Wavelength-selective switches with few-mode fiber integration

Mode division multiplexed (MDM) transmission is prone to mix, and necessitates that all spatial channels on a carrier wavelength remain intact, so that the information set can be unraveled at the receiver following multi-channel coherent detection and digital signal processing. This requirement is extended to the network switching gear, which should ‘jointly switch’ all modes. Wavelength-selective switches supporting joint switching are reviewed, and the interplay between mode shapes, spectral resolution, mode mixing, and channel passband are detailed.