US 12,422,359 B2
Tomographic refractive index profile evaluation of non-symmetrical glass fiber preforms and fibers themselves
Maximilian Schmitt, Buford, GA (US); and Carl Ponader, Buford, GA (US)
Assigned to HERAEUS QUARTZ NORTH AMERICA LLC, Bulford, GA (US); and HERAEUS QUARZGLAS GMBH & CO. KG, Hanau (DE)
Filed by Heraeus Quartz North America LLC, Buford, GA (US); and Heraeus Quarzglas GmbH & Co. KG, Hanau (DE)
Filed on Jun. 26, 2023, as Appl. No. 18/214,156.
Prior Publication US 2024/0426750 A1, Dec. 26, 2024
Int. Cl. G01N 21/41 (2006.01); G01N 21/39 (2006.01); G01N 21/88 (2006.01); G01N 21/17 (2006.01)
CPC G01N 21/412 (2013.01) [G01N 21/39 (2013.01); G01N 21/4133 (2013.01); G01N 21/8851 (2013.01); G01N 2021/1787 (2013.01); G01N 2021/399 (2013.01); G01N 2021/4153 (2013.01); G01N 2021/4193 (2013.01); G01N 2021/8887 (2013.01); G01N 2201/0633 (2013.01); G01N 2201/0813 (2013.01); G01N 2201/104 (2013.01)] 15 Claims
OG exemplary drawing
 
1. 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.