Low-coherence interference demodulation method based on monochrome frequency absolute phase

Abstract

The invention provides a low-coherence interference demodulation method based on a monochrome frequency absolute phase, belonging to the field of optical fiber sensing. The low-coherence interference demodulation method based on the monochrome frequency absolute phase is widely applied to measurements of various static physical quantities, such as temperature, pressure, displacement and refractive index, and detection of object three-dimensional feature. According to the method, a Fabry-Perot sensor is selected as a sensing element for sensing external air pressure intensity variation, an optical wedge is used as an optical path difference space scanning element, and interference strips are formed in a partial area with an optical path difference of zero. The low-coherence interference demodulation method comprises the following steps of: firstly, carrying out Fourier conversion on an interference signal to obtain phase information which is aliased within a section of (-pi, pi); then selecting a phase with a standard frequency as a reference phase, carrying out phase unwrapping according to frequency-phase monotonous properties, and carrying out linear least-squares regression on the unwrapped phase so as to obtain a fitting straight intercept; and finally, dividing the intercept by an integer part of 2*pi, so as to obtain an interference order of a reference frequency; and finally, obtaining the absolute phase of the reference frequency by combining a relative phase obtained through the Fourier conversion. Therefore, the demodulation is realized.

Description

technical field [0001] The invention relates to a low-coherence interference demodulation method based on the absolute phase of monochromatic frequency, which belongs to the field of optical fiber sensing. Background technique [0002] Low-coherence interferometry can overcome the phase ambiguity problem in laser interferometry, and the measurement range is no longer limited to λ / 4. Theoretically, it has an unlimited measurement range, and can measure many absolute physical quantities with high precision and a large range, making low-coherence interferometry Technology has been widely used in the field of optical fiber sensing, such as the measurement of static physical quantities (temperature, pressure, displacement and refractive index), three-dimensional appearance detection of objects and optical coherence tomography. [0003] Locating the envelope peak position or center peak position of the low-coherence interference fringes is a commonly used method to obtain the tran...

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Problems solved by technology

However, the accuracy obtained by directly using the phase slope for demodulation is often not high, and the phase of the monochromatic frequency is directly related to the displacement caused by the measured physical quantity, and can be obtained by discrete Fourier (or phase shift algorithm), but after discrete Fourier transform, The phase aliasing of the phase in the (-π, π) interval, there is 2π or the uncertainty of the interference order, so the interference order must be determined first to recover the absolute phase, so the recovery of the absolute phase or the determination of the interference order is very important question

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