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FEATURE ARTICLE

Microspheres, Photonic Atoms and the Physics of Nothing

Light can become trapped within tiny, transparent spheres. The surprising properties that result may turn "microsphere photonics" into an important new technology

Stephen Arnold

Figure 4. Spectrum of light . . .Click to Enlarge Image

Amazing things can happen inside a tiny transparent sphere, say one that is just 10 micrometers across: Photons can get trapped, bouncing around the interior by total internal reflection, in much the same way that photons are channeled inside optical fibers. In a sphere, the photons orbit around the interior when the frequency of their light is such that an integral number of wavelengths fit into a complete circuit. Photons generated within such a sphere have a strong penchant to travel in such modes, a consequence of the so-called cavity quantum electrodynamic effect. This preference allows a number of interesting applications. A transparent microsphere can, for example, form a particularly efficient laser cavity. It can also function as an optical filter, which could be used to tune into a single signal being carried with many others along a fiber-optic cable. Another future area of application is in biochemical sensing.


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