Sensing Characteristics of a Novel Two-Section Long-Period Grating

The behavior of a temperature self-compensating, fiber, long-period grating (LPG) device is studied. This device consists of a single 325- (mu)m-period LPG recorded across two sections of a single-mode B-Ge-codoped fiber – one section bare and the other coated with a 1- (mu)m thickness of Ag. This structure generates two attenuation bands associated with the eighth and ninth cladding modes, which are spectrally close together ( ~60 nm). The attenuation band associated with the Ag-coated section is unaffected by changes in the refractive index of the surrounding medium and can be used to compensate for the temperature of the bare-fiber section. The sensor has a resolution of +/-1.0 * 10^-3 for the refractive index and +-0.3 (degree)C for the temperature. The effect of bending on the spectral characteristics of the two attenuation bands was found to be nonlinear, with the Ag-coated LPG having the greater sensitivity.