Ferrule-core concentricity measurement systems and methods
Systems and methods of measuring ferrule-core concentricity for an optical fiber held by a ferrule are disclosed. The method includes: generating ferrule distance data by measuring distances to a ferrule outside surface as a function of rotation angle using a distance sensor and rotating either the ferrule or the distance sensor about an axis of rotation that is off-center from the true ferrule axis; aligning the axis of rotation with the fiber core; using the ferrule distance data to determine a position of the true ferrule center relative to the optical fiber core; and measuring the concentricity as the distance between the true center of the ferrule and the optical fiber core.
1. A system for measuring ferrule-core concentricity for an optical fiber held in a central bore of a ferrule, wherein the ferrule has a ferrule outer surface and a ferrule front end, and wherein a section of the optical fiber resides in the central bore of the ferrule at the ferrule front end, the system comprising:
a light source configured to be optically coupled to the optical fiber and emit light that travels through the optical fiber core and out of a front end of the optical fiber;
a distance sensor arranged to measure a ferrule distance between the ferrule outer surface and the distance sensor;
a core sensor arranged to receive and detect light emitted from the optical fiber core at the ferrule front end, the core sensor comprising a substantially doubly telecentric light-collection optical system that collects light emitted by the optical fiber core; and
a rotatable support member that supports the distance sensor and the core sensor relative to the ferrule, the rotatable support member being configured to simultaneously rotate the distance sensor and core sensor about a common axis of rotation, wherein the distance sensor is configured to measure ferrule distance data during rotation and the core sensor is configured to measure core location data during rotation.
2. The system according to claim 1 , wherein the core sensor comprises:
a sensing optical fiber having a front end that receives the collected light; and
a photodetector optically coupled to the sensing optical fiber and that detects the collected light from a back end of the sensing optical fiber.
3. The system according to claim 1 , wherein the core location data comprises optical power data, and wherein the optical fiber core and the axis of rotation are aligned such that the optical power data is substantially constant.
4. The system according to claim 1 , wherein the rotatable support member rotates between rotation angles in the range 0°≤θ≤360°.
5. The system according to claim 1 , wherein:
the light-collection optical system forms an image of the front end of the ferrule and the optical fiber core; and
the core sensor comprises a two-dimensional (2D) image sensor that receives the image of the front end of the ferrule and the optical fiber core and forms therefrom a corresponding digital image.
6. The system according to claim 1 , wherein the core sensor comprises:
a sensing optical fiber having a front end that receives the collected light and an opposite back end;
a reflecting member arranged at the back end of the sensing optical fiber and that reflects the collected light back through the optical fiber and the light-collection optical system and to the optical fiber core;
a light-redirecting element optically coupled to the optical fiber and that redirects the light from the light-collection optical system; and
a photodetector optically coupled to the light-redirecting member and that detects the light from the light-redirecting element.
7. The system of claim 1 , wherein the distance sensor is selected from the group of distance sensors comprising: a laser triangulation gauge, a spectral interference gauge, a capacitance distance gauge, and an interferometer gauge.
8. The system of claim 1 , wherein the core location data comprises either optical digital images of the optical fiber core and ferrule front end or power measurements of light transmitted by the optical fiber core.
9. The system of claim 1 , wherein:
the system further comprises optical connection lines providing optical signal communication to the distance sensor and core sensor; and
a rotation stage attached to the rotatable support member and comprising a rotational feed-through, wherein the optical connection lines pass through the rotational feed-through.
10. The system according to claim 9 , wherein:
the system further comprises a computer or control device that calculates the ferrule-core concentricity from a spectral interference distance calculation using the ferrule distance data and the core location data; and
the spectral interference distance calculation is, to a first approximation, not a function of optical intensity of an optical signal transmitted by the optical connection lines such that disturbances in the coupling of the rotational feed-through that could occur during rotation will not cause artifacts in the concentricity calculation.