Tunable optical filters at telecom wavelengths by interband photorefractive gratings

We present a novel holographic wavelength filter that is based on interband photorefraction. we use an acousto-optic deflector to control the direction of the recording beams and the spacing of the UV induced photorefractive grating. We achieve narrow bandwidths (FWHM=0.13 nm) required for DWDM applications as well as fast tuning times. Experiments were performed with pure potassium niobate crystals, but with the same approach, other crystals that exhibit interband photorefraction can be used for tunable filters as well, in particular materials where interband photorefraction at visible recording beam wavelengths.