Fabrication of DAST Channel Optical Waveguides

In order to use the large, electro‐optic coefficient of a nonlinear optical ionic crystal, 4‐(p‐dimethylaminostyryl)‐1‐methylpyridinium tosylate (DAST), a channel optical waveguide structure is needed. We successfully fabricated a waveguide using two methods: by a dry‐etching technique and by photo‐bleaching. Because DAST has a large optical loss, parts of the waveguide should be composed of a transparent polymer. We used photolithography and a reactive ion etching method to fabricate a serially grafted (conjunct) waveguide of DAST with a transparent polymer waveguide. The waveguide was also fabricated by photobleaching, whereby the refractive indices of the crystal’s a‐ and b‐axes were decreased by degrading the crystal. The cladding part of the DAST waveguide was photobleached by irradiating with UV light. The under‐ and over‐cladding layers of these channel waveguides were composed of a UV‐cured resin that did not dissolve the DAST crystal. The loss of the crystal waveguide for the crystal b‐direction was around 10 dB/cm, due to the scattering loss of the DAST single crystal. The large electro‐optic coefficients of the ionic crystal DAST (4‐(p‐dimethylaminostyryl)‐1‐methylpyridinium tosylate) can only be fully exploited with channel optical waveguides made in part of transparent polymers to cope with DAST’s large optical loss. Two fabrication methods, dry‐etching and photo‐bleaching, are examined. The Figure shows a waveguide with a UV‐bleached cladding and UV‐cured resin top and bottom layers.