Optics: measuring and testing – For optical fiber or waveguide inspection
Patent
1990-05-17
1991-08-27
McGraw, Vincent P.
Optics: measuring and testing
For optical fiber or waveguide inspection
G01N 2184, G01B 1126
Patent
active
050429434
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the assessment of the endfaces of dielectric members, and in particular to the measurement of cleaved optical fibre endface angles. Throughout this specification, the term endface angle should be taken to means the angle between the endface of an optical fibre and the plane perpendicular to the axis of the fibre.
The quality of the endface of an optical fibre can be highly important, particularly in fusion splicing of fibres, and in terminating coupler arrays and devices. In the former case, it is important for the cleaved endface of an optical fibre to be substantially perpendicular to the axis of the fibre, since a non-perpendicular endface can introduce serious misalignment at a fibre splice. Also when terminating a coupler array, it is important that the cleaved endface lies at a sufficiently large angle to the fibre axis to prevent substantially all back-reflection (to avoid cross-talk in duplex systems for example).
Fibre endfaces are commonly produced by cleaving, using dedicated cleaving apparatus. A known method of assessing the quality of a fibre end, particularly in terms of the endface angle, relies on the combination of the angle of reflection of light at the endface and diffraction. This method is described in the following paper: "A measurement technique for optical fibre break angles", C. A. Millar, Opt. Quant., 13 pp 125-131 (1981). A modification of this method is described in European Patent Specification No. 167269.
The main disadvantage of known methods utilising diffraction techniques is that they are difficult to do, and need considerable skill to achieve acceptable results. They are, therefore, not particularly suitable for fields use, where the operator often does not have the requisite skills.
The aim of the invention is to provide an improved method of, and apparatus for, measuring the endface angle of an optical fibre. In particular, the invention aims to provide means for measuring the endface angle of an optical fibre that requires little skill to use, and so can be carried out by normal field operators.
The present invention provides apparatus for measuring the endface angle of a cleaved optical fibre, the apparatus comprising a light source for injecting optical energy into that end of an optical fibre opposite to that whose endface angle is to be measured, means for tapping optical energy passing along the optical fibre in both directions, and means for measuring the signal strength of the optical energy tapped from the optical fibre in both directions, whereby the ratio of said measured signal strengths can be compared with a known relationship between endface angles and the ratio of said measured signals to provide a measure of the endface angle.
In a preferred embodiment, the tapping means is constituted by a pick-up element defining a curved optical waveguiding path, and clamping means for clamping the optical fibre into a curved position which at least substantially conforms to the inner side of the curved path, such that optical energy passing along the optical fibre in both directions is tapped into the curved optical waveguiding path. Advantageously, the pick-up element has a curved portion joining two straight portions, the curved portion defining the curved optical waveguiding path, and the straight portions constituting straight waveguiding paths for directing tapped optical energy to said signal strength measuring means.
Preferably, the signal strength measuring means is constituted by first and second photodetectors, the first photodetector being arranged to measure the signal strength of the optical energy tapped from the optical fibre in one direction, and the second photodetector being arranged to measure the signal strength of the optical energy tapped from the optical fibre in the other direction. Conveniently, the first and second photodetectors are positioned at the free ends of the two straight portions of the pick-up element.
The invention also provides an endface angle measuring apparatus in combination with a cleaving tool,
REFERENCES:
patent: 4652123 (1987-03-01), Neumann
Proceedings of the IEEE, vol. 70, No. 6, Jun. 1982, pp. 683-684, New York, US; K. Iizuka: "Acoustic Time-Domain Reflectometer Used as a Short-Range Fiber-Optic Fault Locator".
Electronic Letters, vol. 20, No. 13, Jun. 1984, pp. 528-530, Stains, Middlesex, GB; C. A. Millar: "Simplified Optical Fibre End-Cleave Angle Measurement Device".
Patent Abstracts of Japan, vol. 9, No. 281 (P-403) [2004], 8th Nov. 1985; JP-A-60 122 347 (Nippon Denshin Denwa Kosha) 29-06-1985.
Patent Abstracts of Japan, vol. 9, No. 174 (P-374) [1897], 19th Jul. 1985; and JP-A-60 49 239 (Nippon Denshin Denwa Kosha) 18-03-1985.
Electronics International, vol. 55, No. 9, May 1982, p. 159, New York US; J. T. Harvey et al.: "Building a Low-Cost Optical Time-Domain Reflectometer".--Whole Document.
Harper Jonathan S.
Hornung Stephen
Mallinson Stephen R.
British Telecommunications public limited company
McGraw Vincent P.
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