Tunable backscattering for single-mode optical fibers in 1.1-1.6-µm spectral region

A very powerful and versatile backscattering apparatus for single-mode fibers has been implemented, which can be tuned to almost every wavelength in the spectral region from 1.06 to 1.6 μm. A Raman source fiber, pumped by a Nd:YAG laser, is filtered by a special conception monochromator (folded path) which, by preserving the image of the output face of the source fiber, allows good launching efficiency into the fiber under test. Directional coupling with suppression of Fresnel reflection is achieved by an acoustooptic modulator, which is insensitive to polarization. Applications to single-mode fibers characterization are discussed, like spectral attenuation, cutoff phenomena as function of length and spot-size propagation.