Dan M. Marom
Today’s fiber-optic communication networks span the globe, delivering broadband information across all market segments and connecting massive datacenters, businesses, and individual user’s homes. As such, optical networks must operate reliably and efficiently when transporting the massive information capacity of the Internet, allowing networks to adapt to growing and changing demand flows and occasional interruptions.
Wavelength-selective switches (WSS) have been instrumental in fulfilling this role, enabling all-optical spectral routing of individual wavelength-division multiplexed (WDM) communication channels at network nodes. The recent introduction of space-division multiplexing (SDM) to the optical communication domain with new fiber types, in order to economically support the exponentially growing capacity, necessitates complementary components for implementing SDM-WDM optical networks. SDM is typically realized with either multi-core or few-mode fibers and great capacity achievements have been demonstrated to-date in each fiber solution.
Wavelength-selective switching functionality for these two fiber types has recently been introduced. A joint-switching WSS concept has been realized for multi-core fibers, enabling information to be encoded and routed on the SDM-WDM optical network as a spatial super-channel (single wavelength channel spanning multiple cores). This spatial super-channel routing concept with joint-switching WSS also extends to few-mode fibers. Hence a single WSS can then be used in analogous fashion to the single-mode fiber networks, thereby heralding the cost-savings benefits of SDM. A WSS with direct few-mode fiber interfaces has been demonstrated with the few-mode beams routed in free-space just as the single mode beam does in a conventional WSS. A study on the pass band filtering effect and mode mixing due to the spectral switching of dispersed components revealed the spatial-spectral interplay in the mode-dependent loss attributes of the few-mode fiber WSS. Such advanced WSS prototypes will serve the next generation transport networks when SDM is fully adopted by carriers.