Bell Labs Claims Laser First

Scientists at Bell Labs have invented a new type of laser that might one day slash the cost of building DWDM systems (see Bell Labs Lights Ultra-Laser).

It's called a "supercontinuum" laser, and it delivers a broad band of wavelengths simultaneously. This should not be confused with widely tunable lasers, which also offer a broad band of wavelengths, but only make one of them available at a time. Tunable lasers promise to reduce inventory costs by making it possible to use one type of laser instead of many different types throughout a DWDM system, whereas a single supercontinuum source could be used to replace all the lasers in a system.

And this idea isn't just pie in the sky. Last year, researchers from NTT Electronics Corp. (NEL) reported an experiment that used a single light source to supply all 106 channels in a DWDM system (see CLEO Report: Pick of the Papers).

However, NEL's light source was a complicated configuration involving a pulsed laser diode, an erbium-doped fiber amplifier (EDFA), and a piece of polarization-maintaining fiber. In the case of Bell Labs' laser, only the semiconductor laser diode is required, and it emits continuous – rather than pulsed – light.

Claire Gmachl and her co-workers report their results in today's issue of Nature (issue 415, p.883).

Gmachl has already made a bit of a name for herself for her work on the so-called "quantum cascade" laser. Invented in 1994 by Bell Labs researchers Federico Capasso (also an author on today's Nature paper) and Jerome Faist, quantum cascade (QC) lasers are designed in a completely different way from ordinary diode lasers. Indeed, the new laser unveiled today is a variation on a QC laser.

To understand how Gmachl's team made the new device, it's worth looking briefly at how an ordinary laser works. Ordinary lasers require both negatively-charged electrons and positively-charged "holes" (places in the crystal where electrons should be, but aren't). They attract each other, and when the electron pops into the hole, it gives up surplus energy as a photon of very specific energy. That energy determines its wavelength.

QC lasers work with electrons only. The semiconductor layers are designed in such a way that the electron can drop energy in a series of small amounts, giving up a photon each time it does so. "Consider it an electronic waterfall," says Bell Labs' description of a QC laser at http://www.bell-labs.com/org/physicalsciences/projects/qcl/qcl.html. The cascade of light generated in this way makes the QC laser much more powerful than existing lasers.

This waterfall effect is key to making the device broadband. Instead of creating all the small steps in the waterfall the same size, they can be made slightly different, so that each successive photon emitted has a slightly different wavelength. The laser reported today had 36 "steps" in the waterfall, each one created by growing thin layers of several different semiconductor materials.

The fact that all the different materials are grown on top of each other is significant because, with a bit of tweaking to the design of the layers, it is possible to create lasing at every wavelength in the band, not just at discrete wavelengths corresponding to the peak gain at each "step." This differentiates the device from so-called multiwavelength lasers, which are made by growing different materials side by side on a semiconductor wafer, and have wavelength spikes at the output.

But there is a catch. Since the electrons only make small energy jumps, the photons tend to have long wavelengths. So far, Bell Labs has only managed to make devices that emit light in the region 4 to 24 microns. (The device reported in Nature actually emitted all wavelengths in the range 6 to 8 microns.) It has been Bell Labs' stated intention for a quite a while to make a device that emits at the shorter telecom wavelengths of 1.3 and 1.55 microns, but so far no progress has been reported in this respect.

— Pauline Rigby, Senior Editor, Light Reading
Page 1 / 2   >   >>
Twistall 12/4/2012 | 10:54:30 PM
re: Bell Labs Claims Laser First Come on, mu! You can't figure out what to do with this? If this isn't the basis for a tuneable lambda device, I don't know what is. Can you say "inventory reduction"? I think you can!
mu-law 12/4/2012 | 10:54:30 PM
re: Bell Labs Claims Laser First This is crap. First one to point out a relevant commercial application for a transducer with "infinite line width" wins...
exphoton 12/4/2012 | 10:54:29 PM
re: Bell Labs Claims Laser First There are two stories in this write-up:

1) A scientific accomplishment, which any technical person will acknowledge is a significant move towards a new type of laser.
2) The use of multiwavelength lasers in real (carrier-class) DWDM systems. Whether for sparing or other uses is not important.

Between 1) and 2) is a chasm, a quantum leap if I may be forgiven for my choice of words.

Transforming the lab result to a real product will need 1) the ability to go to 1.5 microns, 2) a large $$ commitment, 3) about 3-5 more years of development, and 4) a compelling cost reason (why does having one laser with multiple wavelengths help if its cost point - and please include yields, packaging, modulators (you will need one modulator for each wavelength, wont you?), etc - is no better than current fixed or tunable lasers?).

Again, pardon my run-on sentence construction.

Anyway, point to be made: It is this specious connection between the two stories that diminishes the credibility of LR articles.

The_Holy_Grail 12/4/2012 | 10:54:27 PM
re: Bell Labs Claims Laser First ...this sounds like it is in the very early stages of research. Companies would be wise not to get distracted with something 5 yrs out.

Again, which I have harped over and over, science projects are nice, but long term players must focus on the bottom line.
mu-law 12/4/2012 | 10:54:25 PM
re: Bell Labs Claims Laser First "Come on, mu! You can't figure out what to do with this?"

Sorry, I read the article literally before going to Nature... that will teach me, but good; I inferred that the emission spectra was continuous, viz. "it delivers a broad band of wavelengths simultaneously" hence my seemingly orthogonal comment.

In the end, this is the same well known QC stuff rehashed with the same uninteresting *FAR* IR applications.

Regardless, even if this makes it to C/L band it is not clear to me what is gained by distributing (and presumably dissipating) energy across all of those peaks. You still need to modulate this, and then somehow selectively absorb at low loss. At best, a "brute force" approach to tunables IMHO, with emphasis on the "brute".

All the old problems are still there with closed-loop temp control, etc. I may be dull, but the (communications) problem for this solution doesn't beat me over the head. I suspect that efforts like these will be the epitaph for "unguided" commercial research, as another poster points out.

zweisel 12/4/2012 | 10:54:20 PM
re: Bell Labs Claims Laser First ... this article just shows how ignorant this magazine rag is... it epitomizes what crushed this industry... ANALysts.
Peter Heywood 12/4/2012 | 10:54:17 PM
re: Bell Labs Claims Laser First This thread has got on my goat.

Our goal in writing these type of "out of the lab" articles is to point to interesting research projects and explain them in a way that's understandable by non experts.

This has to include citing the possible long term impact on telecom equipment. Otherwise, non-experts will wonder what all the fuss is about - and most of our readers are non-experts.

This article also helps experts in as far as it points to a development they may not be aware of, and points to where they can info direct from scientists.

If this makes us a "rag", so be it. Light Reading is very widely read precisely because we actually try to help folk understand, rather than blinding them with science.


melao 12/4/2012 | 10:54:16 PM
re: Bell Labs Claims Laser First Just for curiosity the applications that Bell Labs foresaw for this laser is shown on the following link:


i saw every type of application BUT telecom.

gea 12/4/2012 | 10:54:15 PM
re: Bell Labs Claims Laser First Does Lucent (part of Bell Labs) still plan to manufacture components? I am slightly suprised that this kind of research is done there, as opposed to Agere (the recently spun off coponent division).
Anyone know the internal coporate spiel on why Lucent still even does materials research?
bongwang 12/4/2012 | 10:54:14 PM
re: Bell Labs Claims Laser First Peter:

I often don't resonate with you, but in this case I heartily agree. LR does an outstanding job of making it possible for non-experts to undertand optical networking and its technologies.

As to this thread, more emotion than thought has been the basis for the posts.

Keep these articles coming, LR has become an important source of information for many thousands of readers, and we do look forward to the daily and weekly updates.

Page 1 / 2   >   >>
Sign In