Efficient Blue-Green Light Phased Array Based on High-Contrast Grating as a Demultiplexer

Wavelength division multiplexing (WDM) technology has been proven to effectively increase the capacity of optical communications in the infrared light band. However, to date, the WDM systems in the visible band only support limited quantity of wavelength channels, with coarse channel spacing of over 20 nm. This is because there are no available multi/demultiplexers (MUX/DeMUX) with fine wavelength spacing for visible light. In this work, we use a high-contrast grating (HCG) structure to effectively separate the blue-green wavelengths with fine spacing. An efficient blue-green light phased array based on HCG aperture is demonstrated to work as the DeMUX in a WDM system. The HCG aperture presents more efficient main-lobe radiation than typical one-dimensional waveguide surface grating arrays with fishbone antennas. The measured main-lobe loss of optical phased array (OPA) with HCG is over 15 dB lower than that of OPA with fishbone antennas, because HCG provides maximum scatterings for blue-green light. A wavelength spacing as small as 4 nm is validated in a blue-green WDM system, which is the finest channel spacing for WDM in visible band to the best of our knowledge.