Silica-based 2 × 2 multimode interference coupler with arbitrary power splitting ratio

The authors propose a novel 2 × 2 multimode interference (MMI) coupler that provides an arbitrary power splitting ratio. The proposed coupler has a cladding-filled gap in the centre of its MMI region. Couplers fabricated using a silica-based planar lightwave circuit exhibited splitting ratios from 0–100% with excess losses < 1 dB.