December 23, 2008

Fiber Gets Real Character

By Jonathan Tombes

There's a fiber-optic star hanging over the industry at year's end. The task of characterizing this promising light requires not wisdom (or wise men) but technical competence and sharp instruments.

The promise of optical transport builds upon five years of international growth. While the Dell'Oro Group has said current levels will contract 10 percent in 2009, that installed base is poised to deliver for greater efficiencies the metro and long haul networks.

On the access side, the spike in investment has been more recent. Dell'Oro said that third-quarter 2008 shipments of passive optical networking (PON) equipment - an area that the cable end of the telco industry is exploring - reached record levels. (For more on PON and RFoG, see the related Tech Guide posted on www.cable360.net/ct.)

No hype, just rules

One sign that this category may have immunized itself against hype and shifted into an operations mode is the readiness with which industry players point to fiber's great, but not limitless, potential.

"The idea that you can do whatever with fiber is not true," said Gregory Lietard, product marketing manager for the North American fiber optic division of JDSU. "Fiber has some limitations, many related to dispersion."

Down-and-dirty attention to fiber's physical layer in 2008 seemed as strong as ever, even more than when non-zero dispersion shifted fiber showed up eight or nine years ago. Recall JDSU's telling acquisition 11 months ago of Westover Scientific, a company that designed and manufactured field and lab microscopes aimed at detecting various contaminants that cause faults in optical networks.

(For an article on Fiber Connector Cleanliness by Steve Lytle, former president of Westover, click here.)

Purchased for $50 million (incidentally, the same figure associated with Harmonic's planned acquisition, announced today, of Scopus), Westover Scientific became the Fiber, Inspect and Test (FIT) division of JDSU and the source of tools that begin what the company calls "fiber link characterization."

Lietard said that process includes the video inspection scope, connector inspection, the measurement of insertion loss and OTDR and optical return loss measurement. Then come the measurements, particularly for transport greater than 10 Gbps, of chromatic dispersion (CD) and the more intractable polarization mode dispersion (PMD).

These test functions follow ITU.G.650.3, which Lietard said called for "not only qualifying the fiber, but qualifying the entire link." Only then does it make sense to characterize the entire optical network and check whether the signal arrives at Point B from Point A "with the expected limits designed by the network equipment manufacturer."

A key word there is "limits." Optics can dazzle, but shouldn't blind.

- Jonathan Tombes

Read more news and analysis on Communications Technology's Web site at www.cable360.net/ct/news/.