Over the past 15 years, I have helped hundreds of clients with network design, planning, and associated fiber management needs. These networks have ranged from the burgeoning CATV HFC days of the mid-1990s through the fiber leak scenarios of telcos to the gigantic bandwidth needs of various FTTH deployment strategies. One of the constants in all of them has been the consideration of link loss budget planning: How far can I go with my current optical power before I have to terminate or amplify? It has always amazed me that most of the time, the first response to distance limitation is to use more optical power in the form of EDFAs, transmitters, and amplifiers. Optical transmission and having the power to get it where you want it can be a costly affair. However, increasing power is not the only way to gain distance.

Perhaps the most overlooked element in network design is the quality performance of one simple item: the fiber patch cord. A quality patch cord not only improves network performance and reliability, it also increases the dollar value of today’s active optical equipment already installed on the network. The key to optimizing your network’s value proposition is to demand a low. DB loss in each installed patch cord.

During my years in the industry, I have often seen mated pairs (two connectors or ends mated through an adapter) loss budgets. 6dB per pair. In a fiber logic run that included 10 end-to-end coupled pairs, I had to assume 6 dB (.6 times a factor of 10) of loss at the connectors only; That’s before calculating the loss associated with fiber length, active equipment, optical components, and splices.

In recent years, Telcordia has established that the dB loss standard should not exceed 4 dB. If you could achieve 50% insertion loss improvement on all your patch cords, think about what you could do for your optical budget …

Using the same example of 10 pairs coupled in a logical fiber section; you can get 2 dB of optical power. Think about the cost difference of going from 19 dB optical launch power to 21 dB compared to upgrading your patch cord performance standard to 2 dB insertion loss, without increasing the price. Calculating 20 dB loss for every kilometer at 1550 nm (no splice loss), the higher performance of the patch cord allows you to extend your existing power by almost another 10 kilometers. At the very least, it gives you some optical headroom to insure against other dimming events that occur after installation.

Guaranteed vs. Typical?

When Telcordia reset the standard to 4 dB loss, most patch cord vendors reported performance levels “typical” of the Telcordia standard. As “typical”, the process to build the patch cord was able to deliver 4 dB performance, but each individual patch cord that came off the line may or may not meet the standard. Did 51% of the cables match the standard? 75%? Few patch cord vendors were “guaranteeing” 4dB loss as it required extensive quality control measures in its production process and very tight tolerances in its test metrics. The supplier perceived these changes as costly and prohibitive. Achieving a “guaranteed” level of performance was expected to result in a great deal of “waste” on the shop floor, as patch cords that did not meet the guaranteed number were set aside as “seconds” or they were polished again to achieve the desired results. Unsure of what they were getting, network designers needed to allow for variations in patch cord performance. As a result, their network designs were unable to fully benefit from the reported performance improvements.

Setting a new standard

Fiber in the outside plant has made guaranteed performance critical to network design. Fiber reach, guaranteed for immediate and continuous performance over the life of the network, is critical to delivering the user experience that FTTp networks promise. As a result, a new class of patch cables is emerging that ensures deep performance in the fiber network. Suppliers that have built their production plants for optimal performance are delivering Guaranteed loss of 2dB.

The guaranteed loss of no more than 2dB reduces the cost of implementing the FTTp network by extending the reach of the network, minimizing the need for amplification at output ports or EDFA, and allows network designers to focus on other elements of their network design. Additionally, manufacturers of this new class of patch cords offer this level of connectivity without a significant cost premium due to the repeatable processes that have been established in their world-class factories. FTTp network designers now have a lot to be excited about!

So how do you know if you are getting the quality patch cable you need for your network?

Step 1 – 100% demand for. 20B or better. Period. This requirement alone will eliminate the desire to be world class.

Step 2 – Ask some simple, but critical, questions about processes, systems, and personnel to ensure a quality-driven, repeatable manufacturing environment exists.

Can you tell me the types of automation you have incorporated into your termination process?

While fiber termination requires many manual processes that must be performed by trained technicians, there are many things to look for in your manufacturer’s processes that automate critical steps in the fiber termination process.

Examples of

Epoxy – What type are they using? Mixed, premixed? How do they degas? This is critical for termination used in uncontrolled environments such as the outside plant. Some will cheat at this step. They may give you great performance data. But will it work properly in harsh environments?

Epoxy dispensing – how is the volume rate controlled? Often times, a simple syringe is used and dispensed at the visual discretion of the personnel performing the work, which can result in variability in the volume of epoxy dispensed. Look for control here with manufacturers using pneumatic syringe dispensing equipment that is also equipped with timers. Epoxies exposed to oxygen are curing and becoming unacceptable for use over time. Again, the performance data may look good, but long-term reliability can suffer if epoxies are not handled and dispensed correctly.

Hack Removal – A very critical part of the process, as a good or bad hackel removal is not discovered until the end of the testing and visual completion process. Most manufacturing environments use a manual process whereby a scriber is used to mark the glass next to the ferrule and break it. A better process is to score the glass on two sides 180 degrees apart and remove the stinger rather than break it. This minimizes the change for the cracks that are only found in the test. The best way is to use automation using a laser blade. This process uses a controlled laser to cut / melt the stinger away from the splint with very tight tolerances, eliminating a manual epoxy removal step that can also cause cracks.

End Face Inspection – This is the process of checking an end face for pits, scratches, cracks, and particles. Do you have one? Many do not. If they can get the connector to perform, they’ll call it good. While there is no recognized industry standard for end condition and cleanliness, there is no question that in a dynamic connector, long-term reliability is greatly compromised as pitting and scratches can accumulate. particles that can contaminate other connectors. For those who have an extreme standard, ask if it is subjective to an operator or if automation is used with a digital image of the extreme, magnified at 400x, compared to a profile that has been preloaded on the equipment and only delivers a condition pass or fail. Ask to see this profile that tells you exactly what kind of defects they will allow. Pits or scratches should not be allowed in contact zone 1, 2 or in an area 8 times the size of the core. This type of process ensures reliability long after the performance data is measured at the factory.

Performance tests: at what wavelengths are they measured? Performance is more sensitive to high wavelengths. Namely. 1550 and 1625. The insertion loss must be equal to or better than x. They are not “typical” results. Loss must be measured at each termination and not be a total or average sum of the patch cord.

End Geometries – Interferometer is an absolute must to develop a polishing process and then to ensure that the process is still capable. Anyone who tells you they don’t have one you should quickly walk away. Ask if any of their geometry standards exceed Telcordia industry standards. If you really want to be involved in the process, ask to see the distribution of key geometric data such as radius of curvature, vertex offset, and fiber undercut / bulge. It is the mean at the margin or right in the middle of the standard. In short, are they passing but “living on the edge”. Could you draw your own histogram and review … Okay, I’m getting carried away here and these are supposed to be fast.

Are you ISO certified?

This is another “elimination” question. While a “no” answer does not necessarily mean that they cannot deliver a quality completion, a “yes” tells you that they have quality systems in place for documentation, processes, training, and a variety of controls for a quality manufacturing environment.