Optimizing Light Coupling into Microresonators with Whispering Gallery Modes for Optical Sorting Techniques

Our goal is to develop an effective device to sort microparticles using Whispering Gallery Mode (WGM) resonances. The device is centered on a tapered optical fiber, immersed in a liquid suspension with microparticles of interest. The fiber is fed by laser light of a particular wavelength. As microparticles come in contact with the tapered section of the fiber, the particles whose resonance match the wavelength of the laser will be selectively moved by evanescent light along the taper into a special container. This method allows for sorting particles with unprecedented selectivity, with immediate applications in photonics, microbiology, biomedicine, and pharmaceuticals. In order to optimize this sorting method, we compare two different fiber-tapering techniques. The first one is chemical etching in hydrofluoric acid; the second technique is heating and pulling the fibers. Both methods allow for making tapers down to a diameter of 1-3 microns. The smaller diameters allow for higher efficiency of light coupling. However, due to their small size, they are more vulnerable to breaking.