Fiber Span Analysis

Span analysis is the calculation and verification of a fiber-optic system's operating characteristics. This encompasses items such as fiber routing, electronics, wavelengths, fiber type, and circuit length. Attenuation and nonlinear considerations are the key parameters for loss-budget analysis. Before implementing or designing a fiber-optic circuit, a span analysis is recommended to make certain the system will work over the proposed link. Both the passive and active components of the circuit have to be included in the loss-budget calculation. Passive loss is made up of fiber loss, connector loss, splice loss, and losses involved with couplers or splitters in the link. Active components are system gain, wavelength, transmitter power, receiver sensitivity, and dynamic range.

Nonlinear effects occur at high bit rates and power levels. These effects must be mitigated using compensators, and a suitable budget allocation must be made during calculations.

The overall span loss, or link budget as it is sometimes called, can be determined by using an optical meter to measure true loss or by computing the loss of system components. The latter method considers the loss associated with span components, such as connectors, splices, patch panels, jumpers, and the optical safety margin. The safety margin sets aside 3 dB to compensate for component aging and repair work in event of fiber cut. Adding all of these factors to make sure their sum total is within the maximum attenuation figure ensures that the system will operate satisfactorily. Allowances must also be made for the type of splice, the age and condition of the fiber, equipment, and the environment (including temperature variations).

August 30, 2011

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