hi,
The simplest couplers are fiber optic splitters. These devices possess at least three ports but may have more than 32 for more complex devices. Figure 1 illustrates a simple 3-port device, also called a tee coupler. It can be thought of as a directional coupler directional coupler. One fiber is called the common fiber, while the other two fibers may be called input or output ports. The coupler manufacturer determines the ratio of the distribution of light between the two output legs. Popular splitting ratios include 50%-50%, 90%-10%, 95%-5% and 99%-1%; however, almost any custom value can be achieved. (These values are sometimes specified in dB values.) For example, using a 90%-10% splitter with a 50 µW light source, the outputs would equal 45 µW and 5 µW. However, excess loss hinders that performance. All couplers and splitters share this parameter. Excess loss assures that the total output is never as high as the input. Loss figures range from 0.05 dB to 2 dB for different coupler types. An interesting, and unexpected, property of splitters is that they are symmetrical. For instance, if the same coupler injected 50 µW into the 10% output leg, only 5 µW would reach the common port.
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