Methods for non-destructively determining parameters of an optical fiber preform
AssigneeWestern Electric Company, Inc.
InventorLaurence S. Watkins
Life of this patent
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Abstract
A narrow laser beam (16) scans a clad optical fiber preform (10) with a narrow, parallel scanning beam of coherent light and the deflection angle (.theta.) thereof measured as the beam exits the preform. The deflection angles (.theta.) of the scanning beam (16) are measured and compared to theoretical or empirically developed deflection angle scans of preforms having known parameters to determine the parameters of the preform. The deflection angle (.theta.) is plotted versus the incident beam position (d) and that plot is integrated to provide a curve (47) that is compared to theoretically developed plots having known parameters to determine parameters of the fiber preform such as refractive index gradient power, .gamma., and the refractive index ratio, .DELTA..
Claims12
A method of determining parameters of a cylindrical optical fiber preform having a core and a cladding, comprising the steps of:
- scanning at least a portion of the cylindrical surface of the preform with a narrow, parallel scanning beam of coherent light, the parallel scanning beam being located within a plane which is perpendicular to the longitudinal axis of the preform, said beam passing through and being refracted by said preform;
- detecting the angular deflections of the refracted scanning beam exiting the preform;
- and
- comparing the detected angular deflections of the scanning beam with angular deflections of beams passing through preforms having known parameters to determine the parameters of the preform.
A method of determining the acceptability of the uniformity and homogeneity of deposited layers in a cylindrical optical fiber preform having a cladding about a graded index core, comprising the steps of:
- scanning at least a portion of the cylindrical surface of the preform with a narrow, parallel scanning beam of coherent light, the parallel scanning beam being located within a plane which is perpendicular to the longitudinal axis of the preform, said beam passing through and being refracted by said preform;
- detecting the angular deflection of the beam as the beam exits the preform;
- and
- comparing the detected angular deflections of the beam with angular deflections of the beam through preforms having acceptable ranges of uniformity and homogeneity.
A method of non-destructively determining the refractive index gradient power, .gamma., in a cylindrical optical fiber preform having a cladding about a graded index core, comprising the steps of:
- (1) scanning at least a portion of the surface of the preform with a narrow, parallel scanning beam of coherent light, the parallel scanning beam being located within a plane which is perpendicular to the longitudinal axis of the preform, said beam passing through and being refracted by said preform;
- (2) detecting the angular deflection of the light beam as the beam exits the preform;
- (3) plotting a curve of the detected deflection angle versus the position of the scanning light beam;
- (4) integrating the curve of the detected deflected angle;
- (5) fitting a polynomial curve to the integrated deflection angle curve;
- and
- (6) determining the refractive index gradient power, .gamma., by comparing the coefficients of the polynomial to theoretically developed curves of the polynomial coefficients versus .gamma..
Apparatus for determining parameters of a cylindrical optical fiber preform having a core and a cladding, comprising:
- means for scanning at least a portion of the cylindrical surface of the preform with a narrow, parallel scanning beam of coherent light, the parallel scanning beam being located within a plane which is perpendicular to the longitudinal axis of the preform, said beam passing through and being refracted by said preform;
- means for detecting the angular deflection of the beam as the beam exits the preform;
- and
- means for comparing the detected angular deflections of the beam with angular deflections passing through preforms having known parameters to determine the parameters of the preform.
Dependencies are inferred from the claim text.