GB2089061A

GB2089061A - Optical fibre-beam expander alignment testing

Info

Publication number: GB2089061A
Application number: GB8038951A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1980-12-04
Filing date: 1980-12-04
Publication date: 1982-06-16
Also published as: GB2089061B

Abstract

Where an optical fibre is terminated by a beam expander, as for instance in a connector, it is necessary for the fibre to have its axis accurately aligned with the axis of the expander, to ensure that the emergent beam is accurately aligned. To do this, the fibre (7) is fed from d source/detector unit (8), and a plane reflecting device (5) such as a mirror is placed normal to the beam path. Hence the beam is reflected back along its path and the return beam strength is monitored at the source/detector unit (8). When its strength is at a maximum the beam is accurately aligned, and the fibre end, which may be in a ferrule, is secured. Thus this use of the principle of auto-collination gives a simple way to adjust fibre alignment. <IMAGE>

Description

SPECIFICATION Optical fibre alignment This invention relates to optical fibre connector of the expanded type, and to the adjustment of the relative alignment of the fibre and the beam expander.

A connector of the above type include a ferrule within which the fibre is terminated, or some other fibre support, whose end is closely adiacent to the beam expander, which is a form of lens, such as a graded index lens or a conventional plano-convex lens, but it may may comprise several reflecting or refracting components which may heve plane, spherical or aspheric surFaces. When two connectors using such expanders are mated the two expanders are relatively close to each other and, due to their relatively large areas, give gord coupling efficiency.The fibre end has to be accurately aligned with the axis of the beam, from the expander, and it is usual to adjust this alignment by movement of the fibre in sits. Then a suitable adhesive mat---, .el, such as an epoxy, is fed into the rrerrule, or to ihe rear of the expander, to secure the fibre end in the desired position.

Current methods of effecting the alignment involve monitoring the position of te emaren': jight beam on a screen some distence sway from the optical syt-em or using some formal oF optical viewing system. it is possible for the emergent beam to be misaligned, e.g. as shown in Fig 1 where 1 is the fibre and 2 is the optical system. Another viewing system (not shown) is generally used to monitor this.

An object of the invention is to provide a simple and economical method of effecting fibre alignment in such a connector.

According to the present invention, there Os provided a method of adjusting the alignment of an optical fibre with a beam expander located nearthe end of that fibre, in which light supplied from a light source/detector unit is transmitted from the fibre and via the beam expander issues from the beam expander as a beam whose axis should be parallel to the axis of the fibre and the expander, in which the light from the expander falls on a plane reflecting surface set at right angles to the desired beam path so that the beam is reflected back along its path via the expander and the fibre to the light source/detector unit, and in which the orientation ofthefibre is adjusted until the signal strength of the return beam is at a maximum, at which point the relative positions of the fibre end and the expander are fixed.

An embodiment of the invention will now be described with reference to Fig 2 of the accompanying drawing.

The arrangement described uses the property of auto-collimation, where the emergent beam is reflected back by a reflecting device 5 along its own path through the lens 6 and back into the fibre 7, the intensity of the return beam being monitored in a device 8 such as a source/detector unit. The reflect- ing device 5, such as a mirror, is accurateiy set at right angles to the emergent beam axis, so that the return signal strength is at a maximum when the beam emerges in the required position normal to the device 5. This has the advantage that the fib e is checked against itself - as opposed to some other fibre which may have different properties.

A viewing system may be used to check for lateral displacement of the beam. Viewing systems can gain axis to the beam by a beam splitter at 9, i.e.

between the optical system and the reflects or at 10 by making the reflecting device only partially reflec ive. An alternative is to interpose an aperture stop of a suitable size at 9, which would reduce the signal strength of the return beam were displaced in any way.

1. A method of adjusting the alignment of an optical fibre with a beam expander located near the end of that fibre, in which light supplied from a light 30urce/detector unit is transmitted from the fibre and via tne beam expander issues from the beam expan de.-- as a beam whose axis should be parallel to the axis of the fibre and the expander, in which the light from the expander falls on a plane reflecting surface set at right angles to the desired beam path so that the beam is reflected back along its path via the expander end the fibre to the light source!detecdor unit and in which the 15 orientation of the fibre is adjusted until the signal strength of the return beam is at a maximum, at which point the relative posi tOils of the fibre end and the expander are -itced.

2. A method as claimed in claim land in which further monitoring is effected with a viewing system which receives light via a beam splitter between the expander and the reflecting device.

3. A method as claimed in claim 1, and in which further monitoring is effected with 3 viewing system on the opposite side of the reflecting device from the expander, the reflecting device being partly reflective.

4. A method as claimed in claim 1. and in which further monitoring is effected by the use of an apertured stop between the lens and the plane reflecting surface so that misalignment produces a substantial reduction in the strength of the return beam.

5. A method of adjusting the alignment of an optical fibre with a beam expander located near the end of that fibre, substantially as described with reference to Fig 2 of the accompanying drawing.

6. Apparatus for carrying out the method of any one of claims 1, 2, 3, 4, or 5.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Optical fibre alignment This invention relates to optical fibre connector of the expanded type, and to the adjustment of the relative alignment of the fibre and the beam expander. A connector of the above type include a ferrule within which the fibre is terminated, or some other fibre support, whose end is closely adiacent to the beam expander, which is a form of lens, such as a graded index lens or a conventional plano-convex lens, but it may may comprise several reflecting or refracting components which may heve plane, spherical or aspheric surFaces. When two connectors using such expanders are mated the two expanders are relatively close to each other and, due to their relatively large areas, give gord coupling efficiency.The fibre end has to be accurately aligned with the axis of the beam, from the expander, and it is usual to adjust this alignment by movement of the fibre in sits. Then a suitable adhesive mat---, .el, such as an epoxy, is fed into the rrerrule, or to ihe rear of the expander, to secure the fibre end in the desired position. Current methods of effecting the alignment involve monitoring the position of te emaren': jight beam on a screen some distence sway from the optical syt-em or using some formal oF optical viewing system. it is possible for the emergent beam to be misaligned, e.g. as shown in Fig 1 where 1 is the fibre and 2 is the optical system. Another viewing system (not shown) is generally used to monitor this. An object of the invention is to provide a simple and economical method of effecting fibre alignment in such a connector. According to the present invention, there Os provided a method of adjusting the alignment of an optical fibre with a beam expander located nearthe end of that fibre, in which light supplied from a light source/detector unit is transmitted from the fibre and via the beam expander issues from the beam expander as a beam whose axis should be parallel to the axis of the fibre and the expander, in which the light from the expander falls on a plane reflecting surface set at right angles to the desired beam path so that the beam is reflected back along its path via the expander and the fibre to the light source/detector unit, and in which the orientation ofthefibre is adjusted until the signal strength of the return beam is at a maximum, at which point the relative positions of the fibre end and the expander are fixed. An embodiment of the invention will now be described with reference to Fig 2 of the accompanying drawing. The arrangement described uses the property of auto-collimation, where the emergent beam is reflected back by a reflecting device 5 along its own path through the lens 6 and back into the fibre 7, the intensity of the return beam being monitored in a device 8 such as a source/detector unit. The reflect- ing device 5, such as a mirror, is accurateiy set at right angles to the emergent beam axis, so that the return signal strength is at a maximum when the beam emerges in the required position normal to the device 5. This has the advantage that the fib e is checked against itself - as opposed to some other fibre which may have different properties. A viewing system may be used to check for lateral displacement of the beam. Viewing systems can gain axis to the beam by a beam splitter at 9, i.e. between the optical system and the reflects or at 10 by making the reflecting device only partially reflec ive. An alternative is to interpose an aperture stop of a suitable size at 9, which would reduce the signal strength of the return beam were displaced in any way. CLAIMS

6. Apparatus for carrying out the method of any one of claims 1, 2, 3, 4, or 5.