FTTx/PON Construction
At this stage, one of the most critical aspects is the qualification of the fiber links, which will ensure that the network is ready for actual traffic and that it will provide subscribers with the service quality they expect. Proper testing is the only way to guarantee that all the required transmission specifications are met by the new fiber network.
| TEST EQUIPMENT | |||||
| TEST TYPE | Power Meter | Light Source | Return Loss Meter |
Automated OLTS Loss Testing |
OTDR |
| Total Optical Loss |  |
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| Backreflection (ORL) | |
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| Link Characterization | |
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Power and Loss Measurement (or Optical Loss Budget)
Why Test Loss?
Insertion loss is measured during the construction phase to ensure that the link complies with the engineering loss specification (also known as loss budget). The loss budget will take into account the system tolerances, so it is crucial to meet this specification to ensure error-free transmission.
| Test Method | Description | Proposed Equipment |
| Loss Testing | The basic tools to measure optical loss are a power meter and a light source, positioned at separate ends of the fiber link under test | FPM-300 Power Meter with FLS-300 Light Source FOT-300 Power Meter with FLS-300 Light Source FOT-600 Optical Loss Test Set |
| Automated Loss and ORL Testing |
Bidirectional, automated optical loss test sets (OLTSs) are used in pairs and contain both a power meter and light source. They provide fully automated bidirectional loss and ORL test results in 10 seconds for up to three wavelengths, as well as a fiber-length measurement. Using an automated OLTS greatly reduces testing time and risk of human error. | FOT-930 Maxtester Optical Loss Test Set FTB-200 Compact Platform/mini-OTDR combo with FTB-3930 MultiTest Module (OLTS) |
| OTDR Testing | OTDRs are used to perform complete link characterization, including loss measurements. The OTDR has the ability to measure and locate connections, splices and splitter points within a network. | FTB-200 Compact Platform/mini-OTDR combo with FTB-7000 OTDR module AXS-100 Access OTDR (handheld mini-OTDR) |
Automated point-to-multipoint testing: Using the FTB-200 or FTB-400 platform equipped with an FTB-3930 MultiTest Module and an FOT-930 MaxTester, a single operator can achieve bidirectional insertion loss (IL) and optical return loss (ORL) testing. The platform with the MultiTest Module is left at the CO and connected to the feeder fiber (F1) at the OLT location. Using an FOT-930 MaxTester, the user will then initiate the automated FasTesT function, which will automatically perform the following operations at the touch of a button:
» Determine bidirectional insertion loss
» Calculate bidirectional ORL
» Measure the fiber length
» Increment the fiber number
» Save the file in the master and/or remote unit (configurable)
Fig 1. Point-to-multipoint automated optical loss testing
Optical Return Loss (ORL) Measurement
Optical return loss (ORL, or backreflection) is caused by the amount of energy reflected back and lost within components and fiber. ORL is a key parameter, as it can significantly affect the transmitter’s performance and, in turn, the service quality delivered to customers. Excessive ORL can result in:
* Increased bit error rate
* Distortion of IPTV signals
* Distortion of analog video signals
* Permanent damage to laser transmitters and connection points
| Test Method | Description | Proposed Equipment |
| ORL Testing | ORL measurement can be performed by using a backreflection tester, or with an OLTS including a backreflection measurement option. | BRT-320 ORL Tester FOT-930 MaxTester Automated Optical Loss Test Set |
| OTDR Testing | An OTDR will provide a measurement of Fresnel reflections as well as the fibers Rayleigh backscattering. The OTDR will then calculate the ORL value for the entire link or a specific section. | AXS-100 Access OTDR (handheld mini-OTDR) FTB-200 Compact Platform/mini-OTDR combo with FTB-7000 OTDR Module |
Fiber Link Characterization
Total link characterization is a very important step in any fiber deployment, as it will provide a snapshot of the entire link including all its interconnection points, fusion splices and fiber sections. Proper link characterization will provide the user with the correct information when performing link commissioning and troubleshooting.
| Test Method | Description | Proposed Equipment |
| ORL Testing | OTDRs are used to perform complete link characterization. The OTDR has the ability to locate and characterize connections, splices and splitter points within a network. This unit allows technicians to test links end to end—including the splitter—to accurately locate and characterize faults. | AXS-100 Access OTDR (handheld mini-OTDR) FTB-200 Compact Platform/mini-OTDR combo with FTB-7000 OTDR Module |
Fig.2 Example of an OTDR test result on a PON with cascaded splitters
Even if these units have enough dynamic range to cover the splitter loss, standard OTDRs cannot test through splitters. The OTDR detector won’t be able to recover from the high loss induced by splitters fast enough to measure the fiber section attenuation and event loss.
Newer generations of OTDRs are designed to allow technicians to test through splitters by using relatively short pulses. Since splitter loss may reach up to 19 dB, the OTDR software is designed to accept high loss values and still mark the end of the fiber at the right location, while automatically detecting and locating any macrobends along the link.