METHOD OF ENHANCING CONTRAST IN PRISM COUPLING MEASUREMENTS OF STRESS

• US 20150308897A1
• Filed: 04/21/2015
• Published: 10/29/2015
• Est. Priority Date: 04/23/2014
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Roussev, Rostislav Vatchev, Young, Emily Elizabeth
• Granted Patent: US 9,696,207 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01J 3/0205 Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
• CPC Class Codes: G01J 3/0229 using masks, aperture plates, spatial light modulators or spatial filters, e.g. reflective filters
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01L 1/241 by photoelastic stress analysis
• CPC Class Codes: G01L 1/242 the material being an optical fibre
• CPC Class Codes: G01N 2021/4166 Methods effecting a waveguide mode enhancement through the property being measured
• CPC Class Codes: G01N 21/4133 Refractometers, e.g. differential
• CPC Class Codes: G01N 21/552 Attenuated total reflection

Abstract

A method and apparatus for improving contrast in prism coupling measurements of waveguide mode spectra, wherein the measured waveguide sample has a surface region of rapidly decreasing index, characterized with normalized slope |λ/n dn/dz|>0.0004. An opaque light-blocking element is placed in the portion of the light beam closest to the plane of the contact between prism and measured sample, on the input side, output side or both sides of the prism. The light blocking element prevents light from the light source to reach a portion of the length of the prism-sample coupling interface along the optical path, prevents light reflected from a portion of the aforementioned length to reach the detector, or both when input and output light-blocking elements are used.

Claims

1. A method of measuring waveguide mode spectra, the method comprising:

forming a coupling interface between a coupling surface of a prism and a surface of a waveguide, the waveguide having a surface region of decreasing index with normalized slope |λ

/n dn/dz|>

0.0004, the surface region extending from a surface into the waveguide sample, and the prism having an input surface and an output surface;

disposing an opaque light-blocking element on at least one of the input surface and the output surface in a portion of a path of a light beam emanating from a light source, the portion being closest to a plane of contact between the coupling surface and the waveguide sample;

at least one of;

blocking at least a portion of the light beam with the opaque light-blocking element, wherein the portion of the light beam is prevented from reaching a portion of the coupling surface along the path of the light beam; and

blocking a first portion of light reflected from the coupling interface with the opaque light-blocking element, wherein the first portion is prevented from reaching a detector;

allowing a second portion of light reflected from the coupling interface to reach the detector; and

detecting the second portion with the detector at a position corresponding to a lowest-order mode, and is less than or equal to 7 times the maximum possible effective coupling length of the lowest-order mode or 7 mm, whichever is less.

2. The method of claim 1, wherein the position corresponding to the lowest-order mode is less than or equal to 5 times the maximum effective coupling length.

3. The method of claim 2, wherein the at least one light-blocking element is located within 30 mm of an edge of the prism.

4. The method of claim 2, wherein the at least one light-blocking element is located within 7 mm of an edge of the prism.

5. The method of claim 2, wherein the waveguide further includes a deep region of decreasing index, the deep region penetrating to a depth of at least 170λ

/n from a surface of the waveguide, and having normalized slope

6. The method of claim 5, wherein the depth of the deep region is at least 200λ

/n.

7. The method of claim 6, wherein at the least one light-blocking element is located at least 30 mm from a plurality of edges of the prism, and provides a substantial difference in illuminated interaction length or detected interaction length between the lowest-order mode and the highest-order mode.

8. The method of claim 7, wherein the light-blocking element is located less than or equal to 100 mm from each of the edges of the prism.

9. A method of measuring waveguide mode spectra, the method comprising:

forming a coupling interface between a coupling surface of a prism and a surface of a waveguide, the waveguide having a surface region of decreasing index with normalized slope |λ

/n dn/dz|>

0.0004, the surface region extending from a surface into the waveguide sample, and the prism having an input surface and an output surface;

disposing an opaque light-blocking element on at least one of the input surface and the output surface in a portion of a path of a light beam emanating from a light source, the portion being closest to a plane of contact between the coupling surface and the waveguide sample, wherein the light-blocking element has a transmission, the transmission being a variable function of distance from the plane of contact with the transmission increasing as the distance from the plane of contact increases, and wherein the light-blocking element having the variable transmission is not a circular aperture;

at least one of;

blocking at least a portion of the light beam with the opaque light-blocking element, wherein the portion of the light beam is prevented from reaching a portion of the coupling surface along the path of the light beam; and

blocking a first portion of light reflected from the coupling interface with the opaque light-blocking element, wherein the first portion is prevented from reaching a detector;

allowing a second portion of light reflected from the coupling interface to reach the detector; and

detecting the second portion with the detector at a position corresponding to a lowest-order mode, and is less than or equal to 7 times the maximum possible effective coupling length of the lowest-order mode or 7 mm, whichever is less.

10. The method of claim 9, wherein the light-blocking element is a plate having spatially varying absorption.

11. The method of claim 9, wherein the light-blocking element has a shape with more open space near a first side that is distal from the prism-sample coupling plane.

12. The method of claim 11, wherein the light-blocking element is made of essentially opaque material.

13. The method of claim 11, wherein the variation in open space from the first side to the prism-sample coupling plane is achieved by a V-shaped cutout.

14. The method of claim 13, wherein of the V-shaped cutout forms an angle of between about 30 degrees and about 50 degrees.

15. The method of claim 9, wherein the light-blocking element is positioned up to 100 mm from at least one edge of the prism.

16. The method of claim 9, wherein the light-blocking element is positioned up to 10 mm from at least one edge of the prism.

17. The method of claim 9, wherein light-blocking elements are disposed on both the input side and the output side of the prism.

18. The method of claim 9, wherein the light-blocking element having the transmission that is a variable function of distance is disposed on one side of the prism and in the optical path, and a rectangular light-blocking element having spatially non-varying transmission is disposed on an opposite side of the prism and in the optical path.