Link power penalty

The extinction ratio of a laser in an optical transmission link is defined as the ratio of the optical power for a logic 1 signal to the power for a logic 0 signal. Ideally, the extinction ratio should be infinite. However, the ratio must be finite in an actual system in order to reduce the rise time of the laser pulses [16]. The nonzero power transmission for a bit of logic 0 causes the power penalty. The power penalty due to the extinction ratio (in linear units) is estimated by... 

Figure 7.15 Design of Gl POF acceptable for Gigabit Ethernet based on link power budget. Broken line denotes limit on power penalty due to the ISI specified by Gigabit Ethernet.

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