Optimized MMI coupler shape for reduced back-reflections

Spurious back-reflections can be a source of concern in photonic integrated circuits. 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 back-reflections can be present when using a 2×1 MMI as a combiner. We investigate methods for reducing these spurious reflections in a generic integration technology. We present a novel MMI shape which is able to reduce reflections by more than 20 dB.