Mode switching and sorting in few-mode fiber ports using a square core multimode optical fiber

We present the operation and characteristics of a multimode interference (MMI)-based optical device for switching a single-mode launched at any of the four (4) few-mode fiber (FMF) input ports to one of the four (4) output FMF ports. The device utilizes a square core multimode fiber as the MMI section, arranged in a splitter-combiner architecture with external phase controllers. We also provide the phase conditions at the controllers such that the same device sorts the azimuthal orders of the incoming mixed-mode field to different output ports. Various operational constraints of the proposed device, such as operational bandwidth, fabrication tolerances, and phase sensitivity, are investigated for practical implementation. Finally, we have proposed a design for a mode sorting application that does not require dynamic phase control.