Low-loss Mie scatterer shown to enhance Q and chirality control in silicon microring

Non-Hermitian systems and spectral degeneracies known as special points (EPs) have been studied to induce relaxation, control light transport, and improve sensor response.

The resonator ring can be brought to EP by controlling the coupling between the degenerate frequency of clockwise and counter-clockwise directions. This has typically been achieved by introducing two or more nano-tips into the resonator mode capacitor.

While this method provides a way to study EP physics, the basic understanding of how the shape of the nano-tips and the size of the symmetry effect of the non-Hermicity of the system is lost, with additional losses from both in-plane and out-of-plane. . The limited stability of the resonance poses a challenge to the effects of EP converters or modulators, which require a stable resonance of the cavity and a fixed laser-cavity detuning.

In a paper published in in LightA scientific team, led by Professor Tingyi Gu from the Department of Electrical and Computer Engineering, University of Delaware, US, and collaborators have developed lithographically-defined asymmetric and symmetric Mie-scatterers.

This allows control of subwavelength transmission and exposure without turning to additional radiation channels. They show that those pre-defined meta-units can bring the system to EP without post-tuning and enable chiral light transportation inside the resonator.

Conversely, a geometric defect, called a meta-unit, leads to an improved quality measured at the transmission port by correspondingly suppressing the backscatter from the surface roughness.

The proposed device platform makes the chiral distribution predefined and backscattering-free resonances required for various applications such as frequency cobs, solitons, sensing, and other optical nonlinear systems such as photon blockade, and excitation oscillators.

The scientists say, “Our work not only opens up a new direction in chiral silicon photonics but is important for the following four reasons. First, it reveals the important role of the spatial asymmetry of the nano-tip and Mie scatterers in bringing the system towards. EP. Second, the scattering a geometrically controlled way to drive a non-Hermitian system to and from the EP is clearly demonstrated.”

“Thirdly, our system is mechanically stable. It allows a reliable comparison between the transmission and the resonator of the perturbed micro-resonator, which shows the contribution of the nano-tip/scatter in diagonal terms. This is different from the usual way of implementing EP with two nano-tips. Fourth, the improvement of the quality of the empirical factor derived from the distribution display is shown for the first time.”