PHILADELPHIANew engineering research at the University of Pennsylvania demonstrates that polaritons have increased coupling strength when confined to nanoscale semiconductors. This represents a promising advance in the field of photonics: smaller and faster circuits that use light rather than electricity.
The research was conducted by assistant professor Ritesh Agarwal, postdoctoral fellow Lambert van Vugt and graduate student Brian Piccione of the Department of Materials Science and Engineering in Penn's School of Engineering and Applied Science. Chang-Hee Cho and Pavan Nukala, also of the Materials Science department, contributed to the study.
Their work was published in the journal Proceedings of the National Academy of Sciences.
Polaritons are quasiparticles, combinations of physical particles and the energy they contribute to a system that can be measured and tracked as a single unit. Polaritons are combinations of photons and another quasiparticle, excitons. Together, they have qualities of both light and electric charge, without being fully either.
"An exciton is a combination of a an electron, which has negative charge and an electron hole, which has a positive charge. Light is an oscillating electro-magnetic field, so it can couple with the excitons," Agarwal said. "When their frequencies match, they can talk to one another; both of their oscillations become more pronounced."
High light-matter coupling strength is a key factor in designing photonic devices, which would use light instead of electricity and thus be faster and use less power than comparable electronic devices. However, the coupling strength exhibited within bulk semiconductors had always been thought of as a fixed property of the material they were made of.
Agarwal's team proved that, with the proper fabrication and finishing techniques, this limit can be broken.
"When you go from bulk sizes to one micron, the light-m
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University of Pennsylvania