Los Angeles (OFC / NFOEC), CA--Verizon, EXFO, and General Photonics have successfully measured polarization-mode dispersion (PMD) on a traffic-bearing long-haul network without impacting neighboring channels carrying live traffic. PMD is measured to determine system impairments for 40G and 100G signal transmissions.
The new new PMD measurement methods can be used to accurately measure the PMD of a traffic-carrying fiber route with active and passive components and mixed fiber sections, including erbium-doped fiber amplifiers (EDFAs), multiplexers, demultiplexers, reconfigurable optical add-drop multiplexers (ROADMs), and optical fibers.
In field trials performed on the Verizon network, two novel methods were used to measure PMD. One method used General Photonics' PMDPro PMD-1000 and SmartLight TCA-1000 devices and was based on light-path PMD compensation. The other method used EXFO prototype equipment that employed algorithms in the company's FTB-5700 dispersion analyzer and was based on statistical analysis of randomly polarized test signals. Both methods were performed on idle channels of a traffic-bearing long-haul network.
No adverse impact
When compared with the expected PMD value of the route, measurements showed a high level of accuracy with no adverse impact on the working channels, demonstrating that both methods are suitable for measuring PMD on traffic-bearing systems.
Details of the field trial were provided during OFC/NFOEC 2011 at the Los Angeles Convention Center in session NWC4 by T.J. Xia of Verizon.
"Advancing technology in PMD measurement--a key component of fiber quality--is an important step toward improving network performance," said Glenn Wellbrock, director of optical transport network architecture for Verizon.
Previously, traditional PMD measurement had only been performed on dark-fiber spans without any equipment and no way to collect PMD information after the fiber was put into service.
"The light-path PMD compensation method is simple, fast and only requires an optical source with a bandwidth contained in a DWDM channel of 50 GHz spacing," said Steve Yao, founder and CEO of General Photonics. "There is absolutely no impact to the live long-haul and ultra-long-haul traffic of the service provider. Only a few seconds are required to make a measurement. Either a channelized ASE source with a bandwidth around 0.2 nm or a 40G signal of any modulation format can be used as the signal source for the PMD monitoring."
"We are delighted to demonstrate that our measurement method, previously only applied to medium distance OTDR-based PMD measurements in a completely different context, can be used through tightly-filtered light paths to characterize link PMD over long-haul distances, thereby opening the door to practical PMD characterization of in-service networks," noted Gregory W. Schinn, director of research and intellectual property at EXFO.
