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The dense blue-green wavelength division multiplexing (WDM) technology has been rarely reported to increase the capacity of optical communications, since there are no available multi/demultiplexers with nanometer-scale wavelength spacing for blue-green light. In this work, a polarization-sensitive optical phased array (OPA) is proposed to effectively separate the blue-green wavelengths with fine spacing by the innovative mode multiplexing. The efficient blue-green OPA based on fishbone waveguide antenna is demonstrated to successfully demultiplex blue-green wavelengths in a WDM optical wireless communication (OWC) system. The key performances of the designed OPA including the chip loss and transmitting efficiency of main lobe have been optimized and analyzed by both simulation and experiments. The proposed OPA presents the desired transmitting efficiency is ∼1%, corresponding to the total loss of around 20 dB. A wavelength spacing as small as 1.2 nm based on the TE and TM mode multiplexing is demonstrated in the blue-green WDM OWC application, which is the first demonstration of nanometer-scale channel spacing for WDM in blue-green band to the best of our knowledge. Furthermore, with On-Off Keying modulation an aggregate data rate of 4 Gbit/s after the recursive least squares equalization was achieved in this WDM system, while the bit error rates for all four channels are far below the forward error correction limit of 3.8×10 −3 .
Liu et al. (Thu,) studied this question.