Intel Announces Laser Breakthrough

AdmiralWeirdbeard writes "Intel has just announced a breakthrough in laser technology allowing a continuous laser wave on a silicon chip. Apparently they devised a method to sap the interfering field of electrons previously generated in silicon by the lasers. Intel says that hardware exploiting the advance might begin appearing at the end of the decade."

Comments

Re:Correct Units?

[Anonymous Coward]

The (first) article states the waveguide is 1.5x1.55micrometers and 48millimeters in length, Has it got the units right on that one?

No, those units look right. If you really read the first article, then you would have seen the picture of the die.

Re:Correct Units?

[k98sven]

The (first) article states the waveguide is 1.5x1.55micrometers and 48millimeters in length, Has it got the units right on that one?

Yes. The Nature article the guys published (20 Jan, vol 433, p292) on this says "4.8 cm".

IANAEE, so maybe its correct, but their going to refine it, or maybe its not linear.

Yes, of course they're going to develop this further. This is the first time they've achived continous-wave laser gain in silicon, obviously the next step is to increase it.
(A smaller cavity requires larger gain)

No it's not linear, the cavity is S-shaped.

Re:Catch 22

[Anztac]

Yeah, they mention in the news.com article that silicon is a poor producer of light, what it is good at though is amplifying it via the Ramen effect.

A Raman laser, in some ways, is ideally suited for silicon. The Raman Effect, discovered in 1928 by Nobel laureate Chandrasekhara Venkata Raman, roughly works as follows: Light hits a substance, causing the atoms in the substance to vibrate. The collision causes some of the photons to gain or lose energy, resulting in a secondary light of a different wavelength. A Raman laser essentially involves taking this secondary light and then amplifying it (by reflecting it and pumping energy into the system) to emit a functional beam. Because of its crystalline structure, silicon atoms readily vibrate when hit with light. The Raman Effect, in fact, is 10,000 times stronger in silicon than standard glass, which should make it far easier to amplify.

Re:Expensive?

[thpr]

define "expensive" for making lasers

Keep in mind that the lasers you are working with are not very precise (the CD player, DVD player), or even only have to be coherent (the laser pointer) and not pulsing. Even with the encoding, the DVD is only transmitting a few Mb/s of information as it encounters pits and lands on a CD/DVD. (4.7GB/2 hours = ~6Mb/s)

The long-haul optical systems and optical switches are transmitting over multi-kilometer fiber optic cable that is transmitting at Gb/s rates. That requires a MUCH better laser, in terms of power, coherency and switching speed. I actually don't know what the lasers cost, but some of the receivers can be in the hundreds for a single receiver at the very high end. The optical systems themselves are rather expensive, being thousands of dollars for a single mid-range board that has a pair of optical receiver/transmitters (2 ports).

But it's not a laser

[Biff Stu]

It's based on Raman shifting. It's a nice way of getting longer wavelength light from shorter wavelength light, but you still need a pricey(non-silicon) laser to make it work. Furthermore, because the Raman process has limited efficiency, you end up loosing much of the efficiency of a conventional (non-silicon) diode laser.

It's only interesting because it can be electronically swiched on and off, so it represents a nice way of getting modulated light into a silicon waveguide. On the other hand, there are modulators with much better efficiency. So it's a cheap but inefficient modulator, which is also a wavelength converter.

Re:But it's not a laser

[Biff Stu]

Try learning physics.

Laser: Light Amplification by Stimulated Emission of Radiation.

The stimulated Raman effect is fundamentally different from stimulated emission. You can't get stimulated emission from Si because it is an indirect bandgap semiconductor. However, it is true that both processes can generate coherent beams of light, and people typically refer to devices that generate coherent light as laser sources, hence the term "Raman Laser".

However, my point is that this device can't convert non-optical energy into optical energy. Furthermore, since it's a non-linear optical process, you can only get the necessary intinsity to drive this process from a coherent source. Therefore you must have an actual laser to start this process. This is something that they state in the articles. However, in the c/net article, the marketing hype starts to take over. They state, "The Santa Clara, Calif.-based company has created a chip containing eight continuous Raman lasers by using fairly standard silicon processes rather than the somewhat expensive materials and processes required for making lasers today." Implying that this gets us away needing old-fashoned expensive lasers. It doesn't.

Yes, they are nice, small coherent light sources that can be easily modulated and integrated into Si, but they aren't lasers, and the efficiency is a problem.

Let's say you want to start making integrated optical circuits. If you want a chip with 100 switches, you must pump each switch with 300 mW. (Well maybe you could cut back to 100 mW, but the efficiency of these things is non-linear, and there will be a threshold power at which they don't work.) Therefore, a device with just 100 switches would require 10 to 30 watts of coherent optical power to drive it. Then you need to worry about the wall-plug efficiency of your pump laser (or lasers) and the bulk of the pump laser.

It's interesting, and it did deserve an article in Nature. However, there's a lot of corporate marketing hype behind all the buzz in the linked articles, and when marketing hype and science mix I get annoyed.

Re:Correct Units?

[Hal-9001]

Wrong. Here is a good explanation in lay terms. You can find much more detailed explanations with a bit of digging.

That site is totally wrong about the origin of coherence in laser light. I sent the following to the site maintainer:

RE: LASERS EMIT COHERENT LIGHT, BUT NOT BECAUSE THE ATOMS EMIT IN-PHASE LIGHT WAVES

I ran across your site, and I would like to point out that your explanation for the coherence of laser light is incorrect. Coherence and phase are intrinsically-related. Measurements of the temporal or spatial coherence of light are in fact measurements of the relative phase of two different samples of a light wave. The fact that stimulated-emission results in an emitted photon that is exactly in-phase with the incident photon does explain spatial coherence. This is because the laser beam originates as a single (or relatively few) spontaneously-emitted photon(s). That photon is amplified by the stimulated-emission process to form the laser beam. Because the path of the initial photon is generally not along the optical axis of the laser cavity, and because it can be coherently scattered as it propagates through the gain medium, it traverses the gain medium along many paths. Thus the entire laser beam inherits its phase from the initial spontaneously-emitted photon, and is therefore fully spatially-coherent. Even if we consider the laser beam to originate from several spontaneously-emitted photons, the result is that beam is the superposition of several fully spatially-coherent beams, which can be shown to be a fully spatially-coherent beam.

You are correct that starlight becomes more spatially-coherent by propagating long distances, but that cannot the mechanism for the spatial-coherence of a laser, as I will explain with a fairly simple counter-example. With Q-switching, it is trivial to switch a laser on and off within 10 nanoseconds, in which time light travels about 3 meters in vacuum. Yet the laser pulse can be measured to be as or more coherent than starlight, even though its propagation distance is on the order of meters rather than light years.

You are correct that the pure color (monochromaticity) of laser light is due to the mirrors (which form a Fabry-Perot or some other resonant cavity), but I would argue that the explanation for the pure color for laser light is at a less advanced level (third-year physics undergraduate) than the explation for its coherence. Coherence is an advanced-undergraduate to graduate-level topic, as a proper analysis of coherence requires Fourier transforms, and the coherence of stimulated emission is a topic in quantum electrodynamics. The most readable but rigorous treatment of optical coherence that I am aware of is _Statistical Optics_ by Joseph Goodman, but even that is written at the advanced-undergraduate to graduate level.