Inverse-Designed Two-Dimensional Grating Coupler with Low Polarization-Dependent Loss

We propose low polarization-dependent-loss (PDL) two-dimensional grating couplers (2D GC) on SOI platform, with perfectly vertical fiber-chip coupling, using inverse design method. Simulation results show that −3.17 dB (−1.90 dB) and −2.10 dB (−1.00 dB) of coupling efficiency can be achieved for 2-port and 4-port structures, without (with) metal mirror beneath the buried oxide. Low PDL of < 0.2 dB and < 0.025 dB can be obtained over a broad bandwidth of 52 nm and 100 nm, respectively. We fabricate and measure the proposed devices of 2-port and 4-port 2D GC. Coupling efficiency of the two are −5.3 dB and −5.0 dB, respectively. The PDL is < 0.7 dB ranging from
$1.49\ \mu\mathrm{m}$
to
$1.57\ \mu\mathrm{m}$
.