Relay device without out-of-band noise and optical frequency transfer system and method thereof

Abstract

The application discloses a relay device without out-of-band noise and an optical frequency transfer system and method thereof, which can realize relay regeneration and amplification of an optical signal received by a previous link, and the regenerated signal is continuously transferred to a next link or output. The relay structure can lock the regenerated light source. Meanwhile, the next link actively compensates the phase noise introduced by the optical signal in the optical fiber link through a servo controller, so that the phase compensation of the received signal light is realized. Through repeated cascade of the relay structure, the local optical frequency signal can be transferred for a long distance, so that the user end obtains the phase-stable optical frequency signal. The application reduces the asymmetry of the transmission structure by adopting an online Faraday rotating mirror, effectively avoids the influence of the out-of-band path noise, and has the advantages of simple system structure, low overall noise and long transmission distance without using a complex temperature control system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical frequency dissemination, in particular to a relay device without out-of-band noise and an optical frequency dissemination system and method. BACKGROUND

[0002] Time and frequency are the most precisely measured physical quantities, which promote the rapid development of high-precision frequency standard related application technology fields, such as basic physics research, satellite navigation, space science, radio astronomy, etc.

[0003] In 2010, Lopez et al. of University of Paris 13 in France adopted a cascaded optical frequency dissemination scheme and carried out a transmission demonstration on two 150 km optical fiber links. A phase-locked loop is used in each stage, which compensates for the link noise of the stage and ensures the regeneration of the ultra-stable optical signal. The relay station connects the optical fiber links of each stage, and the relay station includes a receiving end, a sending end and a regenerative amplification module. The receiving end receives the laser signal transmitted by the previous stage, and after regenerative amplification, the sending end sends it to the next transmission link. Through the cascaded transmission, a transmission stability of 5E-20 / 20h is obtained. [See Lopez O, Haboucha A, Kéfélian F, Jiang H, Chanteau B, Roncin V, Chardonnet C, Amy-Klein A, Santarelli G. Cascaded multiplexed optical link on a telecommunication network for frequency dissemination. Opt Express. 2010 Aug 2; 18(16): 16849-57. doi: 10.1364 / OE.18.016849. PMID: 20721077.]

[0004] In 2015, the French team demonstrated the optical frequency cascade transfer experiment on a total length of 1480km fiber link (Chiodo et al., 2015), the total transfer link is divided into four levels, the three relay devices used in the experiment use heterodyne optical phase locking to realize the regenerative amplification of the transfer signal, 16 EDFA are used to compensate the link loss, and finally the transfer stability index of 2E-20 / 8000s is realized. [See Chiodo N, Quintin N, Stefani F, Wiotte F, Camisard E, Chardonnet C, Santarelli G, Amy-Klein A, Pottie PE, Lopez O. Cascaded optical fiber link using the internet network for remote clocks comparison. Opt Express. 2015 Dec 28;23(26):33927-37. doi: 10.1364 / OE.23.033927. PMID: 26832051.]

[0005] In the same year, the team carried out a two-level optical fiber frequency transfer with a length of 740km, 16 OADM were used to insert and extract the measurement signal in the data flow of the second level, and 7 bidirectional erbium-doped fiber amplifiers (EDFA) were used to amplify the signal of the whole link, and finally the transfer stability of 2E-16 / s was realized. [See O. Lopez, N. Chiodo, F. Stefani, F. Wiotte, N. Quintin, A. Bercy, C. Chardonnet, G. Santarelli, P.-E. Pottie, and A. Amy-Klein, "Cascaded optical link on a telecommunication fiber network for ultra-stable frequency dissemination," in Slow Light, Fast Light, and Opto-Atomic Precision Metrology VIII, International Society for Optics and Photonic"s, 2015, vol. 9378, p. 937823.]

[0006] The above schemes all need precise temperature control modules to suppress out-of-band noise, and the present application can realize high-stability frequency transfer without temperature control. SUMMARY

[0007] The application aims at the prior art and the deficiency of the work, and provides a relay regeneration structure for optical frequency transfer, which utilizes an online Faraday rotating mirror to reduce the asymmetry of the transmission structure, and the in-band link does not need temperature control, and has the advantages of simple system structure, low overall noise, long transmission distance and repeatability.

[0008] To achieve the above object, the technical solution of the application is as follows:

[0009] The relay device without out-of-band noise comprises a first polarization controller, a second frequency shifter, a third Y-type optical coupler, a third online Faraday rotating mirror, a second photodetector, a second direct digital frequency synthesizer, a second reference frequency source, a second frequency division module, a second servo controller, a third direct digital frequency synthesizer, a second laser, a third frequency shifter, a fifth Y-type optical coupler, a fourth Y-type optical coupler, a third photodetector, a fourth frequency shifter, a sixth Y-type optical coupler, a fourth online Faraday rotating mirror, a fifth online Faraday rotating mirror, a fifth frequency shifter, a fourth direct digital frequency synthesizer, a fourth photodetector, a first frequency mixer, a third frequency division module and a third servo controller.

[0010] The first polarization controller is connected with the previous stage through a fiber link, the first polarization controller is connected with the second frequency shifter, the second frequency shifter is connected with the second port of the third Y-type optical coupler, the first port of the third Y-type optical coupler is connected with the third on-line Faraday rotator mirror, the third on-line Faraday rotator mirror is connected with the second photoelectric detector, the output port of the second photoelectric detector is connected with the second frequency division module, the output of the second frequency division module is input to the second reference frequency source together to the second servo controller, the second servo controller is connected with the third direct digital frequency synthesizer, the third direct digital frequency synthesizer is connected to the radio frequency port of the third frequency shifter; the second laser (output to the third frequency shifter, the third frequency shifter is connected with the second port of the fifth Y-type optical coupler, the first port of the fifth Y-type optical coupler is connected with the first port of the fourth Y-type optical coupler, the second port of the fourth Y-type optical coupler is connected with the third port of the third Y-type optical coupler; the third port of the fourth Y-type optical coupler is connected with the fourth frequency shifter, the fourth frequency shifter is connected with the second port of the sixth Y-type optical coupler, the first port of the sixth Y-type optical coupler is connected with the fourth on-line Faraday rotator mirror, the fourth on-line Faraday rotator mirror is connected with the fifth on-line Faraday rotator mirror, the fifth on-line Faraday rotator mirror is connected with the fifth frequency shifter; the third port of the fifth Y-type optical coupler is connected with the third photoelectric detector, the output of the third photoelectric detector is input to one input port of the first frequency mixer; the third port of the sixth Y-type optical coupler is connected with the fourth photoelectric detector, the output of the fourth photoelectric detector is input to the other input port of the first frequency mixer, the output of the first frequency mixer is connected with the third frequency division module, the output of the third frequency division module is input to the second reference frequency source together to the third servo controller, the third servo controller is connected with the fifth direct digital frequency synthesizer, the fifth direct digital frequency synthesizer is connected to the radio frequency port of the fifth frequency shifter; the second reference frequency source is input to the second direct digital frequency synthesizer, the second direct digital frequency synthesizer is connected to the radio frequency port of the second frequency shifter; the second reference frequency source is input to the fourth direct digital frequency synthesizer, the fourth direct digital frequency synthesizer is connected to the radio frequency port of the fourth frequency shifter.

[0011] An optical frequency transfer system using the above-mentioned out-of-band noise-free relay device, comprising a local end and a user end, the local end and the user end are connected through a fiber link, characterized in that N said relay devices are distributed on the fiber link as relay regeneration end repeated cascade, realizing long-distance optical signal transmission, N≥1.

[0012] An optical frequency transfer method using the above-mentioned out-of-band noise-free relay device, characterized in that the method comprises the following steps:

[0013] The optical signal of the upper level transmission enters the relay regeneration end of the current level through the optical fiber link, passes through the first polarization controller, the second frequency shifter, and the third Y-type optical coupler. At the third online Faraday rotating mirror, part of the optical signal returns to the upper level to compensate for the phase noise introduced by the extracted optical fiber link and the reference frequency source of the current level. The optical signal after compensation of the upper level passes through the third online Faraday rotating mirror and is phase-stable. The phase of the optical signal after the second laser is locked to the stable phase of the upper level transmission through the servo control unit.

[0014] Assuming that the optical signal after locking is The optical signal after locking is divided into two paths at the fourth Y-type optical coupler. Part of the signal passes through the third Y-type optical coupler, is reflected at the third online Faraday rotating mirror, and then passes through the third Y-type optical coupler, the fourth Y-type optical coupler, and the fifth Y-type optical coupler to reach the third photodetector. At this time, the signal expression is still E0. The other path of the signal at the fourth Y-type optical coupler passes through the fourth frequency shifter and the sixth Y-type optical coupler. At the fourth online Faraday rotating mirror, the signal is divided into two paths. One path of the signal is reflected and reaches the fourth photodetector again. The signal expression is recorded as E1. The other path of the signal passes through the fourth frequency shifter, the fourth Y-type optical coupler, and the fifth Y-type optical coupler to reach the third photodetector. At this time, the signal expression is recorded as E2. The signal E2 beats with the signal E0, and the beat signal is recorded as E3. The beat signal is transmitted to one input port of the first mixer. The signal expression is

[0015]

[0016]

[0017]

[0018] In the formula, ω1 is the frequency of the radio frequency operation of the fourth frequency shifter, is the phase noise introduced by the reference frequency source of the current level, which is extracted by beating at the third photodetector for compensation.

[0019] The other optical signal at the fourth on-line Faraday rotator passes through the fifth on-line Faraday rotator, the fifth frequency shifter and the optical fiber link to the next stage, and in the next stage, passes through the polarization controller, the frequency shifter, the Y-type optical coupler, is emitted at the on-line Faraday rotator, and is extracted from the phase noise introduced by the optical fiber link and the reference frequency source in the next stage, and the reflected optical signal passes through the fifth frequency shifter, the fifth on-line Faraday rotator, the fourth on-line Faraday rotator, the sixth Y-type optical coupler (38) to the signal at the fourth photoelectric detector, which is denoted as E4, the signal E4 beats with the signal E1, and the beat signal is denoted as E5, and the beat signal is transmitted to the other input port of the first frequency mixer, and the signal expression is

[0020]

[0021]

[0022] In the formula, ω2 and is the frequency and initial phase of the radio frequency operation of the fifth frequency shifter, and ω3 is the radio frequency of the frequency shifter in the next stage, is the phase noise introduced by the optical fiber link, is the phase noise introduced by the reference frequency source in the next stage, which is extracted in the present stage for compensation.

[0023] The signal after the beat signals E3 and E5 are mixed is denoted as The mixed signal is input to the fifth frequency shifter through the servo controller, so that the phase noise introduced by the relay regenerative end and the reference frequency source in the next stage and the optical fiber link is compensated, and the phase is kept stable.

[0024] Compared with the prior art, the beneficial effects of the present application are:

[0025] 1) The present application uses the on-line Faraday rotator to reduce the asymmetry of the transmission structure, and the in-band link does not need temperature control.

[0026] 2) The structure of the present application is repeatable, and the relay station sites are the same.

[0027] 2) The present application is suitable for super-long distance stable phase optical frequency transfer. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 It is a schematic diagram of the local end structure of the relay regenerative optical frequency transfer system.

[0029] Figure 2 It is a schematic diagram of the relay regenerative end structure of the relay regenerative optical frequency transfer system.

[0030] Figure 3The figure is a schematic diagram of a user end structure of a relay regenerative optical frequency transfer system.

[0031] Figure 4 The figure is a schematic diagram of a structure cascade of a relay regenerative optical frequency transfer system. DETAILED DESCRIPTION

[0032] The application will be further described below in conjunction with the embodiments and the drawings, the embodiments are implemented on the premise of the technical solution of the application, and detailed implementation manners and specific work processes are given, but the protection scope of the application is not limited to the following embodiments.

[0033] Embodiment 1

[0034] Firstly refer to Figures 1 to 3 , Figures 1 to 3 The figure is a schematic diagram of a structure of an embodiment of a relay regenerative optical frequency transfer system in the application, as shown in the figure, the relay regenerative optical frequency transfer system in the application comprises a local end 1, a relay regenerative end 2 and a user end 3.

[0035] The local end 1 comprises a first laser 11, a first Y-type optical coupler 12, a first online Faraday rotating mirror 13, a second online Faraday rotating mirror 14, a second Y-type optical coupler 15, a first acousto-optic modulator 16, a first photodetector 17, a first frequency division module 18, a first reference frequency source 19, a first servo controller 20 and a first direct digital frequency synthesizer 21.

[0036] The optical signal to be transferred is emitted by the first laser 11, input from a second port of the first Y-type optical coupler 12, a first port of the first Y-type optical coupler 12 is connected to the first online Faraday rotating mirror 13, the first online Faraday rotating mirror 13 is connected to the second online Faraday rotating mirror 14, the second online Faraday rotating mirror 14 is connected to a first port of the second Y-type optical coupler 15, a second port of the second Y-type optical coupler 15 is connected to the first acousto-optic modulator 16, and an output optical signal of a third port of the second Y-type optical coupler 15 is used for out-of-band testing; a third port of the first Y-type optical coupler 12 is connected to the first photodetector 17, an output port of the first photodetector 17 is connected to the first frequency division module 18, an output of the first frequency division module 18 is input to the first servo controller 20 together with the first reference frequency source 19, the first servo controller 20 is connected to the first direct digital frequency synthesizer 21, and the first direct digital frequency synthesizer 21 is connected to a radio frequency port of the first acousto-optic modulator 16.

[0037] The relay regenerative end 2 comprises a first polarization controller 22, a second acousto-optic modulator 23, a third Y-type optical coupler 24, a third in-line Faraday rotating mirror 25, a second photodetector 26, a second direct digital frequency synthesizer 27, a second reference frequency source 28, a second frequency division module 29, a second servo controller 30, a third direct digital frequency synthesizer 31, a second laser 32, a third acousto-optic modulator 33, a fifth Y-type optical coupler 34, a fourth Y-type optical coupler 35, a third photodetector 36, a fourth acousto-optic modulator 37, a sixth Y-type optical coupler 38, a fourth in-line Faraday rotating mirror 39, a fifth in-line Faraday rotating mirror 40, a fifth acousto-optic modulator 41, a fourth direct digital frequency synthesizer 42, a fourth photodetector 43, a first frequency mixer 44, a third frequency division module 45, a third servo controller 46, a fifth direct digital frequency synthesizer 47.

[0038] The first acousto-optic modulator 16 of the local end 1 is connected with the first polarization controller 22 of the relay regenerative end 2 through an optical fiber link, the first polarization controller 22 is connected with the second acousto-optic modulator 23, the second acousto-optic modulator 23 is connected with the second port of the third Y-type optical coupler 24, the first port of the third Y-type optical coupler 24 is connected with the third online Faraday rotating mirror 25, the third online Faraday rotating mirror 25 is connected with the second photoelectric detector 26, the output port of the second photoelectric detector 26 is connected with the second frequency division module 29, the output of the second frequency division module 29 is input to the second servo controller 30 together with the second reference frequency source 28, the second servo controller 30 is connected with the third direct digital frequency synthesizer 31, the third direct digital frequency synthesizer 31 is connected to the radio frequency port of the third acousto-optic modulator 33; The second laser 32 is output to the third acousto-optic modulator 33, the third acousto-optic modulator 33 is connected with the second port of the fifth Y-type optical coupler 34, the first port of the fifth Y-type optical coupler 34 is connected with the first port of the fourth Y-type optical coupler 35, the second port of the fourth Y-type optical coupler 35 is connected with the third port of the third Y-type optical coupler 24; The third port of the fourth Y-type optical coupler 35 is connected with the fourth acousto-optic modulator 37, the fourth acousto-optic modulator 37 is connected with the second port of the sixth Y-type optical coupler 38, the first port of the sixth Y-type optical coupler 38 is connected with the fourth online Faraday rotating mirror 39, the fourth online Faraday rotating mirror 39 is connected with the fifth online Faraday rotating mirror 40, the fifth online Faraday rotating mirror 40 is connected with the fifth acousto-optic modulator 41; The third port of the fifth Y-type optical coupler 34 is connected with the third photoelectric detector 36, the output of the third photoelectric detector 36 is input to one input port of the first frequency mixer 44; The third port of the sixth Y-type optical coupler 8 is connected with the fourth photoelectric detector 43, the output of the fourth photoelectric detector 43 is input to another input port of the first frequency mixer 44, the output of the first frequency mixer 44 is connected with the third frequency division module 45, the output of the third frequency division module 45 is input to the third servo controller 46 together with the second reference frequency source 28, the third servo controller 46 is connected with the fifth direct digital frequency synthesizer 47, the fifth direct digital frequency synthesizer 47 is connected to the radio frequency port of the fifth acousto-optic modulator 41; The second reference frequency source 28 is input to the second direct digital frequency synthesizer 27, the second direct digital frequency synthesizer 27 is connected to the radio frequency port of the second acousto-optic modulator 23;The second reference frequency source 28 is input to the fourth direct digital frequency synthesizer 42, which is connected to the radio frequency port of the fourth acousto-optic modulator 37.

[0039] The user terminal 3 comprises a second polarization controller 48, a sixth acousto-optic modulator 49, a seventh Y-type optical coupler 50, a sixth on-line Faraday rotator 51, an eighth Y-type optical coupler 52, a sixth direct digital frequency synthesizer 53, a third reference frequency source 54, and a fifth photodetector 55.

[0040] The fifth acousto-optic modulator 41 of the relay regenerative terminal 2 is connected to the second polarization controller 48 of the user terminal 3 through an optical fiber link, which is connected to the sixth acousto-optic modulator 49, which is connected to the second port of the seventh Y-type optical coupler 50, the first port of which is connected to the sixth on-line Faraday rotator 51, which is connected to the first port of the eighth Y-type optical coupler 52, the third port of which is connected to the fifth photodetector 55, the output optical signal of which is used for bidirectional comparison test; the output optical signal of the third port of the seventh Y-type optical coupler 50 is used for out-of-band test; the third reference frequency source 54 is connected to the sixth direct digital frequency synthesizer 53, the output of which is connected to the radio frequency port of the sixth acousto-optic modulator 49.

[0041] The above system is an optical frequency transfer regenerative relay method without out-of-band noise, characterized in that the method comprises the following steps:

[0042] The local terminal:

[0043] The optical signal to be transferred is After passing through the first Y-type optical coupler 12 and the first on-line Faraday rotator 13, the optical signal is divided into two paths, one of which is reflected back through the first Y-type optical coupler 12 to the first photodetector 17, and the signal expression is still E0; the other path passes through the second on-line Faraday rotator 14, the second Y-type optical coupler 15, the first acousto-optic modulator 16, and the signal after the optical fiber link is denoted as E1, and the signal expression is

[0044]

[0045] In the formula, 39 and is the frequency and initial phase of the radio frequency operation of the first acousto-optic modulator 16, is the phase noise introduced by the fiber link. The signal E1 after passing through the first polarization controller 22, the second acousto-optic modulator 23 and the third Y-type optical coupler 24 is denoted as E2, the signal E2 is reflected at the third on-line Faraday rotator mirror 25, and the signal after passing through the third Y-type optical coupler 24, the second acousto-optic modulator 23, the first polarization controller 22 and the fiber link is denoted as E3, and the signal expression is

[0046]

[0047]

[0048] wherein 37 is the frequency of the radio frequency operation of the second acousto-optic modulator 23, is the phase noise introduced by the second reference frequency source 28.

[0049] The signal E3 passes through the first acousto-optic modulator 16, the second Y-type optical coupler 15, the second on-line Faraday rotator mirror 14, the first on-line Faraday rotator mirror 13 and the first Y-type optical coupler 12, and the signal at the first photodetector 17 is denoted as E4, and the signal expression is

[0050]

[0051] The signal E4 is beat with the signal E0, and the beat signal E5 after being divided at the first frequency division module 18 is input together with the reference signal of the first reference frequency source 19 to the first servo controller 20 for locking, and the output direct current error signal Ve enters the servo control unit, and the signal expression is:

[0052]

[0053]

[0054] When the servo control module works in the locking state, Ve is close to 0, and the expression can be further written as:

[0055]

[0056] Compensating the locked signal to the first acousto-optic modulator 16 can compensate the phase noise introduced by the reference frequency source and the fiber link in the relay regenerative end 2.

[0057] The relay regenerative end 2:

[0058] In the relay regenerative end 2, the received signal after passing through the transmission link can be expressed as:

[0059]

[0060] The signal E6 passes through the first polarization controller 22, the second acousto-optic modulator 23, the third Y-type optical coupler 24, the third in-line Faraday rotator 25, and reaches the second photodetector 26. The signal is denoted as E7, and the expression of the signal is

[0061]

[0062] The optical signal emitted by the second laser 32 is The signal E8 passes through the third acousto-optic modulator 33, the fifth Y-type optical coupler 34, the fourth Y-type optical coupler 35, the third Y-type optical coupler 24, the third in-line Faraday rotator 25, and reaches the second photodetector 26. The signal is denoted as E9, and the expression of the signal is

[0063]

[0064] In the expression, 100 and are the frequency and initial phase of the radio frequency operation of the third acousto-optic modulator 33.

[0065] The signal E7 beats with the signal E9. After frequency division at the second frequency division module 29, the beat signal is input together with the reference signal of the second reference frequency source 28 into the second servo controller 30 to be locked to -176. The output direct current error signal Ve enters the servo control unit, and the expression of the signal is:

[0066]

[0067] When the servo control module works in the locked state, Ve is close to 0, and the expression can be further written as:

[0068]

[0069] v3+100=v0-100

[0070] After locking, the optical signal after the third acousto-optic modulator 33 is After passing through the fifth Y-type optical coupler 34 and the fourth Y-type optical coupler 35, the optical signal is divided into two paths. One path passes through the third Y-type optical coupler 24, is reflected at the third in-line Faraday rotator 25, passes through the third Y-type optical coupler 24, the fourth Y-type optical coupler 35, and the fifth Y-type optical coupler 34, and reaches the third photodetector 36. The expression of the signal is still E 10 ; the other path passes through the fourth acousto-optic modulator 37 and the sixth Y-type optical coupler 38, and the expression of the signal is denoted as E 11At the fourth on-line Faraday rotator 39, the signal is divided into two paths, one of which is reflected, and the optical signal is again divided into two paths at the sixth Y-type optical coupler 38. One of the signals reaches the fourth photodetector 43, and the signal expression is still E 11 The other signal passes through the fourth acousto-optic modulator 37, the fourth Y-type optical coupler 35, and the fifth Y-type optical coupler 34, and reaches the third photodetector 36. The signal expression is recorded as E 12 The signal E 12 is beat with the signal E 10 The beat frequency signal is recorded as E 13 The beat frequency signal is input to one input port of the first mixer 44, and the signal expression is

[0071]

[0072]

[0073]

[0074] In the formula, 100 is the frequency of the radio frequency operation of the fourth acousto-optic modulator 37, is the phase noise introduced by the second reference frequency source 28.

[0075] The other signal at the fourth on-line Faraday rotator 39 passes through the fourth on-line Faraday rotator 39, the fifth on-line Faraday rotator 40, the fifth acousto-optic modulator 41, and the optical fiber link. The signal after the fifth on-line Faraday rotator 40 is recorded as E 14 The signal E 14 passes through the second polarization controller 48, the sixth acousto-optic modulator 49, and the seventh Y-type optical coupler 50. The signal after the seventh Y-type optical coupler 50 is recorded as E 15 The signal expression is

[0076]

[0077]

[0078] In the formula, 39 and are the frequency of the radio frequency operation of the fifth acousto-optic modulator 41 and the initial phase, 37 is the frequency of the radio frequency operation of the sixth acousto-optic modulator 49, is the phase noise introduced by the third reference frequency source 54, is the phase noise introduced by the optical fiber link.

[0079] The signal E 15 is reflected at the sixth on-line Faraday rotator 51, and the signal after the seventh Y-type optical coupler 50, the sixth acousto-optic modulator 49, the second polarization controller 48, the optical fiber link, and the fifth acousto-optic modulator 41 is recorded as E 16, the signal expression is

[0080]

[0081] signal E 16 After passing through the fifth online Faraday rotator 40, the fourth online Faraday rotator 39, and the sixth Y-type optical coupler 38, the signal reaches the fourth photodetector 43 and is mixed with the signal E 11 Beat frequency, the beat frequency signal is recorded as E 17 , the signal E 17 The other input port of the first mixer 44 is input with the signal E 13 Mixing, the mixing signal is recorded as E 18 , the mixing signal is input into the third servo controller 46 after being divided by the third frequency division module 45, and the reference signal of the second reference frequency source 28 is input into the third servo controller 46, and the output direct current error signal Ve enters the servo control unit, the signal expression is:

[0082]

[0083]

[0084]

[0085] When the servo control module works in the locking state, Ve is close to 0, and the expression can be further written as:

[0086]

[0087] Compensating the locked signal to the fifth acousto-optic modulator 41 can compensate the phase noise introduced by the reference frequency source and the optical fiber link in the relay regenerative end 2 and the user end 3.

[0088] User end 3:

[0089] In the user end 3, after transmission through the transmission link, the received signal can be represented as:

[0090]

[0091] The signal E 19 After passing through the second polarization controller 48, the sixth acousto-optic modulator 49, the seventh Y-type optical coupler 50, the sixth online Faraday rotator 51, and the eighth Y-type optical coupler 52, the signal expression is The phase noise introduced by the reference frequency source and the optical fiber link in each station is compensated, so that the phase remains stable.

[0092] Embodiment 2

[0093] First, refer toFigure 4 , Figure 4 The structure diagram of the embodiment of the optical frequency transfer relay regenerative structure cascade system of the present application is shown in the figure. The relay regenerative structure can be repeatedly cascaded to realize the transmission of optical frequency over a longer distance.

Claims

1. A repeater device without external noise, characterized in that, It includes a first polarization controller (22), a second frequency shifter (23), a third Y-type optical coupler (24), a third in-line Faraday rotator (25), a second photodetector (26), a second direct digital frequency synthesizer (27), a second reference frequency source (28), a second frequency divider module (29), a second servo controller (30), a third direct digital frequency synthesizer (31), a second laser (32), a third frequency shifter (33), a fifth Y-type optical coupler (34), a fourth Y-type optical coupler (35), a third photodetector (36), a fourth frequency shifter (37), a sixth Y-type optical coupler (38), a fourth in-line Faraday rotator (39), a fifth in-line Faraday rotator (40), a fifth frequency shifter (41), a fourth direct digital frequency synthesizer (42), a fourth photodetector (43), a first mixer (44), a third frequency divider module (45), a third servo controller (46), and a fifth direct digital frequency synthesizer (47); The first port of the first polarization controller (22) is connected to the previous stage via an optical fiber link. The second port of the first polarization controller (22) is connected to the second frequency shifter (23). The second frequency shifter (23) is connected to the second port of the third Y-type optical coupler (24). The first port of the third Y-type optical coupler (24) is connected to the third online Faraday rotator (25). The third online Faraday rotator (25) is connected to the input port of the second photodetector (26). The output port of the second photodetector (26) is connected to the input port of the second frequency divider module (29). The output of the second frequency divider module (29) and the second reference frequency source (28) are input to the second servo controller (30). The second servo controller (30) is connected to the third direct digital frequency synthesizer (31). The third direct digital frequency synthesizer (31) is connected to the radio frequency port of the third frequency shifter (33). The second laser (32) outputs to the third frequency shifter (33), which is connected to the second port of the fifth Y-type optical coupler (34). The first port of the fifth Y-type optical coupler (34) is connected to the first port of the fourth Y-type optical coupler (35), and the second port of the fourth Y-type optical coupler (35) is connected to the third port of the third Y-type optical coupler (24). The third port of the fourth Y-type optical coupler (35) is connected to the fourth frequency shifter (37), which is connected to the... The second port of the sixth Y-type optical coupler (38) is connected to the first port of the sixth Y-type optical coupler (38), which is connected to the fourth in-line Faraday rotator (39). The fourth in-line Faraday rotator (39) is connected to the fifth in-line Faraday rotator (40), which is connected to the fifth frequency shifter (41). The third port of the fifth Y-type optical coupler (34) is connected to the third photodetector (36), and the output of the third photodetector (36) is input to the first mixer. (44) One input port; the third port of the sixth Y-type optocoupler (38) is connected to the fourth photodetector (43), the output of the fourth photodetector (43) is input to another input port of the first mixer (44), the output of the first mixer (44) is connected to the third frequency divider module (45), the output of the third frequency divider module (45) and the second reference frequency source (28) are input to the third servo controller (46), the third servo controller (46) and the fifth direct digital frequency synthesizer The fifth direct digital frequency synthesizer (47) is connected to the radio frequency port of the fifth frequency shifter (41); the second reference frequency source (28) is input to the second direct digital frequency synthesizer (27), which is connected to the radio frequency port of the second frequency shifter (23); the second reference frequency source (28) is input to the fourth direct digital frequency synthesizer (42), which is connected to the radio frequency port of the fourth frequency shifter (37).

2. An optical frequency transmission system utilizing the repeater device without out-of-band noise as described in claim 1, comprising a local end (1) and a user end (3), wherein the local end (1) and the user end (3) are connected via an optical fiber link, characterized in that, N relay devices are distributed along the optical fiber link as relay regeneration ends and repeatedly cascaded to realize long-distance optical signal transmission, where N≥1.

3. An optical frequency transmission method using the repeater device without out-of-band noise as described in claim 1, characterized in that, The method includes the following steps: The optical signal transmitted from the upper level enters the first polarization controller (22) of the relay regeneration end of this level through the optical fiber link, and is then split into two paths after passing through the second frequency shifter (23), the third Y-type optical coupler (24), and the third online Faraday rotator (25): Part of the optical signal is returned to the previous stage via the third Y-type optical coupler (24), the second frequency shifter (23) and the first polarization controller (22) to compensate for the phase noise introduced by the extracted fiber link and the reference frequency source of this stage; another part of the optical signal after compensation by the previous stage maintains a stable phase after passing through the third online Faraday rotator (25), and the phase of the optical signal after the second laser (32) is locked to the stable phase of the previous stage transmission by the servo control unit. Let the optical signal after locking be E0. Where ω0, The frequency and phase of the optical signal are locked after passing through the third frequency shifter (33). After locking, the optical signal is split into two paths at the fourth Y-type optical coupler (35). One part passes through the third Y-type optical coupler (24), is reflected at the third online Faraday rotator (25), and then passes through the third Y-type optical coupler (24), the fourth Y-type optical coupler (35), and the fifth Y-type optical coupler (34) to reach the third photodetector (36). The signal expression at this time is still E0. The other signal at the fourth Y-type optical coupler (35) passes through the fourth frequency shifter (37) and the sixth Y-type optical coupler (38). At the fourth online Faraday rotator (39), the signal is split into two paths. One signal is reflected and split into two paths again at the sixth Y-type optical coupler (38). One signal reaches the fourth photodetector (43) and is denoted as signal E1. ω1 is the radio frequency of the fourth frequency shifter (37). The phase noise is introduced by the reference frequency source at this level. The other signal passes through the fourth frequency shifter (37), the fourth Y-type optical coupler (35), and the fifth Y-type optical coupler (34) and reaches the third photodetector (36), denoted as signal E2. The signals E2 and E0 are subjected to a beat frequency at the third photodetector (36) to extract the phase noise introduced by the reference frequency source of this stage. The beat frequency signal is denoted as E3. The beat frequency signal E3 is transmitted to one input port of the first mixer (44) for compensation. The signal expression is as follows: Another optical signal at the fourth online Faraday rotator (39) passes through the fifth online Faraday rotator (40), the fifth frequency shifter (41), and the optical fiber link to enter the next stage. In the next stage, it passes through the polarization controller, the frequency shifter, and the Y-type optical coupler, and is emitted at the online Faraday rotator. It returns to the repeater regeneration end of this stage, where the phase noise introduced by the optical fiber link and the next stage reference frequency source is extracted. The reflected optical signal passes through the fifth frequency shifter (41), the fifth online Faraday rotator (40), the fourth online Faraday rotator (39), and the sixth Y-type optical coupler (38), and the signal reaching the fourth photodetector (43) is denoted as E4. Signal E4 beats signal E1, denoted as beat frequency signal E5. Beat frequency signal E5 is transmitted to another input port of the first mixer (44), and the signal expression is: In the formula, ω2 and ω3 is the RF operating frequency and initial phase of the fifth frequency shifter (41), and ω3 is the RF operating frequency of the next-stage frequency shifter. It is phase noise introduced by the fiber optic link. The phase noise introduced by the next-level reference frequency source is extracted and used for compensation in this stage; The signal resulting from the mixing of beat frequency signals E3 and E5 is denoted as signal E6. The mixing signal is input to the fifth frequency shifter (41) through the servo controller to compensate for the phase noise introduced by the relay regeneration terminal (2), the reference frequency source of the next stage, and the optical fiber link, so that the phase remains stable.

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