A polarization mode control-based laser frequency stabilization device and a debugging method thereof

Abstract

The application discloses a laser frequency stabilization device based on polarization mode control and a debugging method thereof, and comprises a laser power supply, a double-longitudinal-mode helium-neon laser, a temperature control module, an optical path adjustment module, a fiber coupling module, a wiring module and a signal processing module. The debugging method is characterized in that: the arrangement density of the resistance wire wound on the surface of the laser gain tube is adjusted, and the working parameters of the temperature control module are optimized, so that the preheating time of the frequency stabilization laser is the shortest, and the temperature control precision is the highest; the posture of the polarization beam splitter prism is accurately adjusted in combination with a Fabry-Perot scanning interferometer and an oscilloscope, the double-longitudinal-mode output light of the laser is divided into two paths of test light and reference light which are completely operated in single longitudinal mode, the test light frequency is locked near the center frequency away from the polarization jump point according to the size and variation trend of the reference light intensity, and the efficient polarization maintaining fiber coupling of the free space linear polarization frequency stabilization test light is realized by using a polarization maintaining fiber collimator and a collimator adjustment frame. The product can be used as a frequency stabilization laser source of a wave aberration interferometer.

Description

Technical Field

[0001] This invention belongs to the field of laser application technology, specifically relating to a laser frequency stabilization device and its debugging method based on polarization mode control. The developed single-mode output frequency-stabilized helium-neon laser is particularly suitable for use in wave aberration interferometers. Background Technology

[0002] Helium-neon lasers possess unparalleled advantages in beam quality and stability compared to other lasers, making them widely used in precision interferometric instruments. For example, when used as a light source in wavelet aberration interferometers, the power output via fiber coupling is required to be at the sub-milliwatt level or higher. In such cases, the cavity length of the laser resonator often exceeds 150 mm, easily generating dual or even multiple longitudinal modes. This "frequency impurity" leads to deterioration of the laser's coherence, causing the contrast of the fringes in the interference field to vary with the optical path difference and the longitudinal mode frequency. Furthermore, precision interferometric applications generally require the laser source to have a relative frequency stability better than 10⁻⁶. -7 Due to interference from factors such as temperature, airflow, vibration, and unstable laser tube discharge current, the frequency drift of a freely operating helium-neon laser far exceeds its theoretical linewidth limit, resulting in a relative frequency stability of only 10. -5 ~10 -6 To overcome the above two problems, measures need to be taken to ensure that the dual-longitudinal-mode helium-neon laser outputs high-power, single-longitudinal-mode frequency-stabilized laser, thereby improving the applicability of the laser.

[0003] Frequency-stabilized dual-longitudinal-mode helium-neon lasers can be classified into three categories according to their reference reference: one is the iodine-stabilized laser, which locks the reference light frequency to the iodine saturation absorption spectrum line; another is the longitudinal-mode beat frequency controlled frequency-stabilized laser, which locks the beat frequency signal of the dual longitudinal modes to the radio frequency standard; and the third is the laser gain curve as the center frequency as the reference frequency, which generally stabilizes the laser dual longitudinal modes at the position of equal power.

[0004] Japanese scholars Fumio Murakami et al. were the first to apply iodine saturated absorption frequency stabilization technology to a dual-longitudinal-mode helium-neon laser with an all-cavity internal cavity, thereby improving the laser's relative frequency stability to 10. -9 Magnitude (Fumio Murakami, et al. Frequency Stabilization of 633-nm He-Ne Laser by Using FrequencyModulationSpectroscopy of 127I2 Enhanced by an External Optical Cavity [J]. Electronics and Communications in Japan. 2000, Part 2, Vol. 83, No. 3: 1-9). This method utilizes an auxiliary optical cavity to enhance the external intensity of the laser tail light, thereby enabling it to meet the requirements of... 127 The power requirements for I2 molecule saturation absorption are significant. However, the auxiliary optical cavity requires piezoelectric ceramic elements to tune its length, reducing the overall vibration resistance of the device. Furthermore, the laser output is still a dual-longitudinal-mode laser, therefore it cannot be directly applied to wavefront aberration interferometers.

[0005] The team led by Academician Tan Jiubin of Harbin Institute of Technology proposed a thermal frequency stabilization method in their patent "A Thermal Frequency Stabilization Method and Device for Dual-Longitudinal-Mode Lasers Based on Iodine-Stabilized Reference Light" (CN101615755A). This method locks the output frequency offset of multiple parallel dual-longitudinal-mode lasers to the center frequency of an iodine-stabilized laser, improving the relative frequency stability of the laser to 10. -9 This method not only achieves a significant improvement in frequency stability but also addresses the issue of poor frequency consistency across multiple dual-longitudinal-mode lasers. Furthermore, Academician Tan and his colleagues proposed a novel thermal frequency stabilization method in their patent "Method and Device for Dual-Longitudinal-Mode Thermoelectric Cooling Frequency Locking Based on Iodine Frequency Stabilization Reference" (CN101615759B). This method integrates iodine frequency stabilization technology with dual-longitudinal-mode thermoelectric cooling frequency stabilization technology. Employing a symmetrically designed thermoelectric cooler, it eliminates the impact of radial distortion caused by uneven heating of the laser tube on the output frequency stability, maintaining a long-term frequency stability of 10. -9 This increases the laser's size by a factor of two, while also shortening the preheating time, extending its lifespan, and enhancing its environmental adaptability. However, these lasers are expensive and are generally used only in specific ultra-precision machining equipment, making them unsuitable for applications like wavefront aberration interferometers where high laser frequency stability is not a primary concern.

[0006] Bi Zhiyi et al. from Central China Normal University proposed a laser frequency stabilization method based on longitudinal mode beat frequency control (Bi Zhiyi, Wang Lixia et al. Laser frequency stabilization technology based on longitudinal mode beat frequency control [J]. Chinese Journal of Lasers, 2007, 34(9):1118~1202), which improved the stability of the output frequency of a dual longitudinal mode helium-neon laser to 5. 10 -10(1s integration time). This method is based on the correspondence between laser frequency and longitudinal mode frequency intervals. Precision phase-locked loop (PLL) control technology locks the beat frequency of two adjacent longitudinal modes to the radio frequency standard, thereby controlling the laser resonant cavity length and stabilizing the laser output frequency. In this method, the dual-longitudinal-mode laser has an external cavity structure, using piezoelectric ceramic elements to tune the cavity length, which reduces the device's vibration resistance and results in a relatively long laser warm-up time. The use of a radio frequency source also makes commercial integration difficult. Furthermore, the laser output light remains a dual-longitudinal-mode laser, making wavefront aberration interferometers unsuitable.

[0007] In 1972, Balhorn et al. proposed a laser frequency stabilization method based on adjusting the discharge current of the plasma tube of a laser by adjusting the power difference signal of the dual longitudinal modes, thereby achieving cavity length tuning (R Balhorn, H Kunzmann, FLebowsky. Frequency Stabilization of Internal-Mirror Helium-Neon Lasers[J]. Applied Optics, 1972, 11(4): 742-746). In China, Zhou Zhaofei et al. of Sichuan University also carried out similar research (Li Wenjie, Zhou Zhaofei, Jin Chongjiu. Thermally Stabilized Frequency Source of Dual Longitudinal Mode Laser[J]. Optoelectronic Engineering, 1998(06): 95-98.). The laser frequency stabilization method based on discharge current adjustment has the advantages of low thermal inertia, high adjustment efficiency, and no limitation by laser tube type and material. However, the center frequency of the laser gain curve is easily affected by the change of discharge current, especially when the ambient temperature changes greatly. The relative stability of the laser frequency is generally less than 10. -7 Magnitude;

[0008] To further improve the frequency stability of dual-longitudinal-mode lasers, Reinishaw, a British company, proposed a thermal frequency stabilization method for dual-longitudinal-mode lasers using a heating wire as the actuator (Pre-heat Control System for a Laser, International Patent: WO8801798; Frequency Stabilized Laser and Control System Therefor, International Patent: WO8801799). This method alters the operating current flowing through the heating wire wound around the laser gain tube based on the power difference signal between the two longitudinal modes. This causes the laser resonant cavity to expand or contract according to the heating state of the heating wire, thereby stabilizing the laser's output frequency. This frequency stabilization method has advantages such as simple structure, low cost, and ease of integration. Furthermore, the relative stability of the output frequency of the dual-longitudinal-mode helium-neon laser can be improved to a maximum of 10. -9 Magnitude.

[0009] In summary, frequency-stabilized helium-neon lasers with cavity length adjusted based on dual-mode power difference feedback signals can be used in wavelet aberration interferometers. However, these lasers are mostly power-balanced, and their output power in fiber-coupled configurations is generally less than 0.7 milliwatts. Furthermore, when the stress birefringence of the cavity mirror is high, frequency-stabilized helium-neon lasers with dual-mode power balance still face the risk of mode switching due to optical feedback. Therefore, existing frequency-stabilized dual-mode helium-neon lasers cannot fully meet the requirements of wavelet aberration interferometers. Summary of the Invention

[0010] The purpose of this invention is to propose a laser frequency stabilization device and its debugging method based on polarization mode control. This invention solves the problem that the contrast of interference field fringes of ordinary dual-longitudinal-mode helium-neon lasers decreases due to frequency drift and optical path difference changes within the coherence length measurement range. It achieves frequency stabilization control of the laser and also realizes high-efficiency polarization-maintaining fiber coupling of free-space linearly polarized lasers.

[0011] The technical solution adopted in this invention is: a laser frequency stabilization device based on polarization mode control, comprising a laser power supply, a dual longitudinal mode helium-neon laser, a temperature control module, an optical path adjustment module, an optical fiber coupling module, a wiring module, and a signal processing module.

[0012] The temperature control module includes a heating wire, thermally conductive adhesive, and a heat-conducting tube.

[0013] The optical path adjustment module includes a first laser limiting ring, a second laser limiting ring, an adjustable adapter, a first connecting tube, a clamping body, and a polarizing beam splitter.

[0014] The fiber optic coupling module includes a coupler adapter, a fiber optic collimator, and a collimator adjustment bracket.

[0015] The wiring module includes a second connector and an end cap.

[0016] The signal processing module includes a temperature sensor, a temperature control circuit, a photodetector, a photoelectric conversion circuit, and a microprocessor.

[0017] The positive and negative terminals of the laser power supply are connected to the anode tungsten rod and cathode tungsten rod of the dual-longitudinal-mode helium-neon laser respectively via power lines, thereby supplying power to the dual-longitudinal-mode helium-neon laser.

[0018] The dual-longitudinal-mode helium-neon laser is housed inside a heat pipe, and the dual-longitudinal-mode helium-neon laser and the heat pipe are bonded together with thermally conductive adhesive. The heating wire is coiled around the surface of the gain tube of the dual-longitudinal-mode helium-neon laser.

[0019] The first laser limiting ring and the second laser limiting ring are embedded at both ends of the heat pipe. The second end face of the first laser limiting ring is flush with the cathode end face of the gain tube of the dual-longitudinal-mode helium-neon laser, and the first end face of the second limiting ring is flush with the anode end face of the gain tube of the dual-longitudinal-mode helium-neon laser. The first end of the adjustable adapter is internally connected to the first laser limiting ring, one end of the first connecting tube is externally connected to the second end of the adjustable adapter, and the second end of the first connecting tube is internally connected to a clamping body, which contains a polarizing beam splitter prism.

[0020] The first end of the coupler adapter is connected to the clamp body, and the second end is connected to the collimator adjustment frame. The gold-plated tube of the fiber optic collimator is fixed on the gold-plated tube clamp of the collimator adjustment frame, and the pigtail of the fiber optic collimator with the fiber output head is placed in free space.

[0021] The first end of the second connecting pipe is connected to the end cap, and the second end is externally connected to the limiting ring of the second laser tube.

[0022] The temperature sensor is fixed on the surface of the gain tube of the cathode section of the dual-longitudinal-mode helium-neon laser. The temperature sensor is connected to the temperature control circuit. The photodetector is fixed on the side of the clamp body, with its photosensitive surface facing the laser beam propagating along the reflected light path of the polarizing beam splitter.

[0023] The microprocessor is connected to the temperature control circuit and the photoelectric conversion circuit, respectively, and the photodetector is connected to the photoelectric conversion circuit.

[0024] Furthermore, the end cover of the laser frequency stabilization device is provided with a power cord retainer and a gland for wiring the power cord and conductors.

[0025] Furthermore, the temperature sensor is used to acquire the temperature of the gain tube of the dual-longitudinal-mode helium-neon laser. The acquired temperature analog signal is processed by the temperature control circuit and converted into a temperature electrical signal, which is then transmitted to the microprocessor. The photodetector is used to acquire the reference light intensity analog signal propagating along the reflected light path of the polarization beam splitter. The reference light intensity analog signal is processed by the photoelectric conversion circuit and converted into a reference light intensity electrical signal, which is then transmitted to the microprocessor. The microprocessor adjusts the operating parameters of the temperature control circuit based on the temperature electrical signal and the reference light intensity electrical signal, thereby changing the current flowing through the heating wire, modulating the cavity length of the dual-longitudinal-mode helium-neon laser, and thus outputting a frequency-stabilized laser.

[0026] The debugging method of a laser frequency stabilization device based on polarization mode control according to the present invention comprises the following steps:

[0027] Step 1: Coil the heating wire around the surface of the gain tube of the dual-mode helium-neon laser. Attach the temperature sensor to the cathode section of the gain tube. Place all three components into the heat pipe. Install the first and second laser limiting rings to define the position of the dual-mode helium-neon laser. Pour thermally conductive adhesive between the dual-mode helium-neon laser and the heat pipe. Connect the temperature control circuit to the temperature sensor and the microprocessor respectively. Improve the uniformity of the temperature field of the dual-mode helium-neon laser by adjusting the operating parameters of the temperature control circuit. Once the temperature field of the dual-mode helium-neon laser is uniform, proceed to Step 2.

[0028] Step 2: Assemble the adjustable adapter, first connecting tube, clamp body, polarizing beam splitter, and photodetector in sequence. Connect the photoelectric conversion circuit to the photodetector and microprocessor respectively. Guide the test light propagating from the dual-longitudinal-mode helium-neon laser along the transmission path of the polarizing beam splitter to the external Fabry-Perot scanning interferometer. The Fabry-Perot interferometer is connected to an oscilloscope via a data cable. Adjust the orientation of the polarizing beam splitter according to the waveform displayed on the oscilloscope to decompose the laser's longitudinal modes. Receive the reference light intensity analog signal propagating along the reflected light path of the polarizing beam splitter through the photodetector. After processing by the photoelectric conversion circuit, the reference light intensity analog signal is converted into a reference light intensity electrical signal and transmitted to the microprocessor. The microprocessor controls the temperature control circuit according to the reference light intensity electrical signal to stabilize the test light frequency of the dual-longitudinal-mode helium-neon laser near the center frequency. After the longitudinal modes of the dual-longitudinal-mode helium-neon laser are completely decomposed and the laser frequency is stable, proceed to Step 3.

[0029] Step 3: Construct the optical path for calibrating the polarization direction of the test light in the order of the frequency-stabilized dual-longitudinal-mode helium-neon laser to be coupled, the polarizer, and the power meter. After calibration, construct the optical path for adjusting the polarization attitude of the polarization-maintaining fiber in the fiber collimator in the order of the auxiliary light source, fiber collimator, collimator adjustment frame, calibrated polarizer, and power meter. Align the fast / slow axis of the polarization-maintaining fiber in the fiber collimator precisely with the polarization direction of the free-space test light by rotating the gold-plated tube clamp on the collimator adjustment frame. Connect the output head of the fiber collimator pigtail to the power meter. Adjust the attitude of the fiber collimator by adjusting the collimator adjustment frame to ensure that the free-space laser coupled into the fiber collimator has the highest fiber output power. Proceed to Step 4.

[0030] Step 4: Construct an optical path for testing the stability of the laser output frequency using a fiber-coupled frequency-stabilized dual-mode helium-neon laser, a wavelength meter, and a computer. The fiber optic output light from the frequency-stabilized dual-mode helium-neon laser is fed into the wavelength meter, which is connected to the computer via a data cable. After the frequency-stabilized dual-mode helium-neon laser has warmed up, turn on the wavelength meter and record the frequency drift curve of the output light in real time on the computer.

[0031] Compared with existing frequency stabilization methods for dual-longitudinal-mode helium-neon lasers, this invention has the following characteristics and advantages:

[0032] (1) Based on the Fabry-Perot scanning interferometer, oscilloscope and polarization beam splitter, the present invention splits the orthogonally polarized dual longitudinal mode laser light into two linearly polarized single longitudinal mode laser beams, which solves the problem of frequency aliasing between reference light and test light. The polarization beam splitter also ensures the maximum power output of the test light during the attitude adjustment process.

[0033] (2) The present invention can automatically compensate for frequency drift caused by environmental disturbances by adjusting the thermal balance temperature of the laser, thereby improving the robustness of the frequency stabilized laser.

[0034] (3) This invention locks the frequency of the test light at the center frequency of the laser gain curve, so the test light power of this laser can reach more than 1.5 times that of a conventional power-balanced dual-longitudinal-mode helium-neon laser. In addition, the frequency (power) reference point selected by this invention effectively avoids the multiple mode polarization jump positions caused by optical feedback, especially when the laser cavity mirror stress birefringence is large, thus ensuring the stability of the test light.

[0035] (4) The collimator adjustment frame without axial adjustment used in this invention can achieve high-efficiency coupling through only four-dimensional adjustment of vertical translation, horizontal translation, pitch, and yaw. Moreover, the slight axial displacement of the fiber collimator during the adjustment process will not cause changes in coupling efficiency, which greatly simplifies the complexity of the adjustment mechanism and the difficulty of coupler adjustment. The rotation dimension used for laser linear polarization adjustment is decoupled from other dimensions, which improves the robustness of the system. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a laser frequency stabilization device based on polarization mode control.

[0037] Figure 2 This is a schematic diagram illustrating the working principle of a laser frequency stabilization device based on polarization mode control.

[0038] Figure 3 This is a temperature distribution diagram of a dual-longitudinal-mode helium-neon laser tube.

[0039] Figure 4 The diagram shows the polarization state changes of the laser dual longitudinal modes as the cavity length is tuned during optical feedback. Figures (a) to (c) show the changes in the longitudinal modes during the shortening of the laser cavity length, while figures (d) to (f) show the changes in the longitudinal modes during the lengthening of the laser cavity.

[0040] Figure 5 A schematic diagram of the optical path for adjusting the orientation of a polarizing beam splitter.

[0041] Figure 6a A schematic diagram of the optical path for calibrating the polarization direction of a dual-longitudinal-mode helium-neon laser.

[0042] Figure 6b A schematic diagram of the optical path for adjusting the polarization-maintaining fiber attitude of the fiber collimator.

[0043] Figure 6c This is a schematic diagram of the optical path for high-efficiency coupling of free-space lasers using an optical fiber collimator.

[0044] Figure 7 A schematic diagram of the optical path for testing the frequency stability of the fiber output light of a frequency-stabilized dual-longitudinal-mode helium-neon laser.

[0045] Figure 8 This is the frequency drift curve of a frequency-stabilized laser based on polarization mode control. Detailed Implementation

[0046] Combination Figure 1 , Figure 2 and Figure 3 A laser frequency stabilization device based on polarization mode control includes a laser power supply 1, a dual longitudinal mode helium-neon laser 2, a temperature control module, an optical path adjustment module, an optical fiber coupling module, a wiring module, and a signal processing module.

[0047] The temperature control module includes a heating wire 3, thermally conductive adhesive 4, and a heat-conducting tube 5.

[0048] The optical path adjustment module includes a first laser limiting ring 6, a second laser limiting ring 7, an adjustable adapter 8, a first connecting tube 9, a clamping body 10, and a polarizing beam splitter 11.

[0049] The fiber optic coupling module includes a coupler adapter 12, a fiber optic collimator 13, and a collimator adjustment bracket 14.

[0050] The wiring module includes a second connector tube 15 and an end cap 16.

[0051] The signal processing module includes a temperature sensor 17, a temperature control circuit 18, a photodetector 19, a photoelectric conversion circuit 20, and a microprocessor 21.

[0052] The positive and negative terminals of the laser power supply 1 are connected to the anode tungsten rod and cathode tungsten rod of the dual-longitudinal-mode helium-neon laser 2 respectively via power lines, thereby supplying power to the dual-longitudinal-mode helium-neon laser 2.

[0053] The dual-longitudinal-mode helium-neon laser 2 is disposed inside the heat pipe 5, and the dual-longitudinal-mode helium-neon laser 2 and the heat pipe 5 are bonded together by thermally conductive adhesive 4, and the heating wire 3 is coiled on the surface of the gain tube of the dual-longitudinal-mode helium-neon laser 2.

[0054] The first laser limiting ring 6 and the second laser limiting ring 7 are embedded at both ends of the heat pipe 5. The second end face of the first laser limiting ring 6 is flush with the cathode end face of the gain tube of the dual-longitudinal-mode helium-neon laser 2, and the first end face of the second limiting ring 7 is flush with the anode end face of the gain tube of the dual-longitudinal-mode helium-neon laser 2. The first end of the adjustable adapter 8 is internally connected to the first laser limiting ring 6, and one end of the first connecting tube 9 is externally connected to the second end of the adjustable adapter 8. The second end of the first connecting tube 9 is internally connected to the clamp body 10, and the clamp body 10 contains a polarizing beam splitter prism 11.

[0055] The first end of the coupler adapter 12 is connected to the clamp body 10, and the second end is connected to the collimator adjustment frame 14. The gold-plated tube of the fiber optic collimator 13 is fixed on the gold-plated tube clamp of the collimator adjustment frame 14, and the pigtail of the fiber optic collimator 13 with the fiber optic output head is placed in free space.

[0056] The first end of the second connecting pipe 15 is connected to the end cap 16, and the second end is externally connected to the second laser tube limiting ring 7.

[0057] The temperature sensor 17 is fixed on the surface of the gain tube of the cathode section of the dual longitudinal mode helium-neon laser 2. The temperature sensor 17 is connected to the temperature control circuit 18. The photodetector 19 is fixed on the side of the clamp 10, and its photosensitive surface faces the laser beam propagating along the reflected light path of the polarizing beam splitter 11.

[0058] The microprocessor 21 is connected to the temperature control circuit 18 and the photoelectric conversion circuit 20 respectively, and the photodetector 19 is connected to the photoelectric conversion circuit 20.

[0059] The end cap 16 is equipped with a power cord retainer and a gland for wiring power cords and conductors.

[0060] The temperature sensor 17 is used to acquire the temperature of the gain tube of the dual-longitudinal-mode helium-neon laser 2. The acquired analog temperature signal is processed by the temperature control circuit 18 and converted into an electrical temperature signal, which is then transmitted to the microprocessor 21. The photodetector 19 is used to acquire the analog reference light intensity signal propagating along the reflected light path of the polarizing beam splitter 11. The analog reference light intensity signal is processed by the photoelectric conversion circuit 20 and converted into an electrical reference light intensity signal, which is then transmitted to the microprocessor 21. Based on the electrical temperature signal and the electrical reference light intensity signal, the microprocessor 21 adjusts the operating parameters of the temperature control circuit 18, thereby changing the current flowing through the heating wire 3, modulating the cavity length of the dual-longitudinal-mode helium-neon laser 2, and thus outputting a frequency-stabilized laser.

[0061] A debugging method for a laser frequency stabilization device based on polarization mode control, comprising the following steps:

[0062] Step 1: Coil the heating wire 3 around the surface of the gain tube of the dual-mode helium-neon laser 2. Attach the temperature sensor 17 to the cathode section of the gain tube of the dual-mode helium-neon laser 2. Place all three together into the heat pipe 5. Install the first laser limiting ring 6 and the second laser limiting ring 7 to limit the position of the dual-mode helium-neon laser 2. Pour thermally conductive adhesive 4 between the dual-mode helium-neon laser 2 and the heat pipe 5. Connect the temperature control circuit 18 to the temperature sensor 17 and the microprocessor 21 respectively. Improve the uniformity of the temperature field of the dual-mode helium-neon laser 2 by adjusting the operating parameters of the temperature control circuit 18.

[0063] The surface temperature distribution of the gain tube in the dual-longitudinal-mode helium-neon laser 2 is uneven, specifically: the temperature in the middle section of the gain tube is higher than that in the anode section, and the temperature in the anode section is higher than that in the cathode section. In step 1, the uniformity of the laser temperature field can be improved by adjusting the winding density of the heating wire 3, using high thermal conductivity devices, and optimizing the operating parameters of the temperature control circuit 18. The specific adjustment method is as follows:

[0064] Step 1-1: Using the double-winding method, the heating wire 3 is wound obliquely from the cathode section to the anode section of the gain tube of the dual longitudinal mode helium-neon laser 2, so that the coil arrangement density of the heating wire 3 in the cathode section is greater than that at the anode end, and the arrangement density in the middle section is less than that at the anode end. At the same time, the temperature sensor 17 is fixed in the cathode section of the gain tube where the temperature change is most balanced.

[0065] Steps 1-2: The pose of the dual-longitudinal-mode helium-neon laser 2 is defined by the first laser limiting ring 6 and the second laser limiting ring 7, so that the optical axis of the dual-longitudinal-mode helium-neon laser 2 is aligned with the tube axis of the heat pipe 5.

[0066] Steps 1-3: Fill the space between the heat pipe 5 and the dual longitudinal mode helium-neon laser 2 with thermally conductive adhesive 4;

[0067] Steps 1-4: After the thermally conductive adhesive 4 has fully cured, the temperature control circuit 18 is connected to the temperature sensor 17 and the microprocessor 21 respectively. The microprocessor 21 sets and adjusts the operating parameters of the temperature control circuit 18 to minimize the preheating time of the cold-start dual longitudinal mode helium-neon laser 2 and maximize the temperature control accuracy.

[0068] Once the temperature field of the dual-longitudinal-mode helium-neon laser 2 is uniform, proceed to step 2.

[0069] Combination Figure 4 and Figure 5Due to frequency drift and changes in optical path difference, the interference field fringes of the dual-longitudinal-mode helium-neon laser 2 may be submerged in the background light, causing the wavefront aberration interferometer to malfunction. A polarization beam splitter 11 is often used to achieve single-longitudinal-mode laser output from the dual-longitudinal-mode helium-neon laser 2. However, the feedback light reflected from the crystal surface alters the anisotropy of the laser's optical resonant cavity, intensifying competition between longitudinal modes and causing polarization state reversal. Specifically, when the laser longitudinal mode is tuned to a specific position with the cavity length, the polarization element selects the longitudinal mode that moves towards the center frequency of the laser gain curve as the "dominant mode" and flips its polarization direction by 90°. The longitudinal mode farther from the center of the gain curve is designated as the "disadvantageous mode," and its polarization direction also flips by 90°. Figure 4 Figures (a) to (c) in the figure show the changes in the longitudinal mode during the shortening of the laser cavity length. Figure 4 Figures (d) to (f) illustrate the changes in longitudinal modes during laser cavity length elongation. Polarization transitions in the longitudinal modes also affect the normal operation of the wavelet aberration interferometer. Generally, power-balanced frequency-stabilized dual-longitudinal-mode helium-neon lasers also face the risk of polarization transitions when their cavity mirror stress birefringence is high, and these lasers cannot output maximum power for the test light.

[0070] Step 2: Assemble the adjustable adapter 8, first connecting tube 9, clamp body 10, polarizing beam splitter 11, and photodetector 19 in sequence. The photoelectric conversion circuit 20 is connected to the photodetector 19 and the microprocessor 21 respectively. The test light propagating along the transmission path of the dual-longitudinal-mode helium-neon laser 2 along the polarizing beam splitter 11 is guided into the external Fabry-Perot scanning interferometer 22. The Fabry-Perot scanning interferometer 22 and the oscilloscope 23 are connected via a data cable. Adjust the orientation of the polarizing beam splitter 11 according to the waveform displayed on the oscilloscope 23 to decompose the laser longitudinal mode. The photodetector 19 receives the reference light intensity analog signal propagating along the reflected light path of the polarizing beam splitter 11. After being processed by the photoelectric conversion circuit 20, the reference light intensity analog signal is converted into a reference light intensity electrical signal and transmitted to the microprocessor 21. The microprocessor 21 controls the temperature control circuit 18 according to the reference light intensity electrical signal to stabilize the test light frequency of the dual-longitudinal-mode helium-neon laser 2 near the center frequency.

[0071] Specifically, the output light of the dual-longitudinal-mode helium-neon laser 2 is split into two orthogonal polarization directions and single-mode operation test light and reference light using a polarization beam splitter 11. Based on the power magnitude and variation trend of the reference light, the operating frequency of the test light is locked near the center frequency that is far from the polarization jump point and has the maximum gain. The specific debugging method is as follows:

[0072] Step 2-1: Assemble the adjustable adapter 8, the first connecting tube 9, the clamp body 10, the polarizing beam splitter 11, and the photodetector 19 in sequence. The photoelectric conversion circuit 20 is connected to the photodetector 19 and the microprocessor 21 respectively.

[0073] Step 2-2: The dual-longitudinal-mode helium-neon laser 2 outputs orthogonally polarized dual-longitudinal-mode laser light. The test light propagating along the transmission path of the polarization beam splitter 11 from the dual-longitudinal-mode helium-neon laser 2 is guided into the external Fabry-Perot scanning interferometer 22. The Fabry-Perot scanning interferometer 22 generates an interference signal reflecting the longitudinal mode operation status, which is transmitted to the oscilloscope 23 via a data line and displayed in real time. According to the waveform displayed on the oscilloscope 23, the adjustable adapter 8 is rotated to adjust the orientation of the polarization beam splitter 11. The adjustable adapter 8 is fixed at the position where the test light operates in single-longitudinal-mode mode and outputs maximum power.

[0074] Steps 2-3: The photodetector 19 receives the reference light intensity analog signal propagating along the reflected light path of the polarization beam splitter 11. After being processed by the photoelectric conversion circuit 20, the reference light intensity analog signal is converted into a reference light intensity electrical signal and transmitted to the microprocessor 21. The microprocessor 21 controls the temperature control circuit 18 according to the reference light intensity electrical signal to adjust the thermal equilibrium temperature of the dual-longitudinal-mode helium-neon laser 2, so that the test light frequency of the dual-longitudinal-mode helium-neon laser 2 is stabilized near the center frequency far from the polarization jump point.

[0075] After the second longitudinal mode of the dual-longitudinal-mode helium-neon laser is completely decomposed and the laser frequency is stable, proceed to step 3.

[0076] Step 3: Construct the optical path for calibrating the polarization direction of the test light in the order of the frequency-stabilized dual-longitudinal-mode helium-neon laser 2 to be coupled, polarizer 24, and power meter 25. After calibration, construct the optical path for adjusting the polarization attitude of the polarization-maintaining fiber in the fiber collimator 13 in the order of auxiliary light source 26, polarization-maintaining flange 27, fiber collimator 13, collimator adjustment frame 14, polarizer 24 with calibrated direction, and power meter 25. Rotate the gold-plated tube clamp on the collimator adjustment frame 14 to precisely align the fast axis / slow axis of the polarization-maintaining fiber in the fiber collimator 13 with the polarization direction of the free-space test light. Connect the output head of the pigtail of the fiber collimator 13 to the power meter 25. Adjust the attitude of the fiber collimator 13 by adjusting the collimator adjustment frame 14 so that the free-space laser coupled into the fiber collimator 13 has the highest fiber output power.

[0077] Combination Figure 6a , Figure 6b , Figure 6c The collimator adjustment frame 14, which eliminates the need for axial adjustment, is used to adjust the fiber collimator 13 with a single-mode polarization-maintaining pigtail. This can meet the requirements of high polarization degree and high coupling efficiency when free-space linearly polarized laser is coupled to the fiber for output. The specific adjustment method is as follows:

[0078] Step 3-1: Construct the optical path for calibrating the polarization direction of the test light in the order of the frequency-stabilized dual-longitudinal-mode helium-neon laser 2 to be coupled, polarizer 24, and power meter 25. Rotate polarizer 24 until the power meter 25 reads the maximum. At this time, the transmission axis of polarizer 24 is consistent with the polarization direction of the test light. Fix polarizer 24 to complete the calibration of the polarization direction of the test light.

[0079] Step 3-2: Construct the optical path for adjusting the polarization attitude of the polarization-maintaining fiber in the following order: auxiliary light source 26, polarization-maintaining flange 27, fiber collimator 13, collimator adjustment frame 14, polarizer 24 with calibrated direction, and power meter 25. The auxiliary light source 26 is a frequency-stabilized linear polarization light source output from the fiber. The auxiliary light source 26 and the fiber collimator 13 are connected through the polarization-maintaining flange 27.

[0080] Step 3-3: Start the auxiliary light source 26, rotate the gold-plated tube clamp of the collimator adjustment frame 14 until the power meter 25 reads the maximum value. At this time, the fast axis / slow axis of the polarization-maintaining fiber of the fiber collimator 13 is precisely aligned with the polarization direction of the test light in free space. While keeping the power meter 25 reading at its maximum, fix the gold-plated tube clamp of the collimator adjustment frame 14.

[0081] Steps 3-4: Connect the output head of the fiber collimator 13 pigtail to the power meter 25. Adjust the attitude of the fiber collimator 13 in four directions (up / down, left / right, pitch, and yaw) using the collimator adjustment bracket 14 so that the free space laser coupled into the fiber collimator 13 has the highest fiber output power.

[0082] After the fiber coupling output of the frequency-stabilized dual-longitudinal-mode helium-neon laser is completed, proceed to step 4.

[0083] Step 4: Construct an optical path for testing the stability of the laser output frequency using a fiber-coupled frequency-stabilized dual-mode helium-neon laser 2, a wavelength meter 28, and a computer 29. The fiber output light from the frequency-stabilized dual-mode helium-neon laser 2 is fed into the wavelength meter, and the wavelength meter 28 is connected to the computer 29 via a data cable.

[0084] Combination Figure 7 , Figure 8 The specific method for observing the frequency change of the output light of the frequency-stabilized dual-longitudinal-mode helium-neon laser 2 using a wavelength meter 28 is as follows:

[0085] Step 4-1: Construct the optical path for testing the stability of the laser output frequency in the order of fiber-coupled frequency-stabilized dual-longitudinal-mode helium-neon laser 2, wavelength meter 28, and computer 29. The output head of the fiber collimator 13 is connected to the flange head on the wavelength meter 28, so that the fiber output light enters the wavelength meter 28. The wavelength meter 28 is connected to the computer 29 via a data cable. The computer 29 can record the frequency changes of the fiber output light in real time through the host computer software that comes with the wavelength meter 28.

[0086] Step 4-2: Turn on the power to the frequency-stabilized dual-mode helium-neon laser 2, wavelength meter 28, and computer 29. After the frequency-stabilized dual-mode helium-neon laser 2 has finished warming up, open the host computer software of wavelength meter 28 on computer 29 to record the frequency change of the output light of dual-mode helium-neon laser 2.

Claims

1. A laser frequency stabilization device based on polarization mode control, characterized in that: It includes a laser power supply (1), a dual longitudinal mode helium-neon laser (2), a temperature control module, an optical path adjustment module, an optical fiber coupling module, a wiring module, and a signal processing module; The temperature control module includes a heating wire (3), thermal adhesive (4), and a heat pipe (5); The optical path adjustment module includes a first laser limiting ring (6), a second laser limiting ring (7), an adjustable adapter (8), a first connecting tube (9), a clamp body (10), and a polarizing beam splitter (11). The fiber optic coupling module includes a coupler adapter (12), a fiber optic collimator (13), and a collimator adjustment bracket (14). The wiring module includes a second connector (15) and an end cap (16). The signal processing module includes a temperature sensor (17), a temperature control circuit (18), a photodetector (19), a photoelectric conversion circuit (20), and a microprocessor (21). The positive and negative terminals of the laser power supply (1) are connected to the anode tungsten rod and cathode tungsten rod of the dual longitudinal mode helium-neon laser (2) respectively through power lines, so as to supply power to the dual longitudinal mode helium-neon laser (2). The dual-mode helium-neon laser (2) is set inside the heat pipe (5). The dual-mode helium-neon laser (2) and the heat pipe (5) are bonded together by thermal adhesive (4). The heating wire (3) is coiled around the surface of the gain tube of the dual-mode helium-neon laser (2). The first laser limiting ring (6) and the second laser limiting ring (7) are embedded in the two ends of the heat pipe (5). The second end face of the first laser limiting ring (6) is flush with the cathode end face of the gain tube of the dual longitudinal mode helium-neon laser (2), and the first end face of the second laser limiting ring (7) is flush with the anode end face of the gain tube of the dual longitudinal mode helium-neon laser (2). The first end of the adjustable adapter (8) is connected to the first laser limiting ring (6), and one end of the first connecting tube (9) is connected to the second end of the adjustable adapter (8). The second end of the first connecting tube (9) is connected to the clamp body (10), and the clamp body (10) is equipped with a polarizing beam splitter (11). The first end of the coupler adapter (12) is connected to the clamp (10), and the second end is connected to the collimator adjustment frame (14); the gold-plated tube of the fiber collimator (13) is fixed on the gold-plated tube clamp of the collimator adjustment frame (14), and the pigtail of the fiber collimator (13) with the fiber output head is placed in free space. The first end of the second connecting tube (15) is connected to the end cap (16), and the second end is externally connected to the second laser limiting ring (7); The temperature sensor (17) is fixed on the surface of the gain tube of the cathode section of the dual longitudinal mode helium-neon laser (2). The temperature sensor (17) is connected to the temperature control circuit (18). The photodetector (19) is fixed on the side of the fixture (10), and its photosensitive surface faces the laser beam propagating along the reflected light path of the polarizing beam splitter (11). The microprocessor (21) is connected to the temperature control circuit (18) and the photoelectric conversion circuit (20) respectively, and the photodetector (19) is connected to the photoelectric conversion circuit (20).

2. The laser frequency stabilization device based on polarization mode control according to claim 1, characterized in that: The end cap (16) is provided with a power cord retainer and a gland for wiring power cords and conductors.

3. The laser frequency stabilization device based on polarization mode control according to claim 1, characterized in that: The temperature sensor (17) is used to collect the gain tube temperature of the dual longitudinal mode helium-neon laser (2). The collected temperature analog signal is processed by the temperature control circuit (18) and converted into a temperature electrical signal and transmitted to the microprocessor (21). The photodetector (19) is used to collect the reference light intensity analog signal propagating along the reflected light path of the polarization beam splitter (11). The reference light intensity analog signal is processed by the photoelectric conversion circuit (20) and converted into a reference light intensity electrical signal and transmitted to the microprocessor (21). The microprocessor (21) adjusts the operating parameters of the temperature control circuit (18) based on the temperature electrical signal and the reference light intensity electrical signal, thereby changing the current flowing through the heating wire (3) and modulating the cavity length of the dual longitudinal mode helium-neon laser (2) to output a frequency-stabilized laser.

4. A debugging method for a laser frequency stabilization device based on polarization mode control as described in claim 1, characterized in that, The steps are as follows: Step 1: Coil the heating wire (3) around the surface of the gain tube of the dual-longitudinal-mode helium-neon laser (2), attach the temperature sensor (17) to the cathode section of the gain tube of the dual-longitudinal-mode helium-neon laser (2), and put all three into the heat pipe (5). Install the first laser limiting ring (6) and the second laser limiting ring (7) to limit the position of the dual-longitudinal-mode helium-neon laser (2). Pour thermally conductive adhesive (4) between the dual-longitudinal-mode helium-neon laser (2) and the heat pipe (5). Connect the temperature control circuit (18) to the temperature sensor (17) and the microprocessor (21) respectively. Improve the uniformity of the temperature field of the dual-longitudinal-mode helium-neon laser (2) by adjusting the working parameters of the temperature control circuit (18). After the temperature field of the dual-longitudinal-mode helium-neon laser (2) is uniform, proceed to step 2. Step 2: Assemble the adjustable adapter (8), first connector (9), clamp (10), polarizing beam splitter (11), and photodetector (19) in sequence. Connect the photoelectric conversion circuit (20) to the photodetector (19) and the microprocessor (21) respectively. Guide the test light propagating from the dual longitudinal mode helium-neon laser (2) along the transmission path of the polarizing beam splitter (11) into the external Fabry-Perot scanning interferometer (22). Connect the Fabry-Perot scanning interferometer (22) and the oscilloscope (23) through a data cable. Adjust the polarization beam splitter according to the waveform displayed on the oscilloscope (23). The orientation of the optical prism (11) is used to decompose the longitudinal mode of the laser; the reference light intensity analog signal propagating along the reflected light path of the polarization beam splitter (11) is received by the photodetector (19). After the reference light intensity analog signal is processed by the photoelectric conversion circuit (20), it is converted into a reference light intensity electrical signal and transmitted to the microprocessor (21). The microprocessor (21) controls the temperature control circuit (18) according to the reference light intensity electrical signal to stabilize the test light frequency of the dual longitudinal mode helium-neon laser (2) near the center frequency; when the longitudinal mode of the dual longitudinal mode helium-neon laser (2) is completely decomposed and the laser frequency is stable, the process proceeds to step 3. Step 3: Construct an optical path for calibrating the polarization direction of the test light in the order of the frequency-stabilized dual-longitudinal-mode helium-neon laser (2), polarizer (24), and power meter (25). After calibration, construct an optical path for adjusting the polarization attitude of the polarization-maintaining fiber of the fiber collimator (13) in the order of auxiliary light source (26), polarization-maintaining flange (27), fiber collimator (13), collimator adjustment frame (14), polarizer (24) with calibrated direction, and power meter (25). By rotating the gold-plated tube clamp on the collimator adjustment frame (14), the fast axis / slow axis of the polarization-maintaining fiber in the fiber collimator (13) is precisely aligned with the polarization direction of the free space test light. Connect the output head of the fiber collimator (13) pigtail to the power meter (25). Adjust the attitude of the fiber collimator (13) by adjusting the collimator adjustment frame (14) so ​​that the free space laser coupled into the fiber collimator (13) has the highest fiber output power. Proceed to step 4. Step 4: Build an optical path for testing the stability of the laser output frequency using a fiber-coupled frequency-stabilized dual-mode helium-neon laser (2), a wavelength meter (28), and a computer (29). The fiber output light of the frequency-stabilized dual-mode helium-neon laser (2) is fed into the wavelength meter (28), and the wavelength meter (28) is connected to the computer (29) via a data cable. After the frequency-stabilized dual-mode helium-neon laser (2) has finished warming up, turn on the wavelength meter (28) and record the frequency change of the output light in real time on the computer (29).

5. The debugging method for the laser frequency stabilization device based on polarization mode control according to claim 4, characterized in that, In step 1, after the heating wire (3) is coiled around the surface of the gain tube of the dual-longitudinal-mode helium-neon laser (2), the temperature sensor (17) is attached to the cathode section of the gain tube of the dual-longitudinal-mode helium-neon laser (2), and the three are installed together in the heat pipe (5). The first laser limiting ring (6) and the second laser limiting ring (7) are installed to limit the position of the dual-longitudinal-mode helium-neon laser (2). Thermal adhesive (4) is poured between the dual-longitudinal-mode helium-neon laser (2) and the heat pipe (5). The temperature control circuit (18) is connected to the temperature sensor (17) and the microprocessor (21) respectively. The uniformity of the temperature field of the dual-longitudinal-mode helium-neon laser (2) is improved by adjusting the operating parameters of the temperature control circuit (18), as follows: Step 1-1: Using the double-winding method, the heating wire (3) is wound obliquely from the cathode section to the anode section of the gain tube of the dual longitudinal mode helium-neon laser (2), so that the coil arrangement density of the heating wire in the cathode section is greater than that at the anode end, and the arrangement density in the middle section is less than that at the anode end. At the same time, the temperature sensor (17) is fixed in the cathode section of the gain tube where the temperature change is most balanced. Steps 1-2: The pose of the dual-longitudinal-mode helium-neon laser (2) is defined by the first laser limiting ring (6) and the second laser limiting ring (7), so that the optical axis of the dual-longitudinal-mode helium-neon laser (2) is aligned with the tube axis of the heat pipe (5); Steps 1-3: Fill the space between the heat pipe (5) and the dual longitudinal mode helium-neon laser (2) with thermally conductive adhesive (4). Steps 1-4: After the thermally conductive adhesive (4) has completely cured, the temperature control circuit (18) is connected to the temperature sensor (17) and the microprocessor (21) respectively. The microprocessor (21) sets and adjusts the working parameters of the temperature control circuit (18) so that the preheating time of the cold-start dual longitudinal mode helium-neon laser (2) is minimized and the temperature control accuracy reaches the highest level.

6. The debugging method of the laser frequency stabilization device based on polarization mode control according to claim 5, characterized in that, In step 2, the adjustable adapter (8), the first connecting tube (9), the clamp (10), the polarizing beam splitter (11), and the photodetector (19) are assembled sequentially. The photoelectric conversion circuit (20) is connected to the photodetector (19) and the microprocessor (21) respectively. The test light propagating along the transmission path of the dual longitudinal mode helium-neon laser (2) along the polarizing beam splitter (11) is introduced into the external Fabry-Perot scanning interferometer (22). The Fabry-Perot scanning interferometer (22) and the oscilloscope (23) are connected through a data cable. According to the oscilloscope... (23) The waveform displayed adjusts the orientation of the polarization beam splitter (11) to decompose the laser longitudinal mode; the reference light intensity analog signal propagating along the reflected light path of the polarization beam splitter (11) is received by the photodetector (19). After the reference light intensity analog signal is processed by the photoelectric conversion circuit (20), it is converted into a reference light intensity electrical signal and transmitted to the microprocessor (21). The microprocessor (21) controls the temperature control circuit (18) according to the reference light intensity electrical signal to stabilize the output light frequency of the dual longitudinal mode helium-neon laser (2) near the center frequency, as follows: Step 2-1: Assemble the adjustable adapter (8), the first connecting tube (9), the clamp (10), the polarizing beam splitter (11), and the photodetector (19) in sequence. The photoelectric conversion circuit (20) is connected to the photodetector (19) and the microprocessor (21) respectively. Step 2-2: The dual-longitudinal-mode helium-neon laser (2) outputs orthogonally polarized dual-longitudinal-mode laser. The test light propagating from the dual-longitudinal-mode helium-neon laser (2) along the transmission path of the polarization beam splitter (11) is introduced into the external Fabry-Perot scanning interferometer (22). The Fabry-Perot scanning interferometer (22) generates an interference signal reflecting the longitudinal mode operation status, which is transmitted to the oscilloscope (23) via the data line and displayed in real time. The adjustable adapter (8) is rotated according to the waveform of the oscilloscope (23) to adjust the orientation of the polarization beam splitter (11). The adjustable adapter (8) is fixed at the position where the test light works in single-longitudinal-mode mode and outputs the maximum power. Steps 2-3: The reference light intensity analog signal propagating along the reflected light path of the polarization beam splitter (11) is received by the photodetector (19). After being processed by the photoelectric conversion circuit (20), the reference light intensity analog signal is converted into a reference light intensity electrical signal and transmitted to the microprocessor (21). The microprocessor (21) controls the temperature control circuit (18) according to the reference light intensity electrical signal to adjust the thermal equilibrium temperature of the dual longitudinal mode helium-neon laser (2) so that the test light frequency of the dual longitudinal mode helium-neon laser (2) is stabilized near the center frequency far from the polarization jump point.

7. The debugging method for the laser frequency stabilization device based on polarization mode control according to claim 6, characterized in that, The collimator adjustment frame (14) is an axial adjustment-free collimator adjustment frame. The collimator adjustment frame (14) is equipped with a gold-plated tube clamp for holding the fiber collimator (13). The collimator adjustment frame (14) can adjust the fiber collimator (13) in the up and down, left and right, pitch, yaw and axial rotation directions.

8. The debugging method of the laser frequency stabilization device based on polarization mode control according to claim 7, characterized in that, In step 3, the optical path for calibrating the polarization direction of the test light is constructed in the order of the frequency-stabilized dual-longitudinal-mode helium-neon laser (2), polarizer (24), and power meter (25). After calibration, the optical path for adjusting the polarization attitude of the polarization-maintaining fiber of the fiber collimator (13) is constructed in the order of auxiliary light source (26), polarization-maintaining flange (27), fiber collimator (13), collimator adjustment frame (14), polarizer (24) with calibrated direction, and power meter (25). The fast axis / slow axis of the polarization-maintaining fiber in the fiber collimator (13) is precisely aligned with the polarization direction of the free-space test light by adjusting the collimator adjustment frame (14). The output head of the fiber collimator (13) pigtail is connected to the power meter (25). The attitude of the fiber collimator (13) is adjusted by adjusting the collimator adjustment frame (14) so ​​that the free-space laser coupled into the fiber collimator (13) has the highest fiber output power, as follows: Step 3-1: Build the optical path for calibrating the polarization direction of the test light in the order of the frequency-stabilized dual-longitudinal-mode helium-neon laser (2), polarizer (24), and power meter (25). Rotate the polarizer (24) until the power meter (25) reads the maximum. At this time, the transmission axis of the polarizer (24) is consistent with the polarization direction of the test light. Fix the polarizer (24) to complete the calibration of the polarization direction of the test light. Step 3-2: Build the optical path for adjusting the polarization attitude of the polarization-maintaining fiber in the following order: auxiliary light source (26), polarization-maintaining flange (27), fiber collimator (13), collimator adjustment frame (14), polarizer (24) with calibrated direction, and power meter (25). The auxiliary light source (26) is the linear polarization light source output by the fiber. The auxiliary light source (26) and the fiber collimator (13) are connected through the polarization-maintaining flange (27). Step 3-3: Start the auxiliary light source (26), rotate the gold-plated tube clamp of the collimator adjustment frame (14) until the power meter (25) shows the maximum reading. At this time, the fast axis / slow axis of the polarization-maintaining fiber in the fiber collimator (13) is precisely aligned with the polarization direction of the test light in free space. While keeping the power meter (25) reading at its maximum, fix the gold-plated tube clamp of the collimator adjustment frame (14). Steps 3-4: Connect the output head of the fiber collimator (13) pigtail to the power meter (25). Adjust the attitude of the fiber collimator (13) in four directions (up and down, left and right, pitch and yaw) using the collimator adjustment frame (14) so ​​that the free space laser coupled into the fiber collimator (13) has the highest fiber output power.

9. The debugging method of the laser frequency stabilization device based on polarization mode control according to claim 8, characterized in that, In step 4, an optical path for testing the stability of the laser output frequency is constructed using a fiber-coupled frequency-stabilized dual-mode helium-neon laser (2), a wavelength meter (28), and a computer (29). The fiber output light from the frequency-stabilized dual-mode helium-neon laser (2) is fed into the wavelength meter (28), and the wavelength meter (28) is connected to the computer (29) via a data cable. After the frequency-stabilized dual-mode helium-neon laser (2) has finished warming up, the wavelength meter (28) is turned on, and the frequency change of the output light is recorded in real time on the computer (29), as follows: Step 4-1: Build an optical path for testing the stability of the laser output frequency in the order of fiber-coupled frequency-stabilized dual-longitudinal-mode helium-neon laser (2), wavelength meter (28), and computer (29). The output head of the fiber collimator (13) is connected to the flange on the wavelength meter (28) so that the fiber output light enters the wavelength meter (28). The wavelength meter (28) is connected to the computer (29) through a data cable. The computer (29) records the frequency change of the fiber output light in real time. Step 4-2: Turn on the power to the frequency-stabilized dual-mode helium-neon laser (2), wavelength meter (28), and computer (29). After the frequency-stabilized dual-mode helium-neon laser (2) has finished warming up, record the frequency change of the output light of the dual-mode helium-neon laser (2) on the computer (29).

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