Long-period gratings based on specialty fibers regardless of photosensitivity

We investigate a new fabrication technique for LPFGs by using a surface imprinting or a micro-tapering technique. Transmission characteristics of surface LPFGs deposited on a D-shaped PCF strongly depend on input polarization states, which makes possible to discriminate ambient index and temperature sensitivities. A micro-ridge LPFG fabricated by a micro-tapering method has distinct transmission characteristics based on the photoelastic effect. The strain sensitivity of the micro-tapered LPFGs can be improved by reducing their diameter. We also investigate the effect of the tapered diameter on the sensitivities of the micro-tapered LPFGs.