Active optical cables (AOCs) have, in many places, replaced electrical cables for 10 Gbit/s and faster applications. And why not? AOCs are lighter and can move data faster than wires. The weight and size savings alone provide better air flow, which improves cooling of server farms and communications networks.
An AOC consists of two optical/electrical (O/E) converters connected through a fiber optic cable, as shown in the photo below. The electrical interface must conform to an electrical-interface standard such as InfiniBand, Fibre Channel, Ethernet, USB 3.0, Thunderbolt, or HDMI. The cable below (courtesy of Finisar) has a QSFP+ electrical interface at each end.
An active optical cable has optical/electrical converters at each end,
such as these QSFP+ modules.
AOCs need testing, not just in the engineering, but in production. To accomplish that task, Multilane, a maker of optical and electrical data test equipment, has assempled an AOC production test system.
The diagram below shows the system. It consists of a set of modular instruments:
- A four-lane, 16 Gbit/s BERT (bit-error rate tester), which functions as a programmable pattern generator
- A DSO (digital sampling oscilloscope), which provides eye diagrams and jitter analysis
- A QSFP+ host with extended support to enable four-corner testing
A test system from Multilane consists of a pattern generator,
a sampling oscilloscope, and a QSFP+ host.
I asked Multilane founder Fadi Daou to explain what the system does:
AOCs are being used more and more to establish high-speed Ethernet and InfiniBand backbone connections for cloud computing, handling signals up to 100 Gbit/s. The need for cloud bandwidth is driven by the explosive growth in the use of Internet bandwidth and storage as required by smartphones, tablets, and other devices.
The AOC production testing system comes equipped with an API library, which lets a user communicate with all the hardware components to carry out AOC tests according to 40G Ethernet electrical specifications. Tests include voltage, current and power-consumption measurements, temperature measurements, bulk EEPROM programming for QSFP modules, PPG output signals, eye diagram and jitter measurements, and BER with J2-J9 bathtub curve measurements and four-corner testing.
Do you test active optical cables? If so, what equipment do you use, and what tests do you perform?