14 DAY TRIAL // Optoelectronics is the science that studies the electronic devices that interact with light, in fact a subfield of photonics, that deals with light in both the visible and the invisible spectrum (gamma rays, X-rays, ultraviolet and infrared).
It is based on the quantum mechanical effects of light on semiconducting materials, sometimes in the presence of electric fields and it is the basis in developing quantum computers.
Fast silicon-based chips developed through optoelctronics are hoped to revolutionize computing and telecommunications by greatly increasing the amount of data that can be fed through the system and/or bandwidth, and processed. The speed increase is questionable, and may only rely on parallel computing, since, in fact electricity also travels at the speed of light. Unfortunately, existing devices require too much light and also give off unacceptable amounts of heat.
But now, these chips could be made more efficient using a brand new technique called "energy harvesting," developed by a team at the University of California, Los Angeles (UCLA), in the US.
The team has found a method of making optoelectronic devices more efficient by having them "harvest" electrons to generate current rather than heat.
Amplifying and modulating light, simple optical operations in silicon, or converting one wavelength to another and lasing, require a laser for its intense beam of light that interacts with silicon in a non-linear way, which is necessary for useful optical effects.
This, however, presents a problem known as two-photon absorption. This occurs when part of the silicon's crystal lattice absorbs two photons at once, which frees more electrons to absorb still more photons.
"It's like a chain reaction," says Bahram Jalali, head of UCLA's optoelectronics lab."The problem is fundamental," he adds. "You have to have non-linear processes, so you have to pump silicon hard. When you pump it hard, silicon becomes like a sponge - it absorbs all the light."
Chip manufacturer Intel tried one approach to solving the problem of two-photon absorption, by surrounding a silicon-based laser with positive and negative charges that swept out light-absorbing electrons, but the techniques was highly inefficient, producing 125 times more waste heat than usable light.
The UCLA team discovered that two-photon absorption could instead be harnessed as a way of generating electricity, by adding a diode to a silicon-based laser, thus creating an electric field, which allows the free electrons to be harvested, and as a result makes it possible to generate electric power.
"It's one of the few places where nature allows you to have your cake and eat it too," says Jalali. They managed to implement this photovoltaic effect in two other simple silicon-based applications - an optical modulator and a wavelength converter.
Now, they hope that their findings will work in the full range of optoelectronic applications, from teraflop computer chips to transcontinental communication lines, virtually to any optical device that suffers from loss.