Optical Microresonators Based on Tapered Optical Fibers

我们的目标是在结构锥形光纤中实现高Q微谐振器。谐振器具有高度延长的形状。与硅微球谐振器中常用的赤道模式相比，它们维持低语廊模式，表现出两个空间上分离良好的焦散，共振场强增强。焦散的位置强烈依赖于谐振腔模式对应的闭合光路绕谐振腔轴的转数。因此，不同的模式可以通过在各自的焦散点处耦合进出谐振器的光来选择性地激发。这将通过使用抑制全内反射的辅助锥形光纤来实现。此外，我们所谓的“钟摆模式”的自由光谱范围明显小于赤道低语走廊模式。因此，在一个自由光谱范围内的钟摆模式的调谐可以很容易地实现。谐振器有利的模式几何形状，再加上它们的可调性，为限制和控制光开辟了有趣的前景。作为第一个应用，我们的目标是将有机分子偶联到谐振器模式并观察其荧光的修饰。

We aim to realize high Q microresonators in structured tapered optical fibers. The resonators have a highly prolate shape. They sustain whispering gallery modes which exhibit, in contrast to the equatorial modes commonly used in silica microsphere resonators, two spatially well separated caustics with a resonantly enhanced field strength. The position of the caustics strongly depends on the number of revolutions the closed optical path corresponding to the resonator mode carries out around the resonator axis. Different modes can therefore be selectively excited by coupling light in and out of the resonator at the respective caustic. This will be accomplished by means of auxiliary tapered optical fibers using frustrated total internal reflection. Moreover, the free spectral range of our so-called "pendulum modes" is significantly smaller than for equatorial whispering gallery modes. Therefore, a tuning of the pendulum modes over one free spectral range can easily be achieved. The advantageous mode geometry of the resonators, in combination with their tunability, opens interesting perspectives for confining and controlling light. As a first application we aim to couple organic molecules to the resonator modes and observe a modification of their fluorescence.