Active Optical Cable (AOC)-Explained

T-Blog Editor/ May 9, 2020/ Best practices for data center operations, Data center design and facilities, Data Center Hardware, Datacenter Infrastructure News, Tech Definitions, Tekmart Enterprise Hardware Tips

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By Tekmart Enterprise Support

Here is a brief definition of AOC:

This is a cabling technology that accepts same electrical inputs as a traditional copper cable, but uses optical fiber “between the connectors”. AOC uses electrical-to-optical conversion on the cable ends to improve speed and distance performance of the cable without sacrificing compatibility with standard electrical interfaces.

Who invented AOC their reasons..

Simply put, Active Optical Cable (AOC) assemblies were invented to replace copper technology in data centers and high performance computing (HPC) applications.

The first driver came from InfiniBand technology. As InfiniBand data rates rise and data center clusters grow in size, copper cable technology is getting stretched to its limits. InfiniBand Double Data Rate (DDR) of 20 Gigabits per second (Gbps) means that conventional copper cable is limited to an 8 to 10 meter reach. 

This may be fine for small clusters, but for larger clusters, this physical link distance makes the physical layout of the cluster becomes a real challenge. Due to the inherent bandwidth-distance limitations of high-speed copper cable assemblies, it is not uncommon for designers to embed amplifiers, signal regenerators, or similar devices within a cable assembly.

Copper cable is heavy and bulky, making it difficult to physically manage the datacenter. And because of the nature of electrical signals, electromagnetic interference (EMI) limits copper’s performance and reliability. If you have a scaled-out high performance cluster, these problems really add up.

So that was why Intel and Luxtera invented Active Optical Cable assemblies to fill the gap.

Intel’s design used Vertical-Cavity-Surface-Emitting-Lasers (VCSELs) and a collection of discrete components. On the other hand, Luxtera’s “Blazar” AOC products used CMOS photonics technology. Luxtera was able to integrate most of the transceiver functionality onto a silicon chip, only the laser and the photodetectors were discrete components.

Active Optical Cable assembly has many potential advantages. If the network equipment is properly designed, it becomes possible to have a common electrical port that can accept either passive copper cable or active copper cable, allowing the user to select the appropriate technology and cost with easy reconfiguration.

The optical connector can be an expensive, precision element (particularly for parallel optical links) due to tight manufacturing tolerances. This is eliminated by permanently attaching the fibers to the optics.

The following list presents the major benefits of Active Optical Cable assemblies.

• Longer Reach and Higher Bandwidth
• Secure, Reliable Transport
• Limited EMI/RFI Exposure
• Low Bit-Error Rate (BER) – 10^-15
• Smaller Size and Lower Weight Compared to Copper Cables

ACTIVE OPTICAL CABLE (AOC) ASSEMBLY APPLICATIONS

Active Optical Cable assemblies have been designed to support multiple protocols. Most of them are compliant with SFP+ Ethernet and InfiniBand electrical.  Here is what a typical 40 Gb/s QSFP+ (Quad Small Form-Factor Pluggable Plus) AOC supports.

1. Multirate: 1.0 Gb/s – 10.3125 Gb/s (per lane)
2. 4-Channel full-duplex active optical cable transceiver
3. InfiniBand SDR (2.5Gb/s), DDR (5 Gb/s), QDR (10 Gb/s)
4. Ethernet 10G, 40G
5. Fibre Channel 8G, 10G
6. SAS, SATA 3G, 6G
7. Fibre Channel SAN 10G, 20G, 40G
8. Myrinet 40G

Active Optical Cable assemblies can be used on optical backplanes, rack-to-rack, shelf-to-shelf interconnect, storage, hubs, switches, routers, servers, etc.

Here is a breakdown of AOC market by applications.

• Mainframes/Supercomputers (High Performance Computing – HPC)
• High Definition TV (HDTV)
• Personal Computers
• Consumer Electronics (CE)

Here is a breakdown of AOC market by Bus Interfaces.

• InfiniBand – High-speed interface bus used inside HPC and data centers
• HDMI – High definition multimedia interface
• USB – Universal Serial Bus
• DisplayPort – Bus specification developed by Video Electronics Standards Asso. (VESA)