Endface assessment

Abstract

Features of the endface of a dielectric member are assessed by means of a reflected diffraction pattern. A plurality of light beams 6, 7 which intersect in a region containing the endface 8 can be used to generate a diffraction pattern 10 which subtends an angle of at least 180° at the endface 8. Such a diffraction pattern 10 contains information about the endface 8 and may be used, in particular, to locate the plane in which the endface 8 lies. Embodiments of the invention find particular application in the measurement of endface angles of optical fibres.

I claim: 
     
       1. Apparatus for use in assessing endfaces of dielectric members .Iadd.having a longitudinal axis.Iaddend., comprising .Iadd.mounting .Iaddend.means for mounting a dielectric member such that its end portion is exposed, .Iadd.directing .Iaddend.means for directing collimated light from a plurality of directions onto the inner surface of the endface of the member, .Iadd.said directing means and said mounting means being cooperable such that each of said directions forms an angle less than 90° with the longitudinal axis of said dielectric member, .Iaddend.each such direction being fixed relative to the endface, such as to generate a diffraction pattern which subtends an angle of not less than 180° at the endface, and means to detect at least .[.part.]. .Iadd.180° .Iaddend.of .[.a.]. .Iadd.the .Iaddend.diffraction pattern so generated. 
     
     
       2. Apparatus according to claim 1 wherein said directions each lie at an angle in the range from greater than 0° up to and including 25° to the endface. 
     
     
       3. Apparatus according to claim 2 wherein said directions each lie at the same angle to the endface. 
     
     
       4. Apparatus according to any one of claims 1 to 3 wherein the means for directing light comprises means for directing two mutually orthogonal laser beams to intersect in a region containing the endface. 
     
     
       5. Apparatus according to claim 1, 2 or 3 wherein the diffraction pattern comprises a first part and a second part, the first part being generated by light transmitted through the dielectric member and reflected at the endface and the second part being generated by light transmitted through the dielectric member without reflection at the endface. 
     
     
       6. Apparatus according to claim 1, 2 or 3 wherein the means to detect comprises a substantially hemicylindrical screen whose axis intersects the endface and lies perpendicular to each .[.preselected.]. direction. 
     
     
       7. Apparatus according to claim 1, 2 or 3 wherein the light is monochromatic. 
     
     
       8. A method of assessing the endface of a dielectric member which comprises the steps of mounting the dielectric member such that its end portion is exposed, directing collimated light from a plurality of directions onto the inner surface of the endface of the member, each such direction being fixed relative thereto, such as to generate a diffraction pattern which subtends an angle of not less than 180° at the endface, and detecting the pattern so generated. 
     
     
       9. A method according to claim 8 which further comprises the step of measuring the distance between a portion of the diffraction pattern and a reference marker. 
     
     
       10. A method according to claim 9 wherein the diffraction pattern comprises first part and a second part, the first part being generated by light transmitted through the dielectric member and reflected at the endface, and the second part being generated by light transmitted through the dielectric member without reflection at the end face, the first part being said portion and the second part being said reference marker. 
     
     
       11. A method according to claims 9 or 10 further comprising the step of calculating the endface angle of the dielectric member from the measurement. .Iadd.12. Apparatus according to claim 1 wherein said means for detecting includes a surface for receiving the diffraction pattern, a reference mark on said surface and indicia on said surface for measuring the distance between a portion of the diffraction pattern and the reference mark to ascertain the endface angle of said dielectric member. .Iaddend. .Iadd.13. Apparatus according to claim 12 wherein the diffraction pattern comprises a first part and a second part, the first part being generated by light transmitted through the dielectric member and reflected at the endface and the second part being generated by light transmitted through the dielectric member without reflection at the endface, said reference mark being generated by said second diffraction 
     
     
        pattern part. .Iaddend. .Iadd.14.  Apparatus for use in determining the endface angle of a dielectric member relative to its longitudinal axis, comprising mounting means for mounting a dielectric member such that its end portion is exposed, directing means for directing collimated light from a plurality of directions onto the inner surface of the endface of the member, each such direction being fixed relative to the endface, such as to generate a diffraction pattern which subtends an angle of not less than 180° at the endface, means to detect at least 180° of the diffraction pattern so generated, and means for determining the endface angle of the dielectric means directly from said detection means. .Iaddend. .Iadd.15. Apparatus according to claim 14 wherein said directions each lie at an angle in the range of from greater than 0° up to and including 25° to the endface. .Iadd.16. Apparatus according to claim 15 wherein said directions each lie at the same angle to the endface. .Iaddend. .Iadd.17. Apparatus according to claim 14 wherein the means for directing light comprises means for directing two mutually orthogonal laser beams to intersect in a region containing the endface. .Iaddend. .Iadd.18. Apparatus according to claim 14 wherein the diffraction pattern comprises a first part and a second part, the first part being generated by light transmitted through the dielectric member and reflected at the endface and the second part being generated by light transmitted through the dielectric member without reflection at the endface. .Iaddend. .Iadd.19. Apparatus according to claim 14 wherein the means to detect comprises a substantially hemicylindrical screen whose axis intersects the endface and lies perpendicular to each direction. .Iaddend. .Iadd.20. Apparatus according to claim 14 wherein the light is monochromatic. .Iaddend. .Iadd.21. Apparatus according to claim 14 wherein said means for detecting includes a surface for receiving the diffraction pattern, a reference mark on said surface and indicia on said surface for measuring the distance between a portion of the diffraction pattern and the reference mark to ascertain the 
     
     
        endface angle of said dielectric member. .Iaddend. .Iadd.22.  Apparatus according to claim 21 wherein the diffraction pattern comprises a first part and a second part, the first part being generated by light transmitted through the dielectric member and reflected at the endface and the second part being generated by light transmitted through the dielectric member without reflection at the endface, said reference mark being generated by said second diffraction pattern part. .Iaddend. .Iadd.23. Apparatus according to claim 22 wherein said surface comprises a substantially hemicylindrical screen whose axis intersects the endface and lies perpendicular to each said direction. .Iaddend.