STUDIES ON THE BUTT-COUPLING OF INGAASP-WAVE-GUIDES REALIZED WITH SELECTIVE-AREA METALORGANIC VAPOR-PHASE EPITAXY

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 w ell (e.g. laser-waveguide). The method was applied to butt-coupled wav eguides, 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 t he 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 f actor of 1.7 at 50 mu m wide stripes and decreases exponentially with distance from the stripe (1/e length = 26 mu m). In general the measur ed loss values agree with the numerical simulation at least for stripe widths greater than or equal to 30 mu m. For stripe widths of less th an or equal to 30 mu m loss values I 1 dB have been obtained in all ca ses, but deviations of the calculated loss values occurred, which can be attributed to the regrowth geometry at the interface.