Multiple mode band engineering in 1D grating-based photonic crystal waveguides for multidimensional silicon on-chip filters

Efficient on-chip mode manipulation is essential for scalable and flexible filtering devices in mode-division and hybrid multiplexing systems. A multimode manipulation strategy based on band engineering in one-dimensional grating-based photonic crystal waveguides (PCWs) is proposed. By strategically widening the transverse dimension of a silicon PCW, both the number of supported Bloch modes and their bandgaps are expanded, enabling broadband mode control across three distinct regimes: all-pass, selective-pass, and all-block. Based on this principle, a scalable higher-order mode (HOM) pass-filtering architecture and three compact HOM-pass filters (TE 1 -pass, TE 2 -pass, TE 3 -pass) are demonstrated. Devices fabricated on standard silicon-on-insulator (SOI) exhibit measured bandwidths exceeding 200 nm, 123 nm, and 70 nm, respectively, with extinction ratios (ERs) greater than 20 dB and insertion losses (ILs) below 2 dB. Leveraging these filters as building blocks, we further demonstrate their capability to achieve high ER, low IL filtering devices for polarization and wavelength applications, including a polarizer, a polarization beam splitter, and a wavelength demultiplexer. This work establishes a scalable multimode bandgap-engineering framework for compact, broadband, and multifunctional silicon photonic devices for mode, polarization, and wavelength manipulation.