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 be 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 μm. Besides the improved coupling, the beam divergence of the far-field is also reduced considerably to 9°, accompanied by a significant lowering of the reflected power from the fiber interface