A Demodulation Method of Spatial Domain for Low-Coherence Interferometry With High Accuracy and Adaptability

Chao Wang,Xuezhi Zhang,Kun Liu,Tiegen Liu,Yuanyao Li,Shuang Wang,Junfeng Jiang

doi:10.1109/jphot.2020.2977839

Chao Wang, Xuezhi Zhang + Show 5 more

Open Access

https://doi.org/10.1109/jphot.2020.2977839

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Abstract

A demodulation method of spatial domain based on low-coherence interferometry is proposed. The original signal of spatial domain acquired by linear CCD is filtered with all-phase filter to obtain the fringe pattern, and the phase signal of the spatial frequency domain is retained after filtering. The fringe pattern analysis is employed to avoid phase ambiguity and realize large measurement range in demodulation. Afterwards, using the centroid position of the fringe, the peak position of a single fringe pattern can be obtained, and finally the accurate peak position is calculated with seven-step phase-shifting interferometry. The demodulation method is demonstrated experimentally with Fabry-Perot sensing system. At room temperature, it is proved that the full-scale measurement error is less than 0.019% in the range of 11 kPa to 290 kPa. From −20 °C to 70 °C, the accuracy is stable and the maximum error is less than 0.054 kPa. The demodulation method has the potential to enhance the measurement accuracy and adaptability in actual environment for universal applications.

Highlights

IntroductionDue to the character of absolute distance measurement, low-coherence interferometry (LCI) is widely applied for geometric measurement [1]–[3], optical coherence tomography (OCT) [4], [5] and detection of physical quantity that can be converted to absolute distance in the field of fiber sensing [6]–[8]
Due to the character of absolute distance measurement, low-coherence interferometry (LCI) is widely applied for geometric measurement [1]–[3], optical coherence tomography (OCT) [4], [5] and detection of physical quantity that can be converted to absolute distance in the field of fiber sensing [6]–[8].Up to now, fringe pattern analysis and phase-based algorithm are two primary means of LCI demodulation
When the optical path difference (OPD) generated by the wedge is the same as twice the cavity length of F-P sensor, the LCI fringe appears on the corresponding position of CCD

Summary

Introduction

Due to the character of absolute distance measurement, low-coherence interferometry (LCI) is widely applied for geometric measurement [1]–[3], optical coherence tomography (OCT) [4], [5] and detection of physical quantity that can be converted to absolute distance in the field of fiber sensing [6]–[8]. Fringe pattern analysis and phase-based algorithm are two primary means of LCI demodulation. Fringe pattern analysis employed pattern position of the LCI fringe for demodulation, such as envelope [9] or peak position [10], [11]. This method requires much less computation than.

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