Long period gratings based frequency selective interrogation of micro-resonators along the same fiber

A novel optical fiber coupler to whispering gallery mode (WGM) micro-resonators, which allows frequency selective addressing of different micro-resonators along the same fiber, is proposed. The coupling unit is based on a pair of identical long period fiber gratings (LPGs) and a thick adiabatic taper (> 15 mu m in waist) in between, where evanescent coupling from cladding modes to WGMs takes place. This robust unit can be replicated more times along the same fiber, simply cascading LPGs with different bands. Independent addressing of two different resonators along the same fiber is demonstrated.