Symptom
In the process of commissioning 40G and 10G WDM systems, fiber parameters, especially the attenuation coefficient, fiber loss, and PMD, need be measured. Another parameter, zero dispersion slope, can be used to distinguish between G.653 fibers and G.655 fibers. Therefore, this parameter must be measured.
Cause analysis
It is important to distinguish between G.655 fibers and G.653 fibers, because these two types of fibers require different input optical power. G.653 fibers has strict limitations on input optical power. If the input optical power is beyond the specified range, non-linear effects will be obvious, bit error ratio (BER) will be high, OSNR will be low, and even services will be interrupted.
Specifications of G.655 fibers and G.653 fibers are as follows:
- G.653 fibers are also named dispersion shift fibers (DSFs). The following
are typical parameters of G.653 fibers in the 1550 nm region:
1310 nm band: attenuation coefficient < 0.55 dB/km
1550 nm band: attenuation coefficient < 0.35 dB/km (generally ranges from 0.19 dB/km to 0.25 dB/km)
The zero dispersion point is in the region between 1525 nm to 1575 nm, and the dispersion coefficient in this region is less than 3.5 ps/(nm/km). G.653 fibers have optimal features in the 1550 nm region and therefore are preferred for single-wavelength and ultra long-haul transmission.
- G.655 fibers are also named non-zero dispersion shift fibers (NZDSFs). The
zero dispersion point is moved several wavelengths away from 1550 nm so that the
zero dispersion point is not in the operating wavelength region close to 1550
nm. The following are typical parameters of G.655 fibers:
1310 nm band: attenuation coefficient < 0.55 dB/km
1550 nm band: attenuation coefficient < 0.35 dB/km (generally ranges from 0.19 dB/km to 0.25 dB/km)
The dispersion coefficient absolute value of G.655 fibers for this region is from 1.0 ps/(nm/km) to 10.0 ps/(nm/km).
According to the specifications of the two types of fibers, the attenuation coefficient and fiber loss of G.653 fibers are similar to those of G.655 fibers. Actually, the value ranges of the attenuation coefficient and fiber loss of G.653 fibers overlap with those of G.655 fibers. Actual fiber specifications are determined by manufacturers. The PMD value depends on fiber quality. As a result, users cannot distinguish between G.653 and G.655 fibers using only the preceding parameters.
In this case, another parameter, maximum zero dispersion slope, can be used to distinguish between G.653 and G.655 fibers. This parameter is essential to distinguishing fiber types. Each type of fiber has only a typical zero dispersion slope and the value is not fixed. The value changes slightly and varies according to fibers. Zero dispersion slopes of G.653 and G.655 fibers are as follows:
- G.653 fibers: 0.07600 ps/(nm2·km)
- G.655-LEAF fibers: 0.08365 ps/(nm2·km)
- G.655-TWRS fibers: 0.04780 ps/(nm2·km)
Therefore, you can distinguish between G.653 and G.655 fibers by measuring zero dispersion slopes of them.
