Spectral shaping based on optical waveguides with advanced Sagnac loop reflectors

We propose and theoretically investigate integrated photonic filters based on two coupled Sagnac loop reflectors (SLRs) formed by a self-coupled optical waveguide. Recently we investigated integrated photonic filters based on cascaded SLRs and coupled SLRs. Here, we advance this field by presenting a unique approach of using coupled SLRs formed by a self-coupled optical waveguide. This enables 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 attractive for optical interleavers that need a flat-top symmetric filter shape. Optical interleavers and de-interleavers are core elements for signal multiplexing and demultiplexing in 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 in a wide variety of applications.