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Cladding is key to fibre laser performance

A Southampton Photonics product story
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Edited by the Electronicstalk editorial team Feb 25, 2003

A paper at the ASSP Conference in San Antonio in early February further demonstrates the important and rapid advances being made in cladding-pumped fibre laser technology.

Dr Johan Nilsson of Southampton Photonics and the Optolectronics Research Centre at the University of Southampton, presented results at the ASSP Conference in San Antonio in early February, further demonstrating the important and rapid advances being made in cladding-pumped fibre laser technology.

In published experiments, 3.5W of output power at 980nm from a jacketed air-clad (JAC) ytterbium-doped fibre laser was demonstrated in a nearly diffraction-limited beam.

This is believed to be a world record power at this all-important wavelength.

980nm fibre lasers have important applications in telecommunications and aerospace where they can be used to pump multiple erbium-doped fibre amplifiers.

When frequency-doubled to 490 or 488nm they are the replacement candidates for argon ion lasers for use in instrumentation in many analytical and biomedical applications.

For some time, laboratories worldwide have attempted to produce a single-mode 980nm fibre laser, however, the dopant of choice, ytterbium, stubbornly reabsorbs light generated at 980nm and emits at around 1040nm.

Nilsson presented a threefold solution to the problem.

First, a high-brightness pump module is used that can deliver 5W of multimode power in a 35um beam.

Secondly, a special fibre is fabricated that has a 35um cladding suspended in air.

This high NA "jacketed air clad" (JAC) fibre preserves the brightness of the 915nm pump radiation and reduces the threshold for the 980nm emission from 250 to 400mW.

Finally, the JAC fibre uses SPI's patented ring-doping technology whereby the ytterbium ions are incorporated in a ring around a single-mode core.

Ring-doping technology reduces the re-absorption of the 980nm emission and, moreover, 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.

With the important reductions in cost of ownership and unit size, combined with their greater reliability and longevity, fibre lasers have many advantages over conventional laser technology.

Stuart Woods, SPI's Director of Business Development, commented, "SPI continues to push the fibre laser applications space through our work on specialty fibres and we see a day when many applications currently addressed by traditional solid state and ion lasers, can be substituted on a one-to-one basis by a fibre laser".

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