Research Of The Large-evanescent-field Polarization-maintaining Fiber Sensors Based On The Chemical-etching And Fiber Tapering Techniques

Polarization-maintaining fiber plays an important role in both optical communications and sensing areas. In recent years, polarization-maintaining optical fiber with the large evanescent field has attracted much attention due to its high birefringence and sensitivity. In this article, we investigate three kinds of polarization-maintaining fiber sensors by using the chemical etching and fusion tapering techniques. The spectral responses to external refractive index, temperature, and strain for the proposed structure are measured and analyzed, respectively.Firstly, we demonstrate the evolution of the Bragg gratings inscribed in Panda fiber s with chemical etching. The resonance wavelengths can blueshift with cladding reduction similar to the conventional counterparts. When the stress-applying parts of the fiber are removed, the finalizing grating can be exploited for the temperature-independent refractive index sensing, since the modes corresponding to the two polarizations exhibit the dissimilar responses to the external refractive index change but the same response to temperature.Secondly, we investigate the effects of etching the long period gratings in Panda fibers on the spectral characteristics. We fabricate an LPG in a hydrogen-loaded Panda fiber using the point-to-point writing technique with the help of a 193-nm excimer laser. The wavelength shifts with cladding reduction are demonstrated and the responses to external refractive index change are measured.Finally, a micro-fiber interferometer based on fiber taper modal interferometers proposed. We analyze the spectral characteristics of the interferometer and demonstrate the spectral responses of the structure to external refractive index, temperature, and strain, respectively. With the Fourier transform, it is possible to achieve both the refractive index and temperature responses simultaneously.