Intel makes laser breakthrough

Intel has made a breakthrough in finding a way to mass-produce photonic devices cheaply with the well-tried techniques used to make silicon processors. The technology is unlikely to appear in products until the end of the decade, but it could make ultra-fast optical links mainstream and have a dramatic effect on both computing and lifestyles.

Intel's Photonics Technology Lab announced in 2003 that it had made a silicon photonic modulator that could translate electronic data into light data at 2Gbits/sec (see here). This device has now hit 4Gbits/sec and is on course for 10Gbits/sec, according to Lab director Mario Paniccia.

The latest breakthrough is the creation of an all-silicon laser. First versions will be standalone but the aim is to integrate different photonic devices on to one processor, linking them by silicon waveguides - silicon is transparent to infra-red light.

The laser depends on what is known as the Raman effect, named after an Indian scientist who discovered in 1928 that light can excite atoms to emit photons of a different colour. These photons themselves hit other atoms to create more light at the same so-called Raman wavelength, an effect that can by boosted by adding mirrors to bounce the light about.

In some media, as you pump in more light, you reach a threshold level at which the device emits a powerful beam of a single frequency and phase - a laser beam. Intel's problem was that how ever much light was pumped in, this threshold could not be reached in silicon.

It turned out that as the light input is increased, an increasing number of atoms are hit by two photons at once, which provides enough energy to dislodge an electron. These free electrons tended to block the Raman effect.

Intel's breakthrough came in sandwiching the waveguides between the poles of a diode; an applied voltage sweeps away the rogue electrons, allowing the excited atoms to emit light. The device as it stands still requires an external light source, and one focus of research would be to generate this on-chip, too.

A second big application is an amplifier. A data stream on photons at the Raman wavelength can be boosted by infusing it with light. Raman amplifiers on long-distance links use miles of glass fibre to do what the Intel device does in centimetres, Paniccia said.

The laser could also be used as a modulator by switching the diode on and off to represent data. But Paniccia explained that it is still early days and gave no indication of possible switching frequencies.

The prototype integrated eight Raman lasers on one chip: by using different colours, these could deliver eight data streams down a single piece of fibre. If the 10Gbits/sec throughput of Intel's photonic modulator is realised, the combination represents a system capable of delivering 80Gbits/sec. You can download a flash animation of this here.

See also How photonics will change your life.