Novel coupling device of high peak power pulsed laser to multimode fiber

A novel coupling method for injecting a high peak power laser into a multimode optical fiber through cone-channel condenser is introduced. The novel coupler is investigated by experiments and theories. The design minimizes the irradiance on the fiber input face and reduces its dependence on the system alignment. A simple lens and a special designed cone-channel condenser operate together to transform a laser beam with 5 mm diameter into a smaller one that fits on the 400 μm or 600 μm diameter fiber face. The method resolves the problem that laser induce damage to fiber input end faces. The design principle and method of cone-channel condenser are described by the light transmission theory. The prototype was fabricated without anti-reflection coatings on the end faces. The experimental results show that the transmission efficiency of cone-channel condenser is up to 90%. Though there was 1 mm gap between the cone-channel condenser and a fiber, the coupling efficiency of cone-channel condenser to fiber reach 73%. The maximum transmitted energy before front-face of cone-channel condenser breakdown is 84.5mJ. The transmission capacity of fiber increases by 2-3 times comparing with the traditional method. The interest in this new coupling method is related to the development of transmitting high peak powers through multimode fibers applied to laser-based firing systems for initiating explosives and driving flyer, et al.