Analysis of laser efficiency and thermal effects in kilowatt fiber lasers based on distributed side-coupled fibers

摘要

The laser efficiency and temperature distribution in distributed side-coupled cladding-pumped (DSCCP) fiber lasers are investigated, using a precise and complete analytic model. We show that high-order mode pump handling and (N + 1) (N ≥ 2) DSCCP fibers can achieve a high laser efficiency when the fibers are separated. In terms of multistage pump schemes, a high laser efficiency requires an appropriate pump-node number and arrangement. According to our calculations, the temperature evolution along the signal fiber could give rise to a fluctuation in the case of strong coupling, which could decrease the mode instability threshold. The fluctuation period is usually determined by the DSCCP structure including the pump fiber number, the fiber diameter, and the fiber spacing. It is suggested that the mode instability threshold can be depressed through excellent DSCCP structure design and the selection on an appropriate pump scheme.