Xtellus (Morris Plains, NJ) recently introduced its Wavelength Blocker (WB) 7000, a micro wavelength blocker that the company says is optimized for deployment in cable multiservice-operator and metro optical networks. “The application space is for reconfigurable OADMs [ROADMs], which I think after several years of hype are now sort of becoming table stakes for just about every system provider out there,” says Xtellus business development vice president Jonathan Homa.
Measuring 133×75×15 mm and supporting up to 64 channels, the WB 7000 is designed to drive large-scale deployments of DWDM networks. Employing a proprietary liquid-crystal optical processor, the device is engineered for an operational lifetime exceeding 25 years and provides the low insertion loss and high extinction ratio required for metro deployments, according to the company.
“For ROADMs, what people really want…[is] the ability to drop, add, and pass through traffic in the optical domain, without human intervention…without any electronic conversion” says Homa. “And then, because you have this through traffic that’s being managed in the optical domain, to be able to equalize that traffic to increase transmission performance.”
Michael Howard, principal analyst and co-founder of Infonetics Research, says, “The basic classification of the equipment is that there’s wavelength-selective switches [WSSs], [which] pretty much are defined as multidegree ROADMs, used at a point in the network where you need four or more degrees-that is, interconnecting rings. So the WSS, then, is not what you would use typically for a basic OADM, a single node on a WDM ring, [where] you want to add and drop single wavelengths. The two principal technologies where you don’t need multidegree [ROADMs] are…broadcast-and-select and select designs. And [the] two basic solutions for [such designs] are the PLC [planar lightwave circuit] or the wavelength blocker.”
So what’s the fundamental difference between PLC and wavelength-blocker technologies? “It’s really performance,” says Homa. “Planar-lightwave-circuit technology is sort of limited…it’s like integrated-circuit technology, so you have some fundamental physical limitations in terms of the performance. When you compare [the technologies] side by side, if you take a look at fundamental parameters such as insertion loss, such as PDL, such as passband-passband probably more than anything-PLC really does not match up to the free-space optics that are associated with the wavelength-blocker technologies.”
Counters Howard, “The PLC technology, the companies that have developed it, see it as a more stable, more easily manufactured technology. It’s kind of like the integrated circuit, on a photonic level, so that once they design it, they can stamp them out in a factory fairly easily. Now, if you listen to the wavelength-blocker guys, they’re saying that because their technology is a little less complicated, that you actually pay a premium for the PLC today. In the long run, it seems like something that’s manufacturable, like PLC, might win out, but…function, reliability, and cost are what it always comes down to, so if wavelength-blocker technology is just as reliable as the PLC and costs a little bit less, but has the same function, then some people are going to keep buying the wavelength blocker.”
Based on Xtellus’s compact platform technology, the WB 7000 complements the company’s WB 9000, which is designed for use in regional and long-haul networks. “As we’re starting to see a push now toward fiber to the home to support triple play services, [carriers] are now looking to build-out their metro networks,” observes Homa. “They’re saying, the [WB 9000] has a tried-and-true architecture; it has proven its worth in long-haul networks…there’s just one additional requirement that we need for the metro environment: Make it cheaper! That’s what motivated our development for the WB 7000.”
The company says the WB 7000 can selectively and dynamically pass, equalize, or block “any or all” wavelengths on a DWDM fiber, while incorporating metro-optimized features, including C- or L-band operation at 100- or 200-GHz spacing, <5-dB insertion loss, >40-dB extinction ratio, dynamic equalization up to 15 dB, wide flattop passband functionality (with continuous passband for concatenated channels), and a serial interface. “For a 30% premium you can use a wavelength-blocker ROADM over a fixed OADM solution,” adds Homa, “and have the hooks to upgrade to a multidegree node in the future, should that application become feasible.”