Large Mode Area Yb-Doped Photonic Bandgap Fiber Lasers
Clemson University Research Foundation Clemson United States
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All-solid photonic bandgap fibers PBGF can be spectrally tailored to suppress amplified spontaneous emission ASE and stimulated Raman scattering SRS. Furthermore, this type of fiber is attractive for realizing high-power narrow-linewidth amplifiers as large mode areas can be attained while maintaining single-mode operation. Notably, an Yb-doped PBGF with a core diameter of 50 mum and a calculated effective area of 1450 mum2 was fabricated using the stack and draw technique Figure 1. The microstructures in the cladding are comprised of germanium-doped silica. A low refractive index polymer coating provides a numerical aperture of 0.46 for pumping purposes. The absorption was estimated to be 1 dBm at a pump wavelength of 976 nm. Approximately 11 m of this fiber was mounted on a cold spool possessing a diameter of 53 cm. The PBGF was pumped in a counter-propagating configuration using 976 nm diodes from Laser line. The master oscillator was a non-planar-ring oscillator NPRO operating at 1064 nm. The output of the NPRO was then coupled into a phase modulator for stimulated Brillouin scattering SBS suppression and then amplified using a multi-stage amplifier system manufactured by IPG. The phase modulation frequency was set at 400 MHz and the modulation depth was chosen such that three equal peaks corresponding to the carrier frequency and the two adjacent sidebands were generated. As much as 20 W were used to seed the PBGF. A plot of the signal power vs. pump power is shown in Figure 2. The output signal power obtained was 587 W which represents to the best of our knowledge the highest power reported to date for a PBGF amplifier. The slope efficiency for this amplifier was 70. At the highest output power, there was little sign of SBS.