Tomographic refractive index profile evaluation of non-symmetrical glass fiber preforms and fibers themselves

A method for determining a refractive index profile (RIP) of an object, the method comprising:

• (a) providing the object, the object including an optical object which has a longitudinal axis around which at least one layer extends outwardly wherein the at least one layer lacks a complete rotational symmetry in cross section;
• (b) scanning the object with a light beam, starting with a first projection angle, and creating raw data representing the object through measured data;
• (c) optionally rotating the object and repeating step (b) iteratively until all projection angles have been scanned and all measured data have been created;
• (d) processing the measured data to form a sinogram and, if the optional step (c) has been completed, proceeding to step (f);
• (e) rotating the object and repeating steps (b) and (d) iteratively until all projection angles have been scanned;
• (f) calculating a 2D RIP from the sinogram;
• (g) determining whether an RIP measurement artifact is present in the 2D RIP;
• (h) selecting a line section of interest within the 2D RIP to correct the RIP measurement artifact;
• (i) applying a fitting procedure to the line section of interest;
• and
• (j) determining refractive index steps/gradients and dimensions.