University of Southampton

Neil Gregory Raphael Broderick

David John Richardson

Tanya Mary Monro

Liang C Dong

Daniel William Hewak

Yvonne Deana West

Herman Leonard Offerhaus

Rowland Sammut

Peter Jonathan Bennett

To overcome problems of fabricating conventional core-clad optical fibre from non-silica based (compound) glass, it is proposed to fabricate non-silica based (compound) glass optical fibre as holey fibre i.e. one contining Longitudinal holes in the cladding. This removes the conventional problems associated with mismatch of the physical properties of the core and clad compound glasses, since a holey fibre can be made of a single glass composition. With a holey fibre, it is not necessary to have different glasses for the core and cladding, since the necessary refractive index modulation between core and cladding is provided by the microstructure of the clad, i.e. its holes, rather than by a difference in materials properties between the clad and core glasses. Specifically, the conventional thermal mismatch problems between core and clad are circumvented. A variety of fibre types can be fabricated from non-silica based (compounds) glasses, for example: single-mode fibre; photonic band gap fibre; highly non-linear fibre; fibre with photosensitivity written gratings and other refractive index profile structures; and rare-earth doped fibres (e.g. Er, Nd, Pr) to provide gain media for fibre amplifiers and lasers.

Holey optical fibres of non-silica based glass

An optical fibre has a cladding layer surrounding a core, the cladding layer comprising at least a first, relatively inner generally cylindrical region, a third, relatively outer generally cylindrical region, and a second region disposed between the first and third regions, the second region having a higher refractive index than the first and third regions; and the peak difference in refractive index between the first cladding region and the core being less than about 0.0030.

Optical fiber and optical fiber device

The percentage fraction of fundamental mode power located in the cladding holes of different holey fibers (PF ) is shown as a function of wavelength in microns of the fundamental mode (&lgr;). Properties of two groups of holey fibers are shown. The upper group of three curves shows embodiments of the invention with &Lgr;&equals;0.75 &mgr;m and d/&Lgr;&equals;0.6, 0.7 & 0.8 respectively, where d is the hole diameter and &Lgr; the hole spacing or pitch. The lower group of curves, which are almost superimposed on each other, show properties of holey fibers representative of the prior art with &Lgr;&equals;3.2 &mgr;m and d/&Lgr;&equals;0.6, 0.7 & 0.8 respectively. A huge improvement in the mode power present in the holes is evident. In the prior art curves, the mode power fraction is generally less than 1%, whereas with the illustrated embodiments of the invention, holey fibers with 10-40% of the fundamental mode power in the holes are achieved. Generally the holey fiber should be structured such that the wavelength of the guided light &lgr;>2.2&Lgr;. For telecommunications wavelengths, this means that the hole spacing should be smaller than typical in the prior art, i.e. around 1 &mgr;m or less, and the hole diameter should be as large as possible in relation to the hole spacing, preferably d/&Lgr;>&equals;0.6.

Holey optical fibers

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Southampton, United Kingdom

Neil Gregory Raphael Broderick