We demonstrate a novel kind of tunable optical delays based on dynamic grating generated
by Brillouin scattering in an optical fiber. An axial strain gradient is applied to a 15 m section
of a polarization-maintaining fiber, and the Brillouin reflection grating is generated positionselectively
by controlling the optical frequencies of Brillouin pump waves. Tunable time
delays of up to 132 ns are achieved with an 82 ns Gaussian pulse.
An optical fiber sensor to simultaneously measure strain and temperature was designed and embedded into an adaptive composite laminate which exhibits a shape change upon thermal activation. The sensor is formed by two fiber Bragg gratings, which are written in optical fibers with different core dopants. The two gratings were spliced close to each other and a sensing element resulted with Bragg gratings of similar strain sensitivity but different response to temperature. This is due to the dependence of the fiber thermo-optic coefficient on core dopants and relative concentrations. The sensor was tested on an adaptive composite laminate made of unidirectional Kevlar-epoxy pre-preg plies. Several 150μm diameter pre-strained NiTiCu shape memory alloy wires were embedded in the composite laminate together with one fiber sensor. Simultaneous monitoring of strain and temperature during the curing process and activation in an oven was demonstrated.