Ultralow loss single-mode silica tapers manufactured by a microheater

Using a ceramic thermoelectric heater, we show highly reproducible fabrication of single-mode subwavelength silica tapers with an ultralow loss level. The reproducibility of the process is studied statistically, leading to an average taper transmission of 94%. The best tapers have a transmission superior to 99%, above the level commonly reached by other fabrication methods. The taper profile is inspected along its length and closely follows the exponential profile predicted by the model of Birks and Li. This high degree of control over the taper shape allows a detailed analysis of the transition to the single-mode regime during tapering. As an application of this fabrication method, we present a microlooped taper probe for evanescent coupling experiments requiring fine spatial selectivity. (C) 2010 Optical Society of America