Sensing properties of Bragg grating in highly birefringent and single mode photonic crystal fiber

Microstructured fibers (MOF), also called photonic crystal fibers (PCF), constitute a class of optical fibers, which has a large potential for number of novel applications either in the telecom or in the sensing domain. However, some of the applications require the use of specialty fibers with a doped core. We have made a preliminary exploration of PCF with doped regions and with inscribed Bragg gratings. The extensive study of the fiber cross-section structure in respect to possibilities of writing the Bragg gratings and the sensitivities of PCF Bragg gratings was our main concern. Selective measurement of strain without temperature compensation is achieved with fiber Bragg grating (FBG) in highly birefringent (HB) PCF, since such grating is characterized by two reflection bands corresponding to the two polarization modes generated due to the fiber birefringence. The measurement range of such FBG in HB fiber sensor depends on how strong is the separation of the polarization modes, which is expressed as phase birefringence. In next step, we have modeled, designed and fabricated specialty PCF with Ge doped core in such way that after writing the Bragg grating into the fiber we have obtained a sensors exhibiting low sensitivity to any temperature drifts. Traditional optical fiber sensors are not able to make such a distinction between stress and temperatures and require complex temperature compensation mechanisms.