It is now possible to fashion transparent crystalline materials into axisymmetric optical components having diameters ranging from hundreds down to tens of micrometers, whereas previously, the smallest attainable diameter was 500 μm. A major step in the fabrication process that makes this possible can be characterized as diamond turning or computer numerically controlled machining on an ultrahigh-precision lathe. This process affords the flexibility to make arbitrary axisymmetric shapes that have various degrees of complexity: examples include a flat disk or a torus supported by a cylinder (see figure), or multiple closely axially spaced disks or tori supported by a cylinder. Such optical components are intended mainly for use as whispering-gallery-mode optical resonators in diverse actual and potential applications, including wavelength filtering, modulation, photonic generation and detection of microwaves, and research in quantum electrodynamics and quantum optics.
The first step in the fabrication process is to use a brass tube bore with a 30-μm diamond suspension to cut a small cylindrical workpiece from a plate or block of the selected crystalline material. In a demonstration of the process, the cylindrical workpiece was 1.8 mm in diameter and 5 mm long; in general, different dimensions would be chosen to suit a specific application.
The workpiece is then glued to a metal cap that, in turn, is attached to the rotor of an aerostatic spindle. During the rotation of the spindle, a diamond tool is used to cut the workpiece. A computer program is used to control stepping motors that move the diamond tool, thereby controlling the shape cut by the tool. Because the shape can be controlled via software, it is possible to choose a shape designed to optimize a resonator spectrum.
This work was done by Ivan Grudinin, Anatoliy Savchenkov, and Dmitry Strekalov of Caltech for NASA’s Jet Propulsion Laboratory.
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