We felt it would be helpful to answer the question, what
is an AOC cable? identical
to our most recent tutorial on DAC or Direct Attach Copper cables. We believed
it was time for a brief tutorial since at STH we think it's vital to spread
information, even if many readers already know the answer.
What exactly is an Active Optical Cable (AOC)?
An active optical cable is simply an optical fiber cable
with modules at either end that enables direct communication between devices
via the permanently connected fiber connection. The cable length is
predetermined, and there are specified connections on both ends.
We are primarily concentrating on pluggable optics as
part of our fiber optic guide series. Long-distance data transfer requires
optical communication. The amount of distance that copper connectivity can
reliably and effectively go at those rates is constrained as networks become
faster and we move into the 400GbE era and beyond. For some of the longer DAC cable that
can no longer be handled by copper, these AOCs are one possibility.
The necessity for a photonics transmitter and receiver
at either end prevents one from enjoying the economic advantages of copper
interconnects, which is one of the reasons this connection is less common than
DACs. The AOC cabling is smaller and more flexible than the copper connections
with 100GbE and faster generations. Although the majority of the industry has
already decided on DACs or pluggable optics without permanent wires, we wanted
to discuss AOCs as our readers could still run across them.
A Breakout AOC
We'll mention that the breakout AOC cable is a different significant form of AOC that you could encounter. The "Q" stands for quadruple with modules like QSFP+ for 40GbE networking and QSFP28 for 100GbE networking. The QSFP+ connection seen above may thus be thought of as holding four (quad) SFP+ channels. SFP+ is 10Gbps, QSFP+ is 40Gbps, and we can get 40Gbps of bandwidth by using four (quad) 10Gbps lines.SFP28 and QSFP28 both use the same conceptual framework. To connect to 2-4 slower devices, one technique is to divide the higher-density QSFP+/QSFP28 form factors.
