Device and method for improving performance of NPRO self-feedback interferometer through magnetic field frequency stabilization

Abstract

The invention provides a device and method for improving the performance of an NPRO self-feedback interferometer through magnetic field frequency stabilization, and the device comprises a pumping diode which is used for generating pumping light, and a focusing lens, a spectroscope and a non-planar annular cavity crystal which are sequentially disposed on a light path of the pumping light. The non-planar annular cavity crystal generates stimulated radiation light in the clockwise direction and stimulated radiation light in the anticlockwise direction under the action of the permanent magnet; the stimulated radiation light in the clockwise direction is reflected to a detection target through the spectroscope, is reflected by the detection target, and is incident into the non-planar annular cavity crystal to generate a self-feedback frequency signal; the photoelectric detector is used for collecting a self-feedback frequency signal; and the PID controller is used for mixing the reference frequency signal and the self-feedback frequency signal to generate a correction signal and controlling the magnetic field intensity of the electromagnet so as to accurately adjust the self-feedback frequency. According to the invention, the technical problems of low measurement precision, poor anti-interference capability and difficulty in weak light detection of an NPRO self-feedback interferometer in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of self-feedback interferometer technology, specifically to a device and method for improving the performance of a NPRO (Non-Planar Ring Oscillator) self-feedback interferometer by magnetic field frequency stabilization. Background Technology

[0002] Interferometry is a core technology for precise physical quantity measurement based on the wavelength of light. Its history can be traced back to the pioneering work of Fiso and Michelson in the 19th century. Traditional interferometers, such as the Michelson interferometer, rely on splitting a beam of light, propagating it along different paths, and then recombining it to generate interference. While this heterodyne interferometry method offers high precision, it typically requires complex optical path layouts, strict alignment requirements, and stable reference arms, and is sensitive to environmental noise, limiting its application outside of laboratory environments. To address these issues, a technique that directly injects external feedback light into the laser, using the laser itself as an interference element—Self-Mixing Interferometry (SMI)—has emerged. Its core principle is that the feedback light reflected or scattered back into the laser cavity from an external target interacts with the inherent optical field inside the laser, thereby modulating the laser's output characteristics. This modulated signal then carries the motion information of the external target.

[0003] Based on different signal extraction methods, self-feedback interferometers have mainly developed into two categories: ordinary self-feedback interferometers and frequency-shifting self-feedback interferometers. Ordinary self-feedback interferometers directly detect changes in laser output intensity, resulting in the simplest system structure. However, their signals are easily drowned out by low-frequency noise in the environment, leading to low measurement sensitivity and signal-to-noise ratio. To overcome this bottleneck, frequency-shifting self-feedback interferometers were proposed. Their key technology involves introducing frequency-shifting elements such as acousto-optic modulators (AOMs) into the optical path to introduce a fixed frequency shift to the feedback light. In this way, the physical information to be measured is carried in a high-frequency beat frequency signal. By detecting the phase of this beat frequency signal, the measured information can be calculated, effectively avoiding the low-frequency noise region and significantly improving the measurement sensitivity and stability.

[0004] However, traditional frequency-shifting self-feedback interferometers typically require a separate AOM for frequency shifting and a beam splitter to separate the reference and measurement beams, resulting in complex system structures and reduced energy efficiency. Self-feedback interferometry based on special lasers such as non-planar ring cavities (NPROs) exhibits unique advantages. These lasers themselves can generate bidirectional output light propagating clockwise and counterclockwise under the influence of a magnetic field, naturally creating a frequency difference. Therefore, the "frequency shifting" function can be achieved without an external AOM, paving the way for the development of new self-feedback interferometers with more compact structures, higher stability, and suitability for harsh environments. However, due to mode competition in NPRO self-feedback interferometers and their extreme sensitivity to external magnetic field fluctuations, NPRO self-feedback frequency stability is low, and frequency noise is high at low frequencies, failing to meet the requirements for long-term and high-precision measurements.

[0005] There are three main technical problems in the related technologies:

[0006] 1. Problem of unstable beat frequency: Due to the mode competition inside the NPRO laser and its high sensitivity to external magnetic field fluctuations, the bidirectional output beat frequency of the laser fluctuates significantly. This makes it impossible to perform high-precision frequency and phase measurements, thus limiting the full potential of its core measurement capabilities.

[0007] 2. The system is susceptible to interference: One of the root causes of the unstable beat frequency is its sensitivity to magnetic field noise, which leads to poor reliability of the existing system in real-world environments and large drift in long-term measurement results.

[0008] 3. Insufficient weak signal detection capability: When measuring distant, non-cooperative targets, the feedback light signal is extremely weak. In the context of unstable beat frequency, these weak signals are submerged by noise and cannot be effectively extracted, which limits the performance of existing NPRO interferometers in key application scenarios such as remote sensing. Summary of the Invention

[0009] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a device and method for improving the performance of an NPRO self-feedback interferometer by stabilizing the magnetic field frequency, thereby solving the technical problems of low measurement accuracy, poor anti-interference ability, and difficulty in weak light detection in the existing NPRO self-feedback interferometer.

[0010] To achieve the above-mentioned technical objectives, in a first aspect, the present invention provides a device for improving the performance of an NPRO self-feedback interferometer by stabilizing the magnetic field frequency, characterized in that it comprises:

[0011] A pump diode is used to generate pump light; and a focusing lens, a beam splitter, and a non-planar annular cavity are sequentially arranged in the optical path of the pump light; the focusing lens is used to focus the pump light; the beam splitter is used to separate the pump light and stimulated emission light; the pump light, after being focused, passes through the beam splitter and enters the non-planar annular cavity to generate stimulated emission light;

[0012] A permanent magnet is disposed near the non-planar annular cavity, and the magnetic field generated by the permanent magnet acts on the non-planar annular cavity; the non-planar annular cavity generates clockwise stimulated radiation light and counterclockwise stimulated radiation light under the action of the magnetic field of the permanent magnet.

[0013] An electromagnet is disposed near the non-planar annular cavity. The magnetic field generated by the electromagnet acts on the non-planar annular cavity, and the magnetic field strength at the position of the non-planar annular cavity is adjusted by the electromagnet.

[0014] The clockwise stimulated emission light is reflected by the beam splitter to the detection target, reflected by the detection target, and then reflected by the beam splitter to the non-planar annular cavity, generating a self-feedback frequency signal;

[0015] A photodetector is disposed in the optical path of the self-feedback frequency signal, and the photodetector is used to collect the self-feedback frequency signal;

[0016] The frequency stabilization control module internally generates a reference frequency signal. Its input terminal is connected to the photodetector, and its output terminal is connected to the electromagnet. The mixer in the frequency stabilization control module mixes the reference frequency signal with the self-feedback frequency signal to obtain an error signal. The error signal is filtered by a low-pass filter and then processed by an internal PID controller to generate a correction signal. Based on the correction signal, the magnetic field strength of the electromagnet is controlled, thereby precisely adjusting the self-feedback frequency.

[0017] Compared with the prior art, the beneficial effects of the present invention include:

[0018] This invention proposes a magnetic field frequency stabilization device for an NPRO self-feedback interferometer. By utilizing the relationship that the self-feedback frequency changes with the magnetic field strength, the device controls the magnetic field to compensate for the change in the self-feedback frequency, thereby suppressing the self-feedback frequency noise. At 1 MHz, the frequency noise of the self-feedback frequency is suppressed by 5 orders of magnitude, which significantly improves the detection accuracy of the NPRO self-feedback interferometer. Furthermore, based on the frequency stabilization, the weak light detection limit of the NPRO self-feedback interferometer is explored.

[0019] 1. Improve the stability of the self-feedback frequency signal: By introducing an active frequency stabilization control system, beat frequency jitter caused by mode competition and magnetic field fluctuations is suppressed, enabling the NPRO self-feedback interferometer to perform accurate frequency measurements.

[0020] 2. Enhance the system's anti-interference capability and reliability: Actively compensate for major noise sources such as magnetic field fluctuations through a closed-loop feedback mechanism, reduce the impact of environmental interference on measurement results, and improve the system's long-term stability and reliability in complex environments.

[0021] 3. Expand the detection limits and application range of the interferometer: On the basis of achieving frequency stability, explore the detection potential of the system under extremely weak optical feedback conditions, so that it can effectively detect weak signals from distant non-cooperative targets, and extend to precision measurement applications such as long-distance high-precision vibration and rotation speed.

[0022] According to some embodiments of the present invention, a first optical attenuator is provided between the beam splitter and the detection target. The first optical attenuator is used to attenuate the clockwise stimulated emission light, with the purpose of adjusting the self-feedback intensity.

[0023] According to some embodiments of the present invention, a second optical attenuator is provided between the non-planar annular cavity and the photodetector, the second optical attenuator being used to attenuate the self-feedback frequency signal.

[0024] According to some embodiments of the present invention, it further includes:

[0025] The frequency stabilization control module contains a mixer, a low-pass filter, and a PID controller, which can be implemented using digital or analog circuits.

[0026] According to some embodiments of the present invention, the non-planar annular cavity is composed of a single solid-state laser gain medium, which is a rare-earth ion-doped laser material or glass material, including: Nd:YAG crystal, Yb:YAG crystal, Er:YAG crystal, Tm:YAG crystal, erbium glass, thulium glass, and neodymium glass. The wavelength of the pump light is selected by matching the characteristic absorption peak of a specific rare-earth activating ion doped in the solid-state laser gain medium.

[0027] Secondly, the present invention provides a method for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization, applicable to the apparatus for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization as described in any one of the first aspects, the method comprising the steps of:

[0028] The pump diode emits pump light of a preset wavelength. After being focused by the focusing lens, the pump light is transmitted to the non-planar annular cavity through the beam splitter. The non-planar annular cavity generates stimulated emission light.

[0029] The non-planar annular cavity generates clockwise stimulated radiation light and counterclockwise stimulated radiation light under the action of the basic magnetic field provided by the permanent magnet;

[0030] The clockwise stimulated radiation light is reflected by the beam splitter and transmitted to the detection target. It is then reflected back into the non-planar annular cavity by the detection target, causing the non-planar annular cavity to generate a self-feedback frequency signal.

[0031] The frequency stabilization control module receives the self-feedback frequency signal and generates an error signal by comparing it with an internally preset reference frequency. The error signal is filtered by a low-pass filter and then processed by an internal PID controller to generate a correction signal. The correction signal is output to the electromagnet, and the voltage of the electromagnet is adjusted to change the magnetic field strength it generates. By adjusting the magnetic field strength, the fluctuation of the self-feedback frequency of the non-planar ring cavity is compensated, thereby stabilizing the self-feedback frequency.

[0032] According to some embodiments of the present invention, before the pump diode emits pump light of a predetermined wavelength, the following steps are included:

[0033] The relationship between the voltage of the electromagnet and the self-feedback frequency of the non-planar ring cavity is measured.

[0034] According to some embodiments of the present invention, after the photodetector receives the self-feedback beat frequency signal, the method includes the following steps:

[0035] The waveform of the self-feedback frequency signal is visualized using a spectrum analyzer.

[0036] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, wherein the abstract drawings are to be completely consistent with one of the drawings in the specification:

[0038] Figure 1 A diagram of a device for improving the performance of an NPRO self-feedback interferometer by stabilizing the magnetic field according to an embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of a non-planar annular cavity self-feedback model provided in one embodiment of the present invention;

[0040] Figure 3 A graph showing the relationship between electromagnet voltage and self-feedback frequency is provided in one embodiment of the present invention.

[0041] Figure 4 A magnetic field frequency stabilization result diagram provided in one embodiment of the present invention;

[0042] Figure 5 A graph showing the vibration frequency measurement results provided in one embodiment of the present invention;

[0043] Figure 6 This is a diagram showing the weak light detection limit results provided in one embodiment of the present invention;

[0044] Figure 7 The graph shows the rotational speed measurement results provided in one embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0046] It should be noted that although functional modules are divided in the system diagram and the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the system or the order in the flowchart. The terms "first," "second," etc., in the specification, claims, and the aforementioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0047] Reference Figures 1 to 7 , Figure 1 A diagram of a device for improving the performance of an NPRO self-feedback interferometer by stabilizing the magnetic field according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a non-planar annular cavity self-feedback model provided in one embodiment of the present invention; Figure 3 A graph showing the relationship between electromagnet voltage and self-feedback frequency is provided in one embodiment of the present invention. Figure 4 A magnetic field frequency stabilization result diagram provided in one embodiment of the present invention; Figure 5 A graph showing the vibration frequency measurement results provided in one embodiment of the present invention; Figure 6 This is a diagram showing the weak light detection limit results provided in one embodiment of the present invention; Figure 7 The graph shows the rotational speed measurement results provided in one embodiment of the present invention.

[0048] In one embodiment, the device for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization includes: a pump diode 1 for generating pump light; a focusing lens 2, a beam splitter 3, and a non-planar annular cavity 4 sequentially disposed in the optical path of the pump light; the focusing lens 2 for focusing the pump light; the focused pump light then passes through the beam splitter 3 and enters the non-planar annular cavity 4; a permanent magnet 5 disposed adjacent to the non-planar annular cavity 4; the magnetic field generated by the permanent magnet 5 acts on the non-planar annular cavity 4; and an electromagnet 6 disposed adjacent to the non-planar annular cavity 4; the magnetic field generated by the electromagnet 6 acts on the non-planar annular cavity 4. Under the action of the magnetic field of the permanent magnet 5, the non-planar annular cavity 4 generates clockwise stimulated emission light and counterclockwise stimulated emission light, which is transmitted through the electromagnet 6. The magnetic field strength of the non-planar ring cavity is adjusted; the stimulated emission light in the clockwise direction is reflected by the beam splitter to the detection target, reflected by the detection target 12, and reflected by the beam splitter 3 to the non-planar ring cavity 4, generating a self-feedback frequency signal; the photodetector 8 is set in the optical path of the self-feedback frequency signal, and the photodetector is used to collect the self-feedback frequency signal; the frequency stabilization control module 9 generates a reference frequency signal internally, and is communicatively connected to the photodetector 8 and the electromagnet 6. The frequency stabilization control module 9 mixes the reference frequency signal and the self-feedback frequency signal to obtain an error signal. The error signal is filtered by a low-pass filter and then processed by an internal PID module to generate a correction signal. The magnetic field strength of the electromagnet is controlled based on the correction signal, thereby accurately adjusting the self-feedback frequency.

[0049] This invention addresses the technical problem of unstable self-feedback frequency signals that restricts performance by introducing an active closed-loop frequency stabilization system. The invention employs an electromagnet 6 to feedback-control the magnetic field of a non-planar toroidal cavity 4, significantly suppressing frequency noise in the self-feedback frequency signal at critical frequencies, thereby achieving a leap in measurement accuracy from the Hertzian to sub-Hertz levels. This invention significantly improves the device's anti-interference capability and environmental adaptability, extending its application from controlled laboratory environments to practical scenarios with magnetic field fluctuations. It unlocks the application potential of this method in detecting extremely weak light signals and expands its application scope to high-precision measurement of distant, non-cooperative targets.

[0050] 1. The active frequency stabilization technology of electromagnet 6 is adopted. Electromagnet 6 is used to perform closed-loop control of the frequency of NPRO self-feedback interferometer, which significantly suppresses frequency noise and improves the stability of self-feedback frequency signal and measurement accuracy of NPRO self-feedback interferometer.

[0051] 2. Based on the intrinsic polarization theory, a bidirectional light emission mechanism in a weak magnetic field is proposed. By utilizing NPRO under weak magnetic field conditions, bidirectional light emission is achieved, eliminating the need for a beam splitter and acousto-optic modulator, simplifying the structure and improving energy utilization.

[0052] 3. Based on frequency stabilization and optimization, the detection capability of the NPRO self-feedback interferometer has been pushed to new limits. Experiments have shown that it can detect extremely weak vibration signals as low as 12.2 femtowatts, and on this basis, high-precision vibration and rotation speed measurements have been achieved, significantly expanding its application potential in long-distance, non-cooperative target detection.

[0053] The implementation process of this invention is as follows:

[0054] Pump diode 1 emits 808nm pump light, which is focused by focusing lens 2 and then transmitted through beam splitter 3 (which has high transmittance for 808nm laser and high reflectivity for 1064nm) into non-planar ring cavity 4. Under the action of the magnetic field of permanent magnet 5, non-planar ring cavity 4 generates bidirectional 1064nm stimulated emission light (clockwise CW and counterclockwise CCW direction). At this time, the clockwise (CW) stimulated emission light is reflected by beam splitter 3 to the detection target 12, and then reflected back into the cavity by the detection target 12, which can make the non-planar ring cavity exhibit a self-feedback phenomenon.

[0055] According to the intrinsic polarization theory of nonplanar ring cavities, the modes of the two beams are not degenerate, and the frequency difference is related to the strength of the external magnetic field, typically ranging from hundreds of kHz to several MHz. This is reflected in the spectrum analyzer 10 as a self-feedback frequency signal ranging from hundreds of kHz to several MHz. Since the self-feedback frequency changes with the magnetic field, this principle is used to control the voltage of electromagnet 6 to close the loop and control the magnetic field, thereby controlling the self-feedback frequency and achieving frequency stability.

[0056] The closed-loop control system includes a photodetector 8, a frequency stabilization control module 9, an electromagnet 6, and a non-planar ring cavity 4. The self-feedback frequency signal of the counter-clockwise (CCW) beam is acquired by the photodetector 8 and transmitted to the frequency stabilization control module 9. The reference frequency is generated internally by the frequency stabilization control module 9. The device mixes the self-feedback frequency signal with the internal reference frequency, and the mixed signal is processed by a low-pass filter inside the frequency stabilization control module 9 to generate an error signal. Based on this error signal, the frequency stabilization control module 9 processes it through its internal PID module to generate a correction signal. This signal is input to the electromagnet 6 to actively adjust the magnetic field, thereby precisely regulating the self-feedback frequency.

[0057] The working principle of this invention is as follows: When a magnetic field is applied to the NPRO, it generates two modes each in the clockwise and counterclockwise directions. Due to the different non-reciprocal rotations of polarization during the clockwise and counterclockwise rotations, the four modes have different losses. The laser preferentially outputs the low-loss mode. When the loss difference between the low-loss modes in the clockwise and counterclockwise directions exceeds a certain value, the NPRO operates unidirectionally. By reducing the magnetic field, the loss difference between the modes can be reduced. Under weak magnetic field conditions, the NPRO produces bidirectional light output. At this time, the laser in the clockwise direction is fed back into the laser cavity, producing a self-feedback effect, as shown in the model. Figure 2As shown. Due to mode coupling, the mathematical model shown in formula (1) can be obtained.

[0058]

[0059] In the formula These are the light intensities in the CW and CCW directions after feedback. To provide feedback on the light intensity in the CW and CCW directions, The stimulated emission ratio in laser mode. The sum of losses for the modes in both directions. Losses introduced by self-feedback For CW direction frequency, The photon flight time from non-planar ring cavity 4 to the detection target 12 and back to non-planar ring cavity 4. This refers to the frequency of the beat frequency signal carried on the optical path, specifically the center frequency of the beat frequency signal detected by the photodetector. External physical information is contained within... In the process, when the distance between the non-planar annular cavity 4 and the detection target 12 changes, the phase change of the signal is as follows:

[0060] As can be seen from Equation 2, by demodulating the phase change of the NPRO self-feedback interferometer, the corresponding physical information can be obtained, which can be used for self-feedback interferometry.

[0061] Before frequency stabilization control, the relationship between the electromagnet voltage and the NPRO self-feedback frequency was first measured. Figure 3 The two parameters show a linear relationship with a slope of 1229±22Hz / V and a correlation coefficient of 99.8%. This relationship was used in an NPRO self-feedback interferometer magnetic field frequency stabilization experiment, and the results are as follows... Figure 4 As shown. Figure 4 The blue line represents the noise at the self-feedback frequency without magnetic field control, which is relatively high at low frequencies. The noise after magnetic field stabilization is shown by the red line, significantly reducing the self-feedback frequency noise. The yellow line represents the reference source noise. Vibration frequency was detected under both unstable and stable conditions, and the results are as follows. Figure 5 As shown. From Figure 5 It can be seen that the self-feedback interferometric measurement system has good detection accuracy for vibration frequencies of 30Hz-100kHz under both frequency stabilization and non-frequency stabilization conditions. Under frequency stabilization conditions, the minimum detection frequency is extended from 30Hz to 4Hz.

[0062] Figure 6In the comparison between the frequency measurement signal and the reference frequency signal under two conditions, the maximum frequency error was 1.4Hz under the unstabilized condition and 3.55Hz under the 3σ principle. Under the stabilized condition, the frequency error remained close to 0, and the maximum deviation was 0.17Hz under the 3σ principle. The detection accuracy was significantly improved.

[0063] Based on magnetic field frequency stabilization, the weak light detection capability of the NPRO self-feedback interferometer is studied, such as... Figure 6 As shown by the red dot in the figure, the optical power fed back into the crystal does not exceed 12.2 fw at this time. Meanwhile, the optical power in front of the target is 1... Under the condition that the optical power fed back into the crystal does not exceed 74 fw, the rotational speed was measured, and the experimental results are as follows: Figure 7 As shown, the maximum error is approximately 1.5% in the range of 25–56 rad / s. In summary, the frequency-stabilized NPRO self-feedback interferometer can perform long-distance, high-precision detection under low light conditions.

[0064] A first optical attenuator 11 is disposed between the beam splitter 3 and the detection target 12. The first optical attenuator 11 is used to attenuate the stimulated emission light in the clockwise direction, with the purpose of adjusting the self-feedback intensity. A second optical attenuator 7 is disposed between the non-planar ring cavity 4 and the photodetector 8. The second optical attenuator 7 is used to attenuate the self-feedback frequency signal.

[0065] In one embodiment, the device for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization includes: a pump diode 1 for generating pump light; a focusing lens 2, a beam splitter 3, and a non-planar annular cavity 4 sequentially arranged in the optical path of the pump light; the focusing lens 2 for focusing the pump light; and the focused pump light passing through the beam splitter 3 and incident on the non-planar annular cavity 4; a permanent magnet 5 disposed adjacent to the non-planar annular cavity 4, the magnetic field generated by the permanent magnet 5 acting on the non-planar annular cavity; and an electromagnet 6 disposed adjacent to the non-planar annular cavity 4, the magnetic field generated by the electromagnet 6 acting on the non-planar annular cavity 4. Under the action of the magnetic field of the permanent magnet 5, the non-planar annular cavity 4 generates clockwise stimulated emission light and counterclockwise stimulated emission light. The magnetic field strength of the non-planar annular cavity is adjusted by the electromagnet 6. Stimulated emission light is reflected by a beam splitter to the target, reflected by the target 12, and then reflected by the beam splitter 3 to the non-planar ring cavity 4, generating a self-feedback frequency signal. A photodetector 8 is placed in the optical path of the self-feedback frequency signal and is used to collect the self-feedback frequency signal. A frequency stabilization control module 9 generates a reference frequency signal internally and is communicatively connected to the photodetector 8 and the electromagnet 6. The frequency stabilization control module 9 mixes the reference frequency signal and the self-feedback frequency signal to obtain an error signal. The error signal is processed by a low-pass filter and then processed by an internal PID module to generate a correction signal. The magnetic field strength of the electromagnet is controlled based on the correction signal, thereby precisely adjusting the self-feedback frequency. A spectrum analyzer 10 is communicatively connected to the photodetector 8 and is used to visualize the waveform of the self-feedback frequency signal.

[0066] The non-planar ring cavity is a monolithic structure made of a solid-state laser gain medium, which is a rare-earth ion-doped laser material or glass material, including: Nd:YAG crystal, Yb:YAG crystal, Er:YAG crystal, Tm:YAG crystal, erbium glass, thulium glass, and neodymium glass. The wavelength of the pump light is selected by matching the characteristic absorption peaks of specific rare-earth activating ions doped in the solid-state laser gain medium.

[0067] The frequency stabilization control module contains a mixer, a low-pass filter, and a PID controller, which can be implemented using digital or analog circuits.

[0068] In one embodiment, the method for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization is applied to the device for improving the performance of an NPRO self-feedback interferometer as described above. The method includes the following steps: a pump diode emits pump light of a preset wavelength, which is focused by a focusing lens and then incident on a non-planar annular cavity through a beam splitter; the non-planar annular cavity generates clockwise stimulated emission light and counterclockwise stimulated emission light under the action of a basic magnetic field provided by a permanent magnet; the clockwise stimulated emission light is reflected by the beam splitter and transmitted to the detection target, and then reflected back into the non-planar annular cavity by the detection target, so that the non-planar annular cavity generates a self-feedback frequency signal; a frequency stabilization control module receives the self-feedback frequency signal and mixes it with an internally preset reference frequency to generate an error signal; a low-pass filter filters the error signal, and the frequency stabilization control module processes the filtered error signal through an internal PID module to generate a correction signal, which is input to an electromagnet, and the voltage of the electromagnet is adjusted to change the magnetic field strength it generates. By adjusting the magnetic field strength, the fluctuation of the self-feedback frequency of the non-planar annular cavity is compensated, and the self-feedback frequency is stabilized.

[0069] Before the pump diode emits pump light of a preset wavelength, the process includes: measuring the relationship between the electromagnet voltage and the self-feedback frequency of the non-planar ring cavity. Based on this relationship, a suitable correction signal is generated. The waveform of the self-feedback frequency signal is then visualized using a spectrum analyzer.

[0070] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of the present invention.

[0071] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A device and method for improving the performance of an NPRO self-feedback interferometer by stabilizing the magnetic field frequency, characterized in that, include: Pump diodes are used to generate pump light; And a focusing lens, a beam splitter, and a non-planar annular cavity are sequentially arranged in the optical path of the pump light; A focusing lens is used to focus the pump light; A beam splitter is used to separate pump light and stimulated emission light; the pump light, after being focused, passes through the beam splitter and is incident on the non-planar annular cavity to generate stimulated emission light. A permanent magnet is disposed near the non-planar annular cavity, and the magnetic field generated by the permanent magnet acts on the non-planar annular cavity; the non-planar annular cavity generates clockwise stimulated radiation light and counterclockwise stimulated radiation light under the action of the magnetic field of the permanent magnet. An electromagnet is disposed near the non-planar annular cavity. The magnetic field generated by the electromagnet acts on the non-planar annular cavity, and the magnetic field strength at the position of the non-planar annular cavity is adjusted by the electromagnet. The clockwise stimulated emission light is reflected by the beam splitter to the detection target, reflected by the detection target, and then reflected by the beam splitter to the non-planar annular cavity, generating a self-feedback frequency signal; A photodetector is disposed in the optical path of the self-feedback frequency signal, and the photodetector is used to collect the self-feedback frequency signal; The frequency stabilization control module internally generates a reference frequency signal. Its input terminal is connected to the photodetector, and its output terminal is connected to the electromagnet. The mixer in the frequency stabilization control module mixes the reference frequency signal with the self-feedback frequency signal to obtain an error signal. The error signal is filtered by a low-pass filter and then processed by a PID controller to generate a correction signal. Based on the correction signal, the magnetic field strength of the electromagnet is controlled, thereby precisely adjusting the self-feedback frequency.

2. The device for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization according to claim 1, characterized in that, A first optical attenuator is provided between the beam splitter and the detection target. The first optical attenuator is used to attenuate the clockwise stimulated radiation light, with the purpose of adjusting the self-feedback intensity.

3. The device for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization according to claim 1, characterized in that, A second optical attenuator is disposed between the non-planar annular cavity and the photodetector, and the second optical attenuator is used to attenuate the self-feedback frequency signal.

4. The device for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization according to claim 1, characterized in that, The frequency stabilization control module includes a mixer, a low-pass filter, and a PID controller, which can be implemented using digital or analog circuits.

5. The device for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization according to claim 1, characterized in that, The non-planar ring cavity is a monolithic structure made of a solid-state laser gain medium, which is a rare-earth ion-doped laser material or glass material, including: Nd:YAG crystal, Yb:YAG crystal, Er:YAG crystal, Tm:YAG crystal, erbium glass, thulium glass, and neodymium glass. The wavelength of the pump light is matched and selected according to the characteristic absorption peak of the specific rare-earth activating ions doped in the solid-state laser gain medium.

6. A device and method for improving the performance of an NPRO self-feedback interferometer by stabilizing the magnetic field, applicable to the device for improving the performance of an NPRO self-feedback interferometer by stabilizing the magnetic field as described in any one of claims 1 to 5, characterized in that, The method includes the following steps: The pump diode emits pump light of a preset wavelength, which is then focused by the focusing lens and transmitted through the beam splitter to the non-planar annular cavity. The non-planar annular cavity generates clockwise stimulated radiation light and counterclockwise stimulated radiation light under the action of the basic magnetic field provided by the permanent magnet; The clockwise stimulated emission light is reflected by the beam splitter and transmitted to the detection target. It is then reflected back into the non-planar annular cavity by the detection target, causing the non-planar annular cavity to generate a self-feedback signal. The frequency stabilization control module receives the self-feedback frequency signal extracted by the photodetector, mixes it with an internally preset reference frequency to generate an error signal, the error signal is filtered by a low-pass filter and then processed by an internal PID controller to generate a correction signal, the correction signal is output to the electromagnet, the voltage of the electromagnet is adjusted to change the magnetic field strength it generates, and by adjusting the magnetic field strength, the fluctuation of the self-feedback frequency of the non-planar ring cavity is compensated, thereby stabilizing the self-feedback frequency.

7. The method for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization according to claim 6, characterized in that, Before the pump diode emits pump light of a preset wavelength, the following steps are included: The relationship between the voltage of the electromagnet and the self-feedback frequency of the non-planar ring cavity is measured.

8. The method for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization according to claim 6, characterized in that, After the photodetector extracts the self-feedback beat frequency signal, the steps include: The waveform of the self-feedback frequency signal is visualized using a spectrum analyzer.

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