Plug’n’Play or don’t worry about fiber optics
Nowadays people are used to Plug’n’Play… or do you care when you plug or unplug your USB add on device from your laptop?!? The scenario of changing to high speed I/O connections in data centers seems easy enough, but seldom is, although it should be.
Firstly, the high speed cable must be mechanical and electrically compatible to what the equipment expects. Even passive copper cables do have I²C chips in the plug, which tells the FPGA behind the hole in the front panel the type of cable being inserted. Furthermore, the span (cable length) is in question. Will the cable be capable of transmitting the high speed signal over the required distance? Is the cable’s data rate capability per the latest standard? Does it comply with the data rate posted on the box?
If either length or data rate is not met, people often have to switch to fiber optic transceivers, which can propel them into deeper troubles. When there is only one link to be converted, it is readily achievable. Nowadays LC connectors are easy to handle. Even still, you have to pay attention for dust and cleanliness while plugging the transceiver into the front panel and, thereafter, the LC cable ends into the transceiver.
However, if this changeover from copper to fiber optic has to be done for 3000 ports, the mains power supply may be in danger (3000 times 1.5 watts equals 4.5 kilowatts) or, even worse. The dissipated heat needs to go somewhere, usually handled by the air conditioning system, which consumes at least as much—or more—energy.
What if all this trouble could be forgotten? What if a truly simple solution existed? One does…
Active Optical Cables (AOCs) are the solution to all these issues. AOCs are closed systems, with the fiber firmly connected to the plug ends—like a copper cable. No dust, no cleanliness problems, no worries about the wavelength in the fiber. The advantage of the thin fiber is not only the diameter of the cable allowing many cables in cable trenches, but also the narrow bending radii these fiber cables perform compared to copper cables (1st picture).
AOCs adapt local protocols and data rates. Take the Molex 106410 series which plugs into QSFP interfaces. These cables negotiate automatically data rates from 10,325Gbps down to 1 Gbps and recognize InfiniBand* (QDR/DDR/SDR), Ethernet (40 and 10Gbps), Fibre Channel (10 and 8Gbps), and SAS (6Gbps) protocols – just Plug’n’Play!
Contrary to what people think about active cables these devices only consume <1 watt per end which relieve designers the task of adding heat sinks onto or airflow around QSFP cages, even when stacked and ganged. The neat technology of using a CW (always on) long life DFB laser with a proprietary wave length, which can be guided and modulated in CMOS silicon, reduces the components in the active cable ends (picture 2). This results in extremely good bit error rates (10-18) and a calculated <2.7 FIT per AOC end (at 60% confidence level) proven by 50.000 cables in the field. Using single mode fibers make these cables work reliably up to distances of 4 kilometers (6 miles). Because nobody can pull such long cables from one location to another, Molex offers the same technology with MPO pigtails connected to eight lit up single mode fibers with MPO connectors at both ends.
So, whether you want to connect your high speed servers, storage, or switch equipment over a few meters or spanning miles, consider active optical cables as the solution: Easy to Plug’n’Play, reliable in BER and FIT, low power consumption, small bending radii and prices below USD 350 in single quantities. An added plus—your reduced operating cost for power and air conditioning will pay back for these cables!
*InfiniBand is a registered trademark of the InfiniBand Trade Association