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Microspheres, Photonic Atoms and the Physics of Nothing

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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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