All-optical control of Bragg grating in semiconductor-coated D-shaped fiber.

A Bragg grating was fabricated in a D-shaped fiber that was subsequently coated with an alpha-Si:H semiconductor film. The reflected spectrum was optically controlled by means of evanescent coupling, shifting to shorter wavelengths with increased control-light power. The effective nonlinearity of the fiber was 2.0 x 10(-10) cm(2)/W . The device was optically tuned by 4.3 x 10(-4) nm/mW , leading to 54% (>3-dB) depth modulation for 230 mW of power.

Embedded fiber-optic sensor utilizing the modal power distribution technique.

The modal power distribution technique is applied to a multimode optical fiber embedded in a three-dimensional composite material for real-time characterization and monitoring of the structure. The measurements on the modal power distribution within these fibers, and the subsequent redistribution induced by external perturbation, indicate that the modal power distribution technique is more sensitive than the intensity-modulation technique for smart-structure characterization.