Small perturbations in the dielectric environment around resonant dielectric structures usually lead to a frequency shift of the resonator modes directly proportional to the polarizability of the perturbation. Here, we report experimental observations of strong frequency shifts that can oppose and even exceed the contribution of the perturbations’ polarizability. We show in particular how the mode frequencies of a lithium niobate whispering-gallery-mode resonator are shifted by planar substrates—of refractive indices ranging from 1.50 to 4.22—contacting the resonator rim. Both blue- and redshifts are observed, as well as an increase in mode linewidth, when substrates are moved into the evanescent field of the whispering gallery mode. We compare the experimental results to a theoretical model by Foreman et al. [J. Opt. Soc. Am. B 33, 2177 (2016) [CrossRef] ] and provide an additional intuitive explanation based on the Goos–Hänchen shift for the optical domain, with applications to dielectric structures ranging from meta-surfaces to photonic crystal cavities.

中文翻译：

---

介电扰动：光学谐振器中的异常谐振频率偏移

谐振介电结构周围的介电环境中的小扰动通常会导致谐振器模式的频移直接与扰动的极化率成正比。在这里，我们报告了强烈的频率偏移的实验观察结果，这些频率偏移可能会干扰甚至超过扰动的极化率。我们特别显示了铌酸锂耳语画廊模式共振器的模频率如何通过与共振器边缘接触的折射率为1.50至4.22的平面基板移动。当基板移动到耳语画廊模式的渐逝场中时，会观察到蓝移和红移，以及模式线宽的增加。我们将实验结果与Foreman等人的理论模型进行比较。[J. 选择。Soc。是。乙33，2177（2016）[交叉引用] ]，并提供基于所述古斯汉欣位移用于光学域中的附加直观的解释，以应用电介质结构从元表面的光子晶体的空腔。