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.