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Pulse width is another important parameter to choose. The pulse of light sent by the IU into the fiber should be limited in time duration so that it does not impede the functionality of the interferometer. Strain measurement is created from the interference of the pulse of light going through both the direct (short) path and the long path through the gauge length delay coil. The time duration of the pulse should be chosen so that backscattered energy from the short path does not interfere or overlap with the time window containing the backscatter energy traveling along the long path. Figure 2.4 shows the suggested pulse widths associated with gauge lengths. The value of using a long pulse width as compared to a short one is that more light enters the fiber, and an improved SNR is obtained; however, if the pulse width used is too long so that the time footprint of the pulse is longer than the gauge length, the quality of the strain measurement drops.

Figure 2.4 Recommended pulse width as a function of gauge length.