Long-period fiber-gratings produced by exposure with a low-pressure mercury lamp and their sensing characteristics

A new production method of long-period fiber-gratings using neither a laser nor a fine-positioning system was proposed. A low-pressure mercury lamp emitting 254 nm ultraviolet light was used as a light source. Hydrogen-loaded Ge–B co-doped fiber was exposed to the emission of the lamp through an amplitude mask. A coupling loss up to 23 dB was obtained for a grating period of 212 μm. The maximum coupling loss for a grating period of 460 μm was 18 dB. The growth rate of the refractive index change by mercury-lamp exposure was 1.3 × 10−4/h. The temperature and strain characteristics were measured and compared with those fabricated by excimer-laser exposure. The temperature and strain sensitivities of long-period gratings with a period of 212 μm were higher than those of 460 μm. The temperature and strain sensitivities of those by mercury-lamp exposure were almost equal to those by excimer-laser exposure of the same fiber. The sensitivities of those by excimer-laser exposure of non-loaded fiber were higher than those of hydrogen-loaded fiber by mercury-lamp or excimer-laser exposures except for the temperature sensitivity of a grating period of 460 μm.