An ultrahigh sensitivity polarimetric strain sensor is proposed based upon a four-layer D-shaped optical fiber and surface plasmon resonance (SPR) technology. In contrast to existing SPR-based sensors, which are based on changes in the refractive index of the overlayer, the sensor proposed in this study is based on the change in the refractive index of the fiber core in response to the application of an axial load. Specifically, the phase difference between the P and S waves after passing through the sensor under SPR conditions is measured using a common-path heterodyne interferometer and is used to determine the corresponding change in the refractive index of the core, from which the strain is then inversely derived. The experimental results show that the sensitivity of the proposed sensor is around 2.19×10⁴ deg/ε, i.e., degree/strain. By contrast, that of a conventional (non-SPR) polarimetric fiber sensor is just 5.2×10² deg/ε. To the best of the authors' knowledge, the sensor proposed in this study represents the first reported attempt to exploit the refractive index change of the core of an SPR-based fiber sensor for strain measurement purposes.

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In this study, we adopted common path heterodyne interferometer to measure the optical parameters of linear birefringence materials. The sample is a multiple order quartz quarter-waveplate and six optical parameters including the principal axis, phase retardation, order, thickness and the refractive indices (n. and no) of II waveplate are extracted by using the sequential measurements with two experimental setups.Furthermore, in order to promote the techuique in the fuIl field measurement, we apply CCD (charge couple device) as a detector triggered by CPLD (Complex Programmable Logic Device). The full-field information can be calculated by measuring three frames of the CCD image sequentially. In this paper, we not only successfully obtain six optical parameters in a single point detection, but also the principal axis and phase retardation in a full-field measurement are achieved.

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