Direct write of optical waveguides on chalcogenide thin films using electron beams

Electron beam induced reliefs in $Ge0.2Se0.8$ thin films deposited by pulsed laser deposition on oxide coated silicon wafers are fabricated for the direct write of rib optical waveguides at telecommunication wavelengths. The physical dimensions of the reliefs are experimentally determined as a function of electron beam exposure conditions. Relief heights in excess of three times the initial film thickness are achieved. The lateral translation of the thin film material is observed to be of the order of tens of microns for relatively slow beam scan rates. Numerical simulations based on a full-wave finite element eigenmode analysis support the existence of single mode guided waves. The surface roughness of the optical waveguides, dominated by the pulse laser deposition process, is reduced to approximately $1nm$ by planarization of the thin film, via thermal embossing, prior to electron beam exposure. A bidirectional writing scheme is implemented to remove variations in relief heights observed at waveguide terminations. Nonuniform electron beam exposures are used to demonstrate three-dimensional waveguide tapers useful for the realization of fiber-to-waveguide optical transitions.