Spot-size conversion using uniform waveguide sections for efficient laser-fiber coupling

Using numerically simulated results, it is shown that an efficient laser-to -fiber coupling is possible by incorporating a uniform spot-size converter (SSC) with two nonidentical but phase matched optical waveguides, Using a " diluted" waveguide with a low index contrast, the power coupling loss can b e significantly reduced from 10.4 dB to only 1.15 dB and at the same time 1 .0 dB alignment tolerances can also be improved to achieve +/-1.8 mum, Besi des the improved coupling, the beam divergence of the far-field is also red uced considerably to 9 degrees, accompanied by a significant lowering of th e reflected power from the fiber interface.