Grant: Research Tools and Instruments - Category 1 (<$150,000)

Fibre Bragg gratings are generally written in fibres with ultra-violet lasers, or more recently with femtosecond pulse lasers. In order to increase the refractive index change for the purpose of fabricating strongly reflecting gratings through the exposure to the lasers, it has been necessary to photosensitise the optical fibre by doping the fibre with boron and/or with high pressure hydrogen of order 200Bar. The latter requires special equipment and handling and is the only technique available to write good gratings in standard optical fibres with UV lasers. Femtosecond lasers can be used with hydrogen-free fibres, but are generally used in a point-by-point writing, or with care using a phase-mask. The quality of gratings can be variable, without great care being used. We have recently proposed and shown the writing of excellent gratings in boron and hydrogen-free fibres with a new laser on loan to us, allowing for the first time the writing very strong gratings in almost any optical fibre, using standard UV laser writing techniques. We have shown that strong gratings (R=99%, 3mm long) can be written in standard fibres without any hydrogen. We are the only group in the world to have suggested the use of this laser for grating writing, and shown that very strong gratings can be also written in rare-earth doped fibres as well, without special treatment. This proposal is for the purchase of this laser from its only manufacturer, as it will give us a world lead in the fabrication of complex devices in almost any fibre without special treatment. Life without hydrogen would be greatly simplified.