Abstract
In the Terahertz (THz) domain, we investigate both numerically and experimentally the directional emission of whispering gallery mode resonators that are perturbed by a small scatterer in the vicinity of the resonators rim. We determine quality factor degradation, the modal structure and the emission direction for various geometries. We find that scatterers do allow for directional emission without destroying the resonator's quality factor. This finding allows for new geometries and outcoupling scenarios for active whispering gallery mode structures such as quantum cascade lasers and passive resonators such as evanescent sensors. The experimental results agree well with finite difference time domain simulations.
Highlights
In the Terahertz (THz) domain, we investigate both numerically and experimentally the directional emission of whispering gallery mode resonators that are perturbed by a small scatterer in the vicinity of the resonators rim
We find that scatterers do allow for directional emission without destroying the resonator’s quality factor
Whispering gallery mode (WGM) resonators are frequently used as laser cavities in quantum cascade lasers (QCLs) [1,2,3]
Summary
Whispering gallery mode (WGM) resonators are frequently used as laser cavities in quantum cascade lasers (QCLs) [1,2,3]. This allows for high quality (Q) factors and directional emission from modes localized on stable periodic lightray-orbit [1,4] or by the short term dynamics of the chaotic light ray-dynamics inside the resonator which channels a direct emission port [5,6,7] Efficient coupling of such emitted waves into waveguides has been studied [8, 9]. Fluids, or particles surrounding the resonator influence the evanescent field by either shifting the effective refractive index or by absorption [18,19,20] This alters the modal structure of the resonator, resulting in mode shifts and altered quality (Q) factors. We will show experimental results on the outcoupling performance and compare the results to theory
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