Optical carrier microwave stable transmission system based on temperature control optical fiber delay line

Abstract

According to the optical carrier microwave stable transmission system based on the temperature control optical fiber delay line provided by the invention, accurate reverse compensation is carried out on delay jitter change through the delay compensation module, and excellent delay consistency is shown in ultra-wideband signal transmission; the defect that compensation devices such as a traditional piezoelectric ceramic optical fiber stretcher, an optical phase shifter, a cascade multi-stage optical switch and a motor space optical delay line cannot meet the requirements of large range, high precision, quick response and wide frequency spectrum compensation capability at the same time is overcome; that is to say, the link delay compensation scheme in the transmission system has large-range, high-precision, quick-response and wide-spectrum compensation capabilities, and is particularly suitable for optical fiber transmission links with high stability and consistency requirements on ultra-wideband signal transmission.

Description

Technical Field

[0001] The present invention belongs to the field of communication technology, and in particular relates to a stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line. Background Art

[0002] By utilizing the low loss and large bandwidth advantages of photonic systems, the frequency, amplitude and phase of microwave signals can be regulated in the optical domain, and functional tasks that cannot be achieved by traditional microwave systems can be achieved. Therefore, the stable transmission of optical fiber-borne microwave signals has a wide range of application needs in the fields of interferometric antenna arrays, distributed coherent radars, and large antenna surface deformation correction. For example, in the correction of large antenna surface deformation, my country is planning to build a large millimeter-wave astronomical telescope with a diameter of 60m, requiring the root mean square error of the antenna reflection surface deformation to be less than 30μm. The millimeter-wave adaptive optical measurement method developed in recent years provides an effective solution for real-time high-precision detection and correction of large antenna surface shapes. The key to the millimeter-wave adaptive optical measurement method is to deploy micro-antennas on the antenna panel unit, and use the antenna to transmit microwave signals with highly synchronized phases to monitor and correct antenna surface distortion in real time. This requires that the length of the transmission link is stable at the micron level, or the transmission delay stability must reach the femtosecond level to meet the millimeter-wave band antenna surface error requirements of <30μm. However, the fundamental problem it faces is the instability of optical fiber transmission delay caused by factors such as ambient temperature and vibration. Considering the dispersion effect in optical fiber, there are still differences in the transmission delay of signals of different wavelengths. In special scenarios where the external environment changes severely and long-distance optical fiber is required for stable transmission, this instability difference is more significant. This places extremely high demands on the detection and compensation of link delay changes.

[0003] An ideal delay compensation device needs to have the capabilities of large range, high precision, fast response, and wide spectrum compensation. Existing delay lines include piezoelectric ceramic fiber stretchers, optical phase shifters, cascaded multi-stage optical switches, and motor space optical delay lines. The delay compensation schemes composed of the above delay compensation devices cannot fully meet the requirements for the delay compensation device to have the capabilities of large range, high precision, fast response, and wide spectrum compensation. The compensation accuracy is not high, there is a lack of continuous compensation capability, or it is difficult to compensate for the dispersion inhomogeneity caused by temperature changes during broadband signal transmission.

[0004] Due to the different application scenarios of microwave signal transmission, the delay compensation module composed of existing delay lines cannot simultaneously meet the requirements of high-precision, large-range and wide-spectrum compensation capabilities in the stable optical fiber transmission link. This limits the transmission capabilities of broadband microwave signals in long-distance optical fiber links and in harsh environments. In comparison, the temperature-controlled optical fiber delay line can achieve a wide range of delay adjustment and has dispersion compensation capabilities. However, it has the disadvantages of low compensation accuracy and slow response speed. Summary of the invention

[0005] To solve the above problems, the present invention provides a stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line, which has the capabilities of large range, high precision, fast response and wide spectrum compensation to achieve multi-wavelength compensation and stable transmission.

[0006] A temperature-controlled optical fiber delay line-based light-carrying microwave stable transmission system, comprising a first laser module, a first photodetector, a third photodetector, a first modulator, a first wavelength division multiplexer, a second wavelength division multiplexer, an optical fiber coupler, a polarization beam splitter, a delay compensation module, a single-mode optical fiber with a length of at least 10 km, a vector network analyzer, a radio frequency signal generator, a mixer, and a phase-locked loop;

[0007] The first laser emitted by the first laser module is modulated at the first modulator by the probe signal output by the radio frequency signal generator and the signal to be transmitted output by the vector network analyzer, and the obtained first modulated signal sequentially passes through the polarization beam splitter, the first wavelength division multiplexer, the delay compensation module, the single-mode optical fiber, and the second wavelength division multiplexer to reach the optical fiber coupler;

[0008] The optical fiber coupler divides the first modulated signal into two sub-paths, the first sub-path enters the first photodetector, and the second sub-path is reflected by the Faraday rotator, and sequentially passes through the optical fiber coupler, the second wavelength division multiplexer, the single-mode optical fiber, the delay compensation module, the first wavelength division multiplexer, and the polarization beam splitter to reach the third photodetector;

[0009] The first photodetector performs a beat frequency on the first sub-path to obtain a first beat frequency signal, and the third photodetector performs a beat frequency on the second sub-path to obtain a second beat frequency signal, wherein the first beat frequency signal is input into the vector network analyzer, and the second beat frequency signal is input into the mixer;

[0010] The vector network analyzer determines the stability of the system transmitting the signal to be transmitted according to the phase jitter of the first beat frequency signal;

[0011] The mixer performs phase detection on the second beat frequency signal and the probe signal output by the radio frequency signal generator to obtain a DC error signal;

[0012] The output voltage generated by the DC error signal after being processed by the phase-locked loop is used to control the delay of the delay compensation module, thereby compensating for the delay jitter caused to the signal to be transmitted due to the delay change of the single-mode optical fiber.

[0013] Furthermore, the delay compensation module includes a piezoelectric ceramic optical fiber stretcher and a temperature-controlled optical fiber delay line; the method by which the delay compensation module compensates for the delay jitter caused by the delay change of the single-mode optical fiber to the signal to be transmitted is as follows:

[0014] The output voltage generated by the DC error signal after being processed by the phase-locked loop is directly loaded onto the piezoelectric ceramic fiber stretcher, thereby changing the deformation of the piezoelectric ceramic fiber stretcher, thereby changing the length of the total optical fiber link composed of the delay compensation module and the single-mode optical fiber. When the delay caused by the single-mode optical fiber is shortened and the signal to be transmitted is advanced, the deformation of the piezoelectric ceramic fiber stretcher is increased; when the delay caused by the single-mode optical fiber is increased and the signal to be transmitted is delayed, the deformation of the piezoelectric ceramic fiber stretcher is reduced.

[0015] At the same time, the phase-locked loop monitors and adjusts the voltage of the piezoelectric ceramic fiber stretcher in real time to ensure that the operating voltage range of the piezoelectric ceramic fiber stretcher is always maintained between -Vmax and Vmax, where Vmax is the upper limit of the operating voltage of the piezoelectric ceramic fiber stretcher; when it is monitored that the voltage of the piezoelectric ceramic fiber stretcher is close to -Vmax, a temperature control signal is generated for the temperature-controlled optical fiber delay line according to the DC error signal, so as to reduce the temperature of the temperature-controlled optical fiber delay line, thereby changing the delay of the total optical fiber link and returning the voltage of the piezoelectric ceramic fiber stretcher to an initial state close to 0V; when the voltage of the piezoelectric ceramic fiber stretcher is close to Vmax, a temperature control signal is generated for the temperature-controlled optical fiber delay line according to the DC error signal, so as to increase the temperature of the temperature-controlled optical fiber delay line, thereby changing the delay of the total optical fiber link and returning the voltage of the piezoelectric ceramic fiber stretcher to an initial state close to 0V.

[0016] Furthermore, the temperature-controlled optical fiber delay line includes a temperature-controlled element and an optical fiber, wherein the temperature-controlled element is a semiconductor refrigerator and the length of the optical fiber is 1.5 km.

[0017] Further, the first laser module includes a first laser and a first bias controller;

[0018] The first bias controller is used to adjust the working point of the first modulator so that the first modulator modulates the probe signal and the signal to be transmitted onto the first laser generated by the first laser.

[0019] Furthermore, it also includes a second laser module, a second modulator, and a second photodetector;

[0020] The second laser emitted by the second laser module is modulated by the signal to be transmitted at the second modulator, and the obtained second modulated signal enters the first wavelength division multiplexer; wherein the wavelength of the second laser is different from the wavelength of the first laser;

[0021] The first modulated signal and the second modulated signal are combined into a total modulated signal at the first wavelength division multiplexer, and the total modulated signal passes through the delay compensation module and the single-mode optical fiber in sequence to reach the second wavelength division multiplexer;

[0022] The second wavelength division multiplexer divides the total modulated signal into a first modulated signal and a second modulated signal, the first modulated signal enters the optical fiber coupler, and the optical fiber coupler divides the first modulated signal into two sub-paths for subsequent operations, and the second modulated signal enters the second photodetector;

[0023] The second photoelectric detector performs a beat frequency on the second modulated signal to obtain a third beat frequency signal, and the third beat frequency signal is then input into the vector network analyzer;

[0024] The vector network analyzer determines the stability of the system in transmitting the signal to be transmitted at different wavelengths according to the phase jitter of the first beat frequency signal and the third beat frequency signal.

[0025] Further, the second laser module includes a second laser and a second bias controller;

[0026] The second bias controller is used to adjust the working point of the second modulator so that the second modulator modulates the signal to be transmitted onto the second laser generated by the second laser.

[0027] Beneficial effects:

[0028] 1. The present invention provides a stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line, which accurately reversely compensates for the delay jitter change through a delay compensation module, and exhibits excellent delay consistency in ultra-wideband signal transmission, overcoming the problem that traditional compensation devices such as piezoelectric ceramic optical fiber stretchers, optical phase shifters, cascaded multi-stage optical switches and motor space optical delay lines cannot simultaneously meet the requirements of large range, high precision and fast response; that is, the link delay compensation scheme in the transmission system of the present invention has large range, high precision, fast response and wide spectrum compensation capabilities, and is particularly suitable for optical fiber transmission links that require high stability and consistency for ultra-wideband signal transmission.

[0029] 2. The present invention provides a light-carrying microwave stable transmission system based on a temperature-controlled optical fiber delay line, which adopts a piezoelectric ceramic optical fiber stretcher as a high-precision small-range delay compensation device, and a temperature-controlled optical fiber delay line as a coarse-adjustment large-range delay compensation device, and the two are cascaded to form a delay compensation module; through the cascade operation of the piezoelectric ceramic optical fiber stretcher and the temperature-controlled optical fiber delay line, real-time dynamic balance of link delay is achieved, ensuring the delay stability of the transmission link; at the same time, the present invention achieves high-precision, large-range, and rapid compensation effects in long-distance optical fiber transmission link compensation by designing and manufacturing a temperature-controlled optical fiber delay line and reasonably controlling the temperature of the temperature-controlled optical fiber delay line, while avoiding the delay non-uniformity problem in ultra-wideband signal transmission.

[0030] 3. The present invention provides a stable light-carrying microwave transmission system based on a temperature-controlled optical fiber delay line. To solve the delay non-uniformity problem of different wavelengths caused by optical fiber dispersion in broadband signal transmission, a dual-wavelength laser is used, and a dynamic delay compensation method is designed to verify the stability of the system in transmitting the transmitted signal at different wavelengths. The experiment verifies that the reverse compensation of optical fiber temperature change can be achieved by using a temperature-controlled optical fiber delay line, which eliminates the non-uniformity of transmission delay of different frequency components caused by external temperature changes, ensures the delay uniformity of ultra-wideband signals, and can effectively compensate for delay jitter in a wide frequency spectrum, meeting the high stability requirements of broadband signal transmission in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of a stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line provided by the present invention;

[0032] Figure 2 A schematic diagram showing the variation of the delay of the temperature-controlled optical fiber delay line provided by the present invention with the temperature;

[0033] FIG3( a ) is a schematic diagram of the delay variation under locked and unlocked conditions provided by the present invention;

[0034] FIG3( b ) is a schematic diagram of overlapping Allan deviations of transmission signals under locked and unlocked conditions provided by the present invention;

[0035] FIG4( a ) is a schematic diagram of absolute and relative delay changes of the 1546 nm and 1554 nm channels obtained under the motor space optical delay line control module provided by the present invention;

[0036] FIG4( b ) is a schematic diagram of absolute and relative delay changes of the 1546 nm and 1554 nm channels obtained under the temperature-controlled optical fiber delay line control module provided by the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0038] The experimental system of the present invention consists of a local end and a remote end, and the data to be transmitted is transmitted between the local end and the remote end, and the local end and the remote end are connected by a single-mode optical fiber with a length of at least 10 km; when the signal to be transmitted is transmitted in the 10 km single-mode optical fiber, noise information will be introduced due to changes in the external environment, and the optical fiber transmission delay will also be affected by temperature and stress fluctuations, thereby causing a large delay jitter in the signal to be transmitted.

[0039] The present invention is based on a temperature-controlled optical fiber delay line optical microwave stable transmission system. Figure 1As shown, it includes a first laser module, a second laser module, a first photodetector, a second photodetector, a third photodetector, a first modulator, a second modulator, a first wavelength division multiplexer, a second wavelength division multiplexer, an optical fiber coupler, a polarization beam splitter, a delay compensation module, a single-mode optical fiber with a length of at least 10 km, a vector network analyzer, a radio frequency signal generator, a mixer, and a phase-locked loop; wherein the first laser module includes a first laser and a first bias controller; the second laser module includes a second laser and a second bias controller; the delay compensation module includes a piezoelectric ceramic optical fiber stretcher and a temperature-controlled optical fiber delay line;

[0040] The first laser emitted by the first laser module is modulated at the first modulator by the 9.9 GHz probe signal output by the RF signal generator and the 10 GHz signal to be transmitted output by the vector network analyzer, and the obtained first modulated signal sequentially passes through the polarization beam splitter, the first wavelength division multiplexer, the delay compensation module, the single-mode optical fiber, and the second wavelength division multiplexer to reach the optical fiber coupler; wherein the first bias controller is used to adjust the working point of the first modulator so that the first modulator modulates the probe signal and the signal to be transmitted onto the first laser generated by the first laser.

[0041] The optical fiber coupler divides the first modulated signal into two sub-paths, the first sub-path enters the first photodetector, and the second sub-path is reflected by the Faraday rotator, and sequentially passes through the optical fiber coupler, the second wavelength division multiplexer, the single-mode optical fiber, the delay compensation module, the first wavelength division multiplexer, and the polarization beam splitter to reach the third photodetector;

[0042] The first photodetector performs a beat frequency on the first sub-path to obtain a first beat frequency signal, and the third photodetector performs a beat frequency on the second sub-path to obtain a second beat frequency signal, wherein the first beat frequency signal is input into the vector network analyzer, and the second beat frequency signal is input into the mixer;

[0043] The vector network analyzer determines the stability of the system transmitting the signal to be transmitted according to the phase jitter of the first beat frequency signal;

[0044] The mixer performs phase detection on the second beat frequency signal and the probe signal output by the radio frequency signal generator to obtain a DC error signal;

[0045] The output voltage generated by the DC error signal after being processed by the phase-locked loop is used to control the delay of the delay compensation module, thereby compensating for the delay jitter caused to the signal to be transmitted due to the delay change of the single-mode optical fiber.

[0046] It should be noted that the delay compensation module composed of a cascade of a piezoelectric ceramic optical fiber stretcher (a high-precision small-range delay compensation device) and a temperature-controlled optical fiber delay line (a coarse adjustment large-range delay compensation device) has the following compensation principle and process:

[0047] The far-end return optical signal is beat by the photoelectric detector to obtain a 9.9GHz radio frequency probe signal, and the phase detection is carried out with the 9.9GHz radio frequency probe signal at the local end in the mixer to obtain a zero-frequency intermediate frequency signal (error signal). This signal carries the noise information introduced by the external environment changes in the round-trip link, and its level reflects the noise level in the link. The present invention controls the delay compensation module to perform reverse delay compensation, so that the level of the error signal is restored to zero as much as possible, thereby realizing real-time compensation of link noise.

[0048] Specifically, the method in which the delay compensation module compensates for the delay jitter caused by the delay variation of the single-mode optical fiber to the signal to be transmitted is as follows:

[0049] The output voltage generated by the DC error signal after being processed by the phase-locked loop is directly loaded onto the piezoelectric ceramic fiber stretcher, thereby changing the deformation of the piezoelectric ceramic fiber stretcher, thereby changing the length of the total optical fiber link composed of the delay compensation module and the single-mode optical fiber. When the delay caused by the single-mode optical fiber is shortened and the signal to be transmitted is advanced, the deformation of the piezoelectric ceramic fiber stretcher is increased; when the delay caused by the single-mode optical fiber is increased and the signal to be transmitted is delayed, the deformation of the piezoelectric ceramic fiber stretcher is reduced.

[0050] At the same time, the phase-locked loop monitors and adjusts the voltage of the piezoelectric ceramic fiber stretcher in real time to ensure that the operating voltage range of the piezoelectric ceramic fiber stretcher is always maintained between -Vmax and Vmax, where Vmax is the upper limit of the operating voltage of the piezoelectric ceramic fiber stretcher; when it is monitored that the voltage of the piezoelectric ceramic fiber stretcher is close to -Vmax, a temperature control signal is generated for the temperature-controlled optical fiber delay line according to the DC error signal, so as to reduce the temperature of the temperature-controlled optical fiber delay line, thereby changing the delay of the total optical fiber link and returning the voltage of the piezoelectric ceramic fiber stretcher to an initial state close to 0V; when the voltage of the piezoelectric ceramic fiber stretcher is close to Vmax, a temperature control signal is generated for the temperature-controlled optical fiber delay line according to the DC error signal, so as to increase the temperature of the temperature-controlled optical fiber delay line, thereby changing the delay of the total optical fiber link and returning the voltage of the piezoelectric ceramic fiber stretcher to an initial state close to 0V.

[0051] It can be seen that the present invention realizes the real-time dynamic balance of link delay and ensures the stable locking of the transmission link through the cascade operation of the piezoelectric ceramic optical fiber stretcher and the temperature-controlled optical fiber delay line.

[0052] Furthermore, in order to compare the stability of the system transmitting the signal to be transmitted at different wavelengths, the present invention uses a second laser module, a second modulator, and a second photodetector to form another link branch, as follows:

[0053] After the second laser emitted by the second laser module is modulated by the signal to be transmitted at the second modulator, the obtained second modulated signal enters the first wavelength division multiplexer; wherein the wavelength of the second laser is different from the wavelength of the first laser; the second bias controller is used to adjust the working point of the second modulator so that the second modulator modulates the signal to be transmitted onto the second laser generated by the second laser.

[0054] The first modulated signal and the second modulated signal are combined into a total modulated signal at the first wavelength division multiplexer, and the total modulated signal passes through the delay compensation module and the single-mode optical fiber in sequence to reach the second wavelength division multiplexer;

[0055] The second wavelength division multiplexer divides the total modulated signal into a first modulated signal and a second modulated signal, the first modulated signal enters the optical fiber coupler, and the optical fiber coupler divides the first modulated signal into two sub-paths for subsequent operations, and the second modulated signal enters the second photodetector;

[0056] The second photoelectric detector performs a beat frequency on the second modulated signal to obtain a third beat frequency signal, and the third beat frequency signal is then input into the vector network analyzer;

[0057] The vector network analyzer determines the stability of the system in transmitting the signal to be transmitted at different wavelengths according to the phase jitter of the first beat frequency signal and the third beat frequency signal.

[0058] Based on this, Figure 1 The functions of the components in the stable transmission system of microwave over light based on a temperature-controlled optical fiber delay line can be summarized as follows:

[0059] Two lasers are used to generate two single-frequency optical carriers separated by 8nm; the bias controller is used to effectively adjust and control the working point of the Mach-Zehnder modulator to improve the working stability of the modulator; the Mach-Zehnder modulator is used to modulate the radio frequency microwave signal onto the single-frequency optical carrier generated by the laser; the polarization beam splitter is used to separate the modulated optical carrier according to the two polarization directions of vertical and horizontal directions to achieve polarization separation of the light wave; the wavelength division multiplexer is used to synthesize or separate different wavelengths; the tunable optical delay line is used to compensate for the link delay jitter and dispersion changes caused by changes in the external environment; the single-mode optical fiber is used to transmit the optical carrier to the remote end; the optical fiber coupler is used to separate or synthesize the light wave; the radio frequency signal generator is used to generate the radio frequency signal that locks the optical fiber link; the mixer is used to combine the radio frequency signal generated by the radio frequency signal generator with the radio frequency signal that is transmitted back to the local end at the remote end through the optical fiber link and then transmitted by the photoelectric detector The RF signal output by the detector is homodyne mixed to obtain a DC error signal; the phase-locked loop is used to integrate and amplify the DC error signal output by the mixer to control the adjustable optical delay line to compensate for the delay jitter of the optical fiber link and achieve the locking of the optical fiber link; the photodetector is used to convert the optical signal into an electrical signal; the power amplifier is used to amplify the power of the optical modulated microwave signal to ensure that the signal has sufficient strength and stability in the optical fiber transmission link; the power divider is used to evenly or proportionally distribute the input microwave RF signal to multiple output ends to support multi-channel signal processing; the Faraday rotator uses the Faraday effect to rotate the polarization state of the optical signal by 90° and reflect the optical path, which is used to eliminate polarization-related interference, improve system stability and achieve link delay jitter compensation at the local end; the data sending / receiving acquisition processing system, that is, the vector network analyzer, is used to send data and receive and collect data transmitted to the remote end and perform data processing.

[0060] The present invention combines the piezoelectric ceramic optical fiber stretcher with two delay control modules, namely, a temperature-controlled optical fiber delay line and a motor space optical delay line, to compare the delay characteristics of the two, as follows:

[0061] The light emitted by the 1546nm laser 1 at the local end is modulated by the 10GHz microwave signal output by the vector network analyzer and the 9.9GHz microwave signal output by the RF signal generator, and then passes through the polarization beam splitter and wavelength division multiplexer 1 in sequence, and then enters the link delay control module and the 10km optical fiber link to the remote end. The 9.9GHz signal is used as a probe to sense the link delay change, and the 10GHz signal is the signal to be transmitted.

[0062] After passing through the 70:30 fiber coupler at the far end, 30% of the optical signal is detected by the photodetector 1, and a 10GHz microwave signal is obtained, which enters the vector network analyzer to measure the delay jitter of the transmission signal. After being reflected by the Faraday rotator, 70% of the optical signal is transmitted back to the local end, and after passing through the polarization beam splitter, it enters the photodetector 3 for detection, and a 9.9GHz microwave signal is obtained. The phase detection with the local 9.9GHz reference signal is carried out in the mixer to obtain a DC error signal. The generated error signal enters the phase-locked loop, and the phase-locked loop drives the control delay compensation module to eliminate the influence of temperature and stress fluctuations on the fiber transmission delay during long-term measurement, as well as the uneven dispersion jitter caused by the transmission of optical signals of different frequencies in the optical fiber link, thereby reducing the delay jitter and achieving stable transmission of microwave signals.

[0063] In order to study the transmission delay difference of different wavelengths, 1554nm laser 2 is used as the wavelength of the signal to be transmitted, and the emitted optical signal is modulated by the 10GHz microwave signal output by the vector network analyzer through the Mach-Zehnder modulator. After being combined with the first laser with a wavelength of λ1 by the wavelength division multiplexer 1, it is transmitted to the far end through the link delay control module and the 10km optical fiber link in turn, and then separated by the wavelength division multiplexer 2 and detected by the photoelectric detector 2 to obtain a 10GHz microwave signal, which enters the vector network analyzer to measure the delay jitter of the far-end out-of-loop signal.

[0064] The temperature-controlled optical fiber delay line designed and manufactured by the present invention uses a semiconductor refrigerator (TEC) as a temperature control element, in which 1.5 kilometers of optical fiber are wound. In order to enhance the thermal conductivity between the temperature control element and the optical fiber, a heat-conducting metal is filled between the outer shell and the inner wall. In addition, in order to reduce the heat exchange between the optical fiber and the external environment, the entire device is heat-insulated, which can change the internal temperature by about 40°C. In the experiment, the optical fiber temperature was controlled to vary in the range of 11°C to 52°C, and a vector network analyzer was used to measure the time delay at different temperatures every 1°C. The measurement results are shown in the figure. Figure 2 As shown, there is a good linear relationship between the delay increment and the temperature change. The rate at which the delay changes with temperature, that is, its compensation accuracy, is about 69.13ps / ℃. This experimental result shows that the invention uses a self-made temperature-controlled optical fiber delay line to achieve corresponding delay changes through precise temperature control.

[0065] It should be noted that the transmission stability of the optical fiber link is determined by the phase-locked loop detection and compensation accuracy of the probe signal. Therefore, in order to evaluate the locking effect of the optical fiber link using the temperature-controlled optical fiber delay line as a delay compensation module. The present invention locks the optical fiber link based on the probe signal, and measures the delay changes of the transmission signal under phase-locked and unlocked conditions at the remote end. The measurement results are shown in Figure 3(a). After the 10GHz microwave signal generated by the vector network analyzer is transmitted through the optical fiber link, it enters the vector network analyzer phase after passing through the photodetector beat frequency at the remote end, thereby calculating the delay change. The receiving bandwidth of the vector network analyzer is set to 2Hz. The experimental results show that for an unlocked optical fiber link, the delay change caused by changes in the external environment within 5000 seconds is 693ps. This is because the laboratory temperature is in a continuous rising stage. For a locked optical fiber link, the standard deviation of the delay change is 27.8fs. At the same time, the present invention uses the measured phase data to calculate the overlapping Allan deviation, and the result is shown in Figure 3(b). When the transmission delay changes with the environment, the frequency stability is about 10 -13 When the link is locked, the overlap Allan deviation decreases linearly with the increase of averaging time. The overlap Allan deviation reaches 4.35×10 -17 , showing excellent long-term frequency stability. The stability of the delay change of the optical fiber link in the locked state demonstrates the ability of high-precision phase locking. It shows that the temperature-controlled optical fiber delay line designed and manufactured by the present invention can meet the compensation requirements of stable transmission of high-precision optical fiber links.

[0066] For multi-wavelength signal transmission, the chromatic dispersion change caused by the temperature change of the optical fiber will lead to uneven transmission delay of the optically carried microwave signal at different optical frequencies. In order to verify the compensation effect of the temperature-controlled optical fiber delay line on this delay unevenness, the present invention first closes the optical switch in position B and uses the motor space optical delay compensation module to compensate for the fiber delay change. At the far end, the present invention measures the phase change of the 10GHz microwave signal transmitted by two light sources 8nm apart, and calculates the delay change, as shown in Figure 4(a). Within 4000 seconds, the temperature change of 10 kilometers of optical fiber is 3.5℃. The delay change of the λ1 locking path maintains a stable trend, while the delay change of the λ2 transmission path increases significantly due to the influence of chromatic dispersion. The relative delay change difference obtained by subtracting the delay changes of the two paths is shown in the inset of Figure 4(a). Within 4000 seconds, the cumulative relative delay difference of the two paths is 577 femtoseconds.

[0067] The optical switch is then closed in position A. The present invention replaces the motor space optical delay compensation module with a temperature-controlled optical fiber delay compensation module, and the measurement results are shown in Figure 4(b). Within 4000 seconds, the temperature change of the 10-kilometer optical fiber in the temperature-controlled box is 1.7°C. Although the relative delay change difference caused by the corresponding dispersion change is 280fs, the delay changes of the λ1 locking path and the λ2 transmission path both maintain a stable trend. The relative delay change difference obtained by subtracting the relative delay changes of the two paths is shown in the illustration in Figure 4(b), and the standard deviation of the accumulated relative delay change difference of the two paths is 18.5 femtoseconds. It is verified that the present invention uses a self-made temperature-controlled optical fiber delay line to reversely compensate for the change in optical fiber temperature, which can eliminate the phenomenon of uneven transmission delay of optical signals of different wavelengths due to chromatic dispersion.

[0068] So far, the present invention has demonstrated a multi-wavelength compensation and stable transmission system based on a temperature-controlled optical fiber delay line. The link delay compensation scheme in the system has a large range, high precision, fast response and wide spectrum compensation capabilities. For the transmission of a single-frequency signal in a 10-kilometer optical fiber link, the system achieved a delay jitter standard deviation of only 27.8 femtoseconds within 5000 seconds, showing excellent long-term stability. Compared with conventional delay compensation schemes, this scheme uses a homemade temperature-controlled optical fiber delay line to accurately reverse compensate for temperature changes, and exhibits excellent delay consistency in ultra-wideband signal transmission. This delay compensation scheme is particularly suitable for optical fiber transmission links that require high stability and consistency for ultra-wideband signal transmission.

[0069] In summary, the present invention has the following advantages over the prior art:

[0070] 1. Multi-wavelength compensation system based on temperature-controlled optical fiber delay line:

[0071] A link delay compensation scheme combining a temperature-controlled optical fiber delay line and a piezoelectric ceramic optical fiber stretcher is proposed to achieve delay compensation capabilities with wide spectrum, high precision, large range and fast response.

[0072] 2. Dispersion compensation capability:

[0073] The reverse compensation of fiber temperature change is achieved through the temperature-controlled fiber delay line, eliminating the inhomogeneity of transmission delay of different frequency components caused by external temperature changes, ensuring the delay uniformity of ultra-wideband signals. This makes it possible to transmit broadband signals in long-distance fiber links under harsh environmental conditions.

[0074] 3. Optimization design of optical fiber link delay compensation module:

[0075] Through experimental design, the performance differences between temperature-controlled optical fiber delay lines and motor-based spatial optical delay lines were compared, verifying the superiority of the former in delay compensation accuracy and broadband signal transmission uniformity.

[0076] 4. Extremely low delay jitter:

[0077] In the experiment, the standard deviation of the transmission delay jitter through the 10km optical fiber link was only 27.8fs, demonstrating ultra-high transmission stability.

[0078] 5. Multi-module coordinated optical fiber link stable transmission:

[0079] The system combines multiple modules such as polarization beam splitter, wavelength division multiplexer, mixer, phase-locked loop, etc. to form a synergistic effect to ensure the stability of microwave signals in optical fiber links.

[0080] 6. Wide application potential:

[0081] The system has demonstrated good adaptability in scenarios with drastic changes in the external environment and long-distance ultra-wideband signal transmission. It is particularly suitable for fields such as interferometric antenna arrays and distributed coherent radars that require high-stability signal transmission or high-stability broadband signal transmission.

[0082] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may certainly make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line, characterized in that: It includes a first laser module, a first photodetector, a third photodetector, a first modulator, a first wavelength division multiplexer, a second wavelength division multiplexer, a fiber coupler, a polarization beam splitter, a delay compensation module, a single-mode optical fiber with a length of at least 10 km, a vector network analyzer, a radio frequency signal generator, a mixer, and a phase-locked loop; The first laser emitted by the first laser module is modulated at the first modulator by the probe signal output by the radio frequency signal generator and the signal to be transmitted output by the vector network analyzer, and the obtained first modulated signal sequentially passes through the polarization beam splitter, the first wavelength division multiplexer, the delay compensation module, the single-mode optical fiber, and the second wavelength division multiplexer to reach the optical fiber coupler; The optical fiber coupler divides the first modulated signal into two sub-paths, the first sub-path enters the first photodetector, and the second sub-path is reflected by the Faraday rotator, and sequentially passes through the optical fiber coupler, the second wavelength division multiplexer, the single-mode optical fiber, the delay compensation module, the first wavelength division multiplexer, and the polarization beam splitter to reach the third photodetector; The first photodetector performs a beat frequency on the first sub-path to obtain a first beat frequency signal, and the third photodetector performs a beat frequency on the second sub-path to obtain a second beat frequency signal, wherein the first beat frequency signal is input into the vector network analyzer, and the second beat frequency signal is input into the mixer; The vector network analyzer determines the stability of the system transmitting the signal to be transmitted according to the phase jitter of the first beat frequency signal; The mixer performs phase detection on the second beat frequency signal and the probe signal output by the radio frequency signal generator to obtain a DC error signal; The output voltage generated by the DC error signal after being processed by the phase-locked loop is used to control the delay of the delay compensation module, thereby compensating for the delay jitter caused to the signal to be transmitted due to the delay change of the single-mode optical fiber.

2. The stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line according to claim 1, characterized in that: The delay compensation module includes a piezoelectric ceramic optical fiber stretcher and a temperature-controlled optical fiber delay line; the method by which the delay compensation module compensates for the delay jitter caused by the delay change of the single-mode optical fiber to the signal to be transmitted is as follows: The output voltage generated by the DC error signal after being processed by the phase-locked loop is directly loaded onto the piezoelectric ceramic fiber stretcher, thereby changing the deformation of the piezoelectric ceramic fiber stretcher, thereby changing the length of the total optical fiber link composed of the delay compensation module and the single-mode optical fiber. When the delay caused by the single-mode optical fiber is shortened and the signal to be transmitted is advanced, the deformation of the piezoelectric ceramic fiber stretcher is increased; when the delay caused by the single-mode optical fiber is increased and the signal to be transmitted is delayed, the deformation of the piezoelectric ceramic fiber stretcher is reduced. At the same time, the phase-locked loop monitors and adjusts the voltage of the piezoelectric ceramic fiber stretcher in real time to ensure that the operating voltage range of the piezoelectric ceramic fiber stretcher is always maintained between -Vmax and Vmax, where Vmax is the upper limit of the operating voltage of the piezoelectric ceramic fiber stretcher; when it is monitored that the voltage of the piezoelectric ceramic fiber stretcher is close to -Vmax, a temperature control signal is generated for the temperature-controlled optical fiber delay line according to the DC error signal, so as to reduce the temperature of the temperature-controlled optical fiber delay line, thereby changing the delay of the total optical fiber link and returning the voltage of the piezoelectric ceramic fiber stretcher to an initial state close to 0V; when the voltage of the piezoelectric ceramic fiber stretcher is close to Vmax, a temperature control signal is generated for the temperature-controlled optical fiber delay line according to the DC error signal, so as to increase the temperature of the temperature-controlled optical fiber delay line, thereby changing the delay of the total optical fiber link and returning the voltage of the piezoelectric ceramic fiber stretcher to an initial state close to 0V.

3. The stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line according to claim 2, characterized in that: The temperature-controlled optical fiber delay line comprises a temperature-controlled element and an optical fiber, wherein the temperature-controlled element is a semiconductor refrigerator and the length of the optical fiber is 1.5 km.

4. The stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line according to claim 1, characterized in that: The first laser module includes a first laser and a first bias controller; The first bias controller is used to adjust the working point of the first modulator so that the first modulator modulates the probe signal and the signal to be transmitted onto the first laser generated by the first laser.

5. The stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line according to claim 1, characterized in that: Also includes a second laser module, a second modulator, and a second photodetector; The second laser emitted by the second laser module is modulated by the signal to be transmitted at the second modulator, and the obtained second modulated signal enters the first wavelength division multiplexer; wherein the wavelength of the second laser is different from the wavelength of the first laser; The first modulated signal and the second modulated signal are combined into a total modulated signal at the first wavelength division multiplexer, and the total modulated signal passes through the delay compensation module and the single-mode optical fiber in sequence to reach the second wavelength division multiplexer; The second wavelength division multiplexer divides the total modulated signal into a first modulated signal and a second modulated signal, the first modulated signal enters the optical fiber coupler, and the optical fiber coupler divides the first modulated signal into two sub-paths for subsequent operations, and the second modulated signal enters the second photodetector; The second photoelectric detector performs a beat frequency on the second modulated signal to obtain a third beat frequency signal, and the third beat frequency signal is then input into the vector network analyzer; The vector network analyzer determines the stability of the system in transmitting the signal to be transmitted at different wavelengths according to the phase jitter of the first beat frequency signal and the third beat frequency signal.

6. The stable transmission system of microwaves carried by light based on a temperature-controlled optical fiber delay line according to claim 5, characterized in that: The second laser module includes a second laser and a second bias controller; The second bias controller is used to adjust the working point of the second modulator so that the second modulator modulates the signal to be transmitted onto the second laser generated by the second laser.

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