Abstract

The speaker introduces an unique type of “energy-balanced” zero-index media, whose effective permittivity and permeability are both purely imaginary, but with opposite signs, indicating the coexistence and balance of loss and gain. The speaker shows that such an “energy-balanced” zero-index medium can support “propagation” with the “wavelength” determined by the magnitudes of loss and gain. An interesting physical phenomenon manifested in the medium is that it leads to coherent perfect absorption (CPA) or lasing when proper interference is introduced. In particular, when the loss and gain share the same magnitude, the so-called “CPA lasing”, which was previously proposed in parity-time (PT) symmetric systems, can be realized. The functionality can be tuned from CPA to lasing by tuning the phase of the incident wave. The speaker and his group propose a route to realize such an “energy-balanced” zero-index medium by using a photonic core-shell structure composed of lossy cores coated by shells made of gain media. The unique functionality as a CPA lasing device is confirmed by numerical simulations. Their work reveals unique and intriguing physics which is induced by balanced gain and loss in different parameters of a homogeneous medium.

About the speaker

Prof Yun Lai obtained his Bachelor's degree in Nanjing University in 1999 and his PhD degree in HKUST in 2005. He was a Research Associate in HKUST after graduation and became a Professor in Soochow University in 2011. He is currently a Professor in School of Physical Science and Technology in Soochow University.

Prof Lai's research areas include metamaterials, photonic and phononic crystals, etc. He has published more than 40 papers in Science Citation Index (SCI) journals like Nature Materials and Physical Review Letters, which have been cited for more than 1,400 times.

The seminar is free and open to all. Seating is on a first-come, first-served basis.

HKUST Jockey Club Institute for Advanced Study
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