Circuit Elements at Optical Frequencies: Nanoinductors, Nanocapacitors, and Nanoresistors

We present the concept of circuit nanoelements in the optical domain using plasmonic and nonplasmonic nanoparticles. Three basic circuit elements, i.e., nanoinductors, nanocapacitors, and nanoresistors, are discussed in terms of small nanostructures with different material properties. Coupled nanoscale circuits and parallel and series combinations are also envisioned, which may provide road maps for the synthesis of more complex circuits in the IR and visible bands. Ideas for the optical implementation of right-handed and left-handed nanotransmission lines are also forecasted.

Figure 1

A basic nanoscale circuit in the optical regime. Left: a nonplasmonic sphere with $\epsilon >0$, which provides a nanocapacitor and a nanoresistor; right: a plasmonic sphere with $\epsilon <0$, which gives a nanoinductor and a nanoresistor. Solid black arrows show the incident electric field, and the thinner field lines together with the gray arrows represent the fringe dipolar electric field from the nanosphere.

Figure 2

Parallel and series nanoelements. Top: two fused lossless semicylinders with positive and negative permittivities, illuminated by an optical field; middle: quasistatic potential distributions around and within the structure (solid lines show equipotential surfaces); bottom: equivalent circuits showing parallel and series elements representing the fused structure as seen from the outside.

Figure 3

Nanocircuit synthesis. Top left: conceptual nanoscale circuit formed by rectangular blocks of plasmonic and nonplasmonic segments; bottom left: its equivalent circuit; right: a closed “nanocircuit loop.”

Figure 4

An idea for optical implementation of right-handed and left-handed nanotransmission lines. Top: conventional RH and LH lines using distributed (or lumped) inductor and capacitor elements; middle: plasmonic and nonplasmonic nanostructures may play the role of nanoinductors and nanocapacitors; bottom: as the nanostructures gets closer, in the limit, plasmonic and nonplasmonic layers may be envisioned to constitute layered transmission lines with forward and backward operation.