Azobenzene liquid-crystalline polymer for optical switching of grating waveguide couplers with a flat surface

Grating waveguide couplers with a flat surface were fabricated in an azobenzene liquid-crystalline polymer film by holographic lithography using Ar + laser beams at 488 nm. When a probe beam at 633 nm was incident to one grating of a grating waveguide coupler, the beam propagated in the waveguide and an output beam came out from the other grating with the throughput coupling efficiency of ≈5%. Upon irradiation of the film between two gratings with UV light to cause trans-cis photoisomerization of the azobenzene moiety, the intensity of the output beam was repeatedly switched. It was found that the alternating irradiation at 366 and 436 nm induced reversible changes in the intensity of the guided probe beam.