$C$ -Band Optical 90$^{\circ}$ -Hybrids Based on Silicon-on-Insulator 4 $\times$ 4 Waveguide Couplers

We demonstrate 4times4 multimode interference couplers in a silicon-on-insulator rib waveguide technology that enable compact integrated fully passive optical 90deg-hybrid devices with operation across the
C
-band.