Newswise – Non-Hermitian systems with their spectral degeneracies known as singular points (EPs) have been explored for lasing, controlling light transport and enhancing sensor response. A ring resonator can be driven to EP by controlling the coupling between clockwise and anticlockwise modes of its frequency degeneracy. This is usually achieved by inserting two or more nanotips into the resonator mode volume. Although this method provides a way to study EP physics, there is a lack of basic understanding of how the symmetry of nanotip shape and size affects the non-Hermitianity of the system, as well as additional losses from both in-plane and out-of-plane scattering. . Limited resonant stability challenges the use of EP effects for switches or modulators, requiring stable cavity resonance and fixed laser cavity detuning.
in the new paper Published in eLight, a team of scientists led by Professor Ting Gu from the Department of Electrical and Computer Engineering at the University of Delaware, USA and co-workers have developed lithographically defined asymmetric and symmetric Mie scatterers. It allows subwavelength control of transmission and reflection without switching to additional radiation channels. They show that these predefined meta-units can drive the system to EP without further tuning and enable chiral light transport in the resonator. Counterintuitively, a geometrical defect, called a meta-entity, leads to an enhanced quality factor measured at the transmission port by coherent suppression of backscatter from surface roughness. The proposed device platform enables predetermined chiral light propagation and backscatter-free resonances required for various applications such as frequency combs, solitons, sensors, and other nonlinear optical processes such as photon blocking and regenerative oscillators.
These scientists emphasize the importance of their work:
“Our work not only opens a new direction for chiral silicon photonics, but is important for the following four reasons.
First, it reveals the critical role of the spatial asymmetry of the nano-tip and Mie scatterers in driving the system to EP. Second, the geometry-controlled path of the scatterer moving towards and away from the EP of the non-Hermitian system is illustrated in detail.
Third, our system is mechanically stable. This allows a reliable comparison between the transmission and reflection spectra for a perturbed microresonator, revealing the nano-tip/scatter contribution in the off-diagonal terms. This differs from the conventional way of achieving EP with two nano-tips. Fourth, the enhancement of the empirical quality factor extracted from the transmission spectrum is demonstrated for the first time.
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This work was supported by the Defense Advanced Research Projects Agency (N660012114034) and the Air Force Office of Scientific Research (AFOSR) Multi-University Research Initiative (FA9550-21-1-0202, FA9550-18-1-0235, and FA9550-18). -1-0300).
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