Abstract
Engineering light-matter interactions using non-Hermiticity, particularly through spectral degeneracies known as exceptional points (EPs), is an emerging field with potential applications in areas such as cavity quantum electrodynamics, spectral filtering, sensing, and thermal imaging. However, tuning and stabilizing a system to a discrete EP in parameter space is a challenging task. Here, we circumvent this challenge by operating a waveguide-coupled resonator on a surface of EPs, known as an exceptional surface (ES). We achieve this by terminating only one end of the waveguide with a tuneable symmetric reflector to induce a nonreciprocal coupling between the frequency-degenerate clockwise and counterclockwise resonator modes. By operating the system at critical coupling on the ES, we demonstrate chiral and degenerate perfect absorption with squared-Lorentzian lineshape. We expect our approach to be useful for studying quantum processes at EPs and to serve as a bridge between non-Hermitian physics and other fields that rely on radiation engineering.
Highlights
Engineering light-matter interactions using non-Hermiticity, through spectral degeneracies known as exceptional points (EPs), is an emerging field with potential applications in areas such as cavity quantum electrodynamics, spectral filtering, sensing, and thermal imaging
Our experimental system is composed of an on-chip whispering gallery mode microsphere resonator coupled to a tapered-fiber waveguide (Fig. 1d), which is used to couple light in and out of a resonant mode, and a fiber loop with a polarization controller acting as a tuneable end-mirror (Fig. 1a)
We have identified a resonant mode with intrinsic quality factor of 7:7 ́ 105 in the 1440 nm band and confirmed that in the absence of the end-mirror, the transmission (Tcw detected at D2 and Tccw detected at D1) and reflection spectra (Rcw detected at D1 and Rccw detected at D2) are symmetric for light input in the CW direction and CCW direction
Summary
Engineering light-matter interactions using non-Hermiticity, through spectral degeneracies known as exceptional points (EPs), is an emerging field with potential applications in areas such as cavity quantum electrodynamics, spectral filtering, sensing, and thermal imaging. C Without the end-mirror, the system has symmetric Lorentzian transmission (blue) and reflection (red) spectra for left and right incidence (CW and CCW inputs).
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