With more than 14,500 attendees, last week’s OFC is the biggest event on optical communications worldwide. The massive capacity needs of internet content providers (ICPs) stirred hot debates at the conference and on the show floor. In his plenary talk, Urs Hölzle highlighted that Google’s data center bandwidth is roughly doubling every year, posing serious scaling challenges to the network infrastructure. Optical innovation is key to addressing these ICP challenges, as Microsoft’s Yousef Khalidi points out in his recent Azure blog.

Cloud-scale data center fabrics often extend over multiple facilities spaced up to 80km apart. Tbit/s metro data center interconnect (DCI) solutions employing dense wavelength division multiplexing (DWDM) technology are required to avoid these links from becoming the bandwidth bottleneck. While coherent DWDM optics can be used for such links, their performance and spectral efficiency are not required and their cost and power consumption can be prohibitive.

Direct to the Point

In 2011, ADVA Optical Networking was first to market with a 100Gbit/s direct detect DWDM solution to fill the gap between short-reach intra-data center optics on one side and coherent long-haul optics on the other. Teaming up with Microsoft, Inphi and Arista, ADVA has now demonstrated at OFC 2017 how 56Gbit/s four-level pulse amplitude modulation (PAM4) and silicon photonics can be leveraged to double the fiber capacity of such a 100Gbit/s solution while halving the number of wavelengths and consequently the system cost. Using 200Gbit/s four-channel transmitter and receiver optical subassemblies (TOSAs/ROSAs) combining quantum dot laser and silicon photonics technology from Ranovus, ADVA also demonstrated how this approach can be extended to build cost-effective 400Gbit/s transponder cards.

The optical interfaces are only one part of a metro DCI solution, though. High bit-rate DWDM optics need precise management of optical power and chromatic dispersion. What normally would be a tedious manual process requiring specialized staff, ADVA’s SmartAmp^TM turns into a fully automated rack-and-stack operation, managed via open APIs. The SmartAmp^TM integrates high power erbium-doped fiber amplifiers, wavelength multiplexing/demultiplexing as well as power and dispersion control. Be it in conjunction with Inphi’s ColorZ^TM modules or with ADVA’s transponder cards, the SmartAmp^TM-based Open Line System (OLS) achieves “coherent-like” plug-and-play behavior whilst maintaining direct detect cost points. With low-loss fibers, distances of more than 100km can be reached, making direct detect technology an excellent choice for cost-effective metro DCI.