Systems and methods for measuring the stress profile of ion-exchanged glass
First Claim
1. A method of measuring a stress profile of an ion-exchanged glass substrate based on TM and TE guided mode spectra from an optical waveguide defined in part by an ion-exchange region, the method comprising:
- digitally defining from the TM and TE guided mode spectra respective TM and TE intensity profiles corresponding to TM and TE guided modes, including;
a) coupling light into the optical waveguide through a coupling prism optically coupled to the optical waveguide to define a prism-waveguide interface;
b) reflecting light from the prism-waveguide interface, the reflected light representative of the TM and TE guided mode spectra; and
c) detecting the reflected light with a photodetector array;
determining positions of intensity extrema of the TM and TE intensity profiles;
calculating respective TM and TE effective refractive indices from the positions;
calculating TM and TE refractive index profiles nTM(z) and nTE(z) where z is a distance from a substrate surface by performing one of a) an inverse WKB calculation based on the TM and TE effective refractive indices, or b) fitting calculated guided mode spectra to the TM and TE guided mode spectra using one or more respective assumed functions for nTM(z) and nTE(z); and
calculating the stress profile S(z)=[nTM(z)−
nTE(z)]/SOC, where SOC is a stress optic coefficient for the glass substrate.
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Abstract
Systems and methods for measuring the stress profile of ion-exchanged glass are disclosed, based on the TM and TE guided mode spectra of the optical waveguide formed in the ion-exchanged glass. The method includes digitally defining from the TM and TE guided mode spectra positions of intensity extrema, and calculating respective TM and TE effective refractive indices from these positions. The method also includes calculating TM and TE refractive index profiles nTM(z) and nTE(z) using either an inverse WKB calculation or a fitting process that employs assumed functions for nTM(z) and nTE(z). The method also includes calculating the stress profile S(z)=[nTM(z)−nTE(z)]/SOC, where SOC is a stress optic coefficient for the glass substrate. Systems for performing the method are also disclosed.
108 Citations
16 Claims
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1. A method of measuring a stress profile of an ion-exchanged glass substrate based on TM and TE guided mode spectra from an optical waveguide defined in part by an ion-exchange region, the method comprising:
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digitally defining from the TM and TE guided mode spectra respective TM and TE intensity profiles corresponding to TM and TE guided modes, including; a) coupling light into the optical waveguide through a coupling prism optically coupled to the optical waveguide to define a prism-waveguide interface; b) reflecting light from the prism-waveguide interface, the reflected light representative of the TM and TE guided mode spectra; and c) detecting the reflected light with a photodetector array; determining positions of intensity extrema of the TM and TE intensity profiles; calculating respective TM and TE effective refractive indices from the positions; calculating TM and TE refractive index profiles nTM(z) and nTE(z) where z is a distance from a substrate surface by performing one of a) an inverse WKB calculation based on the TM and TE effective refractive indices, or b) fitting calculated guided mode spectra to the TM and TE guided mode spectra using one or more respective assumed functions for nTM(z) and nTE(z); and calculating the stress profile S(z)=[nTM(z)−
nTE(z)]/SOC, where SOC is a stress optic coefficient for the glass substrate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method of measuring a stress profile formed in an ion-exchanged glass substrate having a surface and a stress optic coefficient SOC, comprising:
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digitally capturing TM and TE guided mode spectra of an optical waveguide defined by the ion-exchanged glass substrate, including performing said digitally capturing the TM and TE guided mode spectra by imaging light representative of the TM and TE guided mode spectra onto a photodetector having pixels with a pixel size, and wherein the curve-fitting includes determining the positions of the TM and TE intensity extrema with a resolution smaller than the pixel size; determining positions of intensity extrema of the TM and TE guided mode spectra by applying curve-fitting to portions of the TM and TE guided mode spectra to establish the respective TM and TE intensity extrema; calculating respective TM and TE effective refractive indices from the positions; calculating TM and TE refractive index profiles nTM(z) and nTE(z) where z is a distance from the substrate surface by performing one of a) an inverse WKB calculation based on TM and TE effective refractive indices, respectively, or b) fitting calculated guided mode spectra to the TM and TE guided mode spectra using one or more assumed functions for nTM(z) and nTE(z); and calculating the stress profile S(z)=[nTM(z)−
nTE(z)]/SOC.- View Dependent Claims (10, 11, 12)
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13. A system for measuring a stress profile of an ion-exchanged glass substrate having a surface, a stress optic coefficient SOC and an ion-exchange region that in part defines an optical waveguide, comprising:
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a photodetector array having an array of pixels and configured to detect light representative of TM and TE guided mode spectra of the optical waveguide and form therefrom a digital representation of the TM and TE guided mode spectra; a controller configured to receive the digital representation of the TM and TE guided mode spectra, the controller having instructions stored in a computer-readable medium that cause the controller to carry out the following calculation to calculate the positions of intensity extrema in the TM and TE guided mode spectra to sub-pixel resolution; determine positions of intensity extrema in the TM and TE guided mode spectra; calculate respective TM and TE effective refractive indices from the positions; calculate, from the TM and TE effective refractive indices, TM and TE refractive index profiles nTM(z) and nTE(z), where z is a distance from the substrate surface, either by performing an inverse WKB calculation or by fitting calculated guided mode spectra to the TM and TE guided mode spectra using one or more assumed functions for nTM(z) and nTE(z); and calculate the stress profile S(z)=[nTM(z)−
nTE(z)]/SOC. - View Dependent Claims (14, 15, 16)
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Specification