Silicon-Based Integrated Terahertz Polarization Beam Splitters

Terahertz (THz) technology offers multifaceted capabilities and disruptive applications in line-of-sight wireless communication, highly sensitive (bio)sensing, imaging and so on. However, the severe lack of polarization devices comparable to those for other electromagnetic frequencies is impeding moving towards practical applications. Here we demonstrate, for the first time, silicon-based integrated, high polarization extinction ratio, low insertion loss, and compact THz polarization beam splitters (PBSs) fabricated by CMOS-compatible technologies based on dielectric environment variation induced evanescent wave coupling effect. Through comprehensively analyzing working principles of conventional two-waveguide-based PBS, a high-performance three-waveguide PBS is successfully realized. Further optimizing the device parameters and working bandwidth, we achieve an integrated broadband PBS based on cascaded asymmetric directional couplers, whose polarization extinction ratios reach up to 20 dB and 32 dB for transverse electric and transverse magnetic modes, respectively, and their 10-dB bandwidth is 32 GHz for a device length of 15.5 mm. These numbers are the highest in silicon-based integrated THz PBSs so far. We believe our observations provide an effective way for exploring on-chip high-performance THz-PBSs for polarization-diverse systems, accelerating the development and application of on-chip THz photonics.