Reconfigurable 3-dB MMI splitter

A tunable multimode interference (MMI) coupler is demonstrated. The device operates by modifying the phase of the multiple images that are formed around the midpoint of the MMI. Current spreading is controlled using a zinc in-diffusion process to selectively define p-i-n regions and effectively regulate the current spreading by controlling the depth of the zinc doping. A tunable MMI coupler has been fabricated. Our initial results show that the device can be easily tuned all the way from a 90:10 to a 30:70 splitting ratio of the optical power transmitted through the two output ports. Further improvement on the device fabrication will lead to a more symmetric tuning response of the device. Nevertheless, the initial results are very encouraging since, to our knowledge, this degree of tuning has never been experimentally demonstrated in similar MMI devices.