Abstract: An active multi-mode-interferometer (MMI) waveguide configuration was introduced and designed for single transverse mode laser diode with high output power. By using InAs/InGaAs/GaAs quantum dots (QD) as the active region, 1.3μm QD laser diode with the 1×1 MMI waveguide configuration was fabricated. It was demonstrated that the QD laser diode with the active MMI configuration exhibited improved heat dissipation and optical performance compared to the device with regular uniform waveguide structure. At a continuous wave injection current of 0.5A, a high output power of 114mW was obtained from the narrow waveguide while the laser diode emitting at 1332nm. The systematic study shows that the device with MMI waveguide configuration is instructive device for the fabrication of single transverse mode light emitting devices with high output power.