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-microm-period LPG recorded across two sections of single-mode B-Ge-codoped fiber--one section bare and the other coated with a 1-microm thickness of Ag. This structure generates two attenuation bands associated with the eighth and ninth cladding modes, which are spectrally close together (approximately 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 x 10(-3) for the refractive index and +/-0.3 degrees 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.