▎ 摘　　要

In the long-wavelength approximation, an effective conductivity tensor is introduced for graphene ribbons (strips) placed periodically at the interface between two media. The resulting conducting surface is considered as a coating for semiconductor nanowire. For the hybrid waves of such nanowire, the dispersion equations are obtained in explicit form. Two types of surface plasmons are found to exist: (i) modified surface plasmons, which originate from the ordinary surface plasmons of a graphene-coated semiconductor nanowire, and (ii) spoof plasmons, which arise on the array of graphene ribbons and may possess forward-wave and backward-wave dispersion. It is revealed that the spoof surface plasmons are low-loss ones, and their frequencies, field-confinement, and group velocities can be tuned widely by adjusting the coil angle and width of the helical graphene strips. (C) 2018 Optical Society of America