All-optical tunable filter with photorefractive planar waveguide and suppression of crosstalk by apodized grating via photorefractive two-wave mixing

Abstract

The wavelength division multiplexing (WDM) technology effectively increases the bandwidth capacity of a communication line without installing additional fibers and increasing data bit rate to high levels. Optical add-drop modules are key components in WDM optical networks. We propose two types of all-optical tunable filter with a photorefractive planar waveguide. The photo-induced index grating in the PR waveguide by control beams drops off a part of wavelength components in the WDM signal beam. It make possible to select the wavelength components of the signal beam by optically adjusting the wave vector of the grating. It is also possible to control bandwidth of the output signal by adjusting the broadening of the grating in the waveguide. The photorefractive effect is known as one of the most efficient nonlinear effects, and therefore the device is controllable by the relative low beam power comparing with the conventional devices using non-linear optical effects. The channel crosstalk is generated by using uniformly broadened index grating. We note that the nonreciprocal energy transfer between the two control beams via a photorefractive two-wave mixing causes the nonuniform index grating like Gaussian profile. We therefore suggest the suppression method of channel crosstalk by adjusting the incident intensity of the control beams.