Tapered InP/InGaAsP waveguide structure for efficient fibre-chip coupling

Abstract
A novel passive InP/InGaAsP waveguide structure for lowloss coupling of monomode fibres to semiconductor devices having waveguides with small elliptical modes has been fabricated. The device consists of a fibre-matched waveguide, a tapered waveguide structure for the necessary mode transformation, and a small spot waveguide. The transformation of the fibre mode into a mode with a spot of 2.0 μm lateral and 1.5 μm vertical extension (FWHM) is demonstrated. Nearly polarisation independent transmission losses, as low as 4.9dB, are measured for uncoated devices with a 900 μm long tapered section.