RESEARCHERS at the Vienna University of Technology have created a system of coupled quantum cascade lasers which switch on when there's reduced energy supply.
The dual-laser system makes use of the common mechanism of wave dissipation (which causes energy loss) to attain its paradoxical capabilities: additional energy can switch it off while a reduction of energy may switch it on.
This in turn, could herald the building of logical circuits using light.
Normal lasers, of course, work in the reverse. Supply a laser with too small an amount of energy and it does nothing. But as the energy supply increases, the laser emits more light.
During computer simulations, the researchers found that when they coupling two small circular lasers to a joint system, a delicate balance of energy gain and loss leads to counter-intuitive physical effects. More energy did not lead to more light, whereas a reduction of energy supply could switch on the light.
The researchers then set about replicating the experiment, using quantum cascade lasers, which emit at terahertz frequencies. These lasers can be finely tuned, and also have a rather large wavelength, making easier for the light wave to pass from one laser into the other.
The interesting coupling effects in the laser are only generated when a special absorbing layer is placed on the lasers, which dissipates part of the light.
The actual mechanism behind the behaviour of the lasers is a complicated mathematical phenomenon. According to the researchers, the mathematical equations behind the lasers lead to the emergence of exceptional points: special intersection points of surfaces in complex spaces.
These exceptional points lead to remarkable physical phenomena.
Such laser coupling can lead to new electro-optical switches. In the future, optical elements could be used to process information, similar to today's electronic elements we are using today.