Johan Nilsson of Southampton Photonics, Inc. (SPI) and the Optolectronics Research Centre at the University of Southampton have demonstrated advances in cladding-pumped fibre lasers.
Nilsson presented results at the ASSP Conference in San Antonio in February, demonstrating 3.5W output at 980nm from a Jacketed Air-Clad ytterbium-doped fibre laser, in a nearly diffraction-limited beam. He believes this to be a world record power at 980nm.
For some time, laboratories worldwide have attempted to produce a single-mode 980nm fibre laser. However, the ytterbium reabsorbs light generated at 980 nm and emits at around 1040 nm.
Nilsson presented a threefold solution to the problem: First, a high-brightness pump module deliver 5W of multimode power in a 35µm beam; secondly, a special fibre is fabricated that has a 35µm cladding suspended in air. The high NA JAC fibre preserves the brightness of the 915nm pump and reduces the threshold for the 980nm emission from 250mW to 400mW. Finally, the JAC fibre uses SPI's ring-doping approach.
Ring-doping technology reduces the re-absorption of the 980nm emission and reduces the gain from the unwanted 1040nm radiation. The result is a laser providing 3.5W of single-mode 980nm radiation with a 400mW threshold and 42% slope efficiency.