Temporal coherent beam combining of pulsed fiber lasers has gained a lot of interest as it could pave the way for fiber lasers to compete with bulk lasers in terms of pulse energy. We purpose to stack up the symmetric output of an oscillator by phase and polarization switching. This way we can avoid the effects of gain dynamics and are able to utilize all the seed power as opposed to regular pulse picking approaches.

We used a 47 MHz femtosecond fiber oscillator centered at 1558 nm (5 nm bandwidth). Feeding the pulse train into a Mach Zehnder interferometer and adding electro optic modulators (EOMs) in both optical paths, we imprint a π phase shift in one path on every other pulse. We then use a polarization beam splitter to combine the two beams and stabilize the resulting polarization with a unity gain significantly lower than MHz. Therefore after the two beams are combined, the π phase shift stays intact and neighboring pulses have their polarization flipped. In a following PBS horizontal and vertically polarized pulses are separated. The vertical polarized pulses are delayed and combined with the next pulse. This halves the repetition rate basically acting like a pulse picker but without discarding 50% of the output power. The efficiency of the experiment was so far limited by linear losses in the PBS and linear losses due to the pickups for the photodiodes. We will give an update un the latest results and our plans to go forward.

Date Published: 21 April 2017
PDF: 1 pages
Proc. SPIE 10083, Fiber Lasers XIV: Technology and Systems, 1008305 (21 April 2017); doi: 10.1117/12.2255868

Published in SPIE Proceedings Vol. 10083:
Fiber Lasers XIV: Technology and Systems
Craig A. Robin; Ingmar Hartl, Editor(s)