Ns-duration transient Bragg gratings in silica fibers

Abstract

We demonstrate, for the first time to our knowledge, fast all-optical switching in standard silica fibers, based on a transient Bragg grating. The grating is implemented in the fiber using an immunization photo-pretreatment process, followed by side illumination with femtosecond laser pulses through a suitable phase mask. Each pulse is nonlinearly absorbed, creating a thermal grating that is washed out by thermal diffusion. Reflections measured from such gratings are characterized by a very fast rise time, nanoseconds duration, and a high extinction ratio.

Femtosecond Transient Bragg Gratings

“…Fiber immunization extremely limits the grating buildup. We characterized the transient grating reflections of an immunized fiber [95]. After completing the photo-treatment process on a standard SMF at a pulse energy of 1 mJ, the pump laser pulse rate was lowered to 2 Hz in order to reduce the average thermal effects, and reflected pulses were measured with our detector.…”

“…The diffusion time is opposite to the square of the grating period; thus, working with first-order grating can reduce the time scale by a factor of four. The applicability to transient thermal grating for higher pulse rate and life time of such device is elaborated elsewhere [95].…”