A fiber-optic frequency transfer relay system with self-adjusting noise suppression parameters

Abstract

The present invention discloses a fiber optic frequency transmission relay system with self-adjusting noise suppression parameters, comprising a plurality of relay stations cascaded in sequence, each relay station comprising a receiving end, an optical amplifier end and a transmitting end connected in sequence, the transmitting end of the previous relay station being connected to the receiving end of the next relay station, wherein the receiving end is used to receive an optical frequency signal from the previous relay station; the optical amplifier end is used to coherently amplify the received optical frequency signal, the transmitting end is used to transmit the coherently amplified optical frequency signal to the next relay station, and measure and eliminate the additional phase noise in the signal transmission link. The fiber optic frequency transmission relay system of the present invention can effectively realize the self-adjustment of noise suppression parameters, thereby realizing the effective suppression of additional phase noise.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber communication, and in particular relates to an optical fiber frequency transmission relay system with self-adjusting noise suppression parameters. Background Art

[0002] As the stability and uncertainty of high-precision optical clock systems have stabilized at 10 -18 It plays an important role in navigation, precision measurement, gravitational wave detection and other fields. Optical frequency transmission technology based on optical fiber is one of the important means to achieve long-distance transmission and comparison of high-precision optical clock signals. For this reason, many countries in the world have planned to establish high-precision optical fiber optical frequency transmission networks.

[0003] At present, optical fiber networks are mainly designed and installed by cascading relay stations. In the process of optical fiber transmission, optical frequency signals will generate additional phase noise due to environmental interference, which will deteriorate the performance of the transmitted optical frequency signals. For this reason, it is necessary to use a phase-locked loop at the transmitting end of the relay station to detect and suppress the additional phase noise of the optical fiber. However, since the magnitude of the optical fiber noise will change with the changes in the environment, when performing the task of optical frequency transmission comparison, it is necessary to adjust and optimize the noise suppression parameters of each section of optical fiber. However, the relay station is located in the field room, making it difficult to achieve high-precision optical frequency transmission. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a fiber optic frequency transmission system with self-adjusting noise suppression parameters. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0005] The present invention provides a fiber optic frequency transmission relay system with self-adjusting noise suppression parameters, comprising a plurality of relay stations cascaded in sequence, each relay station comprising a receiving end, an optical amplifier end and a transmitting end connected in sequence, the transmitting end of the previous relay station being connected to the receiving end of the next relay station, wherein:

[0006] The receiving end is used to receive the optical frequency signal from the previous relay station; the optical amplifier end is used to coherently amplify the received optical frequency signal; the transmitting end is used to transmit the coherently amplified optical frequency signal to the next relay station, and measure and eliminate the additional phase noise in the signal transmission link.

[0007] In one embodiment of the present invention, the transmitting end of each relay station includes a first optical fiber coupler OC1, a first acousto-optic modulator AOM1 and a first Faraday rotator FM1, wherein:

[0008] The first optical fiber coupler OC1 is connected to the optical amplifier end through an optical fiber link, and is used to receive the optical frequency signal after coherent amplification by the optical amplifier end, and transmit a part of the coherently amplified optical frequency signal to the first acousto-optic modulator AOM1, and transmit the other part to the first Faraday rotator FM1;

[0009] The first acousto-optic modulator AOM1 is used to perform positive frequency shift on the received optical frequency signal, and transmit the positive frequency shifted optical frequency signal to the next relay station.

[0010] In one embodiment of the present invention, the receiving end of each relay station includes a second acousto-optic modulator AOM2, a second optical fiber coupler OC2 and a second Faraday rotator FM2, wherein:

[0011] The second acousto-optic modulator AOM2 is connected to the first acousto-optic modulator AOM1 of the previous relay station through an optical fiber link, and is used to receive the positively frequency-shifted optical frequency signal from the previous relay station and transmit it to the second optical fiber coupler OC2; the second optical fiber coupler OC2 is used to transmit a part of the optical frequency signal from the second acousto-optic modulator AOM2 to the second Faraday rotator FM2, and the other part to the optical amplifier end of the current relay station;

[0012] The second Faraday rotator FM2 is used to reflect the received optical frequency signal. The reflected optical frequency signal returns to the first acousto-optic modulator AOM1 of the previous relay station through the second acousto-optic modulator AOM2, and can beat with the reference light in the transmitting end of the previous relay station to obtain phase noise information.

[0013] In one embodiment of the present invention, the first optical fiber coupler OC1 is a two-input and two-output optical fiber coupler, which is respectively connected to the first acousto-optic modulator AOM1 and the first Faraday rotator FM1 through an optical fiber link, and is used to transmit 10% of the optical frequency signal to the first Faraday rotator FM1, and the remaining 90% of the optical frequency signal to the first acousto-optic modulator AOM1; the second optical fiber coupler OC2 is a one-input and two-output optical fiber coupler, which is respectively connected to the second Faraday rotator FM2 and the optical amplifier end through an optical fiber link, and is used to transmit 50% of the optical frequency signal to the second Faraday rotator FM2, and the remaining 50% of the optical frequency signal to the optical amplifier end.

[0014] In one embodiment of the present invention, the transmitting end of each relay station further includes a microcontroller MCU, a first conversion switch SW1, a second conversion switch SW2, a first detector PD1, a first bandpass filter BPF1, a second bandpass filter BPF2, a first logarithmic amplifier LA1, a second logarithmic amplifier LA2, a first power synthesizer distributor PC1, a second power synthesizer distributor PC2, a frequency division phase detector PFD, a PI servo circuit, a first radio frequency signal source RF1, a third radio frequency signal source RF3 and a phase noise test unit, wherein:

[0015] The microcontroller MCU is connected to the first conversion switch SW1, the second conversion switch SW2 and the PI servo circuit, and is used to control the opening or closing of different channels of the first conversion switch SW1 and the second conversion switch SW2 according to the received control instruction;

[0016] The input end of the first detector PD1 is connected to the first optical fiber coupler OC1, and the second bandpass filter BPF2 and the second logarithmic amplifier LA2 are connected in series between the second output end of the first detector PD1 and the second contact of the second conversion switch SW2;

[0017] The first bandpass filter BPF1 and the first logarithmic amplifier LA1 are connected in series between the first output end of the first detector PD1 and the input end of the first power synthesis distributor PC1; the first output end of the first power synthesis distributor PC1 is connected to the first contact of the second conversion switch SW2, the second output end of the first power synthesis distributor PC1 is connected to the frequency division phase detector PFD, and the output end of the frequency division phase detector PFD is connected to the PI servo circuit;

[0018] The third RF signal source RF3 is connected to the first contact of the first conversion switch SW1, and the PI servo circuit is also connected to the first RF signal source RF1;

[0019] Two input ends of the second power synthesizer distributor PC2 are respectively connected to the first radio frequency signal source RF1 and the first conversion switch SW1, and the output end of the second power synthesizer distributor PC2 is connected to the first acousto-optic modulator AOM1;

[0020] The phase noise test unit is connected between the second switch SW2 and the microcontroller MCU;

[0021] The frequency division phase detector PFD is used to process the radio frequency signal from the first power synthesis distributor PC1, obtain a phase error signal and send it to the PI servo circuit; the PI servo circuit is used to drive the first radio frequency signal source RF1 according to the phase error signal;

[0022] The phase noise test unit is used to measure the phase noise in the transmission link and send it to the microcontroller MCU. The microcontroller MCU is used to process the phase noise and adjust the PI parameters in the PI servo circuit to achieve phase noise suppression.

[0023] In one embodiment of the present invention, the receiving end further comprises a second radio frequency signal source RF2 connected to the second acousto-optic modulator AOM2, wherein the second radio frequency signal source RF2 is used to generate a radio frequency signal The radio frequency signal It can be returned to the sending end of the previous relay station through the second acousto-optic modulator AOM2.

[0024] In one embodiment of the present invention, the microcontroller MCU is used for:

[0025] When receiving a control instruction from the operation control system, the first contact of the first conversion switch SW1 is controlled to be connected, and the first contact of the second conversion switch SW2 is controlled to be disconnected and the second contact is controlled to be connected;

[0026] Collecting the first phase noise from the phase noise test unit , and according to the first phase noise Obtaining the theoretical limit of noise suppression :

[0027] ,

[0028] in, represents the Fourier frequency, represents the Fourier frequency The corresponding theoretical limit of noise suppression is, is the time required for light to pass through the optical fiber once, , is the refractive index of the optical fiber, is the speed of light in vacuum, is the length of the connected optical fiber link.

[0029] In one embodiment of the present invention, the microcontroller MCU is also used for:

[0030] The theoretical limit of noise suppression is obtained After that, the first contact of the first conversion switch SW1 is controlled to be disconnected, and the first contact of the second conversion switch SW2 is controlled to be connected and the second contact is controlled to be disconnected;

[0031] After the first contact of the first conversion switch SW1 is disconnected and the first contact of the second conversion switch SW2 is connected, the second phase noise calculated by the phase noise test unit is obtained. , Represents Fourier frequency The corresponding second phase noise.

[0032] In one embodiment of the present invention, the microcontroller MCU is also used for:

[0033] The noise suppression factor a is obtained according to the noise suppression theoretical limit corresponding to different Fourier frequencies and the second phase noise, and the calculation formula is:

[0034] ,

[0035] It is determined whether the noise suppression factor a is less than a set threshold value. If not, the proportional value in the PI servo circuit is adjusted and the noise suppression factor a is calculated again until the noise suppression factor a is less than the set threshold value.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] At present, fiber optic frequency transmission relay systems are arranged and installed in outdoor communication rooms, so it is impossible to judge whether the additional phase noise of the optical fiber has reached the noise suppression limit. The present invention provides a fiber optic frequency transmission relay system with self-adjusting noise suppression parameters, including a plurality of relay stations cascaded in sequence, each relay station including a receiving end, an optical amplifier and a transmitting end connected in sequence, the transmitting end of the previous relay station is connected to the receiving end of the next relay station, the receiving end is used to receive the optical frequency signal from the previous relay station; the optical amplifier is used to coherently amplify the received optical frequency signal, the transmitting end is used to transmit the optical frequency signal after coherent amplification to the next relay station, and measure and eliminate the additional phase noise in the signal transmission link, which can effectively realize the self-adjustment of the noise suppression parameters, thereby realizing the effective suppression of the additional phase noise.

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a module diagram of a fiber optic frequency transmission relay system with self-adjusting noise suppression parameters provided by an embodiment of the present invention;

[0040] Figure 2 is a structural diagram of a sending end provided by an embodiment of the present invention;

[0041] Figure 3 It is a structural schematic diagram of a receiving end and an optical amplifier provided by an embodiment of the present invention;

[0042] Figure 4The present invention provides a noise suppression flow chart of a fiber optic frequency transmission relay system with self-adjusting noise suppression parameters. DETAILED DESCRIPTION

[0043] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description of a fiber optic frequency transmission relay system and method with self-adjustment of noise suppression parameters proposed by the present invention in combination with the accompanying drawings and specific implementation methods.

[0044] The above and other technical contents, features and effects of the present invention are clearly presented in the following detailed description of the specific implementation modes in conjunction with the accompanying drawings. Through the description of the specific implementation modes, the technical means and effects adopted by the present invention to achieve the predetermined purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and explanation purposes and are not used to limit the technical solutions of the present invention.

[0045] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants are intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also other elements that are not explicitly listed. In the absence of more restrictions, the elements defined by the statement "including one..." do not exclude the existence of other identical elements in the article or device including the elements.

[0046] Embodiment 1

[0047] See also Figure 1 , Figure 1 It is a module diagram of a fiber-optic frequency transmission relay system with self-adjusting noise suppression parameters provided by an embodiment of the present invention. The relay system includes multiple relay stations cascaded in sequence, and each relay station includes a receiving end, an optical amplifier end, and a transmitting end connected in sequence, and the transmitting end of the previous relay station is connected to the receiving end of the next relay station, wherein the receiving end is used to receive the optical frequency signal from the previous relay station; the optical amplifier end is used to coherently amplify the received optical frequency signal, and the transmitting end is used to transmit the coherently amplified optical frequency signal to the next relay station, and measure and eliminate the additional phase noise in the signal transmission link. In this embodiment, optical fiber is used to connect two adjacent relay stations, and the receiving end, optical amplifier end, and transmitting end of the same relay station are all connected by optical fiber to transmit signals.

[0048] Further, please see Figure 2 and Figure 3The transmitting end of each relay station includes a first optical fiber coupler OC1, a first acousto-optic modulator AOM1 and a first Faraday rotator FM1, wherein the first optical fiber coupler OC1 is connected to the optical amplifier end through an optical fiber link, and is used to receive the optical frequency signal after coherent amplification at the optical amplifier end, and transmit a part of the coherently amplified optical frequency signal to the first acousto-optic modulator AOM1, and the other part to the first Faraday rotator FM1; the first acousto-optic modulator AOM1 is used to perform positive frequency shift on the received optical frequency signal, and transmit the positive frequency shifted optical frequency signal to the next relay station.

[0049] The receiving end of each relay station includes a second acousto-optic modulator AOM2, a second fiber coupler OC2 and a second Faraday rotator FM2, wherein the second acousto-optic modulator AOM2 is connected to the first acousto-optic modulator AOM1 of the previous relay station through an optical fiber link, and is used to receive the positively frequency-shifted optical frequency signal from the previous relay station and transmit it to the second fiber coupler OC2, and the second fiber coupler OC2 is used to transmit a part of the optical frequency signal from the second acousto-optic modulator AOM2 to the second Faraday rotator FM2, and the other part is transmitted to the optical amplifier end of the current relay station; the second Faraday rotator FM2 is used to reflect the received optical frequency signal, and the reflected optical frequency signal returns to the first acousto-optic modulator AOM1 of the previous relay station through the second acousto-optic modulator AOM2, and can beat with the reference light in the transmitting end of the previous relay station to obtain phase noise information.

[0050] In this embodiment, the first fiber coupler OC1 is a two-input and two-output (2×2) fiber coupler, which is respectively connected to the first acousto-optic modulator AOM1 and the first Faraday rotator FM1 through an optical fiber link, and is used to transmit 10% of the optical frequency signal to the first Faraday rotator FM1, and the remaining 90% of the optical frequency signal is transmitted to the first acousto-optic modulator AOM1 for positive frequency shift; the second fiber coupler OC2 is a one-input and two-output (1×2) fiber coupler, which is respectively connected to the second Faraday rotator FM2 and the optical amplifier end through an optical fiber link, and is used to transmit 50% of the optical frequency signal to the second Faraday rotator FM2, and the remaining 50% of the optical frequency signal is transmitted to the optical amplifier end.

[0051] Specifically, at the transmitting end of the Nth relay station, the optical frequency signal passes through a 2×2 first optical fiber coupler OC1, and 10% of the optical frequency signal is transmitted to the first Faraday rotator FM1 as a reference light, and the remaining 90% of the optical frequency signal is transmitted to the first acousto-optic modulator AOM1 for positive frequency shift. The transmitting end of the Nth relay station is connected to the receiving end of the N+1th relay station through an optical fiber link. At the receiving end of the N+1th relay station, the optical frequency signal enters the second acousto-optic modulator AOM2 and passes through a 1×2 second optical fiber coupler OC2, and 50% of the optical frequency signal is transmitted to the second Faraday rotator FM2. This part of the optical frequency signal is reflected by the second Faraday rotator FM2 and then passes through the second acousto-optic modulator AOM2 and the optical fiber link again to return to the transmitting end of the Nth relay station, for beating with the reference light in the transmitting end of the Nth relay station to obtain the additional phase noise information of the optical fiber link. The remaining 50% of the optical frequency signal is transmitted to the optical amplifier. Figure 3 As shown, in the optical amplifier end, there are a laser and a second detector PD2. The second detector PD2 can measure the beat signal between the received optical frequency signal and the optical frequency signal output by the laser, and lock the phase of the optical frequency signal output by the laser to the received optical frequency signal through a servo system (servo), thereby realizing coherent amplification of the signal light.

[0052] Continue to see Figure 2 The transmitting end of this embodiment also includes a microcontroller MCU, a first conversion switch SW1, a second conversion switch SW2, a first detector PD1, a first bandpass filter BPF1, a second bandpass filter BPF2, a first logarithmic amplifier LA1, a second logarithmic amplifier LA2, a first power synthesis distributor PC1, a second power synthesis distributor PC2, a frequency division phase detector PFD, and a PI servo circuit (in Figure 2 PI in the figure), a first RF signal source RF1, a third RF signal source RF3 and a phase noise testing unit.

[0053] The microcontroller MCU is connected to the first conversion switch SW1, the second conversion switch SW2 and the PI servo circuit, and is used to control the opening or closing of different channels of the first conversion switch SW1 and the second conversion switch SW2 according to the control instructions from the external operation and control system; the input end of the first detector PD1 is connected to the first optical fiber coupler OC1, and the second bandpass filter BPF2 and the second logarithmic amplifier LA2 are connected in series between the second output end of the first detector PD1 and the second contact of the second conversion switch SW2.

[0054] The first bandpass filter BPF1 and the first logarithmic amplifier LA1 are connected in series between the first output end of the first detector PD1 and the input end of the first power synthesizer distributor PC1; the first output end of the first power synthesizer distributor PC1 is connected to the first contact of the second conversion switch SW2, the second output end of the first power synthesizer distributor PC1 is connected to the frequency division phase detector PFD, and the output end of the frequency division phase detector PFD is connected to the PI servo circuit; the third RF signal source RF3 is connected to the first contact of the first conversion switch SW1, and the PI servo circuit is also connected to the first RF signal source RF1.

[0055] The two input ends of the second power synthesis distributor PC2 are respectively connected to the first RF signal source RF1 and the first conversion switch SW1, and the output end of the second power synthesis distributor PC2 is connected to the first acousto-optic modulator AOM1; the phase noise test unit is connected between the second conversion switch SW2 and the microcontroller MCU; the frequency division phase detector PFD is used to process the RF signal from the first power synthesis distributor PC1, obtain the phase error signal and send it to the PI servo circuit; the PI servo circuit is used to drive the first RF signal source RF1 according to the phase error signal; the phase noise test unit is used to measure the phase noise in the transmission link and send it to the microcontroller MCU, and the microcontroller MCU is used to process the phase noise and adjust the PI parameters in the PI servo circuit to achieve phase noise suppression.

[0056] The receiving end also includes a second radio frequency signal source RF2 connected to the second acousto-optic modulator AOM2, and the second radio frequency signal source RF2 is used to generate a radio frequency signal ; RF signal It can be returned to the transmitting end of the previous relay station through the second acousto-optic modulator AOM2.

[0057] The microcontroller MCU of this embodiment is specifically used for: when receiving a control instruction from the operation control system, controlling the first contact of the first conversion switch SW1 to be connected, and controlling the first contact of the second conversion switch SW2 to be disconnected and the second contact to be connected.

[0058] Specifically, Figure 4 As shown, when phase noise suppression is required, the operation control system sends an automatic optimization command (control instruction) to the microcontroller MCU, and the microcontroller MCU controls the first contact of the first conversion switch SW1 (see Figure 2 ①) at SW1 in the middle is connected, and the second contact of the second conversion switch SW2 (see Figure 2 At this time, the first acousto-optic modulator AOM1 can receive the RF signal from the first RF signal source RF1. and a radio frequency signal from a third radio frequency signal source RF3 , by the RF signal and RF signals The reference light and the transmission light signal that passes through the first AOM1, the optical fiber link and the second AOM2 are transmitted to the first detector PD1 through the optical fiber coupler OC1.

[0059] The first detector PD1 divides the detected beat frequency signal into a first signal and the second signal , where the first signal After passing through the first bandpass filter BPF1 (center frequency is ) and the bandpass filtering and power amplification of the first logarithmic amplifier LA1, and then after passing through the first power synthesis distributor PC1, it is connected to the frequency division phase detector PFD. The frequency division phase detector PFD can generate a reference signal (for example, 10MHz), compare the signal from the first power synthesis distributor PC1 with the reference signal, and obtain a phase error signal. The phase error signal is then input into the PI (proportional integral) servo circuit, and the PI servo circuit then drives and adjusts the first RF signal source RF1 to achieve phase noise suppression. It should be noted that at this time, the first contact of the second conversion switch SW2 is disconnected, that is, the first power synthesis distributor PC1 is disconnected from the second conversion switch SW2.

[0060] At the same time, the second signal After the bandpass filtering and power amplification by the second bandpass filter BPF2 and the second logarithmic amplifier LA2, the second switching switch SW2 is connected to the phase noise test unit, which is used to measure the phase noise. The measured phase noise is then collected by the microcontroller MCU and recorded as , then the microcontroller MCU is used to calculate the phase noise After further processing, the theoretical limit of noise suppression is obtained:

[0061] ,

[0062] in, represents the Fourier frequency, Represents Fourier frequency The corresponding theoretical limit of noise suppression is, is the time required for light to pass through the optical fiber once, , is the refractive index of the optical fiber, is the speed of light in vacuum, is the length of the connected optical fiber link.

[0063] Furthermore, the microcontroller MCU is also used to: obtain the theoretical limit of noise suppression After that, the first contact of the first conversion switch SW1 is controlled to be disconnected, and the first contact of the second conversion switch SW2 is controlled to be connected and the second contact is disconnected; after the first contact of the first conversion switch SW1 is disconnected and the first contact of the second conversion switch SW2 is connected, the second phase noise calculated by the phase noise test unit is obtained.

[0064] Specifically, in obtaining the theoretical limit of noise suppression After that, the microcontroller MCU controls the first contact of the first conversion switch SW1 to be disconnected, and controls the first contact of the second conversion switch SW2 to be connected and the second contact to be disconnected. It should be noted that the second contact of the first conversion switch SW1 is not connected to the circuit, that is, it always remains disconnected. At this time, the third RF signal source RF3 is disconnected, and the first acousto-optic modulator AOM1 is only powered by the RF signal. Drive and receive the RF signal from the second RF signal source RF2 The beat frequency signal formed by the multiple RF signals is transmitted to the first detector PD1 through the optical fiber coupler OC1. The first detector PD1 detects the beat frequency signal. , after passing through the first bandpass filter BPF1 (center frequency is ) and the bandpass filtering and power amplification of the first logarithmic amplifier LA1, and then after passing through the first power synthesis distributor PC1, it is connected to the phase noise test unit through the second conversion switch SW2 (channel ① is in the open state). The phase noise test unit generates a second phase noise according to the signal from the first power synthesis distributor PC1, and the microcontroller MCU collects the measured phase noise, which is recorded as , Represents Fourier frequency The corresponding second phase noise. At the same time, the beat frequency signal The reference signal (for example, 10 MHz) enters the phase detector PFD at the same time to obtain a phase error signal.

[0065] Then, the microcontroller MCU calculates the noise suppression factor a according to the theoretical limit of noise suppression corresponding to different Fourier frequencies and the second phase noise. The calculation formula is:

[0066] ,

[0067] That is, the noise suppression factor a is equal to the sum of the ratios of the theoretical limits of noise suppression corresponding to different Fourier frequencies to the second phase noise.

[0068] After obtaining the noise suppression factor a, it is determined whether the noise suppression factor a is less than a set threshold value. If not, the proportional value in the PI servo circuit is adjusted and the noise suppression factor a is calculated again until the noise suppression factor a is less than the set threshold value. In this embodiment, the threshold value is set to 1.2 based on experience.

[0069] Specifically, the noise suppression factor a is used to characterize the noise suppression effect. If a is less than 1.2, the PI combination of the current PI servo circuit is the optimal value and the optimization is completed. If a is greater than 1.2, different PI value combinations are adjusted until a is less than 1.2 and the optimization is completed.

[0070] The present invention provides a fiber optic frequency transmission relay system with self-adjusting noise suppression parameters, comprising a plurality of relay stations cascaded in sequence, wherein each relay station in a sequence comprises a receiving end, an optical amplifier and a transmitting end connected in sequence, the transmitting end of the previous relay station is connected to the receiving end of the next relay station, the receiving end is used to receive the optical frequency signal from the previous relay station; the optical amplifier is used to coherently amplify the received optical frequency signal, the transmitting end is used to transmit the coherently amplified optical frequency signal to the next relay station, and measure and eliminate the additional phase noise in the signal transmission link, which can effectively realize the self-adjustment of the noise suppression parameters, thereby realizing the effective suppression of the additional phase noise.

[0071] In the several embodiments provided by the present invention, it should be understood that the apparatus and method disclosed by the present invention can be implemented in other ways. For example, the apparatus embodiments described above are only illustrative, for example, the division of the modules is only a logical function division, and there may be other division methods in actual implementation, for example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0072] In addition, each functional module in each embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of hardware plus software functional modules.

[0073] 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 fiber optic frequency transmission relay system with self-adjusting noise suppression parameters, characterized in that: It includes multiple relay stations cascaded in sequence, each relay station includes a receiving end, an optical amplifier end and a transmitting end connected in sequence, and the transmitting end of the previous relay station is connected to the receiving end of the next relay station, wherein: The receiving end is used to receive the optical frequency signal from the previous relay station; the optical amplifier end is used to coherently amplify the received optical frequency signal; the transmitting end is used to transmit the coherently amplified optical frequency signal to the next relay station, and measure and eliminate the additional phase noise in the signal transmission link. The transmitting end of each relay station includes a first optical fiber coupler OC1, a first acousto-optic modulator AOM1 and a first Faraday rotator FM1, wherein: The first optical fiber coupler OC1 is connected to the optical amplifier end through an optical fiber link, and is used to receive the optical frequency signal after coherent amplification by the optical amplifier end, and transmit a part of the coherently amplified optical frequency signal to the first acousto-optic modulator AOM1, and transmit the other part to the first Faraday rotator FM1; The first acousto-optic modulator AOM1 is used to perform positive frequency shift on the received optical frequency signal, and transmit the positive frequency shifted optical frequency signal to the next relay station; The transmitting end of each relay station also includes a microcontroller MCU, a first conversion switch SW1, a second conversion switch SW2, a first detector PD1, a first bandpass filter BPF1, a second bandpass filter BPF2, a first logarithmic amplifier LA1, a second logarithmic amplifier LA2, a first power synthesis distributor PC1, a second power synthesis distributor PC2, a frequency division phase detector PFD, a PI servo circuit, a first radio frequency signal source RF1, a third radio frequency signal source RF3 and a phase noise test unit, wherein, The microcontroller MCU is connected to the first conversion switch SW1, the second conversion switch SW2 and the PI servo circuit, and is used to control the opening or closing of different channels of the first conversion switch SW1 and the second conversion switch SW2 according to the received control instruction; The input end of the first detector PD1 is connected to the first optical fiber coupler OC1, and the second bandpass filter BPF2 and the second logarithmic amplifier LA2 are connected in series between the second output end of the first detector PD1 and the second contact of the second conversion switch SW2; The first bandpass filter BPF1 and the first logarithmic amplifier LA1 are connected in series between the first output end of the first detector PD1 and the input end of the first power synthesis distributor PC1; the first output end of the first power synthesis distributor PC1 is connected to the first contact of the second conversion switch SW2, the second output end of the first power synthesis distributor PC1 is connected to the frequency division phase detector PFD, and the output end of the frequency division phase detector PFD is connected to the PI servo circuit; The third RF signal source RF3 is connected to the first contact of the first conversion switch SW1, and the PI servo circuit is also connected to the first RF signal source RF1; Two input ends of the second power synthesizer distributor PC2 are respectively connected to the first radio frequency signal source RF1 and the first conversion switch SW1, and the output end of the second power synthesizer distributor PC2 is connected to the first acousto-optic modulator AOM1; The phase noise test unit is connected between the second switch SW2 and the microcontroller MCU; The frequency division phase detector PFD is used to process the radio frequency signal from the first power synthesis distributor PC1, obtain a phase error signal and send it to the PI servo circuit; the PI servo circuit is used to drive the first radio frequency signal source RF1 according to the phase error signal; The phase noise test unit is used to measure the phase noise in the transmission link and send it to the microcontroller MCU. The microcontroller MCU is used to process the phase noise and adjust the PI parameters in the PI servo circuit to achieve phase noise suppression.

2. The fiber optic frequency transmission relay system with self-adjusting noise suppression parameters according to claim 1, characterized in that: The receiving end of each relay station includes a second acousto-optic modulator AOM2, a second optical fiber coupler OC2 and a second Faraday rotator FM2, wherein: The second acousto-optic modulator AOM2 is connected to the first acousto-optic modulator AOM1 of the previous relay station through an optical fiber link, and is used to receive the positively frequency-shifted optical frequency signal from the previous relay station and transmit it to the second optical fiber coupler OC2; the second optical fiber coupler OC2 is used to transmit a part of the optical frequency signal from the second acousto-optic modulator AOM2 to the second Faraday rotator FM2, and the other part to the optical amplifier end of the current relay station; The second Faraday rotator FM2 is used to reflect the received optical frequency signal. The reflected optical frequency signal returns to the first acousto-optic modulator AOM1 of the previous relay station through the second acousto-optic modulator AOM2, and can beat with the reference light in the transmitting end of the previous relay station to obtain phase noise information.

3. The fiber optic frequency transmission relay system with self-adjusting noise suppression parameters according to claim 2, characterized in that: The first optical fiber coupler OC1 is a two-input and two-output optical fiber coupler, which is respectively connected to the first acousto-optic modulator AOM1 and the first Faraday rotator FM1 through an optical fiber link, and is used to transmit 10% of the optical frequency signal to the first Faraday rotator FM1, and the remaining 90% of the optical frequency signal is transmitted to the first acousto-optic modulator AOM1; the second optical fiber coupler OC2 is a one-input and two-output optical fiber coupler, which is respectively connected to the second Faraday rotator FM2 and the optical amplifier end through an optical fiber link, and is used to transmit 50% of the optical frequency signal to the second Faraday rotator FM2, and the remaining 50% of the optical frequency signal is transmitted to the optical amplifier end.

4. The fiber optic frequency transmission relay system with self-adjusting noise suppression parameters according to claim 3, characterized in that: The receiving end also includes a second radio frequency signal source RF2 connected to the second acousto-optic modulator AOM2, and the second radio frequency signal source RF2 is used to generate a radio frequency signal ; The radio frequency signal It can be returned to the sending end of the previous relay station through the second acousto-optic modulator AOM2.

5. The fiber optic frequency transmission relay system with self-adjusting noise suppression parameters according to claim 1, characterized in that: The microcontroller MCU is used for: When receiving a control instruction from the operation control system, the first contact of the first conversion switch SW1 is controlled to be connected, and the first contact of the second conversion switch SW2 is controlled to be disconnected and the second contact is controlled to be connected; Collecting the first phase noise from the phase noise test unit , and according to the first phase noise Obtaining the theoretical limit of noise suppression : ， in, represents the Fourier frequency, Represents Fourier frequency The corresponding theoretical limit of noise suppression is, is the time required for light to pass through the optical fiber once, , is the refractive index of the optical fiber, is the speed of light in vacuum, is the length of the connected optical fiber link.

6. The fiber optic frequency transmission relay system with self-adjusting noise suppression parameters according to claim 5, characterized in that: The microcontroller MCU is also used for: The theoretical limit of noise suppression is obtained After that, the first contact of the first conversion switch SW1 is controlled to be disconnected, and the first contact of the second conversion switch SW2 is controlled to be connected and the second contact is controlled to be disconnected; After the first contact of the first conversion switch SW1 is disconnected and the first contact of the second conversion switch SW2 is connected, the second phase noise calculated by the phase noise test unit is obtained. , Represents Fourier frequency f The corresponding second phase noise.

7. The fiber optic frequency transmission relay system with self-adjusting noise suppression parameters according to claim 6, characterized in that: The microcontroller MCU is also used for: The noise suppression factor a is obtained according to the noise suppression theoretical limit corresponding to different Fourier frequencies and the second phase noise, and the calculation formula is: ， It is determined whether the noise suppression factor a is less than a set threshold value. If not, the proportional value in the PI servo circuit is adjusted and the noise suppression factor a is calculated again until the noise suppression factor a is less than the set threshold value.

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