基于单个MMI的平顶转换器
Flat-top interleavers based on single MMIs
摘要：
我们首次展示了基于级联马赫-曾德尔干涉仪（MZI）的平顶功率分配器，该干涉仪仅使用单个多模干涉仪（MMI）作为功率分配器。我们以前的设计是基于MZI的4级级联，其中我们使用单MMI和双MMI分别实现85：15和31：69的分光比。这一次，我们提出了一个大大简化的2级配置，只使用单个MMI，包括一个标准的50：50 MMI，和两个锥形MMI，以实现71：29和92：08的分光比。我们已经设计了交织器的基础上，其几何表示的布洛赫球，然后确认有效的二维模拟的积木和整个结构的基础上，本征模展开方法。我们展示了如何重要的是要考虑到所有MMI的输出之间的相位关系，以使一个工作设计。我们已经成功地在我们的微米级硅光子学平台上制造了具有不同沟道间距的器件，并且测量结果证实了它们在宽带上的预期平顶操作。仅使用单MMI分束器，我们不仅可以大大超过标准定向耦合器所实现的带宽，而且还可以确保对制造误差的更高鲁棒性，与之前基于双MMI的演示相比。事实上，与以前的尝试相比，新的结果证明锥形MMI是实现任意分光比的最稳健的方法。
英文摘要：
We demonstrate for the first time flat-top interleavers based on cascaded Mach-Zehnder interferometers (MZIs) which use only single multimode interferometers (MMIs) as power splitters. Our previous designs were based on 4-stage cascades of MZIs, where we used single MMIs and double MMIs to achieve 85:15 splitting ratio and 31:69 splitting ratio respectively. This time, we propose instead a greatly simplified 2-stage configuration using only single MMIs, including a standard 50:50 MMI, and two tapered MMIs to achieve 71:29 and 92:08 splitting ratios. We have designed the interleaver based on its geometrical representation on the Bloch sphere, then confirmed by efficient 2D simulations of the building blocks and of the whole structure, based on the eigenmode expansion method. We show how important is to take into account the phase relations between the outputs of all MMIs in order to make a working design. We have successfully fabricated devices with different channel spacing on our micron-scale silicon photonics platform, and measurement results confirmed their expected flat-top operation on a broad band. Using only single MMI splitters we can not only greatly outperform the bandwidth achieved by standard directional couplers, but we can also ensure much higher robustness to fabrication errors, also compared to previous demonstrations based on double MMIs. Indeed, when compared to those previous attempts, the new results prove tapered MMIs to be the most robust approach to achieve arbitrary splitting ratios.
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