Compact Dual-Mode Adiabatic 3-dB Coupler for the 2-μm Waveband on Silicon Using Fast Quasi-Adiabatic Dynamics

We propose a 2 × 2 dual-mode adiabatic 3-dB coupler for the 2-μm waveband on silicon. The proposed coupler is designed based on fast quasi-adiabatic dynamics. The optimized taper shape is effective to reduce the device length. The length of the coupling region with the optimized taper is at least 3 times shorter than the length of the coupling region with the linear taper. Numerical results indicate that our device with taper length 425 μm provides the excess losses smaller than 0.01 dB and imbalances within ±0.58 dB for both TE0 and TE1 modes in the spectral range of 2.06–2.14 μm. Furthermore, the experimental results demonstrate the functionality of the proposed coupler, and the effectiveness of the design based on fast quasi-adiabatic dynamics. The proposed device is useful for the building of multimode switches in the on-chip mode-division multiplexed network.