Verizon, EXFO, and General Photonics measured polarization mode dispersion (PMD) on a traffic-bearing, long-haul network without impacting neighboring channels carrying live traffic. In field trials performed on the Verizon network, two methods were used to measure PMD, which is measured to determine system impairments for 40G and 100G signal transmissions.
One method used General Photonics' PMDPro PMD-1000 and SmartLight TCA-1000 solutions 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. 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 both methods are suitable for measuring PMD on traffic-bearing systems.
"Advancing technology in PMD measurement--a key component of fiber quality--is an important step toward improving network performance," says Glenn Wellbrock, director of optical transport network architecture for Verizon. "Successfully proving we can measure PMD of an end-to-end light path in a meshed network such as Verizon's, with no impact on the performance of live channels is a significant advancement in measurement technology."
Traditional PMD measurement has previously only been performed on dark fiber spans without any equipment and no way to collect PMD information after the fiber is put into service. In contrast, these two new PMD measurement methods can be used to measure the PMD of a traffic-carrying fiber route with active and passive components and mixed fiber sections, including EDFAs, multiplexers, demultiplexers, ROADMs, and optical fibers.
"The light-path PMD compensation method is simple, fast, and only requires an optical source with a bandwidth contained in a DWDM channel of 50GHz spacing," says 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,” says Gregory W. Schinn, director of research and intellectual property at EXFO.