1988-09-12
1990-09-18
Lee, John D.
65 421, 350 9620, G02B 626
Patent
active
049573381
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the fabrication of fused fibre optic couplers, especially biconical taper couplers, and is concerned in particular with improving the control and optimum management of the fabrication process.
BACKGROUND ART
The usual technique for forming fused biconical taper fibre optic couplers entails disposing respective segments of two or more optical fibres in intimate side-by-side relationship and heating the segments to a temperature sufficient to cause the fibre segments to soften and fuse together. The heated fibres are then longitudinally drawn to cause each of the fused fibres to develop a biconical taper and to thereby form the coupler. A typical disclosure of these steps is to be found in Abebe U.S. Pat. No. 4,612,028.
SUMMARY OF THE INVENTION
It is an object of the invention to provide enhancements of the aforedescribed known technique for fabricating fibre optic couplers which will contribute to bettering existing commercial standards as to, for example, power loss and coupling factor tolerances. The present invention stems from the novel concept of continuously monitoring the tension in the optical fibres during the coupler fabrication process and controlling one or more process variables in response to specific observations of the tension. In accordance with the preferred practice of a first aspect of the invention, this facility is utilised to introduce and control an additional pre-heating step which enhances the condition of the fibres for subsequent fusion and drawing. Most generally, the invention provides in its first aspect a method of fabricating a fused fibre optic coupler, especially but not only a multi-mode biconical taper coupler, comprising:
pretreating respective segments of optical fibre to relieve torsional stress therein; and
heating said pretreated segments while in intimate side-by-side contact to a temperature sufficient to cause the fibre segments to fuse together.
In preferred embodiments, the invention in its first aspect provides a method of fabricating a fused fibre optic coupler, especially but not only a multi-mode biconical taper coupler, comprising:
disposing two or more segments of optical fibre under longitudinal tension, preferably substantially identical tension;
preheating said tensioned fibre segments to a temperature sufficient to soften the segments and thereby substantially relieve said tension by inelastic stretching of the segments; and
after the segments have cooled, re-tensioning the segments and heating them while in intimate side-by-side contact to a temperature sufficient to cause the fibre segments to fuse together.
It is believed that the initial heating step is useful in relieving torsional stress prior to the fusion heating. It is thought that pre-existing unrelieved torsional stress in the fibres contributes to unpredictable excessive power losses in the coupler and particularly to unpredictable excessive tolerances in its coupling factor.
Preferably, the longitudinal tension in the fibres is continuously or periodically monitored to detect when the tension falls substantially to zero during the preheating, whereupon the preheating is terminated and the fibre segments allowed to cool. The degree of cooling will be dependent on circumstances but cooling is not necessarily to ambient temperature. Cooling is more generally to an intermediate temperature above ambient.
Most preferably, the optical fibre segments are brought into said intimate contact by being twisted about each other.
In a second aspect, the invention affords a method of fabricating a fused fibre optic coupler comprising:
heating two or more initially tensioned segments of optical fibre while these segments are in intimate side-by-side contact;
monitoring the longitudinal tension and temperature of each of said segments, directly or indirectly; and
when the tension in the segments falls to a predetermined threshold value, thereafter continuing to raise the temperature of the segments a predetermined number of degrees above their temper
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"Multimode Directional Coupler Development", by Thorncraft et al. 19th Australian Conference on Optical Fibre Technology, 12/2-5/85, Perth Aust.
Dabbs Timothy P.
Kennedy David R.
Rashleigh Scott C.
Thorncraft David A.
Heartney Phan T.
Lee John D.
The Commonwealth of Australia
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