Enhanced photonic bandgap in ion-implanted lithium niobate waveguides by improving index contrast

We report on utilizing focused ion beam milling and selective wet-etching techniques to enlarge the optical barrier in helium ion-implanted lithium niobate single crystals. We realized a high-efficiency narrow-bandwidth photonic band filter by introducing an air cavity as the optical barrier on a waveguide portion. The air cavity was created beneath the Bragg gratings (1-D photonic crystals) to strengthen the light confinement and optical response. The experimental performance of photonic crystals with and without air cavity is presented and compared with the theoretical modeling. These photonic crystal devices with high refractive-index contrast make a further step towards ultracompact optical circuit integration and applications based on single crystals.