Note: The transmission distances listed in the table are only for reference. The actual transmission distance may be slightly different as a result of the joint influence of factors such as fiber quality of the engineering optical cable, number of the welding points, welding loss, connector loss, and so on.
The optical transmission distance is affected by the attenuation and the dispersion of the fiber. For G.652 fiber, since the 1310 nm region is zero-dispersion window (its dispersion coefficient is less than 3.5 ps/nm.km), generally only the attenuation factor is required to be considered. But for 1550 nm window, since the dispersion coefficient is 18 ps/nm.km, both the attenuation and the dispersion are required to be considered. The smaller one of the attenuation-limited distance and the dispersion-limited distance shall be used as the available transmission distance
The optical transmission distance is affected by the attenuation and the dispersion of the fiber. For G.652 fiber, since the 1310 nm region is zero-dispersion window (its dispersion coefficient is less than 3.5 ps/nm.km), generally only the attenuation factor is required to be considered. But for 1550 nm window, since the dispersion coefficient is 18 ps/nm.km, both the attenuation and the dispersion are required to be considered. The smaller one of the attenuation-limited distance and the dispersion-limited distance shall be used as available transmission distance.
The attenuation-restricted distance can be worked out by the formula below:
(See the attached formula 5-1.)
Generally, the engineering margin is 5–8dB. As for the optical fiber attenuation per kilometer, in 1310 nm window is 0.4 dB/km, and in 1550 nm window is 0.25 dB/km.
The dispersion-restricted distance can be worked out by the formula below:
(See the attached formula 5-2.)
According to ITU-T Recommendation G.957, the maximum optical transmitting source dispersion can be calculated by the following formula:
(See the attached formula 5-3.)
For the single longitudinal mode laser, value for e is 0.306, which is equivalent to 1dB optical path penalty; for L-16.2, value for e is 0.491, which is equivalent to 2dB optical path penalty; for the multi-longitudinal mode laser, value for e is 0.115.The root-mean-square spectral width is 1/6.07 of the -20dB spectral width
All the above STM-16/4/1 optical interfaces are standard ones as stipulated in ITU-T Recommendation G.957 and G.691.They can get longer transmission distances with help of optical fiber amplifiers.
The STM-64 optical interface is a G.691-compliant standard optical interface, its REG distance is calculated with the worst-case design approach stipulated in ITU-T Recommendation G.957. The formula is as follows:
L= (PSEL-PREL-PP-C-MC)/ (af+as)
Where,
L: RS distance
PSEL: Minimum mean launched power when the service life of point S terminates
PREL: Worst sensitivity (BER ≤ 1 x 10-12) when the serving life of point R terminates
PP: Optical path penalty
C: Connector losses, 0.5 db for each connector, C is 2 x 0.5 = 1.0db
MC: Optical cable margin, 3 dB
af: Optical fiber attenuation coefficient
as: Average splicing loss per kilometer
Its dispersion-restricted distance is calculated as follows:
S-64.2b
L = 800/20 = 40 km
L-64.2b
L = 1600/20 = 80 km
V-64.2a
L = (1600+1000)/20=130 km
Dispersion of G.655 fiber
There exists serious dispersion limit when STM-64 optical signal transmitting on G.652 fiber. For G.655 fiber, its dispersion coefficient is about 1.0×6.0 ps/nm.km in 1550 nm wavelength window, and its attenuation coefficient is less than 0.25 dB/km.
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