Dependence of the Transmission Characteristics of Versatile D-shaped Fibers on Temperature and Ambient Index Changes for Different Input Polarization States

We investigate the dependence of the transmission characteristics of versatile D-shaped fibers on temperature and ambient index changes for different input polarization states. Various D-shaped fibers with different surface structures, such as a thin layer and periodic surface gratings, were fabricated by coating a photoresister (PR.) on the surface of a D-shaped fiber. For the D-shaped fiber with a thin layer, a TE mode has a higher temperature sensitivity than a TM mode because the TE mode has a continuous tangential electric field at the boundary between the surface of the D-shaped fiber and the thin layer whereas the TM mode has a discontinuous electric field at the boundary between the two regions. For the D-shaped fiber with periodic surface gratings, the TE mode also has a higher temperature sensitivity than the TM mode. The temperature sensitivity of the D-shaped fiber with periodic surface gratings is higher than that with a thin layer because of the large surface area of the PR affected by the external temperature change. We also measure the sensitivities of two D-shaped fibers to the ambient index change. For the D-shaped fiber with a thin layer or periodic surface gratings, the sensitivity of the TM mode to the ambient index change is higher than that of the TE mode because the evanescent field of the TM mode is more sensitive to the external index change than that of the TE mode