6.3 Power Balance and Dispersion
This section is addressed to giving an explanation on how the number of amplifiers has
been chosen, and which fiber has been deployed at each link and why.
The maximum distance available for each link is determined by two main factors:
attenuation and dispersion.
6.3.1 Dispersion
It is important to keep in mind that dispersion is the most negative effect, because
compensating it is more expensive than deploying fiber with a better dispersion
coefficient.
To calculate the dispersion of our links, we are based on recommendation G.957. This
recommendation indicates the maximum value of dispersion for a link. The maximum
value varies depends on the STM used as shown in the table below:
Fig…..Dispersion values for STM cards
Type of STM card
Maximum dispersion (ps/nm)
STM 1
1600
STM 4
1600
STM 16
1600
For the calculation of dispersion of a fiber we have used the following formula,
taking into accunt that the fiber that we has a Single-Mode behavior:
∆𝝉𝒊𝒏𝒕𝒓𝒂 = ∆ 𝒍𝒂𝒎𝒅𝒂 ∗ 𝑫𝒊𝒏𝒕𝒓𝒂 ∗ 𝑳
Where: ∆𝑙𝑎𝑚𝑑𝑎 = optical fiber bandwidth (nm)= 1 nm
𝐷𝑖𝑛𝑡𝑟𝑎 = dispersion coefficient (ps/nm*km)
L = fiber length (km)
The value of 𝐷𝑖𝑛𝑡𝑟𝑎 changes according to the fiber that we will use in each link. In our
case, we have chosen the followings types of Corning fabricant:
Fig… Dispersion values for chosen fiber
Type of fiber
Maximum Dispersion
(pm/nm km )
Corning SMF-28e+ Optical Fiber G.652
18
Corning LEAFTM G.655-Compliant (NZDS) Fiber
4,6
According with this we obtained the maximal distance allowed to transmit over the link,
without dispersion.
Maximal distance (Corning SMF-28e+ Optical Fiber G.652) = 88 km
Maximal distance (Corning LEAFTM G.655-Compliant (NZDS) Fiber) = 347 km
6.3.2 Technical characteristics of the equipment
All along a transmission link, characteristics of the equipment influence the power balance
of the link. In this part of the project we will analyze the attenuation introduced by the
equipment’s used in our network. Losses in signal quality are modeled by: optical fiber
losses, connectors, splices and losses due to multiplexers and de-multiplexers. The
general equation for obtaining the total link losses is:
𝑨(𝒅𝑩) = 𝜶 ∗ 𝑳 + 𝜶𝒔 ∗ 𝒙 + 𝜶𝒄 ∗ 𝒚
Where:
𝛼 is the attenuation factor through the distance [dB/km];
L is the link distance in km
𝛼𝑠 is the mean splice loss (dB)
x is the total number of splices for any given link
𝛼𝑐 is the mean loss due to the STM connectors, mux/de mux
connectors, amplifiers connectors
y is the total number of connectors
6.3.3 Fibers
Optical fiber typically consists of a transparent core surrounded by a transparent cladding
material with a lower index of refraction. Light is kept in the core by total internal reflection.
This causes the fiber to act as a waveguide. Fibers which support many propagation paths or
transverse modes are called multi-mode fibers (MMF), while those which can only support a
single mode are called single-mode fibers (SMF).
The single mode optical fibers have a diameter of the nucleus smaller than multimode
fibers, allowing a single way forward is (propagation mode and not oscillation mode) and
prevent the multimodal dispersion. Single mode fibers are also characterized by a lower
attenuation than multimode fiber, but the coupling of light becomes more complicated
and the tolerances of connectors and splices are stricter.
In contrast to the multimode fibers, single mode fibers allow to be up to great distances
and transmit higher bit rates, which are mainly limited by the chromatic dispersion and
non-linear effects. For all these reasons we have chosen to use single mode fibers in
onCAT network.
Fig… Type of Single Mode Fiber
Type of fiber
Maximum
Att.
Dispersion (pm/nm
(dB/km)
km )
No Channels
Att. Fusion
Fibers (dB/
5km)
Corning SMF-28e+
Optical Fiber G.652
0,2
18
16
0,02
Corning LEAFTM G.655Compliant (NZDS) Fiber
0,25
4,6
80
0,02
System fiber-mux/de-mux in coupled by connectors. Each system fiber + mux/demux is
composed by 6 connectors.
Fig…Connectors loss
Att Connectors (dB)
0,2
Losses associated to the connecters are known as Insertion Losses and they are usually
lower than 1 dB. Those losses define the power loss when coupling the fiber ends or in
other words, the power loss due to coupling mismatch and small differences in reflection
index.
6.3.4 Optical Amplifier
An optical amplifier is used in long fiber links to make useful the low power received signal.
This device decoder the received data, regenerates the digital pulses and overwrites the
regenerator section of the frame (RSOH). Finally, sends it again over the path to the next
node.
Fig …Type of amplifier
EDFA OA 4500
Amplifiers Series
Total input signal power
Total ouput signal power
Signal Gain
-30 to 2 dBm
21,5 dBm
19 to 32 dBm
Fig…Gain performance of EDFA OA 4500 Amplifiers Series
Gain
Maximum output
power = 21,5 dBm
32 dB
19 dB
Sensitivity
-30 dBm
-10,5 dBm
Pr max
2 dBm
Power
received
Fig…Power performance of EDFA OA 4500 Amplifiers Series
Output
power
21,5 dBm
2 dBm
Sensitivity
-30 dBm
-10,5 dBm
Pr max
2 dBm
Power
received
Fig…. STM cards characteristics
Type of STM card
Transmited Power (dBm)
Sensitivity (dBm)
Maximum dispersion (ps/nm)
Source linewidth (nm) (SM
laser)
STM 1
-5
-34
1600
STM 4
-3
-28
1600
STM 16
-2
-27
1600
1
1
1
We will work with STM 16 characteristics , because this card is more restrictive. We use
for transmitted power Tx= -2 dBm and for sensitivity Rx= -27 dBm.
Total Attenuation
We make the attenuation calculation using the following formula:
𝒅𝑩
𝜶𝒕𝒐𝒕𝒂𝒍 = 𝜶𝒇𝒊𝒃𝒆𝒓 ( ) ∗ 𝑳 (𝒌𝒎) + 𝜶𝒄𝒐𝒏𝒏𝒆𝒄𝒕𝒐𝒓𝒔 ∗ 𝟒 + 𝜶𝒑𝒐𝒓 𝒔𝒍𝒊𝒄𝒆 ∗
𝒌𝒎
𝒐
𝒏 𝒔𝒍𝒊𝒄𝒆𝒔 + 𝜶𝒎𝒖𝒙 ∗ 𝟐(𝒎𝒖𝒙 𝑻𝒙 𝒂𝒏𝒅 𝒅𝒆𝒎𝒖𝒙 𝑹𝒙)
In order to fix the maximal distance Lmax that allows us to transmit a signal without using
amplifiers we will use the following formula:
𝜶𝒎𝒂𝒙 = [(𝑹𝒙 − 𝑻𝒙) + 𝜶𝑻𝒐𝒕𝒂𝒍 ]/[𝜶𝑭𝒊𝒃𝒆𝒓 + ( 𝜶𝒔𝒍𝒊𝒄𝒆𝒔 /𝟓)]
Considering the characteristics of optical multiplexers and demultiplexers presented in the
chapter number 6.2.1, we make the calculation of Lmax considering next cases:
WDM technology
CWDM 1 channels
CWDM 2 channels
CWDM 8 channels
DWDM 8 channels
DWDM 13 channels
DWDM 40 channels
Att Mux/Demux
0 (No use mux)
4,6
7,4
8
7
12
L max
120,59
94,12
80,4
62,20
66,14
46,46
After we obtain the maximal distance Lmax that allows us to transmit the signal without
using amplifiers, we look to links that are bigger than Lmax. In order to have a proper
transmission, for this links we use amplifiers.
For links with one amplifier we calculate the new maximal distance, Lmax, at which the
amplifier can transmit the signal. There can be situations in which the amplifier is not able
to cover all the link distance, when transmitting the signal. For this case we will use the
same formula when we make the new Lmax calculation, but we will use the transmitted
power from datasheet of the amplifier and the sensibility from datasheet of the demultiplexer. For the value of new Lmax we obtain the links that needs 2 amplifiers.
When we calculate the Lmax for links that need more than one amplifier we have to
calculate also the maximal distance between 2 amplifiers. For this distance we use the
input power 2 dBm, representing the addition between the signal gain of the amplifier and
the sensibility of the amplifier.
For links that are using 2 Fibers SP-Ring Protection, we take in count also the traffic for
the protection. That means we have double number of STM cards representing protection
and working traffic.
For the value of new Lmax, representing the maximal distance at which we can transmit a
signal using an amplifier and adding the maximal distance at which the signal can be
transmitted without using an amplifier, we obtain the number of AO that we need in each
link. In our case we have links for which we don’t use amplifiers and links in which we
needs one or two amplifiers.
Fig…. Link with one amplifier
ADM/DXC
Mux
AO
Demux
ADM/DXC
Fig … Lmax calculate for links with one or more amplifiers
Link
description
No. Channels
Pt
Sensibility
Lmax
Lmax from
STM to AO
Lmax from
AO to STM
Lmax from
AO to AO
Lmax from
STM to AO
Lmax from
AO to STM
Lmax from
AO to AO
DWDM 13 channels
-2
-30
93,31
DWDM 13 channels
2
-27
97,25
DWDM 13 channels
2
-30
109,06
DWDM 8 channels
-2
-30
91,34
DWDM 8 channels
2
-27
91,34
DWDM 8 channels
2
-30
99,21
Fig… Link with 2 amplifier
AO
ADM/DXC
Mux
AO
Demux
ADM/DXC
Fig… Lmax calculated for links with one amplifier and 2 amplifiers
Real
No.
Lmax
# AOs L max with 1 AO
Link
Distance channels WDM technology without AO used
or 2 AO
1
182,68
Igualada-Manresa
78,8
6
DWDM 8 channels
62,2
1
182,68
Tarragones – Montsia
74
6
DWDM 8 channels
62,2
1
190,55
Lerida - Tarragona
104
13
DWDM 13 channels
66,14
1
190,55
Lerida - Tarragona 2
97,9
13
DWDM 13 channels
66,14
2
299,6
Lerida - Manresa- Gerona
223
13
DWDM 13 channels
66,14
2
299,6
Lerida - Monjo- Gerona
254
13
DWDM 13 channels
66,14
1
190,55
Tarragona - Barcelona
97,4
13
DWDM 13 channels
66,14
1
190,55
Tarragona - Barcelona 2
87
13
DWDM 13 channels
66,14
1
190,55
Barcelona - Blanes-Gerona 119,9
13
DWDM 13 channels
66,14
1
190,55
Barcelona - Gerona
102
13
DWDM 13 channels
66,14
In this section of the project we assure the proper signal transmission in all our network.
Using optical amplifiers we get sure that signal transmission over the fiber has the needed power
to travel all along the network.