Design and Analysis of a Mode-Coupler-Based Multimode Multidrop Si Dielectric Waveguide Channel for Sub-THz/THz Interconnect

This article presents aG-band mode-coupler-based multimode multidrop Si dielectric waveguide (DWG) for sub-terahertz (THz)/THz interconnect. Four types of mode couplers, includingE₁₁ʸ–E₁₁ʸ,E₁₁ʸ–E₂₁ʸ,E₁₁ʸ–E₃₁ʸ, and quasi-TEM toE₁₁ʸmode couplers, are analyzed, designed, and demonstrated. The quasi-TEM toE₁₁ʸcoupler is a microstrip line (MSL)-to-DWG transition.E₁₁ʸtoE₂₁ʸandE₁₁ʸtoE₃₁ʸmode couplers with satisfied phase matching enable two more mode transmissions along the same waveguide. The mode-coupling theory, including the coupling coefficient, the coupling efficiency, crosstalk, and bandwidth, is studied and analyzed mathematically and guides the development of a one-side tapered coupler to boost the bandwidth. Tapered structures are employed as the smooth transition between DWG sections and mode filters to minimize the mode interference in (de)multiplexers and as the radiation terminals to reduce the reflection. The measured minimum transition loss is about 5 dB with the 3-dB bandwidth of 143–200, 151–185, and 155–174 GHz for the three modes, respectively, and the measured crosstalks between modes are less than −26 dB. A multimode multidrop sub-THz interconnect system is also demonstrated with CMOS-based transmitters (TXs)/receivers (RXs) and achieves an aggregate data rate of 65 Gb/s and the energy efficiency of 1.6 pJ/b with a bit error rate (BER) of10⁻¹².