Energy-efficient laser may provide breakthrough optical chip interconnects

Scientists at the University of Michigan have developed a polariton laser that works at room temperature and can do its job 250 times more economically than average lasers. The invention may lead to a breakthrough in optical interconnects for chips.

The laser that the researchers from the University of Michigan and Intel have developed is a polariton laser. The light source is based on quasiparticles called polaritons. The polaritons form a condensate, similar to a Bose-Einstein condensate, producing coherent light. Polariton lasers were already demonstrated in 2003, but then the lasers were pumped using laser light. The researchers have now succeeded in electrically pumping the lasers, whereby the polariton lasers turned out to be very economical. In addition, the researchers managed to run the lasers at room temperature instead of supercooled.

The science team succeeded for the first time in developing a polariton laser that runs on electricity and functions at room temperature. The laser produces polaritons by using electricity to excite samples of the semiconductor gallium arsenide in a cavity. The polaritons decay and transfer their energy to photons, which then escape from the cavity as a coherent, monochromatic beam of light.

In a demonstration, the team obtained an ultraviolet light beam of one millionth of a watt. The laser operates with a current of 169 amps per square centimeter. A comparable system based on an average laser would require 250 times as much. “For the past 50 years we’ve relied on lasers to create coherent light, and now we’ve got something else based on a totally new principle,” said Pallab Bhattacharya, a professor at the University of Michigan, adding that the finding is actually not a laser, because it does not stimulate the emission of radiation, but the diffusion of polaritons.

Bhattacharya sees applications for the chip industry. Optical interconnects can provide fast, economical communication between computing cores in multicores, among other things. The scientists’ research was published last month in Physical Review Letters and is now described by IEEE Spectrum, among others.