相干破坏布拉格滤波器：超越片上抑制极限
Coherency-broken Bragg filters: surpassing on-chip rejection limitations
摘要：
具有高抑制水平的选择性片上光学滤波器是各种先进光子电路的关键部件。然而，在最先进的片上器件中可实现的最大抑制受到由制造缺陷引起的相位误差的严重限制。由于相干相互作用，不需要的相移会导致有害的相消干涉，使滤波器响应失真，无论选择何种策略（谐振器、干涉仪、布拉格滤波器等）。在这里，我们提出并通过实验证明了一种完全不同的方法来克服这一根本限制，该方法基于相干性破坏的布拉格滤波器。我们利用单模波导分离的模式工程波导布拉格光栅之间的非相干相互作用，即使在存在制造误差的情况下，也能产生有效的级联。这种技术上独立的方法允许滤波器级与中等性能的无缝组合，从而大幅提高片内抑制。基于这一概念，我们实验证明片上非相干级联的Si布拉格滤波器的记录光抑制超过80 dB的C波段。
英文摘要：
Selective on-chip optical filters with high rejection levels are key components for a wide range of advanced photonic circuits. However, maximum achievable rejection in state-of-the-art on-chip devices is seriously limited by phase errors arising from fabrication imperfections. Due to coherent interactions, unwanted phase-shifts result in detrimental destructive interferences that distort the filter response, whatever the chosen strategy (resonators, interferometers, Bragg filters, etc.). Here we propose and experimentally demonstrate a radically different approach to overcome this fundamental limitation, based on coherency-broken Bragg filters. We exploit non-coherent interaction among modal-engineered waveguide Bragg gratings separated by single-mode waveguides to yield effective cascading, even in the presence of fabrication errors. This technologically independent approach allows seamless combination of filter stages with moderate performance, providing a dramatic increase of on-chip rejection. Based on this concept, we experimentally demonstrate on-chip non-coherent cascading of Si Bragg filters with a record light rejection exceeding 80 dB in the C-band.
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