OFDR Diagnostics by a Phase Change Detection

Yoh IMAI  Keigo IIZUKA  Masaaki IMAI  

IEICE TRANSACTIONS on Communications   Vol.E75-B   No.4   pp.281-284
Publication Date: 1992/04/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Advanced Optical Communication Technologies for New Applications)
optical communication,  

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A new type of optical frequency domain reflectometry is demonstrated. Optical carrier frequency is swept so that a phase of the backscattered light is shifted. Then, an interference output of the backscattered light is Fourier transformed. The farther the scattering point locates, the faster the phase of the backscattered light changes. Hence, the Fourier spectrum of the interference output displays the fault distribution along a wave-guide. In the present scheme, the theoretical resolution is inversely proportional to the frequency sweeping range of the optical source and is given by z=c/2nf, where f is the frequency sweeping range of the optical source. In a preliminary experiment, a Michelson type interferometer in which a target fiber of 20cm length is inserted in a probing arm. The reference arm is adjusted to be longer than the probing arm by about 1.8m. This is because the interference term between the backscattering light and the reference light should be separated from the interference term formed by the backscattering light itself. A LD pumped Nd: YAG ring laser whose frequency sweeping range is 20GHz is used as a variable wavelength source. The calculated resolution is 5mm for n=1.5 in fiber. A resultant spectrum in which the two peaks correspond to the reflections at both the fiber ends is obtained.