GB2089065A

GB2089065A - A sealed bushing for an optical fibre

Info

Publication number: GB2089065A
Application number: GB8133464A
Authority: GB
Original assignee: Cables de Lyon SA
Current assignee: Cables de Lyon SA
Priority date: 1980-11-13
Filing date: 1981-11-06
Publication date: 1982-06-16
Also published as: FR2493952B1; DE3144662A1; FR2493952A1; GB2089065B; DE3144662C2

Abstract

The bushing is placed in a wall (1) of an enclosure. An optical fibre (3) enters the enclosure, and the bushing serves to prevent leakage of water or other fluid into the enclosure, in spite of high pressure difference, such as found on the sea bed. The bushing comprises a disk (2) with a central hole for the fibre. The thickness of the bushing is about the same as the diameter of the fibre. The disk is sealed to the wall at (6) and the fibre is glued in the hole at (5) over the entire length of the hole. The disk may be of precious-stone material or metal. <IMAGE>

Description

SPECIFICATION A sealed bushing for an optical fibre The present invention relates to bushing for an optical fibre, said bushing providing sealing against a high pressure difference.

Such bushings are used for keeping two environments apart.

Sealed bushings of the kind using a pierced precious-stone ring are already known. The optical fibre passes through the hole and sealing is obtained by gluing the fibre along the length of the hole. Such bushings are much thicker than the diameter of the fibre, resulting in the fibre being glued over a length corresponding to the thickness of the ring. This makes it difficult to avoid microcurves of the fibre in the hole, in spite of all the precautions taken to keep the optical fibre properly aligned.

Finally, in some applications, the bushing must withstand very large pressure differences. Undersea cables, for example, must be capable of withstanding a pressure difference of 700 bars.

Preferred embodiments of the present invention provide bushings whose sealing is good up to pressures of at least 700 bars, and which considerably reduce the problems of microcurves compared with the above-mentioned known bushings.

The present invention provides a sealed bushing for an optical fibre, said bushing being intended to withstand a high pressure difference between its two ends, and comprising a disk with a central hole for passing an optical fibre which is glued to the disk over the entire length of the hole, said disk having one of its faces sealed to the bottom of a recess provided in the wall of an enclosure, wherein the thickness of said disk is about equal to the diameter of the optical fibre.

In a first embodiment the disk is pressed down onto a sealing ring in the bottom ofthe recess by means of a threaded stopper.

In a second embodiment, the disk is glued to a frusto-conical end of an intermediate member. The frusto-conical end is then pressed down by a stopper against a frusto-conical portion at the bottom of a hole in the wall of the enclosure.

Embodiments ofthe invention are described by way of example with reference to the accompanying drawings, in which: Figure lisa section through a first embodiment of the invention; Figure 2 is a section through a first variant of the invention; Figure 3 is an exploded section through a second variant of the invention; and Figure 4 shows the variant of Figure 3 assembled and on a larger scale.

Figure 1 shows a first embodiment of a bushing in accordance with the invention. The figure shows a wall 1, a disk 2, an optical fibre 3, a circular recess 4 in the wall 1,said recess being of slightly larger diameter than the disk, and as deep as the disk is thick. A hole 7 centred on the recess 4 passes through the wall 1. The diameter of the hole is considerably larger than that of the optical fibre, but smaller than that of the disk. The optical fibre 3 passed through a hole in the centre of the disk. The fibre is glued to the disk along the entire length of the hole in the disk. The glue is referenced 5 in Figure 1.

Likewise, the disk is glued at the bottom of the recess 4 to the wall 1 by means of glue referenced 6. Only one face of the disk is thus glued. The layers of glue provide disk-to-wall sealing and fibre-to-disk sealing.

The disk is either of precious-stone material or of metal. Its thickness is about equal to the diameter of the optical fibre, which may be stripped or still covered by its primary covering. The play between the hole in the disk and the fibre is about 10 microns.

The glue may be a polyacrylic diester, an acrylic or an epoxy. The high pressure side is the same as the side of the wall in which the recess 4 is placed, i.e.

the un-glued side of the disk 2, whereby the disk is pressed towards the bottom of the recess.

Figure 2 shows a variant of the bushing shown in Fig lure 1. In Figure 2, there is a recess 9 in the high pressure side of the wall land it is several times as deeper than the thickness of the disk. The recess is tapped along its inside surface. A stopper 8 is screwed into the recess. The middle of the stopper is pierced by a hole 10 of the same diameter as the hole 7 through the wall 1. The bottom of the recess is provided with a sealing ring 11 housed in a circular groove in the floor of the recess. The disk is pressed against the sealing ring 11 by the stopper 8, thereby ensuring sealing. As in Figure 1,the optical fibre is glued in the hole through the disk by glue 5.

Figure 3 is a exploded view of another variant of the bushing shown in Figure 1, while Figure 4 is a view of the same variant after assembly, and to a larger scale. In these figures, the stopper is referenced 13. It is threaded at one end. Atubular inter- mediate member 14 has a central hole in which the fibre slides freely. The disk 2 is at the upper end (as shown in the drawing) of the member 14, and is made of metal or precious stone. The optical fibre 3 passes through the disk 2. a Tapped ring 15 can be screwed onto an outer thread of the intermediate member 14. A tapped hole 16 is made in the wall 1 and leads down to a passage 17 via a frusto-conical portion 18. The tapped hole 16 is on the low pressure side ofthe wall 1.

A hole 20 passes through the stopper 13 and the lower end thereof where it passes through a head 21 of the stopper is the same diameter as the bottom end of the intermediate member 14. The upper end 23 of the hole 20 through the stopper 13 is the same diameter as the ring 15. There is a shoulder 19 where the diameter of the hole 20 changes. The ring 15 is screwed onto the intermediate member 14 and the resulting assembly is placed in the stopper 13, with the ring engaging the shoulder 19. The disk with the optical fibre glued through the middle is itself glued into a recess made in the top end of the intermediate member 14, which top end is frusto-conical in shape.

The stopper 13 is screwed into the hole 16 ofthewall 1 in such a manner as to bring the top end of the intermediate member 14 into contact with the frusto-conical portion 18 of the wall 1, to seal it thereto.

The sealed bushing shown in Figure 1 is fixed in the sense that since the disk 2 is glued to the wall 1, it cannot be easily removed with the optical fibre for replacement by another disk and fibre assembly. In contrast, in the variants shown in Figures 2,3 and 4, the optical fibre can be changed. In the Figure 2 var iant, the disk and fibre assembly is changed, while in the variant of Figures 3 and 4, the disk and fibre and intermediate member assembly is changed.

In the Figures 3 and 4 variant, the intermediate member 14 is automatically centred relative to the hole 16 in the wall 1 by interaction ofthefrusto- conical portions. This has the effect of centering the fibre in the hole 16. Thus the position of the optical fibre is better defined than in the embodiments of Figure 1 or Figure 2. The Figures 3 and 4variant is thus preferred whenever an optical fibre needs to be accurately positioned by a sealed bushing.

Claims

1. A sealed bushing for an optical fibre, said bushing being intended to withstand a high pressure difference between its two ends, and comprising a disk with a central hole for passing an optical fibre which is glued to the disk over the entire length of the hole, said disk having one of its faces sealed to the bottom of a recess provided in the wall of an enclosure, wherein the thickness of said disk is about equal to the diameter of the optical fibre.

2. A bushing according to claim 1, wherein the diameter of the hole is about ten microns greater than the diameter ofthefibre.

3. A bushing according to claim 1 or 2, wherein the disk is pressed down onto a sealing ring in the bottom of the recess by means of a threaded stopper.

4. A bushing according to claim 1 or 2, wherein the disk is glued to a frusto-conical end of a threaded intermediate tubular member, wherein a ring is screwed onto said threaded intermediate member from its frusto-conical end, wherein a stopper that is pierced by a hole and is externally threaded is fitted over the intermediate member, with a shoulder in said hole engaging said ring, wherein said stopper is screwed into a hole made in the wall of an enclosure, said hole leading via a frusto-conical portion to a passage that passes out through the other side of the wall, and wherein said frusto-conical end is applied to said frusto-conical portion to provide a seal between the intermediate member and the wall.

5. A bushing according to any one of claims 1 to 4, wherein the glue is a polyacrylic diester.

6. A bushing according to any one of claims 1 to 4, wherein the glue is an acrylic.

7. A sealed bushing for an optical fibre, substantially as herein described with reference to and as illustrated in the accompanying drawings.