Silicon nanophotonic chips featuring Sagnac loop reflectors as a basis for advanced optical spectral filters

We present and investigate theoretically photonic integrated filters based on 2 Sagnac coupled loop reflectors (SLRs) that are arranged in a self-coupled optical waveguide. We recently presented photonic integrated filters based on coupled and cascaded SLRs. In this paper, we advance this field by investigating a unique approach of employing coupled SLRs formed by self-coupled waveguides. This allows us to achieve high performance filter functions including Fano-like resonances and wavelength interleaving with a simpler design and a higher fabrication tolerance by tailoring coherent mode interference in the device. Our design takes into account the device fabrication issues as well as the requirements for practical applications. As a guide for practical device fabrication, an analysis of the impact of the structural parameters and fabrication tolerance on each filter function is also provided. The Fano-like resonances show a low insertion loss (IL) of 1.1 dB, a high extinction ratio of 30.2 dB, and a high slope rate (SR) of 747.64 dB/nm. The combination of low IL and high SR promises this device for Fano resonance applications. Our device also can achieve wavelength de-interleaving function with high fabrication tolerance which is advantageous for applications such as optical interleavers that require a symmetric flat-top filter shape. Optical de-interleavers and interleavers are key components for optical signal multiplexing and demultiplexing for wavelength division multiplexing optical communication systems. Versatile spectral responses with a simple design, compact device footprint, and high fabrication tolerance make this approach highly promising for flexible response shaping for many applications.