Mr. Hanfeng Xu Profile

Hanfeng Xu

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Publications (2)

Proceedings Article | 10 May 2023 Paper

A phase modulation based interference visibility optimization method for optical fiber hydrophone transmission system

Hong Zhang, Hanfeng Xu, Dongming Li

Proceedings Volume 12554, 1255412 (2023) https://doi.org/10.1117/12.2651329

KEYWORDS: Visibility, Phase modulation, Optical fibers, Modulation, Scattering, Interferometry, Sensing systems, Light sources

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In long-distance fiber-optic sensing and communication systems, phase modulation methods are usually employed to suppress stimulated Brillouin scattering (SBS), thereby increasing the stimulated Brillouin threshold. However, when phase modulation is added to the light source, the linewidth is broadened by the periodic modulation and the coherence length is reduced. In a large-scale multiplexed fiber optic hydrophone system, the optical pulse interference visibility returned by the fiber optic hydrophone is affected by the optical path difference, phase modulation amplitude and frequency, etc., resulting in reduced visibility of interference fringes. In practical applications, it is difficult to fully compensate the optical path difference between the hydrophone and the time-delay interferometer. In the case of large optical path difference, the phase modulation amplitude and frequency need to be optimized to improve the visibility of the interference pulse. In order to solve this problem, this paper first theoretically analyzes the principle of SBS suppression by light source phase modulation. The laboratory builds a fiber optic hydrophone remote transmission test system, and uses a spectrum analyzer to measure the backscattering spectrum of the transmission fiber to obtain the suppression of SBS. The best parameters for the suppression of the effect, the interference visibility of the hydrophone is tested on this basis, the phase noise of the hydrophone with poor visibility is tested, and the phase noise consistency of the tested hydrophone at 1kHz. By optimizing the modulation parameters of the phase modulator and changing the modulation frequency by using the method of equal step size, the interference visibility of the interference pulse is improved. Improve the visibility of the hydrophone with poor visibility from 0.42 to 0.89, the phase noise of the hydrophone is reduced, effectively balancing the Brillouin threshold and interference visibility, and greatly improving the noise of the hydrophone The consistency is of great significance to the engineering application of the optical fiber hydrophone remote transmission system.

Proceedings Article | 10 October 2020 Poster + Presentation + Paper

Vibration measurement technique for repeated fiber-optic hydrophone transmission cable system

Huichun Bian, Hanfeng Xu, Bo Ye

Proceedings Volume 11554, 115541C (2020) https://doi.org/10.1117/12.2573733

KEYWORDS: Fiber optics, Optical fiber cables, Vibrometry, Fiber optics tests, Ocean optics, Signal detection, Acoustics, Environmental monitoring, Environmental sensing, Geometrical optics

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Fiber-optic hydrophone can be used to monitor and detect the weak acoustic signal in the marine environment. It has the characteristics of high sensitivity, good frequency response and wide dynamic range. In order to detect the acoustic signal in the open sea, the repeated fiber-optic hydrophone transmission system is necessary to realize the long-distance transmission. Due to the unidirectional optical isolation of the repeater in the optical transmission path, the Rayleigh back-scattered light of the optical cable after the repeater cannot be returned to be detected, so there is no means to monitor the status of the optical cable after the repeater. In order to realize the monitoring of the vibration state of the submarine cable after the repeated fiber-optic hydrophone transmission systems, a vibration measurement technique based on the combination of distributed acoustic sensing(DAS) technology and the optical cross coupling technology between each amplifier pair of the repeater is proposed. In order to reduce the influence of optical surge caused by the returned optical pulse amplification, the multi-wavelength pulse of optical fiber hydrophone is used as the filling light pulse of distributed vibration detection. The Rayleigh back-scattered light with vibration information is amplified by the repeater through the cross-coupling path, then detected and demodulated by Heterodyne detection technology, and the vibration information is acquired. A distributed fiber-optic vibration sensing system for repeated fiber-optic hydrophone transmission system is established in the laboratory. The system can not only use the multi-wavelength light of fiberoptic hydrophone as the filling light of distributed vibration detection, but also filter the Rayleigh back-scattered light induced by the multi-wavelength light , so as to improve the signal-to-noise ratio of detection. The system can accurately locate the vibration of optical cable within 5km after the repeater in real time, and the maximum measured vibration frequency is 2kHz. The power spectrum density fluctuation at 1kHz is less than 2dB. The experimental results show that the coupling optical path does not affect the demodulation of the fiber-optic hydrophone array signal by the fiber- optic hydrophone demodulation system.

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