Optics: measuring and testing – For optical fiber or waveguide inspection
Patent
1991-03-19
1992-04-28
McGraw, Vincent P.
Optics: measuring and testing
For optical fiber or waveguide inspection
65 311, G01N 2184
Patent
active
051081733
DESCRIPTION:
BRIEF SUMMARY
The invention relates to methods and apparatus for setting the orientation of an optical fibre having at least one planar section extending along its length.
Optical fibres have recently been developed which, instead of having a conventional circular cross-section, have a semi-circular section. These fibres are known as D-fibres. D-fibres provide a relatively simple means of access to the fibre core and can form the basis of several fibre-based devices.
In order to fabricate a device incorporating such a fibre, it is necessary to identify the planar section or flat on the fibre. In practice, identifying a parallel flat section on a fibre of only 125 micron diameter and orientating it correctly is not simple. One method which has been used in the past is to allow the D-fibre to bend since, because of its cross-section, this fibre is forced to orientate itself such that the flat lies to the inside or outside of the bend. A previous method of identification simply involved holding a length of fibre horizontally and allowing one end to droop down. This resulted in a tendency for the flat to lie up or down and by careful scrutiny of the light reflected from the flat surface it was possible to identify the flat. This method has several disadvantages: it is very operator dependant, unreliable, difficult to see the reflected light, and even when the flat has been identified the fibre still has to be rotated into the correct orientation for mounting.
In accordance with the one aspect of the present invention, a method of setting the orientation of an optical fibre having at least one planar section extending along its length comprises irradiating the fibre with a beam of radiation, monitoring radiation reflected by the fibre, and rotating the fibre until the intensity of the monitored radiation reaches a maximum or exceeds a threshold.
In accordance with a second aspect of the present invention, apparatus for setting the orientation of an optical fibre having at least one planar section extending along its length comprises a fibre support assembly including rotatable means whereby an optical fibre may be supported and rotated; and detection means for irradiating at least one region of the fibre with a beam of radiation sensing radiation reflected by the fibre, and indicating when the intensity of the sensed radiation reaches a maximum or exceeds a threshold.
We have devised a method and apparatus which enables the orientation of these optical fibres to be set automatically with a minimum of operator intervention. The invention makes use of the fact that the optical fibre will not reflect light equally while it is rotated, the maximum amount of reflection occurring when the radiation beam impinges on the flat.
Typically, the radiation will comprise optical radiation, such as infra-red radiation generated by a light emitting diode but other types of radiation are also suitable.
In one preferred embodiment, the method comprises a preliminary step of imparting a bend in the optical fibre. This has the advantage of restricting the location of the planar section, in the case of a D-fibre, to one of two orientations and thus reduces the uncertainty involved in locating the planar section. The rotating means preferably comprises a rotably mounted curved guide. This provides a simple way of controlling the orientation of the optical fibre and at the same time, as explained above, limits the position of the planar section to one or two orientations thereby simplifying the setting steps. Furthermore, the orientation will be fixed. Typically, the curved guide will comprise a curved tube similar to a hyperdermic.
The invention is particularly suited to the automatic generation of optical fibre sections of known orientation and the method preferably comprises setting the orientation of each end of a section of optical fibre to be substantially the same by performing a method according to the first aspect of the invention, clamping the ends and thereafter severing the section of optical fibre adjacent to the clamped ends. The cut
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patent: 3088297 (1963-05-01), Kapany et al.
patent: 4102661 (1978-07-01), Dudderar et al.
patent: 4668264 (1987-05-01), Dyott
patent: 4686361 (1987-08-01), Bard
Achurch Nicholas E.
Cassidy Stephen A.
Copple Ian P.
British Telecommunications public limited company
McGraw Vincent P.
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