Micro ridge long-period fiber gratings inscribed on a polarization-maintaining fiber for measurement of strain

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.