Bragg Gratings in Suspended-Core Photonic Microcells for High-Temperature Applications

We report a novel type-II photonic crystal fiber Bragg grating for high-temperature applications. The Bragg grating is inscribed in a low-loss in-fiber structure named suspended-core photonic microcell, which is postprocessed from a commercial pure-silica photonic crystal fiber. Grating samples with core diameters of about 4 μm were made by using a focused near-infrared femtosecond laser and a phase mask, and then tested in a tube furnace from room temperature to about 1200 °C. The thermal response of the Bragg resonant wavelength was measure to be about 12 and 16 pm/°C, respectively, at the temperature around 100 °C and 1000 °C. The grating spectrum remained stable in a 10-h isothermal annealing at 1000 °C and started decaying at about 1120 °C with the rate of about 0.02 dB/min. This type of grating possesses flexibilities in both waveguide and grating structure design, exhibits good high-temperature performance, hence would be promising platform for building wavelength-division-multiplexed fiber sensors and tunable devices with a wide working temperature range.