An ultracompact 3×1 MMI power-combiner based on Si slot-waveguide structures

Today, photonic integrated circuits (PIC) that work with a high-modulation speed (100Gb/s and beyond) are required to use more optical power to overcome the losses. One solution is to use a high-level laser with a hundred milliwatts power. However, for a microchip circuit, this solution can be problematic due to the nonlinear effects and high cost. Therefore, to solve this issue, we propose a new design of a 3×1 multimode interference (MMI) power combiner based on a slot waveguide structure that can utilize slot-waveguide technology for reducing losses. In this study, the full-vectorial beam propagation method (FV-BPM) was used to find the optimal geometrical parameters of the MMI coupler, inputs/output taper, and the slot waveguide structure. Simulation results show that after light propagation of 9.82 μm the beam combiner efficiency can reach 97.6 % working within the C-band range. Also, to reduce back reflection losses an angled MMI was designed using a finite difference time domain (FDTD) method and results show a low back reflection of 40 dB. This unique design can lead to an efficient and compact combiner for multiple coherent sources that work with PIC chips.