An Ultra-compact Four-channel Wavelength Demultiplexer by Inverse Design

Integrated photonics devices now play an increasingly significant role in lots of fields. In this paper, we demonstrate a
$\mathbf{1}\times \mathbf{4}$
wavelength demultiplexer (WDM) on standard silicon-on-insulator (SOI) platform working in the O-band by using inverse design algorithm. The device exhibits high transmission efficiencies and low crosstalk characteristics for the four 30nm-spacing channels (1271nm, 1291nm, 1311nm and 1331nm) with the footprint of
$\mathbf{6}\boldsymbol{\mu} \mathbf{m}\times \mathbf{6}\boldsymbol{\mu} \mathbf{m}$
and
$\mathbf{8}\boldsymbol{\mu} \mathbf{m}\times \mathbf{8}\boldsymbol{\mu} \mathbf{m}$
. The average peak transmission efficiencies of the
$\mathbf{6}\boldsymbol{\mu} \mathbf{m}\times \mathbf{6}\boldsymbol{\mu} \mathbf{m}$
and
$\mathbf{8}\boldsymbol{\mu} \mathbf{m}\times \mathbf{8}\boldsymbol{\mu} \mathbf{m}$
devices are more than 97.40% and 99.63%. The highest crosstalk is less than -25.38dB and -33.04dB respectively. The lowest bandwidth at a crosstalk of -20dB for the two dimensions are 4.00nm and 8.87nm, which can satisfy the requirement of laser wavelength drift tolerance in current data center transmission systems.