Compact InP spot-size converter with vertically tapered core layer formed by micro-loading effect

A compact (200 μm) spot-size converter (SSC) with a vertically tapered core layer is developed, which is fabricated with a simple wafer process using the micro-loading effect. It is confirmed that the vertical spot size of the SSC exceeded 2 μm, which was double that of the original waveguide. As a result, an InP waveguide integrated with the SSCs exhibited a coupling loss of <1 dB per facet for a lensed fibre with a 2.5 μm mode-field diameter. The fluctuation in the total of coupling and excess losses of the SSC was <0.5 dB.