Apparatus and method for determining refractive index profile in a cylindrical article

• US 4,441,811 A
• Filed: 09/10/1981
• Issued: 04/10/1984
• Est. Priority Date: 09/10/1981
• Status: Expired due to Fees

• Current Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Original Assignee: Corning Glass Works Inc. (Corning Incorporated)
• Inventors: Smith, David J., Melezoglu, Cevdet
• Primary Examiner(s): ROSENBERGER, RICHARD A
• Application Number:
  US06/300,796
• Time in Patent Office: 943 Days
• Field of Search: 356/73.1, 356/128, 356/129
• US Class Current: 356/128
• CPC Class Codes: G01N 21/412 Index profiling of optical fibres

Abstract

Apparatus and a method for analyzing the refractive index profile of a cylindrical, transparent optical waveguide preform, utilizing a scanning light beam to traverse a fixed preform and a refractor to direct light deflected by the preform onto a displacement sensor, is described.

Claims

1. In optical apparatus for analyzing the optical characteristics of a transparent, cylindrical, radially symmetric article comprising source means for generating a narrow collimated beam of light along a path, rotatable reflecting means positioned at an interception point on the path for reflecting light from the interception point over a range of selected angles in a scanning plane, support means for supporting the transparent cylindrical article in index-matching fluid at a fixed work station in the scanning plane such that the article intersects said plane at right angles thereto, first convergent refracting means L1 having focal length f₁ positioned between the reflecting means and the work station and on an optical axis joining the interception point and the cylinder axis of the article for directing light from the reflecting means through the cylindrical article, second convergent refracting means L2 of focal length f₂ positioned on the optical axis behind the article to refract the light traversing the article, and displacement sensor means on the optical axis behind refractor L2 for intercepting the light refracted thereby, the improvement characterized in that:

the second convergent refractor L2 of focal length f₂ is positioned a distance f₂ from the cylinder axis of the article, with the displacement sensor being positioned a distance f₂ from the second convergent refractor L2, such that a displacement value d(t) output by the sensor, corresponding to the displacement from the optical axis at the sensor of a narrow light beam reaching the sensor from the source, corresponds exactly to the ray displacement function (t-y(t)) from the integral expression;

##EQU6## for calculating the refractive index profile of a cylindrical article.

2. In the method of determining a refractive index value n(r) at radius r of a transparent, cylindrically symmetric article of outer radius a and outer refractive index n_c wherein parallel light rays are directed through a planar cross-section of the article at entrance heights t corresponding to the distances of the rays from an optical axis parallel with the rays and intersecting the cylinder axis of the article, and the points of intersection y(t) of the rays exiting the cylinder with an observation plane spaced a distance L from the cylinder axis are ascertained and used to calculate the value of n(r) from the integral expression:

##EQU7## the improvement wherein a convergent refractor L2 of focal length f₂ is positioned on the optical axis at a distance f₂ from the cylinder axis of the article to intercept a narrow collimated light beam traversing the cylinder from the source, said refractor then directing the beam onto a displacement sensor positioned a distance f₂ from refractory L2 such that the value of the displacement d(t) of the beam from the optical axis at the displacement sensor corresponds to and can be substituted for the value (t-y(t)) in the said integral expression.