A system and method for realizing optical frequency comparison based on intermediate point

Abstract

The present invention discloses a system and method for realizing optical frequency comparison based on an intermediate point, wherein the system splits the light input from the local end to obtain a first light beam and a second light beam; splits the first light beam to obtain a first sub-beam and a second sub-beam, transmits the first sub-beam back to the local end, and transmits the second light beam to the remote end; receives the first sub-beam reflected from the local end, and detects the first sub-beam reflected from the local end to obtain a detection light, and detects the second sub-beam to obtain a detection light E0; receives the second light beam reflected from the remote end, and detects the second light beam reflected from the remote end to obtain a detection light; receives the light input from the remote end, and detects the light input from the remote end to obtain a detection light; obtains a beat frequency signal according to the obtained detection light; performs a frequency comparison between the local end and the remote end according to the beat frequency signal to obtain a comparison result. The present invention can ensure the synchronization during frequency comparison, and has a better residual noise suppression effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical frequency comparison, and in particular relates to a system and method for realizing optical frequency comparison based on an intermediate point. Background Art

[0002] Time plays an important role in life and production, and time frequency measurement is the most accurately measured physical quantity in the world. The optical frequency standard provided by the optical atomic clock is two orders of magnitude more unstable than the conventional atomic clock. It is a laser frequency with higher frequency stability. At present, the optical fiber optical frequency transmission stability of several research groups has reached It has promoted the development of high-precision frequency standard science fields, such as satellite navigation, radio astronomy, geodesy, etc. These applications rely on high-precision optical atomic clocks and precise frequency comparison systems to connect optical atomic clocks located in different geographical locations to form an optical clock network for frequency comparison. Modern optical fiber communication technology has many advantages such as large information capacity, low loss, strong anti-interference ability and low cost. With the development of optical fiber manufacturing technology and the popularization of optical fiber communication networks, the use of optical fiber networks to transmit atomic clock signals has shown great technical and precision advantages.

[0003] There are currently two solutions for optical frequency comparison using optical fiber. One is a two-way optical frequency transmission dual-end frequency comparison solution, where the optical frequency signal at the local end is transmitted to the remote end through an optical fiber link for data collection, and the optical frequency signal at the remote end is transmitted to the local end through the same optical fiber link for data collection, and then optical frequency comparison is performed; the other is a two-way optical frequency single-end frequency comparison solution, where the optical frequency signal at the local end is transmitted to the remote end through an optical fiber link, and then returned from the remote end to the local end, and the optical frequency signal at the remote end is transmitted to the local end through the same optical fiber link, and both signals are collected and compared at the local end.

[0004] However, the two-way optical frequency transfer double-end comparison solution requires data collection at two locations, which cannot guarantee the synchronization of data collection at the two locations, which will affect the accuracy of the comparison results. Although the two-way optical frequency transfer single-end frequency comparison solution can collect data at the same location and the synchronization is not affected, the residual noise suppression is four times that of the former. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a system and method for realizing optical frequency comparison based on an intermediate point.

[0006] The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] The present invention provides a system for realizing optical frequency comparison based on an intermediate point, the system is included in the intermediate end, and the system comprises: a first acousto-optic modulator and a second acousto-optic modulator, a beam splitting module, a detection module and a frequency comparison module;

[0008] The first acousto-optic modulator is used to receive light input from a local end, and transmit the received light input from the local end to the beam splitting module;

[0009] The beam splitting module is used to transmit the light input from the local end to the first acousto-optic modulator. Splitting the first beam to obtain a first beam and a second beam, splitting the first beam to obtain a first sub-beam and a second sub-beam, transmitting the first sub-beam to the first acousto-optic modulator, transmitting the second sub-beam to the detection module, and transmitting the second beam to the second acousto-optic modulator;

[0010] The first acousto-optic modulator is further used to return the first sub-beam to the local end, and transmit the first sub-beam reflected from the local end to the beam splitting module;

[0011] The beam splitting module is further used to transmit the first sub-beam reflected back from the local end to the detection module;

[0012] The detection module is used to detect the first sub-beam reflected by the local end to obtain a detection light , at the same time, detecting the second sub-beam to obtain detection light E0;

[0013] The second acousto-optic modulator is used to transmit the second light beam to a remote end, receive the second light beam reflected by the remote end, and receive light input by the remote end;

[0014] The detection module is also used to detect the second light beam reflected from the remote end to obtain the detection light , and detecting the light received from the remote end to obtain the detection light , and according to the detection light E0, the detection light , the detection light and the detection light , and obtain multiple beat frequency signals;

[0015] The frequency comparison module is used to perform frequency comparison between the local end and the remote end according to the multiple beat frequency signals to obtain a comparison result.

[0016] In some embodiments, the beam splitting module includes: an optical coupler and a Faraday mirror;

[0017] The optical coupler is used to transmit the light input from the local end to the first acousto-optic modulator. Perform beam splitting to obtain a first light beam and a second light beam, and transmit the first light beam to the Faraday mirror, while transmitting the second light beam to the second acousto-optic modulator;

[0018] The Faraday mirror is used to reflect the first light beam back to the optical coupler;

[0019] The optical coupler is further used to split the first light beam to obtain a first sub-beam and a second sub-beam, transmit the first sub-beam to the first acousto-optic modulator, and transmit the second sub-beam to the detection module;

[0020] The Faraday mirror is further used to reflect the first sub-beam reflected from the local end to the detection module.

[0021] In some embodiments, the detection module is further used to detect the detection light The detection light E0 is processed by beat frequency to obtain a first beat frequency signal , for the detection light The detection light E0 is processed by beat frequency to obtain a second beat frequency signal , and, for the detection light The detection light E0 is processed by beat frequency to obtain a third beat frequency signal .

[0022] In some embodiments, the first beat frequency signal The expression is as follows:

[0023] ;

[0024] in, represents the driving angular frequency of the local AOM, represents the driving angular frequency of the first AOM, represents the phase noise of the optical fiber link between the local end and the intermediate end, Indicates time.

[0025] In some embodiments, the second beat frequency signal The expression is as follows:

[0026] ;

[0027] in, represents the driving angular frequency of the second AOM, represents the driving angular frequency of the remote end AOM, represents the phase noise of the optical fiber link between the intermediate end and the remote end, Indicates time.

[0028] In some embodiments, the third beat frequency signal The expression is as follows:

[0029] ;

[0030] in, represents the driving angular frequency of the local AOM, and denote the driving angular frequencies of the first AOM and the second AOM respectively, represents the driving angular frequency of the remote end AOM, represents the frequency of the light output by the local end, represents the frequency of the light output from the remote end, represents the phase of the light output from the local end, represents the phase of the light output from the remote end, represents the phase noise of the optical fiber link between the local end and the intermediate end, represents the phase noise of the optical fiber link between the intermediate end and the remote end, Indicates time.

[0031] In some embodiments, the frequency comparison module is further used to determine the first beat frequency signal and the second beat frequency signal The second frequency division is obtained by dividing the frequency by two, and the third beat frequency signal is A mixing process is performed with the two-frequency division signal to obtain a comparison signal, and the frequency difference term contained in the comparison signal is used as a comparison result of the frequencies of the light output by the local end and the remote end.

[0032] In some embodiments, the expression of the comparison signal is as follows:

[0033] ;

[0034] in, represents the comparison signal, represents the frequency of the light output by the local end, represents the frequency of the light output from the remote end, represents the phase of the light output from the local end, represents the phase of the light output from the remote end, Indicates time, and The comparison result of the frequency of the light output by the local end and the remote end is represented.

[0035] The present invention also provides a method for realizing optical frequency comparison based on an intermediate point, which is applied to the above-mentioned system for realizing optical frequency comparison based on an intermediate point, and the method comprises:

[0036] Receive light input from a local end, and Performing beam splitting to obtain a first light beam and a second light beam;

[0037] Splitting the first light beam to obtain a first sub-beam and a second sub-beam, transmitting the first sub-beam back to the local end, and transmitting the second light beam to the remote end;

[0038] receiving the first sub-beam reflected from the local end, and detecting the first sub-beam reflected from the local end to obtain a detection light , and detecting the second sub-beam to obtain detection light E0;

[0039] receiving the second light beam reflected from the remote end, and detecting the second light beam reflected from the remote end to obtain a detection light beam; ;

[0040] Receive the light inputted by the remote end, and detect the light inputted by the remote end to obtain the detection light ;

[0041] According to the detection light E0, the detection light , the detection light and the detection light , and obtain multiple beat frequency signals;

[0042] A frequency comparison between the local end and the remote end is performed according to the multiple beat frequency signals to obtain a comparison result.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention can collect and compare the optical frequencies of the local end and the remote end at the intermediate end, thereby ensuring the synchronization during frequency comparison and eliminating the need for additional synchronization operations, thereby solving the problem of synchronous measurement. In addition, the residual noise suppression effect of the present invention is better than that of the existing single-end frequency comparison scheme, and when the distances from the intermediate end of the present invention to the local end and the remote end are equal, the residual noise suppression effect of the present invention can achieve the residual noise suppression result of the existing double-end frequency comparison scheme.

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 is a schematic diagram of the structure of an intermediate comparison terminal provided in an embodiment of the present invention;

[0047] Figure 2 is a flow chart of a method for realizing optical frequency comparison based on an intermediate point provided by an embodiment of the present invention;

[0048] Figure 3 It is a structural diagram of a frequency transmission and comparison system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0050] The present invention provides a system for realizing optical frequency comparison based on an intermediate point, the system is included in the intermediate end, and the system comprises: a first acousto-optic modulator and a second acousto-optic modulator, a beam splitting module, a detection module and a frequency comparison module;

[0051] A first acousto-optic modulator, used for receiving light inputted from a local end, and transmitting the received light inputted from the local end to a beam splitting module;

[0052] The beam splitting module is used to split the light input from the local end transmitted by the first acousto-optic modulator Splitting the first beam to obtain a first beam and a second beam, splitting the first beam to obtain a first sub-beam and a second sub-beam, transmitting the first sub-beam to a first acousto-optic modulator, transmitting the second sub-beam to a detection module, and transmitting the second beam to a second acousto-optic modulator;

[0053] The first acousto-optic modulator is further used to return the first sub-beam to the local end, and transmit the first sub-beam reflected from the local end to the beam splitting module;

[0054] The beam splitting module is also used to transmit the first sub-beam reflected from the local end to the detection module;

[0055] The detection module is used to detect the first sub-beam reflected from the local end and obtain the detection light , at the same time, the second sub-beam is detected to obtain the detection light E0;

[0056] A second acousto-optic modulator, used to transmit the second light beam to the remote end, receive the second light beam reflected by the remote end, and receive light input from the remote end;

[0057] The detection module is also used to detect the second light beam reflected from the remote end to obtain the detection light , and detecting the light inputted by the remote end to obtain the detection light , and according to the detection light E0, the detection light , detection light and the probe light , and obtain multiple beat frequency signals;

[0058] The frequency comparison module is used to compare the frequencies of the local end and the remote end according to multiple beat frequency signals to obtain a comparison result.

[0059] Exemplarily, the light emitted by the local end can be expressed as: ,in, Indicates the light emitted by the local end, Indicates the frequency of the light output from the local end, Represents the phase of the light output from the local end. Correspondingly, the light input from the local end and transmitted by the first acousto-optic modulator received by the beam splitting module is It can be expressed as: ,in, represents the driving angular frequency of the local AOM, represents the driving angular frequency of the first AOM, Represents the phase noise of the optical fiber link between the local end and the intermediate end, Indicates time.

[0060] Exemplarily, the detection light E0= .

[0061] For example, the detection light It can be expressed as:

[0062] .

[0063] For example, the detection light It can be expressed as:

[0064] ;

[0065] in, represents the driving angular frequency of the second AOM, represents the driving angular frequency of the remote end AOM, Represents the phase noise of the fiber link between the intermediate end and the remote end.

[0066] For example, the detection light It can be expressed as:

[0067] ;

[0068] in, Indicates the frequency of the light output from the remote end, Indicates the phase of the light output from the remote end.

[0069] In some embodiments, the above-mentioned system for implementing optical frequency comparison based on the intermediate point can be integrated in the intermediate end (also referred to as the intermediate comparison end) as a part of the intermediate end; in some embodiments, the above-mentioned system for implementing optical frequency comparison based on the intermediate point can also directly constitute an intermediate end.

[0070] In some embodiments, the beam splitting module includes: an optical coupler and a Faraday mirror. Specifically, the optical coupler is used to split the light E1 input from the local end and transmitted by the first acousto-optic modulator to obtain a first light beam and a second light beam, and transmit the first light beam to the Faraday mirror, while transmitting the second light beam to the second acousto-optic modulator; the Faraday mirror is used to reflect the first light beam back to the optical coupler; the optical coupler is also used to split the first light beam to obtain a first sub-beam and a second sub-beam, transmit the first sub-beam to the first acousto-optic modulator, and transmit the second sub-beam to the detection module. The Faraday mirror is also used to reflect the first sub-beam reflected from the local end to the detection module.

[0071] Here, the detection module may specifically be a photodetector. For example, Figure 1 It is a structural diagram of the middle comparison end, such as Figure 1 As shown, the middle end includes a first acousto-optic modulator AOM2, a second acousto-optic modulator AOM3, an optical coupler OC2, a Faraday mirror FM2, a photodetector PD and a frequency comparison module.

[0072] In some embodiments, the plurality of beat frequency signals include: a first beat frequency signal , the second beat frequency signal and the third beat frequency signal Specifically, the detection module is also used to detect the light Perform beat frequency processing with the detection light E0 to obtain the first beat frequency signal , for the detection light The second beat frequency signal is obtained by performing beat frequency processing with the detection light E0. , and, for the detection light The third beat frequency signal is obtained by performing beat frequency processing with the detection light E0. .

[0073] Exemplarily, the first beat frequency signal It can be expressed as: .

[0074] Exemplarily, the second beat frequency signal It can be expressed as: .

[0075] Exemplarily, the third beat frequency signal It can be expressed as: ;

[0076] In some embodiments, the frequency comparison module is further configured to determine the first beat frequency signal and the second beat frequency signal The second frequency division is obtained, and the third beat frequency signal is The comparison signal is obtained by mixing with the two-frequency division signal, and the frequency difference term contained in the comparison signal is used as the comparison result of the frequency of the light output by the local end and the remote end.

[0077] Exemplary, comparison signal It can be expressed as: ,in, Indicates the comparison result of the frequency of the light output by the local end and the remote end.

[0078] The present invention can collect and compare the optical frequencies of the local end and the remote end at the intermediate end, thereby ensuring the synchronization during frequency comparison and eliminating the need for additional synchronization operations, thereby solving the problem of synchronous measurement. In addition, the residual noise suppression effect of the present invention is better than that of the existing single-end frequency comparison scheme, and when the distances from the intermediate end of the present invention to the local end and the remote end are equal, the residual noise suppression effect of the present invention can achieve the residual noise suppression result of the existing double-end frequency comparison scheme.

[0079] Figure 2 is a flow chart of a method for realizing optical frequency comparison based on an intermediate point provided by an embodiment of the present invention, the method is executed by the above-mentioned intermediate end, such as Figure 2 As shown, the method includes:

[0080] S101, receiving light input from the local end, and processing the received light input from the local end Beam splitting is performed to obtain a first light beam and a second light beam.

[0081] S102 , split the first light beam to obtain a first sub-beam and a second sub-beam, transmit the first sub-beam back to the local end, and transmit the second sub-beam to the remote end.

[0082] S103, receiving the first sub-beam reflected from the local end, and detecting the first sub-beam reflected from the local end to obtain a detection beam , and, detect the second sub-beam to obtain detection light E0.

[0083] S104, receiving the second light beam reflected from the remote end, and detecting the second light beam reflected from the remote end to obtain a detection light beam. .

[0084] S105, receiving the light inputted from the remote end, and detecting the light inputted from the remote end to obtain the detection light .

[0085] S106, according to the detection light E0, the detection light , detection light and the probe light , and obtain multiple beat frequency signals.

[0086] S107: Perform frequency comparison between the local end and the remote end according to the multiple beat frequency signals to obtain a comparison result.

[0087] It should be noted that the above step numbers do not represent the execution order of the steps. Some of the above steps can be executed in parallel, and some steps can be executed sequentially. For example, S103~S105 can be executed in parallel, and S101~S102 and S106~S107 can be executed sequentially.

[0088] The intermediate end can be used in a frequency transmission and comparison system to compare the frequencies of the local end and the intermediate end. Accordingly, in the frequency transmission and comparison system, the local end is used to generate light and transmit it to the intermediate end. The intermediate end is used to use a first acousto-optic modulator to receive the light input from the local end, and transmit the received light input from the local end to a beam splitting module, and use the beam splitting module to transmit the light input from the local end transmitted by the first acousto-optic modulator. Split the beam to obtain a first beam and a second beam, split the first beam to obtain a first sub-beam and a second sub-beam, transmit the first sub-beam to the first acousto-optic modulator, transmit the second sub-beam to the detection module, and use the detection module to detect the second sub-beam to obtain detection light E0, and use the first acousto-optic modulator to return the first sub-beam to the local end, transmit the second beam to the second acousto-optic modulator, and use the second acousto-optic modulator to transmit the second beam to the remote end. The local end is also used to receive the first sub-beam and reflect the first sub-beam to the first acousto-optic modulator at the intermediate end. The remote end is used to receive the second beam and reflect the second beam to the second acousto-optic modulator at the intermediate end, and generate light and transmit it to the intermediate end. The intermediate end is also used to detect the first sub-beam reflected from the local end using the detection module to obtain the detection light , detect the second light beam reflected from the remote end and obtain the detection light , and detecting the light inputted by the remote end to obtain the detection light ; Use frequency comparison module according to detection light E0, detection light , detection light and the probe light , multiple beat frequency signals are obtained, and the frequencies of the local end and the remote end are compared according to the multiple beat frequency signals to obtain a comparison result.

[0089] For example, Figure 3 Figure 1 is a schematic diagram of the structure of a frequency transmission and comparison system. Figure 3 As shown,

[0090] The local end includes: a laser to be compared 1, a Faraday mirror 1 ( Figure 3 FM1 is used in the representation), optocoupler 1 ( Figure 3 OC1 is used in the representation), acousto-optic modulator 1 ( Figure 3 AOM1 is used in the figure), where the light output by laser 1 is expressed as , the driving angular frequency of AOM1 is The middle comparison end includes: acousto-optic modulator 2 ( Figure 3 AOM2 is used in the representation), Faraday mirror 2 ( Figure 3 FM2 is used in the representation), acousto-optic modulator 3 ( Figure 3 AOM3 is used in the representation), optical coupler 2 ( Figure 3 OC2 is used in the representation), photodetector ( Figure 3 PD is used in the representation) and the frequency comparison unit ( Figure 3 ), wherein the driving angular frequencies of AOM2 and AOM3 are respectively and The remote end includes: a laser to be compared 2, a Faraday mirror 3 ( Figure 3 FM3 is used in the representation), optocoupler 3 ( Figure 3 OC3 is used in the representation) and AOM 4 ( Figure 3 AOM4 is used in the figure), where the light output by laser 2 is expressed as , the driving angular frequency of AOM4 is .

[0091] The light output from laser 1 After passing through optical OC1 and AOM1, it enters optical fiber link 1 and is transmitted to the intermediate comparison end. After passing through AOM2, it is expressed as , is the phase noise of fiber link 1, Split into two beams by OC2, A beam of light is reflected by FM2 and then divided into two beams by OC2, one of which enters PD for detection. The detection light is represented by E0, where E0= , the other beam returns to the local end through optical fiber link 1, is reflected back to the intermediate comparison end by FM1, and then reflected to PD by FM2 for detection. The detection light is expressed as ; The other beam of light passes through AOM3 and enters the optical fiber link 2 to be transmitted to the remote end, passes through AOM4 and OC3 in turn, is reflected back to the middle comparison end by FM3, and enters the PD for detection after passing through OC2. The detection light can be written as , is the phase noise of optical fiber link 2.

[0092] The light from laser 2 passes through OC3 and AOM4 at the remote end, then enters optical fiber link 2 and is transmitted to the intermediate comparison end. After passing through AOM3 and OC2, it enters PD for detection. The detection light is written as .

[0093] PD beats the detection light E2 and the detection light E0 to obtain a beat signal ,and, , PD to the detection light Beat with the detection light E0 to get the beat signal ,and, , PD to the detection light Beat with the detection light E0 to get the beat signal ,and, After that, the frequency comparison unit will and The two-way frequency By mixing the two lights, you can get the comparison result of the two lights. ,in, This is the final frequency comparison result.

[0094] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0095] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0096] In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality of components. Certain measures are recorded in different embodiments, but this does not mean that these measures cannot be combined to produce good effects.

[0097] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A system for realizing optical frequency comparison based on an intermediate point, characterized in that: The system is included in the middle end, and the system includes: a first acousto-optic modulator and a second acousto-optic modulator, a beam splitting module, a detection module and a frequency comparison module; The first acousto-optic modulator is used to receive light input from a local end, and transmit the received light input from the local end to the beam splitting module; The beam splitting module comprises: an optical coupler and a Faraday mirror; The optical coupler is used to split the light E1 transmitted by the first acousto-optic modulator and inputted from the local end to obtain a first light beam and a second light beam, and transmit the first light beam to the Faraday mirror, and transmit the second light beam to the second acousto-optic modulator; The Faraday mirror is used to reflect the first light beam back to the optical coupler; The optical coupler is further used to split the first light beam to obtain a first sub-beam and a second sub-beam, transmit the first sub-beam to the first acousto-optic modulator, and transmit the second sub-beam to the detection module; The first acousto-optic modulator is further used to return the first sub-beam to the local end, and transmit the first sub-beam reflected from the local end to the Faraday mirror; The Faraday mirror is further used to transmit the first sub-beam reflected back from the local end to the detection module; The detection module is used to detect the first sub-beam reflected by the local end to obtain the detection light E2, and at the same time, detect the second sub-beam to obtain the detection light E0; The second acousto-optic modulator is used to transmit the second light beam to a remote end, receive the second light beam reflected by the remote end, and receive light input by the remote end; The detection module is further used to detect the second light beam reflected by the remote end to obtain detection light E3, and to detect the received light input by the remote end to obtain detection light E4, and to obtain a plurality of beat frequency signals according to the detection light E0, the detection light E2, the detection light E3 and the detection light E4; The frequency comparison module is used to perform frequency comparison between the local end and the remote end according to the multiple beat frequency signals to obtain a comparison result.

2. The system for realizing optical frequency comparison based on an intermediate point according to claim 1, characterized in that: The detection module is further used to perform beat frequency processing on the detection light E2 and the detection light E0 to obtain a first beat frequency signal E5, perform beat frequency processing on the detection light E3 and the detection light E0 to obtain a second beat frequency signal E6, and perform beat frequency processing on the detection light E4 and the detection light E0 to obtain a third beat frequency signal E7.

3. The system for realizing optical frequency comparison based on intermediate points according to claim 2, characterized in that: The expression of the first beat frequency signal E5 is as follows: Wherein, ω1 represents the driving angular frequency of the local AOM, ω2 represents the driving angular frequency of the first AOM, represents the phase noise of the optical fiber link between the local end and the intermediate end, and t represents time.

4. The system for realizing optical frequency comparison based on an intermediate point according to claim 2, characterized in that: The expression of the second beat frequency signal E6 is as follows: Wherein, ω3 represents the driving angular frequency of the second AOM, ω4 represents the driving angular frequency of the AOM at the remote end, represents the phase noise of the optical fiber link between the intermediate end and the remote end, and t represents time.

5. The system for realizing optical frequency comparison based on an intermediate point according to claim 2, characterized in that: The expression of the third beat frequency signal E7 is as follows: Wherein, ω1 represents the driving angular frequency of the AOM at the local end, ω2 and ω3 represent the driving angular frequencies of the first AOM and the second AOM respectively, ω4 represents the driving angular frequency of the AOM at the remote end, ωL represents the frequency of the light output by the local end, ωR represents the frequency of the light output by the remote end, represents the phase of the light output from the local end, represents the phase of the light output from the remote end, represents the phase noise of the optical fiber link between the local end and the intermediate end, represents the phase noise of the optical fiber link between the intermediate end and the remote end, and t represents time.

6. The system for realizing optical frequency comparison based on an intermediate point according to claim 2, characterized in that: The frequency comparison module is further used to determine the binary frequency of the first beat frequency signal E5 and the second beat frequency signal E6 to obtain a binary frequency signal, mix the third beat frequency signal E7 with the binary frequency signal to obtain a comparison signal, and use the frequency difference item contained in the comparison signal as the comparison result of the frequency of the light output by the local end and the remote end.

7. The system for realizing optical frequency comparison based on the intermediate point according to claim 6, characterized in that: The expression of the comparison signal is as follows: Wherein, E8 represents the comparison signal, ωL represents the frequency of the light output by the local end, ωR represents the frequency of the light output by the remote end, represents the phase of the light output from the local end, represents the phase of the light output by the remote end, t represents time, and ωL-ωR represents the comparison result of the frequencies of the light output by the local end and the remote end.

8. A method for realizing optical frequency comparison based on an intermediate point, characterized in that: Applied to the system according to any one of claims 1 to 7 above, the method comprises: receiving light inputted from a local end, and splitting the light E1 received from the local end to obtain a first light beam and a second light beam; Splitting the first light beam to obtain a first sub-beam and a second sub-beam, transmitting the first sub-beam back to the local end, and transmitting the second light beam to the remote end; receiving the first sub-beam reflected from the local end, detecting the first sub-beam reflected from the local end to obtain detection light E2, and detecting the second sub-beam to obtain detection light E0; receiving the second light beam reflected from the remote end, and detecting the second light beam reflected from the remote end to obtain detection light E3; receiving light inputted from the remote end, and detecting the received light inputted from the remote end to obtain detection light E4; Obtaining a plurality of beat frequency signals according to the detection light E0, the detection light E2, the detection light E3 and the detection light E4; A frequency comparison between the local end and the remote end is performed according to the multiple beat frequency signals to obtain a comparison result.

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