Fiber Optic Design Guide - Maite y Mario

Fiber Optics
E2-3
Example
Fiber Optic
FIBT Design Tool
#1. The C/N you would
like to see from the
link is 54 dB.
#2. The system has 78
channels. The C/N
of 54 dB intersects
with the 78 channel
curve at 3 dBm.
#3. The optical link
budget for this link
is 7 dBm.
#4. Link
Budget: 7 dBm
Receiver
Input: +3 dBm
Minimum
Tx
Output: 10 dBm
Round up to 11 dBm
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1. What is the acceptable C/N you want to see at the output of the fiber optic receiver?
__________dB (#1)
2. Determine the optical input needed at the receiver to maintain your C/N from above. Find the C/N fig-
Carrier-to-Noise (dB)
ure on the Y axis on the chart below. Follow that figure across until you come to the curve that corre-
sponds to your channel loading. Follow this intersection down to the X axis to determine the optical
input power. This is the level that you need to hit the receiver with in order to maintain the C/N that
you picked in Step #1.
__________dB (#2)
60
58
56
54
52
50
48
46
44
42
40
38
36
-14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4
3. What is the link budget? This is the sum of all the losses from the Tx to the Rx.
__________dBm (#3)
Optical Input Power (dBm)
4. Determine the transmitter power necessary to complete the link:
Link Budget (#3) ___________ dBm
Receiver Input (#2) + ___________ dBm
Minimum Transmitter Output = ___________ dBm (#4)
5 Channels
10 Channels
24 Channels
40 Channels
78 Channels
110 Channels
You should round this number up to the next dBm to build in a margin of error to cover any unseen
items in the link budget.