Kabish Wisal

Editor’s summary High-power fiber lasers are used in a range of scientific fields in addition to their standard use for technology. However, increases in laser output power are limited by nonlinear effects that can damage the optical components and reduce the beam quality. Rothe et al. used a spatial wavefront-shaping technique for multimode fiber lasers that mitigates the detrimental processes, thus enabling output power to be increased appreciably while maintaining beam quality. —Ian S.

Abstract In many linear and nonlinear systems, time-reversal symmetry makes it possible to control the output waves by appropriately shaping the input waves. However, time-reversal symmetry is broken in systems with energy dissipation, necessitating a different approach for relating the input and output fields. We theoretically consider a saturated multimode fibre amplifier in which light generates a heat flow and suffers thermo-optical nonlinearity, thus breaking time-reversal symmetry.

Popular Summary Optical fibers are used widely in communications and as media for the amplification of light. When the power level of the light within a fiber becomes sufficiently high, new effects arise due to a nonlinear interaction between the light and the fiber material. One of the most harmful effects is reflection of light from forward-to-backward propagation through interaction with mechanical vibrational waves in the fiber, an effect known as stimulated Brillouin scattering (SBS).