40/100G – A Major Shift to Parallel Optics?

by Lisa Huff

Parallel-optics have been around for more than a decade – remember SNAP12 and POP4? These were small 12 and four-fiber parallel-optics modules that were developed for telecom VSR applications. They never really caught on for Ethernet networks though. Other than a few CWDM solutions, volume applications for datacom transceivers have been serial short-wavelength ones. At 40G, this is changing.

High performance computing (HPC) centers have already adopted parallel optics at 40 and 120G using InfiniBand (IB) 4x and 12x DDR. And, they are continuing this trend through their next data rate upgrades – 80 and 240G. While in the past I thought of HPC as a small, somewhat niche market, I now think this is shifting due to two major trends:

• IB technology has crossed over into 40 and 100-Gigabit Ethernet in the form of both active optical cable assemblies, CFP and CXP modules.
• More and more medium-to-large enterprise data centers are starting to look like HPC clusters with masses of parallel processing

Many of the top transceiver manufacturers including Avago Technologies and Finisar, as well as some startups have released several products in the last year to support these variants with short-reach solutions. The initial offerings are AOC products using QSFP+ and CXP form factors, which both use VCSEL and PIN arrays. At least one, Reflex Photonics , has released a CFP module that also uses these devices. To date, the only other transceiver product that seems to be available so far is the QSFP+ 40G module from MergeOptics , which is a natural extension of its QSFP AOCs. These products are already being deployed for IB systems and are planned to be used for the initial 40G Ethernet networks as well.

Once parallel-optics based transceivers are deployed for 40/100G networks, will we ever return to serial transmission?