Search

We experimentally demonstrate spatial beam self-cleaning in an Yb-doped graded-index multimode fiber taper, both in passive and active configurations. The input laser beam at 1064 nm was injected for propagation from the small to the large core side of the taper, with laser diode pumping in a counterdirectional configuration. The Kerr effect permits to obtain high-beam quality amplification with no accompanying frequency conversions. As a result, our nonlinear taper amplifier may provide an important building block for multimode fiber lasers and amplifiers.

An all-silica photonic bandgap fiber composed of a low-index core surrounded by alternating high- and low-index rings allows us to achieve a large mode area (500 microm(2)) and large chromatic dispersion. Sharp resonances from the even Bragg mode to odd ring modes theoretically lead to 20,000 ps/(nm km) chromatic dispersion when large bends are applied. By nature, sharp resonances are sensitive to inhomogeneities along the fiber length. Under experimental conditions, the resonances are broadened and the dispersion coefficient is decreased to 1000 ps/(nm km). However, to the best of our knowledge, this is the largest dispersion coefficient reported using a large mode area fiber.

Photonic bandgap fibers have already proved their huge potential for guiding light in air over kilometric lengths. Nowadays, solid-core bandgap fibers draw considerable attention due to their unusual properties. For instance, the bandgap effect may lead to very large mode area operation, management of the chromatic dispersion curve, spectral filtering or bend loss reduction, all features that could enhance fiber laser performances. Recent results about the design, fabrication and characterization of large mode area solid-core bandgap fibers are presented. Prospects of further development of bandgap fiber lasers are discussed.