A phase-shifted fiber grating demodulation system based on a laser frequency stabilization system

Abstract

The application provides a phase shift fiber grating demodulation system based on a laser frequency stabilization system, which comprises a laser frequency stabilization system for long-term frequency offset locking of laser emitted light; wherein the laser frequency stabilization system comprises an optical frequency comb and a heterodyne interference optical path, the optical frequency comb is connected with the heterodyne interference optical path and is used for receiving the light emitted by the laser; the laser frequency stabilization system further comprises a photoelectric detector, a frequency discrimination circuit and a frequency-voltage conversion circuit, the photoelectric detector is used for converting the light passing through the heterodyne interference optical path into an electric signal; the frequency discrimination circuit is connected with the photoelectric detector and is used for receiving the electric signal; the frequency-voltage conversion circuit is connected with the frequency discrimination circuit and is used for converting the electric signal into an error voltage signal; a PC control host acquires the error voltage signal and outputs a feedback control signal to perform long-term frequency offset locking on the laser emitted light. The application can improve the long-term stability of the laser by multiple orders of magnitude and can realize long-term frequency offset locking.

Description

Technical Field

[0001] This invention relates to the field of signal demodulation technology, and in particular to a demodulation system based on a phase-shifted fiber grating of a laser frequency stabilization system. Background Technology

[0002] With the development of modern measurement technology, fiber optic sensors have attracted widespread attention due to their high sensing accuracy, strong anti-interference capabilities (e.g., immunity to electromagnetic interference, electrical insulation, corrosion resistance, intrinsic safety), light weight, small size, and variable shape; and the ability to perform distributed measurements. However, traditional methods for measuring strain are complex, have poor repeatability, and are easily affected by the external environment, which to some extent limits the practical application of fiber optic sensing.

[0003] A single-point phase-shifting fiber grating (PSG) introduces a sudden phase shift at a specific location within a uniform fiber Bragg grating, creating a phase-shift peak with an extremely narrow linewidth in the stopband of its transmission spectrum. This extremely narrow linewidth (typically less than 10 pM) allows for the detection of minute changes in external factors such as strain, temperature, vibration, humidity, and ultrasound. By measuring the magnitude of this change in the phase shift peak, the change in external factors can be inferred, thus providing higher sensitivity in fiber optic sensing. Since PSGs are fabricated based on uniform fiber Bragg gratings, they share similar sensing characteristics.

[0004] Currently, a common method for converting demodulated phase shift peaks into strain for calculation is to first calibrate the phase-shifted fiber grating for temperature and strain. A reference grating is established, and the received signal is delayed using fiber delay windings. Placing all fibers together avoids the effects of wavelength drift and temperature fluctuations. Then, laser scanning is used to obtain error curves, determining the initial values ​​of the resonant center and sideband frequencies, as well as the scaling factor. During the measurement process, two groups are subjected to constant strain, and one group is subjected to sinusoidal strain. The power spectral density of each fiber is sampled, and the strain is demodulated. This experimental condition can achieve nanoscale strain measurement, but it suffers from complex procedures, low repeatability, and high experimental costs in frequency stabilization and locking. Summary of the Invention

[0005] To address the technical problems of complex procedures and low repeatability in frequency stabilization and frequency locking when converting demodulated phase shift peaks into strain calculations in existing technologies, one objective of this invention is to provide a demodulation system based on a laser frequency stabilization system using a phase-shifting fiber grating. The demodulation system includes:

[0006] A laser, a laser frequency stabilization system, and a laser controller modulation system, wherein the laser frequency stabilization system is used to perform long-term frequency locking on the light emitted by the laser;

[0007] The laser frequency stabilization system includes an optical frequency comb and a heterodyne interference optical path. The optical frequency comb is connected to the heterodyne interference optical path and is used to receive the light emitted by the laser.

[0008] The laser frequency stabilization system also includes a photodetector, a frequency discrimination circuit, and a frequency-to-voltage conversion circuit. The photodetector is used to convert light passing through the heterodyne interference optical path into an electrical signal.

[0009] The frequency discrimination circuit is connected to the photodetector and is used to receive electrical signals;

[0010] The frequency-to-voltage conversion circuit is connected to the frequency discrimination circuit and is used to convert the electrical signal into an error voltage signal.

[0011] The PC control host collects the error voltage signal and outputs a feedback control signal. Through the laser controller modulation system, it controls the frequency of the light emitted by the laser and performs long-term frequency offset locking on the light emitted by the laser.

[0012] Furthermore, the laser controller modulation system includes: a first signal generator, a second signal generator, a radio frequency signal generator, a phase modulator, an intensity modulator, and an acousto-optic modulator;

[0013] The feedback control signal output by the PC control host is sent to the intensity modulator via the radio frequency signal generator;

[0014] The feedback control signal output by the PC control host is sent to the acousto-optic modulator via the second signal generator.

[0015] Furthermore, the signal generated by the first signal generator is divided into three paths: the first path is acquired by the PC control host, the second path is sent to the phase modulator, and the third path is sent to the acousto-optic modulator via the second signal generator.

[0016] Furthermore, the laser controller modulation system also includes an acousto-optic modulator driver for acquiring signals sent by the second signal generator and sending them to the acousto-optic modulator.

[0017] Furthermore, the demodulation system also includes a data acquisition unit for acquiring the error voltage signal output by the frequency-voltage conversion circuit and the signal generated by the first signal generator, and sending them to the PC control host.

[0018] The present invention provides a demodulation system based on a phase-shifted fiber grating of a laser frequency stabilization system, which can improve the long-term frequency offset locking of lasers with wavelengths in the optical frequency spectrum range and improve the stability by two orders of magnitude.

[0019] This invention provides a demodulation system based on a phase-shifted fiber grating of a laser frequency stabilization system. The laser frequency stabilization system is constructed by measuring the frequency of the beat frequency signal through a frequency-voltage conversion circuit, converting the frequency value into an error signal, and then controlling the laser through a feedback control loop of the main control program. This can improve the long-term stability of the laser by several orders of magnitude and achieve long-term frequency offset locking.

[0020] This invention provides a demodulation system for a phase-shifted fiber Bragg grating based on a laser frequency stabilization system. This system is structurally stable, low-cost, and allows for controlled laser stabilization for over one hour, providing a foundation for high-precision frequency locking. The phase-shifted fiber Bragg grating under laser frequency stabilization allows for longer sampling times in nanostrain measurement, minimizing the influence of the laser's internal structure and external environment, resulting in more accurate data. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 The schematic diagram illustrates the structure of a demodulation system based on a laser frequency stabilization system and a phase-shifted fiber grating according to the present invention.

[0023] Figure 2 The diagram shows the laser wavelength drift within 800 seconds before and after locking the light emitted by the laser in one embodiment of the present invention. Detailed Implementation

[0024] To make the above and other features and advantages of the present invention clearer, the invention will be further described below with reference to the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explanation to those skilled in the art and are exemplary only, not restrictive.

[0025] To address the technical issues of complex procedures and low repeatability in frequency stabilization and frequency locking during the calculation of demodulation phase shift peak conversion into strain in existing technologies, such as... Figure 1 The diagram shows a structural schematic of a demodulation system for a phase-shifted fiber grating based on a laser frequency stabilization system according to the present invention. According to an embodiment of the present invention, a demodulation system for a phase-shifted fiber grating based on a laser frequency stabilization system is provided, comprising: a laser 101, a laser frequency stabilization system 102, and a laser controller modulation system. The laser 101 is connected to the laser frequency stabilization system 102. The laser frequency stabilization system 102 is used for long-term frequency locking of the light emitted by the laser 101.

[0026] The laser frequency stabilization system 102 includes an optical frequency comb 1021 and a heterodyne interference optical path 1022. The optical frequency comb 1021 connects the laser 101 and the heterodyne interference optical path 1022 and is used to receive the light emitted by the laser 101. The beat frequency signal of the controlled light (the light received from the laser 101) and the optical frequency comb 1021 and the heterodyne interference optical path 1022 contains information about the frequency difference Δf between the light and the reference comb teeth.

[0027] The laser frequency stabilization system 102 also includes a photodetector 1023, a frequency discrimination circuit 1024, and a frequency-to-voltage conversion circuit 1025. The photodetector 1023 is used to convert the light passing through the heterodyne interference optical path 1022 (containing information about the frequency difference Δf between the light and the reference comb teeth) into an electrical signal.

[0028] The frequency discrimination circuit 1024 is connected to the photodetector 1023 and is used to receive electrical signals and further reduce the frequency to f′.

[0029] Frequency-to-voltage conversion circuit 1025, connected to frequency discriminator circuit 1024, is used to convert electrical signals into error voltage signals V. i .

[0030] According to an embodiment of the present invention, a demodulation system based on a phase-shifted fiber grating of a laser frequency stabilization system further includes a PC control host 107, which acquires error voltage signals V. i It outputs a feedback control signal and controls the frequency of the light emitted by the laser 101 through the laser controller modulation system, thereby performing long-term frequency offset locking on the light emitted by the laser 101.

[0031] In a specific embodiment, the optical frequency comb 1021 is a ytterbium-doped fiber femtosecond optical frequency comb, which amplifies the spectral range to 1550nm through photonic crystal fiber, corresponding to the center wavelength of the standard phase-shifted fiber grating 112, and the laser 101 is an NKTAdjustik-E15 narrow linewidth laser.

[0032] According to an embodiment of the present invention, the laser controller modulation system includes: a first signal generator 108, a second signal generator 110, a radio frequency signal generator 109, a phase modulator 103, an intensity modulator 104, and an acousto-optic modulator 105.

[0033] According to an embodiment of the present invention, the PC control host 107 acquires the error voltage signal V. i The signal generated by the first signal generator 108 is combined with the signal output by the feedback control signal. In a preferred embodiment, the demodulation system further includes a data acquisition unit 106 for acquiring the error voltage signal V output by the frequency-to-voltage conversion circuit 1025. i The signal generated by the first signal generator 108 is sent to the PC control host 107.

[0034] The first signal generator 108 generates a signal that is divided into three paths: the first path is acquired by the PC control host 107, the second path is sent to the phase modulator 103, and the third path is sent to the acousto-optic modulator 105 via the second signal generator 110.

[0035] The feedback control signal output by the PC control host 107 is sent to the intensity modulator 104 via the radio frequency signal generator 109.

[0036] The feedback control signal output by the PC control host 107 is sent to the acousto-optic modulator 105 via the second signal generator 110. In a preferred embodiment, the laser controller modulation system further includes an acousto-optic modulator driver 111, which is used to acquire the signal sent by the second signal generator 110 and send it to the acousto-optic modulator 105.

[0037] Because the optical frequency comb 1021 introduces spontaneous emission, and its output energy is unstable after being broadened by a photonic crystal, the signal-to-noise ratio of the light emitted by the laser 101 to the beat frequency signal of the optical frequency comb 1021 is low. To improve noise immunity, the PC control host 107 needs to adjust the V signal before feedback control. i Mean filtering is performed. According to the laser frequency stabilization system 102 provided by this invention, PDH technology and sideband interrogation technology are used to stabilize the laser frequency to the resonant frequency of the phase-shifted fiber grating 112. Combined with time-division multiplexing technology, the influence of environmental factors can be further reduced by using fiber delay rolls of different lengths. This allows the demodulation system based on the phase-shifted fiber grating of the laser frequency stabilization system of this invention to acquire data over a longer period in a more stable environment, thus enabling more accurate acquisition of strain information.

[0038] like Figure 2 The diagram shown in one embodiment of the present invention illustrates the laser wavelength drift within 800 seconds before and after laser light locking. This experiment demonstrated the long-term frequency stability of a 1550nm narrow-linewidth laser 101, achieving frequency locking for over 1 hour, thus improving frequency stability by at least two orders of magnitude. Figure 2 The image on the left shows the laser wavelength drift within 800 seconds before the laser beam locks in. Figure 2 The image on the right shows the laser wavelength drift within 800 seconds after the laser light is locked.

[0039] This invention can lock the controlled laser for a long time when the beat frequency signal-to-noise ratio is low. It can stabilize the frequency of lasers with wavelengths in the optical comb spectrum range. It has a wide range of applications, stable device performance, and low cost.

[0040] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A demodulation system based on a phase-shifted fiber grating of a laser frequency stabilization system, characterized in that, The demodulation system includes: a laser, a laser frequency stabilization system, a laser controller modulation system, and a PC control host; The laser frequency stabilization system is used to lock the frequency of light emitted by the laser for a long period of time. The laser frequency stabilization system includes an optical frequency comb and a heterodyne interference optical path. The optical frequency comb is connected to the heterodyne interference optical path and is used to receive the light emitted by the laser. The laser frequency stabilization system also includes a photodetector, a frequency discrimination circuit, and a frequency-to-voltage conversion circuit. The photodetector is used to convert light passing through the heterodyne interference optical path into an electrical signal. The frequency discrimination circuit is connected to the photodetector and is used to receive electrical signals; The frequency-to-voltage conversion circuit is connected to the frequency discrimination circuit and is used to convert the electrical signal into an error voltage signal. The laser controller modulation system includes: a first signal generator, a second signal generator, a radio frequency signal generator, a phase modulator, an intensity modulator, and an acousto-optic modulator; The first signal generator generates a signal that is divided into three paths: the first path is acquired by the PC control host, the second path is sent to the phase modulator, and the third path is sent to the acousto-optic modulator via the second signal generator; the laser controller modulation system also includes an acousto-optic modulator driver, which is used to acquire the signal sent by the second signal generator and send it to the acousto-optic modulator; The PC control host collects the error voltage signal and outputs a feedback control signal. Through the laser controller modulation system, it controls the frequency of the light emitted by the laser and performs long-term frequency offset locking on the light emitted by the laser. The feedback control signal output by the PC control host is sent to the intensity modulator via the radio frequency signal generator; The feedback control signal output by the PC control host is sent to the acousto-optic modulator via the second signal generator.

2. The demodulation system according to claim 1, characterized in that, The demodulation system also includes a data acquisition unit, which is used to acquire the error voltage signal output by the frequency-voltage conversion circuit and the signal generated by the first signal generator, and send them to the PC control host.

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