A distributed fiber optic frequency transmission method and system

Abstract

The present invention relates to the technical field of fiber optic frequency transmission, and specifically to a distributed fiber optic frequency transmission method and system. The distributed fiber optic frequency transmission system consists of a transmitting end and a plurality of receiving ends, which are connected by an optical fiber link. The optical signal transmission module at the transmitting end divides the laser light generated by the laser into reference light and modulated light. The modulated light is transmitted to the receiving end after positive frequency shift and wavelength division multiplexing, and the return light is received at the same time. The signal processing module processes the beat frequency of the reference light and the return light to obtain a radio frequency signal, and then performs phase processing to obtain an instantaneous frequency value and converts it into an optical signal through modulation by an optical transmitter. The optical modulator module at the receiving end demodulates the modulated optical signal to obtain an instantaneous frequency value, and uses the frequency value to drive the modulator at the receiving end to obtain the final optical frequency signal. The system realizes distributed high-precision optical frequency transmission.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber frequency transmission, and in particular to a distributed optical fiber frequency transmission method and system. Background Art

[0002] Advances in atomic cooling technology have enabled optical clock systems to operate stably and output optical frequency signals with extremely high precision. The stability and uncertainty of the optical frequency signal have reached 10 -18 This is an extremely high level of precision. This high-precision optical frequency signal plays an indispensable role in many important fields such as navigation and timing, gravitational wave detection, precision spectral measurement and geodesy. For example, in the field of navigation and timing, high-precision optical frequency signals can improve the accuracy of positioning and timing; in gravitational wave detection, precise optical frequency signals help to more accurately detect the microscopic space-time distortion caused by gravitational waves; in precision spectral measurement, high-precision optical frequency signals can improve the resolution of spectral measurement; in geodesy, more accurate geodetic measurements can be achieved. With the growing demand for high-precision optical frequency signals in various fields, many users have a demand for this high-precision optical frequency signal. In order to meet this demand, optical fiber-based high-precision optical frequency signal transmission technology has become a research hotspot. Optical fiber has the advantages of low transmission loss and large bandwidth, and is suitable for the transmission of high-precision optical frequency signals.

[0003] Although the solution of increasing the number of response transmitters can try to meet the needs of multiple users for high-precision optical frequency signals, there are obvious problems. First, the cost is very high, which means that a large amount of money needs to be invested in equipment, construction and maintenance. Secondly, this solution is not easy to expand user capacity and cannot adapt well to the growing user needs, which limits its scalability in practical applications.

[0004] The scheme of adding reflection points at the transmitting end is intended to allow multiple users to obtain additional link noise information at the receiving end to achieve noise suppression, thereby obtaining high-precision optical frequency signals. However, as the number of users increases, this scheme will encounter serious problems. Due to multiple reflections, the optical frequency signals between users will interfere with each other, which will deteriorate the optical signal-to-noise ratio of the optical signal obtained by the user. The deterioration of the optical signal-to-noise ratio is not conducive to the realization of large-capacity high-precision optical frequency distributed transmission, thereby limiting the effectiveness of this scheme in meeting the needs of multi-user high-precision optical frequency signals. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a distributed fiber optic frequency transmission method and system in view of the deficiencies in the above-mentioned prior art, so as to solve the technical problem that large-capacity high-precision distributed optical frequency transmission cannot be achieved between users.

[0006] The objective of the present invention is achieved by the following technical solutions:

[0007] In a first aspect, the present invention provides a distributed fiber optical frequency transmission system, comprising a transmitting end and a corresponding plurality of receiving ends, wherein the transmitting end and the plurality of receiving ends are connected via an optical fiber link;

[0008] The optical signal transmission module is used to separate the laser light generated by the laser into reference light and modulated light, and then perform positive frequency shift processing on the modulated light to obtain a first optical signal, transmit the first optical signal to a corresponding number of receiving ends through wavelength division multiplexing processing and an optical fiber link, and receive return light from each receiving end;

[0009] The signal processing module is used to perform beat frequency processing on the reference light and the return light from each receiving end to obtain a first radio frequency signal; perform phase processing on the first radio frequency signal to obtain an instantaneous frequency value of the first radio frequency signal, and convert the instantaneous frequency value into a transmission optical signal to be transmitted to each receiving end;

[0010] The receiving end includes a signal transmission module and a signal driving module, wherein the signal transmission module is used to modulate the first optical signal output by the received optical signal transmission module and reflect the modulated part of the first optical signal as return light to the transmitting end;

[0011] The signal driving module is used to convert the received transmission optical signal into an instantaneous frequency value, and then drive the modulated first optical signal in the signal transmission module to perform negative frequency shift processing to obtain an optical frequency signal acting on the receiving end user.

[0012] As a further improvement of the present invention, the optical signal transmission module includes, in sequence along the signal transmission direction: a first coupler, a first modulator, and a first wavelength division multiplexer; a first Faraday rotator is also arranged between the first coupler and the first modulator;

[0013] The first coupler is used to divide the laser light into reference light and modulated light;

[0014] The first modulator is used to perform positive frequency shift processing on the modulated light, and the processed modulated light is used as the first optical signal and then transmitted through the first wavelength division multiplexer and the optical fiber link to each receiving end;

[0015] The first wavelength division multiplexer is used to combine and process the first optical signal output by the first modulator and the transmission optical signal output by the signal processing module, and transmit them to each receiving end through a corresponding number of optical fiber links at the receiving end;

[0016] The first Faraday rotator is used to reflect the reference light to the signal processing module.

[0017] As a further improvement of the present invention, the signal processing module includes a photodetector, a phase processing module and an optical transmitter;

[0018] The photoelectric detector is arranged between the first coupler and the first wavelength division multiplexer, and is used to perform beat frequency processing on the reference light and the return light from each receiving end to obtain a first radio frequency signal corresponding to each receiving end;

[0019] The phase processing module is used to perform phase processing on the first RF signal to obtain an instantaneous frequency signal of the first RF signal, and apply the instantaneous frequency signal to the optical transmitter; the optical transmitter is used to convert the instantaneous frequency signal into a transmission optical signal, and transmit it to the corresponding receiving end through a corresponding number of optical fiber links at the receiving end.

[0020] As a further improvement of the present invention, the phase processing module includes a power division amplifier and a number of frequency processing submodules corresponding to the number of receiving ends; the frequency processing submodules sequentially include a filter, a signal conditioning unit, a binary frequency divider, an IQ phase detector and a phase extension unit;

[0021] The power divider amplifier is used to divide the first radio frequency signal into a number corresponding to the receiving end, and transmit them to the frequency processing submodule respectively;

[0022] In the frequency processing submodule, the first radio frequency signal is filtered by a filter, and then processed by a signal conditioning unit and a binary divider to obtain a second radio frequency signal containing optical fiber additional phase noise;

[0023] The second radio frequency signal is processed by the IQ phase detector and the phase stretching unit to obtain an instantaneous frequency value.

[0024] As a further improvement of the present invention, the signal transmission module includes: a second wavelength division multiplexer, a second modulator, a third coupler and a third modulator; a second Faraday rotator is further arranged after the third coupler;

[0025] The second wavelength division multiplexer is used to perform wavelength division processing on the first optical signal output by the optical signal transmission module and the transmission optical signal output by the signal processing module;

[0026] The third coupler is used to divide the first optical signal output by the second wavelength division multiplexer into two parts, one part is used as the return light, and the other part is used as the second optical signal; the second optical signal is transmitted to the third modulator after passing through the third coupler; the return light is reflected by the second Faraday rotator and then returned to the signal processing module through the optical fiber link;

[0027] The third modulator is used to perform negative frequency shift processing on the second optical signal.

[0028] As a further improvement of the present invention, the signal driving module is arranged between the second wavelength division multiplexer and the third modulator, and includes an optical receiver and a driver;

[0029] The transmission optical signal output by the signal processing module is converted into an instantaneous frequency signal after passing through the optical receiver, and the instantaneous frequency signal drives the third modulator through the driver.

[0030] As a further improvement of the present invention, the system further comprises a first radio frequency generator and a second radio frequency generator;

[0031] The first RF generator is arranged at the first modulator side of the transmitting end, and the RF signal generated by the first RF generator acts on the first modulator;

[0032] The second RF generator is arranged at the second modulator side of the receiving end, and the RF signal generated by the second RF generator acts on the second modulator.

[0033] In a second aspect, the present invention provides a distributed fiber optical frequency transmission method, which is implemented based on the above-mentioned distributed fiber optical frequency transmission system, and includes:

[0034] The laser light generated by the laser is divided into reference light and modulated light;

[0035] Performing positive frequency shift processing on the modulated light to obtain a first optical signal, performing wavelength division multiplexing processing on the first optical signal and transmitting the first optical signal through an optical fiber link, and then transmitting the first optical signal to corresponding receiving ends respectively;

[0036] After the first optical signal is modulated by each receiving end, a return light of the receiving end is obtained after reflection, and the return light is subjected to beat frequency processing with the reference light to obtain a first radio frequency signal corresponding to each receiving end;

[0037] After performing phase processing on the first radio frequency signal, an instantaneous frequency value of the first radio frequency signal is obtained;

[0038] The instantaneous frequency value is converted into a transmission optical signal, which is transmitted to each receiving end through an optical fiber link. The modulated first optical signal in the receiving end is subjected to negative frequency shift processing according to the instantaneous frequency value to obtain an optical frequency signal acting on the receiving end user.

[0039] As a further improvement of the present invention, the instantaneous frequency value is:

[0040]

[0041] In the formula, is the instantaneous frequency value, is the first frequency, is the second frequency, Adding noise phase to the fiber, is the first phase, is the second phase, t is the time, The phase sum value of the modulated light changes over time. The first frequency and the first phase are obtained when the modulated light is subjected to positive frequency shift processing, and the second frequency and the second phase are obtained when the modulated light is modulated at each receiving end. The phase sum value is the sum of the first phase, the second phase and the phase of the optical fiber additional noise.

[0042] As a further improvement of the present invention, the optical frequency signal acting on the receiving end user specifically includes:

[0043]

[0044] In the formula, E 6 is the final optical frequency signal, is the initial frequency of the modulated light output by the laser, is the instantaneous frequency value, is the first frequency, is the second frequency, Adding noise phase to the fiber, is the first phase, is the second phase, is the initial phase of the modulated light output by the laser, is the phase change corresponding to the negative frequency shift processing of the modulated first optical signal, It is modulated light generated by a laser; the first frequency and the first phase are obtained when the modulated light is subjected to a positive frequency shift process, and the second frequency and the second phase are obtained when the modulated light is subjected to a modulation process at each receiving end.

[0045] The beneficial effects of the present invention are as follows: the distributed fiber optical frequency transmission system of the present invention adopts a distributed structure, including a transmitting end and a plurality of receiving ends, and the number of receiving ends can be flexibly expanded according to actual needs, and is suitable for application scenarios of different scales. The transmitting end and the receiving end are connected by an optical fiber link, and the low loss characteristics of the optical fiber are utilized to realize long-distance frequency transmission and cover a large geographical range. By dividing the laser light generated by the laser into reference light and modulated light, after being processed by the optical signal transmission module and the signal processing module at the transmitting end, phase noise suppression and large-capacity high-precision optical frequency distribution are realized, and after being processed by the receiving end signal transmission module and the signal driving module, high-precision and low-loss optical frequency transmission can be realized. It is ensured that each receiving end receives the same optical frequency signal as the transmitting end, thereby improving the stability and reliability of the entire system. The first radio frequency signal is phase processed and converted into a transmission optical signal, and negative frequency shift processing is performed at the receiving end, etc., to ensure the accuracy and stability of frequency transmission. The first optical signal is transmitted to the corresponding receiving end through wavelength division multiplexing processing and an optical fiber link, which improves the efficiency and reliability of signal transmission, reduces interference between signals, and enables users to obtain high-quality optical frequency signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 is a schematic diagram of the structure of a distributed fiber optical frequency transmission system in an embodiment of the present invention;

[0048] Figure 2 is a schematic flow chart of a distributed fiber optical frequency transmission method according to an embodiment of the present invention;

[0049] In the figure, OC1-first coupler; FM1-first Faraday rotator; PD1-photodetector; AOM1-first modulator; WDM1-first wavelength division multiplexer; OC2-second coupler; WDM2-second wavelength division multiplexer; AOM2-second modulator; FM2-second Faraday rotator; OC3-third coupler; AOM4-third modulator; RF1-first radio frequency generator; RF2-second radio frequency generator; RF3-third radio frequency generator; WDM3-third wavelength division multiplexer; AOM3-fourth modulator; AOM5-fifth modulator; FM3-third Faraday rotator; E 1 - Laser output from the laser; E 2 - The modulated light is transmitted to the receiving end through the optical fiber link and the corresponding optical signal is modulated and processed; E 3 -Return light from each receiving end; E 4 - a first radio frequency signal; E 5 - a second radio frequency signal; - instantaneous frequency signal; - a first frequency; - a second frequency; -Third frequency. DETAILED DESCRIPTION

[0050] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] Explanation of relevant terms:

[0052] WDM (Wavelength Division Multiplexing): Wavelength division multiplexing is a technology that transmits multiple optical signals of different wavelengths simultaneously in one optical fiber.

[0053] PD (PhotoDetector): Photodetector, a device that converts light signals into electrical signals.

[0054] FM (Faraday Rotator Mirror): Faraday rotator mirror, an optical device based on the Faraday effect.

[0055] AOM (Acousto-Optic Modulator): An optical device that uses the acousto-optic effect to control the intensity, frequency, and direction of light.

[0056] OC (Optical Fiber Coupler): An optical device that can couple optical signals from one or more input optical fibers to one or more output optical fibers.

[0057] RF (Radio Frequency): Radio frequency transmitter, which transmits electromagnetic waves in the frequency range of 3kHz to 300GHz.

[0058] IQ phase detector: Based on the processing of orthogonal (I / Q) signals. In communication systems, signals are usually divided into in-phase (I) components and quadrature (Q) components. The I component and the Q component are two mutually orthogonal signals that can be obtained by orthogonal modulation of the input signal.

[0059] The concept of the present invention is to provide a distributed fiber optic frequency transmission method and system, wherein the system mainly includes a transmitting end and a corresponding plurality of receiving ends, and the transmitting end and the plurality of receiving ends are connected via an optical fiber link.

[0060] The transmitting end includes an optical signal transmission module and a signal processing module. The optical signal transmission module is used to divide the laser generated by the laser into reference light and modulated light, and then perform positive frequency shift processing on the modulated light to obtain a first optical signal, and transmit the first optical signal to a corresponding number of receiving ends through wavelength division multiplexing processing and an optical fiber link, and receive the return light from each receiving end. The optical signal transmission module is responsible for dividing the laser generated by the laser into reference light and modulated light. After the modulated light is processed by positive frequency shift, it is transmitted through an optical fiber link. In order to transmit the signal to multiple receiving ends, a corresponding number of optical fiber links are provided for the receiving ends, and the optical signal transmitted by each optical fiber link corresponds to one receiving end. In addition, the module is also responsible for receiving the optical signal returned by each receiving end. High-precision optical frequency transmission can be achieved.

[0061] The signal processing module is used to perform beat frequency processing on the reference light and the return light from each receiving end to obtain the first RF signal. After phase processing on the first RF signal, the instantaneous frequency value of the first RF signal is obtained, and the instantaneous frequency value is converted into a transmission optical signal and transmitted to each receiving end, thereby ensuring the accuracy and stability of frequency transmission.

[0062] The receiving end includes a signal transmission module and a signal driving module.

[0063] The signal transmission module is used to modulate the first optical signal output by the received optical signal transmission module, and reflect the modulated part of the first optical signal as return light to the transmitting end, thereby realizing distributed reception and detection. This helps to expand the coverage of the system and improve the flexibility and scalability of the system.

[0064] The signal driving module is used to convert the received transmission optical signal into an instantaneous frequency value, and then drive the modulated transmission first optical signal in the signal transmission module to perform negative frequency shift processing to obtain the final optical frequency signal acting on the receiving end user.

[0065] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, wherein the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0066] Example 1

[0067] like Figure 1 As shown, this embodiment provides a distributed fiber optical frequency transmission system, including a transmitting end and a corresponding plurality of receiving ends, wherein the transmitting end and the plurality of receiving ends are connected via an optical fiber link.

[0068] The transmitting end includes an optical signal transmission module and a signal processing module.

[0069] The optical signal transmission module is used to divide the laser light generated by the laser into reference light and modulated light. The modulated light is subjected to positive frequency shift processing to obtain a first optical signal, and the first optical signal is transmitted to a corresponding number of receiving ends through wavelength division multiplexing processing and an optical fiber link, and the return light of each receiving end is received.

[0070] Among them, the optical signal transmission module includes: a first coupler OC1, a first modulator AOM1, and a first wavelength division multiplexer WDM1 in sequence along the signal transmission direction; a first Faraday rotator FM1 is also arranged between the first coupler OC1 and the first modulator AOM1. The first coupler OC1 divides the laser into reference light and modulated light. The first modulator AOM1 is used to perform positive frequency shift processing on the modulated light, and the processed modulated light is used as the first optical signal. The first optical signal is transmitted to each receiving end after passing through the first wavelength division multiplexer WDM1 and the optical fiber link. The first wavelength division multiplexer is used to merge and process the first optical signal output by the first modulator AOM1 and the transmission optical signal output by the signal processing module, and transmit them to each receiving end through the optical fiber links corresponding to the number of receiving ends. The first Faraday rotator FM1 can reflect the reference light to the signal processing module.

[0071] In this embodiment, the laser used is a narrow linewidth laser, and the first coupler OC1 is a 2*2 fiber coupler with a splitting ratio of 9:1, in which 10% of the laser is transmitted to the first Faraday rotator FM1 as reference light; 90% of the laser is transmitted in the optical signal transmission module as modulated light. In the transmission path of the optical signal, a Faraday rotator is used for reflection. The Faraday rotator has non-reciprocity, which can effectively prevent the reverse transmission and interference of the optical signal, thereby improving the reliability and stability of the system. The modulation frequency of the first modulator AOM1 usually ranges from tens of MHz to several GHz. The number of channels of the first wavelength division multiplexer WDM1 is set according to the number of receiving ends.

[0072] The signal processing module is used to obtain a first radio frequency signal after performing beat frequency processing on the reference light and the return light from each receiving end; obtain an instantaneous frequency value of the first radio frequency signal after performing phase processing on the first radio frequency signal, and is also used to convert the instantaneous frequency value into a transmission optical signal.

[0073] Specifically, the signal processing module includes a photodetector PD1, a phase processing module and an optical transmitter.

[0074] The photodetector is arranged between the first coupler OC1 and the first wavelength division multiplexer WDM1, and is used to transmit the reference light and the return light of each receiving end. After the beat frequency processing, the first RF signal corresponding to each receiving end is obtained , where the first RF signal Contains twice the fiber-added phase noise.

[0075] The phase processing module is used to process the first radio frequency signal Perform phase processing to obtain the instantaneous frequency signal of the first RF signal , applying the instantaneous frequency signal to the optical transmitter. The optical transmitter converts the instantaneous frequency signal into a transmission optical signal, which is transmitted to the corresponding receiving end through the corresponding number of optical fiber links at the receiving end.

[0076] The phase processing module includes a power divider amplifier and a number of frequency processing submodules corresponding to the number of receiving ends. The frequency processing submodules include a filter, a signal conditioning unit, a binary frequency divider, an IQ phase detector, and a phase extension unit.

[0077] The power divider amplifier is used to divide the first radio frequency signal into a number corresponding to the receiving end, and transmit them to the corresponding frequency processing submodules respectively.

[0078] In the frequency processing submodule, the first RF signal is filtered by the filter, and then processed by the signal conditioning unit and the binary divider to obtain the second RF signal containing the additional phase noise of the optical fiber. .

[0079] After the second radio frequency signal is processed by the IQ phase detector and the phase stretching unit, an instantaneous frequency value is obtained.

[0080] In the frequency processing submodule, the first RF signal is filtered through a filter, and then processed by a signal conditioning unit and a binary divider to obtain a second RF signal containing one times the additional phase noise of the optical fiber. After the second RF signal is processed by an IQ phase detector and a phase extension unit, an instantaneous frequency value is obtained. The instantaneous frequency value is loaded onto the optical transmitter. The optical transmitter converts the instantaneous frequency value into an optical signal and sends it to the first wavelength division multiplexer WDM1. The instantaneous frequency value can be accurately extracted through signal conditioning and effectively utilized. The sophisticated signal processing method ensures that the system can work stably in various environments and provide users with reliable optical frequency signals.

[0081] In addition, a second coupler OC2 is also provided on the optical fiber link in this embodiment, and the second coupler OC2 divides the optical fiber link into a number of parts corresponding to the number of receiving ends. The first optical signal output by the first wavelength division multiplexer WDM1 is divided into a number of optical signals corresponding to the number of receiving ends after passing through the second coupler OC2, and is transmitted to the corresponding receiving end through the corresponding optical fiber link.

[0082] The receiving end includes a signal transmission module and a signal driving module. The device structures of the receiving ends in this embodiment are the same. Figure 1 Only part of the structural end construction diagram is shown.

[0083] It is used to modulate the first optical signal output by the received optical signal transmission module, and reflect the modulated part of the first optical signal as return light to the transmitting end.

[0084] Among them, the signal transmission module includes in sequence along the signal transmission direction: a second wavelength division multiplexer WDM2 (i.e., the third wavelength division multiplexer WDM3 in the receiving end N), a second modulator AOM2 (i.e., the fourth modulator AOM3 in the receiving end N), a third coupler OC3 and a third modulator AOM4 (i.e., the fifth modulator AOM5 in the receiving end N); a second Faraday rotator FM2 (i.e., the third Faraday rotator FM3 in the receiving end N) is also arranged after the third coupler OC3.

[0085] The second wavelength division multiplexer WDM2 is used for performing wavelength division processing on the first optical signal output by the optical signal transmission module and the optical signal output by the signal processing module.

[0086] The third coupler OC3 divides the first optical signal output by the second wavelength division multiplexer into two parts, one of which is used as the return optical signal. The other part is used as the second optical signal. The second optical signal is transmitted to the third modulator AOM4 after passing through the third coupler OC3. The return light is reflected by the second Faraday rotator FM2 and then returns to the signal processing module through the optical fiber link.

[0087] The third modulator AOM4 is used to perform negative frequency shift processing on the second optical signal.

[0088] The signal driving module is used to convert the sectioned optical signal into an instantaneous frequency value, and then drive the second optical signal in the signal transmission module to perform negative frequency shift processing to obtain an optical frequency signal acting on the receiving end user.

[0089] Specifically, the signal driving module is arranged between the second wavelength division multiplexer WDM2 and the third modulator AOM4, and includes an optical receiver and a driver.

[0090] The transmission optical signal output by the signal processing module is converted into an instantaneous frequency signal after passing through the optical receiver, and the instantaneous frequency signal drives the third modulator AOM4 through the driver.

[0091] The second wavelength division multiplexer divides the received signal into a third radio frequency signal and a first optical signal. After the first optical signal is processed by the second modulator with positive frequency shift, it is transmitted to the third coupler, and the third coupler transmits the return light to the second Faraday rotator, which forms reflected light after passing through the second Faraday rotator. The reflected light is returned to the photodetector at the transmitting end through the optical fiber link again. The other part of the transmitted optical signal is output to the third modulator.

[0092] In addition, the system also includes a first radio frequency generator RF1 and a second radio frequency generator RF2. The first radio frequency generator RF1 is arranged at the first modulator AOM1 side of the transmitting end, and the first frequency signal (ie, the first frequency) generated by the first radio frequency generator The second RF generator RF2 is arranged on the second modulator AOM2 side of the receiving end, and the second frequency signal (ie, the second frequency) generated by the second RF generator Acting on the second modulator AOM2. In addition, the modulators used in this embodiment are all acousto-optic modulators. In the receiving end N, the third RF generator RF3 is equivalent to the second RF generator in the receiving end 1, generating a third frequency Acts on the fourth modulator AOM3.

[0093] Specifically, the signal expressions corresponding to the above modules during the processing are as follows:

[0094] The light field of the laser output is expressed as:

[0095]

[0096] In the formula, E 1 is the laser output of the laser, is the initial frequency of the modulated light output by the laser, is the initial phase of the modulated light output by the laser. The modulated optical signal is transmitted to the receiving end through the optical fiber link. After modulation processing at the receiving end, the corresponding optical signal expression is:

[0097]

[0098] In the formula, The modulated light is transmitted to the receiving end through the optical fiber link, and the corresponding optical signal after modulation processing at the receiving end is is the initial frequency of the modulated light output by the laser, is the instantaneous frequency value, is the first frequency, is the second frequency, Adding noise phase to the fiber, is the first phase, is the second phase, is the initial phase of the modulated light output by the laser. The first frequency and the first phase are obtained when the modulated light is subjected to positive frequency shift processing. The second frequency and the second phase are obtained when the modulated light is subjected to modulation processing at each receiving end. is the phase change of the modulated light after it passes through the optical fiber link and the receiving end, and t is the transmission time of the modulated light in the transmission system.

[0099] The specific expression of the return light at each receiving end is:

[0100]

[0101] In the formula, Return light from the receiving end, is the phase change corresponding to the returned light. The specific expression of the first RF signal corresponding to each receiving end is:

[0102]

[0103] In the formula, is the first radio frequency signal, is the phase change of the return light from the receiving end after the beat frequency processing with the reference light in time t. The phase change of the return light from the receiving end is twice that of the one-way propagation, and the corresponding phase sum in the one-way propagation is the sum of the first frequency, the second frequency and the additional phase noise of the optical fiber.

[0104] The RF signal is filtered by the filter, and then processed by the signal conditioning unit and the binary divider to obtain a processed second RF signal. The specific expression of the second RF signal is:

[0105]

[0106] is the second radio frequency signal.

[0107] The optical receiver receives the second RF signal from the optical transmitter, performs demodulation processing, and obtains the corresponding instantaneous frequency value. :

[0108]

[0109] In the formula, is the instantaneous frequency value, is the change of the phase and value of the modulated light over time, and the phase and value is the sum of the first phase, the second phase and the phase of the additional noise of the optical fiber. The driver uses this instantaneous frequency value to drive the third modulator to perform negative frequency shift processing, where the optical signal calculation expression corresponding to the output end of the third modulator is:

[0110]

[0111] In the formula, is the optical signal corresponding to the output end of the third modulator, is the phase change corresponding to the negative frequency shift processing of the modulated first optical signal, is the modulated light generated by the laser. Finally, a high-precision optical frequency signal is obtained at the output end of the third modulator, i.e., the user port.

[0112] The system in this embodiment adopts a distributed architecture, connecting several receiving ends through one transmitting end, and using wavelength division multiplexing technology to divide the modulated light into several optical signals and transmit them to the corresponding receiving ends respectively. This design enables the system to provide optical frequency signals to multiple users at the same time, has a large-capacity distribution capability, and can meet the needs of different users.

[0113] Each receiving end has an independent modulator and processing module, which can perform personalized modulation and processing on the optical frequency signal. This independent processing method not only improves the flexibility of the system, but also avoids the crosstalk of optical frequency signals between users, ensuring that each user can obtain high-quality optical frequency signals.

[0114] Example 2

[0115] like Figure 2 As shown, a distributed fiber optical frequency transmission method provided in this embodiment is implemented based on the distributed fiber optical frequency transmission system in Example 1. The method mainly includes:

[0116] The laser light generated by the laser is divided into reference light and modulated light.

[0117] The modulated light is subjected to positive frequency shift processing to obtain a first optical signal, and the first optical signal is subjected to wavelength division multiplexing processing and optical fiber link transmission, and then transmitted to corresponding receiving ends respectively.

[0118] After the first optical signal is modulated and processed by each receiving end, a return light of the receiving end is obtained after reflection, and the return light is subjected to beat frequency processing with the reference light to obtain a first radio frequency signal corresponding to each receiving end.

[0119] After performing phase processing on the first radio frequency signal, an instantaneous frequency value of the first radio frequency signal is obtained.

[0120] The instantaneous frequency value is converted into a transmission optical signal, which is transmitted to each receiving end through an optical fiber link. The modulated first optical signal in the receiving end is subjected to negative frequency shift processing according to the instantaneous frequency value to obtain an optical frequency signal acting on the receiving end user.

[0121] Specifically, the narrow linewidth laser passes through a 2×2 first coupler OC1, 10% of the reference light is reflected by the first Faraday rotator, 90% of the modulated light is connected to the first modulator 1 (AOM1, positive frequency shift mode) for positive frequency shift, and then enters the optical fiber link through wavelength division multiplexing, and is divided into multiple paths through the second coupler OC2, one path is connected to the receiving end 1, and the other path is connected to other receiving ends. Since the receiving end device has the same structure, this embodiment takes the receiving end 1 as an example for specific description. The optical frequency signal enters the wavelength division multiplexing of the receiving end 1 and enters the second modulator AOM2 (positive frequency shift mode) for frequency shift, and then passes through the third coupler OC3 and is divided into two parts, one part is reflected by the second Faraday rotator FM2 as return light, and the other part of the optical signal is connected to the third modulator AOM4 for output. The output light is the high-precision optical frequency signal required by the user.

[0122] The return light is reflected by the second Faraday rotator FM2, and then returns to the photodetector PD1 at the transmitting end through the optical fiber link to beat the reference light to obtain the first RF signal. The first RF signal contains twice the additional fiber phase noise. Therefore, through signal conditioning and a 2-way divider, the second RF signal is obtained. The second RF signal contains one times the additional fiber phase noise. Then, through IQ phase detection and phase extension, the instantaneous frequency value of the second RF signal is obtained. By loading the instantaneous frequency value onto the optical transmitter and demodulating it at the receiving end, the instantaneous frequency value is obtained at the receiving end. , the instantaneous frequency value is used to directly drive the third modulator AOM4 (negative frequency shift mode) through the driver to obtain a high-precision optical frequency signal. This method achieves high-precision optical frequency distribution with large capacity by suppressing phase noise at the user end, and this method does not have optical frequency signal crosstalk between users, so that users can obtain high-quality optical frequency signals.

[0123] Among them, the light field of the laser output laser is expressed as:

[0124]

[0125] In the formula, E 1 is the laser output of the laser, is the initial frequency of the modulated light output by the laser, is the initial phase of the modulated light output by the laser.

[0126] The modulated optical signal is transmitted to the receiving end through the optical fiber link. After modulation processing at the receiving end, the corresponding optical signal expression is:

[0127]

[0128] In the formula, The modulated light is transmitted to the receiving end through the optical fiber link, and the corresponding optical signal after modulation processing at the receiving end is is the initial frequency of the modulated light output by the laser, is the first frequency, is the second frequency, Adding noise phase to the fiber, is the first phase, is the second phase, is the initial phase of the modulated light output by the laser. The first frequency and the first phase are obtained when the modulated light is subjected to positive frequency shift processing. The second frequency and the second phase are obtained when the modulated light is subjected to modulation processing at each receiving end. is the phase change of the modulated light after it passes through the optical fiber link and the receiving end, and t is the transmission time of the modulated light in the transmission system.

[0129] The specific expression of the return light at each receiving end is:

[0130]

[0131] In the formula, Return light from the receiving end, is the phase change corresponding to the returned light. The specific expression of the first RF signal corresponding to each receiving end is:

[0132]

[0133] In the formula, is the first radio frequency signal, is the phase change of the return light from the receiving end after the beat frequency processing with the reference light in time t. The phase change of the return light from the receiving end is twice that of the one-way propagation, and the corresponding phase sum in the one-way propagation is the sum of the first frequency, the second frequency and the additional phase noise of the optical fiber.

[0134] The first RF signal is filtered through a filter, and then processed by a signal conditioning unit and a binary divider to obtain a processed second RF signal. The specific expression of the second RF signal is:

[0135]

[0136] The optical receiver receives the RF signal from the optical transmitter, performs demodulation processing, and obtains the corresponding instantaneous frequency value. :

[0137]

[0138] In the formula, is the instantaneous frequency value, is the variation of the phase sum value of the modulated light over time, where the phase sum value is the sum of the first phase, the second phase and the phase of the optical fiber additional noise.

[0139] The driver uses the instantaneous frequency value to drive the third modulator to perform negative frequency shift processing, wherein the optical signal calculation expression corresponding to the output end of the third modulator is:

[0140]

[0141] In the formula, is the optical signal corresponding to the output end of the third modulator, is the phase change corresponding to the negative frequency shift processing of the modulated first optical signal, It is the modulated light generated by the laser.

[0142] Finally, a high-precision optical frequency signal is obtained at the output end of the third modulator, namely the user port.

[0143] By dividing the laser light generated by the laser into reference light and modulated light, and performing positive frequency shift processing and wavelength division multiplexing on the modulated light, the stability and accuracy of the optical signal during transmission are ensured. At the same time, the optical signal is modulated and reflected at the receiving end, and through a specific combination of couplers and modulators, fine control of the optical frequency signal is achieved, laying the foundation for ultimately obtaining high-precision optical frequency signals. The beat frequency processing, signal conditioning, frequency division, and IQ phase detection operations performed between the transmitting and receiving ends can accurately obtain the instantaneous frequency value of the RF signal. By loading the instantaneous frequency value onto the optical transmitter and demodulating it at the receiving end, and then using the frequency value to drive the modulator in the negative frequency shift mode, the phase noise is effectively suppressed and the accuracy of the optical frequency signal is improved.

Claims

1. A distributed fiber optical frequency transmission system, characterized in that: It includes a transmitting end and a corresponding plurality of receiving ends, wherein the transmitting end and the plurality of receiving ends are connected via an optical fiber link; The transmitting end includes an optical signal transmission module and a signal processing module; The optical signal transmission module is used to separate the laser light generated by the laser into reference light and modulated light, and then perform positive frequency shift processing on the modulated light to obtain a first optical signal, transmit the first optical signal to a corresponding number of receiving ends through wavelength division multiplexing processing and an optical fiber link, and receive return light from each receiving end; The signal processing module is used to perform beat frequency processing on the reference light and the return light from each receiving end to obtain a first radio frequency signal; perform phase processing on the first radio frequency signal to obtain an instantaneous frequency value of the first radio frequency signal, and convert the instantaneous frequency value into a transmission optical signal to be transmitted to each receiving end; The receiving end includes a signal transmission module and a signal driving module, wherein the signal transmission module is used to modulate the first optical signal output by the received optical signal transmission module and reflect the modulated part of the first optical signal as return light to the transmitting end; The signal driving module is used to convert the received transmission optical signal into an instantaneous frequency value, and then drive the modulated first optical signal in the signal transmission module to perform negative frequency shift processing to obtain an optical frequency signal acting on the receiving end user.

2. The distributed fiber optical frequency transmission system according to claim 1, characterized in that: The optical signal transmission module includes, in sequence along the signal transmission direction: a first coupler, a first modulator, and a first wavelength division multiplexer; a first Faraday rotator is also arranged between the first coupler and the first modulator; The first coupler is used to divide the laser light into reference light and modulated light; The first modulator is used to perform positive frequency shift processing on the modulated light, and the processed modulated light is used as the first optical signal and then transmitted through the first wavelength division multiplexer and the optical fiber link to each receiving end; The first wavelength division multiplexer is used to combine and process the first optical signal output by the first modulator and the transmission optical signal output by the signal processing module, and transmit them to each receiving end through a corresponding number of optical fiber links at the receiving end; The first Faraday rotator is used to reflect the reference light to the signal processing module.

3. The distributed fiber optical frequency transmission system according to claim 2, characterized in that: The signal processing module includes a photodetector, a phase processing module and an optical transmitter; The photoelectric detector is arranged between the first coupler and the first wavelength division multiplexer, and is used to perform beat frequency processing on the reference light and the return light from each receiving end to obtain a first radio frequency signal corresponding to each receiving end; The phase processing module is used to perform phase processing on the first RF signal to obtain an instantaneous frequency signal of the first RF signal, and apply the instantaneous frequency signal to the optical transmitter; the optical transmitter is used to convert the instantaneous frequency signal into a transmission optical signal, and transmit it to the corresponding receiving end through a corresponding number of optical fiber links at the receiving end.

4. The distributed fiber optical frequency transmission system according to claim 3, characterized in that: The phase processing module includes a power divider amplifier and a number of frequency processing submodules corresponding to the number of receiving ends; the frequency processing submodules include a filter, a signal conditioning unit, a binary frequency divider, an IQ phase detector and a phase extension unit in sequence; The power divider amplifier is used to divide the first radio frequency signal into a number corresponding to the receiving end, and transmit them to the frequency processing submodule respectively; In the frequency processing submodule, the first radio frequency signal is filtered by a filter, and then processed by a signal conditioning unit and a binary divider to obtain a second radio frequency signal containing optical fiber additional phase noise; The second radio frequency signal is processed by the IQ phase detector and the phase stretching unit to obtain an instantaneous frequency value.

5. The distributed fiber optical frequency transmission system according to claim 1, characterized in that: The signal transmission module includes: a second wavelength division multiplexer, a second modulator, a third coupler and a third modulator; a second Faraday rotator is also arranged after the third coupler; The second wavelength division multiplexer is used to perform wavelength division processing on the first optical signal output by the optical signal transmission module and the transmission optical signal output by the signal processing module; The third coupler is used to divide the first optical signal output by the second wavelength division multiplexer into two parts, one part is used as the return light, and the other part is used as the second optical signal; the second optical signal is transmitted to the third modulator after passing through the third coupler; the return light is reflected by the second Faraday rotator and then returned to the signal processing module through the optical fiber link; The third modulator is used to perform negative frequency shift processing on the second optical signal.

6. The distributed fiber optical frequency transmission system according to claim 1, characterized in that: The signal driving module is arranged between the second wavelength division multiplexer and the third modulator, and includes an optical receiver and a driver; The transmission optical signal output by the signal processing module is converted into an instantaneous frequency signal after passing through the optical receiver, and the instantaneous frequency signal drives the third modulator through the driver.

7. The distributed fiber optical frequency transmission system according to claim 1, characterized in that: The system also includes a first radio frequency generator and a second radio frequency generator; The first RF generator is arranged at the first modulator side of the transmitting end, and the RF signal generated by the first RF generator acts on the first modulator; The second RF generator is arranged at the second modulator side of the receiving end, and the RF signal generated by the second RF generator acts on the second modulator.

8. A distributed fiber optical frequency transmission method, based on the distributed fiber optical frequency transmission system according to any one of claims 1 to 7, characterized in that: include: The laser light generated by the laser is divided into reference light and modulated light; Performing positive frequency shift processing on the modulated light to obtain a first optical signal, performing wavelength division multiplexing processing on the first optical signal and transmitting the first optical signal through an optical fiber link, and then transmitting the first optical signal to corresponding receiving ends respectively; After the first optical signal is modulated by each receiving end, a return light of the receiving end is obtained after reflection, and the return light is subjected to beat frequency processing with the reference light to obtain a first radio frequency signal corresponding to each receiving end; After performing phase processing on the first radio frequency signal, an instantaneous frequency value of the first radio frequency signal is obtained; The instantaneous frequency value is converted into a transmission optical signal, which is transmitted to each receiving end through an optical fiber link. The modulated first optical signal in the receiving end is subjected to negative frequency shift processing according to the instantaneous frequency value to obtain an optical frequency signal acting on the receiving end user.

9. The distributed fiber optical frequency transmission method according to claim 8, characterized in that: The instantaneous frequency value is: In the formula, is the instantaneous frequency value, is the first frequency, is the second frequency, Adding noise phase to the fiber, is the first phase, is the second phase, t is the time, The phase sum value of the modulated light changes over time. The first frequency and the first phase are obtained when the modulated light is subjected to positive frequency shift processing, and the second frequency and the second phase are obtained when the modulated light is modulated at each receiving end. The phase sum value is the sum of the first phase, the second phase and the phase of the optical fiber additional noise.

10. The distributed fiber optical frequency transmission method according to claim 8, characterized in that: The optical frequency signal acting on the receiving end user specifically includes: Where E6 is the final optical frequency signal, is the initial frequency of the modulated light output by the laser, is the instantaneous frequency value, is the first frequency, is the second frequency, Adding noise phase to the fiber, is the first phase, is the second phase, is the initial phase of the modulated light output by the laser, t is the time, is the phase change corresponding to the negative frequency shift processing of the modulated first optical signal, It is modulated light generated by a laser; the first frequency and the first phase are obtained when the modulated light is subjected to a positive frequency shift process, and the second frequency and the second phase are obtained when the modulated light is subjected to a modulation process at each receiving end.

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