How to optimize fiber attenuation

How to Optimize Fiber Attenuation Analysis Average cable fiber loss is sometimes thought of as a way to mask the multiple highly attenuating fibers in a cable. Averaging does not adequately define the distribution of fiber attenuation in a cable, especially when the cable contains many high-attenuation fibers. In this regard, manufacturers and the industry have standardized on maximum fiber attenuation to protect end users from inaccurate mathematical calculations that do not accurately represent the attenuation performance of a single fiber optic cable.

Significant improvements in fiber attenuation, such as lower attenuation coefficients and reduced point discontinuity specifications. Likewise, the fiber optic cabling industry has greatly improved its processes to greatly reduce or even eliminate additional attenuation in the cabling process, known as cabling variation. Even the measurement systems used to evaluate the performance of fiber optic cables in the factory and field have greatly improved. Therefore, the actual single-fiber attenuation in the cable deviates greatly from the specified maximum single-fiber attenuation. System designers continue to rely on link loss calculations as the basis for worst-case attenuation, but these cases occur far less frequently than their historical specifications.

Due to the conservative nature of the maximum single-core fiber specification, the maximum performance of the optical link may not be achieved. Clearly, another metric is needed to more precisely define the attenuation of fiber optic cables and "combined" links while maintaining a degree of conservatism related to the maximum single-fiber specification.

Link Design Attenuation

To determine how this new metric was specified, the fiber attenuation profile in actual fiber optic cables was randomly sampled from the generated average attenuation values, spanning 2 to 20 fiber lengths. Then analyze the resulting graph, shown in Figures 1A and 1B, with up to 20 fiber connections, to determine the span required to approach steady state. The number of links across steady state represents the minimum required to produce a technically reliable average attenuation. Figures 1A and 1B clearly illustrate that only eight series connections produce stable fiber attenuation. Other methods can be used to achieve the same result.

Fiber attenuation distribution in series for multiple fiber links

Additional statistical processing is required to correctly generate the proposed specification. Limits for link design attenuation can be derived at steady state points, shown for eight serial links. The proposed link design attenuation is indicated by the green line, representing a 99.9% confidence threshold based on the specification of the eight connected links. This result supports the concept of using link design attenuation to optimize network design and maintain reasonable guard bands.

Cascaded fiber attenuation distribution for multi-fiber links

The industry has established a precedent (IEC 60794-3) for the final application of PMD in the design of statistical processing links. To maintain consistency with existing standards, twenty spans can be used to determine link design attenuation values. Monte Carlo simulations show that only eight spans are sufficient to achieve stable performance of link design attenuation. Using an extra span does not result in a significant increase in performance. Additionally, a smaller number of spans helps to better align the specification with the access network.

Comparison of Maximum Fiber Attenuation Characteristics

Several benefits of using this link design attenuation rather than the maximum fiber attenuation become apparent. The transmission distance of long-distance lines can reach farther distances. FTTH deployments can serve larger areas by increasing the radial distance between the Optical Line Terminal (OLT) at the CO end and the Optical Network Terminal (ONT) at the premise end. This ensures high-performance fiber contained in high-quality fiber, the most complete design capability and achievable application space available today.