Noise reduction with adaptive filtering scheme on interferometric fiber optic hydrophone

doi:10.1016/j.ijleo.2020.164648

Optik

Volume 211, June 2020, 164648

https://doi.org/10.1016/j.ijleo.2020.164648 Get rights and content

Highlights

•
Interferometric demodulation method using 3×3 coupler improves the detection range and reduces some other noise.
•
The adaptive filter improves the anti-interference and adaptability of the system.
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The scheme can be introduced into the signal processing of sensor units, arrays and even networks.
•
Compared with traditional LMS algorithm, it solves the problem of fixed step parameter and improves the adaptability and robustness.

Abstract

Fiber optic hydrophones have been widely used in underwater sounding, vibration detection and marine geological exploration due to their high sensitivity, wide frequency response range and strong anti-electromagnetic interference capability. In this paper, an adaptive filtering scheme based on Least Mean Square algorithm (LMS) is proposed to improve the detection sensitivity of hydrophones. Aiming to eliminate noise interference, a reference interferometer with the same parameters as the signal interferometer is added to the optical structure. Then, two 3 × 3 couplers are placed to demodulate the sensing signal and the noise signal respectively. Finally the adaptive filtering process is adopted to eliminate the noise effectively. The experimental results show that the proposed scheme can reduce the harmonic distortion signal and the noise signal. The suppression capability of the harmonic distortion signals at 1000 Hz is about 19 dB, and the signal-to-noise ratio is improved by about 23 dB.

Graphical abstract

Introduction

The sound pressure sensitivity and anti-interference ability of fiber optic hydrophones, which were introduced in 1977, are much superior to those of traditional piezoelectric ceramic hydrophones. Compared with the traditional piezoelectric hydrophone, the fiber optic hydrophone has obvious advantages such as high sensitivity, wide frequency response range, light structure, strong anti-electromagnetic interference capability, resistance to harsh environment and easy large-scale array formation [1]. However, the noise problem faced by the development of large-scale array and long-distance transmission of fiber-optic hydrophones is also increasingly obvious, mainly including the intensity noise and phase noise of the laser and the noise caused by the circuit and digital demodulation of the system [2], some noise eventually turns into phase noise of the system, which increases the difficulty of weak signal detection and limits the development of long-distance transmission of fiber-optic hydrophone arrays.

The adaptive filtering technology mainly adjusts the filter parameters through the adaptive algorithm to achieve the best estimation of the system noise, and then achieve the optimal noise cancellation effect. In recent years, adaptive filtering technology has been widely used in the fields of wireless communication, voice signal processing, radar navigation, etc. Due to its small amount of calculation and suitable for real-time processing, it has also begun to be applied to the field of optical fiber sensing. In 2015, Romashk R. V. et al. [3] proposed and studied the implementation of an adaptive fiber-optic hydrophone with a membrane fiber sensor as the sensitive component. The experimental results show that the scheme improves the noise immunity and sensitivity of the hydrophone. In 2016, Vikash Chandra et al. [4] proposed and experimented with a two-channel fiber Mach-Zehnder interferometer to eliminate the intensity noise, which can improve the quality of the demodulated signal by 3 dB. In 2018, Fei Liu et al. [5] reduced the noise floor of the heterodyne interferometric fiber sensor by adjusting the parameters of the acousto-optic modulator. The experimental results show that the phase noise caused by the acousto-optic modulator can be reduced at the optimal driving power to -130 dB. However, most of the above studies use the traditional signal detection method based on phase-generated carrier (PGC) [6,7] and the noise reduction method that changes the optical structure and instrument parameters. Not only the limited signal detection range, but also the poor adaptability and robustness, it will additionally cause some other noise such as random noise and circuit noise.

In this paper, the adaptive filtering technique based on Least Mean Square algorithm (LMS) and interferometric demodulation method using 3 × 3 coupler [8] are used to eliminate the noise of the interferometric fiber-optic hydrophone. Finally, the results show that this scheme can effectively filter the harmonic distortion signal and noise signal of the fiber optic hydrophone.

Section snippets

System structure of interferometric fiber optic hydrophone

Commonly used signal detection schemes include interferometric demodulation method using 3 × 3 coupler and signal detection method based on phase-generated carrier (PGC), but the 3 × 3 coupler phase demodulation scheme does not require modulation of carrier signal, has a simple principle and a large signal detection range, and also reduces the requirements of the laser, and reduces phase noise and random noise.

The system structure of noise generation and signal detection of interferometric

Adaptive filtering scheme

There are two main types of common adaptive algorithms: the least mean square algorithm (LMS) and the recursive least square algorithm (RLS). The RLS algorithm uses the minimum weighted difference between the original channel and the reference channel as the criterion, and can quickly adaptively track, but the amount of computation is also large; the LMS algorithm uses the minimum mean square value of the difference between the original channel and the reference channel as the criterion,

Experiments and results

According to Fig. 1, the corresponding optical system structure is designed, and the valid signal is set to a sine wave with amplitude 2, and the noise signal is set to Gaussian white noise. The sampling rate of the system signal is set to 40 kHz and the number of samples is 20,000. The adaptive filter length is set to 128, the adaptive algorithm is the LMS algorithm, the step size parameter $μ$ is set to a variable value and automatically adjusted to the optimal value.

In the case where the

Conclusions

In this paper, an adaptive filtering scheme based on LMS algorithm is proposed for the sensing signal of interferometric fiber-optic hydrophone. Adaptive filtering can adjust its own parameters as the signal changes to achieve the best filtering effect. It can replace classical filters with fixed parameters, poor adaptability and robustness, and is introduced into the signal processing of sensor units, arrays and even networks. It can be seen from the results that the adaptive filtering can

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors would like to acknowledge the support of National Natural Science Foundation of China (NSFC) under grant 61205089 and 61604135, Projects of Wuhan Science and Technology Program under grant 2017010201010130.

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Original research articleNoise reduction with adaptive filtering scheme on interferometric fiber optic hydrophone

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

System structure of interferometric fiber optic hydrophone

Adaptive filtering scheme

Experiments and results

Conclusions

Declaration of Competing Interest

Acknowledgments

Sensors

Fiber-optic sensing: a historical perspective

J. Lightw. Technol.

Laser adaptive fiber-optic hydrophone

Bull. Lebedev Phys. Inst.

Elimination of light intensity noise using dual-channel scheme for fiber MZI-based FBG sensor interrogation

IEEE Sens. J.

Acousto-optic modulation induced noises on heterodyne-interrogated interferometric fiber-optic sensors

J. Lightw. Technol.

Development of high sensitivity eight-element multiplexed fiber laser acoustic pressure hydrophone array and interrogation system

Photonic Sens.

Thin cable fiber-optic hydrophone array for passive acoustic surveillance applications

IEEE Sens. J.

Optical fiber interferometers with 3×3 directional couplers: analysis

J. Appl. Phys.

Effects of intensity noise in digital demodulation for fiber laser sensor

IEEE Photonics Technol. Lett.

Original research article
Noise reduction with adaptive filtering scheme on interferometric fiber optic hydrophone