School of Physics & Technology, Key Laboratory of Artificial Micro/Nano Structure of Ministry of Education, Wuhan University, Wuhan 430072, China.
Lab Chip. 2020 Aug 7;20(15):2656-2662. doi: 10.1039/d0lc00395f. Epub 2020 Jun 24.
Resonators have been used in a wide range of fields, such as biochemical detection and microscale lasers. In recent years, optofluidic resonators have attracted a significant amount of attention owing to their unique liquid environments. Liquids containing biochemical samples can be designed to pass through the ring resonators or to directly form droplets, for sample sensing. Liquid diffusion is an important property in optofluidic applications, such as gradient refractive index lenses and waveguides. However, liquid diffusion has not been used in the study of optofluidic resonators, for both possible sensing characteristics, and unidirectional emission that is mostly acted as light sources. Here, we introduce a gradient refractive index profile formed by liquid diffusion in annular channels into a circular resonator, forming a gradient-index resonator with a tunable unidirectional emission. For both simulations and experiments, the squeezed and non-rotationally symmetrical light intensity profile was first obtained in a circular resonator. The squeezed light profile enables unidirectional emission in circular resonators, which is difficult to achieve in conventional ones. The squeezed light profile and unidirectional emission are determined by the refractive index difference of the liquids used, the dimension of the circular channels, and the working wavelengths. In experiments, different dimensions of bending radii were demonstrated and a tunable squeezed light intensity profile and unidirectional emission were exhibited. Interestingly, the squeezed coefficient of light, which was about 1.8 for a bending radius of 100 μm, enabled emission with a divergence angle as small as 14 degrees, which could be used for laser emission applications in the future. This work reveals the significant potential of the novel liquid gradient refractive index resonator, which provides a practicable approach for optofluidic resonator emission applications and also has potential for use in optofluidic sensing based on the squeezed light profile.
谐振器在生化检测和微尺度激光器等多个领域得到了广泛的应用。近年来，由于其独特的液体环境，光流体谐振器引起了人们的极大关注。可以设计含有生化样本的液体流过环形谐振器或直接形成液滴，以进行样品感应。液体扩散是光流体应用中的一个重要特性，例如梯度折射率透镜和波导。然而，液体扩散尚未应用于光流体谐振器的研究中，这可能是因为其具有潜在的传感特性，以及作为光源的单向发射特性。在这里，我们在圆形谐振器中引入了由环形通道中的液体扩散形成的梯度折射率分布，形成了具有可调谐单向发射的梯度折射率谐振器。通过模拟和实验，我们首先在圆形谐振器中获得了压缩和非旋转对称的光强分布。这种压缩光分布使得在圆形谐振器中实现单向发射成为可能，而这在传统的谐振器中是很难实现的。压缩光分布和单向发射取决于所使用的液体的折射率差、圆形通道的尺寸和工作波长。在实验中，我们演示了不同尺寸的弯曲半径，并展示了可调谐的压缩光强度分布和单向发射。有趣的是，对于弯曲半径为 100 μm 的情况，光的压缩系数约为 1.8，这使得发射的发散角小至 14 度，这在未来可能用于激光发射应用。这项工作揭示了新型液体梯度折射率谐振器的巨大潜力，为光流体谐振器的发射应用提供了一种可行的方法，并且基于压缩光分布，也有可能用于光流体传感。
