We experimentally investigated a simple and new technique for the fabrication of micro-ridge long-period gratings (MRLPGs) based on polarization-maintaining fibers (PMFs). The cladding region of the PMFs was etched periodically using a wet etching technique resulting in the periodic formation of micro-ridges on the surface of the PMF. The PMF-based MRLPGs has two resonant peaks because of the birefringence of the PMF. The extinction ratios of two resonant peaks of the PMF-based MRLPGs were effectively improved by increasing the applied strain because of the photoelastic effect.

We propose a refractive index sensor using Sagnac loop interferometers configured by using tapered polarizationmaintaining fibers (PMFs). Reduction of the PMF diameter results in enhancement of the ambient index sensitivity of the tapered-PMF-based Sagnac interferometer.

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Micro-ridge long-period fiber gratings (MRLPFGs) inscribed on a polarization-maintaining fiber (PMF) were demonstrated. The cladding region of the PMFs was periodically etched by using a wet etching technique, resulting in the periodic micro-ridges in the surface of the PMF. The PMF-based MRLPFGs has two resonant peaks because of the birefringence of the PMF. Two resonant peaks of the PMF-based MRLPFGs were generated by increasing the applied strain because of the photoelastic effect. The peak depth is only changed by increasing the external strain. It means that the proposed PMF-based MFLPFGs are very useful for the application to strain sensors.