A novel flexible, reliable and easy to use technique for the fabrication of optical spot size converters for InP based PICs
Spot size converters (waveguide tapers) are key elements for photonic integrated circuits (PICs) since they significantly reduce the effort and cost of the device packaging. In comparison to other technologies like micro lenses or lensed fibres the implementation of spot size converters can also reduce the optical insertion loss of the devices. The basic technological challenge is the fabrication of a vertical ramp with a maximum height of around 1 mu m and a length of 500-1000 mu m. Several approaches to form this ramp have been reported including shadow mask etching, shadow mask epitaxy and selective area growth. All this methods have in common that they require special processes which are rather complicated, expensive and inflexible in terms of tailoring of the ramp profile. In this paper, we present a novel method for the fabrication of spot size converters which can produce almost arbitrary taper profiles and requires only standard lithography and etching processes and can therefore easily be implemented into standard waveguide processes.