The Art of the Impossible: Sorting Dielectric Microspheres by using Light

Use of resonant light forces opens up a unique approach to high-volume sorting of microspherical resonators with 1/Q accuracy, where Q is the resonance quality factor. Based on a two-dimensional model, it is shown that the sorting can be realized by allowing spherical particles to traverse a focused beam. Under resonance with the whispering gallery modes (WGM), the particles acquire significant velocity along the laser beam which should allow sorting dielectric microspheres with almost identical positions of their WGM resonances. This is an enabling technology for developing super-low-loss coupled-cavity structures and devices.