Chen Yang, Domínguez Bucio Thalia, Khokhar Ali Z, Banakar Mehdi, Grabska Katarzyna, Gardes Frederic Y, Halir Robert, Molina-Fernández Íñigo, Cheben Pavel, He Jian-Jun
Opt Lett. 2017 Sep 15;42(18):3566-3569. doi: 10.1364/OL.42.003566.
A silicon nitride waveguide is a promising platform for integrated photonics, particularly due to its low propagation loss compared to other complementary metal-oxide-semiconductor compatible waveguides, including silicon-on-insulator. Input/output coupling in such thin optical waveguides is a key issue for practical implementations. Fiber-to-chip grating couplers in silicon nitride usually exhibit low coupling efficiency because the moderate index contrast leads to weak radiation strengths and poor directionality. Here, we present the first, to the best of our knowledge, experimental demonstration of a recently proposed apodized-imaging fiber-to-chip grating coupler in silicon nitride that images an in-plane waveguide mode to an optical fiber placed at a specific distance above the chip. By employing amplitude and phase apodization, the diffracted optical field of the grating is matched to the fiber mode. High grating directionality is achieved by using staircase grating teeth, which produce a blazing effect. Experimental results demonstrate an apodized-imaging grating coupler with a record coupling efficiency of -1.5 dB and a 3 dB bandwidth of 60 nm in the C-band.
氮化硅波导是集成光子学中一个很有前景的平台，特别是与其他互补金属氧化物半导体兼容波导（包括绝缘体上硅）相比，其具有低传播损耗。在这种薄光波导中的输入/输出耦合是实际应用中的一个关键问题。氮化硅中的光纤到芯片光栅耦合器通常耦合效率较低，因为适度的折射率对比度会导致辐射强度较弱和方向性较差。在此，据我们所知，我们首次对最近提出的氮化硅变迹成像光纤到芯片光栅耦合器进行了实验演示，该耦合器将平面内波导模式成像到放置在芯片上方特定距离处的光纤上。通过采用幅度和相位变迹，光栅的衍射光场与光纤模式相匹配。通过使用产生闪耀效应的阶梯光栅齿实现了高光栅方向性。实验结果表明，一种变迹成像光栅耦合器在C波段具有创纪录的-1.5 dB耦合效率和60 nm的3 dB带宽。
