UV-Inscription, Polarization-Dependant Loss Characteristics and Applications of 45° Tilted Fiber Gratings

We have UV-inscribed and theoretically and experimentally analyzed fiber gratings with the structure tilted at 45 degrees and implemented this type of devices as an in-fiber polarizer. A systematic investigation has been carried out on the characterization of 45 degrees tilted fiber gratings (45 degrees TFGs) in terms of the polarization-dependant loss (PDL) and thermal response. The detailed theoretical modeling has revealed a linear correlation between the grating length and the PDL, which has been proved by the experimental results. For the first time, we have examined the UV beam diffraction from a tilted phase mask and designed the UV-inscription system to suit the 45 degrees TFG fabrication. Experimentally, a 24 mm long 45 degrees TFG UV-inscribed in standard telecom single-mode fiber exhibited around 25 dB PDL at 1530 nm and an over similar to 300 nm bandwidth of PDL spectrum. By the concatenation method, a 44 mm long grating showed a PDL as high as 40 dB that is close to the high polarization extinction ratio of commercial products. Moreover, we have revealed that the PDL of 45 degrees TFGs has low thermal influence, which is desirable for real application devices. Finally, we experimentally demonstrated an all-fiber twist sensor system based on a 45 degrees and an 81 degrees TFG.