Reflectivity-tunable fiber Bragg grating reflectors

We report a novel device that modulates the Bragg reflectivity of a fiber grating by exciting the transverse vibration of the fiber through an acoustic wave. The excitation of the transverse vibration, leading to fiber microbending, induces the coupling of the fiber core mode into cladding modes. This leads to the reduction of core-mode power and hence that of Bragg reflection. This mechanism provides us a means to control the reflectivity after a fiber Bragg grating is fabricated. The numerical results based on a simple micro-bending model agree well in trend with the experimental data.