REFLECTION PROPERTIES OF MULTIMODE INTERFERENCE DEVICES

We report on the reflection properties of multimode interference (MMI) devices: we distinguish between reflection back into the input wavegu ides and internal resonance modes due to the occurrence of simultaneou s self-images. Because of self-imaging, reflection can be extremely ef ficient, even in the case of MMI devices with optimized transmission. This conclusion is confirmed hy the observed spectral behavior of InP- based ring lasers incorporating MMI 3dB couplers and MMI power splitte rs. Several techniques are proposed to minimize the influence of these reflections.