CN-122015636-A - Device and method for improving performance of NPRO (non-return-to-zero) self-feedback interferometer through magnetic field frequency stabilization

CN122015636ACN 122015636 ACN122015636 ACN 122015636ACN-122015636-A

Abstract

The application provides a device and a method for improving the performance of an NPRO (non-return-to-back) interferometer by stabilizing a magnetic field, comprising a pumping diode, a focusing lens, a spectroscope and a non-planar annular cavity crystal, wherein the pumping diode is used for generating pumping light, and the focusing lens, the spectroscope and the non-planar annular cavity crystal are sequentially arranged on an optical path of the pumping light; the non-planar annular cavity crystal generates clockwise stimulated radiation light and anticlockwise stimulated radiation light under the action of the permanent magnet, the clockwise stimulated radiation light 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 the 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. The application solves the technical problems of low measurement precision, poor anti-interference capability and difficult weak light detection of the NPRO self-feedback interferometer in the prior art.

Inventors

GUO CHANGLEI
LI WENXUN
Ma Chunzhao
LIU DANQING
XU JIE

Assignees

中山大学

Dates

Publication Date: 20260512
Application Date: 20260106

Claims (8)

1. The device and the method for improving the performance of the NPRO self-feedback interferometer by magnetic field frequency stabilization are characterized by comprising the following steps: a pump diode for generating pump light; the device comprises a pump light source, a beam splitter, a focusing lens, a beam splitter, a non-planar annular cavity, a focusing lens, a beam splitter and a beam splitter, wherein the focusing lens, the beam splitter and the non-planar annular cavity are sequentially arranged on the light path of the pump light; 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. The electromagnet is arranged close to the non-planar annular cavity, a magnetic field generated by the electromagnet acts on the non-planar annular cavity, and the magnetic field intensity of the position of the non-planar annular cavity is adjusted through the electromagnet; The clockwise stimulated radiation light is reflected to a detection target through the spectroscope, reflected to the non-planar annular cavity through the spectroscope and generated into a self-feedback frequency signal; the photoelectric detector is arranged on the optical path of the self-feedback frequency signal and is used for collecting the self-feedback frequency signal; The frequency stabilization control module internally generates a reference frequency signal, the input end of the frequency stabilization control module is connected with the photoelectric detector, the output end of the frequency stabilization control module is connected with the electromagnet, the frequency 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 the low-pass filter and then is processed by the PID controller to generate a correction signal, and the magnetic field intensity of the electromagnet is controlled based on the correction signal, so that the self-feedback frequency is accurately regulated.
2. The apparatus for frequency-stabilizing and enhancing performance of NPRO self-feedback interferometer as claimed in claim 1, wherein a first optical attenuator is disposed between said beam splitter and the detection target, said first optical attenuator being adapted to attenuate said clockwise stimulated radiation light for the purpose of adjusting self-feedback intensity.
3. The device for improving the performance of the NPRO self-feedback interferometer through frequency stabilization of a magnetic field according to claim 1, wherein a second optical attenuator is arranged between the non-planar annular cavity and the photodetector, and the second optical attenuator is used for carrying out attenuation processing on the self-feedback frequency signal.
4. The device for improving the performance of the NPRO self-feedback interferometer by using the magnetic field frequency stabilization according to claim 1, wherein the frequency stabilization control module comprises a mixer, a low-pass filter and a PID controller, which can be implemented by a digital circuit or an analog circuit.
5. The device for improving the performance of an NPRO self-feedback interferometer by using a magnetic field with stable frequency according to claim 1, wherein the non-planar annular cavity is a monolithic structure made of a solid laser gain medium, the solid laser gain medium is a rare earth ion doped laser material or glass material, and comprises Nd: YAG crystal, yb: YAG crystal, er: YAG crystal, tm: YAG crystal, erbium glass, thulium glass and neodymium glass, wherein the wavelength of the pump light is selected in a matching way according to the characteristic absorption peak of specific rare earth activated ions doped in the solid laser gain medium.
6. A device and a method for improving the performance of an NPRO self-feedback interferometer by magnetic field frequency stabilization, which are applied to the device for improving the performance of the NPRO self-feedback interferometer by magnetic field frequency stabilization according to any one of claims 1 to 5, and are characterized in that the method comprises the following steps: the pump diode emits pump light with preset wavelength, and the pump light is converged by the focusing lens and then transmitted to the non-planar annular cavity through the spectroscope; the non-planar annular cavity generates clockwise stimulated radiation light and counterclockwise stimulated radiation light under the action of a basic magnetic field provided by the permanent magnet; The clockwise stimulated radiation light is transmitted to a detection target after being reflected by the spectroscope, and then is reflected back to the interior of the non-planar annular cavity by the detection target, so that the non-planar annular cavity generates a self-feedback signal; The frequency stabilization control module receives the self-feedback frequency signal extracted by the photoelectric detector, mixes the self-feedback frequency signal with an internal preset reference frequency to generate an error signal, processes the error signal through the low-pass filter, processes the error signal through the internal PID controller to generate a correction signal, outputs the correction signal to the electromagnet, adjusts the voltage of the electromagnet to change the magnetic field intensity generated by the electromagnet, and compensates the fluctuation of the self-feedback frequency of the non-planar annular cavity through the adjustment of the magnetic field intensity to realize the stability of the self-feedback frequency.
7. The method for improving the performance of an NPRO self-feedback interferometer in a frequency stabilized manner by a magnetic field of claim 6, comprising the steps of, before the pump diode emits pump light of a predetermined wavelength: And measuring the relation between the electromagnet voltage and the self-feedback frequency of the non-planar annular cavity.
8. The method of magnetic field frequency stabilization to enhance performance of an NPRO self-feedback interferometer of claim 6, comprising the steps of, after the photodetector extracts the self-feedback beat signal: And visually displaying the waveform of the self-feedback frequency signal through a frequency spectrograph.

Description

Device and method for improving performance of NPRO (non-return-to-zero) self-feedback interferometer through magnetic field frequency stabilization Technical Field The invention relates to the technical field of self-feedback interferometers, in particular to a device and a method for improving the performance of an NPRO (Non-PLANAR RING Oscillator, non-planar annular cavity) self-feedback interferometer by magnetic field frequency stabilization. Background Interferometry is a core technology for performing accurate physical quantity measurement based on the wavelength of light waves, and its history can be traced back to the pioneering work of the 19 th century fei-he and michelson et al. Traditional interferometers, such as Michelson interferometers, rely on the fact that a beam of light is split and then propagates in different paths to be combined to generate interference, and although the heterodyne interferometry method is high in accuracy, complicated optical path layout, strict alignment requirements and stable reference arms are generally needed, and the heterodyne interferometry method is sensitive to environmental noise and limited in application in non-laboratory environments. To solve these problems, a technique of directly injecting external feedback light into the laser and using the laser itself as an interference element, self-feedback interferometry (SMI), has been developed. The core principle is that feedback light reflected or scattered back to the laser cavity from an external target interacts with an inherent optical field inside the laser, so that the output characteristic of the laser is modulated, and the modulated signal carries the motion information of the external target. Based on the difference of signal extraction modes, the self-feedback interferometer mainly develops into two types, namely a common self-feedback interferometer and a frequency-shifting self-feedback interferometer. The common self-feedback interferometer directly detects the change of the laser output intensity, the system has the simplest structure, but the signal is easily submerged by low-frequency noise in the environment, and the measurement sensitivity and the signal-to-noise ratio are low. To overcome this bottleneck, a frequency-shifting self-feedback interferometer is proposed, and a key technology of the frequency-shifting self-feedback interferometer is to introduce a frequency-shifting element such as an acousto-optic modulator (AOM) in an optical path, so as to introduce a fixed frequency offset for feedback light. Therefore, the physical information to be measured is carried in a high-frequency beat signal, the measured information can be calculated by detecting the phase of the beat signal, a low-frequency noise section is effectively avoided, and the sensitivity and the stability of measurement are remarkably improved. However, conventional frequency-shifted self-feedback interferometers typically require a separate AOM to shift the frequency and use a beam splitter to separate the reference light from the measurement light, resulting in complex system structures and reduced energy utilization. Self-feedback interference techniques based on special lasers such as non-planar ring cavities (NPROs) present unique advantages. The laser can generate bidirectional light which is transmitted clockwise and anticlockwise under the action of a magnetic field, and naturally forms frequency difference, so that the frequency shift function can be realized without an external AOM, and a new way is opened up for developing a novel self-feedback interferometer which is more compact in structure, higher in stability and more suitable for severe environment application. However, since the NPRO self-feedback interferometer has mode competition and is extremely sensitive to external magnetic field fluctuation, the NPRO self-feedback frequency stability is low, the frequency noise is high at a low frequency, and long-time and high-precision measurement cannot be satisfied. Three main technical problems exist in the related art: 1. The beat frequency is unstable, namely, due to the mode competition existing in the NPRO laser and the high sensitivity to the fluctuation of an external magnetic field, the generated bidirectional light-emitting beat frequency has obvious jitter, so that the NPRO laser cannot perform high-precision frequency and phase measurement, and the core measurement capability of the NPRO laser is limited. 2. The system is easy to be interfered, one of the sources of unstable beat frequency is sensitivity to magnetic field noise, so that the existing system is poor in reliability in a real environment and large in drift of long-term measurement results. 3. The problem of insufficient weak signal detection capability is that when the measurement is carried out on a remote and non-cooperative target, feedback optical signals are extremely weak, and under the background of unstable beat frequency,