Abstract
In this paper, we discuss about the optical phase measurement of optical fiber sensing system with coherent light sources by zero fringe homodyne interferometry (ZFM).
Authors present zero fringe integration method (ZFIM) as modified ZFM. Zero interference fringe is obtained by superimposing the optic axis, wavefront and polarization direction of the signal and reference optical waves. The optical phase of signal wave is evaluated by calculating the arctangent value of the intensity ratio of zero fringes with phase difference of π/2 each other. By using the sign of differential value of the arctangent function with respect to time, it is distinguished whether the optical phase is increasing or decreasing. The value of phase shifting range from zero to (1/2+n)π is obtained by summing the differential value and adding ±nπ to the summation, which plus and minus sign and the end of periode of phase shift n are determined by using the discontinuity of arctangent function.
Next, we manufactured the optical phase measurement apparatus for trial due to the ZFIM and experimentally examined the optical phase measurement by putting strain on the birefringent optical fiber length along. As the results, we measured the strain of 2.5×10-6-0.2×10-6, or the phase shift of 5.5-0.5 rad, and showed that ZFIM is useful for optical phase measurement of fiber sensing system by using homodyne interferometry.
