Etch-eroded fiber coupler for whispering-gallery-mode excitation in high-Q silica microspheres

A simple and inexpensive technique for the excitation of whispering-gallery-modes in silica microspheres is presented. In this technique, the cladding of a single-mode optical fiber is etched chemically in order to expose the fiber´s evanescent field. The cladding can be eroded partially, or removed completely with continued etching into the core. The etch-erosion procedure requires a minimum of specialized equipment and preparation time.