Optical components

Intel's Modest Modulator

Intel Corp. (Nasdaq: INTC) hit the headlines yesterday with news that it had invented a new kind of optical modulator based on a "transistor-like" silicon device (see Intel Builds Modulator in Silicon).

Modulators are a key component that encode data onto a light beam. Usually they are made out of other materials such as lithium niobate or indium phosphide. Intel's silicon modulator has the advantage of being compatible with standard electronics manufacturing, and although it's not as fast as commercially available devices, it is a factor of 50 times faster than any previous silicon-based modulator. Details were published this week in the peer-reviewed journal Nature.

The mainstream press looks to be in love with Intel's announcement, but experts say the technology has plenty of shortfalls and isn't likely to have a commercial impact any time soon. Some even believe there could be negative fallout from Intel's PR machine, which has played up the announcement enormously for the masses.

"It's not a breakthrough worthy of so much attention," says Tom Hausken, director of optical component research at Strategies Unlimited. "I hope that they don't feed a new round of hype, centered this time on silicon photonics".

Modulator Mini-Tutorial

In fairness to Intel, the modulator device is novel. It's based on a Mach-Zehnder interferometer, a widget that splits the light along two paths and then recombines it. If a phase shift can be introduced into one of the arms, so that it is 180 degrees out of phase, then the two light beams will interfere destructively when they recombine, which gives a "zero" at the output. If there is no phase shift, the beams combine constructively, leading to a "one" at the output. This is a common technique for building modulators.

The clever part is in how Intel induces a phase shift. Rather than using the thermo-optic effect (heat) to change the refractive index of the device, as earlier devices did, the device has an oxide electrode at the top. When a voltage is applied, charge carriers accumulate next to the electrode, which changes the refractive index locally. This effect is fast because no current actually flows in the device.

The modulator was developed at Intel's basic-research organization, the Corporate Technology Group, and involved researchers at the Santa Clara, Calif., headquarters and in Intel's Jerusalem location.

The company praised its own achievement as a key step towards building optical components entirely out of silicon. This is a natural target for a company that's such an expert in silicon electronics, and it's also the target of research efforts the world over.

"This is a significant step toward building optical devices that move data around inside a computer at the speed of light," said Patrick Gelsinger, Intel's senior vice president and CTO in a statement. "It is the kind of breakthrough that ripples across an industry over time enabling other new devices and applications." The company believes its work will pave the way towards the more widespread use of optics inside and between computers.

Reality Check

Those are big claims. But there are plenty of reasons why Intel's modulator isn't going to change the world any time soon.

For starters, the whole idea of moving data at the speed of light is misleading, says Hausken. What really matters is the modulation speed you can achieve, and in Intel's prototype device, this isn't very high.

Intel's modulator has a bandwidth of 1 GHz. Traditional encoding techniques assign one bit to each modulation cycle, which means a 1GHz modulator transmits data at 1 Gbit/s. This may be just about fast enough for some applications in datacom, but many telecom applications would require rates of 10 GHz.

Second, by Intel's own admission, this is a very early-stage device. There is plenty of work to be done before its performance approaches that of commercially available modulators. Parameters such as optical loss must also be improved.

"It is now easier to foresee the fabrication of even faster silicon based modulators, but the technical challenge is still substantial," Graham Reed, from the University of Surrey in the U.K., wrote in an article that accompanied the Nature paper. Reed is from the research team that spun out Si-Light Technologies Ltd., a company working on silicon photonics.

Third, Intel has only built one piece of the silicon puzzle, and that's no good on its own. The showstopper for silicon optics has been the fact that silicon doesn't emit light easily, so it's been difficult to make a silicon laser. Although a couple of research teams have made progress towards this goal, right now they still seem to be some way off from having commercial products (see Silicon Starts to Shine).

"Making a modulator is not a problem," says Andy Carter, VP of research and development for Bookham Technology plc (Nasdaq: BKHM; London: BHM). "But you've got to have a laser. At the moment, you can't make a laser out of silicon, so you've got to have two materials and co-package them. At the low end, that's too expensive to do."

Will Intel be making a silicon laser? Apparently not. "Right now the activities are around doing everything else in silicon," says Mario Paniccia, director of Intel's photonics research lab. Intel's approach will be to attach a III-V laser -- one made of materials such as gallium arsenide or indium phosphide, he says. Ultimately Intel would like to wrap CMOS circuitry around the laser as well.

So if you haven't got a silicon laser anyway, why not use the best material for the job? And it isn't silicon!

What may prove the most difficult barrier to overcome for silicon photonics is economics. Although the equipment and many of the manufacturing methods for producing silicon photonics already exist, that's not enough. Electronics rely on chips being produced in huge volumes, something that's not likely to happen with photonics, at least for the foreseeable future. "There isn't enough volume [in photonics], and you can't get economies of scale for low volumes," Hausken notes.

— Pauline Rigby, Senior Editor, Light Reading

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dljvjbsl 12/5/2012 | 2:27:02 AM
re: Intel's Modest Modulator http://www.nytimes.com/2004/02...

This is the New York Times article discussing this development.

From the article:

Although the technical report in Nature focuses on the device, that is only one component of a communications system that Intel says that it will demonstrate at its annual developer conference here next week - transmitting a movie in high-definition video over a five-mile coil of fiber optic cable.

"If Intel and other semiconductor technology companies can develop silicon optically as successfully as they have electronically, then silicon is certainly set to grow in stature as an optical material," Graham Reed, a physicist at the University of Surrey in England, wrote in a commentary on the Intel paper that was also published in the journal. Dr. Reed is the holder of the previous 20-megabit silicon optical switching speed record that Intel shattered.

The article also states that commercial products will be available from this technology at the end of the deacade


Intel will be demonstrating this technology at a conference as part of a broadband transmission system

These two comments do seem to be more sanguine about the technology than the LightReading article.
beachboy 12/5/2012 | 2:26:54 AM
re: Intel's Modest Modulator The last post must be written by an Intel employee.
Pauline's article made total sense - perhaps except when she mentioned about modulators being driven by the thermo-optic effect. You can sure drive an MZI using heat but it ain't very fast.
redface 12/5/2012 | 2:26:53 AM
re: Intel's Modest Modulator This silicon modulator tops out at 1GHz or so. For that speed, directly modulated lasers are good enough and you don't need external modulator which is what the Intel modulator is.
emm22 12/5/2012 | 2:26:52 AM
re: Intel's Modest Modulator "Third, Intel has only built one piece of the silicon puzzle, and that's no good on its own. The showstopper for silicon optics has been the fact that silicon doesn't emit light easily, so it's been difficult to make a silicon laser"

"Making a modulator is not a problem," says Andy Carter, VP of research and development for Bookham Technology plc (Nasdaq: BKHM - message board; London: BHM). "But you've got to have a laser. At the moment, you can't make a laser out of silicon, so you've got to have two materials and co-package them. At the low end, that's too expensive to do"

I don't think the above two comments are fair. Becasue in order to drive data at high speed, you either have a laser which is directly modulated or you have a modulator+a cheap GaAs laser. Since the laser used in modulators is a continuous wave, it will be very cheap. Even today's semiconductor lasers such as VCSELs are cheap and their output power increased almost exponentially. when you project this to 5-10 years out, prices will drop exponetially too. You may be able to buy lasers for few cents. Therefore, getting a Si modulator fast enough to drive data at high speed by is good enough by itself. This is not one side of the puzzle. This is wiil be a Jackpot if one manages to make CMOS compatible Si modulators. In fact, I argue that it is better to focus on modulators based on Silicon than chasing emission of light from Silicon.

talkingmoose 12/5/2012 | 2:26:50 AM
re: Intel's Modest Modulator The Intel reseachers fail to recognize work published nearly 15 years ago in Applied Physics Letters!

"All-silicon integrated optical modulator for 1.3 -¦m fiber-optic interconnects"

B. R. Hemenway, O. Solgaard, and D. M. Bloom

Applied Physics Letters Vol 55(4) pp. 349-350. July 24, 1989

We report an all-silicon fiber-optic light modulator which relies on free-carrier optical dispersion and mode filtering in single-mode fibers. Greater than 10% peak-to-peak intensity modulation over a 200 MHz bandwidth for 10 mA rf current modulation at 1.3 -¦m wavelength is demonstrated.
Curious George 12/5/2012 | 2:26:46 AM
re: Intel's Modest Modulator Agreed - not such a big deal...
whyiswhy 12/5/2012 | 2:26:41 AM
re: Intel's Modest Modulator Publish in Nature???!!!???

Probably couldn't get past the laughter of the peer reviewers at APL or JLT.

Charge-based electro-optic devices just will not make the speed-cut, since a photon's wavelenght is huge compared to an electrons. Simply stated, 0.09 micron wide optical waveguides are extremely lossy.

Isn't Nature the rag that published the articles about room temperature superconductivity a few years back?

Tom Hausken 12/5/2012 | 2:26:29 AM
re: Intel's Modest Modulator Pauline Rigby asked me to post other comments I made to LightReading. I can split hairs over the language used, but nonetheless, the Intel achievement is notable for its novel approach in silicon, and deserves credit within the IEEE for that.

However, articles in the New York Times and Nature go further, and suggest that it opens a massive door to all kinds of wonderful things. The journal Nature even makes a connection to Moore's Law. The trouble is, Moore's Law is very specific. It applies well to digital microprocessors. It does not apply well to analog electronics, image sensors and detectors, and lasers and waveguides. One reason is obvious: the wavelength of light does not scale.

Intel made presentations at Photonics West on related subjects, but so far has not explained how the Si modulator (with an InP laser) would have an advantage over a directly modulated InP laser, even in principle.

To get the greatest advantage out of silicon, you have to fabricate the devices using the design rules and equipment you use for volume production. History has not been kind in this regard. Moreover, what is considered volume in the high-speed communications market is very small potatoes in electronics. Consequently, the production would be at the same volume as is already done in the industry, yielding no advantage.

I don't dispute that Intel can do better. And, other achievements will certainly follow that build on the overall solution. But without further explanation from Intel, it sounds a lot like a search for Atlantis.

Tom Hausken
Dr_Moose 12/5/2012 | 2:26:28 AM
re: Intel's Modest Modulator Intel is most likely not thinking short term here (it is research as they point out - also why it is published in Nature which is still one of the best peer-reviewed journals worldwide).

A couple of key points:

- this is not a "telecom" device but a "datacom" device, i.e. transport of information over short distances. Datacom devices have the potential to sell in annual volumes of millions or more ultimately

- one reason why there are no optical devices on most consumer electronics is the cost (chicken and egg argument here). A CMOS-compatible modulator removes at least one cost hurdle

- if I was Intel, wouldn't I want to do research and development on say including an optical-based 1 GHz ethernet connection for example integrated on each Pentium that I sell?

No new development is a slam-dunk commercial success. It took the laser aboutu 25 years to find a consumer application (CD players).

I would watch the development of this technology over the next 5 years or so before critically judging its impact.

BTW - talkingmoose - the modulator done by Bloom's group was not a "waveguide" modulator but a bulk modulator. Of course the core physics - use the electron plasma to modulate optical phase - is the same.

pabs 12/5/2012 | 2:26:27 AM
re: Intel's Modest Modulator What about a truly integrated solution for light detection compatible with Si CMOS ?
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