Research on fiber optic interferometric vibration measurement system based on internal modulation

Jia Peng; Xie Jiandong; Lou Yingtian; Yang Ye; Yang Tao

doi:10.12086/oee.2025.240233

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Jia P, Xie J D, Lou Y T, et al. Research on fiber optic interferometric vibration measurement system based on internal modulation[J]. Opto-Electron Eng, 2025, 52(1): 240233. doi: 10.12086/oee.2025.240233

Citation:

Jia P, Xie J D, Lou Y T, et al. Research on fiber optic interferometric vibration measurement system based on internal modulation[J]. Opto-Electron Eng, 2025, 52(1): 240233. doi: 10.12086/oee.2025.240233

Research on fiber optic interferometric vibration measurement system based on internal modulation

Precision Measurement Laboratory, Zhejiang Sci-Tech University, Zhejiang, Hangzhou 310018, China

Fund Project: National Key Research and Development Program (2022YFF0705803), Science Foundation of Zhejiang Sci-Tech University (11122932612222, 23222133-Y)

More Information

^*Corresponding author: xiejiandong@yeah.net
CSTR: 32245.14.oee.2025.240233

Received Date 07 October 2024

Revised Date 09 December 2024

Accepted Date 10 December 2024

Published Date 25 January 2025

Abstract

Abstract

A fiber microprobe vibration measurement system based on internal modulation has been developed. A sinusoidal phase modulated laser source is generated by modulating the current of the distributed feedback laser (DFB) with a sinusoidal signal. After passing through a fiber circulator and a fiber microprobe, the output laser beam is used to measure the displacement of a vibration source. The returned laser beam interferes with the reference laser reflected by the fiber microprobe to generate a phase generated carrier (PGC) interference signal. A real-time PGC signal processing algorithm is designed through a programmable logic gate array (FPGA) digital computing platform. A five-parameter ellipse fitting method is unitized to extract the error items introduced by additional intensity modulation and other factors and compensate for the phase nonlinear error. The fast Fourier transform (FFT) algorithm is unitized to analyze the vibration displacement. Theoretical analysis was conducted and a vibration measurement system was built. A series of experiments were conducted, including PGC signal demodulation, displacement measurement, and vibration measurement. The experimental results show that the vibration frequency range of the system covers 1142 Hz. In the 10 µm step displacement experiment, the average deviation measured is 0.173 µm. The resolution of vibration measurement is 1.221 Hz, and the harmonic distortion is less than 1.36%. The measurement system is expected to be applied in the field of precise vibration measurement.
- vibration measurement /
- internal modulation /
- microprobes /
- phase generated carrier /
- ellipse fitting

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References

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Overview

Overview

Vibration measurement is significant and widely used in the fields of spacecraft performance evaluation, material damage detection, machinery diagnostics, and acoustic sensing. Specifically, the vibration measurement based on a sinusoidal phase modulation laser interferometer has become a lasting research focus because of the advantages of strong anti-electromagnetic interference, high sensitivity, and large dynamic range. Sinusoidal phase modulation interferometers based on external modulation use adding piezoelectric ceramics or electro-optic modulators to the reference arm of the optical path. Introducing additional components will increase the hardware cost of the measurement system and result in a longer reference arm, which may introduce drift errors. Differently, sinusoidal phase modulation interferometers based on internal modulation directly modulate the laser current sinusoidally. The advantage is that no additional modulation devices need to be introduced. Besides, the collimator, spectroscope, and reference mirror in the measurement optical path can be integrated into a single fiber microprobe, improving practicality. However, it inevitably has periodic nonlinear errors caused by the phase modulation depth, carrier phase delay, and additional intensity modulation, which limits the accuracy of vibration measurement.

In this paper, a fiber microprobe vibration measurement system based on internal modulation has been developed to solve the problems mentioned above. A sinusoidal phase modulation laser source is generated by modulating the current of a distributed feedback laser (DFB) with a sinusoidal signal. After passing through a fiber circulator and a microprobe, the output laser beam is used to measure the displacement of the vibration source. The returned laser beam interferes with the reference laser reflected by the microprobe to generate a phase generated carrier (PGC) interference signal. A real-time interference signal processing algorithm is designed based on a programmable logic gate array (FPGA) digital computing platform. The error items introduced by additional intensity modulation and other factors are extracted through five-parameter ellipse fitting to compensate for the phase nonlinear error, and achieve high-precision measurement of vibration displacement. The fast Fourier transform (FFT) algorithm is used to analyze the vibration displacement. Theoretical analysis was conducted and a vibration measurement verification system was built. Interference signal demodulation experiments, step displacement measurement experiments, and vibration measurement experiments were carried out. The experimental results show that the vibration frequency range of the system covers 1142 Hz. In the 10-µm step displacement experiment, the average deviation measured is 0.173 µm. The resolution of vibration measurement is 1.221 Hz, and the harmonic distortion is less than 1.36%. The measurement system is expected to be applied in the field of precision vibration measurement.