Tapered Multi-Mode Interference Waveguide for High-Power Self-Organizing Single-Mode Semiconductor Laser Arrays

A 1 x N, tapered, multi-mode interference (MMI) coupler is numerically studied for use in a self-organizing semiconductor laser-array system. The MMI structure is linearly tapered in a way such that the single-port side is wider than the N-port side. The single-port waveguide is N times wider than the other ports to maintain intensity similar to that in each of the N-port waveguides. Using such a device, the N-ports of a semiconductor laser array can be coherently combined in a self-organizing architecture. This modified MMI design increases the output power threshold for catastrophic optical damage while maintaining only single-mode excitation of a wide single port output. The device is nonadiabatic with a single-pass power transmission of 98%. A power imbalance up to 40% in a single port reduces the device efficiency by less than 1%, while a waveguide roughness as large as 70 nm rms detracts only 3% from the device efficiency. When designed to work at 1 mu m wavelength, the structure has a full-width half-maximum pass-band of 10 nm, which can provide wavelength selectability when used in a self-organized semiconductor laser-array system.