Direct Optical Initiation (DOI), uses a moderate energy laser to shock initiate secondary explosives, via either a flyer
plate or exploding metal foil. DOI offers significant performance and safety advantages over conventional electrical
initiation. Optical fibres are used to transport the optical energy from the laser to the explosive device.
A DOI system comprises of a laser, one or more optical fibres, and one or more laser detonators. Realisation of a DOI
system is greatly eased by the use of fibre-to-fibre connections, allowing for easy integration into bulkheads or other
interfaces, such as firing tanks and environmental test chambers. Fibres to fibre connectors capable of transmitting the
required energy densities are not commercially available.
Energy densities in the region of 35 J cm-2 are required for initiation, above the damage threshold of typical optical
fibres. Laser-induced damage is typically caused by laser absorption at the input face due to imperfections in the surface
polishing. To successfully transmit energy densities for DOI, a high quality fibre end face finish is required.
A fibre-to-fibre connection utilizing micro-lens array injection into a large-core, tapered optical fibre, a hermetic fibre
bulkhead feedthrough, and a disposable test fibre has been developed. This permits easy connection of test detonators or
components, with the complex free-space to fibre injection simplified to a single operation. The damage threshold and
transmission losses of the fibre-to-fibre connection have been established for each interface.