4.2 Choice and substantiation of the type of optical fibers
Typical characteristics of standard single-mode optical fibers (OF) and with the shifted and flattened dispersion according to [4, 5] are shown in the table. 4.2. We choose the type of OF depending on the number of ПЦП, the data transfer speed, distance between endpoints and human settlements along the route of the fiber-optic line, as well as the principles of construction of a network connection, the task of which the transmission line solves. In the majority of cases the step-multimode optic fibers are used. At high speeds of the information transmission, when the length of the elementary cable section (ECS) is limited by dispersion, dispersion-shifted fibers are used. If this equipment is used in wavelength division multiplexing (DWDM), it is possible to use fibers with flattened dispersion.
Table 4.2 - Characteristics of optical fiber
Type of fiber |
Attenuation
|
Wavelength
of the zero-dispersion
|
The slope of the dispersion curve S0, ps / (nm2 • km) |
Chromatic
dispersion coefficient
|
||
1,31 mkm |
1,55 mkm |
|||||
1,31 mkm |
1,55 mkm |
|||||
Stepped |
0,4 |
0,35 |
1,301 |
0,092 |
3,5 |
18 |
With shifted dispersion |
– |
0,35 |
1,550 |
0,085 |
– |
1 – 10 |
With flattened dispersion |
0,34 |
0,22 |
– |
– |
|
|
,
dB / km, at the wavelength
,
mkm
,
ps / (nm km)
3,5
4.3 Choice and substantiation of the optical cable
Choice of the construction of optical cable is determined by the number of OF, the conditions and the planned method of laying and operation of the cable. The most common modular cables, their cells includes several optical modules(with two, four, or up to 12 OF), spirally arranged around a central power element(fiberglass rod (Fig. 4.2, a)), steel wire or cable in a plastic cover. Recently, however, more and more widely used are cables, cells of which are a single optical module with a thick-walled plastic tube (Fig. 4.2, b). Type of external coatings [6, 7], is selected according to the table. 4.3. Permissible pulling stress for all types of OC is usually 1000 N / cm. The minimum bend radius must be less than 20d, where d - diameter of the cable. Construction length of optical cable is on average (2 - 6 km), but not less than 1 km. In the city, as a rule, OC with construction length (1 - 2 km) are used.
After selecting the type of covering [7], specify the type of optical cable according to the instructions (see Table 4.4). It should be mentioned that, in general, the methods of marking of OC on different manufacturers are different. One typical method of marking of optical cables, such as ПАТ «Завод«Південкабель», is shown in Table. 4.4.
Table 4.3 - Types of coatings
№
|
Laying conditions |
Installation method |
Permissible pulling stress, кН |
Armor coatings |
|
1 |
2 |
3 |
4 |
5 |
|
1. |
Directly in the sewerage |
spinning using blanks |
2,0 – 3,5
|
-without armor - corrugated steel - braid |
|
2. |
In the sewerage, in the auxiliary plastic pipes |
spinning using blanks |
2,0 – 3,5
|
the same
|
|
3. |
In the sewerage or in the soil in the tubes of the silicone coating |
spinning using blanks or using cable blowing jet |
2,0 – 3,5 |
the same
|
|
4. |
Directly into the soil of III-IV categories |
using cable stacker or into trench |
7 – 8
|
- round wire - steel tape |
|
5. |
Transitions of the navigable rivers, in swamps, rocky soil |
Depending on the conditions |
20 – 96
|
full metal jacket with armor of round wires |
|
6. |
On airlines |
Hanging on poles |
15 – 25 or more depending on the length of section and wind loading |
– fiberglass – synthetic yarn with high elasticity
|
|
Table 4.4 - Types of optic cables
1
|
||||||||||||||||||||||||||
1 |
2 |
3 |
4 |
|||||||||||||||||||||||
1 |
Type of cable |
O |
fiber optic |
|||||||||||||||||||||||
2 |
Protective layer
|
а |
with alumopolymer protective layer |
|||||||||||||||||||||||
Without designation |
without alumopolymer protective layer |
|||||||||||||||||||||||||
3 |
Type of armouring or the armouring elements
|
Ар |
layer of aramid threads |
|||||||||||||||||||||||
Би |
armour of two spirally laid steel galvanized tapes |
|||||||||||||||||||||||||
Бг
|
armour of longitudinally laid steel zetabon tape |
|||||||||||||||||||||||||
К
|
armour of one layer of circular steel galvanized wires |
|||||||||||||||||||||||||
2К
|
armour of two layers of circular steel galvanized wires |
|||||||||||||||||||||||||
Сп |
armour of fiberplastic rods |
|||||||||||||||||||||||||
Without designation |
without armour and the armouring elements
|
|||||||||||||||||||||||||
4 |
Outer sheath type
|
П |
polyethylene sheath |
|||||||||||||||||||||||
Пн
|
sheath of flame retardant polymer compound |
|||||||||||||||||||||||||
1 |
2 |
3 |
4 |
|
Outer sheath type
|
Пп
|
inner polyethylene sheath between the layers of the armouring of 2K type and the outer polyethylene sheath |
5 |
Central strength element type
|
З |
steel rope or steel wire with polyethylene coating |
Without designation |
dielectric central strength element (fiberplastic rod and etc.)
|
||
6 |
Temperature type making
|
ХЛ
|
From minus 60°С up to 60°С |
Without designation |
from minus 40°С up to 60°С |
||
7 |
Quantity of optical fibers in the cable |
||
8 |
Optical fiber type
|
E
|
single-mode as per the recommendations of ITU-T G.652B |
A
|
enhanced single mode optical fibre (ESMF) as per the recommendations of ITU-T G.652D |
||
C
|
non zero single mode shifted as per the recommendations of ITU-T G.655 |
||
M |
multimode with core and sheath ratio of 50/125 mkm as per the recommendations of ITU-T G.651 |
||
B |
multimode with with core and sheath ratio of 62,5/125 mkm as per the recommendations of IEC 60793-2 |
||
9 |
Number of elements in the core |
||
10 |
Optical fibers distribution in tubes |
||
11 |
Quantity of copper insulated wires in cable (without designation on their absence) |
||
12 |
Permissible pulling stress, kN |
||