Optical coherence effects on a fiber-sensing Fabry-Perot interferometer

The temporal coherence effect of a light source on a fiber-optic Fabry-Perot interferometer is described. The ratio of the end-mirror separation h to the coherence length L(c) of a single-frequency laser source gives an important parameter to specify the transmission characteristics of the interferometer. A criterion to determine the largest permissible mirror separation, h(c), is discussed and given by h(c) = (0.l/2pi)L(c), The peak transmission and finesse are heavily dependent on the ratio h/L(c). The sensing sensitivity is also discussed in association with the ratio h/L(c).