fourth optical fiber coupler, and a transmitting end acousto-optic modulator; The regenerative cavity-stabilized laser of this stage is further used to transmit the optical frequency signal of this stage to the first photodetector through the fourth optical fiber coupler, the second optical fiber coupler and the first optical fiber coupler in sequence, and to transmit the optical frequency signal of this 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 sequence; The acousto-optic modulator at the transmitting end is used to perform positive frequency shift on the optical frequency signal of this level, and transmit the positive frequency shifted optical frequency signal of this level through the sum wavelength division multiplexing system to the optical fiber transmission link between the relay station and the next level relay station.

[0007] Optionally, each stage of the relay station further includes: a second photoelectric detector, a two-frequency division processor; a third fiber coupler, configured to reflect the optical frequency signal of the current stage transmitted through the fourth fiber coupler and the second fiber coupler to the second photodetector via the connected second 45-degree Faraday rotator, and to reflect the feedback optical signal of the current stage transmitted through the sum wavelength division multiplexing 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; The second photoelectric detector is used to perform beat frequency processing on the optical frequency signal of the current stage and the feedback optical signal of the current stage to obtain a feedback beat frequency signal, and transmit the feedback beat frequency signal to the binary frequency division processor; A two-frequency division processor is used to process the feedback beat frequency signal to obtain a noise signal of the optical fiber transmission link between the relay station and the next-stage relay station, and transmit the noise signal of the optical fiber transmission link between the relay station and the next-stage relay station to the data exchange unit for storage through the frequency counting unit; The data interaction unit is also used 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.

[0008] Optionally, each stage of the relay station further includes: a receiving end acousto-optic modulator; The demultiplexing system is specifically used to split the signal transmitted by the upper relay station to obtain the optical signal transmitted by the upper relay station to the data exchange unit, and the optical frequency signal to be frequency-shifted transmitted by the upper relay station to the receiving end acousto-optic modulator; The receiving end acousto-optic modulator is used to perform positive frequency shift on the optical frequency signal to be frequency-shifted transmitted by the previous relay station to obtain the optical frequency signal transmitted by the previous relay station to be transmitted to the first optical fiber coupler; The first optical fiber coupler is used to reflect the optical frequency signal transmitted by the previous relay station to the first photodetector using the connected first 45-degree Faraday rotator, and to transmit the optical frequency signal transmitted by the previous relay station to the transmission link between the previous relay station and the relay station through the receiving end acousto-optic modulator and the wavelength division multiplexing system.

[0009] Optionally, the relay station is an N-th level relay station, and the optical signal transmitted by the previous level relay station is an optical signal transmitted by the N-1-th level relay station, where 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 relay station is: ; in, It is an optical fiber transmission link between the transmitting device and the first-level relay station in the optical fiber frequency relay transmission system; for Additional noise signal on ; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the receiving end respectively; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the transmitting end respectively; is the time variable; It is the optical fiber transmission link between the first-level relay station and the second-level relay station; for Additional noise signal on ; It is the optical fiber transmission link between the N-1th level relay station and the Nth level relay station; for Additional noise signals on the relay station; each relay station is equipped with a receiving end acousto-optic modulator and a transmitting end acousto-optic modulator; It is the optical fiber transmission link between the sending device and the first-level relay station; for The additional phase noise on It is the optical fiber transmission link between the first-level relay station and the second-level relay station; for The additional phase noise on It is the optical fiber transmission link between the N-1th level relay station and the Nth level relay station; for The additional phase noise on

[0010] Optionally, the optical signal transmitted by the N-1th level relay station includes a signal of frequency difference information between optical frequency signals emitted by regenerative cavity-stabilized lasers in every two adjacent relay stations in the preceding sequence: ; in, The first-stage beat frequency signal output by the first photodetector in the first-stage relay station; and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the first-stage relay station respectively; and are the angular frequency and phase of the original optical frequency signal respectively; The second-stage beat frequency signal output by the first photodetector in the second-stage relay station; and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the second-stage relay station respectively; The N-1th level beat frequency signal output by the first photodetector in the N-1th level relay station; and are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-1th relay station; and are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-2th relay station; It is the optical fiber transmission link between the N-2th level relay station and the N-1th level relay station; for The additional phase noise on

[0011] Optionally, the beat frequency signal output by the first photodetector is for: ; in, and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the Nth relay station respectively; and They are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-1th relay station.

[0012] Optionally, the fiber optical frequency relay transmission system further includes: a sending device, the sending device being connected to the first-stage relay station, the first-stage relay station corresponding to the previous-stage relay station being the sending device, and the original cavity-stabilized laser in the sending device emitting an original optical frequency signal; the sending device includes: Original cavity-stabilized laser for emitting original optical frequency signals : ; in, and are the angular frequency and phase of the original optical frequency signal respectively; is the time variable; The original photoelectric detector is used to beat the original optical frequency signal and the feedback optical signal between the transmitting device and the first-stage relay station to obtain the original beat frequency signal : ; in, 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 respectively the angular frequency and phase of the acoustic wave modulation signal of the transmitting end acousto-optic modulator in the transmitting device; is the time variable; It is the optical fiber transmission link between the sending device and the first-level relay station; for The additional phase noise on An original two-frequency division processor is used to process the original beat frequency signal to obtain a noise signal of the optical fiber transmission link between the transmitting device and the first-stage relay station; The original data interaction unit is used 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 and wavelength division system.

[0013] Optionally, each level of relay station further includes: The GPS servo rubidium clock of the global positioning system is used to control the transmission signal and second pulse synchronization between the relay station and the next level relay station.

[0014] On the other hand, an embodiment of the present application further provides a fiber optic frequency relay transmission method that does not require a phase-locked loop. The fiber optic frequency relay transmission method is applied to any of the above-mentioned fiber optic frequency relay transmission systems, and the method includes: For each relay station, the signal transmitted by the previous relay station is split using a wavelength division multiplexing (WDM) system to obtain an optical signal transmitted by the previous relay station that is transmitted to the data exchange unit, and an optical frequency signal transmitted by the previous relay station that is transmitted to the first photodetector. The optical signal includes: a noise signal of the preceding optical fiber transmission link, and a signal indicating the frequency difference between optical frequency signals emitted by regenerative cavity-stabilized lasers in each of two adjacent relay stations. emitting an optical frequency signal of the current stage using a regenerative cavity-stabilized laser of the current stage, and transmitting the optical frequency signal of the current stage to a next-stage relay station through a sum wavelength division multiplexing 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 previous-stage relay station; Using the first photoelectric detector, the optical frequency signal of the current stage and the optical frequency signal transmitted by the previous stage relay station are beat to obtain the beat frequency signal of the current stage; The data exchange unit is used to mix and sum the beat signal of the current stage and the optical signal transmitted by the previous stage relay station to obtain a mixed beat signal, and the mixed beat signal and the optical signal transmitted by the previous stage relay station are transmitted to the next stage relay station through the sum wavelength division system; The first acousto-optic modulator is used to frequency-shift the current-level optical frequency signal based on the mixed beat frequency signal to obtain the current-level optical frequency signal that is identical to the original optical frequency signal of the fiber optical frequency relay transmission system, and the current-level optical frequency signal is transmitted to the user end.

[0015] The technical solution provided by this application can achieve at least the following beneficial effects: The embodiments of the present application provide a fiber optic frequency relay transmission system and method that does not require a phase-locked loop. The fiber optic frequency relay transmission system includes: a multi-stage relay station cascaded in sequence through an optical fiber transmission link, and each stage relay station includes: a wavelength division multiplexing system for splitting the signal transmitted by the previous stage relay station to obtain the optical signal transmitted by the previous stage relay station to the data exchange unit, and the optical frequency signal transmitted by the previous stage relay station to the first photodetector; wherein the optical signal includes: a noise signal of the preceding optical fiber transmission link, 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 preceding sequence; the regenerative cavity stabilized laser of this stage is used to emit the optical frequency signal of this stage and transmit the optical frequency signal of this stage to the next stage relay through the wavelength division multiplexing system. station; wherein, the frequency of the optical frequency signal at this level is greater than the frequency of the optical frequency signal emitted by the regenerative cavity-stabilized laser in the upper-level relay station; a first photodetector is used to beat the optical frequency signal at this level and the optical frequency signal transmitted by the upper-level relay station to obtain the beat frequency signal at this level; a data interaction unit is used to mix and sum the beat frequency signal at this level and the optical signal transmitted by the upper-level relay station to obtain a mixed beat frequency signal, and transmit the mixed beat frequency signal and the optical signal transmitted by the upper-level relay station to the next-level relay station through the sum wavelength division multiplexing system; a first acousto-optic modulator is used to frequency-shift the optical frequency signal at this level based on the mixed beat frequency signal to obtain an optical frequency signal at this level that is the same as the original optical frequency signal of the optical fiber optical frequency relay transmission system, and transmit the optical frequency signal at this level to the user end. In this way, in each relay station, first, the optical frequency signal of the current stage emitted by the regenerative cavity stabilized laser of the current stage and the optical frequency signal transmitted by the previous relay station are beat by the first photoelectric detector inside the relay station, and the frequency difference information signal between the optical frequency signal emitted by the regenerative cavity stabilized laser in the current relay station and the previous relay station is obtained; then, the noise signal attached to the received preceding optical fiber transmission link, the frequency difference information signal between the optical frequency signals emitted by the regenerative cavity stabilized laser in each two adjacent relay stations in the preceding sequence, and the frequency difference information signal between the optical frequency signals emitted by the regenerative cavity stabilized laser in the current relay station and the previous relay station are received through the internal data interaction unit. The frequency difference information between the optical frequency signals emitted by the regenerative cavity-stabilized laser in the first-level relay station is mixed and summed to obtain a mixed beat signal; finally, the first acousto-optic modulator is driven to perform frequency shift compensation based on the mixed beat signal; in this way, the noise accumulation generated in the signal transmission process in the traditional phase-locked loop scheme can be completely eliminated, so that the noise term in the optical frequency signal output by each level of relay station to the user end is completely offset, that is, a high-precision original optical frequency signal is provided to the user end, and long-distance, high-precision optical frequency transmission can be achieved on the basis of reducing the complexity of system design.

[0016] It should be understood that the above general description and the following detailed description are merely exemplary and explanatory, and are not intended to limit the technical solutions provided by the embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0018] Figure 1 A schematic structural diagram of a fiber optic frequency relay transmission system without a phase-locked loop provided in an embodiment of the present application; Figure 2 A schematic diagram of the specific structure of a relay station in actual application included in the fiber optic frequency relay transmission system without a phase-locked loop provided in an embodiment of the present application; Figure 3 A schematic diagram of the specific structure of a transmitting device in a fiber-optic frequency relay transmission system without a phase-locked loop provided in an embodiment of the present application in actual application; Figure 4 A flowchart of a fiber optic frequency relay transmission method without a phase-locked loop is provided in an embodiment of the present application. DETAILED DESCRIPTION

[0019] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0020] In the following description, reference is made to “some embodiments”, which describes a subset of all possible embodiments, but it will be understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0021] In the following description, the terms "first\second\third" are merely used to distinguish similar objects and do not represent a specific ordering of the objects. It is understandable that "first\second\third" can be interchanged with a specific order or sequence where permitted, so that the embodiments of the present invention described herein can be implemented in an order other than that illustrated or described herein.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art in the art of the embodiments of the present invention. The terms used herein are only for the purpose of describing the embodiments of the present invention and are not intended to limit the embodiments of the present invention.

[0023] Example 1 See also Figure 1 FIG. 1 is a schematic diagram of a fiber optic frequency relay transmission system without a phase-locked loop provided in an embodiment of the present application. The fiber optic frequency relay transmission system 10 includes: a plurality of relay stations cascaded sequentially through optical fiber transmission links, Figure 1 The relay station 200 and the relay station 300 of the upper level of the relay station 100 are shown. Figure 1 The relay station 100 shown in FIG is used as an example for description, wherein each level of the relay station 100 includes: The wavelength division multiplexing system 101 is used to split the signal transmitted by the upper relay station 200 to obtain the optical signal transmitted by the upper relay station 200 and transmitted to the data exchange unit 104, and the optical frequency signal transmitted by the upper relay station 200 and transmitted to the first photodetector 103.

[0024] The optical signal includes: a noise signal of the preceding optical fiber transmission link and a signal of frequency difference information between optical frequency signals emitted by regenerative cavity stabilized lasers in every two adjacent relay stations.

[0025] The regenerative cavity stabilized laser 102 of this stage is used to emit the optical frequency signal of this stage and transmit the optical frequency signal of this stage to the next stage relay station 300 through the wavelength division system 106.

[0026] The frequency of the optical frequency signal at this stage is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the relay station 200 at the previous stage.

[0027] The first photodetector 103 is used to beat the optical frequency signal of the current stage and the optical frequency signal transmitted by the previous stage relay station 200 to obtain the beat frequency signal of the current stage; The data exchange unit 104 is configured to mix and sum the beat signal of the current stage and the optical signal transmitted by the previous stage relay station 200 to obtain a mixed beat signal, and transmit the mixed beat signal and the optical signal transmitted by the previous stage relay station 200 to the next stage relay station 300 via the sum wavelength division multiplexing system 106; The first acousto-optic modulator 105 is used to frequency-shift the current optical frequency signal based on the mixed beat frequency signal to obtain a current optical frequency signal that is identical to the original optical frequency signal of the fiber optical frequency relay transmission system 10, and transmit the current optical frequency signal to the user end 400.

[0028] In some embodiments of the present application, the relay station 200, the relay station 100 and the relay station 300 in the fiber optic optical frequency relay transmission system 10 are cascaded in sequence through a fiber optic transmission link; wherein, the signal transmitted by the relay station 200 through the fiber optic transmission link enters the relay station 100, and the signal is split by the wavelength division multiplexing system 101, and 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.

[0029] In some embodiments of the present application, the optical signal transmitted to the data exchange unit 104 includes: a noise signal of the preceding optical fiber transmission link, and a signal indicating the frequency difference between the optical frequency signals emitted by the regenerative cavity-stabilized lasers in each of two adjacent relay stations. In other words, if the relay station 100 is a third-level relay station in the fiber-optic frequency relay transmission system 10, then the optical signal it receives is transmitted by the second-level relay station in the fiber-optic frequency relay transmission system 10. The noise signals of the preceding optical fiber transmission link included in the optical signal include: a noise signal of the optical fiber transmission link between the transmitting device in the fiber-optic frequency relay transmission system 10 and the first-level relay station, a noise signal of the optical fiber transmission link between the first-level relay station and the second-level relay station, and a 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, its preceding optical fiber transmission link includes: the optical fiber transmission link between the sending device in the optical fiber optical frequency relay transmission system 10 and the first-level relay station, 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 optical signal includes the preceding frequency difference information signal between the optical frequency signals emitted by the regenerative cavity-stabilized lasers in each two adjacent relay stations, including: the frequency difference information signal between the sending device and the optical frequency signal emitted by the regenerative cavity-stabilized laser in the first-level relay station, and the frequency difference information signal between the optical frequency signals emitted by the regenerative cavity-stabilized lasers in the first-level relay station and the second-level relay station.

[0030] It should be noted that the fiber optical frequency relay transmission system 10 also includes a sending device ( Figure 1 (not shown in the figure), the sending device is connected to the first-level relay station in the fiber optical frequency relay transmission system 10 through an optical fiber transmission link, that is, the upper-level relay station corresponding to the first-level relay station is the sending device.

[0031] In some embodiments of the present application, the relay station 100 may not only include the above-mentioned: wavelength division multiplexing (WDM) system 101, the local regenerative cavity stabilized laser 102, the first photodetector (PD) 103, the data exchange unit 104, the first acousto-optic modulator 105 and the sum wavelength division system 106; it may also further include: multiple optical fiber couplers (OC), a binary frequency processor (f / 2), multiple 45-degree Faraday Rotation Mirrors (FM), a frequency counting unit, etc., to specifically implement the transmission of related signals.

[0032] In some embodiments of the present application, the regenerative cavity stabilized laser 102 of this stage is taken as the N-stage regenerative cavity stabilized laser (Laser N) in the N-stage relay station in the fiber optical frequency relay transmission system 10, which can emit the optical frequency signal of this stage. It can be expressed by formula (1): Formula (1); in, and The angular frequency and phase of the optical signal emitted by the N-stage regenerative cavity stabilized laser; is the time variable.

[0033] In some embodiments of the present application, the regenerative cavity-stabilized laser in each relay station in the fiber-optic frequency relay transmission system 10 emits an optical signal with a frequency greater than that of the optical signal emitted by the regenerative cavity-stabilized laser in the previous relay station. Furthermore, the optical signal emitted by the regenerative cavity-stabilized laser in the fiber-optic frequency relay transmission system 10 can have a frequency range of 5 MHz to 50 MHz.

[0034] In some embodiments of the present application, the data exchange unit 104 may further include: an optical receiver, a data processor, and an optical transmitter.

[0035] In some embodiments of the present application, each relay station 100 further includes: a first fiber coupler, a second fiber coupler, a third fiber coupler, a fourth fiber coupler, and a transmitting end acousto-optic modulator ( Figure 1 (neither shown): The regenerative cavity-stabilized laser 102 of this stage is also used to transmit the optical frequency signal of this stage to the first photodetector 103 through the fourth optical fiber coupler, the second optical fiber coupler and the first optical fiber coupler in sequence, and to transmit the optical frequency signal of this 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 sequence.

[0036] The transmitting end acousto-optic modulator is used to perform positive frequency shift on the optical frequency signal of this stage, and transmit the positive frequency shifted optical frequency signal of this stage to the optical fiber transmission link between the relay station 100 and the next stage relay station 300 through the sum wavelength division system 106.

[0037] In some embodiments of the present application, each relay station 100 further includes: a second photodetector, a two-frequency division processor ( Figure 1 (neither shown): The third fiber coupler is configured to reflect the optical frequency signal of the current stage transmitted by the fourth fiber coupler and the second fiber coupler to the second photodetector using the connected second 45-degree Faraday rotator, and to reflect the feedback optical signal of the current stage transmitted through the sum wavelength division multiplexing system 106 and the transmitting-end acousto-optic modulator to the second photodetector.

[0038] The feedback optical signal of this stage is the feedback optical signal transmitted between the relay station 100 and the next-stage relay station 300.

[0039] The second photoelectric detector is used to perform beat frequency processing on the optical frequency signal of the current stage and the feedback optical signal of the current stage to obtain a feedback beat frequency signal, and transmit the feedback beat frequency signal to the binary frequency division processor.

[0040] The binary frequency processor is used to process the feedback beat frequency signal to obtain the 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.

[0041] The data exchange unit 104 is further configured to transmit the noise signal of the optical fiber transmission link between the relay station 100 and the next-stage relay station 300 to the next-stage relay station 300 via the wavelength division multiplexing system 106 .

[0042] Correspondingly, each relay station 100 further includes: a receiving end acousto-optic modulator ( Figure 1 (not shown): The wavelength demultiplexing system 101 is specifically used to split the signal transmitted by the upper-level relay station 200 to obtain the optical signal transmitted by the upper-level relay station 200 and transmitted to the data exchange unit 104, and the optical frequency signal to be frequency-shifted transmitted by the upper-level relay station 200 and transmitted to the receiving-end acousto-optic modulator.

[0043] The acousto-optic modulator at the receiving end is used to perform positive frequency shift on the optical frequency signal to be frequency-shifted transmitted by the upper relay station 200 to obtain the optical frequency signal transmitted by the upper relay station 200 to be transmitted to the first optical fiber coupler.

[0044] The first fiber 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 wavelength division multiplexing system 101.

[0045] In some embodiments of the present application, each stage of relay station 100 further includes: Global Positioning System (GPS) servo rubidium clock ( Figure 1 ), which is used to control the transmission signal between the relay station 100 and the next-stage relay station 300 to be synchronized with the second pulse.

[0046] Here, you can refer to Figure 2 FIG2 is a schematic diagram of the specific structure of a relay station included in a fiber-optic frequency relay transmission system without a phase-locked loop provided in an embodiment of the present application in actual application; wherein, in the fiber-optic frequency relay transmission system without a phase-locked loop, relay station N-1 (N-1th stage relay station), relay station N (Nth stage relay station), and relay station N+1 (N+1th stage relay station) are sequentially cascaded through an optical fiber transmission link; in relay station N: Using WDM1 (corresponding to Figure 1 The wavelength division multiplexing system shown in the figure divides the signal transmitted by the relay station N-1 into signals corresponding to two channels (a first channel and a second channel); wherein the first channel is connected to the data exchange unit N, and the second channel is used to transmit the optical frequency signal transmitted by the relay station N-1.

[0047] Here, the optical frequency signal transmitted by relay station N-1 passes through Figure 2 The AOMR (receiver acousto-optic modulator) shown in the figure performs positive frequency shifting and transmits the positive frequency shifted signal to OC1 (first fiber coupler); wherein, the right end of OC1 is connected to FM1 (first 45-degree Faraday rotator), which transmits the positive frequency shifted signal to PD1 (first photodetector) for processing.

[0048] At the same time, the frequency of the optical signal emitted by Laser N (i.e., the regenerative cavity-stabilized laser in relay station N) is set to be greater than the frequency of the optical signal emitted by the regenerative cavity-stabilized laser in relay station N-1. Here, the N-level optical frequency signal emitted by Laser N is divided into three parts through the OC4 (fourth fiber coupler), that is, transmitted through three transmission channels, where: The first transmission channel: passes through OC2 (the second optical fiber coupler) and OC1 and enters PD1. In this way, PD1 will perform beat frequency processing on the optical frequency signal and the positive frequency-shifted signal mentioned above.

[0049] The second transmission channel: through OC3 (i.e. an optical fiber coupler), AOML (transmitter acousto-optic modulator) and WDM2 (corresponding Figure 1 The wavelength division system shown in ); wherein, the OC3 is connected to FM2 (the second 45-degree Faraday rotator).

[0050] The third transmission channel is transmitted to AOM3 (the first acousto-optic modulator), which negatively shifts the frequency of the received signal.

[0051] Here, the data exchange unit N may further include: an optical receiver, a data processor, and an optical transmitter.

[0052] Here, PD1 will get the signal from the beat frequency through Figure 2 The transmission path shown is: Band-Pass Filter (BPF) 1 → Line Amplifier 1 (LA) → Frequency Counting Unit → Data Interchange Unit N); At the same time, the data exchange unit N can also be transmitted through Figure 2 The Data Distribution Service (DDS) shown drives AOM3 to negatively shift the frequency of the received signal (the signal sent by Laser N transmitted through OC4).

[0053] In addition, the internal hardware structure of relay station N+1 is exactly the same as that of relay station N. It will also synchronously feed back the signal transmitted by relay station N to relay station N through the internal OC1 connected to FM1. That is, relay station N will receive the feedback signal at WDM2 and transmit the feedback signal to PD2 through AOML (which will perform positive frequency shift on the received signal) and OC3 connected to FM2. In this way, PD2 will beat the received feedback signal with the optical frequency signal to obtain a beat signal, and then transmit the beat signal through Figure 2 The transmission channel shown is: BPF2→f / 2→frequency counting unit→data exchange unit N for transmission.

[0054] refer to Figure 2 As shown, the relay station N further includes a GPS servo rubidium clock for controlling the transmission signal and second pulse synchronization between the relay station N and the relay station N+1.

[0055] In some embodiments of the present application, the output corresponding to the GPS servo rubidium clock includes: a signal with a frequency of 10 MHz, a second pulse signal ( Figure 2 1PPS shown) etc.

[0056] In some embodiments of the present application, the fiber optical frequency relay transmission system further includes: a sending device, the sending device is connected to 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 the original optical frequency signal; Figure 3 FIG. 1 is a schematic diagram of a specific structure of a transmitting device in a fiber optical frequency relay transmission system without a phase-locked loop provided in an embodiment of the present application in actual application; wherein the transmitting device includes: Original cavity-stabilized laser ( Figure 3 Laser shown), used to emit original optical frequency signal : Formula (2); in, and are the angular frequency and phase of the original optical frequency signal respectively; is the time variable.

[0057] Original photodetector ( Figure 3 PD shown in FIG), used to beat the original optical frequency signal and the feedback optical signal between the transmitting device and the first-stage relay station to obtain the original beat frequency signal : Formula (3); in, 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 respectively the angular frequency and phase of the acoustic wave modulation signal of the transmitting end acousto-optic modulator in the transmitting device; is the time variable; It is the optical fiber transmission link between the sending device and the first-level relay station; for The additional phase noise on

[0058] Original divide-by-two processor ( Figure 3f / 2 as shown), 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.

[0059] Raw data interaction unit ( Figure 3 a data interaction unit in the transmission device), configured to receive and store the noise signal of the optical fiber transmission link between the transmitting 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 transmitting device and the first-level relay station to the first-level relay station through the original and wavelength division multiplexing system.

[0060] In some embodiments of the present application, the original two-way frequency division processor ( Figure 3 f / 2) shown as the noise signal of the optical fiber transmission link between the sending device and the first-level relay station transmitted to the data exchange unit : Formula (4).

[0061] Here, the noise signal of the optical fiber transmission link between the sending device and the first-level relay station , will be recorded in real time by the frequency counter in the sending device and transmitted to the next level relay system (first level relay station) through the data interaction unit.

[0062] In other words, in the first-level relay station of the fiber optical frequency relay transmission system, the optical frequency signal (first-level optical frequency signal) output by the regenerative cavity stabilized laser inside it is for: Formula (5); in, and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the first-stage relay station respectively; is the time variable.

[0063] Correspondingly, the first photodetector in the first-stage relay station performs corresponding beat frequency processing on the above-mentioned current-stage optical frequency signal (first-stage optical frequency signal) and the optical signal fed back by the second-stage relay station to obtain the current-stage beat frequency signal (first-stage beat frequency signal). for: Formula (6).

[0064] In this way, the data processing unit inside the first-level relay station Mix and subtract the optical signal sent from the transmitting device to the first-level relay station to obtain the mixed beat frequency signal of this level : Formula (7).

[0065] Here, the optical signal sent from the transmitting device to the first-level relay station can be shown by the following formula (8), which only includes: the noise signal of the optical fiber transmission link between the transmitting device and the first-level relay station (because for the first-level relay station, there is no signal of the frequency difference information between the optical frequency signals emitted by the regenerative cavity-stabilized lasers in each two adjacent relay stations in the previous sequence), that is, as shown in the above formula (4).

[0066] Correspondingly, the mixed beat frequency signal of this level , through the optical transmitter and DDS inside the first-level relay station, drive AOM3 (perform negative frequency shift operation) so that the user end connected to the first-level relay station receives the first-level optical frequency signal : Formula (8).

[0067] In some embodiments of the present application, the relay station is an N-th level relay station, the optical signal transmitted by the previous level relay station is an optical signal transmitted by the N-1-th level relay station, and N is an integer greater than 2. The following formula (9) can be used to express the noise signal of the preceding optical fiber transmission link included in the optical signal transmitted by the N-1-th level relay station: Formula (9); in, It is an optical fiber transmission link between the transmitting device and the first-level relay station in the optical fiber frequency relay transmission system; for Additional noise signal on ; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the receiving end respectively; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the transmitting end respectively; is the time variable; It is the optical fiber transmission link between the first-level relay station and the second-level relay station; for Additional noise signal on ; It is the optical fiber transmission link between the N-1th level relay station and the Nth level relay station; for Additional noise signals on the relay station; each relay station is equipped with a receiving end acousto-optic modulator and a transmitting end acousto-optic modulator; It is the optical fiber transmission link between the sending device and the first-level relay station; for The additional phase noise on It is the optical fiber transmission link between the first-level relay station and the second-level relay station; for The additional phase noise on It is the optical fiber transmission link between the N-1th level relay station and the Nth level relay station; for The additional phase noise on

[0068] Correspondingly, the following formula (10) can be used to express that the optical signal transmitted by the N-1th relay station includes the frequency difference information between the optical frequency signals emitted by the regenerative cavity-stabilized lasers in every two adjacent relay stations: Formula (10); in, The first-stage beat frequency signal output by the first photodetector in the first-stage relay station; and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the first-stage relay station respectively; and are the angular frequency and phase of the original optical frequency signal respectively; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the receiving end respectively; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the transmitting end respectively; is the time variable; It is the optical fiber transmission link between the sending device and the first-level relay station; for The additional phase noise on The second-stage beat frequency signal output by the first photodetector in the second-stage relay station; and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the second-stage relay station respectively; It is the optical fiber transmission link between the first-level relay station and the second-level relay station; for The additional phase noise on The N-1th level beat frequency signal output by the first photodetector in the N-1th level relay station; and are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-1th relay station; and are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-2th relay station; The optical fiber transmission link between the N-2th relay station and the N-1th relay station; for The additional phase noise on

[0069] Continuing from the above description, in the case where the optical signal transmitted by the previous relay station is the optical signal transmitted by the N-1 relay station, and N is an integer greater than 2, the relay station at this level is the N-th relay station, and the beat frequency signal of this level emitted by the first photodetector inside it is It can be expressed by formula (11): Formula (11); in, and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the Nth relay station respectively; and are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-1th relay station; It is the optical fiber transmission link between the N-1th level relay station and the Nth level relay station; for The additional phase noise on and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the receiving end respectively; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the transmitting end, respectively.

[0070] In this way, in the relay station of this level (N-level relay station), the internal data exchange unit will receive the signals described by the above formulas (9) to (11), and perform mixing and summing on the above signals to obtain the mixed beat frequency signal shown in the following formula (12): : Formula (12).

[0071] Here, following the above description, formula (1) shows the optical frequency signal of this level emitted by the regenerative cavity stabilized laser in this level relay station (N level relay station): Here, the obtained mixed beat signal can be used Drive the first acousto-optic modulator in the relay station of this level to Perform frequency shift processing to obtain the same optical frequency signal as the original optical frequency signal of the relay transmission system : Formula (13).

[0072] And the optical frequency signal of this level Delivered to the user, the With the original optical frequency signal same.

[0073] The fiber optic frequency relay transmission system without a phase-locked loop provided by the embodiment of the present application comprises: a multi-stage relay station cascaded in sequence through an optical fiber transmission link; in each stage relay station, first, the optical frequency signal of the current stage emitted by the regenerative cavity stabilized laser of the current stage and the optical frequency signal transmitted by the previous stage relay station are beat by the first photoelectric detector inside the relay station, so as to obtain a signal of frequency difference information between the optical frequency signal emitted by the regenerative cavity stabilized laser in the current relay station and the optical frequency signal emitted by the regenerative cavity stabilized laser in the previous stage relay station; then, the noise signal attached to the received preceding optical fiber transmission link and the optical frequency signal emitted by the regenerative cavity stabilized laser in every two adjacent relay stations in the preceding stage are beat by the internal data interaction unit. The signals of frequency difference information between the optical frequency signals and the signals of frequency difference information between the optical frequency signals emitted by the regenerative cavity-stabilized laser in the current relay station and the previous relay station are mixed and summed to obtain a mixed beat signal; finally, the first acousto-optic modulator is driven to perform frequency shift compensation based on the mixed beat signal; in this way, not only can the noise accumulation generated in the signal transmission process in the traditional phase-locked loop scheme be completely eliminated, thereby achieving complete cancellation of the noise terms in the optical frequency signal output by each relay station to the user end, that is, providing the user end with a high-precision original optical frequency signal, but also long-distance, high-precision optical frequency transmission can be achieved on the basis of reducing the complexity of system design.

[0074] Example 2 See also Figure 4 FIG. 1 is a flow chart of a method for optical fiber frequency relay transmission without a phase-locked loop provided in an embodiment of the present application; the method is applied to any of the above-mentioned optical fiber frequency relay transmission systems, and the method includes: Step 401: For each relay station, use the wavelength division multiplexing system to split the signal transmitted by the previous relay station to obtain the optical signal transmitted by the previous relay station to the data exchange unit and the optical frequency signal transmitted by the previous relay station to the first photodetector.

[0075] The optical signal includes: a noise signal of the preceding optical fiber transmission link and a signal of frequency difference information between optical frequency signals emitted by regenerative cavity stabilized lasers in every two adjacent relay stations.

[0076] Step 402: Utilize the regenerative cavity stabilized laser of this stage to emit the optical frequency signal of this stage, and transmit the optical frequency signal of this stage to the next stage relay station through the sum wavelength division system.

[0077] The frequency of the optical frequency signal at this stage is greater than the frequency of the optical frequency signal emitted by the regenerative cavity stabilized laser in the previous stage relay station.

[0078] Step 403: Use the first photoelectric detector to beat the optical frequency signal of the current stage and the optical frequency signal transmitted by the previous stage relay station to obtain the beat frequency signal of the current stage.

[0079] Step 404: Use the data exchange unit to mix and sum the beat signal of this stage and the optical signal transmitted by the previous stage relay station to obtain a mixed beat signal, and transmit the mixed beat signal and the optical signal transmitted by the previous stage relay station to the next stage relay station through the sum wavelength division system.

[0080] Step 405: Use the first acousto-optic modulator to frequency-shift the current-stage optical frequency signal based on the mixed beat frequency signal to obtain a current-stage optical frequency signal that is identical to the original optical frequency signal of the fiber optical frequency relay transmission system, and transmit the current-stage optical frequency signal to the user end.

[0081] It should be noted that the description of the method embodiment is similar to the description of the system embodiment described above, and has similar beneficial effects as the system embodiment. For technical details not disclosed in the system method embodiment of this application, please refer to the description of the system embodiment of this application for understanding.

[0082] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0083] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts 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, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0084] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0085] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A fiber optic frequency relay transmission system without a phase-locked loop, characterized in that: include: Multiple relay stations are cascaded through optical fiber transmission links. Each relay station includes: A wavelength division multiplexing system is configured to split the signal transmitted by the previous relay station to obtain an optical signal transmitted by the previous relay station and transmitted to the data exchange unit, and an optical frequency signal transmitted by the previous relay station and transmitted to the first photodetector; wherein the optical signal includes: a noise signal of the preceding optical fiber transmission link, and a signal indicating the frequency difference between the optical frequency signals emitted by the regenerative cavity-stabilized lasers in each of two adjacent relay stations; The regenerative cavity-stabilized laser of this stage is used to emit the optical frequency signal of this stage and transmit the optical frequency signal of this stage to the next stage relay station through the sum wavelength division system; wherein the frequency of the optical frequency signal of this stage is greater than the frequency of the optical frequency signal emitted by the regenerative cavity-stabilized laser in the previous stage relay station; The first photoelectric detector is used to beat the optical frequency signal of the current stage and the optical frequency signal transmitted by the previous stage relay station to obtain the beat frequency signal of the current stage; A data exchange unit is used to mix and sum the beat signal of this stage and the optical signal transmitted by the previous stage relay station to obtain a mixed beat signal, and transmit the mixed beat signal and the optical signal transmitted by the previous stage relay station to the next stage relay station through the sum wavelength division system; The first acousto-optic modulator is used to frequency-shift the current-stage optical frequency signal based on the mixed beat frequency signal to obtain the current-stage optical frequency signal that is identical to the original optical frequency signal of the optical fiber optical frequency relay transmission system, and transmit the current-stage optical frequency signal to the user end.

2. The fiber optic frequency relay transmission system according to claim 1, characterized in that: Each relay station further includes: a first optical fiber coupler, a second optical fiber coupler, a third optical fiber coupler, a fourth optical fiber coupler, and a transmitting end acousto-optic modulator; The regenerative cavity-stabilized laser of this stage is further used to transmit the optical frequency signal of this stage to the first photodetector through the fourth optical fiber coupler, the second optical fiber coupler and the first optical fiber coupler in sequence, and to transmit the optical frequency signal of this 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 sequence; The acousto-optic modulator at the transmitting end is used to perform positive frequency shift on the optical frequency signal of this level, and transmit the positive frequency shifted optical frequency signal of this level through the sum wavelength division multiplexing system to the optical fiber transmission link between the relay station and the next level relay station.

3. The fiber optic frequency relay transmission system according to claim 2, characterized in that: Each level of relay station also includes: a second photoelectric detector, a two-frequency division processor; a third fiber coupler, configured to reflect the optical frequency signal of the current stage transmitted through the fourth fiber coupler and the second fiber coupler to the second photodetector via the connected second 45-degree Faraday rotator, and to reflect the feedback optical signal of the current stage transmitted through the sum wavelength division multiplexing 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; The second photoelectric detector is used to perform beat frequency processing on the optical frequency signal of the current stage and the feedback optical signal of the current stage to obtain a feedback beat frequency signal, and transmit the feedback beat frequency signal to the binary frequency division processor; A two-frequency division processor is used to process the feedback beat frequency signal to obtain a noise signal of the optical fiber transmission link between the relay station and the next-stage relay station, and transmit the noise signal of the optical fiber transmission link between the relay station and the next-stage relay station to the data exchange unit for storage through the frequency counting unit; The data interaction unit is also used 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 fiber optic frequency relay transmission system according to claim 3, characterized in that: Each level of relay station also includes: a receiving end acousto-optic modulator; The demultiplexing system is specifically used to split the signal transmitted by the upper relay station to obtain the optical signal transmitted by the upper relay station to the data exchange unit, and the optical frequency signal to be frequency-shifted transmitted by the upper relay station to the receiving end acousto-optic modulator; The receiving end acousto-optic modulator is used to perform positive frequency shift on the optical frequency signal to be frequency-shifted transmitted by the previous relay station to obtain the optical frequency signal transmitted by the previous relay station to be transmitted to the first optical fiber coupler; The first optical fiber coupler is used to reflect the optical frequency signal transmitted by the previous relay station to the first photodetector using the connected first 45-degree Faraday rotator, and to transmit the optical frequency signal transmitted by the previous relay station to the transmission link between the previous relay station and the relay station through the receiving end acousto-optic modulator and the wavelength division multiplexing system.

5. The fiber optic frequency relay transmission system according to claim 1, wherein: The relay station is an N-th level relay station, and the optical signal transmitted by the previous level relay station is an optical signal transmitted by the N-1-th level relay station, where 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 relay station is: ； in, It is an optical fiber transmission link between the transmitting device and the first-level relay station in the optical fiber frequency relay transmission system; for Additional noise signal on ; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the receiving end respectively; and are the angular frequency and phase of the acoustic wave modulation signal of the acousto-optic modulator at the transmitting end respectively; is the time variable; It is the optical fiber transmission link between the first-level relay station and the second-level relay station; for Additional noise signal on ; It is the optical fiber transmission link between the N-1th level relay station and the Nth level relay station; for Additional noise signals on the relay station; each relay station is equipped with a receiving end acousto-optic modulator and a transmitting end acousto-optic modulator; It is the optical fiber transmission link between the sending device and the first-level relay station; for The additional phase noise on It is the optical fiber transmission link between the first-level relay station and the second-level relay station; for The additional phase noise on It is the optical fiber transmission link between the N-1th level relay station and the Nth level relay station; for The additional phase noise on 6. The fiber optic frequency relay transmission system according to claim 5, wherein: The optical signal transmitted by the N-1th relay station includes the frequency difference information between the optical frequency signals emitted by the regenerative cavity stabilized lasers in every two adjacent relay stations: ； in, The first-stage beat frequency signal output by the first photodetector in the first-stage relay station; and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the first-stage relay station respectively; and are the angular frequency and phase of the original optical frequency signal respectively; The second-stage beat frequency signal output by the first photodetector in the second-stage relay station; and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the second-stage relay station respectively; The N-1th level beat signal output by the first photodetector in the N-1th level relay station; and are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-1th relay station; and are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-2th relay station; It is the optical fiber transmission link between the N-2th level relay station and the N-1th level relay station; for The additional phase noise on 7. The fiber optic frequency relay transmission system according to claim 5 or 6, characterized in that: The beat frequency signal of this stage output by the first photodetector for: ； in, and are the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the Nth relay station respectively; and They are respectively the angular frequency and phase of the optical signal output by the regenerative cavity stabilized laser in the N-1th relay station.

8. The fiber optic frequency relay transmission system according to claim 1, characterized in that: The fiber optical frequency relay transmission system further includes: a sending device, the sending device is connected to the first-level relay station, the first-level relay station corresponds to the previous-level relay station as the sending device, and the original cavity-stabilized laser in the sending device emits the original optical frequency signal; the sending device includes: Original cavity-stabilized laser for emitting original optical frequency signals : ； in, and are the angular frequency and phase of the original optical frequency signal respectively; is the time variable; The original photoelectric detector is used to beat the original optical frequency signal and the feedback optical signal between the transmitting device and the first-stage relay station to obtain the original beat frequency signal : ； in, 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 respectively the angular frequency and phase of the acoustic wave modulation signal of the transmitting end acousto-optic modulator in the transmitting device; is the time variable; The optical fiber transmission link between the sending device and the first-level relay station; for The additional phase noise on An original two-frequency division processor is used to process the original beat frequency signal to obtain a noise signal of the optical fiber transmission link between the transmitting device and the first-stage relay station; The original data interaction unit is used 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 and wavelength division system.

9. The fiber optic frequency relay transmission system according to claim 1, characterized in that: Each level of relay station also includes: The GPS servo rubidium clock of the global positioning system is used to control the transmission signal and second pulse synchronization between the relay station and the next level relay station.

10. A fiber optic frequency relay transmission method without a phase-locked loop, characterized in that: The fiber optic frequency relay transmission method is applied to the fiber optic frequency relay transmission system according to any one of claims 1 to 9, and the method comprises: For each relay station, the signal transmitted by the previous relay station is split using a wavelength division multiplexing (WDM) system to obtain an optical signal transmitted by the previous relay station that is transmitted to the data exchange unit, and an optical frequency signal transmitted by the previous relay station that is transmitted to the first photodetector. The optical signal includes: a noise signal of the preceding optical fiber transmission link, and a signal indicating the frequency difference between optical frequency signals emitted by regenerative cavity-stabilized lasers in each of two adjacent relay stations. emitting an optical frequency signal of the current stage using a regenerative cavity-stabilized laser of the current stage, and transmitting the optical frequency signal of the current stage to a next-stage relay station through a sum wavelength division multiplexing 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 previous-stage relay station; Using the first photoelectric detector, the optical frequency signal of the current stage and the optical frequency signal transmitted by the previous stage relay station are beat to obtain the beat frequency signal of the current stage; The data exchange unit is used to mix and sum the beat signal of the current stage and the optical signal transmitted by the previous stage relay station to obtain a mixed beat signal, and the mixed beat signal and the optical signal transmitted by the previous stage relay station are transmitted to the next stage relay station through the sum wavelength division system; The first acousto-optic modulator is used to frequency-shift the current-level optical frequency signal based on the mixed beat frequency signal to obtain the current-level optical frequency signal that is identical to the original optical frequency signal of the fiber optical frequency relay transmission system, and the current-level optical frequency signal is transmitted to the user end.

Images