How to buy fiber-optic products

How to buy fiber-optic products

Proven through years of experience in lightwave technologies and applications, these guidelines should help first-time purchasers make intelligent choices when they are ordering fiber-optic components

eric r. pearson

pearson technologies inc.

Faced with a bewildering array of optical devices and technologies, newcomers in the lightwave field endure a challenging task when they are choosing and buying fiber-optic products. To ease that burden, here are 16 rules on how to sidestep common selection problems and, most likely, avoid overspending.

These rules primarily focus on procuring lightwave cables, connectors and opto-electronic devices but can be applied to most lightwave products. The information has been accumulated from approximately two decades of experience in developing, selling, buying and installing optical products. In practice, fulfill this chief purchasing principle: Buy only the product performance needed for the application.

General directions

Develop and list on a summary sheet the desired specifications for the particular product--whether cable, connector or opto-electronic. A comprehensive list of product specifications prevents the omission of an important requirement when you are dealing with potential suppliers.

Consult at least four vendors of the desired product. This multivendor approach assists in (a) establishing a competitive price, (b) verifying information accuracy, (c) resolving price and performance differences, and (d) uncovering any overlooked performance consideration.

Analyze any conflicting information from different vendors before you choose a product. Ask for test data to support a vendor`s product claims. Disregard a vendor that cannot provide test data.

Choose a supplier that has been in business for at least five years. Experienced suppliers are knowledgeable about common product problems, offer proficient advice, and are skilled in product repairs and support.

Avoid buying a product that has a low serial number. This designation generally indicates a new production run. Historically, these low-numbered products are prone to early assembly errors.

Learn the cost impact of the different technologies for each product. For example, understand the cost factors of ST and SC connectors; loose-tube, break-out and premises cabling; and light-emitting and laser diodes.

Do not pay the increased cost of unused high performance. In general, most commercial lightwave products exceed their listed specifications.

Opto-electronics rules

Expect similar price and performance figures from different suppliers of the same product. Most, but not all, opto-electronics suppliers purchase from the same manufacturers such active devices as light-emitting diodes, lasers and photodiodes.

Anticipate that products with the same nomenclature might not function identically. Low-cost components could possibly be deficient in providing full functionality.

Note that differences in prices among similar products from different suppliers tend to result from additional, but not required, functions. Examples of these functions include dual power supplies, status indicators, performance alarms and automatic switching.

Fiber-optic cable instructions

Ask the cable manufacturer if a stock cable is available that comes close to meeting your application requirements. If the application calls for a 6-fiber cable, for example, query the manufacturer whether a production-rejected multi-fiber cable--say, a 12-fiber cable (or higher fiber count)--that contains some substandard fibers is in stock. Negotiate with the manufacturer to buy this cable for a lower than usual 8-fiber-cable price. Manufacturers prefer not to keep substandard products in their inventory.

Attempt to get the best possible cable price consistent with application performance and delivery needs. The fiber-optic cable market is highly competitive, and prices can differ by as much as 40%.

Check the premium price for a high-performance fiber-optic cable when a standard cable might prove sufficient. Make sure that the cable design specifications match the application need. In practice, most applications do not take full advantage of the capabilities of standard fiber-optic cables. On the other hand, take into account the cable manufacturer`s reliability, workmanship, delivery and quality factors.

Connector regulations

Choose fiber-optic connectors that have operating limits equal to or greater than the expected range of operating conditions imposed by the application environment. Connector performance tends to correlate directly with installation ease; that is, the easier the installation process, the more reduced the performance. For example, the cable-retention strength specifications of three major epoxyless/adhesiveless connectors, which use a mechanical technique for gripping the fiber-optic cable, are lower than those for connectors that use a curing epoxy or adhesive. However, this decreased performance is important only if the connector is to be subjected to severe pull loading.

Consider, as another example, a fiber-optic connector that is preloaded with an adhesive and requires preheating. Such connectors generally have a lower upper temperature operating limit than those connectors that implement a curing epoxy or adhesive. Again, the decreased performance is critical only if the connector is to be subjected to excessive temperatures.

Evaluate ST, FC and SC fiber-optic connectors thoroughly. Even though these types of connectors possess low cost, low loss and low reflectance, they still might not perform satisfactorily in high shock, vibration or contaminated environments. These environments are apt to disconnect or damage the coupled fibers and diminish cable performance.

Compare the lower performance, lower price connectors that contain stainless steel or liquid crystal polymer ferrules with the higher performance and price of connectors that have ceramic ferrules--based on the application. Moreover, when damaged connectors are being repaired, ceramic ferrules prove more difficult and expensive to repolish. u

Eric R. Pearson is president of Pearson Technologies Inc. in Acworth, GA.

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