363-206-295
Technical Specifications
10-16 Issue 1 December 1997
¶ Optical path penalty includes effects of dispersion, reflection and jitter that occur on the
optical path. The 23G/23G-U has 5.0 dB of total margin. Optical path penalty is normally
1.0 dB. This allows for a maximum dispersion of 92 psec/nm in the 1310 nm wavelength
range. To allow for span lengths greater than 40 km, 2.0 dB is allocated for optical path
penalty. This allows a maximum dispersion of 120 ps/nm. 1.0 dB is allocated for the
optical path penalty for the 23H/23H-U for operation in the 1550 nm wavelength range.
This allows a maximum dispersion of 1800 ps/nm.
** One connector (0.75 dB) on each end is assumed to connect station cable to outside
plant.
†† Unallocated margin, or safety margin, is typically specified from 0 dB to 3 dB.
‡‡ The 23G/23G-U requires an external lightguide buildout as part of the connector
assembly for loopbacks and for loss budgets less than 10 dB. The 23H/23H-U requires
an external lightguide buildout as part of the connector assembly for loopbacks and for
loss budgets less than 19 (23H) or 10 (23H-U) dB.
§§ Budget available for both station and transmission cable and splices.
¶¶ Attenuation and dispersion can be the limiting factors in span length. For OC-12
systems, the maximum distance could be either attenuation limited or dispersion limited.
The limits must be calculated based on both factors and the lesser of the two defines the
actual maximum span length. A rough rule of thumb for attenuation-limited systems
operating in the 1310 nm wavelength range is 0.45 dB/km. This estimate includes typical
cable loss (0.4 dB/km) and splice loss (0.2 dB per splice, 11 total splices) associated
with single-mode fiber in the 1310 nm range. A rough rule of thumb for systems
operating in the 1550 nm wavelength range on modern nondispersion shifted fiber is
0.25 dB/Km.
Allowing 2.0 dB for the optical path penalty implies 120 ps/nm total dispersion in the
1310 nm wavelength range. Typical maximum slope for single-mode fiber in this
wavelength is 0.092 ps/nm squared per km. Typical nondispersion shifted fiber has a
zero dispersion wavelength between 1300 and 1320 nm. Given these assumptions, the
maximum span length for the 23G/23G-U is 51km.
For OC-12 systems operating in the 1550 nm wavelength range, the maximum distance
is dispersion limited. Allowing 1 dB for the optical path penalty implies 1800 ps/nm total
dispersion. Typical modern nondispersion shifted fiber has 18 ps/(nm•km) dispersion in
the 1550 nm wavelength range. Given these assumptions, the maximum span length for
the 23H/23H-U is 100 km.
Maximum span length can be calculated more precisely based on particular fiber and
splice characteristics and local engineering rules.
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