LR-8 optical demultiplexers based on silicon nanowires targeted for 400  GbE in datacenter applications

We propose and experimentally validate a novel, to the best of our knowledge, LR-8 optical demultiplexer architecture based on a four-stage multiple delayed interferometer employing discrete path-length differences and multimode-interference couplers to achieve spectral flatness and suppress crosstalk. An intentional half-length offset path difference in the third stage breaks the inherent spectral periodicity in the wavelength domain, while interferometer-type band-rejection filters in the fourth-stage further suppress out-of-band noise without any penalty for the main signals, thereby improving the crosstalk extinction ratio (XER). Fabricated silicon-nanowire devices exhibit flat-topped, non-periodic LR-8 passbands under TE-polarized input, with a measured XER of >11<i>d</i><i>B</i> in good agreement with analytical predictions. We further experimentally investigate the impact of statistical random phase errors, arising from fabrication imperfections and/or intentional waveguide design variations, on the spectral degradation of the LR-8 device. With its compact footprint, flat spectral response, and high integrability, the proposed device shows strong potential for next-generation 800-GbE-class data-center interconnects.