An active optical cable (AOC) combines optical fiber with integrated transceivers at each end, converting electrical signals to light and back within a single cable assembly. AOCs provide high bandwidth, longer reach, lower weight and immunity to EMI/RFI, making them well suited to data centers, high-performance computing and other high-speed interconnect applications.
Key Takeaways
- Active optical cables integrate optical fiber and active transceivers into one factory-terminated cable assembly.
- AOCs convert electrical signals to optical signals at one end and back to electrical signals at the other.
- Compared with copper cabling, AOCs support longer reach and high bandwidth while reducing cable weight and EMI/RFI susceptibility.
- AOCs can simplify deployment compared with using separate pluggable optical transceivers and fiber patch cables.
- Common applications include data centers, high-performance computing, rack-to-rack links, servers, switches, routers, storage, Ethernet, InfiniBand and Fibre Channel.
We’ve talked about Active Optical Cables (AOC) and their ability to use the same electrical inputs as traditional cables, but with optical fibers between the connectors. They deliver faster speeds and distance performance compared to copper cables while maintaining compatibility with standard electrical interfaces. We’ve delved into their use in the realm of USB and the benefits they bring. Now, we’re going to take a closer look at fiber AOCs and all they have to offer.
For protocol-specific guidance, see our overview of USB active optical cables and their use in longer-distance USB connections.
What Is an Active Optical Cable?
An active optical cable, also called an active fiber optic cable or AOC cable, is a factory-terminated fiber cable assembly with permanently attached optical transceivers. The optical interfaces are enclosed within the connector ends and are not user-accessible.
AOCs are opto-electronic devices used in place of standard fiber optic transceivers due to ease of deployment and lower cost compared to using individual transceivers with separable fiber optic cable assemblies. The basic concept of a fiber AOC is to embed active optical transceivers into the assembly, as opposed to using separate pluggable fiber optical transceivers and standard, connectorized fiber cables. This makes an AOC a type of fiber optic transceiver cable.
How Do Active Optical Cables Work?
An AOC uses the same electrical inputs as traditional cables, but sends the signal over optical fiber between the connectors. At the transmitting end, the AOC transceiver electronics convert the host’s electrical signal into light. That light travels through the fiber, and at the receiving end the electronics convert it back into an electrical signal for the connected device.
This electrical-to-optical conversion happens inside the optical cable assembly, so the host device sees the same electrical interface it would see with a conventional cable.
AOC vs DAC: What Is the Difference?
A direct attach copper cable (DAC) is a passive copper assembly. In an AOC vs DAC comparison, DACs are typically preferred for very short connections, while AOCs provide longer reach, lower weight, smaller cable diameter and immunity to electromagnetic interference.
Because they are lighter and smaller than copper cables, AOCs can also make data center cabling physically easier to manage. When comparing an active optical cable vs direct attach cable, consider the distance of the link and the environment it runs through.
AOC vs Separate Transceivers and Fiber Cables
Conventional optical links use removable transceivers and separate fiber patch cables. An AOC simplifies deployment and eliminates exposed optical connections, but its length and end configurations cannot be changed.
Unlike an AOC’s permanently attached optical ends, a conventional duplex fiber connection uses a removable two-fiber cable between compatible transceivers.
In an AOC vs optical transceiver decision, an AOC trades the modularity of a pluggable optical transceiver and separate duplex fiber cable for ease of deployment and lower cost.
Benefits of Active Optical Cables
Mainly invented to replace copper cabling in data centers and high performance computing applications, AOCs offer a list of benefits that can make older technologies seem obsolete:
- Longer reach: AOCs reach farther than comparable passive copper cables.
- High bandwidth: They handle higher bandwidth and provide secure, reliable transmissions.
- EMI/RFI immunity: Because they carry signals as light, AOCs limit EMI/RFI and provide low bit-error rates, making them an EMI-resistant cable option.
- Reduced weight: AOC assemblies are smaller and lighter than copper cables, making the datacenter physically easier to manage. This lightweight fiber cable design also supports high-density cable management.
- Improved airflow: Thinner, lighter cables can leave more room for airflow in racks.
These benefits make AOCs a popular high-speed optical cable choice.
Limitations of Active Optical Cables
AOCs are not the right fit for every link. Consider these limitations:
- Power: AOCs require power from the host ports, so AOC power consumption is a factor in the overall design.
- Cost: They cost more than passive DACs.
- Bend radius: They must observe minimum bend-radius requirements, as with any fiber cable.
- Modularity: They are less modular than separate transceivers and fiber cables, since length and end configurations are fixed.
Check AOC compatibility with your host equipment before ordering.
Common AOC Form Factors and Applications
AOCs are ideal for short-range, multi-lane data communication and interconnect applications. These assemblies support a range of protocols including Ethernet, InfiniBand and Fibre Channel.
Common form factors include SFP+, SFP28, QSFP+ and QSFP28, along with breakout configurations. A QSFP active optical cable or SFP active optical cable is chosen to match the port type on the host device, and an AOC breakout cable splits one higher-speed port into several lower-speed connections.
Typical applications include:
- Rack-to-rack connections in data center fiber cabling
- Optical backplanes
- Storage
- Servers, switches and routers
- High-performance computing
- USB devices, such as a USB 3.0 powered hub
How to Choose an Active Optical Cable
When choosing an active optical cable, verify the following:
- Data rate: the speed your link requires.
- Protocol: for example, Ethernet, InfiniBand or Fibre Channel.
- Form factor: such as an SFP AOC cable or QSFP AOC cable that matches your host ports.
- Host compatibility: confirm AOC compatibility with your switch, server or other equipment.
- Cable length: select the optical cable length your link needs, since it cannot be changed after purchase.
- Operating temperature: make sure the cable is rated for the environment.
- Breakout configuration: if you need to split one port into several.
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Frequently Asked Questions About AOCs
What Is an Active Optical Cable (AOC)?
An AOC is a factory-terminated fiber cable assembly with permanently attached optical transceivers. It uses the same electrical inputs as traditional cables but carries the signal over fiber.
How Does an Active Optical Cable Work?
The electronics at the transmitting end convert the electrical signal into light. The receiving end converts the light back into an electrical signal.
What Is the Difference Between an AOC and a DAC Cable?
A DAC is a passive copper cable typically preferred for very short connections. An AOC offers longer reach, lower weight, a smaller diameter and immunity to electromagnetic interference.
What Are the Advantages of Active Optical Cables?
AOCs offer longer reach than passive copper, high bandwidth, reduced weight, improved airflow and immunity to EMI/RFI.
When Should You Use an AOC Instead of Separate Transceivers and Fiber Patch Cables?
Use an AOC when ease of deployment and lower cost matter and a fixed length and end configuration will work. Choose separate transceivers and fiber cables when you need modularity.