Efficient and scalable side pumping scheme for short high-power optical fiber lasers and amplifiers

A new and simple method of pumping short high-power optical fiber lasers and amplifiers is described. In our approach, several passive coreless optical fibers are brought into direct contact alongside a single rare-earth doped active fiber which constitutes the active medium of the laser (amplifier). Pump light is delivered through the passive coreless fibers and penetrates into the active fiber via evanescent field coupling. To enhance the pump absorption in the gain medium, high-order spatial modes are excited in the pump delivery fibers, and an active fiber with high concentration of the dopant ions is used. As a demonstration of the viability of our approach, test results are reported on a 12-cm-long Er⁺³-Yb⁺³ codoped phosphate glass fiber laser. The laser output reaches 5 W using 23-W pumping into six coreless fibers. Above threshold, the laser has ∼24% optical-to-optical conversion efficiency (with ∼64% being the theoretical maximum). The linearity of the input-output characteristic for the laser suggests that the output power can be scaled up by applying higher pump power.