High precision measurement of refractive index profile of cylindrical glass bodies

Patent metadata

Field	Value
Publication number	US-9989458-B2
Application number	US-201514928018-A
Country	US
Kind code	B2
Filing date	Oct 30, 2015
Priority date	Oct 31, 2014
Publication date	Jun 5, 2018
Grant date	Jun 5, 2018

Abstract

According to some embodiments a method of measuring the refractive index profile of a consolidated glass body having a cylindrical surface comprises the steps of: (a) forming an image of a slit behind the glass body; (b) optionally pre-scanning the cylindrical surface of the test glass body or a reference glass body and analyzing the data within a fixed window to determine the likely location of the zero-order, un-diffracted beam while ignoring other diffracted beams; (c) optionally adjusting the optical power to improve the intensity of the data within the fixed window in order to improve the analysis; (d) predicting the trajectory of the zero-order beam through the preform based on the sampling location x i (incidence position) of the light impinging on the cylindrical surface and the location at which the zero-order beam impinges on the detector; (e) measuring the cylindrical surface of a glass body while using the estimated location of the zero-order beam and adjusted optical power to set the center of a floating window and the beam power at each measurement point; (e) determining deflection angles of the exiting zero-order beam within the floating window at each sampling location; (e) calculating the refractive index profile of glass body by utilizing a transformation function which determines refractive index at each location based upon the measured deflection angle function of the beam.

First claim

What is claimed is:

1. A method-of measuring the refractive index profile of a consolidated glass body with a cylindrical surface, the method comprising the steps of:
a. scanning the cylindrical surface of the consolidated glass body using an optical beam that emanates from an aperture, such that an image of the aperture is formed downstream from the consolidated glass body, between the consolidated glass body and at least one optical detector, and sampling the cylindrical surface with the optical beam at multiple sampling locations x i ;
the multiple sampling locations x i being separated by distances Δx, such that x i =x i−1 +Δx, with the image of the aperture having a width w, and Δx<w; wherein w is smaller than the diameter of the consolidated glass body;

b. detecting locations where zero-order optical beams and corresponding to the sampling locations x i impinge on at least one optical detector after passing through the consolidated glass body;
c. determining deflection angles of the zero-order beams corresponding to the multiple sampling locations x i ;
d. calculating the refractive index profile of the consolidated glass body based on the deflection angles of the zero-order optical beams corresponding to the multiple sampling locations.

2. The method according to claim 1 , the method further comprising the step of:
predicting the trajectory of the zero-order optical beams through the consolidated glass body based on (i) the sampling locations x i of the optical beam impinging on the cylindrical surface of the consolidated glass body, and (ii) the locations at which the corresponding zero-order beams impinge on the at least one optical detector.

3. A method of measuring the refractive index profile of a consolidated glass body with a cylindrical surface, the method comprising the steps of:
a. scanning the cylindrical surface of the consolidated glass body using an optical beam that emanates from an aperture, such that an image of the aperture is formed downstream from the consolidated glass body, between the consolidated glass body and at least one optical detector, and sampling the cylindrical surface with the optical beam at multiple sampling locations x i ;
b. detecting locations where zero-order optical beams corresponding to the sampling locations x i impinge on at least one optical detector after passing through the consolidated glass body:
c. determining deflection angles of the zero-order beams corresponding to the multiple sampling locations x i ;
d. calculating the refractive index profile of the consolidated glass body based on the deflection angles of the zero-order optical beams corresponding to the multiple sampling locations,
wherein
the image of the aperture has a width w, wherein measurement sampling spacing Δx across the cylindrical surface of consolidated glass body is less than or equal to w; and
for each sampling location x i of the scan, where x i =x i−1 +Δx, predicting a trajectory of the zero-order beam through the consolidated glass body based on sampling location x i of the optical beam impinging on the cylindrical surface and the location at which the zero-order beam is expected to impinge on the at least one optical detector; and
discarding from final analysis data for higher order diffracted beams that are detected by the detector.

4. The method according to claim 3 , wherein the step of calculating the refractive index profile of the consolidated glass body is performed by utilizing a transformation function which determines the refractive index at multiple locations within the consolidated glass body based on a deflection angle of the zero-order optical beam corresponding to one sampling location x i and the deflection angles of zero-order optical beams corresponding to prior sampling locations.

5. A method of measuring the refractive index profile of a consolidated glass body with a cylindrical surface, the method comprising the steps of:
a. scanning the cylindrical surface of the consolidated glass body using an optical beam that emanates from an aperture, such that an image of the aperture is formed downstream from the consolidated glass body, between the consolidated glass body and at least one optical detector, and sampling the cylindrical surface with the optical beam at multiple sampling locations x i ;
b. detecting locations where zero-order optical beams corresponding to the sampling locations x i impinge on at least one optical detector after passing through the consolidated glass body;
c. determining deflection angles of the zero-order beams corresponding to the multiple sampling locations x i ;
d. calculating the refractive index profile of the consolidated glass body based on the deflection angles of the zero-order optical beams corresponding to the multiple sampling locations wherein
the image of the aperture has a width w, wherein a measurement sampling spacing Δx across the cylindrical surface of consolidated glass body is less than or equal to w; and
for each sampling location x i of the scan, where x i =x i−1 +Δx, predicting a trajectory of the zero-order beam through the consolidated glass body based on the sampling location x i of the optical beam impinging on the cylindrical surface and the location at which the zero-order beam is expected to impinge on the at least one optical detector; and
discarding from final analysis data for small angle diffracted beams that are detected by the detector.

6. A method of measuring the refractive index profile of an optical fiber preform having a cylindrical surface comprising the steps of:
a. scanning the cylindrical surface of the optical fiber preform through multiple sampling location x i separated by distances Δx, such that x i =x i−1 +Δx with an illuminated slit such that an image of the slit is formed behind the optical preform, with the image of the slit having a width w, and Δx<w;
b. for each sampling location x i =x i−1 +Δx, predicting a trajectory of the zero-order beam through the preform based on the sampling location x i of the optical beam impinging on the cylindrical surface of the optical preform and the location at which the zero-order beam is expected to impinge on at least one optical detector;
c. detecting the location where the exiting zero-order beams corresponding to sampling location x i impinge on at least one optical detector, and discarding data about higher order diffracted beams and small angle diffracted beams detected by the at least one optical detector for each sampling location x i ;
d. determining a deflection angle of the exiting zero-order beam corresponding to each sampling location x i of the scan;
e. calculating the refractive index profile of the preform by utilizing a transformation function which determines the refractive index at each sampling location x i based on the deflection angle of the beam corresponding to that location and other scanned sampling locations that are adjacent to x i but greater in distance from the center of the preform.

7. The method of claim 6 , wherein said transformation function is an Abel transform.

8. The method of claims 6 , wherein w/8≤Δx≤w/2.

9. The method of claim 8 , wherein said scanning is performed with a slit that is 100 μm to 25 mm long and has a width w′ between 50 μm and 200 μm.

10. The method of claim 6 , wherein: (a) the slit is between 100 μm to 25 mm long and has a tapered width w′(z) along the direction of the axis of the preform z, and 50 μm ≤w′≤200 μm, and the image of the slit has width w(z), and (b) sampling spacing Δx between the multiple sampling locations x i is such that:
(⅛minimum slit width) ≤Δx≤(½minimum slit width).

11. The method of claim 10 further compri

Assignees

• Corning Inc

Inventors

• Cook Ian David
• Fontaine Norman Henry
• Wu Qi
• Gollier Jacques

Classifications

• G01N21/412 Primary

  Index profiling of optical fibres · CPC title

• G01M11/37

  in which light is projected perpendicularly to the axis of the fibre or waveguide for monitoring a section thereof · CPC title