A review of higher-order mode pass filtering techniques

Mode Division Multiplexing (MDM) is regarded as a promising technology to overcome the bottleneck of the future demand for high data transmission rates. Multimode fibers are replacing traditional single mode fibers to cope with the increasing bandwidth requirements. MDM works with multiple light modes, and these modes are bound to be coupled with other propagating modes as they pass through guided media. A mode filter removes unwanted modes from the signal received at the receiver after demultiplexing. As a result, designing a highly potential high-order mode pass filter is desired to meet the capacity crunch using the MDM technology. Currently, remarkable research works have been conducted on mode filtering. This paper presents an overview of recent developments in mode filtering techniques along with their designs and fabrication processes. In particular, the mode filter made from different types of materials is reviewed to illustrate the potential of the designs in improving the system performance. Even though commercial success has not been materialized, this work will provide promising prospects in mode filtering techniques for increased flexibility and the choice of different mode filters.