Theoretical limit and framework of dynamic modulation in spoof surface plasmon polariton interconnects

Spoof-surface-plasmon-polariton (SSPP) interconnects are potential candidates for next-generation interconnects to satisfy the growing demand for high-speed, large-volume data transfer in chip-to-chip and inter-chip communication networks. As in any interconnect, the viability and efficiency of the modulation technique employed will play a crucial role in the effective utilization of SSPP interconnects. In light of the lack of a comprehensive platform for the performance analysis of SSPP signal modulation, this work presents a theoretical framework that contributes to the following: 1) predictions of the maximum attainable modulation speed, limited by geometric dispersion in SSPP waveguide, 2) quantification of the fundamental trade-off relation between modulation speed and energy-efficiency for an arbitrary design of SSPP structure, 3) extension of the analysis over a broad category of SSPP modulation technique. In conjunction, a novel SSPP signal modulation technique is introduced, involving controlled alteration of the resonant condition of the SSPP interconnect using a variable resistor. Analyzing a sample SSPP waveguide with a 7 GHz cut-off frequency, the study identifies a potential similar to 28% change in its transmission-band by varying the implanted resistor from 5k ohm to 5 ohm, a range of values practically attainable with gate-controlled, state-of-the-art submicron scale field-effect transistors. The assertions of the theoretical model have been independently validated by finite-element method based numerical simulations, which show that the underlying concept can be utilized to realize the digital modulation scheme of the amplitude shift keying. For a millimeter-scale SSPP channel having 2.75 GHz transmission bandwidth, up to 300 Mbps modulation speed with nominal power loss is achieved in a standard, thermal-noise limited communication system. By scaling the interconnect to micrometer dimensions, the speed can be augmented up to 10 Gbps for data transfer over 100 mm distance with >= 80% energy efficiency. Essentially, the presented theory is the first of its kind that provides the foundational design guideline for designing and optimizing diverse range of SSPP modulators.