Exceptional points enhance sensing in an optical microcavity
Exceptional points enhance sensing in an optical microcavity
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DOI：
10.1038/nature23281
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发表时间：
2017-08-10
期刊：
影响因子：
64.8
通讯作者：
Yang, Lan
中科院分区：
文献类型：
--
作者：
Chen, Weijian;Ozdemir, Sahin Kaya;Yang, Lan
传感器在日常生活的许多方面发挥着重要作用，例如家庭安全系统中的红外传感器，环境监测中的颗粒传感器和移动的手机中的运动传感器。高质量的光学微腔是传感应用的主要候选者，因为它们能够在非常有限的体积内增强光与物质的相互作用。这种装置的实例包括机械换能器（1）、磁力计（2）、单粒子吸收光谱仪（3）和用于测量单个粒子大小（4）和检测纳米级物体（例如单个纳米粒子和原子离子）的微腔传感器（5-7）。传统上，光学微腔附近的非常小的扰动引入线宽的变化或与扰动的强度成比例的共振的频移或分裂。在这里，我们展示了一种替代的传感方案，通过该方案，当在被称为例外点的非厄米光谱简并处操作时，可以增强微腔的灵敏度（8-16）。在我们的实验中，我们使用两个纳米级散射器来调谐回音壁模式的微型环形腔，其中光通过连续的全内反射以精确和受控的方式沿着沿着凹面传播到例外点（12，13）。随后进入腔的倏逝场的目标纳米级物体从其例外点扰动系统，导致频率分裂。由于例外点附近的复平方根拓扑结构，该频率分裂缩放为扰动强度的平方根，因此比在传统的非例外点感测方案中观察到的分裂更大（对于足够小的扰动）。我们对异常点增强灵敏度的演示为具有前所未有的灵敏度的传感器铺平了道路。
Sensors play an important part in many aspects of daily life such as infrared sensors in home security systems, particle sensors for environmental monitoring and motion sensors in mobile phones. High-quality optical microcavities are prime candidates for sensing applications because of their ability to enhance light-matter interactions in a very confined volume. Examples of such devices include mechanical transducers(1), magnetometers(2), single-particle absorption spectrometers(3), and microcavity sensors for sizing single particles(4) and detecting nanometre-scale objects such as single nanoparticles and atomic ions(5-7). Traditionally, a very small perturbation near an optical microcavity introduces either a change in the linewidth or a frequency shift or splitting of a resonance that is proportional to the strength of the perturbation. Here we demonstrate an alternative sensing scheme, by which the sensitivity of microcavities can be enhanced when operated at non-Hermitian spectral degeneracies known as exceptional points(8-16). In our experiments, we use two nanoscale scatterers to tune a whispering-gallery-mode micro-toroid cavity, in which light propagates along a concave surface by continuous total internal reflection, in a precise and controlled manner to exceptional points(12,13). A target nanoscale object that subsequently enters the evanescent field of the cavity perturbs the system from its exceptional point, leading to frequency splitting. Owing to the complex-square-root topology near an exceptional point, this frequency splitting scales as the square root of the perturbation strength and is therefore larger (for sufficiently small perturbations) than the splitting observed in traditional non-exceptional-point sensing schemes. Our demonstration of exceptional-point-enhanced sensitivity paves the way for sensors with unprecedented sensitivity.