  In this article, we propose a programmable plasmonic waveguide system (PPWS)
to achieve several different functions based on metal coding metamaterials
(MCMs) and inverse design technology. There is no need to spend much time on
considering the relation between the function and the structure because the
MCMs in the PPWS are reprogrammable. In order to demonstrate the effectiveness
of the PPWS, we utilize it to achieve several filtering functions, including
bandstop and bandpass filters. The simulation results exhibit that the
performance of filters is improved based on genetic algorithm, particle swarm
optimization, multi-traversal direct-binary search and simulated annealing.
Especially, the bandwidth and quality factor for the narrow-band filter can
reach 6.5 nm and 200.5. In addition to the simple filtering functions, some
relatively complex transmission characteristics can be obtained by using the
PPWS, such as plasmon-induced transparency-like effects. In conclusion, genetic
algorithm is considered as the most efficient inverse design method for our
system due to its less optimization time and stable performance. In comparison
with the previous works, our proposed PPWS not only provides a general
framework for obtaining an effective, flexible and compact plasmonic device but
also shows the applications of inverse design on photonics devices.
