Fourier Pulse Shaper for High Power Fiber Coupled Lasers and Supercontinuum Sources

Femtosecond pulse shaping, a widely used technology, enables the generation of light sources with arbitrary amplitude, phase and polarization in the ultrafast regime. This technology has seen applications in fiber and nonlinear optics, OCT, confocal microscopy, bandpass filtering etc. However, these shapers work primarily at low optical powers under the 100mW level, limited by in and out coupling optics, shaper configurations and optical design of the shaper. Recently, another exciting field of research has been high power fiber laser sources. Various high power fiber sources based on a variety of nonlinear phenomena such as high power supercontinuum sources, Raman lasers etc have been demonstrated. However, owing to 10s of W class optical powers involved, Fourier shaping in this field has not been utilized effectively thereby limiting many potential applications. Here, we demonstrate a scalable design for a high power Fourier shaper in 4-f configuration capable of handling 20 W of CW lasers with a working bandwidth of over 450nm between 1-1.5 micron connecting the two very important Yb and Er emission windows. Our design implements a transmissive geometry thereby isolating input and output beams which is otherwise provided by fiber coupled circulators, a component unavailable at high power levels for a broadband source. Cladding mode stripping is effectively implemented to heat-sink the uncoupled laser light to ensure high power operations feasible. The design also takes accounts of modifications in fiber coupled collimators and amplitude masks to conform with the demands of high power fiber laser technology.