LATERALLY TAPERED INP-INGAASP WAVE-GUIDES FOR LOW-LOSS CHIP-TO-FIBER BUTT COUPLING - A COMPARISON OF DIFFERENT CONFIGURATIONS

Low-loss chip-to-fiber coupling can be achieved by on-chip spot-size t ransformers. Two simple versions using laterally tapered InP-InGaAsP w aveguides at the 1.55 mu m wavelength have been fabricated: one consis ting of two differently tapered layers, the other with only one taper. The influence of the taper shape and of fabrication tolerances on the ir performance is compared both experimentally and theoretically. The optimum insertion loss for a single transformer without antireflection coating, including Fresnel losses, amounts to 1.1 dB.