FEATURE
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Fibre providers increase power

Nick Morris reviews the state of the burgeoning fibre laser industry

In recent years fibre lasers have begun to be talked about as a possible viable alternative to semiconductor and gas lasers. Fibre lasers hold a number of attractions. As well as very good beam quality the long, thin design geometry of a fibre laser means that a fibre laser is often smaller than its equivalent-powered semiconductor or gas laser.

This geometry also means a fibre laser has very good cooling characteristics, hence fibre lasers do not suffer from temperature dependent refractive index changes, unlike rod lasers. If a system uses optical fibre waveguides, using fibre lasers negates the effect of free space optics, as the only optical transitions will be from optical glass to optical glass.

As with many laser applications, the uses of fibre lasers can be split broadly into two categories: high power applications, such as metal cutting, engraving, and welding, and low power uses, such as measurement and data transfer.

So what is the current state of the fibre laser market, and what does the future hold? We asked key market players, to find out.

Søren Løvgreen Lauridsen, sales manager at Koheras, the Danish fibre laser specialist, says: 'In terms of low power, single frequency distributed feedback (DFB) fibre lasers have been adopted as standard off-the-shelf bench-top sources, and are now in use as laboratory equipment at many research institutes and universities. Penetrating into the industrial sector, and the defence industry (for applications such as sensing) takes more time, because of the long transition cycle of technology shifts, and also because each customer is trying to solve a different problem.

'There are many advantages to using single frequency fibre lasers, such as narrow line width and long coherence length, low noise (both frequency and intensity noise), ultra stable, mode hop-free operation, lightweight and robust packaging, selectable wavelength, multi-wavelength systems, pump redundancy, and immunity to electromagnetic interference, that outweigh conventional technologies. However, for some low-end applications, with less stringent demands to sensor resolution and sensitivity, the marginally higher cost compared to semiconductor lasers is typically a showstopper for more aggressive market penetration.

'After six or seven years of extensive development, and customisation towards specific design requirements, we are now seeing the lasers put into operation in large-scale production sensor systems worldwide - especially for coherent sensor applications, such as perimeter sensing, oil exploration, submarine detection, and wind Doppler lidar. The customers within these sectors have finalised stages of evaluation and approved the technical advantages over other laser technologies. They've worked closely with us to fit specific optical and mechanical requirements into their systems.

'In the future, I think we are going to see some further technology shift from semiconductors and different YAGs to DFB fibre lasers for high resolution coherent sensing. There is room for further improvement, but that is essentially related to critical laser packaging for demanding environmental conditions in off-shore and airborne installations, and for a couple of space projects.'

When asked about high power lasers, Lauridsen says: 'There is no doubt that high power fibre lasers need to prove their advantages over and above other laser technologies - in particular, with regards to long-term stability and reliability (where the track record is somewhat limited at present). Performance wise, fibre lasers are very strong replacement candidates to conventional lasers, due to their all-fibre coupled design, high beam quality, low maintenance costs, and high wall-plug efficiency. This message needs to be conveyed to users by successful case studies from early adopters. Fibre lasers need to be available from not one, but several suppliers, to create a competitive market. This will accelerate market penetration, and offer users a number of sources, which is a key parameter for industrial users.'

Chuong Hoang Tran, business developer at Koheras, adds: 'In terms of high power lasers for industrial applications, we believe that fibre lasers will gradually replace CO2 or YAG lasers for many applications, such as printing, marking, engraving, and cutting. Within the material-processing segment a pulsed laser is often required. This favoured the YAG laser in the past. The development of pulsed fibre laser technology heralds a new era for material processing applications. Currently, the adaptation of new technology into existing industrial sectors is somewhat limited, due to the fact that fibre lasers don't have a proven long track record compared to CO2 or YAG lasers. Another problem has been the limited number of vendors working on fibre lasers.

'In the future, we believe that there will be two trends for high-power fibre lasers. One will be the development of the laser to even higher power at multiple kilowatts. Cutting and welding applications will drive this trend. The other will be an improvement of lower power (lower than 200W) laser quality, in terms of beam quality, long-term stability, flexibility to interface with the surrounding system, pulse control, fibre delivery, and so on. The later trend will be pushed by applications like marking, engraving and welding of thinner materials. Last but not least, one should not forget medical applications.'

When asked about the long-term future of fibre lasers, Jakob Dahlgren Skov, CEO of Koheras, says: 'We foresee a convergence of technologies in visible wavelengths. For example, we hope to use a high power, 1064nm fibre laser, with a relatively high efficiency, to create a single frequency, mode hop-free, green laser. With the scalability in power, one can easily imagine a new breed of such visible fibre lasers'.

Sifam Fibre Optics manufactures fibre lasers and fibre laser components. Paul Ellis, CEO, says: 'Fibre lasers are now taken seriously by both manufacturers and users of established laser technology, where a few years ago they were not. Sifam Fibre Optics has a complete passive product portfolio for the fibre laser market. Similarly, a number of laser diodes are now manufactured with fibre lasers in mind, showing a serious drift in the thought process of the traditional hi-power laser markets.

'Basic fibre laser configurations have been fully proven and are viable commercial products. Continuing development, to optimise designs further, has helped to broaden the scope of potential applications. Marking systems using fibre lasers are clearly offering improvements over the CO2 laser systems that previously dominated this sector. There are many other application areas, where potential has not yet been fully realised, but laser marking is progressing fastest.'

High-powered lasers are needed for such applications. The constantly increasing power requires fibre components that have to be continuously optimised to handle those power levels. Ellis continues: 'As fibre laser power levels increase, the ability of the housing design to safely withstand and dissipate power lost through the component becomes critical. Special features are incorporated into our high power packages to ensure there is no leakage of power through the cladding of the output fibre, and to optimise the dissipation of power through advanced heat sink design.

'As for the future, I believe we'll see higher powers, simpler configurations, higher reliability, cheaper running costs than solid state, and ultimately, cheaper equipment prices.'

Fibre lasers are still in their infancy in terms of technical development and market penetration but they have many advantages over competing laser sources, which could drive them more toward mainstream acceptance.