  We proposed plasmonic effect based narrow band tunable terahertz switches
consisting of multilayered graphene metamaterial. Though several terahertz
optical switches based on metamaterials were previously reported, these
switches had complicated fabrication processes, limited tunability, and low
modulation depths. We designed and simulated ingenious four and eight state
terahertz optical switch designs that can be functional for multimode
communication or imaging using the finite-difference time-domain simulation
technique. The plasmonic bright modes and transparency regions of these
structures were adjusted by varying the chemical potential of patterned
graphene layers via applying voltage in different layers. The structures
exhibited high modulation depth and modulation degree of frequency, low
insertion loss, high spectral contrast ratio, narrow bandwidth, and high
polarization sensitivity. Moreover, our proposed simple fabrication process
will make these structures more feasible compared to previously reported
terahertz switches. The calculated modulation depths were 98.81% and 98.71%,
and maximum modulation degree of frequencies were ~61% and ~29.1% for four and
eight state terahertz switches, respectively. The maximum transmittance in
transparency regions between bright modes and the spectral contrast ratio were
enumerated to be 95.9% and ~96%, respectively. The maximum insertion losses
were quite low with values of 0.22 dB and 0.33 dB for four and eight state
terahertz switches, respectively. Our findings will be beneficial in the
development of ultra-thin graphene-based multistate photonic devices for
digital switching, sensing in terahertz regime.
