Optical Frequency Domain Reflectometry (OFDR) is a special technology which is used for the analysis of optical light paths and reflection characteristics in optical fibers and components. Unlike Optical Time Domain Reflectometry (OTDR) OFDR works in the frequency domain using continuous wave (CW) light sources which enables higher signal to noise ratios. In a typical OFDR system a tunable laser source is swept over a certain wavelength band (e.g. 1535nm-1565nm). The light is then sent into a fiber and consequently brought into interference with a reference arm. From the Fourier transformation of the resulting signal the spatial distribution of the reflected light is measured. The reflection can results from the intrinsic Rayleigh scattering of the glass or can be enlarged by in fiber, low reflective, continuously written Fiber Bragg Gratings (FBG). The measurement of strain and temperature is done by tracking the changes of the Rayleigh or FBG reflection pattern or peaks. The advantage of using FBGs over Rayleigh is an increased signal to noise ratio which leads to higher measurement speeds. With OFDR measurement technology it is possible to measure strain or temperature in sub-Millimeter resolution over several 10´s of meters.