Random hole optical fibers

Conventional telecommunications fibers rely on a refractive index difference between the core and cladding region to confine light to the central core region. The refractive index difference is produced by different compositions of glass in the core and cladding regions. In contrast, holey optical fibers rely on an array of air holes in the cladding to confine light to the fiber core. Ordered hole fibers have been fabricated in the past by many groups by drawing an array of glass tubes stacked around a solid central core. These holes are ordered carefully into a predetermined array. In this paper, we describe a new technique to produce holes (or pores) in the cladding region, which are randomly distributed around the solid central core. These new fibers have been made by drawing a preform, consisting of a porous outer cladding region surrounding a solid central core region, into a fiber. A gas producing powder has been incorporated into the preform such that during the fiber drawing process, the pores are formed in-situ in the preform cladding region. This in-situ gas production method produces small diameter, long, thin tubular pores in the fiber. Controlling the processing parameters can control the physical dimensions and distribution of the pores in the fiber. In some of the preforms that have been prepared, the porous cladding region has been prepared by sol gel techniques. In other preforms, the pores have been introduced by a variety of different techniques. The preform fabrication process and fiber drawing process used to produce these new holey fibers as well as the results of the morphological study elucidating the size, shape and distribution of the porous phase are presented.