Low phase noise light generated microwave phase stable transmission device

Abstract

The application discloses a low-phase-noise photo-generated microwave stable phase transmission device, comprising a local end and a remote end connected through an optical fiber, wherein the local end comprises an optical frequency comb signal source, a first optical beam splitter, a first photodetector, a first switch filter group, a first optical filter, a first optical amplifier and a phase compensation unit; and the remote end comprises a second optical beam splitter, a second photodetector, a second switch filter group, a second optical filter, a second optical amplifier and an optical reflector. The application overcomes the problem that the phase of microwave signals at the local end and the remote end is out of step due to environmental factors such as vibration and temperature change during long optical fiber transmission, and realizes stable phase synchronous transmission of low-phase-noise microwave signals.

Description

Technical Field

[0001] This invention relates to the field of stable phase optical transmission technology, and in particular to a low phase noise optically generated microwave stable phase transmission device. Background Technology

[0002] In the field of microwave signal generation technology, optically generated microwave technology has attracted widespread attention due to its ability to generate microwave signals with extremely low phase noise. Its basic principle is to use control methods such as phase-locked loops to lock the repetition frequency of an optical frequency comb onto an ultra-stable laser, and then use a photodetector to convert this ultra-stable optical frequency comb into an electrical signal in the microwave frequency band, thereby achieving low-noise frequency division conversion from optical to microwave. However, in applications where ultra-stable optical frequency combs are transmitted over long distances via optical fibers to distribute microwave signals, the fiber optic links are susceptible to interference from environmental factors such as vibration and temperature changes, causing random phase fluctuations in the transmission path. This results in phase deviations between the microwave signals received at the local end and the remote end, failing to meet the requirements of high-precision synchronization applications.

[0003] As a representative achievement in the field of photogenerated microwaves, X. Xie et al. published a paper in *Nature Photonics* (Photonic microwave signals with zeptosecond-level absolute timing noise, 2017, 11(1): 44-47) reporting a scheme to lock the repetition frequency of an optical frequency comb to the frequency of a single-frequency ultrastable laser using an optical phase-locked loop and a servo control system. This scheme can transfer the normalized frequency fluctuation of the optical frequency of the single-frequency ultrastable laser to the repetition frequency of the optical frequency comb, and then generate microwave signals through a photodetector. Since the phase noise of the generated microwave signal is reduced by 20log10(N / n) dB compared to the optical frequency (where N / n is the ratio of the optical frequency to the microwave frequency), this method can achieve microwave signals with extremely low phase noise. However, this scheme still faces the problem of phase loss caused by fiber disturbance during long-fiber transmission and distribution of the ultrastable optical frequency comb, and its microwave spectrum is distributed in a comb shape, making it difficult to flexibly switch frequencies according to requirements in practical applications, thus limiting its engineering applicability in multiple scenarios.

[0004] To address the phase stabilization issue in long fiber optic transmission, existing technologies (Dai Zejing, Wang Kai, Wu Pengsheng, Yu Hao. Broadband Signal Phase Stabilization Transmission System Based on Microwave Photonic Link [P]. National Invention Patent, CN109104247A) have achieved signal phase synchronization between the local and remote ends by introducing an optical phase stabilization loop to compensate for phase fluctuations in the fiber optic link in real time. However, for ultra-stable optical frequency combs, their wide spectral range and numerous comb teeth result in low average optical power per comb tooth under the condition of limited saturated output power of the optical amplifier. When using such ultra-stable optical frequency comb signals for optical phase stabilization detection, the low power of the RF signal used for phase monitoring after photoelectric conversion directly affects the phase detection accuracy of the optical phase stabilization loop, limiting further improvement in phase stabilization performance.

[0005] In summary, there is an urgent need to propose a device that can inherit the low phase noise advantage of ultra-stable optical frequency combs, achieve long-distance stable phase transmission, and have flexible microwave frequency selection capabilities, so as to meet the growing demand for high-precision stable phase microwave signal synchronization and distribution. Summary of the Invention

[0006] In order to solve the technical problems existing in the background art, the present invention proposes a low phase noise optically generated microwave phase-stable transmission device.

[0007] The present invention proposes a low phase noise optically generated microwave phase-stable transmission device, comprising a local end and a remote end connected by optical fiber. The local end includes: an optical frequency comb signal source, a first optical beam splitter, a first photodetector, a first switching filter bank, a first optical filter, a first optical amplifier, and a phase compensation unit. The remote end includes: a second optical beam splitter, a second photodetector, a second switching filter bank, a second optical filter, a second optical amplifier, and an optical reflector. The optical frequency comb signal output from the optical frequency comb signal source is split into multiple signals by the first optical beam splitter. At least one signal is output as a local radio frequency signal after passing through the first photodetector and the first switching filter group. At least one signal is input to the phase compensation unit after passing through the first optical filter and the first optical amplifier in sequence. The phase compensation unit also receives another signal input from the optical frequency comb signal source. The optical signal output by the phase compensation unit is transmitted to the second optical beam splitter via optical fiber. The second optical beam splitter splits the received optical signal into two paths. One path is output as a remote radio frequency signal after passing through the second photodetector and the second switching filter group. The other path passes through the second optical filter, the second optical amplifier, and the optical reflector in sequence and returns to the phase compensation unit along the original optical path. The phase compensation unit performs phase compensation on the optical signal transmitted to the remote end based on the phase difference between the two input signals inside it, so as to achieve phase synchronization between the local radio frequency signal and the remote radio frequency signal.

[0008] Preferably, the first optical beam splitter splits the optical frequency comb signal into three paths: The first path enters the first photodetector and the first switching filter group. The second path passes through the first optical filter and the first optical amplifier in sequence before entering the first port of the phase compensation unit. The third path is directly input to the second port of the phase compensation unit. The optical signal output from the third port of the phase compensation unit is transmitted to the second optical beam splitter via optical fiber and receives the optical signal returned from the remote end.

[0009] Preferably, the phase compensation unit includes: a third photodetector, a first bandpass filter, a mixer, a low-pass filter, a control unit, a second bandpass filter, a fourth photodetector, an optical circulator, and an adjustable optical delay line. The optical signal input to the first port of the phase compensation unit is divided into two paths: one path passes through the third photodetector and the first bandpass filter before entering the mixer, and the other path passes through the first and second ports of the optical circulator before entering the adjustable optical delay line. The output of the adjustable optical delay line serves as the output of the third port of the phase compensation unit. The return optical signal received by the third port of the phase compensation unit passes through the adjustable optical delay line, then through the second and third ports of the optical circulator, and then through the fourth photodetector and the second bandpass filter before entering the mixer. The output of the mixer passes through the low-pass filter before entering the control unit. The control unit controls the delay amount of the adjustable optical delay line according to the output signal of the low-pass filter.

[0010] Preferably, the first optical filter and the second optical filter have the same passband spectrum and are used to perform spectral bandpass filtering on the input optical frequency comb signal.

[0011] Preferably, the second optical amplifier is a bidirectional optical amplifier, used to simultaneously amplify optical signals input in both the forward and reverse directions.

[0012] Preferably, the first switch filter group and the second switch filter group each include multiple electrical switches and multiple electrical filters. The multiple electrical switches and multiple electrical filters are electrically connected in a one-to-one correspondence. By switching the corresponding electrical filters through different electrical switches, the passband frequency is switched to perform bandpass filtering on the microwave frequency comb output by the corresponding photodetector.

[0013] Preferably, the optical frequency comb signal source includes an ultra-stable laser source, an optical frequency locking unit, and an optical frequency comb source. The optical frequency comb source locks the optical frequency with the ultra-stable laser source through the optical frequency locking unit to generate an ultra-short optical pulse sequence.

[0014] Preferably, the first optical beam splitter divides the optical frequency comb signal into 2n+1 paths, one of which is used to generate a local radio frequency signal, and the remaining 2n paths are respectively passed through their respective optical filters, optical amplifiers, phase compensation units and corresponding remote components to output n remote radio frequency signals, so as to realize the expansion of distributed transmission nodes.

[0015] The low-phase-noise optically generated microwave phase-stabilized transmission device proposed in this invention has the following advantages: 1. This invention constructs a closed-loop feedback structure based on a phase compensation unit between the local end and the remote end. The phase of the reference optical signal is compared with that of the optical signal returned from the remote end after transmission through optical fiber. The phase error introduced by the optical fiber link is extracted, and the delay of the adjustable optical delay line is adjusted in real time by the control unit to dynamically compensate for the phase fluctuation. This effectively overcomes the problem of phase loss between the local end and the remote end microwave signals due to environmental factors such as vibration and temperature changes during long optical fiber transmission in the background technology, and realizes stable phase synchronization transmission of low phase noise microwave signals.

[0016] 2. This invention sets optical filters before the optical amplifiers at the local and remote ends to perform spectral bandpass filtering on the ultra-stable optical frequency comb to compress the number of comb teeth in the input optical amplifier. This concentrates the limited power of the optical amplifier on a few comb teeth, significantly improving the optical power of each comb tooth. This effectively solves the problems in the background technology where the large number of comb teeth of the ultra-stable optical frequency comb leads to low optical power per comb tooth, insufficient power of the phase monitoring radio frequency signal, and limited phase detection accuracy of the optical phase-stable loop. It also significantly improves the phase-locking accuracy of the phase-stable loop.

[0017] 3. This invention sets up switching filter banks at both the local and remote ends. By synchronously switching the passband frequencies of the switching filter banks at both ends, it realizes the synchronous switching of the local RF signal and the remote RF signal frequencies, which solves the problem in the background technology that the microwave spectrum is distributed in a comb shape and it is difficult to flexibly switch frequencies according to needs in practical applications. At the same time, through the multi-path distribution of the first optical beam splitter, it can simultaneously distribute stable microwave signals to multiple remote nodes, which has good system scalability and engineering practicality. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a low-phase-noise optically generated microwave phase-stable transmission device proposed in this invention; Figure 2 This is a schematic diagram of the optical frequency comb signal source of a low phase noise optically generated microwave phase-stable transmission device proposed in this invention; Figure 3 This is a schematic diagram of the optical filter spectrum of a low phase noise optically generated microwave phase-stable transmission device proposed in this invention. Figure 4 This is a schematic diagram of the spectrum switching of the switching filter bank in a low phase noise optically generated microwave phase-stable transmission device proposed in this invention. Detailed Implementation

[0019] refer to Figure 1As shown, this embodiment of the invention provides a low phase noise optically generated microwave phase-stable transmission device, including a local end and a remote end connected by optical fiber. The local end includes: an optical frequency comb signal source, a first optical beam splitter, a first photodetector, a first switching filter bank, a first optical filter, a first optical amplifier, and a phase compensation unit. The remote end includes: a second optical beam splitter, a second photodetector, a second switching filter bank, a second optical filter, a second optical amplifier, and an optical reflector.

[0020] like Figure 2 As shown, the optical frequency comb signal source includes an ultra-stable laser source, an optical frequency-locking unit, and an optical frequency comb source. The optical frequency comb source locks its optical frequency with the ultra-stable laser source through the optical frequency-locking unit, and the optical frequency comb source generates a repetition frequency of [missing value]. The ultrashort optical pulse sequence, represented in the frequency domain as ,in It is an integer. The repetition frequency, This represents the carrier envelope offset. The optical frequency comb signal output by this optical frequency comb signal source is split into multiple signals by the first optical beam splitter.

[0021] The first optical beam splitter divides the optical frequency comb signal into three paths. The first optical frequency comb signal enters the first photodetector to complete photoelectric conversion, generating a frequency interval of [missing information]. A series of microwave signals, namely a low phase noise microwave frequency comb, are input into the first switching filter group for bandpass filtering to filter out the desired microwave components. The first switching filter bank outputs a low-phase-noise local radio frequency signal. By locking the phase of the optical frequency comb source to the ultra-stable laser source through a phase-locked loop, and using the ultra-stable laser as a reference signal, the spectral purity is transferred to the microwave via the optical frequency comb, thus achieving the conversion of the ultra-stable laser source optical frequency to the microwave frequency. If the frequency is divided, the phase noise of the resulting microwave is reduced by 20log10(N / n) dB relative to the phase noise of the ultra-stable laser source optical frequency, where N / n is the ratio of the optical frequency to the microwave frequency. Therefore, a low-phase-noise optically generated microwave signal can be obtained by photoelectric conversion of the optical frequency comb signal source signal.

[0022] like Figure 3 As shown, the second optical frequency comb signal undergoes spectral bandpass filtering through the first optical filter, and the output optical signal of the first optical filter contains frequencies of... and The two frequency comb teeth are amplified by the first optical amplifier. The output optical signal from the first optical amplifier enters the first port of the phase compensation unit, where it undergoes photoelectric conversion by the third photodetector. The output frequency is [frequency value missing]. The phase reference radio frequency signal.

[0023] The third optical frequency comb signal is directly input to the second input terminal of the phase compensation unit. The signal output terminal of the phase compensation unit outputs the optical frequency comb signal and receives the optical signal returned from the remote end. The optical frequency comb signal output from the signal output terminal of the phase compensation unit is transmitted through optical fiber to the second optical beamsplitter. The second optical beamsplitter splits the optical frequency comb signal into two optical frequency comb signals. One of the optical frequency comb signals is output by the second optical beamsplitter to the second photodetector to complete photoelectric conversion, generating a frequency interval of [missing information]. A series of microwave signals, namely low phase noise microwave frequency combs, are input to a second switching filter bank for bandpass filtering. The second switching filter bank outputs a low phase noise far-end radio frequency signal. Another optical frequency comb signal is output to a second optical filter via a second optical beamsplitter, completing spectral bandpass filtering. The filtering spectrum of the second optical filter is the same as that of the first optical filter, such as... Figure 3 As shown, the output optical signal of the second optical filter contains frequencies of and The optical signal from the second optical filter is amplified by the two frequency comb teeth of the optical amplifier. This second optical amplifier is a bidirectional amplifier, capable of simultaneously amplifying both forward and reverse input light. The output light from the second optical amplifier enters a reflector, where it is reflected. The reflected light then passes through the second optical amplifier and the second optical filter before being output to the second optical beamsplitter. The beamsplitter outputs the light signal, which is then transmitted via optical fiber to the signal output of the phase compensation unit.

[0024] The phase compensation unit includes a third photodetector, a first bandpass filter, a mixer, a low-pass filter, a control unit, a second bandpass filter, a fourth photodetector, an optical circulator, and an adjustable optical delay line. The third photodetector receives the frequency input to the first input terminal of the phase compensation unit. and The two frequency comb teeth transmit optical signals and complete photoelectric conversion, with an output frequency of [frequency value missing]. The phase reference RF signal enters the first bandpass filter for bandpass filtering. The center frequency of the first bandpass filter is... The output signal of the first bandpass filter enters the mixer. The first input port of the optical circulator receives the optical signal input from the first input terminal of the phase compensation unit, and the second input / output port of the optical circulator outputs this optical signal into the adjustable optical delay line. The adjustable optical delay line outputs the optical signal to the signal output terminal of the phase compensation unit. The signal output terminal of the phase compensation unit receives the frequency returned from the remote end. and The two frequency comb-tooth optical signals are output to an adjustable optical delay line. The adjustable optical delay line then outputs the same signal to the second input / output port of an optical circulator. The third output port of the optical circulator outputs the same signal to a fourth photodetector for photoelectric conversion, with an output frequency of [frequency value missing]. The phase monitoring radio frequency signal enters the second bandpass filter for bandpass filtering. The center frequency of the second bandpass filter is... The output signal of the second bandpass filter enters the mixer. The output signals of the first and second bandpass filters are mixed together in the mixer. The mixed signal output by the mixer is then low-pass filtered. The output signal of the low-pass filter enters the control unit, which generates a control signal to control the delay of the adjustable optical delay line, thereby compensating for phase errors during fiber optic transmission in real time, and achieving phase locking and closed-loop control between the local RF signal and the remote RF signal.

[0025] like Figure 4 As shown, the first and second switching filter groups each include multiple electrical switches and multiple electrical filters. The multiple electrical switches and multiple electrical filters are electrically connected in a one-to-one correspondence. By switching the corresponding electrical filters through different electrical switches, the passband frequency of the switching filter group is switched, thereby realizing bandpass filtering and frequency switching of the low phase noise microwave frequency comb output by the photodetector.

[0026] The number of local optical filters, optical amplifiers, phase compensation units, and remote components can be configured to expand the remote transmission node. The first optical beam splitter divides the optical frequency comb signal output from the optical frequency comb signal source into 2n+1 paths. One path outputs a local radio frequency signal through the first photodetector and the first switching filter group, while the other 2n paths output n remote radio frequency signals through their respective optical filters, optical amplifiers, phase compensation units, and corresponding remote components.

[0027] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low phase noise photogenerated microwave phase stable transmission apparatus comprising a local end and a remote end connected by an optical fiber, characterized in that, The local end includes: an optical frequency comb signal source, a first optical beam splitter, a first photodetector, a first switching filter bank, a first optical filter, a first optical amplifier, and a phase compensation unit; the far end includes: a second optical beam splitter, a second photodetector, a second switching filter bank, a second optical filter, a second optical amplifier, and an optical reflector. The optical frequency comb signal output from the optical frequency comb signal source is split into multiple signals by the first optical beam splitter. At least one signal is output as a local radio frequency signal after passing through the first photodetector and the first switching filter group. At least one signal is input to the phase compensation unit after passing through the first optical filter and the first optical amplifier in sequence. The phase compensation unit also receives another signal input from the optical frequency comb signal source. The optical signal output by the phase compensation unit is transmitted to the second optical beam splitter via optical fiber. The second optical beam splitter splits the received optical signal into two paths. One path is output as a remote radio frequency signal after passing through the second photodetector and the second switching filter group. The other path passes through the second optical filter, the second optical amplifier, and the optical reflector in sequence and returns to the phase compensation unit along the original optical path. The phase compensation unit performs phase compensation on the optical signal transmitted to the remote end based on the phase difference between the two input signals inside it, so as to achieve phase synchronization between the local radio frequency signal and the remote radio frequency signal.

2. The apparatus of claim 1, wherein, The first optical beam splitter splits the optical frequency comb signal into three paths: The first path enters the first photodetector and the first switching filter group. The second path passes through the first optical filter and the first optical amplifier in sequence before entering the first port of the phase compensation unit. The third path is directly input to the second port of the phase compensation unit. The optical signal output from the third port of the phase compensation unit is transmitted to the second optical beam splitter via optical fiber and receives the optical signal returned from the remote end.

3. The apparatus of claim 2, wherein, The phase compensation unit includes: a third photodetector, a first bandpass filter, a mixer, a low-pass filter, a control unit, a second bandpass filter, a fourth photodetector, an optical circulator, and an adjustable optical delay line. The optical signal input to the first port of the phase compensation unit is divided into two paths. One path passes through the third photodetector and the first bandpass filter before entering the mixer. The other path passes through the first and second ports of the optical circulator before entering the adjustable optical delay line. The output of the adjustable optical delay line serves as the output of the third port of the phase compensation unit. The return optical signal received by the third port of the phase compensation unit passes through the adjustable optical delay line, then through the second and third ports of the optical circulator, and then through the fourth photodetector and the second bandpass filter before entering the mixer. The output of the mixer passes through the low-pass filter before entering the control unit. The control unit controls the delay amount of the adjustable optical delay line according to the output signal of the low-pass filter.

4. The apparatus of claim 1, wherein, The first optical filter and the second optical filter have the same passband spectrum and are used to perform spectral bandpass filtering on the input optical frequency comb signal.

5. The apparatus according to claim 1, characterized in that, The second optical amplifier is a bidirectional optical amplifier, used to simultaneously amplify optical signals input in both the forward and reverse directions.

6. The apparatus according to claim 1, characterized in that, The first and second switching filter groups each include multiple electrical switches and multiple electrical filters. The multiple electrical switches and multiple electrical filters are electrically connected in a one-to-one correspondence. By switching the corresponding electrical filters through different electrical switches, the passband frequency is switched to perform bandpass filtering on the microwave frequency comb output by the corresponding photodetector.

7. The apparatus according to claim 1, characterized in that, The optical frequency comb signal source includes an ultra-stable laser source, an optical frequency locking unit, and an optical frequency comb source. The optical frequency comb source locks the optical frequency with the ultra-stable laser source through the optical frequency locking unit to generate an ultra-short optical pulse sequence.

8. The apparatus according to claim 1, characterized in that, The first optical beam splitter divides the optical frequency comb signal into 2n+1 paths. One path is used to generate a local radio frequency signal, while the remaining 2n paths are respectively processed by their respective optical filters, optical amplifiers, phase compensation units, and corresponding remote components to output n remote radio frequency signals, thereby realizing the expansion of distributed transmission nodes.

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