FABRICATION OF OPTICAL BEAMWIDTH TRANSFORMERS FOR GUIDED-WAVES ON INP USING WEDGE-SHAPED TAPER STRUCTURES

A waveguide device is proposed for spot-size transformation of an optical beam from the 1-mu-m range to about 8-mu-m using a wedge-shaped taper. The structure can be entirely integrated on an InP-based optoelectronically integrated circuit. It is shown by numerical simulation that the width of the thin end of the wedge has a major influence on the transformation loss of such a device. By using direct writing e-beam lithography and reactive ion etching as well as subsequent InP regrowth, we were able to produce the required structures. The beamwidth transformation capability is confirmed by optical measurements.