Fiber optical frequency domain reflectometer

One of the main ways to develop nondestructive testing devices for fiber communication systems is to use optical reflectometry in the frequency domain (OFDR) and the LFM-technique. There are some problems in OFDR-systems which are determined by the complexity degree of modulation type realization, low energy characteristics of frequency modulators and large scattering losses on reflectometer units in general. In the present paper we consider some common and special solutions for these problems. Especially a new LFM-technique based on dual-frequency laser radiation, which can help us to develop a compact reflectometer, is presented. Basic consideration of single frequency radiation transformation into two frequency radiation is given. The elements of the LFM technique for the reflectometer are given. We determined the output radiation parameters and their connection with the degree of internal and external disturbances and coordinates along the axis of the fiber, and calculated the accuracy characteristics of system. We showed that two frequency output radiation carried more information and could help us to obtain results close to that of the two-mode reflectometer. The experimental set-up of a structural testing system and the first practical results are given.