The AFCS Forum has recently published papers on the use of AFM in conducting maintenance and troubleshooting operations in fiber facilities.

Remote Fiber Testing & Monitoring

Fiber network operators utilize remote fiber test systems (RFTS) to provide a variety of critical functions:

• Rapid fault detection, isolation, and location, thereby enabling immediate response  
• Remote qualification of fiber route prior to provisioning
• Baseline documentation of fiber route characteristics for subsequent troubleshooting
• Early detection of signal degradation

The centerpiece of the RFTS system is the optical time domain reflectometer (OTDR), which measures optical performance in fiber over a range of 80 to 140 kms. An OTDR works by injecting a series of pulses into the fiber and measuring reflection as a function of time. The reflected light characteristics are analyzed to determine the location of faults, such as fiber breaks, and attenuation, including splice losses

Shortcomings of Legacy RFTS Systems

Today’s RFTS systems suffer from several shortcomings, stemming from their dependence on manual fiber connectivity. First, a number of expensive components are required to make the OTDR available to the fiber infrastructure:

• 1:N switch: Switches an OTDR port to one of N fibers, typically 12 to 48   
• WDM coupler: Connects the OTDR signals to lit fibers being tested
• ODF or Patch Panel or ports: Connect the WDM coupler and/or switch to the fiber network 
• Patch Cords: Connect the OTDR to the switch, the switch to the WDM, and the WDM to the ODF  

Due to the high cost of WDM couplers and 1:N switches, today’s RFTS typically cover at most 10% of the fiber infrastructure. This is generally sufficient to detect and locate fiber breaks, which usually result from a cable cut impacting a large number of fibers. However, such low coverage limits the utility of RFTS in identifying single-fiber cuts and in performing other valuable functions such as periodic monitoring and line qualification.

AFM-Test

The integration of testing equipment with FiberZone AFM enables remote, automated management capabilities over the entire fiber infrastructure. AFM-Test integration allows test equipment to be very cost-effectively shared across the fiber infrastructure. 

AFM-RFTS
An automated RFTS system is established by connecting the OTDR optical port to one of the ports of the AFM. Each fiber connected to the AFM can be switched to a test position, availing the full functionality of the OTDR to 100% of the fiber. The OTDR is controlled remotely via the AFM system, minimizing the need for local control equipment and staff. AFM-RFTS thereby provides RFTS capabilities to the entire fiber infrastructure, enabling fault detection and location of each individual fiber, without the need to dispatch technicians.

The combination of AFM-RFTS with Optical Signal Monitoring (OSM, available in a variety of network equipment) provides even more cost-effective troubleshooting. OSM enables the early detection of signal degradation. Each port’s optical power is continuously observed and compared with baseline measurements. When this comparison indicates signal impairment, the network manager can issue a command to the AFM to switch live traffic to a different route. Then, the AFM-RFTS module switches the OTDR to the affected port to locate the problem. The OTDR is only needed when OSM indicates a problem, eliminating the need for costly 1:N switches or WDM couplers to provide access to the OTDR

AFM-OPT
Optical Path Test (OPT) is used to qualify point-to-point connectivity of dark fiber, prior to provisioning. A calibrated signal is transmitted, and actual insertion loss measured across the path. 

The AFM-OPT module extends this capability across multiple locations, over any path connected to an AFM system. AFM-OPT saves truck rolls and hours of labor when qualifying a path across multiple links. In addition, by making OPT available to 100% of the fibers, the provisioning of low performance routes is eliminated. 

Network-Wide AFM-Test
The network wide deployment of AFM-Test systems across multiple locations minimizes capital equipment costs, by enabling expensive test equipment to be shared, and significantly reduces operating expenses, by eliminating truck rolls.

With network-wide AFM-RFTS, a small number of long-range OTDRs can cover a very wide area. Paths through multiple AFM systems can be quickly established from a central control station, enabling the OTDR to test remote fibers all along the path. Given the low insertion loss of FiberZone AFM, a single OTDR can cover an entire metropolitan area, to a radius of about 140 km.