Fabrication and Measurement of Sidewall Gratings Integrated in Hybrid As2S3 -Ti:LiNbO3 Optical Waveguides

In this paper, we demonstrated the fabrication and measurement of sidewall gratings integrated in a hybrid type of optical waveguide: As₂S₃-Ti:LiNbO₃. This hybrid waveguide is constructed by patterning arsenic tri-sulfide (As₂S₃) strips on the midline of titanium-diffused channel waveguide in lithium niobate (Ti:LiNbO₃). Sidewall gratings are written on both sidewalls of As₂S₃ strips by electron beam lithography (EBL) with 3% PMMA resist and a dose 350 μC/cm ² at 50-kV electrons. The measured reflectance bandwidth was between 2.4 and 6.7 nm. Coupling coefficients ranging from 2.5 to 8.9 mm^-1 were obtained. A transmission peak with a 3-dB bandwidth of ~0.25 nm was observed in the rejection band of a 432 μm-long phase-shifted sidewall grating. Such sidewall gratings integrated in hybrid As₂S₃-Ti:LiNbO₃ waveguide can be used for numerous integrated optical devices including optical filters, switches, modulators, lasers, sensors, and wavelength division multiplexing (WDM).