High-index overlay for high reflectance DBR gratings in LiNbO3 channel waveguides

A thin overlay of high refractive index material is used to obtain high reflectance DBR waveguides in lithium niobate. Silicon, deposited by e-beam evaporation, is found to be a suitable material for this purpose because of its high refractive index, transparency to 1.3- and 1.5-μm wavelengths, opacity to the visible spectrum, and ease of etching. Experimental results match the theory extremely well and, to the best of our knowledge, exhibit the highest reflection per unit length from a lithium niobate corrugated waveguide reported to date on on insulator technology, waveguide filters.