High reflectance DBR gratings in LiNbO3 channel waveguides for WDM applications

We have proposed and implemented a new concept for fabricating high reflectance DBR grating channel waveguides in materials such as LiNbO₃ which bypasses many of the problems associated with previous techniques. First, annealed proton exchanged channel waveguides were fabricated on the surface of a LiNbO₃ substrate using a standard process. Next, we deposited 1800 A of silicon on the surface by e-beam evaporation. A first-order grating (with a period of 359 nm) was formed on the surface of the silicon with commercial photoresist and standard holography using an argon laser at λ=457.9 nm. The grating was transferred to the silicon layer by RIE. No additional buffer layer was added. Our preliminary results show higher reflection than any other previously reported. The optimized process is expected to find applications in commercially viable devices. These include key devices of WDM systems such as tunable rare-earth doped DFB lasers, modulators, and tunable filters; as well as SHG devices