3Com 5104M-FL1 Example Fiber Link With Mechanical Splice, Meter Fiber Link With Mechanical Splice

Maximum Link Distance Calculation

The following examples use the information provided in the previous pages to calculate the maximum allowable fiber optic link distance between two ports.

Example: Fiber Link With Mechanical Splice

In the following example, two ONline Concentrators are connected using fiber. If we use 62.5/125 fiber cable, the optical power budget according to Table 2-3 is 14.5 dB. Figure 2-1 shows an example of a 2000 meter fiber link with a mechanical splice.

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2000 meters

Mechanical

Splice

2.0 km Fiber Cable = 10 dB loss worst case using 5 dB/km loss fiber cable

1 Mechanical Splice = 1 dB loss worst case Path Loss = 11 dB

Figure 2-1. 2000 Meter Fiber Link With Mechanical Splice

The total path loss is 11 dB. Because the overall power budget is 14.5 dB, this leaves 3.5 dB to spare, so the link can be made.

Ensure you do not overdrive a receiver (that is, the received optical power level is not greater than the maximum receive sensitivity level of the fiber connector). In this case, the maximum possible transmit power, -12 dB + 3.0 dB = -9 dB (see Table 2-3). The power loss over the link is 11 dB. This means that the power level of the signal will drop to -20.0 dB by the time it reaches the receiver. Because the maximum receiver sensitivity is -8.0 dB, there is no overdrive problem.

Designing and Expanding the Network 2 - 11