[OPTICAL REVIEW Vol. 9, No. 2 (2002) 49-53]
Spatial Resolution Enhancement in BOTDR by Spectrum Separation Method
Natsuki NITTA, Mitsuhiro TATEDA and Takashige OMATSU
Graduate School of Science and Technology, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
(Received August 28, 2001; Accepted January 25, 2002)
BOTDR (Brillouin optical-fiber time domain reflectometry) is a promising technique for measuring the strain distribution along an optical fiber which can be used for diagnosing civil structures. However, there is a trade-off between the spatial and the frequency resolutions, and its practical spatial resolution is limited to about 1 m; to date the application scope has been restricted. In order to enhance the spatial resolution without decreasing the measurement accuracy, we intentionally introduce two kinds of strain within the spatial resolution length determined by the optical pulse width, which results in Brillouin gain spectrum separation. In this paper, we describe the theoretical analysis of the spectrum separation method together with experimental verification, where a spatial resolution of 0.5 m is demonstrated. We further propose a new parabolic data fitting method especially effective in the spectrum separation method.
Key words: BOTDR, strain distribution, spatial resolution, Brillouin gain spectrum, spectrum separation, fitting a parabola