High performance phase demodulator for interferometric optical fiber sensor using novel ameliorated PGC algorithm

Abstract

ABSTRACT We demonstrate a high performance phase demodulator for interferometric optical fiber sensor using novel ameliorated PGC algorithm. Theoretical and experimental resu lts show that the novel ameliorated PGC algorithm has the high stability of resist rapid change of light and low harmoni c distortion advantages. Experiment results show that phase demodulator has a resolution of 2×10 -5 rad / ¥ Hz, a dynamic range of 112 dB @ 50 Hz, a linearity of better than 0.9999 and a THD of below 0.1 %. Keywords: phase demodulator,phase generated carrier (PGC),interferometric optical fiber sensor, harmonic distortion 1. INTRODUCTION Interferometric optical fiber sensors have attracted considerable research interest due to their advantages of high sensitivity, high stability, high linearity, and easiness of multiplexing [1-3]. The measurands are recovered by a phase demodulator from the phase shift of the interferometric optical fiber sensor. A high performance phase demodulator with high resolution, large dynamic range, high linearity and low distortion is essential for signals detection in the field applications of sonar systems, seismic de tection and natural resources exploration. The high resolution phase demodulator for interferometric optical fiber sensor is based on interferometry. An interferometric optical fiber sensor is employed to convert the external signal into the phase shift [2, 3]. Several phase demodulation schemes have been reported, including active homodyne, passive homodyne using a 3×3 coupler or phase generated carrier (PGC), and heterodyne [4-6]. The PGC demodulation scheme is considered as the most widely used method among them due to the distinct advantages of high resolution, large dynamic range, good linearity, and the capability of real-time demodulation for large-scale interferometric optical fiber sensors array. In the PGC demodulation scheme, a high-frequency sinusoidal phase modulation is applied to the tunable laser to generate a phase carrier,which up-converts the desired phase-shift signal onto the sidebands of the carrier frequency. By detecting one odd harmonic and one even harmonic of the PGC interference signal, a pair of quadrature components containing the phase-shift signal are then acquired, with which the bias-induced-fading can be overcome. To recover the phase shift of interferometric optical fiber sensors from the quadrature components, the traditional PGC algorithm employs the differential-and-cross-multiplying approach (PGC-DCM)[7] or the arctangent approach (PGC-Arctan)[8]. However, the PGC-DCM algorithm is correlated with the li ght intensity and has poor stability[9], while the PGC-Arctan algorithm has serious harmonic distortions when the PGC modulation depth C deviates from 2.63 ra d. Recently, we have proposed a novel ameliorated PGC algorithm based on arc cotangent function and differential-self-multiplying (PGC-Arccot-DSM), which has both low harmonic distortion and high stability. In this paper, we demonstrate a high performance phase demodulator for interferometric optical fiber sensors using novel ameliorated PGC-Arccot-DSM algorithm. The principles and the corresponding experimental system are presented. The performances of the phase demodulator are demonstrated, including phase resolution, dynamic range, linearity and total harmonic distortions (THD).