Optical Switching Gets Flexible

Several optical components makers will use the upcoming Optical Fiber Communication Conference and Exhibit (OFC) to showcase new configurable optical switches that are smaller and more flexible than today's wares.

It's already starting: Today SpectraSwitch Inc., a startup specializing in liquid crystal technology, unveiled an eight-channel, reconfigurable optical switch geared to makers of metropolitan network equipment (see SpectraSwitch Unveils Wave of Products). It plans to show the new part at the conference as an alternative to larger, bulkier optical switch modules.

The SpectraSwitch product is among the first components to surface that claim to be "reconfigurable": that is, flexible enough to accommodate dynamic channel changes and able to fit a variety of needs for manufacturers of optical switching systems.

For instance, SpectraSwitch says the same small part can be used to create an add/drop multiplexer, a DWDM terminal, or an optical switch. Because the same tools are used to create and modify each part, manufacturers save money on retooling.

"Most people think of components as a fixed commodity," says SpectraSwitch CEO Lindsay Austin. "We think [our product] has the flexibility of a module, with the compactness of a component."

Austin says the component, dubbed the WaveWalker IOC, owes its virtues to liquid-crystal technology, in which the polarization of light is changed via filters in order to achieve passing, dropping, or attenuation of wavelength channels (see Optical Switching Fabric, page 7). Because it doesn't rely on moving parts, it is more durable, longer lasting, and cheaper to make than parts based on techniques such as MEMS (micro-electro-mechanical system), Austin says.

SpectraSwitch's WaveWalker measures five inches square by half an inch high and supports up to 64 100GHz channels via thin-film filters, according to the vendor.

According to SpectraSwitch marketing director Denise Oliver, the company sees its key opportunity in selling to OEMs that are looking for 32 to 64 channels in their optical switch components. That appears to put the company in line with makers of metropolitan-area networking gear. To support higher channel counts, such as those presently being eyed for long-haul networks, Oliver says SpectraSwitch plans to use different filters to accommodate narrower channel spacing. But she says this probably won't happen until 40-Gbit/s takes off, which won't occur for some months yet.

SpectraSwitch is among the first liquid-crystal component makers to offer a reconfigurable switch of the type that can be used to selectively add, drop, or pass channels. Rival Chorum Technologies Inc., for instance, offers reconfigurable simple switches based on liquid-crystal technology, but no reconfigurable OADMs (optical add/drop multiplexers). Chorum says it will unveil a new product family geared to this segment at OFC.

Others also plan OFC unveilings. Corning Inc. (NYSE: GLW), which announced its liquid-crystal PurePath Spectral Equalizer at OFC a couple of years ago (see Corning Boosts PurePath Production), plans to show newer, smaller versions of that product at the show.

Corning's PurePath Spectral Equalizer isn't, strictly speaking, a switch. Instead, it is designed to optimize the use of amplifiers by varying the attenuation of light, in a "select and broadcast" approach. But spokespeople have long said that the technology used in the PurePath can be readily adapted to optical switching. It's not yet clear and hasn't been confirmed, however, whether this is what Corning will unveil at OFC.

So far, liquid crystal appears to be making inroads in reconfigurable optical switches. Makers of MEMS switches haven't provided similar parts yet, although they're working on it. JDS Uniphase Inc. (Nasdaq: JDSU; Toronto: JDU), for example, plans to show configurable optical switch components at OFC, based in part on the technology it announced last week (see JDSU: MEMS Aren't Just Memories).

— Mary Jander, Senior Editor, Light Reading
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saradrumond 12/5/2012 | 1:59:56 AM
re: Optical Switching Gets Flexible Good afternoon,
I am designing an optical cross connect in witch I am going to use for the space switch a non blocking CLOS optical switch.
I need to know how to calculate the attenuation caused by the CLOS switch. I think it should depend on Lse (loss per switch element), Lfs (fiber-switch loss) and N (number of entries)GǪ Considering that there are a maximum of 4N ( (sqr(2N)) - 1) switch elements in a Clos Switch.

Cloud you please help me?

Thank you,

Sara Silva

dljvjbsl 12/5/2012 | 1:59:54 AM
re: Optical Switching Gets Flexible How many layers are there in the Clos network that you are designing 1,3,5 7 ... ? The loss will come from that.

saradrumond 12/5/2012 | 1:59:22 AM
re: Optical Switching Gets Flexible The Clos switch I am thinking of has three layers.

Thank you,

dljvjbsl 12/5/2012 | 1:59:21 AM
re: Optical Switching Gets Flexible How many contacts in each layer and how much loss at each?
saradrumond 12/5/2012 | 1:59:20 AM
re: Optical Switching Gets Flexible The Clos switch I am thinking of has N inputs and N outputs.

The first layer is made by N/n switches, each a nxk switch.
The second layer is made by k switches, each a N/n x N/n switch.
The third layer is made by N/n switches, each a kxn switch.

Where k=2n-1.

This leads to a maximum of 4N( (sqr(2N) -1) switch elements in the Clos switch.

The loss in the switchGǪ I want to represent them by Lse (loss per switch element) and Lfs (loss fiber-switch)


kokoro 12/5/2012 | 12:31:35 AM
re: Optical Switching Gets Flexible Let's come back to the basic technological question that one could have reading the article...

...Is Lyquid Crystal technology suitable for optical switching, both simple (the bare switch) and complex (optical switch fabric)???

Is it really ready for TODAY's networkns and applications?

What main advantages does it offer over competing technologies?

Any insight?

flanker 12/4/2012 | 10:51:35 PM
re: Optical Switching Gets Flexible So far, liquid crystal appears to be making in roads in reconfigurable optical switches

Where? This technology has about as much future as TDMA in wireless applications.

^Eagle^ 12/4/2012 | 10:51:26 PM
re: Optical Switching Gets Flexible Small correction here. Chorum has been making and shipping various versions of reconfigurable Liquid Crystal devices to vendors for some time. These include simple devices like their very fine control DVA (Digital VOA), 1x2, 2x2 switches, their SmartSwitch (a 2x2 recofigurable switch with built in load balancing, power leveling, of each port independently or a variable bidirectional splitter...), they built the first 4x4 and 8x8 LC based switches for the MONET project, and demonstrated the 1st Liquid Crystal based Dynamic Gain Flatten Filter (tunable multistage fine grained fast and very flat....less that 0.5db variation....leveling the entire Erbium amp output in several milliseconds across the C or L band). Chorum demonstrated this LC based DGFF several months before anyone else.....first showed it at Go by the Chorum booth at OFC or go to their web site. I don't know if Chorum is shipping it or has volume on it...as Chorum keeps pretty tight lipped about their customers...all we know is that they have over 12 major design wins and only a couple are the already announced long haul platforms.

Not knocking Corning or Spectra....just know Chorum is far into real high volume multimillion dollor revenue on LC based products. I am sure Chorum has shipped far more different kinds of modules for sampling based on LC than ANY other vendor in the market and has far more experience in this technology than Spectra or Corning....and they have been generating significant revenue from shipping LC product for quite a while.
Chorum should not be left out of any serious discussion on reconfigurable products based on LC.

Unfortunately, I, like everyone else, don't know who Chorum is shipping to or what the mix of passives vs reconfigurable LC stuff they are shipping .

Maybe LR could get Chorum to show us a bit more.....
hyperunner 12/4/2012 | 10:51:21 PM
re: Optical Switching Gets Flexible Hmmm, I dunno.

I'd agree that LC is limited to ring OADMs, but that's an important market right now.

I've got a bad feeling about using a technology like MEMS, that has moving parts, in the core of a carrier network.

I know folks like Lucent and Nortel (who makes Nortel's 3D MEMS?) say they've waggled those mirrors a gazillion times to see if there's a problem, but the bottom line is that if a solid-state alternative to MEMS for big OXCs were to come along, I suspect the carriers would prefer it.

And 3D MEMS in particular seems to have an issue with the volume of control code for those analogue mirror positions. I heard that Lucent were admitting to a million lines of control code for their 256x256 array in the Lambdarouter, and 256 ports isn't that big. Imagine how much code is needed for a 1000x1000 array!!

Looking at other packages that have a million lines of code, like IOS and Windows, I'm not sure I'd want to take a risk with a network that was supposed to be reliable.

Looking at this pragmatically, there's no alternative today to 3D MEMS if you want to build a big, all-optical OXC. But in the current market conditions, who needs a big, all-optical OXC? In fact looking at Corvis's numbers, who needs a small all-optical OXC?

I'm sure that the future network core will be all-optical, with OEO on the edge for grooming, but by the time this network architecture appears I'd hope that some genius somewhere will have thought of a real carrier-grade alternative to MEMS.

gardner 12/4/2012 | 10:51:18 PM
re: Optical Switching Gets Flexible
And 3D MEMS in particular seems to have an issue with the volume of control code for those analogue mirror positions. I heard that Lucent were admitting to a million lines of control code for their 256x256 array in the Lambdarouter, and 256 ports isn't that big. Imagine how much code is needed for a 1000x1000 array!!

Do you really think it scales that way? What do you think they do? Cut and paste pieces of code around for each mirror? Sheesh!
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