Apparatus and methods for measuring mode spectra for ion-exchanged glasses having steep index region

• US 9,983,064 B2
• Filed: 10/24/2014
• Issued: 05/29/2018
• Est. Priority Date: 10/30/2013
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Roussev, Rostislav Vatchev, Schneider, Vitor Marino
• Primary Examiner(s): Ton, Tri
• Assistant Examiner(s): BRYANT, REBECCA CAROLE
• Application Number:
  US14/523,171
• Publication Number:
  US 20150116713A1
• Time in Patent Office: 1,313 Days
• CPC Class Codes: G01J 4/02 Polarimeters of separated-field type; Polarimeters of half-shadow type
• CPC Class Codes: G01N 2021/4126 Index of thin films
• CPC Class Codes: G01N 2021/434 Dipping block in contact with sample, e.g. prism
• CPC Class Codes: G01N 21/23 Bi-refringence
• CPC Class Codes: G01N 21/43 by measuring critical angle
• CPC Class Codes: G02B 5/04 Prisms
• CPC Class Codes: G02B 5/06 Fluid-filled or evacuated prisms
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence

Abstract

Apparatus and methods for measuring mode spectra for ion-exchanged glass substrates having a steep index region are disclosed. An interfacing fluid is provided between the coupling prism and the glass substrate. The interfacing fluid thickness is selected so that the variation in modal birefringence with fluid thickness is reduced to an acceptable level. The coupling prism can include a prism coating on the coupling surface so that the substrate-prism interface includes the prism coating. The coupling prism can also include stand-off members that serve to define the thickness of the interfacing fluid.

Claims

1. A method of measuring TM and TE mode spectra of an ion-exchanged glass substrate having a bulk refractive index n_s, a surface, a refractive index profile n as a function of depth x below the surface, and a near-surface region R1, comprising:

interfacing a coupling prism of refractive index n_p to the substrate surface to define a prism-substrate interface, with an interfacing fluid of refractive index n_f and thickness d1 residing between the coupling prism and substrate surface, wherein n_f≤

n_s<

n_p, wherein region R1 satisfies

2. The method of claim 1, further comprising providing one or more stand-off members on at least one of the coupling surface of the coupling prism and the substrate surface to define the thickness d1.

3. The method of claim 1, wherein the coupling prism includes a coupling surface having a coating, wherein the coating comprises a coating thickness d2 and a coating refractive index n_c, wherein n_c≤

n_f.

4. The method of claim 3, wherein the coating thickness d2 and the coating refractive index n_c satisfy 0.2λ

≤

n_c·

d2≤

0.8λ

.

5. The method of claim 3, wherein at least one of the interfacing fluid thickness d1 and the coating thickness d2 is constant as a function of position.

6. The method of claim 3, wherein n_c+0.15(n_eff^t−

n_c)≤

n_f≤

n_c+0.30(n_eff^t−

n_c), where n_eff^t represents a middle of a target range of an effective index n_eff where lowest-order modes of the TE and TM mode spectra are expected to occur.

7. The method of claim 3, wherein (n_s−

0.01)≤

n_f≤

n_s.

8. The method of claim 3, wherein the prism coating comprises SiO₂, CaF₂, or MgF₂.

9. The method of claim 1, wherein the interfacing fluid has a median thickness d1_m, and wherein (0.5)·

d1_m≤

d1≤

(1.5)·

d1_m at all positions in the area illuminated by the measuring light.

10. A method of measuring TM and TE mode spectra of an ion-exchanged glass substrate having a bulk refractive index n_s, a surface, a refractive index profile n as a function of depth x below the surface, and with a near-surface region R1, comprising:

interfacing a coupling prism of refractive index n_p to the substrate surface to define a prism-substrate interface, with the coupling prism having a coupling surface with a coating, the coating having a coating thickness d2 and a coating refractive index n_c wherein 0.2λ

≤

n_c·

d2≤

0.8λ

;

providing an interfacing fluid of refractive index n_f and thickness d1 between the prism coating and substrate surface, wherein n_c≤

n_f≤

n_s<

n_p, wherein region R1 satisfies

11. The method according to claim 10, further comprising selecting indices n_c and n_f and coating thickness d2 such that a variation of mode birefringence Δ

B≤

B_tol for at least first and second lowest-order modes for each of the TM and TE mode spectra, where B_tol is a tolerance on the variation in the mode birefringence.

12. The method of claim 10, wherein the coating thickness d2 and the coating refractive index n_c satisfy 0.45λ

≤

n_c·

d2≤

0.8λ

.

13. The method of claim 10, wherein n_c+0.15(n_eff^t−

n_c)≤

n_f≤

n_c+0.30(n_eff^t−

n_c) where n_eff^t represents a middle of a target range of an effective index n_eff where lowest-order modes of the TE and TM mode spectra are expected to occur.

14. The method according to claim 10, wherein the glass substrate includes in-diffused K+ and Ag+ ions.