Robust silicon 3-dB coupler using inverse engineering based optimization

We propose a scheme to optimize the adiabaticity of silicon 3-dB couplers for broadband operation. Using inverse engineering based optimization, a 125 μm long silicon 3-dB coupler with a maximum imbalance of 0.8 dB from 1.4 to 1.7 μm and good fabrication tolerance is obtained.