FEATURE
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The colour of invention

Oxxius has established itself as a leading player in DPSS lasers for multiple wavelengths, as Warren Clark discovers

The photonics industry is littered with small and medium-sized companies formed by innovative engineers who spotted a gap in the market. Oxxius most definitely falls into that category, formed in 2002 by Thierry Georges and Raymond Le Bras, who saw an opportunity to build a blue DPSS laser – something that had previously been unachievable.

Georges had been involved in photonics since the late 1980s, having worked in California for more than a decade. On returning to France, he moved to the telecoms industry, setting up his own company, Algety Telecom, which he later sold to Corvis.

During his time in photonics, Georges had seen the emergence of the diode-pumped solid-state (DPSS) laser as a potential replacement for bulky and expensive gas lasers. So, having spent a few years out of the field of DPSS lasers at the turn of the millennium, he was surprised to find that uptake of this technology had not been more widespread on his return. ‘I couldn’t believe that, 10 or 15 years after DPSS lasers had emerged, people were complaining about gas lasers yet still using them,’ says Georges. ‘So, I decided to look into the reasons why this might be.

‘In 2002 I saw that red diode lasers were available on the market, as found in DVD players, and a few green DPSS lasers were around. Gallium Nitride violet laser diodes, developed for the BluRay players, started to be commercially available too. However, there were no blue lasers able to replace the 488nm line of the Argon gas laser. So, together with Raymond, I started Oxxius with a view to developing a blue DPSS laser – and probably green too. We set out to use diodes to create a broad offering, particularly aimed at the biophotonics field.’

At the time, no other company had commercialised a blue DPSS laser, and most green DPSS lasers were beset with reliability issues. ‘It was tough to create a product that offered the required level of operation over a long period of time,’ says Georges. ‘This was largely due to the fact that the cavity involves aligning four to six components, and ensuring that those components remained aligned throughout the lifetime of the product. For there to be stability, the overall length of the cavity cannot vary by anything more than the tiniest of margins. For example, in a cavity of 30 to 40mm, the variation cannot be more than 100nm.

‘When I came back into this field, I saw that semiconductor lasers were intrinsically monolithic, and were able to operate reliably over a long period of time. We decided then to base our laser design on a monolithic assembly.

‘Crystals are needed to make amplifiers, polarisers, filters and frequency doublers, and all of these functionalities are essential parts of a laser cavity. Our theory was that, if you can optically contact all these crystals, you have a monolithic source that can operate with a diode for years with stability and reliability. It avoids the problem of having separate mounts that may otherwise move slightly throughout the lifetime of the product. The monolithic nature of the cavity reduces the impact that changes in temperature and other factors may have on the length of the cavity to within acceptable limits. It also suppresses the risk that dust or other chemicals come inside the cavity, leading to detrimental effects.’

The concept enabled Georges to develop a stable green laser, and begin work on a blue laser. ‘The laser cross section for generating blue wavelength is very weak, so losses in the cavity need to be kept to a minimum. Because our crystals are optically contacted and perfectly aligned, Fresnel reflection has much less of an impact on losses.’ This discovery led to Oxxius’ first blue laser being developed and tested in 2005 in the Norwegian Sea by Ifremer, the French Research Institute for Exploration of the Sea, where it detected minerals and plankton at depths of 4,000 metres.

With this proof of concept in place, Oxxius sought venture funding to help it commercialise the technology. Georges already had venture capital contacts from his time at Algety, and with his successful track record in building up that earlier company, he raised €2.4m of funding with relative ease. A second round of funding followed two years later.

‘One advantage of our design is that, once you’ve made a laser in one colour, it’s very simple to replicate it in another colour,’ says Georges. Hence, a yellow laser followed just a few weeks later, which was also relevant for the bio market. The company also foresaw the likelihood that the need for new wavelengths would increase over time, and with the continuing development of new fluorochromes absorbing light at different wavelengths, this has proved to be the case. ‘We are able to offer many wavelengths from this one design,’ he says. This flexibility was key in Oxxius being able to increase the volume of its sales, and thereby reduce the cost of production over time too.

‘We have been able to introduce new wavelengths, such as 553nm, which have gone on to become industry standard wavelengths for the flow cytometry market,’ continues Georges. The low-loss characteristics of the cavity have also enabled Oxxius to develop an orange wavelength laser through Raman shifting, as it can cope with the delicacy of this non-linear process.

‘We believe we now offer the best coverage of the visible spectrum,’ claims Georges, ‘through a combination of our diode lasers modules, our DPSS lasers and our Raman shift based lasers.’ What’s more, Oxxius is about to provide all three of these technologies in exactly the same laser head, with the same footprint. ‘We worry about the technology inside, so the customer doesn’t have to,’ says Georges. ‘We provide the same laser head, with the same interface, so even if the customer wants to change the wavelength, we can do so with minimum impact on integration.’

Le Bras left the company three years ago to pursue other interests, and Oxxius now has 25 people at its base in Lannion in Brittany, France. It is a thriving area for the photonics market, with several small start-ups and established companies around, as well as a research centre for optical communications.

Oxxius sells its lasers to scientists or OEM integrators for use in systems, such as flow cytometers. ‘Our single frequency lasers are also useful for other applications, such as interferometry and Raman spectroscopy, in which we have established business along the way,’ says Georges.

‘Our goal is to work with more OEM integrators and develop our sales in biophotonics,’ he concludes, ‘and we are well set up for higher volume production.’