A reconfigurable multimode interference splitter for sensing applications

A reconfigurable 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 section. This modifies the properties of the following set of images, and light can be directed to a specific output waveguide, which is therefore ideal to develop a reconfigurable MMI coupler. In our device the phase change is achieved by current injection, and therefore minimizing current spreading is crucial for optimal operation. A zinc in-diffusion process has been implemented to selectively define p–n regions and effectively regulate current spreading by controlling the depth of the zinc doping. Using this process, a reconfigurable 3 dB MMI coupler has been fabricated. Our experimental results revealed that the device can be easily set to a perfect 3 dB splitter using only 0.7 mA of current injection. In addition, the device can be adjusted all the way from a 90:10 to a 30:70 splitting ratio. The results are very encouraging since, to our knowledge, this degree of tuning of the optical power has never been experimentally demonstrated in MMI devices. Furthermore, this concept can easily be applied to a wide variety of semiconductor photonic switches that operate on MMI effects.