New Metrics for Optical Cable Attenuation Optimized

Over the years, single-core fiber attenuation in the largest fiber optic cable has become the industry standard for fiber attenuation performance. This ensures that the system designer can account for the worst-case attenuation of the link design. Thanks to today's highly advanced fiber and cable manufacturing techniques, the frequency of maximum fiber attenuation events in these cables is increasingly rare, and secondly, more representative attenuation specifications are necessary.

This proposed metric, Link Design Attenuation (based on typical attenuation), defines a more practical value of attenuation for use in cable performance analysis and system design.

background

Historically, the maximum single-core fiber attenuation in a fiber optic cable has been used as a specification for fiber attenuation performance. This is necessary in the past, due to the discontinuity of fiber splices, the non-uniformity of fiber-based attenuation, and the early stage of cabling processing, which may cause the fiber attenuation value in some fiber optic cables to be significantly higher than other fibers in the same fiber optic cable. System designers and end users design the attenuation values ​​for these highest attenuation fibers as protection specifications for maximum attenuation.

During this period, average cabled fiber loss was sometimes considered a means of masking multiple high attenuation fibers in a cable. Averaging does not adequately define the fiber attenuation distribution in a cable, especially when the cable contains multiple high attenuation fibers. In this regard, manufacturers and industry standardize maximum fiber attenuation to protect end users from inaccurate mathematical calculations that do not accurately represent the attenuation performance of individual fiber optic cables.

The fiber optic cable industry has undergone tremendous improvements in its nearly 40-year history. Significant improvements in fiber attenuation, such as lower attenuation coefficients and reduced point discontinuity specifications. Likewise, the fiber optic cabling industry has also highly improved its processes to greatly reduce or even eliminate additional attenuation in the cabling process, known as cabling variables. Even the measurement systems used to evaluate the performance of fiber optic cables in factories and in the field have improved considerably. As a result, the actual single fiber attenuation in the cable deviates significantly from the specified maximum single fiber attenuation. System designers continue to base link loss calculations as a basis for worst-case attenuation, but these instances are much less frequent than their historical specification.

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 that more precisely defines the attenuation of the fiber optic cable and "built-up" link, while maintaining some degree of conservatism in relation to the maximum single-core fiber specification.

link design attenuation

To determine how this new metric is specified, the fiber attenuation distribution in an actual fiber optic cable is a random sampling of the average attenuation values ​​generated, spanning from two to twenty fiber lengths. The resulting plots, shown in Figures 1A and 1B, with up to 20 fiber optic connections, were then analyzed to determine the required span to approach steady state. The number of links spanning steady state represents the minimum required to produce a technically credible 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.

Tandem fiber attenuation distribution for multiple fiber links

Additional statistical processing is required in order to correctly generate the proposed specification. The limit for link design attenuation can be derived at the steady state point, which is shown to be eight serial links. In Figures 2A and 2B, the proposed link design attenuation is represented by the green line, representing the 99.9% confidence threshold according to 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.

Concatenated Fiber Attenuation Distribution for Multi-Fiber Links

The industry has established a precedent (IEC 60794-3) for the definitive application of PMD in statistical processing link design. To maintain consistency with existing standards, twenty spans may be used to determine link design attenuation values. Monte Carlo simulations show that only eight spans are sufficient to achieve a stable performance of link design attenuation. Using the extra span does not result in a significant increase in capability. In addition, the smaller number of spans helps to better align the specification with the access network. Table 1 provides an example of how link design decay can benefit customers by ensuring higher levels of performance.

Comparison of Maximum Fiber Attenuation Characteristics

Several benefits of utilizing this link design attenuation instead of maximum fiber attenuation become apparent. The transmission distance of long-distance lines can reach longer distances. Fiber-to-the-home deployments can serve larger areas by increasing the radial distance between the optical line terminal (OLT) at the central office end and the optical network terminal (ONT) at the premises end. This ensures that high-performance fibers contained in a high-quality fiber optic cable, today's fullest design capabilities, and application space that can be realized.

Summarize

The full performance of the optical fiber system cannot be achieved by using the maximum attenuation value of the optical fiber in the network design optical cable. Tier 1 cable manufacturers such as Optical Communications have made improvements in the cabling process, and the use of a new metric, link design attenuation (based on typical values ​​from our spec sheet) can be used to determine a system's loss budget. The supporting data clearly shows that this still provides an acceptable degree of conservatism for network designers.