Lasing in a gain-guided, index-antiguided fiber

Abstract

Fiber lasers are not readily be made to oscillate in a single transverse mode, so the beam quality is not suitable for some application. As an alternative, the University of Central Florida's College of Optics and Photonics demonstrated a laser that oscillates on the lowest-order transverse mode. It has a large core with limited optical intensity that can be scaled to very high powers. Unlike conventional optical fibers, the fiber does not rely on total internal reflection to confine light to the core. The refractive index of the cladding is greater than that of the core so that the fiber is index-antiguided. When doped with lasing ions and optically pumped, a point is reached where the gain between core-cladding reflections is equal to the loss at each reflection. This point is the gain guiding, where propagation through a length of fiber takes place with no net loss. Once the threshold for gain-guiding has been achieved, more gain is required to overcome other resonator losses to reach the threshold for lasing but when the laser threshold is attained, the gain saturates at the threshold value and never goes any higher. The laser oscillates only in the lowest-order mode independent of pump power or core size. Show more