Interferometric measurement method for guide holes and fiber holes parallelism and position in multi-fiber ferrules

Abstract

An interferometric measurement method precisely determines parallelism and 3D position of guide pin holes and fiber holes in multi-fiber ferrules used in connectors. The parallelism and position are measured for the ferrule with inserted reference guide pins and reference fibers by scanning the ferrule from side in an interferometric system. Fiber hole deviations from designated locations on the ferrule end face and distance between the fiber holes and the guide pin holes are calculated as well.

Claims

1. A method for interferometric measurement of the geometry of a multi-fiber optic ferrule used in a connector, the method comprising: positioning one or more fibers into a respective one or more fiber holes in the ferrule; positioning guide pins into at least respective first and second guide pin holes in the ferrule; and scanning a side face of the ferrule with an interferometric microscope to obtain interferometric data of at least the one or more fibers and guide pins, wherein the side face of the ferrule is perpendicular to an end face of the ferrule and the one or more fibers pass through the end face, where the end face is positioned one of perpendicular or parallel to an optical axis of the interferometric microscope.

2. The method of claim 1, wherein the interferometric data is obtained by focusing the interferometric microscope on a side face of the guide pins and a side face of the one or more fibers and obtaining a fringe pattern on the guide pins and the one or more fibers.

3. The method of claim 1, further comprising: determining angles of the guide pins relative to the optical axis based on the interferometric data to determine the parallelism of the guides pins relative to one another; and determining angles between the one or more fibers and the system Z axis that is defined as an average line between the guide pin axes.

4. The method of claim 1, further comprising: determining based on the interferometric data one or more of (a) deviations of the one or more fiber hole locations from a designated location for each respective fiber hole; (b) a distance between the one or more fiber holes, and (c) a distance between the guide pin holes.

5. The method of claim 1, wherein the one or more fibers are conventional fibers with bare fiber ends.

6. The method of claim 1, wherein the one or more fibers further comprise reference objects similar in geometrical dimensions to the conventional fibers with bare fiber ends and are made of a hard material such that the objects will not deform by their own weights.

7. The method of claim 1, wherein the guide pins are conventional guide pins used in male multi-fiber connectors.

8. The method in claim 1, wherein the guide pins comprise objects having geometrical dimensions similar to conventional guide pins used in male multi-fiber connectors and are made of a hard material.

9. The method of claim 1, further comprising: positioning the ferrule relative to the interferometric microscope with a fixture configured to position the ferrule end face position parallel to the optical axis of the interferometric microscope and position the ferrule for scanning of the side face of the ferrule.

10. The method of claim 1, further comprising: positioning the ferrule relative to the interferometric microscope with a fixture that includes a mirror element configured to turn the optical axis of the interferometric microscope by 90 degrees and enable the ferrule end face to be positioned perpendicular to the optical axis of the interferometric microscope.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The presented method can be better understood with reference to the following drawings. Like reference numerals designate corresponding parts throughout several drawings.

(2) FIG. 1 is a schematic view of the measurement system in its exemplary embodiment.

(3) FIG. 2 is a top view of a measurement object ready for testing.

(4) FIG. 3 is a schematic view of the measurement system which includes a connector fixture equipped with a mirror.

(5) FIG. 4 is a flowchart of the measurement method in accordance with the present invention.

(6) FIG. 5 is an end face view of the object being measured that illustrates the optical interface coordinate system and fiber hole deviations along axis X and Y.

(7) FIG. 6 is a top view of the object being measured with the illustrated guide pin angles.

(8) FIG. 7 is a side view of the object being measured with the illustrated guide pin angles.

(9) FIG. 8 is a top view of the object being measured with the illustrated fiber angles.

(10) FIG. 9 is a side view of the object being measured with the illustrated fiber angles.

REFERENCE NUMERALS IN THE DRAWINGS

(11) TABLE-US-00001 1 interferometric microscope 2 opening on the microscope front panel 3 special fixture for side measurements of multi- 4 multi-fiber ferrule ready for measurement fiber connectors 5, 5′ reference guide pins 6, 6′ guide pin holes 7, 7′ axes of the reference guide pins 8 system Z axis 9, 9′ X angles between the system Z axis and the 10, 10′ Y angles between the system Z axis and reference guide pins' axes the guide pins' axes 11 reference fiber ribbon 12 X angle between the system Z axis and the first fiber in the ribbon 13 X angle between the system Z axis and the 14 X angle between the system Z axis and the second fiber in the ribbon last fiber in the ribbon 15 Y angle between the system Z axis and the 16 Y angle between the system Z axis and the first fiber in the ribbon second fiber in the ribbon 17 Y angle between the system Z axis and the 18 fiber holes (top view) last fiber in the ribbon 19 designated locations of fiber holes on the 20 fiber hole in its real location end face 21 fiber hole deviation along axis X 22 fiber hole deviation along axis Y 23 special fixture with a mirror element for measurements of multi-fiber connectors 24 enlarged mirror element

DETAILED DESCRIPTION OF THE INVENTION

(12) Reference will now be made in detail to the presented measurement method illustrated in the accompanying drawings.

(13) FIG. 1 illustrates an exemplary embodiment of the present invention. The reference number 1 represents an interferometric microscope. A special fixture 3 for side measurements of multi-fiber ferrules is mounted on the microscope which has an opening 2 to receive the fixture. A multi-fiber ferrule 4 is inserted into the fixture for side face measurements. The ferrule contains first and second reference guide pins and a reference fiber ribbon inserted into the ferrule as explained by FIG. 2.

(14) FIG. 2 shows a top view of a multi-fiber ferrule 4 in a state ready for testing. In original state, the multi-fiber ferrule has first and second guide holes 6 and 6′ in which first and second alignment guide pins 5 and 5′ are inserted. The multi-fiber ferrule 4 also has a number of fiber holes 18, depending on the type of a multi-fiber connector being manufactured. The number of the fiber holes could vary from 2 for MTRJ multi-fiber connectors, to 4, 6, 8, 12, 16, 24, 48, 72 and other for other connector types. FIG. 2 schematically shows only first two and last two fiber holes.

(15) The fiber holes can be arranged in rows. The number of fiber rows in multi-fiber connectors could exceed one. The measurement method represented in the present invention allows measuring the parallelism of the fiber holes for one fiber row or for multiple fiber rows. For simplicity purposes, the multi-fiber ferrule is illustrated with one row on the accompanying drawings.

(16) The measurement method represented in the present invention is aimed at interferometric measurement of guide holes 6 and 6′ parallelism and fiber angles of a multi-fiber ferrule.

(17) In the original state of the ferrule, the two guide holes 6 and 6′ are empty. To make the interferometric measurements of the guide holes possible, two reference guide pins 5 and 5′ are inserted into the guide holes as shown on FIG. 2. Any guide pins that are used in manufacturing of male MTRJ or MTP/MPO fiber optic connectors can be used for this purpose. The reference guide pins are inserted into the ferrule for measurement purposes in the same way they are inserted for the purpose of manufacturing male multi-fiber connectors.

(18) Alternatively, it is possible to use other objects similar to the guide pins by their geometrical dimensions and made of hard materials.

(19) In the original state of the ferrule being measured, the fiber holes 18 are empty. For the purpose of the interferometric measurements, a reference fiber ribbon 11 is inserted into the fiber holes. The reference fiber ribbon 11 should be prepared for measurements. Fiber ends in the ribbon should be stripped from the outer coating so that bare fiber ends rise above the end face surface for the purpose of interferometric measurements as shown on FIG. 2. The lengths for which the bare fiber ends should rise above the surface are limited by the interferometric microscope field of view, from few microns to any larger length. The larger the length the better the measurement precision.

(20) FIG. 3 shows the interferometric system in which a multi-fiber ferrule is positioned along the optical axis of the microscope. It consists of interferometric microscope 1 with opening 2 for mounting a fixture 23 with inserted ferrule 4. The fixture 23 is equipped with a prism element 24 that has a mirror coating on its base rectangular side. The mirror turns the interference image from the connector side face by 90 degrees and directs it into the microscope objective. The mirror side of the prism element can have a rectangular ledge when there is a need to decrease scanning range and measurement time.

(21) FIG. 4 illustrates a method of measuring the parallelism of guide holes and fiber holes, as well as fiber hole locations, in multi-fiber ferrules used in connectors according to the present invention. The parallelism is measured by an interferometric microscope. Special fixture for side face scanning is provided together with the microscope for positioning of the ferrule in the measurement system. The special fixture is mounted on the interferometric microscope and the ferrule is inserted into the fixture.

(22) According to the proposed method, the ferrule is measured with inserted reference fiber ribbon with bare fiber ends and the reference guide pins. The fiber ribbon is prepared for measurements as described in the explanation for FIG. 2 and has bare fiber ends.

(23) After the ferrule is inserted into the special fixture and is ready for measurements, the interferometric microscope is focused and a fringe pattern is successively obtained on the reference guide pins and the reference fiber ribbon. Interferometric data is obtained from the reference guide pins and the reference fiber ribbon.

(24) Then calculations of relative angles of the reference guide pins along axis X and along axis Y are performed. When the relative angles are known, the position of the system Z axis which is the averaged line of the two guide pin holes is determined.

(25) The final two steps are calculations of angles X and Y between each fiber hole and the system Z axis. Deviations from designated location along axis X and Y for each fiber and distance between fiber holes and guide hole are calculated as well.

(26) FIG. 5 explains a system of coordinates X and Y. An X-axis passes through centers of first and second guide holes 6 and 6′ on the ferrule end face. A perpendicular Y-axis passes through the midpoint of the line connecting the guide hole centers.

(27) FIG. 5 also illustrates deviations of fiber holes from designated locations on the end face. Only one fiber in its deviated location is shown schematically.

(28) The reference number 19 represents designated locations of the fiber holes according to the industry standards. The reference number 20 represents a fiber hole deviated from its designated location.

(29) The fiber hole deviations along axes X and Y are shown by number 21 and 22 respectively.

(30) The top and side views of the ferrule 4 represented on FIG. 6 and FIG. 7 respectively demonstrate relative angles of the axes 7 and 7′ of the reference guide pins 5 and 5′. The reference numerals 9 and 9′ designate the angles along axis X between the averaged line 8 (the system Z axis) and the guide pin axes 7 and 7′ respectively.

(31) The reference numerals 10 and 10′ designate the angles along axis Y between the averaged line 8 (the system Z axis) and the guide pin axes 7 and 7′ respectively.

(32) The top and side views of the ferrule 4 represented on FIG. 8 and FIG. 9 respectively demonstrate the angles between the fiber axes in the reference fiber ribbon 11 and the system Z axis 8. For simplicity reasons, only first, second and last fibers are shown on FIG. 8 and FIG. 9. The reference numerals 12, 13 and 14 designate the angles along axis X between the averaged line 8 and the axes of the first, second and last fiber respectively.

(33) The reference numerals 15, 16 and 17 designate the angles along axis Y between the system Z axis 8 and the axes of the first, second and last fibers respectively.