Understanding Fiber Patch Cord Performance

With each passing day, fiber optics has become increasingly affordable, widely used for high data-rate systems such as FDDI, multimedia, ATM, or any other network that requires the transfer of large, time-consuming data files. As one of the most basic elements consisting of fiber optics in optical networks, fiber patch cord, or fiber optic patch cable and fiber optic jumper, composes of a fiber optic cable capped with a connector on each end. (In this sense, fiber patch cord can be classified by the connector types, like LC fiber cable, SC fiber optic cable, MTP/MPO cable, etc..). Judging from its structure, patch cord seems to be too simple. But actually, it plays a really important role in the overall network performance whose main problems are caused by patch cord performance. Thus, understanding fiber patch cord performance comes as the priority.

In order to have an in-depth understanding of fiber patch cord performance, this text will be spread from two aspects: the perfect patch cord and polishing conditions.

“Perfect Patch Cord”

When a patch cord made by a mated pair of connectors has near zero insertion loss and a relative power loss, then it’s called perfect patch cord whose performance should be in accordance with fiber splicing loss that is on the order of 0.02dB. It needs to meet these requirements: insertion loss <0.05dB and return loss >58dB.

  • Notices on Making “Perfect Patch Cord”

To make a “perfect patch cord”, the endface has to be kept clean, meaning that cleanliness of the production line and the cleaning technique are very important. Besides, the endface geometry of the ferrule must be controlled and the proper polishing must be operated.

As for loss reduction, it’s advised to properly align the fiber cores within the ferrules of two mated patch cords. The main factors that influence core alignment are ferrule inner diameter, ferrule concentricity, and ferrule outside diameter (OD). Understanding all relevant parameters and putting them under control is essential in making a “perfect patch cord” which must have sub-micron connector concentricity. The following figure shows the relation between insertion loss and connector concentricity.

Graph showing the trend of insertions loss versus Fiber Concentricity error

  • Notes on Testing “Perfect Patch Cord”

A reference cable is required to test a “perfect patch cord”. This cable should be at least at least comparable to the “perfect patch cord”. In order to get the accurate measurements, other parameters also need to be controlled while testing “perfect patch cord”, during which a high-quality adapter is used to ensure a consistent insertion loss.

Polishing Connectors

End-face cross section diagram of a fiber optic connector ferruleWhile polishing connectors, the endface on microscopic grits has to be grounded to remove excess epoxy from the surface and scratches from the fiber endface, as well as shaping the ferrule and glass.

Most of the current ceramic ferrules are pre-domed. For instance, the endface is shaped to have an optimum radius of curvature (ROC) and the as-small-as-possible apex offset (AO), as shown below. Apex offset is an offset of the apex point of ROC. In such case, the polishing must use a polishing grit hard enough to remove the epoxy from the ferrule and the scratches on the fiber endface, but not hard enough to significantly alter the ferrule geometry. If a ferrule is not pre-domed, the proper geometry must be formed through extended polishing.

  • Polishing Process

The polishing process is done as followings: firstly to remove epoxy from the ferrule front surface, then form or keep the dome, and finally to shine the fiber surface. Depending on the polisher and connectors, optimization must be made on the polishing pressure, time, and speed.

  • Polishing Inspection

After finishing polishing, a microscope with a magnification of at least 400x is used for visual inspection of scratches and damages. A “perfect patch cord” isn’t allowed to have any visible scratch on the fiber endface. Scratches through the fiber core can not only affect optical performance but also damage any other fiber endface they contact. For these reasons, scratches need to be minimized. In order to guarantee optimal performance, it is not only important to adhere to the polishing procedure, but also to the cleaning procedures. Once the fiber surface is clean, scratch-free, and confirmed to have endface geometry within specifications, insertion loss and return loss should fall into the expected specification.

Conclusion

By understanding and controlling factors that have effects on patch cord performance, it’s possible to build a “perfect patch cord” having an insertion loss equal to that of a fusion splice (near zero insertion loss). Fiberstore, as a professional fiber patch cord manufacturer, supplies various patch cords of high quality at low prices, like LC to SC fiber patch cable available at different lengths and in single-mode and multimode versions. For example, the 1m LC UPC to SC UPC 10G 50/125 OM3 Duplex Patch Cord at Fiberstore just costs you US$ 2.60, much less than what’s offered by other suppliers, say $22.99 at CABLES TO GO.

Author: Angel

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