Multimode Interference couplers with reduced parasitic reflections

Parasitic reflections can deteriorate the performance of a photonic integrated circuit. This is especially true in circuits containing amplifiers, but even in passive circuits, small reflections can already have a strong influence on circuit performance. It is known that strong reflections can be present when using a 2 × 1 multimode interference coupler (MMI) as a combiner. We investigate methods for reducing these spurious reflections in a generic integration technology. We present a novel MMI shape whose measurements show reduced reflections by 17.5 dB.