Over the years, single core fiber attenuation has become the industry standard of optical fiber attenuation performance in the largest optical cable. This ensures that the system designer can take into account the worst case of attenuation in link design. Relying on today's highly advanced fiber and cable manufacturing technologies, the frequency of the largest optical fiber attenuation events in these cables is becoming rarer and rarer, and secondly, a more representative attenuation specification is also necessary. This proposed index, link design attenuation (based on typical attenuation), defines a more practical attenuation value, which is applied to fiber optic cable performance analysis and system design.
Historically, the largest single core fiber attenuation has been used as a standard for optical fiber attenuation. It is necessary that, in the past, due to the discontinuity of optical fiber contacts, the non-uniformity of fiber attenuation and the initial stage of wiring processing may result in the attenuation of optical fiber in some optical cables significantly higher than that in other optical fibers. System designers and end users design the attenuation values of these maximum attenuation fibers as the maximum attenuation protection specification.
During this period, the average loss of cable optical fiber is sometimes considered to be the means to mask multiple high attenuation optical fibers. On average, the attenuation of optical fiber in optical cable is not fully defined, especially when the fiber optic cable contains multiple high attenuation optical fibers. In this regard, manufacturers and industries standardize the maximum optical attenuation, in order to protect the end-user due to inaccurate mathematical operation, not accurately show the attenuation performance of individual optical cable. Fiber optic cable industry in the past 40 years of history, has undergone tremendous improvements. The attenuation of optical fiber is obviously improved, such as lower attenuation coefficient and lower cross section specification. Similarly, the optical cabling industry also highly improves its process to greatly reduce or even eliminate the additional attenuation in routing, called wiring variables. Even the measurement system used to evaluate the performance of the factory and the field fiber optic cable has improved a lot. As a result, the actual single fiber attenuation in the optical cable deviates significantly from the specified maximum single fiber attenuation. System designers continue to compute link loss as the basis for worst-case attenuation, but these instances are much lower than their historical specifications. The maximum performance of optical links may not be achieved due to the conservative nature of the largest single core optical fiber specifications. Obviously, another indicator is needed to more accurately define the attenuation of the optical cable and the "built" link, while maintaining a certain degree of conservatism related to the specification of the largest single core fiber.
Link design attenuation
To determine how this new metric is specified, the attenuation of fiber distribution in a real optical cable is the average attenuation produced by random sampling, spanning two to twenty lengths of fiber. Results as shown in figures 1A and 1B, as many as 20 cables are connected, and then analyzed to determine the required span close to the steady state. The number of links reaching a steady state represents the minimum value required to produce a reliable average decay rate. Graphs 1A and 1B clearly illustrate stable optical fiber attenuation after only eight series connection. You can use other methods to achieve the same result.
Figure 1A (left), 1B (right): a plurality of optical fiber link serial optical fiber attenuation distribution
Additional statistical processing is needed to generate the recommended specifications correctly. The limit of the link design attenuation can be obtained at the steady state point, which is proved to be the eight series link. In figure 2A and 2B in the design of the link attenuation by the green line, according to the eight link representation of 99.9% confidence threshold. This result supports the concept of using link design attenuation to optimize network design and maintain a reasonable frequency band protection.
The industry has established a precedent for statistical processing of PMD applications in link design (IEC 60794-3). In order to maintain consistency with the existing standards, twenty spans can be used to determine the link design attenuation values. Monte Carlo simulations show that only eight spans are sufficient to achieve the stable performance of link design attenuation. The use of extra spans does not result in significant enhancement of capacity. In addition, a smaller span helps to align the specification with the access network better. Table 1 provides an example of how link design attenuation benefits customers by ensuring a higher level of performance.
Table 1: link design attenuation examples and comparison of the largest fiber attenuation characteristics in the currently implemented ITU-T G652.D standard
Several advantages of using this link to design attenuation instead of maximum fiber attenuation become apparent. The transmission distance of long distance lines can be longer. The deployment of fiber to the home 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 house end. This ensures high performance fiber in a high quality fiber optic cable, the most adequate design capabilities, and the available application space.
Using the network to design the maximum attenuation of optical fiber in optical cable can not achieve all the performance of optical fiber system. First class optical cable manufacturers, such as Corning communications in the wiring process improvements, the use of a new metric, link design attenuation (from our specification table based on typical values) can be used to determine the loss budget of a system. Supporting data clearly shows that it still provides an acceptable Conservatism for network designers.