Spot-size converter using vertical ridge taper for low fibre-coupling loss in 2.5%-Δ silica waveguides

A novel spot-size converter based on a vertical ridge waveguide taper for super-high-Δ silica waveguides is demonstrated. This structure can be formed with a simple fabrication process. The coupling loss between a singlemode fibre and a 2.5%-Δ silica waveguide was reduced to 0.31 dB/point compared to 2.7 dB/point for conventional straight waveguides.