Higher-order diffraction of long-period microfiber gratings realized by arc discharge method.

We report novel microfiber long period gratings (MF-LPGs) characterized by higher-order diffraction, which are fabricated using an arc discharge method. It is shown that an 11-period MF-LPG can exhibit an extremely high resonant dip (>30 dB) and a low transmission loss (<1.0 dB). A series of grating samples with elongated periods, from 400 μm to 1000 μm, and different diffraction orders have been fabricated and studied in contrast to the previously reported counterparts. The proposed structures have high reproducibility, stability, flexibility, and low production costs. Moreover, the resonant wavelength has a large refractive index (RI) sensitivity (up to ~3762.31 nm/RI-unit around RI = 1.383) and a very low temperature coefficient (~3.09 pm/°C at 1401.3 nm) for a structure with a diameter of 9.6 μm. The theoretical analysis shows good agreement with the experimental results. Our study should be useful for future applications of MF-LPGs in micro-scale in-fiber devices and sensors.