Research on a C+L band wavelength selective switch with a 2K LCoS

With the continuous growth in the capacity demands of the optical networks and the slowdown in improving the spectrum efficiency, enhancing the bandwidth utilization of the existing optical fibers has become a critical solution. Thus, expanding the C-band transmission to C+L band, and even S+C+L band, is currently a hot topic in the field of optical fiber communication. Wavelength Selective Switches (WSS), as key components of reconfigurable optical add/drop multiplexer (ROADM) nodes, enable the optical network with dynamic channel configuration in wavelength granularity. Liquid Crystal on Silicon (LCoS) is widely employed as the optical engine in WSS due to its capability of flex-grid and ports expansion. There are two approaches for a C+L band WSS, dispersing the C+L band optical signals in one row on a LCoS chip with 4K pixels or dispersing the C-band and L-band optical signals in two rows on a 2K LCoS chip. This paper proposes a C+L WSS scheme based on a 2K LCoS chip. In the horizontal direction, an edge filter is set in the front access unit (FAU) to separate the C-band and L-band optical signals, which enables them to incident on the grating with different incident angle and the same diffraction angle, thus the two bands are dispersed on the LCoS at the same region horizontally. In the vertical direction, another edge filter is placed within the right-angle prism in front of the LCoS to separate the C-band and L-band optical signals into two rows on the LCoS. A 1×20 C+L WSS (1524~1572nm /1576~1624nm) is designed and simulated. For each wavelength switched to each output, the coupling efficiency is >81.32% and the beam confinement factor on the LCoS is >6.32, which enables the WSS with low loss and wide passband. This innovative approach shows high performance and reduces cost, making it a promising solution for future optical network.