Silicon broad-band channel-drop filter based on an apodized photonic crystal nanobeam grating

Photonic crystal nanobeam gratings (PCNGs) enable broad-band and flat-top reflection responses within short grating lengths due to their large coupling coefficients. In this Letter, we propose and experimentally demonstrate a channel-drop filter (CDF) based on a dual-waveguide apodized PCNG. The dual-waveguide structure realizes the decoupling of grating apodization from mode conversion. The reflected light is separated with low loss through a broadband asymmetric directional coupler (ADC). This design allows effective apodization using laterally shifted holes, which eases the fabrication requirements. The fabricated device on a silicon-on-insulator (SOI) platform exhibits a 3-dB bandwidth of 40.1 nm, an extinction ratio (ER) of 20 dB, a sidelobe suppression ratio (SLSR) of 19.5 dB, and an insertion loss (IL) of less than 1.5 dB, demonstrating a strong potential for integrated on-chip broadband filtering applications.