Dual-wavelength nonlinear sound pressure demodulation method and system for fiber optic fabry-perot hydrophone

Abstract

The invention discloses a dual-wavelength nonlinear sound pressure demodulation method and system of an optical fiber Fabry-Perot hydrophone, belonging to the technical field of optical fiber sensing. The method includes the following steps: 1) Obtain two reflection spectra; 2) Set the operating wavelengths of the two lasers, and determine the initial phase respectively; 3) Phase conversion of the reflection spectrum, curve fitting and solving the inverse function; 4) Calculate the optical phase respectively The amount of change is to determine the amount of change in the cavity length; 5) demodulate the nonlinear sound pressure according to the coupling model. The dual-wavelength nonlinear sound pressure demodulation method and system of the optical fiber Fabry-Perot hydrophone provided by the present invention has no theoretical sound pressure demodulation upper limit, high demodulation accuracy, overcomes phase ambiguity, flexible demodulation, and can correct the demodulation results Accuracy gives evaluation and other advantages.

Description

technical field [0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to the sound pressure demodulation technology of a hydrophone. Background technique [0002] High intensity focused ultrasound (HIFU) has received extensive attention in recent years and has developed rapidly. First of all, HIFU can be used as a new research platform in the fields of medicine, physics, chemistry and materials science. Secondly, HIFU is an extreme condition in the field of acoustics. Its major innovative research in various fields is no less than the extreme conditions that we are familiar with, such as ultra-high pressure, ultra-vacuum, strong magnetic field, strong radiation, high and low temperature. It is of great significance to promote the development of science and technology and social economy in our country. As the sound pressure is the core parameter of HIFU, it is extremely important to accurately measure and demodulate the soun...

AI Technical Summary

Problems solved by technology

But this method also has the following disadvantages: 1) Since the linear range is very narrow, the sound pressure demodulated after exceeding the linear range is obviously smaller than the actual sound pressure, resulting in large calculation errors; 2) Since it is a linear demodulation method, There is an upper limit for interference signal output, so there is an upper limit for sound pressure demodulation; 3) There is a phase ambiguity problem, that is, when the phase change caused by sound pressure is near the extreme point, the slight change of the phase of the fiber optic Fabry-Perot hydrophone will be extremely Insensitive, small changes in the phase hardly cause changes in the interference signal, and it is also impossible to determine whether the change in the phase is increasing or decreasing; 4) It cannot be demodulated flexibly, because the positive and negative sound pressures are usually asymmetrical, the positive and negative sound pressure The cavity length increase and cavity length decrease are also different, resulting in a large gap in the output signal; 5) It is impossible to evaluate the accuracy of the demodulated sound pressure results

Limited by these five problems, the optical fiber Fabry-Perot hydrophone is greatly limited when it uses the best linear bias point direct measurement method for sound pressure demodulation

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