Simple fiber-optic Fabry-Perot sensor

In this paper we describe a simple interferometer which relies upon the interference of light reflected from the ends of a single length of a single-mode fiber. The fiber length thus forms a long-path plane mirror fiber Fabry-Perot (FFP) interferometer. In the scheme reported uncoated fiber ends are used, and the interference due to backreflected light from both ends is monitored. This configuration has an advantage in that the source and detector electronics are used near the same fiber end, while the other is left free. Measurements of the backreflected light also ensure good fringe visibility, and for uncoated fiber ends, near perfect cosine squared fringes are generated. In this way the sensor more closely represents a common path Michelson interferometer. A further advantage of this scheme may be realized by employing a multimode laser and matching the free spectral range of the FFP to the longitudinal mode spacing of the laser.