Friday, June 30, 2006

"CHIPS: Silicon laser harnessed"

Continuous-wave silicon lasers were demonstrated for the first time last year by Intel Corp. But the new lasers generated too much heat to be practical for CMOS devices. Researchers at the University of California at Los Angeles now claim to have the solution: Harness the excess energy with a photovoltaic effect that converts heat back into electricity to power the chip. The researchers also beat Intel in the race for the world's first silicon laser in 2004, when they reported a pulsed silicon laser. The laser could not operate continuously because it produced excess hot electrons. In 2005, Intel followed up with a technique for sinking hot electrons, clearing the way for the first continuous-wave silicon laser. The first version did not use excess energy. The UCLA group has again topped Intel by showing how a Raman scattering architecture can be used in CMOS devices to harness excess energy from hot electrons. The mechanism, stimulated Raman scattering, sidesteps silicon's indirect bandgap that prevents normal lasing. However, Raman scattering works through double-photon absorption, which creates hot electrons as a byproduct and generates excess heat. The researchers claimed that a photovoltaic sink not only enables continuous operation of silicon laser chips, optical amplifiers and similar photonic devices, but it can now be economically incorporated into CMOS. Moreover, the excess energy can now be harvested to drive other CMOS circuitry.