SHOW PREVIEW: PHOTONICS WEST FIBRE PROVIDERS Te 2µm wavelength has advantages over 1µm,
A dedicated conference session will be held at Photonics West on the recently completed ISLA project, an R&D project developing components for 2µm fibre lasers. Greg Blackman speaks to Gary Stevens of Gooch and Housego, who will be one of the presenters at the trade fair in San Francisco in February
F
ibre lasers are now well established in materials processing and are gradually taking market share from CO2
lasers. Most fibre sources operate at 1µm wavelength because
the components for building these lasers – like high power pump diodes and technology for erbium- doped fibre amplifiers – have been adopted and developed by the telecoms industry, which makes them inexpensive and accessible. Te ISLA R&D project, or ‘Integrated disruptive
components for 2µm fibre lasers’, aims to bring about advances in 2µm fibre sources by making the components needed to build these lasers more readily available. ‘It [ISLA] was all about developing a supply chain
of components, which has been the big hindrance of adopting this technology [2µm fibre lasers]. Tere’s nowhere to buy the pump diodes, for example,’ explained Gary Stevens at UK-based photonics components supplier Gooch and Housego (G&H). Stevens will present a paper on the ISLA project at the Photonics West trade fair, which will take place in San Francisco from 13 to 18 February 2016. Te ISLA project officially ended in June 2015,
but various aspects of it are still ongoing. A 0.5kW, 2µm continuous wave (CW) laser is being assembled at the Optoelectronics Research Centre (ORC) in Southampton, UK. Te unit will then be shipped to Rofin in Hamburg, Germany next year for material processing tests. Meanwhile, Lumentum, formerly JDSU, is building a pulsed 2µm system. Te project has seen advances in thulium and
holmium fibres, which the ORC has pushed to 70 per cent and 75 per cent slope efficiencies respectively. Te improvements in fibre efficiency mean higher power lasers can be made. G&H developed pump combiners and amplitude
modulators, among other components; Trinity College Dublin made graphene-based modelockers; while II-VI Laser Enterprise, formally Oclaro, built the 793nm pump diodes. Developing these components is one of the successes of the project, Stevens said: ‘Certainly
16 LASER SYSTEMS EUROPE ISSUE 29 • WINTER 2015
before this project started, G&H wouldn’t have had catalogue 2µm parts. Now you can order a 2µm fibre-coupled acousto-optic modulator for q-switching. It’s a similar story for the pump diodes, which is the key part of the laser. A 793nm pump diode is not a telecoms device; you can’t buy them from many different suppliers. ‘Now it’s possible to go and
order all the parts you need to build a 2µm fibre laser and for them to be reliable,’ he added. Tere are commercial 2µm
especially for processing polymers where absorption is greater. An absorbent layer has to be applied to plastics when welding with 1µm fibre lasers, whereas this layer is not needed at 2µm, because the material absorbs the laser radiation directly. Te 0.5kW CW laser being built for ISLA was intended for this application. Te other benefit is that a 2µm optical fibre has a
possible to go and order all the parts you need to build a 2µm fibre laser
Now it’s
fibre lasers available – IPG Photonics offers a 200W CW thulium fibre laser and a nanosecond pulsed version with an output power up to 20W. Nufern also provides this kind of technology. ‘Tey are a commercial reality, but they aren’t used to the extent that a 1µm ytterbium laser is,’ explained Stevens.
larger core size, which means theoretically that the fibres can handle higher powers than 1µm fibres. However, Stevens noted that exploiting the power potential of 2µm fibres wasn’t an explicit objective of the project. ‘In principle, there’s nothing stopping you building a 2µm laser on a similar cost level to a 1µm laser; it’s all about volume at the moment,’ Stevens said. ‘When you sell tens of thousands of 1µm lasers you get a very good cost reduction. ‘A few years ago it would have been
very difficult to build one [a 2µm laser], because a reliable supply of components
didn’t exist,’ he continued. ‘Hopefully now you should see that adoption happen a bit more. You’ve got to have the applications to do it as well – now that you can get a 2µm laser, people are using them for things and that’s driving the applications that are then creating a pull for more lasers.’
ISLA conference session, 16 February 2016 from 8:30am to 10:00am
Integrated disruptive components for 2µm fibre lasers (ISLA): Project overview and passive component development Gary Stevens, Gooch and Housego The presentation will give an overview of the project, before presenting results on passive component development for 2µm fibre lasers. This includes fused fibre couplers and combiners, including wideband couplers with a coupling ratio that only varies by ±12 per cent over 400nm.
Acousto-optic devices for operation with 2µm fibre lasers Jon Ward, Gooch and Housego; Gary Stevens, Gooch and Housego; and Peter Shardlow, University of Southampton
A report on recent developments of
acousto-optic (AO) modulators optimised for use with fibre systems operating at or around 2µm. The paper will describe two designs of AO tunable filters intended for laser tuning. Both designs have been demonstrated intracavity in 2µm fibre lasers.
Broadband saturable absorber mirrors
Kangpeng Wang, Aidan Baker- Murray, and Werner Blau, Trinity College Dublin
As part of the ISLA project, graphene saturable absorber mirrors (SAMs) were fabricated by a simple wet deposition process onto a metal mirror substrate. Their intensity response was tested at various infrared wavelengths in a so-called i-scan setup.
Thulium-doped silica fibres optimised for high lasing efficiency
Peter Shardlow, Deepak Jain, Richard Parker, Jayanta Sahu, and W. Andrew Clarkson, University of Southampton Two-micron lasers are of interest for a range of applications as well as providing a platform for nonlinear frequency conversion to the mid-IR band. By optimising the dopant concentration within the thulium fibre core, a beneficial two-for-one cross-relaxation process can be exploited, allowing efficiencies far-above the quantum limit for 793nm pumping. The presentation reports on recent work targeted at improving the two-for-one cross-relaxation efficiency through optimising fibre core composition and doping profiles.
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