School Seminar Program

Light trapping with unusual waves: Bound states in the continuum

Mr Kirill Koshelev
Nonlinear Physics Centre, Research School of Physics, ANU

Interference is a common wave phenomenon in physics, whereby two or more waves pass through one another to produce a combined waveform. The effects of interference can be observed for all types of waves, but interference associated with light in optics and photonics has attracted special attention since Thomas Young’s pioneering experiments in 19th century.

Destructive interference governs the principle of operation of devices called optical resonators. Resonators are used to confine light but for only a limited time because of unavoidable light emission. Recently, an unusual form of destructive interference was discovered, associated with so-called bound state in the continuum (BICs) [1], which allow to trap a light wave in a confined space for, in theory, endless time. BICs are formed by the destructive interference of several ordinary light waves that have a similar wave’s velocity and direction of propagation. In the BIC regime, the resonator is characterized with infinite quality factor – a quantity which means the ratio of the light trapping time to the period of the wave’s oscillation. For real resonators, the quality factor of BICs is very high yet finite, dramatically improving their properties.

I will review the recent developments in the BIC physics with applications to photonics, including novel opportunities for the development of on-chip biosensors, compact quantum sources, and lasers that consume little power. I will pay a special attention to our contribution to this field highlighting the recent demonstration of the record-high efficiency of light frequency conversion at the nanoscale using a nonlinear nanoantenna with BIC waves [2].
[1] C. W. Hsu et al. Bound states in the continuum, Nature Reviews Materials 1, 16048 (2016).
[2]. K. Koshelev et al Subwavelength dielectric resonators for nonlinear nanophotonics, Science 367, 288 (2020).

Kirill Koshelev is a senior PhD student at the Nonlinear Physics Centre. His major research interest is in dielectric photonic nanostructures, nonlinear nanophotonics, and optical resonators.

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