Penn Theorists To Create Optical Circuit Elements

Inthe Aug. 26 issue of Physical Review Letters, currently online, thePenn theorists outline how familiar circuit elements -- inductors,capacitors and resistors could be created on the nanoscale (about abillionth of a meter) in order to operate using infrared or visiblelight. The Penn researchers describe how nanoscale particles of certainmaterials, depending on their unique optical properties, could work ascircuit elements. For example, nanoscale particles of certain metals,such as gold or silver, could perform the same function in manipulatingan "electric" current as an inductor does on a circuit board.

Opticalelectronics would make it possible to create faster computerprocessors, construct nanoscale antennas or build moreinformation-dense data- storage devices. Optical electronics could alsohave exotic applications that simply are not possible with conventionalelectronics, such as the ability to couple an electronic signal to anindividual molecule or the creation of biological circuits.

"Thewavelength of light can be measured in hundreds of nanometers and thetechnology is now available to create structures that would operate onthe same or smaller scale as the wavelength of light," wrote NaderEngheta, lead author, and H. Nedwill Ramsey, professor in theDepartment of Electrical and Systems Engineering of Penn's School ofEngineering and Applied Science. "Our work is theoretical, of course,but we do not foresee any sizable barriers to our plan to make thesecircuit elements in the near future."

Before they coulddescribe how to create optical circuit elements, Engheta, his coauthorsand students Alessandro Salandrino and Andrea Al had to first envisionhow nanoscale materials might interact with light. To do so they lookedat a property critical to basic wave interaction called permittivity,which describes how a particular substance affects electromagneticfields. If a small sphere is created, about a few tens of nanometersacross, they explained, light would affect it differently based on itspermittivity.

According to their models, the theoristsdemonstrated that nano-sized sphere made up of a nonmetallic materialsuch as glass with permittivity greater than zero would act like aminiaturized capacitor. A nano-sized sphere made up of a metallicmaterial such as gold or silver with a permittivity less than zerowould act like a miniaturized inductor. Either material could alsofunction like a miniaturized resistor, depending on how the opticalenergy is lost in it.

"So now we have three basic elements of acircuit," Enghata said. "Stacked one upon the other, you could createfairly advanced combinations of circuitry. It is even possible to usethese elements to create 'nano' transmission lines and 'nano' cables.

"Foryears, conventional circuit elements have been the basic building blocin making functional circuits at lower frequencies," Engheta said. "Butnow we have the tools to push back the limits of speed and power onelectronics. This technology could have innumerable applications forconsumer products, advanced instrumentation and even medicine."