Quick answer: An SFP optical cable is either an active optical cable with fixed modules moulded on each end, or a fiber patch cord used with separate SFP modules. AOC reaches 100 m and beyond at 10G with lower power and no cleaning, but the module is captive. A patch cord with pluggable modules is serviceable and works with any vendor coding.
Three products get called SFP cable: DAC, AOC and plain fiber patch. They solve the same problem at different distances and with different failure modes, and the choice usually comes down to reach and to who has to service the link later.
The three cable types in an SFP+ port
Direct attach copper
A DAC is a twinaxial copper cable with SFP+ shells crimped on. It is the cheapest option up to about 5 m at 10G, and up to 3 m it is passive with no electronics. Beyond that it becomes active, drawing power and costing close to AOC.
Active optical cable
An AOC has an electrical to optical converter inside each shell, a multimode fiber ribbon in between, and no user serviceable parts. At 10G it reaches 100 m, at 25G about 70 m. Power draw is roughly 0.3 W per end against 1 W for a 10GBASE-SR module pair, and there is no connector to clean.
Fiber patch cord with modules
A standard duplex patch cord plus two SFP modules. Reach depends on the module and fiber type: 300 m over OM3, 400 m over OM4, 10 km over single mode. This is the only option that can be repaired, retargeted or reused across vendors.
Reach, power and cost compared
| Type | 10G reach | Power per end | Vendor coding | Serviceable |
|---|
| Passive DAC | 3 m | 0 W | Usually universal | No |
| Active DAC | 7 m to 10 m | 0.1 W | Often coded | No |
| 10G AOC | 100 m | 0.3 W | Often coded | No |
| SFP+ SR with OM4 | 400 m | 1 W | Universal or coded | Yes |
| SFP+ LR with OS2 | 10 km | 1 W | Universal or coded | Yes |
Where AOC wins and where it does not
Rack to rack inside a room
This is the sweet spot. AOC is thin, light, immune to electrical noise, and cheaper than a module pair plus a patch cord at 20 to 50 m. It also removes the dirtiest failure mode in fiber: a contaminated end face that nobody cleaned.
Any link that may need to change
An AOC is captive. If a port is repurposed, the whole cable goes in the bin. Where the topology is still moving, modules and patch cords cost more today and less over three years.
Coding and compatibility
Some switches accept only vendor coded optics. AOC shells are coded at the factory and cannot always be reflashed, while many SFP+ modules can. Check the switch documentation before ordering, because a returned AOC is worthless to both sides.
Diagnosing a link that will not come up
Start with the digital diagnostic readings rather than swapping hardware. A switch port reports transmit power, receive power and temperature for each optic. Receive power at minus 20 dBm where the budget expects minus 3 dBm means a dirty connector or a bent fiber, not a dead module. Receive power at zero means the fiber is looping back or the module is transmitting into itself.
If the link is up but drops under load, look at temperature and at error counters. A module running above 70 C in a rack with poor airflow derates and starts dropping frames. A coding mismatch shows as a module that is detected but never enables, and the switch log usually names the vendor it expected.
Practical scenarios
- Two top of rack switches 15 m apart: 10G AOC, one cable, no cleaning kit, no module inventory.
- Server to switch in the same rack: passive DAC at 2 m, lowest cost and lowest latency.
- Building to building at 500 m: single mode patch cord with LR modules, because AOC stops at 100 m.
- Lab bench with changing hardware: OM4 patch cords and pluggable modules so any port can be recabled in minutes.
FAQ
Is an SFP optical cable the same as fiber?
An AOC contains fiber but terminates in a fixed SFP shell. A fiber patch cord is bare fiber with LC or SC connectors and needs separate modules.
Can I plug an AOC into any SFP+ port?
Physically yes. Electrically it depends on coding and on whether the port accepts third party optics.
Do AOC cables need cleaning?
No. The optical interface is sealed inside the shell. The electrical contacts benefit from occasional cleaning but are far less sensitive than a fiber end face.
Next step
Pick by distance and by how often the link will change. Up to 3 m, passive DAC is the cheapest reliable answer; 10 m to 100 m at 10G, AOC is the clean choice. For anything longer, or for links you expect to repatch, use a multimode fiber cable and separate modules. Beyond 400 m, move to a single mode fiber patch cable, and check the OM3 LC fiber patch cable before ordering patch cords with the wrong polish.
