Fabrication of nonlinearly shaped optical waveguide tapers on InP with precise design-parameter control

An entirely integrated reliable and low-loss interconnection between an InP-based optoelectronic circuit and a single-mode optical fiber is presented. This spot transforming device is characterized by a two-layer buried waveguide with laterally tapered geometry. Investigations of the characteristics of the negative tone electron beam resist AZ PN 114 show that it is possible to transfer almost any arbitrary shape of an optical waveguide with a width between 80 and 1200 nm to a directly written mask for dry etching without proximity correction or sophisticated writing strategy. The geometries can be maintained to within 20 nm with respect to the structure design. During subsequent reactive ion etching steps for the InGaAsP-waveguide layers, a very precise etch depth control by a process ellipsometer is possible in the range of 5 nm or less. Optical measurements confirm the spot-size transformation characteristics of our taper device.