Strained LaserHow did it start?

On holiday in 1986, Prof Alf Adams (FRS Distinguished Professor of Physics) struck an idea which has had a massive impact on almost all of us – at work, at home and in the way we choose to communicate. It’s estimated that the technologies and products which have been enabled by his invention - the strained quantum well laser - are worth many billions of dollars, worldwide. The strained quantum well laser was the catalyst to the faster digital world we all inhabit, and has been used in everything from car manufacture to the internet.

Prof Alf Adams recalls: “I was walking along the beach in Bournemouth, and the idea just jumped out. The more you take control of light, the more efficiently you can use it – how could we increase the power of lasers?”

Straining the laser:

Having studied semiconductor lasers at the Tokyo Institute of Technology during the early 1980s, Prof Adams returned to the University of Surrey to work on increasing the efficiency and power of lasers.

Lasers convert electrical energy into light power or ’photons’, and, since 1960, had been used in a variety of ways, including medical, printing and military applications. This first generation of semiconductor lasers was constructed using a regular array of crystals layered onto a surface, into which electrical energy was pumped to produce amplified power.

In a quantum well laser, there is an extremely thin layer of semiconducting crystals in which the laser light is generated. Prof Adams discovered that, if the crystal lattice of this layer was grown in a way which put it under strain, it could be ‘squashed’ into a certain shape, producing a more controlled, concentrated beam of light.

This concept was completely counter to laser research at the time, which was directed at focusing the laser, rather than straining it. But the strained quantum well laser offered a higher data capacity, while using less electrical energy. It was much more efficient and powerful than any other laser at the time.

First commercial applications to everyday use

Prof Adams first published an academic paper in 1986, and in 1988, the University of Surrey was awarded a £518,841 grant from the Engineering and Physical Sciences Research Council (EPSRC) to develop the technology with industry partner, Phillips Electronics, who were already using earlier forms of laser within compact discs.

CD players were a luxury device then, but using a strained laser allowed them to become more efficient, more compact and cheaper. Over time, these efficiencies have increased, so that, today, the same sized disc has a far higher data capacity. If consumers can buy a technology which ‘does more’ it becomes increasingly popular. The last two decades have seen households, schools and workplaces enthusiastically adopt new developments and the greater capacity and richness of information they offer – from CDs and DVDs to Blu-ray.

These lasers are also used in many other sectors, including computers and optical phone lines, scanners and readers at supermarket checkouts. Prof Adams’ ‘blue sky’ research has led to the creation of many new products, as well as enabling existing products or services to evolve in ways unforeseen at the time they were introduced.

Telecommunications

Prof Adams initially explored a variety of applications for his new laser, in particular, the telecommunications industry. Like a lot of research ideas, his approach was considered too risky at the time, so the strained quantum well laser had to wait a few years before the technology was adopted. Today, every telecommunications laser is now a strained laser.

The internet

Prof Stephen Sweeney was a PhD student working under Prof Adams between1995-1999. After working on semiconductor lasers at Marconi, he came back to the University of Surrey as an academic in 2002, just ahead of Prof Adams retirement. He now leads the Photonics Group at the university.

Prof Sweeney describes how developments made at the University of Surrey led to strained lasers being used in digital communications:

“My role was to look at the limitations of the laser technology and to develop faster and more efficient lasers for communications.”

The technology produces short and powerful pulses of light to transfer information extremely fast, “at the speed of light” and when pushed through optical fibres as carriers, allowed for the accelerated development of telecommunications, and eventually the Internet. Every telecommunications laser is now a strained laser.

“The Internet currently consumes about 1% of total energy consumption, which doesn’t sound a lot but web usage is increasing exponentially.” Prof Sweeney says “so developing the strained laser further will bring down

costs, energy consumption and the environmental impact of the Internet.”

More developments

Research at the University of Surrey’s Advanced Technology Institute, led by Prof Sweeney, continues to create new uses for lasers, for example:

  • Sensing equipment: portable environmental pollution monitoring sensors which can detect gases, or other pollutants, in the air
  • Solar cells: energy applications which can capture sunlight
  • Solid state lighting: LEDs which are high yielding, but low energy

Prof Sweeney is finding that the focus of research today has a greater emphasis on efficiency. He says: “The two most critical areas of photonics research are in the environment and energy. For example, we can make the internet even faster and more widely available, but at the same time using much less energy.”