Nanocircuit Elements, Nano-Transmission Lines and Nano-Antennas Using Plasmonic Materials in the Optical Domain

 

 

 

Nader Engheta

 

University of Pennsylvania, Department of Electrical and Systems Engineering

200 South 33rd Street, Philadelphia, Pennsylvania 19104, U.S.A.

Email: engheta@ee.upenn.edu

 

 

Optical wave interaction with metallic nanoparticles is currently one of the exciting problems in nanotechnology and nano-photonics.  For some noble metals such as Ag, Au, the plasma frequency is in the visible or ultraviolet (UV) wavelengths, and therefore their permittivities have negative real parts in the infra-red (IR) and visible regimes.  The interaction of optical signals with these metals involves surface plasmonic resonances.  A nanoparticle, when exposed to optical signals, can thus be interpreted as a lumped “nano-capacitor” or “nano-inductor” operating at the optical frequencies, depending on whether its material is non-plasmonic or plasmonic, respectively.  When the material has some loss, a “nano-resistor” may also be present.  

 

Using these three nanocircuit elements, more complex circuits at optical frequencies can be formed by arranging various plasmonic and non-plasmonic nanostructures near each other and interacting with each other.  For instance, if one forms two parallel linear chains of closely-spaced plasmonic nanoparticles with an array of non-plasmonic spheres between the first two lines, this will approximately provide a ladder network of series nano-inductors and shunt nano-capacitors, which in fact makes an optical nano-transmission line.  Such transmission lines can act as guided-wave structures in the optical regime with a lateral cross section far less than the operating wavelength, analogous to the conventional transmission line in the microwave regime.  However, at the microwave and lower frequencies, the metallic elements in the structure exhibits high conductivity and thus support the flow of conduction current, whereas in the optical domain metals behave quite differently and therefore the plasmonic characteristics of the line can instead play an important role.  Changing the size and geometry of the nanostructures may modify the values of these equivalent nano-elements of circuit. This idea may be extended to more complex circuits with various applications for nano-photonic and nanoelectronic circuits involving such structures as nano-inductors, nano-capacitors, and nano-resistors with potential applications in high-capacity data storage, molecular and cellular imaging, and nanolithography.  It is important to note that one can also consider the “dual” of this nano-transmission line, i.e., a line in which the location of plasmonic and non-plasmonic nanoparticles are interchanged, i.e., one can have series capacitors and shunt inductors.  Such a nano-transmission line may exhibit a negative refractive index for 1-dimensional optical wave propagating along the line.  This is the optical version of the “left-handed” transmission lines in the microwave domains that have been studied by several groups investigating the microwave planar left-handed transmission-line metamaterials.  

 

The concept of nanocircuit elements can naturally lead to the idea of nano-antennas for nanometer-sized transmitting and receiving systems in which the nanostructure is connected to a driving source or a load, e.g., a nano-transmission line or a near-field scanning optical microscope (NSOM).  Analysis and modeling of radiation properties of such nanosystems, as receiving or transmitting antennas at the optical frequencies, can provide insights into the design and potential applications of these nanoelements.   

 

In this talk, some of these ideas will be discussed and a sample of the results of our theoretical studies on these nano-systems will be presented.

 

 

Nader Engheta is a Professor of Electrical and Systems Engineering at the University of Pennsylvania.  He received the B.S.E.E. degree from the University of Tehran in 1978, and the MS and the Ph.D. degrees in electrical engineering from Caltech in 1979 and 1982, respectively.  After spending one year as a postdoctoral research fellow at Caltech and four years as a Senior Research Scientist at Kaman Sciences Corporation’s Dikewood Division, he joined the faculty of the University of Pennsylvania, where he is currently a Professor.  He is also a member of the Mahoney Institute of Neurological Sciences, and a member of the Bioengineering Graduate Group at the University of Pennsylvania.  He was the graduate group chair of electrical engineering from July 1993 to June 1997.

 

He is a Guggenheim Fellow, a recipient of the IEEE Third Millennium Medal, a Fellow of IEEE, a Fellow of the Optical Society of America, and was an IEEE Antennas and Propagation Society Distinguished Lecturer in 1997-1999. He is an Associate Editor of IEEE Antennas and Wireless Propagation Letters.  In addition, he has been the recipient of the UPS Foundation Distinguished Educator term Chair in 1999-2000, the Fulbright Naples Chair award in 1998, a NSF Presidential Young Investigator (PYI) award in 1989, the S. Reid Warren, Jr. Award for distinguished teaching (two times) from UPenn's School of Engineering and Applied Science, the Christian F. and Mary R. Lindback Foundation Award in 1994, and the W. M. Keck Foundation's 1995 Engineering Teaching Excellence Award.

 

His areas of research activities include fields and waves phenomena, metamaterials, nano-electromagnetism, theory of nano-optics and nanophotonics, modeling of nanostructured materials, miniaturized antennas, biomimetic/bio-Inspired polarization imaging and sensing, reverse-engineering of polarization vision and information sensing in nature, hyperspectral imaging, through-wall microwave imaging, electromagnetics of event-related brain cortical potentials, mathematics of fractional operators and fractal domains.  He has organized/co-organized various special sessions on the topic of metamaterials and complex media in international symposia and conferences.   He has guest edited/co-edited several special issues, namely, the special issue of Journal of Electromagnetic Waves and Applications on the topic of "Wave Interaction with Chiral and Complex Media" in 1992, part special issue of the Journal of the Franklin Institute on the topic of “Antennas and Microwaves (from the 13th Annual Benjamin Franklin Symposium) in 1995, special issue of the Wave Motion on the topic of “Electrodynamics in Complex Environments” (with L. B. Felsen) in 2001, and special issue of the IEEE Transactions on Antennas and Propagation on the topic of “Metamaterials” (with R. W. Ziolkowski) in 2003.