DESIGN AND FABRICATION OF MONOLITHIC OPTICAL SPOT SIZE TRANSFORMERS (MOSTS) FOR HIGHLY EFFICIENT FIBER-CHIP COUPLING

A novel type of monolithic optical spot size transformer realized in t he InP/InGaAsP material system combines many desirable features like h igh fiber-chip coupling efficiency, large spot size transformation, hi gh tolerances for fiber alignment, simple fabrication, and straightfor ward integrability with other devices. The spot size transformation is accomplished by two waveguide sections tapered in the vertical and la teral directions, respectively. We discuss design issues, describe the fabrication process, give experimental results, and present the monol ithic integration of the spot size transformers with a current control led directional coupler switch.