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

This article presents a $G$ -band mode-coupler-based multimode multidrop Si dielectric waveguide (DWG) for sub-terahertz (THz)/THz interconnect. Four types of mode couplers, including $E_{11}^{y}$ – $E_{11}^{y}$ , $E_{11}^{y}$ – $E_{21}^{y}$ , $E_{11}^{y}$ – $E_{31}^{y}$ , and quasi-TEM to $E_{11}^{y}$ mode couplers, are analyzed, designed, and demonstrated. The quasi-TEM to $E_{11}^{y}$ coupler is a microstrip line (MSL)-to-DWG transition. $E_{11}^{y}$ to $E_{21}^{y}$ and $E_{11}^{y}$ to $E_{31}^{y}$ mode 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) of $10^{-12}$ .