US 12,345,629 B2
Enhanced evanescent prism coupling systems and methods for characterizing stress in chemically strengthened curved parts
Rostislav Vatchev Roussev, Painted Post, NY (US); and Nathaniel David Wetmore, Corning, NY (US)
Assigned to CORNING INCORPORATED, Corning, NY (US)
Filed by CORNING INCORPORATED, Corning, NY (US)
Filed on Nov. 28, 2022, as Appl. No. 18/070,022.
Claims priority of provisional application 63/283,594, filed on Nov. 29, 2021.
Prior Publication US 2023/0168186 A1, Jun. 1, 2023
Int. Cl. G01N 21/31 (2006.01); G01N 21/25 (2006.01); G01N 21/27 (2006.01)
CPC G01N 21/31 (2013.01) [G01N 21/255 (2013.01); G01N 21/274 (2013.01); G01N 2201/0634 (2013.01); G01N 2201/127 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A method of obtaining a corrected digital mode spectrum for a chemically strengthened (CS) substrate having a curved surface and a near-surface waveguide adjacent the curved surface, comprising:
optically coupling a measurement light beam into and out of the near-surface waveguide using a coupling prism, the coupling prism interfaced with the curved surface of the CS substrate to define a coupling interface;
transmitting the measurement light beam coupled out of the near-surface waveguide through the coupling prism along an axis through a detector optical system to a digital detector;
digitally capturing transverse magnetic (TM) and transverse electric (TE) mode spectra of the CS substrate with the digital detector, the evanescent prism coupling system having a system calibration for measuring flat CS substrates, wherein the TM and TE mode spectra comprise respective TM and TE mode lines having a variable spacing Δx and a corresponding effective index difference Δneff wherein Δx∝Δneff for the system calibration;
establishing a calibration correction representative of a difference in the digitally captured TM and TE mode spectra as compared to a reference TM and TE mode spectra for a reference CS substrate;
applying the calibration correction to the digital mode spectrum image to form the corrected digital mode spectrum that can be processed using the system calibration for measuring flat CS substrates; and
processing the corrected digital mode spectrum using the system calibration to determine at least one of:
a) a refractive index profile of the CS substrate; or
b) one or more stress-related characteristics of the curved CS substrate being measured.