Recent advances in silicon (Si) microphotonics have enabled novel devices for the terahertz (THz) range based on dielectric waveguides. In the past couple of years, dielectric waveguides have become commonplace for THz systems to mitigate issues in efficiency, size, and cost of integration and packaging using metal-based waveguides. Therefore, THz systems have progressively evolved from cumbersome collections of discreet components to THz-wave integrated circuits. This gradual transition of THz systems from numerous components to compact integrated circuits has been facilitated at each step by incredible advances in all-Si waveguides allowing low-loss, low dispersion, and single-mode waveguiding operation. As such, all-Si waveguides position themselves as highly efficient interconnects to realize THz integrated circuits and further large-scale integration in the THz range. This review article intends to reevaluate the evolution stages of THz integrated circuits and systems based on all-Si waveguides.

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This study presents ultra-low-loss and broadband all-silicon dielectric waveguides for the WR-1 band (0.75–1.1 THz). The waveguides are built in high-resistivity silicon (10 kΩ-cm) and integrated with supportive frames fabricated from the same silicon wafer in a single etch process to achieve a compact design. We pursued low-loss, broadband, substrateless, unclad and effective medium waveguides. Smaller propagation losses of 0.3 dB/cm and 0.1 dB/cm were achieved for the unclad and effective medium waveguides, respectively. The 3 dB bandwidth was not encountered in the frequency range of interest and was as broad as 350 GHz. An unclad waveguide was employed to devise a Y-junction to demonstrate its practical applications in terahertz imaging. An integrated circuit card was successfully scanned. In addition, we developed unclad waveguide, effective medium waveguide, and Y-junction modules. The modules incorporated an input/output interface compatible with a standard WR-1 flange (254 μm × 127 μm). Unlike the conventional hollow waveguide modules, the unclad waveguide and effective medium waveguide modules reported total loss improvements of 6 dB and 8 dB, respectively, across the operation band. Our results provided a systematic way of achieving low-loss, compact, and versatile modules in the WR-1 band based on all-dielectric-waveguide platforms.

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