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.