High-Density Fiber Connections Solve Some Problems but Cause New Ones for Giant Data Centers

There is no doubt that our world is increasingly digitally interconnected. Today there are about 4 billion smart phones in use worldwide. High-speed 4G and 5G wireless networks make it possible to stream games, videos, and data-intensive apps like Roku and Waze to billions of mobile devices. Artificial intelligence apps like Alexa and “smart” home appliances are ubiquitous data hogs. New analytical tools such as high-frequency financial trading, credit card fraud detection, and even real-time aircraft tracking and maintenance only are possible due to the enormous predictive power of big data.

Globally, we’re addicted to our data. Cisco estimates internet traffic will increase 127-fold from 2005 to 2021. Here’s the rub: Every single one of these devices end up connecting to a giant data center, somewhere.

Data centers are an astounding, fast-growing service industry. Starting from nearly zero 20 years ago, Emerson Network Power estimates today there are 510,000 data centers worldwide with global revenues around $174 billion. The unbeatable value-added proposition offered by data centers is the massive collection and manipulation of raw data into real-time products, such as when Waze converts cell phone information into traffic advisories or when Alexa responds to voice commands. But data center growth creates a new set of problems.

Data Center Worries

Most worryingly, data centers are huge. At a staggering 7.2 million square feet, “The Citadel” in Reno, NV, is billed as the largest and most efficient data center in the United States. It’s getting to the point where “hyperscale” data centers of more than 200,000 square feet — serving companies like Facebook, Google, Amazon and Microsoft — are becoming the norm.

Data centers are not as “green” as people think. Data centers use enormous quantities of electricity. By 2025, they will consume 4.5% of the world’s electrical production and emit 2% of the world’s greenhouse gases. Andrew Donohoe, a senior analyst with 451 Research, recently wrote, “The challenge of cooling modern data centers has been likened to using a room full of air conditioners to cool a room full of heaters. It is difficult, expensive, and inefficient.” The net effect is that northern locations in Canada, Iceland, Finland, and even the Artic are preferred because the naturally cold environment reduces cooling costs.

Putting all one’s digital eggs in a single, far-away basket can be risky. Performance matters; latency delays caused by distant data centers degrade crucial time-sensitive computations, such as artificial intelligence responses, navigation for autonomous vehicles, and vital financial transactions.

Data centers in Houston proved very vulnerable after Hurricane Harvey. Emerson Power estimates typical data centers average 2.5 outages per year, with an average outage duration of 134 minutes. That works out to 2.8 million hours of downtime globally. This vulnerability reinforces the importance of reliability, diversity, redundancy, and uptime. Guaranteeing reliability becomes more expensive as data centers grow.

The cure to all of these problems is to make data centers smaller, closer, and more energy efficient. Achieving these goals requires squeezing faster fiber into a smaller footprint. The logical place to start is with the fiber connectors themselves. The migration from SC- to LC-style configurations, as the industry already has done, has enabled devices to shrink. Mulitfiber connectors can increase capacity without increasing size but are hard to handle. Facing these enormous technological, financial, and ecological pressures, what’s next?

Three new types of connector options are gaining traction across the industry. These new configurations are (a) the CS duplex connector system for the next-generation QSFP-DD transceivers, (b) 16-fiber-array MT-based connectors, and (c) lens-array ferrules for parallel optic and silicon photonics applications. All three aggregate more fiber into a smaller footprint.

All three connector styles also bring their own drawbacks as well as benefits. All connectors are inherently dirty because of the moving parts like springs, connectors, and latches, all of which generate wear debris; more connectors mean more debris. Specifiers will want inspection and cleaning products that will do the job right the first time. There will be no time, no people, and certainly no budget for do-overs.

CS Single-Fiber and Duplex Connectors

Senko Advanced Components is leading the development of the CS duplex connector working as part of the QSFP-DD MSA, and the CS is widely considered to be the best option of the three. This design utilizes the tried-and-true standard 1.25-mm LC form factor ferrule, but with tighter spacing between the ferrules. With the CS design, pitch is reduced to 3.8 mm from the LC standard of 6.25 mm. The result is a theoretical capacity increase of 80%. Senko claims the new connector is specifically designed for 400G optimization using the next generation of QSFP-DD transceivers.

Techs installing and sustaining these networks will need cleaning products that are effective, affordable, and actually fit into CS ports. The clearances on CS adapters are very tight, which makes it difficult for cleaning tools to get inside the ferrule. High-quality fiber cleaning sticks can navigate around the mechanical housing of the connector, but inexpensive cotton swabs will be too large. Foam swabs lack the rigidity to clean properly. Bulky mechanical “push to clean” tools simply won’t fit. Fortunately, 1.25-mm tools are now reaching the market that accommodate CS-style ports.

Some companies have “duplex” cleaning tools that purport to clean both end-faces of a duplex connector simultaneously. However, most of these tools are engineered for the standard LC duplex form-factors, so the cleaners’ barrels will not fit into the adapter port. Additionally, the cleaning tips won’t align to the new CS connector ferrules. Even more importantly, techs need to inspect and clean each end-face, both sides. If only one end-face is dirty, a duplex tool still will clean both, which is wasteful. Extra cleaning also can induce static charges. All in all, these can be quite costly, especially if the tech is simply cleaning every end-face.

Multifiber Connectors

Probably the biggest near-term winner may be multifiber connectors. Manufacturers are migrating from the traditional 12-fiber arrays to a 16-fiber array using the same 2.5-mm x 6.4-mm standard MT ferrule footprint. These connectors are most often used on optical backplanes, where the data jumps from the fiber transport into the switch for routing. However, optical backplanes are the dirtiest location in a rack because of all the moving parts, cooling fans, etc.

Not only are the new connectors denser, they comprise different materials of construction. The new MT connectors are 80% glass, with reduced quantities of plastic resins to improve thermal expansion control. While these components are very stable, glass and plastic parts are electrical insulators and will retain static charges almost forever. Because of this, the biggest problem becomes how to clean and inspect such complex and dense configurations.

In terms of inspection, Fiber QA has a multi-fiber inspection system on the market today that seems to work well. Both VIAVI Solutions and EXFO also are working on inspection gear for these new super-dense arrays.

Lens Arrays

The new “lens array” connectors basically are expanded beam lenses on a microscopic scale. Lens arrays are offered by Intel, US Conec, Corning, Fujikura, Molex, CommScope, and many other companies. These designs collimate the optical signal and eliminate the need for physical contact. They use a very small, tightly focused “spot size” beam to pass the signal into the receiving lens. This approach minimizes problems associated with scratching and contamination between the lenses. This technology is simple, passive, and precise, and enjoys lower manufacturing costs. Some manufacturers claim that cleaning is not required, which would be an obvious cost-savings. What they should be claiming is that these designs are uncleanable.

The lens array ferrules are molded using plastic resins that easily can be shaped to the optical prescription of the lens. Unfortunately, molded plastics are soft, so the end-face is vulnerable to scratching and almost impossible to clean. Particulates that migrate into the central signal “spot zone” or scratches on the surface of the lens that are close to the spot zone will degrade the signal. Similarly, residues on the lenses change the index of refraction. This condition randomly degrades the signal as the angle of incidence changes when the light passes between the lenses.

The only real-world tool for cleaning lens arrays is a can of optical-grade duster, and that’s not ideal. The air stream will not remove sticky residues. The rapid flow of the gas across the end-face can cause static to accumulate to it, causing dust particles to migrate into the central spot zone on the lens’ surface.

Lens arrays are as vulnerable as they appear. At the microscopic level of fiber end-faces, a data center is a hostile environment and the lenses are made from materials that retain static and attract dust. The lenses are open to the air and lodged in racks that vibrate from fans and traffic. Dust and wear-debris will be attracted into these open-air static “magnets.” Lastly, while the manufacturers may clean their end-faces — as best they can — they don’t clean their plugs and end-caps. In short, this is a design that may work fine in the lab, but not in the real world with lint, dust, pollen, exhaust fumes, and people.

Your Best Cleaning Options

To obtain the promised benefits of massive data centers, cleaning fiber end-faces will remain a priority. As such, it is vital to clean both the end-faces and the alignment holes. This means while some push-to-clean tools are helpful, they’re an incomplete answer. Foam swabs and cotton swaps are ineffective and “wound-cloth” swabs are the wrong shape and not lint-free enough to manage the task. Paper wipes are also unsuitable. The only answer on the market today are certain brands of high-purity polymer cleaning sticks that can clean the multi-fiber arrays; fatter “XMT” sticks can even clean guide pins.

In terms of cleaning fluids, optical-grade dusters can push the dry particulate dust out of the way to help with the seating of the two faces for perfect alignment. If further cleaning is required, a super-pure, fast-drying fluid would be the best. Slow-drying isopropyl alcohol is a poor choice for cleaning these complex configurations and water has the wrong chemical characteristics (surface tension, latent heat, etc.). So the best choices are fast-drying, nonflammable liquids packaged in ultra-pure, nonrefillable containers.

Mike Jones is the MicroCare vice president — international. A graduate of Grove City College, he served in the Air Force and 13 years with AT&T before joining MicroCare in 1990. Now the vice president of international sales, Mike travels throughout Latin America, Asia, Europe, Africa, and the Middle East helping customers with their critical cleaning needs.