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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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rocksolid 12/5/2012 | 3:26:26 AM
re: Intel Claims Laser Breakthrough This is still R&D, but think out 3-5 years. If Intel can in fact get the complete optical train to work in silicon, this would open up the possibility of full electrical-optical integration.

You'd want to do this across multiple channels as well, but you could then have your lasers and detectors integrated on the same chip as your signal processing electronics. Wow!

That would be the death of optical components companies as they exist today (of course 3-5 years from now most will be dead anyways!).
Steve0616 12/5/2012 | 3:26:25 AM
re: Intel Claims Laser Breakthrough 3-5 years? might want to rethink that one.
BigFiberDog 12/5/2012 | 3:26:25 AM
re: Intel Claims Laser Breakthrough 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.

As for Modulators and waveguides, the coolest work being done in this area is by Luxtera.
JeffChetin 12/5/2012 | 3:26:24 AM
re: Intel Claims Laser Breakthrough ...or SiOptical?
Balet 12/5/2012 | 3:26:23 AM
re: Intel Claims Laser Breakthrough ...or another 3-4 startups working on that?
The big question is how those Luxteras can compete against $$ and human power of Intel.
May be they are hoping to be bought by Intel if they make any minor breakthroughs.
Fazevelocity 12/5/2012 | 3:26:22 AM
re: Intel Claims Laser Breakthrough Doesn't anyone remember ASOC???
All the problems around singlemode guides, pol dependance, pin structures etc were solved way back. Graham Reed at Surrey University had this area of research in the early 90's (incidentally, he's posted in Intels website with a whitepaper on the subject of Si optics). Going back a bit further, Richard Soref did the initial work with numerical methods to establish the geometrical confinement parameters on Si ridge waveguides in about 86-88, if I remember correctly.
What I'm saying is that most of the problems other than source/detector are already solved and understood, even for CMOS processing. Take a look at ECOC and PW2000+ papers from Bookham and you'll see hybrid integration, passive alignment techniques, waveguide polarisation-insensitivity etc...all worked out.
The free-carrier effect has been a major problem here and the traditional device capacitance kept pin modulators in the sub 10MHz range - fine for EVOAs, but not much good for telco line rates!
Yes, granted you need an external pump source from a direct bandgap material to pump this laser, but I disagree that this is wavelength conversion per se. No tunability here, just good ol' Raman effect. The impact here is now, a single pump could be on a PCB, feeding many of these devices.
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...
dmw_qqqq 12/5/2012 | 3:26:21 AM
re: Intel Claims Laser Breakthrough Well, this can be viewed as a significant advance in the sense of pure resesrch, but mass marketing it?

I still remember INTL was proudly showing off its tunable laser a couple of years ago, what happened to it since?

-dmW
deauxfaux 12/5/2012 | 3:26:19 AM
re: Intel Claims Laser Breakthrough Caltech did this first, UCLA second, Intel third. Duly recorded in AppPhysLet, Nature, even lowly SciAm

None of this matters. There is no electrically pumped gain medium. All of this great research requires good 'ol fashioned III-V pumps

Possibilities? Press Releases
Balet 12/5/2012 | 3:26:15 AM
re: Intel Claims Laser Breakthrough Not only press releases but also additional funding to those poor startups trying to make a revolution.

The applications for high frequency modulated light in lasing Si waveguide are well above telecom.
dmw_qqqq 12/5/2012 | 3:26:13 AM
re: Intel Claims Laser Breakthrough We don't know why INTL claims what it claims. Because in its white paper, it says it's working on Si because it is tired of exotic and expensive materials like InP and GaAs. Yet its latest "breakthrough" still relies on these materials it trashes at first hand.

In their Nature papers, they simply said an external cavity diode laser (ECDL) was used as pump, at nowhere it reminds people that the pump is a different animal from the Si Raman laser cavity.

-dmW
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