Studies on the butt-coupling of InGaAsP-waveguides realized with selective area metalorganic vapour phase epitaxy

Abstract

A method for the characterisation of the process-induced optical loss in butt-coupled passive waveguides will be described. In principle the results are valid for any active-passive waveguide butt-coupling as well (e.g. laser-waveguide). The method was applied to butt-coupled waveguides, which were grown by selective area metal organic vapour phase epitaxy (MOVPE). Different etching procedures for the preparation of the masked mesa stripes were examined, which considerably influenced the regrowth behaviour close to the mesa edge. The optical loss at the interface was found to depend primarily on the thickness difference of the waveguides. The excess layer thickness due the regrowth near the mesa is proportional to the width of the masked stripe. It reaches a factor of 1.7 at 50 μm wide stripes and decreases exponentially with distance from the stripe ( 1 e length = 26 μ m ). In general the measured loss values agree with the numerical simulation at least for stripe widths ≥30 μm. For stripe widths of ≤30 μm loss values ≤1 dB have been obtained in all cases, but deviations of the calculated loss values occurred, which can be attributed to the regrowth geometry at the interface.