Optical fibre step-index

Figure 14.32 Types of optical fibre (a) stepped index fibre, (b) graded index fibre and (c) monomode fibre...

Figure 12.3 Principle of mode propagation and dispersion in optical fibres. Top multi-mode step-index fibre bottom single-mode step-index fibre. Typical intensity profiles of the beams exiting the fibre are shown on the right, exhibiting a speckle pattern for the multi-mode fibre and a Gaussian profile for the single-mode fibre...

A modified crucible technique allows the preparation of gradient index optical fibres [276,301]. In this technique, a larger distance between the nozzles of inside and outside crucible is used, so that the glass leaving the inner crucible flows through the melt of the outer crucible. During this time, ion diffusion occurs to form a parabolic index profile. An ion diffusion process can also be initiated during an additional thermal treatment step. 

Special optical fibres can also be produced by a modified jacketing method [270]. A tapered glass preform is produced by suction casting of the core material into a tube made of the cladding material. This initial preform is then drawn off and loosely joined to circular positioned outer tube glasses to form a secondary preform, which is used for the fibre drawing process. This method allows the production of multi-layer fibres with large refractive index steps. 

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