Method of measuring circularity of an optical fiber
Distortion introduced by an imaging system is characterized by positioning a generally cylindrical object and imaging optics in a first relative angular position about an axis of rotation that substantially coincides with the longitudinal axis of the object and employing the imaging optics to image the end face of the object on a detector. First and second definitions of the shape of the image of the periphery of the end face of the object are extracted from image data provided by the detector when the object and the imaging optics are in first and second relative angular positions. The first and second definitions are compared.
1. A method of characterizing distortion introduced by an imaging system that comprises imaging optics and a detector, the method comprising:
providing a generally cylindrical object having a peripheral surface, an end face and a longitudinal axis,
positioning the object with the longitudinal axis substantially coinciding with an axis of rotation, the object and the imaging optics being in a first relative angular position about the axis of rotation,
employing the imaging optics to image the end face of the object on the detector,
extracting a first definition of the shape of the image of the periphery of the end face of the object from image data provided by the detector when the object and the imaging optics are in the first relative angular position,
effecting relative rotation of the imaging optics and the object about the axis of rotation to a second relative angular position,
extracting a second definition of the shape of the image of the periphery of the end face of the object from image data provided by the detector when the object and the imaging optics are in the second relative angular position,
calculating a function that characterizes measurement distortion introduced by the imaging system, and
applying said function to at least one of the first and second definitions to determine physical distortion of the peripheral surface of the cylindrical object.
2. A method according to claim 1 , comprising effecting relative rotation of the object and the imaging system about the axis of rotation to at least third and fourth angular positions, extracting third and fourth definitions of the shape of the image of the periphery of the end face of the object from image data provided by the detector when the object is in the third and fourth angular positions respectively, and mathematically effecting a relative transform of the first, second, third and fourth definitions to a common center and angular position.
3. A method according to claim 2 , wherein the step of calculating the function that characterizes measurement distortion introduced by the imaging system utilizes an ensemble of definitions of the shape of the image of the periphery of the end face of the object.
4. A method of characterizing a feature of an optical fiber segment composed of a core and a cladding, the fiber segment having an end face and a longitudinal axis and the cladding having a peripheral surface, the method comprising:
positioning the fiber segment with the longitudinal axis of the fiber segment substantially coinciding with an axis of rotation, the fiber segment being in a first angular position about the axis of rotation,
imaging the end face of the fiber segment on a detector,
extracting a first definition of the shape of the peripheral surface of the cladding at the end face of the fiber segment from image data provided by the detector when the fiber segment is in the first angular position,
effecting relative rotation of the fiber segment and the detector about the axis of rotation to a second angular position,
extracting a second definition of the shape of the peripheral surface of the cladding at the end face of the fiber segment from image data provided by the detector when the end face of the fiber segment is in the second angular position,
calculating a function that characterizes measurement distortion of the first and second definitions, and
applying said function to at least one of the first and second definitions to determine physical distortion of the peripheral surface of the cladding.
5. A method according to claim 4 , comprising effecting relative rotation of the fiber segment and the detector about the axis of rotation to at least third and fourth angular positions, extracting third and fourth definitions of the shape of the peripheral surface of the cladding at the end face of the fiber segment from image data provided by the detector when the end face of the segment is in the third and fourth angular positions respectively, and mathematically effecting a relative transform of the first, second, third and fourth definitions to a common center.
6. A method according to claim 4 , wherein the image of the end face of the fiber segment includes an edge between the core and the cladding and the method comprises:
extracting a first definition of the shape of the edge from image data provided by the detector when the fiber segment is in the first angular position,
extracting a second definition of the shape of the edge from the image data provided by the detector when the end face of the fiber segment is in the second angular position, and
comparing the first and second definitions of the shape of the edge.
7. A method according to claim 6 , further comprising effecting relative rotation of the fiber segment and the detector about the axis of rotation to at least third and fourth angular positions, extracting third and fourth definitions of the shape of the edge from image data provided by the detector when the end face of the segment is in the third and fourth angular positions respectively, and mathematically effecting a relative transform of the first, second, third and fourth definitions of the shape of the edge to the common center.
8. A method according to claim 7 , comprising adjusting each of the first, second, third and fourth definitions of the shape of the edge to define an ellipse, each ellipse having a center, defining the locus of the centers of the ellipses, and defining a circle that optimally fits the locus of the centers of the ellipses.
9. Apparatus for characterizing a feature of an optical fiber segment composed of a core and a cladding, the fiber segment having an end face and a longitudinal axis and the cladding having a peripheral surface, the apparatus comprising:
a holder for positioning the fiber segment with the longitudinal axis of the fiber segment substantially coinciding with an axis of rotation,
a detector,
a lens for imaging the end face of the fiber segment held by the holder on the detector,
a mechanism for effecting relative rotation of the fiber segment and the detector about the axis of rotation to at least first and second distinct angular positions,
a processor for acquiring image data provided by the detector when the fiber segment is in the first and second angular positions relative to the detector, the processor being programmed to
extract a first definition of the shape of the peripheral surface of the cladding at the end face of the fiber segment from the image data provided by the detector when the fiber segment is in the first angular position,
extract a second definition of the shape of the peripheral surface of the cladding at the end face of the fiber segment from the image data provided by the detector when the end face of the fiber segment is in the second angular position,
calculate a function that characterizes measurement distortion of the first and second definitions, and
apply said function to at least one of the first and second definitions to determine physical distortion of the peripheral surface of the cladding.