NOVEL OPTICAL WAVEGUIDES : FROM DIELECTRIC TO PLASMONIC

Abstract

Lithium niobate is an important material for fabricating optoelectronic devices due to its novel optical properties especially the high electro-optical coefficient. However, it is quite difficult to etch this material due to its poor reactivity with common etchants and selectivity issues. In this work, an elegant way of fabricating suspended waveguides in lithium niobate is developed. Using combined techniques, monolithic fabrication of strip waveguides and photonic crystals is available in bulk lithium niobate now. A symmetric cladding structure (air-lithium niobate-air) can be formed once the buried sacrificial layer introduced by ion implantation is removed by chemicals, resulting in significantly enhanced light confinement in the waveguide as well as dramatically reduced propagation losses. The influence of waveguide sidewall on device performance is also investigated in detail. Ultra-high aspect ratio (50:1) photonic crystals are fabricated. Subsequently, all the novel structures realized in lithium niobate are introduced to noble metals, leading to fascinating plasmonic waveguides. Such devices have found important applications in developing nanophotonics and integrated optics. As typical examples, color filters under transmission and reflection testing modes are demonstrated using nanorings and rods, respectively. In particular, the nanorod color filter could be applied in digital light processing techniques since each mirror or pixel can be made very small to achieve a high resolution. More interestingly, a pronounced plasmon induced resonance peak is observed in symmetric plasmonic patterns with ultra-small gaps which can find important applications in plasmon-assisted sensing and imaging.