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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."
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.
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.
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.
~Anztac
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).
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.
Using the Raman effect, the chip firm has produced an optically pumped laser, with outputs up to 9mW.
"We have proved that silicon can be considered as a gain material," said Mario Paniccia, director of Intel's photonics technology lab.
. . .
At 300mW pump input, the laser outputs around 6mW. The slope efficiency, with a 25V bias on the PIN diode, is 4.3 per cent. Half power linewidth is claimed to be better than 80MHz.
So what exactly does it mean that silicon is a "gain" material if the laser output is one 30th the energy of the pump input?
Also, they mentioned something about optical modulation in the article; do you know if this proof-of-concept chip can actually modulate the light? I wonder if just reversing the bias would do it . . .
Oh well. I guess I'll have to read the Nature article when I get to work. We have pretty nifty online access to a lot of scientific journals.
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in the laser lab where I work:
solid state diode laser, 5W at 532nm: $40,000
YLF laser, 20W at 532nm: $40,000
Titanium doped sapphire crystal: $1000
optics to make 400mW ultrafast laser: $10,000+
cost of buying comparable kit from KML: priceless!
no, actually $100-300k
not that these lasers are exactly general use.
I'm just pointing out that lasers and materials can be very expensive.
The laser is coherent because the emitted photons are in phase.
Hundreds? Try thousands of dollars for the high end, high speed, long-haul laser transmitters and receivers. Hell, a plain LED (not laser) based short-haul (SX) gigabit ethernet transceiver will cost you $150 to $400. The gigabit LX/LH transceivers can cost you upwards of $1000, and that's just for run of the mill gigabit ethernet stuff. 10 Gigabit is about $4000 per transceiver.
The best explanation I've seen for the coherence of stimulated emission is "Rereading Einstein on Radiation" by Daniel Kleppner in this month's issue of Physics Today. The explanation is that light-matter interaction can be modeled as a driving force applied to an oscillator (like a pendulum or spring). In the presence of a driving force, an oscillator absorbs or emits energy depending on its current phase with respect to the phase of the driving force. A simple example is pushing someone on a swing (which is a pendulum, and therefore an oscillator). If you push them at the right times, they swing higher and higher--the oscillator absorbs energy. If you pull on the swing at those times, they swing less and less--the oscillator loses energy.
In light-matter interaction, the electromagnetic attraction between an electron and an atomic nucleus can be modeled as a spring, and the driving force is an incident electromagnetic wave, i.e. incident light. In a stimulated emission process, an atom (oscillator) loses energy in the presence of an incident photon (driving force). If the energy is emitted as a photon exactly out-of-phase with the incident photon (fully anti-coherent), the two photons would destructively interefere, reducing the net energy of the system and therefore violating conservation of energy. In fact, if the emitted photon is anything other than exactly in-phase with the incident photon, conservation of energy is violated. Thus the emitted photon must be exactly in-phase with the incident photon, and is therefore fully coherent with the incident photon.
"It take 9 months to bear a child, no matter how many women you assign to the job."
"It take 9 months to bear a child, no matter how many women you assign to the job."