Consider this scenario: The network design has been done and the link loss budgets are being calculated for active optics specifications and recommendations. A few of your runs to outlier serving areas are stretching the distance limitations of your optical budget as your mated pair count, from the true cross-connect in your CO to your distribution hub and out to your Last Mile access neighborhoods, reaches a total of 10. This, coupled with your fiber distance, splices, and optical components along the way, has you coming up 2dB short of your optimal receive power.

What to do? You’ve checked your math and everything appears correct. Launch power, events, etc., all measure correctly. Your terminated fiber meets the performance standard….

It appears the only resolution is to increase your launch power optics. The introduction of an amplifier addresses the issue, but at a hefty price tag -- the costs add up.

At times amplifying technology is a lifesaver. But it’s not your only option. The solution may be as simple as improving the performance and quality of your terminations. Not only will this reduce your cost, but by improving your guaranteed loss at each end, you can reduce your power consumption by 10% -- significantly improving your carbon footprint.

A Loss-ing Prospect
Over the past 15 years, networks have ranged from the booming CATV HFC days of the mid-1990s to the gargantuan bandwidth needs of some of the country’s largest FTTH deployments. One of the constants in all of them has been the consideration of link loss budget planning: How far out can I get with my current optical power before I have to terminate or amplify?

More often than not, the first answer to distance limitation is to plop in more optical power in the way of EDFAs, transmitters, and other types of amplifiers. Optical transmission and having the power to get it where you want it to go can be an expensive affair. However, boosting power is not the only way to gain distance.

Perhaps the most overlooked element of a network design is the quality performance of a simple item: the fiber patch cord. A quality patch cord not only improves performance and reliability of the network, but it also stretches the dollar value of current active optical equipment already installed in the network. The key to optimizing the value proposition of your network is to require a low dB loss on every installed patch cord.

Over time, we have seen mated pair (i.e., 2 connectors or endfaces mated through an adapter) loss budgets of .6dB per pair. In a logical fiber run that included 10 mated pairs end to end, so we had to assume 6dB (.6 multiplied by a factor of 10) of loss in connectors alone -- that’s before the loss associated with fiber length, active equipment, optical components, and splicing is calculated.

In recent years, Telcordia has established that the standard for dB loss should be no more than .4dB. When Telcordia reset the standard to .4dB of loss, most patch cord vendors reported performance levels that were “typical” of the Telcordia standard. As “typical,” the process to build the patch cord was capable of delivering .4dB performance. But, each individual patch cord that came off the line may or may not meet the standard.

The question became: Did 51% of the cords match the standard? Did 75%? Few patch cord vendors were “guaranteeing” the .4dB loss, as it required extensive quality control measures in their production process and very tight tolerances in their test metrics. These changes were perceived by the vendor as expensive and cost-prohibitive.

Achieving a “guaranteed” performance level was expected to result in extensive production floor scrap, as patch cords that didn’t meet the guaranteed number were either set aside as seconds or re-polished to achieve the desired results. With no certainty as to what they were getting, network designers needed to allow for variation in patch cord performance. As a result, their network designs were not able to fully benefit from the reported performance enhancements.

Figure 1. After the fiber patchcord is polished and endface-checked, it is tested for Insertion Loss (IL) and Return Loss (RL).

The Best Kind of Loss: A Decreasing One
Fiber in the outside plant has made guaranteed performance critical to network design. Reach of the fiber -- guaranteed for immediate and on-going performance for the life of the network -- is critical to delivering the user experience that FTTP networks promise. As a result, a new class of patch cords is emerging which guarantees performance deep into the fiber network – rather than just claiming typical performance. A guarantee to .4dB would truly allow the network design engineer to enhance his network designs because he didn’t need to account variability in performance.

But the market cannot be satisfied with .4dB performance. Vendors must continue to build their production processes for optimal performance: Guaranteed performance at a .2dB loss addresses the future-proofing that FTTP networks require.

Guaranteed performance at a .2dB loss, achieves an insertion loss improvement on all your patch cords of 50%. Let’s think about what that could do for your optical budget….

Using the same example of 10 mated pairs in a logical fiber run, you can gain 2dB of optical power. Think about the extra costs introduced by moving from an optical launch power of 19dB to 21dB. Plus, calculating .2dB of loss for every kilometer at 1550nm (without any splice loss), the increased performance of the patch cord allows you to extend your existing power almost another 10 kilometers. At the very least, it gives you some optical headroom for insurance against other attenuation events that come post-installation. At the same time that you are lowering your costs and extending your network distance, you are also reducing your energy consumption by 10%. Multiply that 10% by a 10,000 home network, and you are significantly affecting your carbon footprint and your weight on the power grid.

Guaranteed loss of no more than .2dB lowers the cost of FTTP network deployment by extending the network reach, minimizing the need for amplification in out-ports or EDFAs, and allowing the network designers to concentrate on other elements of their network design. What’s more, manufacturers of this new class of patch cord are delivering this level of connectivity without a significant cost premium because of the repeatable processes that have been established within their world-class factories.

FTTP network designers now have a lot to be excited about!

Johnny Hill is the chief operating officer of Clearfield, Inc. Hill has approximately 15 years of strategic and hands-on experience in the telecom networking industry. Hill’s expertise includes issues such as fiber management, harsh environments, network design and transport, network equipment, and more. For more information, visit www.clearfieldconnection.com.

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