Measurement of axially nonsymmetrical refractive-index distributions of optical fiber preforms by a triangular mask method.

Nondestructive measurement of the axially nonsymmetrical refractive-index distribution of an optical fiber preform is described. A new method, called the triangular mask, is employed to measure the deflection angle of the probing rays that travel through the preform. This method is somewhat similar to, but a little simpler than, the spatial filtering technique used in the measurement of axially symmetrical preforms by Sasaki et al. Most of the data collections and processing are automated. The 2-D index distribution is computed from the deflection angles. The accuracy of the computer algorithm is estimated by computer simulations. Examples of experimental results are compared with the results of a destructive measuring technique.