Taper couplers for coupling between laser and silicon waveguide with large allowable tolerance

A taper coupler with multimode input and single mode output is presented for coupling between edge emitting laser diode and silicon waveguide. The tapered coupler structure is optimized and tolerance for laser diode placement is studied. A typical coupling efficiency of -2dB is achieved from laser diode to silicon waveguide. With tolerance of +/- 4μm laterally or vertically, the variation of the coupling efficiency is about 3dB. The tolerance is large compared with other methods. Tilting angle at laser diode and the small gap between tapered coupler and silicon waveguide also affect the overall coupling. From our studies, horizontal and vertical offsets are more critical for laser diode placement in order to have a good coupling. The new design can be applied to photonics packaging because it will make passive assembly easier by having larger tolerance for packaging compared with the conventional method with lens.