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Optical components

Intel Claims Laser Breakthrough

In what could be a milestone for photonics, Intel Corp. (Nasdaq: INTC) claims to have developed the first silicon-based continuous-wave laser and is presenting the data in Nature tomorrow.

But on a conference call with reporters this morning, Intel representatives were quick to note that this program is still in the research phase, with practical, available-for-sale silicon lasers still years off.

"The silicon photonics research and [its associated] building blocks are still a research program, but we hope to transfer that technology [to real-world use] by the end of the decade," says Mario Paniccia, director of Intel's photonics technology lab.

The initial version of the laser has an output of 8 mW, compared with 10 mW for many commercial lasers. Paniccia notes that Intel's laser is still a rough draft, not optimized for maximum power.

Silicon-based photonics has long been a quest for Intel and others (see Light From Silicon). With the truckloads of research dollars that pour into chip manufacturing, it's much cheaper to build a device in silicon rather than in indium phosphide or gallium arsenide, two of the materials commonly used for photonics. Moreover, chips in silicon can be integrated with relative ease, creating smaller optical modules that can include electronics on-chip.

But silicon doesn't emit light, and historically, silicon chips haven't been fast enough to detect or modulate the optical signals used in telecom. All told, Paniccia notes that six innovations are required to make silicon photonics work:
  • The light source (today's announcement)
  • Waveguides in the silicon, to guide the light
  • A modulator, as Intel announced last year (see Intel's Modest Modulator )
  • Detectors, to receive the light in silicon
  • Packaging and assembly
  • Intelligence (i.e., the chips Intel does already)


Intel has gotten the waveguides done, and demonstrated automated assembly last fall at the Intel Developer's Forum. That leaves the detectors as the only piece Intel hasn't discussed publicly. "We hope in 2005 we will produce some technical work there," Paniccia says.

Researchers at The University of California, Los Angeles (UCLA) demonstrated a silicon laser in the fall (see UCLA Claims First Silicon Laser). But that laser delivered light in a pulse of less than 50 picoseconds, Paniccia notes. Such pulse lasers aren't practical in most applications and are usually a laboratory precursor to a more useful, continuous-wave laser.

As with UCLA's project, Intel's silicon laser uses Raman Amplification -- the same photonic effect used in Raman amplifiers for long-distance transmissions. Here's the plan: When a beam of light creates vibrations in the lattice of silicon atoms, this gives off energy in the form of light at a new wavelength. If that light intersects a second beam of the same wavelength (this would be the beam carrying data), the result is amplification of the second beam. Repeated amplification eventually causes the beam to reach the threshold current, where intense light (the laser beam) emits.

Silicon happens to be a happy home for the Raman effect. "The Raman gain coefficient is 10,000 times stronger in silicon than in amorphous glass fiber," Paniccia says. "We can do in centimeters what's done today in kilometers."

But the Raman method hit a snag. Every now and then, two photons would hit a silicon atom simultaneously, and the resulting energy would kick out an electron. Because electrons get reabsorbed into the material slowly, these free electrons would build up, creating a cloud that disrupted the laser's process.

It's this "two-photon absorption" that limited the UCLA laser to 50-picosecond pulses rather than continuous-wave output, Paniccia says. Intel ran into the same problem. By November, the company had gotten only a pulse-wave version of its laser to work; those results got published in January. Intel had gotten the continuous-wave laser to work by then -- on the day before Christmas, as it turns out (awwww).

Intel overcame two-photon absorption by implanting material in the silicon to create an electrical field that grabs the electrons. "I can suck out the electrons similar to a vacuum cleaner," Paniccia says gracefully. This, er, "sucking" is what made Intel's continuous-wave breakthrough possible.

Silicon photonics could lead to increased reach for lasers. Some fancier applications could be made possible too; Paniccia describes the possibility of using silicon waveguides to create a Wavelength Division Multiplexing (WDM) feed out of one light source, for example.

The silicon laser is nice for telecom, but the more glamorous applications could lie in medical equipment and sensors, where a tunable silicon laser could replace models that cost tens of thousands of dollars. Intel also has its eye on optical interconnects for chips and backplanes, not just for the speed of optics, but because thin optical fibers take up less space than electrical cables, leaving more space to get computers and servers cooled down.

— Craig Matsumoto, Senior Editor, Light Reading For more on this topic, check out:

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Dr.Q 12/5/2012 | 3:26:12 AM
re: Intel Claims Laser Breakthrough The pump laser must still be InP or GaAs or some other active material. That's where their tunable laser (on a silicon platform) comes in.
But . . . it still needs the laser diode to get the Breakthrough up and running.

- Dr. Q
deauxfaux 12/5/2012 | 3:26:11 AM
re: Intel Claims Laser Breakthrough But the demands of the high volume markets are so unforgiving of technologies that carry costs above cheap, reliable parts that there is no way for something like this to succeed in a "low cost niche market."

If this is the best that they've got, they should stick to CMOS.

redface 12/5/2012 | 3:26:11 AM
re: Intel Claims Laser Breakthrough "Leave it to Intel to get the packaging sorted out. They know how to put a high performance device with stringent RF specs into mass market for a few hundred dollars. What's to say that a hybrid electrical/optical socket or package for this purpose won't be developed to accomodate this need, or even just an MCM??? Leave it to Intel and have faith, it will happen..."

I don't believe that Intel will be able to do it, not on some design so backward. Their entire silicon photonics endeaver has been a huge waste of money, because it is so expensive to develop and in the end the performance is nowhere near the traditional approaches, so it will only find a low cost niche market to play in where the profit margin is very low and competition from cheap labor is fierce.
Steve0616 12/5/2012 | 3:26:08 AM
re: Intel Claims Laser Breakthrough if it means the "complete optical train to work in silicon" like the post mentioned, then 10-15 years.
[email protected] 12/5/2012 | 3:26:08 AM
re: Intel Claims Laser Breakthrough Care to put a time frame on it?
DZED 12/5/2012 | 3:26:08 AM
re: Intel Claims Laser Breakthrough For us dummies could you define exactly what the optical train is?
I think many of the optical building blocks are nearly there, maybe at the Gb/s rates needed but getting close, but as a packaging guy I know nothing... :)

PS surface mount hybrid optical/electronic packages certainly exist. Taking it down either to the on-chip, or chip to chip level could be interesting.
DZED 12/5/2012 | 3:26:07 AM
re: Intel Claims Laser Breakthrough Bookham had pretty much all of this a while ago.
The fibre was typically the tricky bit.

Its embarrassing they dumped it all in favour of DWDM devices which eventually no-one wanted.

Integrating laser/detector/fibre functions onto a CMOS chip was very smart.
Trying to make an AWG/VMUX on CMOS was very dumb.
At one point Bookham had 200+ R+D people on AWGs, one person on actives, doh...

Interestingly its reckoned Rickman bought back all his patents from Bookham once ASOC was closed down.

Pretty clever eh? Develop a technology, take in $1bn at IPO, then walk away with the patents.
deauxfaux 12/5/2012 | 3:26:07 AM
re: Intel Claims Laser Breakthrough Dzed

Generally: optical train = all optical surfaces, subcomponents and/or waveguides between a source or detector and the fiber.

In the case of a typical laser, most people would call the submount, collimating & objective lenses, isolator and fiber tip as the optical train.

The Intel announcement presupposes a GaAs or InP pump (with any coolers) sitting on a submount, with 1 or 2 lenses and probably an isolator to get light into the silicon substrate, finally feeding the Raman laser.

Clearly, this adds a lot of complexity for no additional benefit.
vermillion 12/5/2012 | 3:26:06 AM
re: Intel Claims Laser Breakthrough The most important interest in optical integration on silicon seems to be in defense research (DARPA program "EPIC"). It has little to do with telecom. However, if the program really results in optoelectronic building blocks on Si, they could be applied in a number of applications.

But the Raman laser itself if not that significant! Mario Paniccia himself was saying at Photonics West that it is a research thing only, and that the light source will be off-chip, non-silicon.
vermillion 12/5/2012 | 3:26:06 AM
re: Intel Claims Laser Breakthrough Hear, hear!

This is one of the most misleading articles I have ever seen on LR.

-v

"Shame on you LR, for not confessing in the midst of all your usuall Tabloid like hype that is Raman Laser is still pumped by another laser that is not silicon. What they are really demonstrating is wavelength conversion which is really boring since you still need something III-IV to make things work."
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