  Here we apply the optical nanocircuit concepts to design and analyze in
detail a three-dimensional (3-D) plasmonic nanotransmission line network that
may act as a negative-refraction broadband metamaterial at infrared and optical
frequencies. After discussing the heuristic concepts at the basis of our
theory, we show full-wave analytical results of the expected behavior of such
materials, which show increased bandwidth and relative robustness to losses.
The possibility and constraints of getting a 3-D fully isotropic response is
also explored and conditions for minimal losses and increased bandwidth are
discussed. Full-wave analytical results for some design examples employing
realistic plasmonic materials at infrared and optical frequencies are also
presented, and a case of sub-wavelength imaging system using a slab of this
material is numerically investigated.
