Fiber lasers and amplifiers with reduced optical nonlinearities employing large mode area fibers

摘要

Fiber lasers have recently received a lot of attention after the dramatic increase in output power achieved from single fibers. In particular, Ytterbium doped fibers offer a very low quantum defect and a very broad emission between 1 and 1.1 μm. Triggered by the progress in high-brightness pump diodes and the availability of large-mode-area (LMA) gain fibers, several fiber lasers with output powers in the 1kW range from a single fiber have been demonstrated. While these demonstrations typically employ a length of gain fiber pumped via free-space coupling and free space optics as the high reflector, there are fewer reports of integrated all-fiber laser cavities, e.g. [4]. The availability of high-power fiber-optic components and the assembly thereof is therefore crucial for making this technology accessible for a variety of applications. Fiber lasers and amplifiers are very attractive light sources for applications requiring high power as well as excellent beam quality, because they are much less susceptible to thermo-optic distortions than conventional solid-state lasers. A transform-limited beam quality (M~2=1) is possible even at kW level output power. Another advantage is the excellent overlap between the signal light and the pump absorption achievable in properly designed fibers. This allows a very efficient operation and up to 80% of optical conversion efficiency have been demonstrated based on the launched pump power. Once assembled, fiber-optic modules do not require alignment and are therefore inherently robust. The tight confinement of the laser light combined with the long interaction length in fibers also makes them prime candidates for high gain systems.