Equal input, compact optical power coupler based on a nano-pixel structure designed with machine learning

A multi-mode interference (MMI) waveguide has been widely researched and developed to realize an optical power coupler. MMI coupler exhibits the superior performance of the "Equal intensity coupling" characteristics, however, it has a problem that excess loss occurs if the phase-matching condition is not satisfied at all of the input ports. The phase condition depends on the number of input ports, and relatively complicated phase control is required, thus, it is desired to realize an optical power coupler without complicated phase adjustment. In order to avoid the phase-control difficulty, a nano-pixel power coupler is investigated in this paper. The nano-pixel-based coupler has the merit of ultra-compact dimension which is close to the wavelength order, therefore, it is expected that less excess loss even under simple "equal" phase conditions. The structure was examined using FDTD and the simulated results show equal input (intensity and phase) coupling capabilities with a low excess loss of 0.11 dB.