Optical waveguides – With optical coupler – Particular coupling structure
Patent
1991-02-08
1993-07-27
Ullah, Akm E.
Optical waveguides
With optical coupler
Particular coupling structure
385 30, G02B 600, G02B 636
Patent
active
052316823
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of mounting an optical fibre of particular, but not exclusive, application to mounting D-fibres. D-fibres are optical fibres having a D-shaped cross-section with the core of the fibre near the linear portion of the cross-section.
BACKGROUND OF THE INVENTION
Fibres have been used as optical couplers by removing part of the cladding surrounding the fibre core of a pair of fibres and placing them in contact. The reduced cladding allows coupling between the cores due to their close proximity. One method of forming such a coupler is to make half-coupler blocks by embedding a gently curved fibre in a glass substrate and polishing it to remove a portion of the cladding. A pair of these half-coupler blocks can then be placed together to form an optical coupler. The surfaces of the substrates being flush with the exposed fibre surfaces hold the fibres in the desired position. The manufacturing process is, however, time consuming and needs to be carried out with great care to ensure the correct amount of fibre cladding is removed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of mounting an optical fibre which largely overcomes these disadvantages.
Accordingly, there is provided a method of mounting an optical fibre having a flat surface which includes the step of pressing the fibre into a heated thermoplastic substrate with a former surface until the flat surface of the fibre is flush with any adjacent surface of the substrate.
By flat surface is meant the surface defined by the linear portion of the cross-sections of an optical fibre, as found for example with rectangular or D-shaped optical fibres, notwithstanding that the surface may be curved or twisted before, during or after mounting. The surface shape of the former will determine the final disposition of the flat surface whether it be curved, rippled or in a single plane.
The invention is based on the fact first appreciated by the applicant that the resultant surface formed by the substrate and flat surface of the optical fibre can be made flat to about 0.4 microns which compares favourably with polished silica half couple blocks described above.
The thermoplastic material is preferably a co-polymer of poly (2,6-dimethyl-p-phenylene oxide) and polystyrene, but may be of polypropylene or polymethylmethacrylate polystyrene or other suitable thermoplastic material.
The invention also finds application in mounting an optical fibre for use in a wavelength selective optical coupler where it is required to hold a D-fibre, for example, with the flat surface fixed in an undulatory form as described in the applicant's application GB8813667 titled "A Wavelength Selective Optical Coupler" filed on the 9th Jun. 1988. This is achieved by preparing the former surface with the required undulations which are then impressed on the fibre as it is passed into the substrate.
According to a further aspect of the present invention there is provided an optical device which comprises an optical fibre having a flat surface embedded in a thermoplastic substrate with the flat surface flush with any adjacent surface of the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
This method of mounting an optical fibre and various applications of the method will now be described with reference to the accompanying drawings in which:
FIG. 1 is a perspective view illustrating a method of mounting an optical fibre according to the present invention;
FIG. 2 is a perspective view of a D-fibre being pressed to be held in an undulating formation;
FIG. 3 is a perspective view of an undulating optical fibre produce by the method illustrated by FIG. 2;
FIG. 4 is a plan view of a D-fibre mounted in a substrate by the method of the present invention in which electrodes have been embedded in the substrate at the same time as the fibre;
FIG. 5 is a perspective view illustrating a method of mounting of D-fibre in a non-continuous mount so as to allow the D-fibre to be deflectable; and
FIG. 6 is a perspective
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British Telecommunications public limited company
Ullah Akm E.
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