Robust 2 x 2 multimode interference optical switch

A robust 2 x 2 photonic switch based on multimode interference (MMI) effects is proposed. We demonstrate that the device is very tolerant to material modifications and typical fabrication errors. This is a result of the MMI design and the high symmetry of the switch. The key parameter for the operation of the device is that the input light forms a pair of well defined self-images exactly in the middle of the switch. The index modulated regions precisely overlap the positions where these two self-images are formed. By creating identical contact features at these locations, any refractive index change induced in the material as a result of electrical isolation will be replicated in both self-images, and therefore the off-state output will not be altered. In the same way, offset and dimension errors are reflected symmetrically on both self-images and do not seriously affect the imaging. The characteristics of the switch under different scenarios are investigated using the finite difference beam propagation method. By employing this configuration, crosstalk levels better than -20 dB are achievable over a wavelength range of 100 nm while maintaining polarization independence.