Response of fiber-optic long-period gratings operating near the phase-matching turning point to the deposition of nanostructured coatings

The response of the dual resonant bands of a fiber-optic long-period grating operating near the phase-matching turning point to the deposition of a nanostructured coating is investigated. The dual central wavelengths of the resonant bands are observed to show a high sensitivity to the thickness of the coating but with opposite signs. Appropriate design of the device, based on the grating period, the refractive index and thickness of the coating, and the fiber composition, can allow the sensitivity of the central wavelengths of the dual resonant bands to the optical thickness of the coating to be optimized. A sensitivity of 1.45 nm/nm is observed experimentally. (C) 2008 Optical Society of America.