Low-loss fibre-chip coupling by buried laterally tapered InP/InGaAsP waveguide structure

Abstract
A passive InP/InGaAsP spot-size transformer for low-loss coupling of semiconductor optoelectronic devices to singlemode fibres has been fabricated entirely on InP. Using a buried two-layer laterally tapered section, spot-size transformation is demonstrated from below 2μm up to 8 μm, the spot size of a dispersion-shifted fibre at 1550 nm. For a chip without antireflection coating a total insertion loss of 2.7 dB was achieved at a taper length of ∼600 μm.