  The polarimetric self-coherent system using a direct-detection-based
Stokes-vector receiver (SVR) is a promising technology to meet both the cost
and capacity requirements of the short-reach optical interconnects. However,
conventional SVRs require a number of optical components to detect the state of
polarization at high speed, resulting in substantially more complicated
receiver configurations compared with the current
intensity-modulation-direct-detection (IMDD) counterparts. Here, we demonstrate
a simple and compact polarimetric self-coherent receiver based on a thin
dielectric metasurface and a photodetector array (PDA). With a single
1.05-$\mu$m-thick metasurface device fabricated on a compact silicon-on-quartz
chip, we implement functionalities of all the necessary passive components: a
1$\times$3 splitter, three polarization beam splitters with different
polarization bases, and six focusing lenses. Combined with a high-speed PDA, we
demonstrate self-coherent transmission of 20-GBd 16-ary quadrature amplitude
modulation (16QAM) and 50-GBd quadrature phase-shift keying (QPSK) signals over
a 25-km single-mode fiber. Owing to the surface-normal configuration, it can
easily be scaled to receive spatially multiplexed channels from a multicore
fiber or a fiber bundle, enabling compact and low-cost receiver modules for the
future highly parallelized self-coherent systems.
