편광상이 배치구조 기반 광섬유 필터 및 응용에 대한 연구

Abstract

This thesis proposes and implements optical fiber filters based on a polarization-diversity loop configuration (PDLC) and their applications. As their applications to optical communication systems and optical fiber hydrogen detection sensors. As applications to optical communications, a fiber Bragg grating (FBG) filter was proposed to demonstrate an inline conversion between transmission and reflection spectra of an FBG without reconfiguration of the filter structure containing the FBG. The proposed apparatus consists of a polarization beam splitter, an FBG, and two quarter-wave plates (QWP’s). Without requiring rearrangement of input/output ports or additional optical switches, the spectral switching operation of the FBG was carried out through proper adjustment of the QWP’s contained in the proposed filter. Further, an enhanced spectral conversion of an FBG was also demonstrated with increased degree of freedom in polarization control through addition of a half-wave plate. All the proposed filters were fabricated, and the theoretical prediction was verified by experimental results. As another application to optical fiber sensors, an optical fiber sensor for hydrogen leak detection was proposed and demonstrated by using a polarization-maintaining fiber (PMF) coated with palladium thin film. The sensing mechanism of the proposed sensor is based on mechanical stress induced by the palladium coating when it absorbs hydrogen. The stress generated by the palladium coating stretches the PMF along the longitudinal direction changing its birefringence and thus shifts the interference spectrum of the comb filter composed of the PDLC, the PMF, and the waveplates.