SPOT SIZE TRANSFORMER WITH A PERIODICALLY SEGMENTED WAVE-GUIDE BASED ON INP

We report what is to our knowledge the first optimization of a spot si ze transformer by use of a periodically segmented waveguide for photon ic integrated circuits based on InP. It is shown that a nonlinear vari ation of the segmentation ratio along the propagation direction allows one to make an adiabatic transition of a short length. A simple metho d based on the study of a beveled edge transition is presented for the optimization of such a device. Internal losses in the transition regi on as low as 1.2 dB are obtained between a coupling waveguide and a si mple heterostructure waveguide, with a very high transition spot size expansion factor.