The elusive goal of integrating lasers and electronics has come a big step closer with the first growth of nanoscale lasers directly on silicon. The tiny lasers are made from compound semiconductors that can emit light far more efficiently than silicon itself can.
Integrating optical processing into electronic chips holds great promise for high-performance computing. Electronics are very good at processing information because electrons interact strongly with each other. However, as electrons are moved to transfer information, those interactions also cause background noise and weaken the signal, and so cutting-edge chips are pushing the limits of what electrons can do carrying signals on circuit boards and in the chips themselves.
In contrast, photons have little effect on each other, so they can transfer information much more efficiently than electrons. That's why fibre-optic cables have replaced wires in the main circuit boards of high-performance computers as well as in cables running kilometres or more.
Computers suffer a crucial limitation when it comes to working with light, however: although silicon can transmit and detect light signals, it can't generate light efficiently. Compound semiconductors such as gallium arsenide and indium phosphide are needed to make good lasers. Chip maker Intel and the University of California, Santa Barbara, have succeeded in bonding indium-phosphide lasers to silicon so tightly that light generated in the indium-phosphide layer is transferred into silicon light guides. However, such bonding is costly and cannot be integrated into standard chip manufacture, and it hasn't been possible to "grow" lasers made of those materials on silicon.
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