Massachusetts Institute of Technology

Kelsey Yee

Steven J Augst

Jason Edward Langseth

Christopher Hwang

John Kim

Franklin Jose

Yin Wan Tam

Incoherently combining light from different lasers while maintaining high brightness is challenging using conventional fiber bundling techniques, where fibers from different lasers are bundled adjacently in a tight-packed arrangement. The brightness can be increased by tapering the tips of the bundled fibers to match a single, multi-mode output fiber, e.g., one whose core that is just wide enough to fit the input cores. This increases the brightness of the beam combining. In addition, reducing the outer diameters of the signal fiber claddings allows the signal fibers to be bundled closer together, making it possible to couple more signal fiber cores to the core of a multi-mode output fiber. Similarly, reducing the outer diameter of the pump fiber cladding and/or etching away corresponding portions of the signal fiber cladding in a pump/signal combiner makes it possible to couple more pump light into the signal fiber cladding, again increasing brightness.

Incoherently combining lasers

Stimulated Brillouin scattering (SBS) limits the maximum power in fiber lasers with narrow linewidths. SBS occurs when the power exceeds a threshold proportional to the beam area divided by the effective fiber length. The fiber lasers disclosed here operate with higher SBS power thresholds (and hence higher maximum powers at kilohertz-class linewidths) than other fiber lasers thanks to several techniques. These techniques include using high-absorption gain fibers, operating the laser with low pump absorption (e.g., &#x2264;80%), reducing the length of un-pumped gain fiber at the fiber output, foregoing a delivery fiber at the output, foregoing a cladding light stripper at the output, using free-space dichroic mirrors to separate signal light from unabsorbed pump light, and using cascaded gain fibers with non-overlapping Stokes shifts. The upstream gain fiber has high absorption and a larger diameter for high gain, and subsequent gain fiber has a smaller diameter to improve beam quality.

Single-frequency fiber amplifier with distal cladding stripper

Growing community of inventors

Arlington, MA, United States of America

Kelsey Yee