Broadband Communities

MAR-APR 2014

BROADBAND COMMUNITIES is the leading source of information on digital and broadband technologies for buildings and communities. Our editorial aims to accelerate the deployment of Fiber-To-The-Home and Fiber-To-The-Premises.

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88 | BROADBAND COMMUNITIES | www.broadbandcommunities.com | MARCH/APRIL 2014 FIBER TESTING initially connected to the source with a short jumper cable, and the source power level is measured and stored as the 0 dB reference level for that wavelength. As the source's output power levels and the power meter's detector response are diferent at each wavelength, the power meter must be referenced to the source at each test wavelength. Once the source and power meter have been referenced at each test wavelength, the source – with the reference jumper still attached – is connected to one end of the fber under test. Te power meter is connected to the other end of the fber under test. Received power level is measured and displayed, and the power meter can compare the received power level to the stored reference, directly displaying optical loss in dB. Simple power meters measure power at only one wavelength at a time. To make loss measurements at multiple wavelengths, the source must be confgured for each test wavelength in turn. At the same time, the power meter operator must select the appropriate wavelength at the power meter so the correct detector calibration factor and reference level are applied. Tis is both time consuming and error prone, as it requires coordination between the source operator on one end and the power meter user at the other end of the fber-under test. To reduce test time and eliminate this potential for errors, AFL's FLX380 FlexTester includes Wave ID. A Wave ID source transmits light at each wavelength alternately. A Wave ID power meter automatically synchronizes to the received wavelengths, eliminating the need to manually switch the source and power meter between wavelengths (see Fig. 2). OUT-OF-SERVICE OTDR TESTS OTDR testing is typically completed as the FTTx PON is being deployed. Te feeder fbers connecting the central ofce to fber distribution hubs are typically the longest links in the PON, are usually the frst fbers installed and may include multiple splices. Tese may be tested as point-to-point links before the splitter is installed at the fber distribution hub. If a splitter is spliced to the feeder fber before testing, the loss through each of the splitter legs may be verifed. However, this requires testing from each of the multiple splitter outputs and requires a launch fber (1,000 meters recommended) to allow the splitter loss to be clearly seen and measured. Splitter losses through each leg cannot be easily verifed by testing from the central ofce end of the feeder fber. Distribution fbers are typically tested, using an OTDR, after installation and connection to the splitter. Once attached to the splitter, these fbers may be tested only from the downstream access point or subscriber premises (if the drop fber is also installed and connected). High- resolution traces of the distribution and drop fbers may be obtained using narrow pulses, but the OTDR may not be able to measure the splitter loss using narrow pulses. Wider pulses improve the OTDR's dynamic range, enabling it to more accurately measure the loss of the attached splitter. OTDR testing during FTTx PON installation testing is usually performed only at 1310 and 1550 nm. During operation, the FTTx PON always utilizes 1490 nm in the downstream direction and 1310 nm in the upstream direction. It may additionally utilize 1550 nm as a second downstream wavelength. Optical loss is highest at 1310 nm and lowest at 1550 nm, and bending-induced loss is highest at 1550 nm. If end-to-end loss is within acceptable limits at both 1310 and 1550 nm, it is nearly certain to be acceptable at 1490 nm. If no excess losses or refections are found at 1310 or 1550, none are likely to be found at 1490 nm. Even if the PON will initially be operated using only 1490 and 1310, testing at 1310 and 1550 nm can detect any micro- or macrobends and ensures that the FTTx PON is capable of adding 1550 nm operation in the future. v Michael Scholten is senior product marketing manager at AFL, one of the world's leading manufacturers of fber optic cable. Te company's product portfolio includes fber optic cable, transmission and substation accessories, outside-plant equipment, connectors, fusion splicers, test equipment and training. Its service portfolio includes market-leading positions with the foremost communications companies supporting inside plant central ofce, EF&I;, outside plant, enterprise and wireless areas. www.AFLglobal.com Fig. 2: Store reference and measure loss using Source and Power Meter with Wave ID. BBC_Mar14.indd 88 3/14/14 3:22 PM

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