Efficient Active-to-Passive Light Coupling of InGaAsP/InP Laser Using Subwavelength Coupler

We propose a subwavelength coupler for efficient light coupling from an InGaAsP/InP laser to a passive waveguide. The active-to-passive coupling device is designed on the asymmetric twin waveguide (ATG) platform with two InGaAsP layers: one is used as the laser active layer, and the other with a wider band gap is used as the guiding layer of the passive waveguide. By introducing subwavelength trenches in the active InGaAsP layer, the subwavelength coupler is designed to provide a gradual effective index transition region, and it couples the light between the vertically separated active and passive layers. Simulation result shows that coupling efficiency of 86.5% is achieved at a length of only 31 μm.