A defocused transfer function of experimental microscopic bright-field images, closely connected with the evaluation of the relative refractive index profile of axially symmetric optical fibers, is presented. It is shown that with this function it is possible to obtain, with high precision, the defocused bright-field images of investigated fibers from their focus images and then to easily evaluate the relative refractive index profiles of the fibers.
A simple experimental technique for the measurement of refractive index profiles of axially symmetric optical fibers is presented. This method is based on image phase gradients introduced into a transmitted optical field by a fiber sample. An image of the phase gradients is obtained using a technique based on bright field microscopy. Then a relative refractive index profile of optical fibers is reconstructed by means of the inverse Abel transform.
Using a simple non-destructive and non-interferometric technique, we obtained an approximation of the average index
profile for a partially symmetrical air-silica microstructured optical fiber. The method proposed in [1] for conventional
fibers, where an image of the phase gradients is introduced into a transmitted optical field by a fiber sample, was used.
An image of the phase gradients was obtained using a technique based on bright field microscopy. Then, an average of
the refractive index profile for optical fibers was reconstructed using the inverse Abel transform.
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