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Optical components

Startup Touts 'Tunable Demultiplexer'

Lots of startups are developing tunable lasers, and quite a few are developing tunable filters, but Sparkle Optics Inc. is working on something else that’s tunable -- a tunable demultiplexer.

A demultiplexer, in this context, is a widget used in wave division multiplexing (WDM) systems to split light into different colors, or wavelengths, so that a single fiber can actually carry multiple streams of data, each on a slightly different wavelength. Making it tunable, as Sparkle is doing, means that the band of wavelengths it's dealing with can be changed, almost on a whim.

Opinions differ on whether demultiplexers really need to be tunable-on-a-whim in this way. But Santanu Basu, who heads up Sparkle Optics, a tiny contract R&D firm, clearly has applications up his sleeve. For the time being, however, he’s fobbing people off with a niche one -- saying that such a device could be a boon for systems integrators that want to buy a single demultiplexer for their labs, one that could work anywhere in the C, L, or S bands.

Anyhow, Basu figures his tunable demultiplexer has a number of advantages over arrayed waveguide gratings (AWGs), one of the existing ways of splitting white light into different wavelengths. In particular, it’s practical for small channel counts, it doesn’t require temperature control (which consumes power), and, as noted, it’s tunable.

How does it do all this? Because it's based on a diffraction grating, says Basu, and these properties are inherent to the technology.

It's important to note that Sparkle isn't the only company developing grating-based demultiplexers. In fact, there's a growing band of players, including APA Optics Inc. (Nasdaq: APAT), Highwave Optical Technologies, Lightchip Inc., Photonetic (now part of GN Nettest), and Zolo Technologies Inc.. These companies already have products out.

Sparkle, on the other hand, has quite a bit of work to do. Basu says he's built a six-channel prototype out of bulk optical components, like lenses and ruled gratings. The prototype has a channel spacing of 50 GHz, which is good. It has an optical loss of 10.7 dB, which is bad. And the dimensions are 11.3 x 3.7 x 1.3 inches, which is laughably huge.

"It's a small beginning," acknowledges Basu, without irony. "Once we have completed the technology licensing, we will make a second generation in small quantities. We will improve the size, the crosstalk loss, and polarization-dependent loss."

It should be possible to reduce optical losses to less than 6 dB, which is lower than commercially available AWGs, he adds.

Sparkle's competitors are not easily impressed, however. Mike Wearsch, VP of business development at Zolo says that what's needed is reconfigurability, not band tuning. "If you're making an add/drop multiplexer, you need to be able to drop any six channels, not just the six channels next to each other," he says. Zolo, he notes, is working on a way of doing this using MEMS (micro-electro-mechanical system) technology.

AWG vendors are quick to point out that grating-based devices in general could have a big drawback: reliability. "How do you expect it to stand up to vibration when it's going to be hand-made in Asia with cheap labor?" says John Midgley, CEO of Lightwave Microsystems Corp.

Basu counters this criticism by saying that he's planning to make the demultiplexer smaller and more robust by miniaturizing and integrating fewer components onto a silicon optical bench.

All of this work is being undertaken by Sparkle under R&D contracts with Silicon Valley companies, Light Reading has learned.

Basu -- a graduate of Stanford University and former IBM Corp. (NYSE: IBM) researcher -- didn't want to reveal the identities of the companies sponsoring his work, but did give a few hints.

Both companies are in the Bay area, he said. One is an established manufacturer of lasers, not just for telecommunications but for a wide range of applications. The most likely candidate is Coherent Inc. (Nasdaq: COHR), which has its headquarters in Santa Clara. This also fits with Coherent's recent decision to refocus the company on telecom components (see Coherent's Strategy Shift Explained).

The other vendor is a "strong telecom player," and it's not JDS Uniphase Inc. (Nasdaq: JDSU; Toronto: JDU), which has decided to back AWGs (arrayed waveguide gratings) all the way, says Basu.

— Pauline Rigby, Senior Editor, Light Reading
http://www.lightreading.com Want to know more? The big cheeses of the optical networking industry will be discussing this very topic in a session at Opticon 2001, Light Reading's annual conference, being held in San Jose, California on Aug 13-16. Check it out on Opticon2001.

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Shiva 12/4/2012 | 8:03:00 PM
re: Startup Touts 'Tunable Demultiplexer'
I agree with calpole, that the biggest obstacle that will be faced with system manufacturers utalizing the tunable demux will be the interference of channels noticed when tuning takes place.

For this reason, Tunable filters are preferred, especially those that can acheive tuning without affecting the through channels (hitless tuning). A few companies are advertising this feature over a 41 channel (@100GHz spacing)(i.e Ondax)at an insertion loss of 2dB.

Introduction and integartion of this type of product would dispose of mux/demux.

calpole 12/4/2012 | 8:03:01 PM
re: Startup Touts 'Tunable Demultiplexer' The biggest trouble with the tunable demux will
be while tuning, one channel will affect other.
Even if that happens for microsecond, the essence
of the advantage with tunable Demux is lost.
Unless this problem is solved, fixed add/drop
using 2*2 switch can never be upgraded to a
tunable add/drop [ flexible wavelength
tried to a port] architecture.
-Calpole
Petabit 12/4/2012 | 8:03:10 PM
re: Startup Touts 'Tunable Demultiplexer' Hi realoptics,

Since we are now making this personal, let me change my perspective:

"Petabit is wrong again on filter based devices. What he saw may not a simple 80 channel device based simply on filters,"

Not saw, designed. And shipped. It is an economic solution that scales from a few channels to hundreds. It allows carriers to buy as much mux/demux as they need, and then expand it later on. It makes more economic sense for carriers to go this way, rather than take a huge captical cost hit for an AWG or echelle grating.

I agree that the grating based solutions work better for high channel counts (>20), but there are almost no systems out there with that many channels. Most fibre routes have 4-8 channels on them, and so you don't need huge AWG based devices for the vast majority of routes.

It is a major coup of the marketing machines of several companies to convince outsiders that todays systems have 80+ channels. Most of the systems can do that, but almost none are deployed. I'm waiting for someone to come back with 'I saw a 100 channel system at xxx'. Fine, you saw that, but it very much the exception not the rule.

And Mr realoptics, I may have been exaggerating in claiming Lightwave Microsystems were the only AWG player. Fine, I retract that statement, but are you going to accept that Avanex's VIPA is much more than just an interleaver? It can do everything an AWG can do - possibly because they are both based on multiple beam interference. It has some different trade-offs, which is why it is treated as a different technology.

P.
realoptics 12/4/2012 | 8:03:21 PM
re: Startup Touts 'Tunable Demultiplexer' Petabit is wrong again on filter based devices. What he saw may not a simple 80 channel device based simply on filters, it should be filter based devices plus interleavers, and the insertion loss may be at 8-10 dB. Again, once grating based device is successful, there will be no use for the filter and interleaver combination for high channel number applications at all.

Do we also learned that whatever on one company's website may not true at all, take a look at Nanovation's website today,you may be also impressed and excited after their lies.
redface 12/4/2012 | 8:03:25 PM
re: Startup Touts 'Tunable Demultiplexer' Hi Petabit:

I generally agree with your comments. The reason I take issue with Midgley is his statement in the article "How do you expect it to stand up to vibration when it's going to be hand-made in Asia with cheap labor?". Here Midgley is directly linking reliability with cheap labor which I disagree. If he had mentioned the length of the grating device as a reliability concern, I would not have had any issue. In a world of fiberoptics which is filled with hype and misrepresentation, I believe a little more preciseness in communication definitely helps.

I do believe grating devices have a much tougher time getting Bellcore qualification compared to AWG.

Regarding Avanex's VIPA, it is a demultiplexer, not an interleaver. It is very easy to see if one reads Avanex's patents. It can be used as a tunable dispersion compensator. However, the size of this device does make it nearly impossible to be made reliably.
mrtp4 12/4/2012 | 8:03:25 PM
re: Startup Touts 'Tunable Demultiplexer'
The idea of the Echelle Grating is to combine the scalability and performance of bulk-gratings with the high-volume manufacturability of AWGs.

The biggest benefit of EG comes from the much smaller device size, which gives better yields and allows for more on-chip integration.

Compared to AWG, crosstalk is inherently better in Echelle Grating, and power requirements are much lower (closer to 1W, vs 5W). Insertion loss is currently about the same, <6dB, although theoretically it should be better than AWGs.

The real difficulty in making Echelle Grating Mux/Demux is the PDL, and only one or two companies have succeeded in fixing that. Optenia is one. There is a white paper that compares the technologies at www.optenia.com

benson 12/4/2012 | 8:03:29 PM
re: Startup Touts 'Tunable Demultiplexer' Petabit;

You are completely wrong about the commercial situation regarding AWG's.

Both Hitachi Cable and NEL have shipped thousands of AWG's. In the case of Hitachi Cable, they have shipped more than 9000 AWG's over the past 6 years. Lightwave Microsystems is not even close.

Neither of these companies have an IPO to launch, nor a stock to sell in the US. Hence, both go quietly about their job.

You are reporting on marketing hype, not the actual commercial situation.

Benson

Petabit 12/4/2012 | 8:03:32 PM
re: Startup Touts 'Tunable Demultiplexer' I admit my grand sweeping statement about who could make AWGs was a bit over the top. I still stand by the assertion that Lightwave Microsystems are one of the leaders in actually shipping AWGs in commercial volume.

I note that no-one else has had a go at John Midgley though.

"The key drawback for filter based technology is hard to scale, it is pretty hard, if it is not possible to make any mux/demux with 16 or more channels."

I think you're wrong there. I can think of a commercial product that has shipped several billion worth of units where 80 channels are done with thin film filters.

"Another point is wrong is on Avanex's so called VIPA, it is really an interleaver."

According to the Avanex website, the interleaver is called a 'Asymmetric Nonlinear Interferometer' and VIPA is something different.

P.
wchieh6 12/4/2012 | 8:03:33 PM
re: Startup Touts 'Tunable Demultiplexer' One article in May talked about echelle grating.
Is there anyone konw about the real performance of echelle grating based Mux/Demux with respect to AWG?
realoptics 12/4/2012 | 8:03:40 PM
re: Startup Touts 'Tunable Demultiplexer' Petabit is wrong on commenting '...the only one'! as also pointed out by the other letter, NEL, PIRI, Hitachi, and other more than 2 dozens companies are all having different levels of success. NEL, by far is the best supplier in AWG and they've been doing research for 16 years before they saw some fruits. Lightwave certainly is not the only one and is only 'close to commercialization'

The key drawback for filter based technology is hard to scale, it is pretty hard, if it is not possible to make any mux/demux with 16 or more channels.

Another point is wrong is on Avanex's so called VIPA, it is really an interleaver, The Avanex VIPA is only good for intermidiate solution, it is going to be deemed as useless when grating and AWG based technologies are fully mature.

Realoptics

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