optical frequency domain reflectometry (OFDR)

Optical Frequency Domain Reflectometry (OFDR) is a method for determining backscatter which, in contrast to Optical Time Domain Ref lectometry( OTDR), is based on the wavelength measurement of light and not on the temporal assignment of the reflected light signal.

In Optical Frequency Domain Reflectometry, a continuous wave signal is injected into the optical fiber. The injected light is reflected at minute inhomogeneities that may be in the grating structure and changes its wavelength due to Raman scattering. The backscattered light reaches the input of the optical fiber, where its wavelength is measured.

Due to the continuous wave operation and a narrow band detection of the backscattered wavelength, a much higher signal-to- noise ratio is achieved with OFDR. The light detected for measurement is evaluated by signal processing in the wavelength, its magnitude and phase. Conclusions about the fault location are only possible if the detected backscattered signal is evaluated as a function of frequency in its complex form by means of Fourier transformation.