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Why do most of the optical fibers test at 1310/1550nm?

Why do most of the optical fibers test at 1310/1550nm: This is the brilliant question for the telecom engineers.most of the engineers and technician uses this parameter 1310/1550nm but many technicians do not know why I am using this parameter or Why do most of the optical fibers test at 1310/1550nm. Today I will try to cover this topic in details.

Generally all technician uses the OTDR that supports 1310 and 1550 nm to confirm splice loss, fiber attenuation rates, discrete reflectance and fiber length.For DWDM testing (which usually also goes up to the 1600nm range), however, a three-lambda OTDR that performs
tests at 1310, 1550, and 1625nm is required.

OTDR testing of an Optical fiber
OTR Testing on an Optical Fiber

Why 1310/1550 transmission wavelength required for Optical fiber testing

For many years, the transmission wavelengths were only 850 nm, 1310 nm and 1550 nm. Cable manufacturers were designing their production so that the fibers had the best performance for those wavelengths. Even Insertion loss testing is typically performed with a power meter and a light source with both 1310 and 1550 nm wavelength outputs.

When the DWDM technology was introduced,multiple close wavelengths were transmitted at the same time. This has generated a development of new fibers, specifically targeted for those applications: the so-called ITU-T G.655 non-zero dispersion shifted fiber, or well known fibers such as Leaf fiber from Corning,TrueWave from Lucent, or Teralight from Alcatel.

They are optimized for best use in the 1550 nm window, mainly the C band (1530- 1565 nm). However, we are at the first stage of DWDM implementation, and new requirements are arising. Fiber specifications such as bend and loss (in dB/km) are at present only required at 1550 nm for the different fiber types by international standards.

The EIA/TIA-455-62A “Optical fiber macrobend attenuation” provides information about macro bending. However, manufacturers usually provide the- attenuation figures (in dB/km) at 1310 nm and 1550 nm, attenuation at the water peak (around 1385 nm), attenuation versus wavelength around 1310 nm and 1550 nm, and attenuation versus bending (fiber wrapped around a mandrel of a specified diameter) around 1310 nm and 1550 nm.

As the most important fiber parameters for network installation are still splice loss, link loss, ORL (optical return loss), it is necessary to get the associated test equipments. Those instruments are mainly loss test sets, which could provide 1310/1550 and 1625 nm loss testing in one unit, combined 1310/1550/1625 nm OTDRs (optical time domain reflectometers), and 1310/1550 and 1625nm ORL testers.

OTDRs are ideal tools to detect and locate the bends of a fiber link (the three traces at 1310, 1550 and 1625nm. Often this assumption remains that at the lower distance of 40KM, the measurement of an optical fiber can be do at 1310nm, and more than 40KM distance of optical fiber can be measure at 1550nm transmission wavelength.This is also true to hold but not everywhere.

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