Simple and low-loss fibre-to-chip coupling by integrated field-matching waveguide in InP

A nested taper structure in InGaAsP/InP, using only horizontally tapered waveguides, transforms the fundamental mode of an integrated waveguide to the mode profile of a singlemode fibre. Taper tips below 300 nm width have been achieved with standard technology. Very first measurement results show an insertion loss of only 4 dB for a 1 mm long device without any antireflective coating or immersion fluid.