Design of optical wavelength demultiplexer based on off-axis meta-lens

We propose an off-axis meta-lens-based optical wavelength demultiplexer. The performance of the device initially proposed with four output channels (1527-1596 nm, channel spacing 23 nm) composed of an optical fiber array is analyzed by both scalar diffraction theory and ray tracing method. The results show that the fiber energy coupling efficiency of the demultiplexer could be larger than 89% and the channel bandwidth is about 9 nm. Influences of the two key parameters, focal length f and off-axis angle α, are also investigated. We find that the minimum spectral linewidth of the channel is inversely proportional to the sine of α and nearly independent of f for a meta-lens with large F-number (F>5), while the effective spectral range is negatively (positively) dependent on α (f). These results are significant in guiding us to build small and compact demultiplexing devices for optical telecommunication.