Temperature control optical fiber stretcher and optical carrier microwave stable transmission device

Abstract

The invention discloses a temperature control optical fiber stretcher and an optical carrier microwave stable transmission device, and belongs to the technical field of communication and information transmission. The temperature control optical fiber stretcher comprises a shell which is of a box-shaped structure made of a metal material and is provided with an openable cover body; the piezoelectric ceramic optical fiber stretcher is arranged in the shell, is subjected to insulation treatment through heat-conducting silicone grease and conducts heat to the shell; the temperature control optical fiber delay line is arranged in the shell, is connected with the piezoelectric ceramic optical fiber stretcher and conducts heat to the shell through heat conduction silicone grease; and the temperature control device is arranged on the outer wall of the shell and can adjust the temperature of the shell, the piezoelectric ceramic optical fiber stretcher and the temperature control optical fiber delay line. According to the temperature control optical fiber stretcher, the piezoelectric ceramic optical fiber stretcher integrated in the shell achieves time delay compensation, the temperature control optical fiber time delay line completes consistency of large-range time delay compensation and multi-wavelength signal time delay compensation, and meanwhile the time delay compensation range of optical fibers of the part is expanded through the active temperature control module of the device.

Description

Technical Field

[0001] This invention relates to the field of communication and information transmission technology, specifically to a temperature-controlled fiber optic stretcher and an optical microwave stable transmission device. Background Technology

[0002] In the field of microwave photonics, optically-borne microwave stable transmission technology has significant advantages in achieving high-precision, low-noise microwave signal transmission, and is widely used in high-precision time and frequency synchronization and national defense and military security. In the field of time and frequency transmission, the second stability of hydrogen clocks has reached 102. -13 The magnitude increases, and the accuracy of the optical clock is thus improved to 10⁻⁶. -19 The scale is enormous. Traditional time-frequency transmission methods can no longer meet the transmission requirements of such high-precision time-frequency signals. Thanks to the low loss, high bandwidth, and high stability of optical fibers, fiber optic transmission links exhibit superior performance in time-frequency transmission. In the field of national defense and military security, phased array radar, as a significant innovation in radar technology, requires a high degree of synchronization among radar signals. Therefore, how to achieve stable signal transmission has become a key issue facing this technology.

[0003] Currently, active correction and compensation of fiber optic transmission delay is essential to address the problems encountered in the above applications. Delay compensation devices have evolved from electrical delay lines and digital delay lines to fiber optic delay lines, and are widely used in communications, radar, and other fields. Electrical delay lines offer high flexibility and low cost, but their accuracy is limited in high-frequency signal transmission and they are susceptible to noise interference. With the development of digital technology, digital delay lines have emerged, providing higher accuracy and flexibility. After the widespread application of optical communication, fiber optic delay lines, due to their high speed and high bandwidth characteristics, have become the preferred choice for high-precision delay adjustment. Fiber optic delay lines can be divided into two types: digital incremental and analog continuous. Digital incremental delay lines adjust the delay by changing the fiber length through cascaded optical switches, which is easy to integrate but has lower accuracy; analog continuous delay lines achieve continuous adjustment by adjusting the fiber refractive index or using fiber gratings, offering higher accuracy. Overall, although electrical delay lines, digital delay lines, and digital incremental fiber optic delay lines have advantages in some applications, analog continuous fiber optic delay lines are more ideal for delay compensation systems requiring high accuracy and high stability.

[0004] Domestic and international research teams have conducted extensive research on stable microwave signal transmission, focusing on addressing the signal transmission delay instability caused by changes in optical fiber material properties due to external environmental factors. Especially in long-distance broadband microwave signal transmission, higher technical requirements are placed on key performance indicators of optical fiber transmission links, including transmission distance, delay stability, and signal frequency bandwidth. To ensure that the microwave signal transmitted through the optical fiber link remains highly synchronized with the signal before transmission, high-precision compensation is needed for delay jitter caused by external environmental disturbances during transmission. Microwave signal stable transmission compensation schemes based on optical fiber transmission links are currently mainly divided into two types: one achieves stable signal transmission through pre-compensation of the transmitted signal, and the other ensures stable signal transmission by changing the optical fiber transmission delay. The former compensates for phase before signal transmission to offset signal delay jitter caused by the transmission link, ensuring phase stability during optical fiber transmission. The latter compensates for transmission signal delay jitter by precisely adjusting the delay in the optical fiber link, mainly by controlling the wavelength of the optical carrier or changing the fiber length, ensuring phase stability during transmission. The first method, based on RF signal phase pre-compensation, can achieve stable transmission of optical microwave signals, but the stability of fiber optic transmission links based on this method is currently only in the picosecond range. Furthermore, this method only detects and compensates for phase jitter in single-frequency probe signals and cannot achieve stable transmission of broadband optical microwave signals. Therefore, further research is needed on delay compensation techniques applicable to both high-frequency and broadband signals. The second method, achieving stable transmission through fiber optic link delay control, utilizes optical carrier frequency modulation for stable optical microwave transmission, achieving wide-range delay compensation in long-distance fiber optic transmission links. However, it cannot simultaneously balance response speed and compensation accuracy; currently, the transmission stability of fiber optic transmission links based on this method is typically in the picosecond range. Additionally, by introducing an adjustable optical delay line into the fiber optic transmission system, high-precision delay compensation can be achieved by adjusting the fiber length. In stable optical microwave transmission systems, commonly used delay compensation devices include fiber phase shifters (FPS), piezoelectric fiber stretchers (PFS), motorized optical delay lines (MODL), and temperature-controlled fiber spools (TFS). These different types of delay compensation devices each have specific advantages and applicable ranges. Among them, FPS adjusts the delay by stretching the fiber length using piezoelectric devices, offering advantages such as fast response speed and high accuracy.PFS (Programmable Fiber Optic Spectrometer) stretches optical fiber through piezoelectric ceramic deformation, thereby adjusting the optical signal transmission delay. It is suitable for applications requiring high response bandwidth, fast response, and high-precision compensation but with a small compensation range. MODL (Modular Fiber Optic Delay) adjusts the position of the optical output lens or mirror in free space using an electric motor, thereby changing the optical path of the transmitted signal and thus altering the transmission delay. It is suitable for situations with a large compensation range but low precision, slow response speed, and discontinuous operation. TFS (Transient Fiber Optic Spectrometer) controls the transmission delay of optical microwave signals by changing the fiber temperature to adjust its refractive index. These delay compensation devices each have their advantages in different aspects. Depending on the actual needs, different types of devices are often cascaded and combined to simultaneously meet requirements for compensation range, precision, and response speed.

[0005] In summary, existing optical microwave stable transmission technologies still lack sufficient research on delay compensation schemes that balance the range, accuracy, and response speed of delay compensation, and delay compensation schemes for stable transmission of broadband microwave signals and multi-wavelength signals have not yet been verified. Therefore, in the application of long-distance time-frequency transmission systems and phased array radars, there is a lack of research on large-scale, high-precision delay compensation and multi-wavelength signal stable transmission technologies. Summary of the Invention

[0006] This invention provides a temperature-controlled fiber optic stretcher and an optical microwave stable transmission device, aiming to at least partially solve the above-mentioned technical problems.

[0007] As a first aspect of the present invention, a temperature-controlled fiber optic stretcher is provided, comprising: The outer casing is a box-shaped structure made of metal and has an openable lid; The piezoelectric ceramic fiber stretcher is located inside the housing and is insulated by thermally conductive silicone grease, which conducts heat to the housing. A temperature-controlled fiber optic delay line is located inside the housing and connected to the piezoelectric ceramic fiber stretcher, and conducts heat to the housing through thermally conductive silicone grease. A temperature control device, located on the outer wall of the housing, can adjust the temperature of the housing, the piezoelectric ceramic fiber stretcher, and the temperature-controlled fiber delay line. The temperature-controlled fiber stretcher of this invention integrates a piezoelectric ceramic fiber stretcher within its housing to achieve delay compensation. The temperature-controlled fiber delay line achieves consistent delay compensation over a wide range and for multi-wavelength signals. Specifically, it achieves high precision and fast delay response through the inverse piezoelectric effect of the piezoelectric ceramic ring. Simultaneously, the device's active temperature control module expands the delay compensation range of this portion of the fiber. This integrates delay compensation devices, and the temperature control device, by cooling the housing, can simultaneously affect both the piezoelectric ceramic fiber stretcher and the temperature-controlled fiber delay line, improving control accuracy.

[0008] The outer shell contains a first cylindrical structure and a second cylindrical structure sleeved on the outside of the first cylindrical structure; the piezoelectric ceramic fiber stretcher is disposed inside the first cylindrical structure; and the fiber of the temperature-controlled fiber delay line is wound around the second cylindrical structure.

[0009] The second cylindrical structure is detachably fixed inside the outer shell, and the second cylindrical structure and the first cylindrical structure are arranged coaxially.

[0010] The outer casing is made of copper and has multiple planar outer wall surfaces; the temperature control device includes a semiconductor cooling chip and a heat dissipation device disposed on the outer wall surface.

[0011] The fiber length of the fiber delay line is not less than 200m.

[0012] The fiber length of the piezoelectric ceramic fiber stretcher is not less than 60m.

[0013] The outer wall of the outer shell is provided with thermal insulation material.

[0014] The optical fiber of the piezoelectric ceramic optical fiber stretcher is wound in a flat or symmetrical manner.

[0015] The optical fiber winding tension is 5g or 30g.

[0016] As a second aspect of the present invention, an optical microwave stable transmission device is also provided, comprising a local end and a remote end connected by an optical fiber link of not less than 2 km, and further comprising the above-mentioned temperature-controlled optical fiber stretcher. The local terminal includes a reference clock, a data transmission / reception / acquisition and processing device, a first power amplifier, a first power coupler, a second power amplifier, a second power coupler, a Mach-Zehnder modulator, a bias controller, a polarization beam splitter, a first photodetector, a second photodetector, a mixer, a Faraday rotator, an optical fiber coupler, and a single-mode optical fiber. The data transmission / reception / acquisition and processing device compares the first local receiving end signal input to the second power coupler and the second local receiving end signal input to the second photodetector with a reference clock, tests the signal delay jitter inside and outside the loop respectively, and outputs a microwave signal. The microwave signal output by the data transmission / reception / acquisition and processing device is amplified by the first power amplifier and then received by the first power coupler. A portion of the amplified signal is used as the local oscillator signal of the mixer, and the other portion is modulated by the Mach-Zehnder modulator to generate an optical radio frequency signal. The Mach-Zehnder modulator is biased by a bias voltage controller to ensure that it is locked at the quadrature operating point in real time. The optical radio frequency signal first passes through a polarization beam splitter and then enters a temperature-controlled fiber stretcher. Subsequently, it enters a fiber optic link composed of single-mode fibers and is transmitted to the remote end. The optical signal transmitted through the optical fiber link is split into two parts after passing through the optical fiber coupler: one part is converted into an electrical signal by the second photodetector and enters the data transmission / reception / acquisition processing device to measure the link loop external delay jitter; the other part is reflected by the Faraday rotator and transmitted back to the local end, and after passing through the polarization beam splitter, it enters the first photodetector to output the first local end received signal. The first local end received signal is received by the second power coupler through the second power and input to the data transmission / reception / acquisition processing device and the mixer; the mixer is connected to the phase-locked loop, and the phase-locked loop is connected to the temperature-controlled optical fiber stretcher.

[0017] Based on the above solutions, it can be seen that the temperature-controlled fiber optic stretcher and optical microwave stable transmission device of the present invention have at least one of the following beneficial effects compared with the prior art: The temperature-controlled fiber optic stretcher of this invention integrates a piezoelectric ceramic fiber optic stretcher within its housing to achieve delay compensation. The temperature-controlled fiber optic delay line achieves consistent delay compensation across a wide range and for multi-wavelength signals. Specifically, it achieves high precision and rapid delay response through the inverse piezoelectric effect of the piezoelectric ceramic ring. Furthermore, the active temperature control module of the device expands the delay compensation range of this portion of the fiber. This integration of delay compensation devices, coupled with the temperature control device's ability to simultaneously influence both the piezoelectric ceramic fiber optic stretcher and the temperature-controlled fiber optic delay line by cooling the housing, improves control accuracy. The parallel winding scheme of this invention offers advantages in terms of process cost and compensation range, while the symmetrical winding scheme exhibits better temperature stability. Low-tension winding is beneficial for improving delay compensation accuracy, while high-tension winding can increase the delay compensation range. Attached Figure Description

[0018] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments will be briefly described below.

[0019] Figure 1 This is a schematic diagram of the temperature-controlled fiber optic stretcher of the present invention; Figure 2 Here is a structural diagram of the shell; Figure 3 Model diagram of the shell and the first cylindrical structure Figure 4 This is a model diagram of the second cylindrical structure; Figure 5 This is a model diagram of the cover. Figure 6 This is a schematic diagram illustrating the flat winding method for winding optical fibers using a piezoelectric ceramic fiber stretcher. Figure 7 This is a schematic diagram illustrating the symmetrical winding method of an electric piezoelectric ceramic fiber stretcher for optical fibers. Figure 8 The delay variation characteristics of a piezoelectric ceramic fiber stretcher under positive excitation voltage; Figure 9 The delay variation characteristics of a piezoelectric ceramic fiber stretcher under negative excitation voltage; Figure 10 The time delay response coefficients of three piezoelectric ceramic fiber stretchers under positive and negative voltages; Figure 11 The frequency response of three piezoelectric ceramic fiber stretchers is shown under a sweep frequency of 200 Hz to 10 kHz. Figure 12 The temperature-dependent delay response curve of the piezoelectric ceramic fiber stretcher under positive excitation voltage; Figure 13 Temperature-delay response curve of a piezoelectric ceramic fiber optic stretcher under negative excitation voltage; Figure 14 The frequency response of a 5g flat-wound piezoelectric ceramic fiber stretcher at five different temperature points under a sweep frequency from 200 Hz to 10 kHz. Figure 15 This is a graph showing the temperature change during refrigeration. Figure 16 This is a graph showing the heating and temperature changes. Figure 17 Temperature control accuracy graphs at different target temperatures; Figure 18 This is a graph showing the range of delay variations in fiber optic transmission for cooling and heating.

[0020] Figure 19 This is a schematic diagram of a stable optical microwave transmission device. Figure 20 Delay jitter diagrams for a 2 km round-trip fiber optic link under locked, locked outside, and unlocked states within the ring; Figure 21 The amplitude variation diagram shows the locked, locked, and unlocked states of a 2 km round-trip transmission fiber optic link under the conditions of in-ring locking, out-of-ring locking, and unlocked states. Figure 22 Overlapped Allen variance plots of the stability of 10 GHz microwave signals in locked, locked and unlocked states of a 2 km round-trip transmission fiber optic link.

[0021] In the above figures, the meanings of the reference numerals are as follows: In the figure: 1. Outer shell; 11. First cylindrical structure; 12. Second cylindrical structure; 13. Cover; 2. Piezoelectric ceramic fiber stretcher; 3. Temperature-controlled fiber delay line; 4. Temperature control device. Detailed Implementation

[0022] To better understand the technical solutions of the embodiments of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] join Figures 1 to 22 The present invention discloses a temperature-controlled fiber optic stretcher, including a housing 1, a piezoelectric ceramic fiber optic stretcher 2, a temperature-controlled fiber optic delay line 3, and a temperature control device 4.

[0025] The outer shell 1 is a box-shaped structure made of metal, and the outer shell 1 has an openable cover 13.

[0026] The piezoelectric ceramic fiber stretcher 2 is disposed inside the housing 1, and is insulated by thermally conductive silicone grease and conducts heat to the housing 1.

[0027] The temperature-controlled fiber optic delay line 3 is located inside the housing 1 and is connected to the piezoelectric ceramic fiber optic stretcher 2. It conducts heat to the housing 1 through thermally conductive silicone grease.

[0028] Temperature control device 4 is located on the outer wall of housing 1 and can adjust the temperature of housing 1, piezoelectric ceramic fiber stretcher 2 and temperature-controlled fiber delay line 3.

[0029] The temperature-controlled fiber optic stretcher of this invention integrates a piezoelectric ceramic fiber optic stretcher 2 within its housing 1 to achieve delay compensation. A temperature-controlled fiber optic delay line 3 ensures consistent delay compensation across a wide range and for multi-wavelength signals. This is achieved through the inverse piezoelectric effect of the piezoelectric ceramic ring, resulting in high precision and rapid delay response. Furthermore, the active temperature control module of the device expands the delay compensation range of this portion of the fiber. This integration of delay compensation devices is realized. Moreover, the temperature control device 4, by cooling the housing 1, can simultaneously influence both the piezoelectric ceramic fiber optic stretcher 2 and the temperature-controlled fiber optic delay line 3, improving control accuracy.

[0030] See Figures 2 to 5The outer casing 1 is entirely made of copper, specifically pure copper, which has good thermal conductivity. Inside the casing 1 is a first cylindrical structure 11 and a second cylindrical structure 12 fitted over the first cylindrical structure 11. The first cylindrical structure 11 and the second cylindrical structure 12 form a double-ring structure. In use, the piezoelectric ceramic fiber stretcher 2 is placed inside the first cylindrical structure 11, and the fiber of the temperature-controlled fiber delay line 3 is wound around the second cylindrical structure 12. This allows for more efficient use of the internal space of the casing 1, achieving a smaller, more integrated design.

[0031] The second cylindrical structure 12 is detachably fixed inside the outer casing 1. The second cylindrical structure 12 can be fixed to the outer casing 1 by means of bonding, threaded connection, or other methods. The second cylindrical structure 12 and the first cylindrical structure 11 are arranged coaxially. This improves integration, increases the space utilization inside the outer casing 1, and helps reduce the volume of the outer casing 1.

[0032] The outer casing 1 has multiple planar outer wall surfaces. The temperature control device includes semiconductor cooling chips and heat dissipation devices disposed on the outer wall surfaces. More specifically, in this embodiment, the outer casing 1 has a hexagonal structure with six planar outer wall surfaces, which are the outer surfaces of the outer casing 1. A semiconductor cooling chip and a heat dissipation device are disposed on each outer wall surface. Insulation material can be further disposed on the outer wall of the outer casing 1 to achieve a heat preservation effect. The insulation material can be polyurethane foam, which can almost completely isolate the outer casing 1 from heat exchange with the external environment. One side of the six semiconductor cooling chips achieves bidirectional temperature control of the outer casing 1 by switching current polarity, while the other side uses thermally conductive silicone grease to fix the heat dissipation device and promptly dissipate the heat generated by the semiconductor cooling chips. The piezoelectric ceramic fiber optic stretcher 2 is insulated and isolated on the inner side of the outer casing 1 using thermally conductive silicone while ensuring high thermal conductivity.

[0033] The optical fiber length of the optical delay line is not less than 200m. The optical fiber length of the piezoelectric ceramic optical fiber stretcher 2 is not less than 60m.

[0034] like Figure 6 and Figure 7 As shown, the piezoelectric ceramic fiber stretcher 2 mechanically stretches the optical fiber through the inverse piezoelectric effect, achieving precise control of optical signal delay with a delay control accuracy at the fs level. In this embodiment, the optical fiber is wound with a constant tension of 5g, using both flat winding and symmetrical winding methods.

[0035] Figure 6 The diagram shows a flat-winding method for optical fiber. The fiber entry point of the parallel winding device is located in the innermost layer. Under high-pressure excitation, excessive radial extrusion force may be generated due to the expansion of the ceramic ring, which may lead to the risk of deterioration of the signal transmission quality inside the optical fiber. Figure 7In the symmetrical winding method shown, the fiber exit point of the symmetrically wound device is on the outermost layer, which can effectively avoid the radial extrusion force.

[0036] Parallel winding offers advantages in terms of simple process and low cost, while also ensuring the stability of signal transmission within the optical fiber.

[0037] This application sets up three devices: a 5g flat-wound piezoelectric ceramic fiber stretcher, a 5g symmetrically wound piezoelectric ceramic fiber stretcher, and a 30g flat-wound piezoelectric ceramic fiber stretcher, to compare and analyze the influence of tension parameters on the delay compensation characteristics of these devices.

[0038] like Figure 8 The figure shows the time-delay variation characteristics of the piezoelectric ceramic fiber stretcher 2 under positive excitation voltage. Figure 9 The figure shows the delay variation characteristics of the piezoelectric ceramic fiber stretcher 2 under negative excitation voltage. Para.Data represents the measured data of the parallel winding device; Para.Fi represents the fitted data of the parallel winding device; Symm.Data represents the measured data of the symmetrical winding device; and Symm.Fit represents the fitted data of the symmetrical winding device. Figure 10 The delay response coefficients of three piezoelectric ceramic fiber stretchers 2 under positive and negative voltages are given. Figure 11 The frequency responses of three piezoelectric ceramic fiber stretchers were analyzed under a sweep frequency range of 200 Hz to 10 kHz. It is evident that all three devices meet the high-precision delay compensation requirements of stable optical microwave transmission links in terms of the key indicators mentioned above. Regarding optical power stability, the peak-to-peak insertion loss fluctuation is less than 0.09 dB (standard deviation ≤ 0.022 dB), ensuring signal transmission quality. Regarding delay response, excellent linearity is exhibited in both positive and negative excitation regions. Regarding frequency response, it remains below the device resonant frequency within the operating frequency range below 10 kHz, with frequency response fluctuation controlled within 8.5~11.9 fs / V. Simultaneously, the test results validate the effectiveness of the device design. The parallel winding scheme has advantages in terms of process cost and compensation range, while the symmetrical winding scheme exhibits better temperature stability. Low-tension winding is beneficial for improving delay compensation accuracy, while high-tension winding can improve the delay compensation range. This differentiated characteristic provides a theoretical basis for device selection in different application scenarios.

[0039] like Figures 12 to 14As shown, the delay and frequency response output characteristics of a 5g flat-wound piezoelectric ceramic fiber stretcher were tested and analyzed at different temperatures. Specifically, the delay and frequency response characteristics were tested at five different temperature environments, from 15℃ to 35℃, with 5℃ intervals. Experimental data show that in the positive excitation voltage region (0 to 180 V, 20℃ temperature rise range), the peak delay compensation caused solely by the inverse piezoelectric effect increased by 44.31%. In the negative excitation voltage region (0 to -180 V, 20℃ temperature rise range), the peak delay compensation caused solely by the inverse piezoelectric effect increased by 39.35%, and the average slope of the temperature-delay trend expression showed a good linear relationship. Within the 20℃ temperature rise range, the frequency response improvement across the entire frequency band (200 Hz to 10 kHz) caused solely by the inverse piezoelectric effect was approximately 5% to 10%. This provides a theoretical basis for the design of temperature-controlled fiber stretchers and guidance for parameter optimization under wide-temperature-range operating requirements. Temperature-controlled fiber optic stretchers achieve wide-range delay compensation and consistent delay compensation across a broad spectrum and multiple wavelengths by changing the temperature of the fiber. They also achieve high-precision and fast-response delay compensation through the inverse piezoelectric effect of piezoelectric ceramic fiber optic stretchers.

[0040] The temperature-controlled fiber optic stretcher of this application achieves high-precision and fast delay response through the inverse piezoelectric effect of the piezoelectric ceramic ring in the inner ring, while also expanding the delay compensation range of this part of the fiber through the active temperature control module of the device. On the other hand, it realizes the integration of delay compensation devices, and a single device can simultaneously achieve large-range, high-precision, and fast-response delay compensation as well as consistency of wide-spectrum, multi-wavelength delay compensation.

[0041] This application addresses the need for delay compensation devices in stable optical microwave transmission systems to possess a wide range, high precision, fast response, and consistent delay compensation across a broad spectrum. A temperature-controlled fiber optic stretcher was designed. The delay compensation capability of the device's inner-ring self-developed piezoelectric ceramic fiber stretcher was systematically tested, including the optical power stability, delay response, and frequency response characteristics of the stretcher under different winding methods and tensions, as well as its delay response and frequency response characteristics under varying temperature conditions. Experimental results demonstrate its excellent power stability (≤0.09 dB), delay response linearity, and frequency stability. This verifies that the device can meet the high-precision and fast-response delay compensation requirements of stable optical microwave transmission links. Furthermore, this application tested the temperature control capability of the temperature-controlled fiber optic stretcher, including its temperature control range and accuracy, as well as the device's delay compensation range. It can achieve a maximum cooling range of 19.5 ℃, a maximum heating range of 24.3 ℃, and a total temperature control range of 43.8 ℃. Within a 500 s measurement time, the temperature control accuracy is better than 0.012 ℃, and the delay compensation range reaches 865.61 ps. Figures 14-17 As shown, this verifies that the device meets the requirements for wide-range and multi-wavelength delay compensation in stable optical microwave transmission links.

[0042] like Figures 19 to 22 As shown, this embodiment of the invention also discloses an optical microwave stable transmission device, including a local end and a remote end connected by an optical fiber link of not less than 2km, and also including the above-mentioned temperature-controlled optical fiber stretcher. The local end includes a reference clock, a data transmission / reception / acquisition and processing device, a first power amplifier, a first power coupler, a second power amplifier, a second power coupler, a Mach-Zehnder modulator, a bias controller, a polarization beam splitter, a first photodetector, a second photodetector, a mixer, a Faraday rotator, an optical fiber coupler, and a single-mode optical fiber. The data transmission / reception / acquisition and processing device compares the first local receiving end signal input to the second power coupler and the second local receiving end signal input to the second photodetector with the reference clock, tests the signal delay jitter inside and outside the loop respectively, and outputs a microwave signal. The microwave signal output by the data transmission / reception / acquisition processing device is amplified by the first power amplifier and then received by the first power coupler. A portion of the amplified signal is used as the local oscillator signal of the mixer, and the other portion is modulated by the Mach-Zehnder modulator to generate an optical radio frequency signal. The Mach-Zehnder modulator is biased by a bias voltage controller to ensure that it is locked at the quadrature operating point in real time. The optical radio frequency signal first passes through a polarization beam splitter and then enters a temperature-controlled fiber stretcher. Subsequently, it enters a fiber optic link composed of single-mode fibers and is transmitted to the far end. The optical signal transmitted through the fiber optic link is split into two parts after passing through the fiber optic coupler: one part is converted into an electrical signal by the second photodetector and enters the data transmission / reception / acquisition processing device to measure the link loop delay jitter; the other part is reflected by the Faraday rotator and transmitted back to the local end, and after passing through the polarization beam splitter, it enters the first photodetector to output the first local end received signal. The first local end received signal is received by the second power coupler through the second power and input to the data transmission / reception / acquisition processing device and the mixer; the mixer is connected to the phase-locked loop, and the phase-locked loop is connected to the temperature-controlled fiber tensioner.

[0043] More specifically, a vector network analyzer is used as the data transmission / reception / acquisition and processing device. The local and remote ends are connected by a 2km fiber optic link. At the local end, the 10 GHz microwave signal output from the vector network analyzer is amplified and split into two parts by a power coupler. One part is modulated by a Mach-Zehnder modulator to generate an optical radio frequency (RF) signal from a narrow-linewidth fiber laser, where the modulator's bias voltage is controlled by a bias voltage controller to ensure it is locked at the quadrature operating point in real time; the other part serves as a reference signal. The RF signal first passes through a polarization beam splitter, then enters a temperature-controlled fiber stretcher, and subsequently enters the fiber optic link for transmission to the remote end.

[0044] At the remote end, the optical radio frequency signal is split into two parts by a 50:50 single-mode coupler. One part is converted into an electrical signal by a photodetector and enters a vector network analyzer to measure the external delay jitter of the link loop. The other part is reflected by a Faraday rotator and transmitted back to the local end. After passing through a polarization beam splitter, it enters a photodetector to obtain a 10 GHz microwave signal. After amplification, it is split into two paths. One path is converted into an electrical signal by a photodetector and enters a vector network analyzer to measure the internal delay jitter of the link loop. The other path is phase-discriminated with the 10 GHz reference signal at the local end to obtain a DC error signal carrying the transmission link delay jitter. This DC error signal enters a zero-difference phase-locked loop (PLL) and, after amplification and filtering, is used to control a temperature-controlled fiber optic stretcher to achieve stable transmission of the microwave signal.

[0045] To evaluate the delay compensation effect of a temperature-controlled fiber stretcher in a stable microwave optical transmission system and the stability of a 2 km round-trip fiber optic link, a 10 GHz microwave signal generated by a vector network analyzer was transmitted through the fiber optic link, then beat by a photodetector at the remote end before being phase-detected by the vector network analyzer to calculate the out-of-loop delay jitter. The receiving bandwidth of the vector network analyzer was set to 2 Hz. Experimental results are as follows: Figure 21 As shown, for an unlocked fiber optic link, the delay variation caused by changes in the external environment is 108.9 ps within 3600 s. This is due to the fluctuating laboratory temperature. For a locked fiber optic link, the standard deviation of the delay jitter is 23.9 fs. The 10 GHz microwave signal, after transmission through the fiber optic link, is returned to the local end, beats through a photodetector, and then enters a vector network analyzer for phase detection, thereby calculating the delay jitter within the loop. For a locked fiber optic link, the standard deviation of the delay jitter within the loop is only 6.4 fs within 3600 s.

[0046] In the locked state of the fiber optic link, the impact of environmental changes on the transmission stability of the fiber optic link is effectively suppressed. However, the delay jitter outside the loop is more pronounced than inside the loop, mainly due to the delay variations of electronic components such as cables, optical fibers, and photodetectors outside the phase-locked loop. The fiber optic link stability test verifies that the temperature-controlled fiber optic stretcher designed in this paper has a wide range, high precision, and fast response delay compensation capability. Furthermore, it also shows that the scheme adopted in this paper has the ability to detect and compensate for delay jitter in fiber optic transmission links with high precision, and the system can achieve long-term stability of tens of femtoseconds.

[0047] Signal power variation also determines the transmission stability of microwave signals. Therefore, this paper uses a vector network analyzer to measure delay jitter while monitoring the amplitude variation of the transmitted signal. The experimental results are as follows: Figure 22As shown, in the unlocked state of the fiber optic link, the standard deviation of signal amplitude jitter over 3600 s is 0.008 dB. In the locked state of the fiber optic link, the standard deviations of signal amplitude jitter inside and outside the loop over 3600 s are 0.007 dB and 0.010 dB, respectively. This demonstrates that the system has excellent long-term power stability.

[0048] To thoroughly evaluate the stability of the fiber optic link, the overlap Allan offset was calculated using measured 10 GHz microwave signal phase data. The results are as follows: Figure 22 As shown. For unlocked fiber optic links, due to the influence of external environmental changes on the fiber optic transmission system, random walk noise exists, and the frequency stability over average time periods of 1 s and 1000 s is 2.89 × 10⁻⁶. -12 and 4.72×10 -14 The system frequency stability is poor. For the locked fiber link, the out-of-loop frequency stability over average time periods of 1 s and 1000 s is 1.75 × 10⁻⁶. -14 and 3.86×10 -17 The frequency stability within the ring is 3.72 × 10⁻⁶. -15 and 8.49×10 -18 Compared to the unlocked state of the fiber optic link, it exhibits excellent long-term frequency stability. Furthermore, the overlap Allan deviation decreases linearly with increasing averaging time, with a more significant improvement in stability. The stability of delay and amplitude variations in the fiber optic link under locked conditions demonstrates high-precision phase locking capability. This indicates that the temperature-controlled fiber optic stretcher designed and fabricated in this application can meet the compensation requirements for stable transmission of high-precision fiber optic links.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A temperature-controlled fiber optic stretcher, characterized in that, include: The outer casing is a box-shaped structure made of metal and has an openable lid; The piezoelectric ceramic fiber stretcher is located inside the housing and is insulated by thermally conductive silicone grease, which conducts heat to the housing. A temperature-controlled fiber optic delay line is located inside the housing and connected to the piezoelectric ceramic fiber stretcher, and conducts heat to the housing through thermally conductive silicone grease. A temperature control device is installed on the outer wall of the housing, which can adjust the temperature of the housing, the piezoelectric ceramic fiber stretcher, and the temperature-controlled fiber delay line.

2. The temperature-controlled fiber optic stretcher according to claim 1, characterized in that, The outer shell contains a first cylindrical structure and a second cylindrical structure sleeved on the outside of the first cylindrical structure; the piezoelectric ceramic fiber stretcher is disposed inside the first cylindrical structure. The optical fiber of the temperature-controlled optical fiber delay line is wound around the second cylindrical structure.

3. The temperature-controlled fiber optic stretcher according to claim 2, characterized in that, The second cylindrical structure is detachably fixed inside the outer shell, and the second cylindrical structure and the first cylindrical structure are arranged coaxially.

4. The temperature-controlled fiber optic stretcher according to claim 1, characterized in that, The outer casing is made of copper and has multiple planar outer wall surfaces; the temperature control device includes a semiconductor cooling chip and a heat dissipation device disposed on the outer wall surface.

5. The temperature-controlled fiber optic stretcher according to claim 1, characterized in that, The fiber length of the fiber delay line is not less than 200m.

6. The temperature-controlled fiber optic stretcher according to claim 1, characterized in that, The fiber length of the piezoelectric ceramic fiber stretcher is not less than 60m.

7. The temperature-controlled fiber optic stretcher according to claim 1, characterized in that, The outer wall of the shell is provided with thermal insulation material.

8. The temperature-controlled fiber optic stretcher according to claim 1, characterized in that, The optical fiber of the piezoelectric ceramic optical fiber stretcher is wound in a flat or symmetrical manner.

9. The temperature-controlled fiber optic stretcher according to claim 8, characterized in that, The optical fiber winding tension is 5g or 30g.

10. A stable optical microwave transmission device, comprising a local end and a remote end connected by an optical fiber link of not less than 2 km, characterized in that, It also includes a temperature-controlled fiber optic stretcher as described in any one of claims 1 to 9; The local terminal includes a reference clock, a data transmission / reception / acquisition and processing device, a first power amplifier, a first power coupler, a second power amplifier, a second power coupler, a Mach-Zehnder modulator, a bias controller, a polarization beam splitter, a first photodetector, a second photodetector, a mixer, a Faraday rotator, an optical fiber coupler, and a single-mode optical fiber. The data transmission / reception / acquisition and processing device compares the first local receiving end signal input to the second power coupler and the second local receiving end signal input to the second photodetector with a reference clock, tests the signal delay jitter inside and outside the loop respectively, and outputs a microwave signal. The microwave signal output by the data transmission / reception / acquisition and processing device is amplified by the first power amplifier and then received by the first power coupler. A portion of the amplified signal is used as the local oscillator signal of the mixer, and the other portion is modulated by the Mach-Zehnder modulator to generate an optical radio frequency signal. The Mach-Zehnder modulator is biased by a bias voltage controller to ensure that it is locked at the quadrature operating point in real time. The optical radio frequency signal first passes through a polarization beam splitter and then enters a temperature-controlled fiber stretcher. Subsequently, it enters a fiber optic link composed of single-mode fibers and is transmitted to the remote end. The optical signal transmitted through the optical fiber link is split into two parts after passing through the optical fiber coupler: one part is converted into an electrical signal by the second photodetector and enters the data transmission / reception / acquisition processing device to measure the link loop external delay jitter; the other part is reflected by the Faraday rotator and transmitted back to the local end, and after passing through the polarization beam splitter, it enters the first photodetector to output the first local end received signal. The first local end received signal is received by the second power coupler through the second power and input to the data transmission / reception / acquisition processing device and the mixer; the mixer is connected to the phase-locked loop, and the phase-locked loop is connected to the temperature-controlled optical fiber stretcher.

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