Fabry-Perot resonances in tapered hollow-core fibers

We are studying the frequency selective properties of a tapered silica capillary for applications in multiwavelength optical communications. The 22-nm wall thickness capillary presents Fabry-Perot resonances at 6.4 THz intervals in the 1500-nm band. With resonances as sharp as 1 .5 nm such capillaries could serve as stable inexpensive fibered Fabry-Perot reference filters.