Radiance CWDM System 17
User Guide
This section contains more detailed information about using the Radiance
CWDM System.
Calculating the Transmission Power Budget
When designing an optical link, one of the factors to consider is the transmission
power budget. The power budget is required for determining the maximum
distance a link can support. The transmission power budget is the difference
between the optical transmitter output power and the receiver sensitivity:
Power Budget = TX Power - RX Sensitivity
[EQ. 1]
Example 1: A -2 dBm optical transmitter and a -25 dBm receiver provide a
total transmission power budget of 23 dBm.
Power Budget = TX Power - RX Sensitivity
= -2 dBm
- (-25 dBm)
= 23 dBm
In a CWDM system, every point where a channel is dropped, added, or passed
results in a loss of signal strength. When calculating the power budget for a
CWDM link, all losses must be added together and then subtracted from
Equation 1 above:
Power Budget = TX Power - RX Sensitivity - Losses
[EQ. 2]
Refer to
Technical Specifications
for the expected loss values for the CWDM/
OADM modules. A link is defined as the connection between the point where a
signal begins and the point where it ends. Because the CWDM/OADM modules
do not regenerate signals, the link distances are calculated from CWDM SFP to
SFP. In the CWDM power budget equation, the TX Power and RX Sensitivity
are the specifications for the CWDM transceivers being used.
Example 2: Calculate the power budget for Link A in the diagram below. Link A
is the distance from CWDM SFP #1 to CWDM SFP #4.
Mux/Demux #2
T
X
R
X
Exp
Mux/Demux #1
T
X
R
X
Mux/Demux #3
T
X
R
X
Exp
Mux/Demux #4
T
X
R
X
CWDM SFP
#1
CWDM SFP
#4
Link A
