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MPO connectors are available with 12 fibers or 24 fibers:
12-fiber MPO connector (40G, SR4, eSR4, and 100G SR4 transceivers use 8 of the available 12 fibers. The
four center fibers are unused. )
Figure 3: End face of a 12-fiber connector and channel assignment
MPO transceivers typically use four channels to communicate. These channels are assigned using the
outer eight fibers (the center four are unused).
Transmit channels are one set of four fibers, and the receive channels are on the other set of four fibers.
Because of this, the cables used and fiber cable connections from endpoint to endpoint effectively create
a crossover connection.
Be aware that using two crossover cables in series cancels this effect and no connection will be
established. An odd number of crossovers combined with straight-thru fiber connections will effect a
crossover connection.
The channel layout indicates that the left four fibers are Transmit, and must reach the opposite
transceiver Receive channels (and in proper channel order).
Optical parameters
This guide provides average transmit and receive power ranges for transceiver modules.
Transmit power
Transmit power is the power at which the transmitter of an optical transceiver module transmits optical
signals, in dBm.
Receive power
Receive power is the power at which the receiver of an optical transceiver module receives optical signals, in
dBm.
Use of attenuators
Transceivers are designed to transmit light pulses at a power level that accounts for loss in the fiber optic
cabling, and meets the receiver input thresholds of the link partner optical transceiver.
If you are using a fiber cable with less light loss than expected (for example, in a test environment and you
do not have a 40km spool of SMF available), use attenuators to affect the transmit level to within the receive
sensitivity of the other transceiver -- you will need to condition both fibers (sends in both directions). If not
done, you risk overdriving the Receive end and permanently damaging the transceiver. For example, a 40G
ER4 has a highest transmit level of 4.5dBm, but the Receive Sensitivity can be no higher than -4.5dBm. That
means there must be at least a 9dBm loss on the light level to be within the standards (4.5 - (-4.5) = 9dBm
required).
Chapter 1 Overview
11
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