Fiber coupled ultra high Q microsphere resonators

Summary form only given. Whispering gallery modes (WGMs) of silica microspheres have attracted considerable attention owing to their enormous quality factors (Q's of nearly 10 billion have been measured). In early work, optical coupling to the WGMs was achieved through frustrated total internal reflection from the back face of a prism. More recently, direct coupling from optical fiber has been reported using either half-block couplers or fiber in which a narrow tapered region has been prepared (typically a few microns in diameter). Of these methods fiber taper coupling has been shown to produce an excellent coupling efficiency of 99.8% in cavities that are near critically coupled.