Grating-assisted codirectional coupler filter using electrooptic and passive polymer waveguides

We propose and demonstrate a band-rejection filter based on grating-assisted forward coupling between an electrooptic (EO) polymer waveguide and a passive polymer waveguide. The passive polymer waveguide is used as a low-loss optical path, and the EO polymer waveguide is used for dropping the optical signal at a given wavelength. The grating is etched on top of the EO polymer waveguide, which satisfies the phase-matching condition for the power exchange between the two asynchronous waveguides. Using the grating with a period of 63.4 μm, we achieve significant power exchange between the two waveguides with a 3-dB bandwidth of 4.4 nm at a wavelength of 1533 nm. Next, we demonstrate that photobleaching may be effectively used as a permanent tuning method of the center wavelength in fabricating the proposed device. The center wavelength for the maximum coupling can be adjusted in a range of more than 25 nm by photobleaching without extra loss. Lastly, we investigate changes of the filter characteristics induced by poling and demonstrated wavelength tuning by the poling-induced EO effect