GB2271432A - Threaded lens holder for a fibre optic cable - Google Patents

Abstract

Fibre optic cables are used as light guides for illumination purposes, for example on the decks of boats for a fibre optic cable, which terminates in a threaded portion, comprises a housing 10 arranged to be fixed in or adjacent to an aperture in a support means and defining a cavity 20 for receiving a lens 2 mounted into a lens mount 15, the mount 15 comprising a threaded portion 4 to engage the threaded portion of the fibre optic cable. The housing 10 is arranged so that the lens mount 15 can be engaged with the fibre optic cable and positioned in the housing after the housing is fixed to the support means. <IMAGE>

Description

Lens holder for a Fibre Optic Cable Field of the Invention This invention relates to a lens holder for a fibre optic cable, particularly where the function of the fibre optic cable is to provide light for illumination purposes and the function of the lens holder is to retain a lens that focuses the light.

Description of the Prior Art An optical fibre is a transparent, dielectric fibre, used for conducting light. Typically, the fibres are made of thin flexible glass or plastic filaments with ground and polished ends and can be bundled together using epoxy; often, the fibres are not arranged as an ordered array, in which case a so called incoherent bundle is formed. Incoherent bundles are used as light guides for a variety of lighting purposes, for example, in regions where electrical cabling needed to provide power to a light source, such as an incandescent lamp, poses a threat because of the presence of inflammable materials.

Typically, a high power light source will illuminate one end of the bundle, resulting in light emission from the remote end at a usually high fraction of the intensity of the incident light. Fibre optics are well known in the art and will not therefore be further described here.

Generally, an incoherent bundle will terminate in a lens so that there is an attractive pattern of light on the surface on which the beam is incident, the pattern being an image of the group of fibres in the bundle. It is usual to provide that the bundle, commonly referred to as a 'tail', terminates in a sleeve with an external screw thread.

Typically, a lens holder as depicted inFigure 1, in which a lens is permanently fixed, has a matching internal screw thread so that the holder can be screwed onto the end of the bundle. If the bundle is being used to guide light around a boat, into, for example, one cabin, then the usual procedure is for the bundle to be passed through a roughly made hole in the ceiling or wall of the cabin so that it protrudes several centimetres.

The holder is then screwed onto the bundle and the holder pushed up to abut against the sides of the hole, being fixed into position there using some conventional material such as plaster or cement. An alternative to the holder, incorporating a fixed lens, is the variable focus movable lens illustrated in Figure 2. This design includes a lens mount, similar to the fixed lens holder, which is itself mounted within a housing in which it is free to swing, being supported by a pair or axles extending from the housing wall. The housing includes a pair of sprung members that can be bent upwards to allow the housing, once the mount is threaded onto the end of the bundle, to be moved up through the hole in the wall or ceiling through which the bundle protrudes.Once the housing is sitting in the hole, the members can be allowed to move downwards so that the housing is held firmly in position.

One problem with both of the above prior art approaches is that the manner in which the holder is fixed in position is not particularly fast, easy, or convenient. For example, manipulating the sprung members can be particularly awkward. Also, once the prior art housing is in position, it is not at all easy to remove it, which may be desirable in order to access the bundle, for example.

Further, in prior art designs focusing is achieved by varying the distance of the lens in the lens holder from the end face of the bundle. The aim of focusing is to focus an image of the end face of the bundle upon the surface on which the light beam from the bundle falls. This is done by screwing the lens holder or mount onto the bundle by the amount required to produce the required distance between the end face of the bundle and the lens. Typically, this has to be done whilst the bundle is protruding several centimetres from the access hole since only then can the holder be rotated to allow focusing, i.e. only before the housing is in its final position is it free to be rotated. Accurate focusing is a function of both image distance, i.e. distance from the final position of the lens to the surface to be illuminated, and object distance, i.e.

distance between the end face of the bundle and the lens, and can be upset by quite small movements of the lens. Consequently, the requirement for the focusing to be done whilst the holder is some centimetres from its final position makes accurate focusing extremely difficult and time consuming since the person installing the device has essentially to guess how the change in image distance that occurs when the holder is pushed back up the several centimetres should be compensated for by a preceding adjustment of the image distance, i.e. extent to which the holder or mount is screwed onto the bundle.

Objects of the Invention It is an object of the invention to provide a lens holder for a fibre optic cable that is fast, easy and convenient to use. It is a further object to provide such a lens holder that overcomes the difficulties in focusing associated with the prior art design.

Statement of the Invention In accordance with the present invention, a lens holder, for a fibre optic cable which terminates in a threaded portion, comprises: a housing arranged to be fixed in or adjacent to an aperture in a support means and defining a cavity for receiving a lens mounted into a lens mount, the lens mount comprising a threaded section sized to engage the threaded portion of the fibre optic cable, wherein the housing is arranged so that the lens mount can be engaged with the fibre optic cable and positioned in the housing after the housing is fixed in or adjacent to the aperture of the support means.

Preferably, this is achieved by providing that the lens mount is not attached to the housing prior to the housing being fixed in or adjacent to the aperture, unlike all prior art arrangements. As a consequence, such a lens holder is easier to install than conventional designs.

In a preferred embodiment, the lens mount when received into the cavity of the housing can be rotated to vary the amount of cable engaged by the threaded section of the mount in order to vary the distance between the lens and the end face of the bundle.

This greatly facilitates accurate focusing since the mount can be simply rotated within a housing already finally fixed in position to effect focusing. Unlike prior art designs, the mount when actually focused is at the final image distance, so that the guesswork inevitably associated with installing earlier designs is obviated.

Conveniently, the housing comprises an externally threaded chamber arranged to engage a receiving means that has been positioned in or adjacent to the aperture in the support means such that the housing is fixed in or adjacent to the aperture when engaged with the receiving means; The housing may be a cylindrical housing and the lens mount may then be substantially spherical in shape to be rotatable in the housing to provide an illuminating beam of predetermined direction.

Brief Description of the Drawings The invention will now be described with reference to the accompanying drawings of which: Figure 1 depicts a cross sectional view through fixed lens prior art lens holder; Figure 2 depicts a cross sectional view through movable lens prior art lens holder; Figure 3 depicts a cross sectional view through a lens holder in accordance with the present invention.

Detailed Description Referring now to Figure 1, there is shown at 1 a prior art lens holder of generally cylindrical shape that holds at one end a fixed lens 2. The lens holder 1 comprises a tapering waist section 3 and an end portion that comprises an internal screw thread, sized to engage with a screw threaded head 6 that terminates the industry standard fibre optic cable bundle 5. In use, the bundle 5 is passed through a roughly cut aperture 8 in the wall or other support, and the lens holder 1 screwed down onto the head of the bundle 5. The lens holder 1 is then pushed back into the aperture 8 and fixed in position. When the bundle is connected to an appropriate light source, light is fed to the lens 2 via the bundle 5 and brought to a predetermined focus.

Referring to Figure 2 now, a more elaborate design of prior art lens holder is shown.

This design includes a lens 2 fixed inside a funnel shaped lens mount 15, mounted within a housing 10 on a pair of short axles 11 about which it is free to swing, allowing the direction of the emitted beam to controlled. The funnel of the mount 15 tapers to an internally threaded section arranged to engage with the screw threaded head of a fibre optic bundle [not shown]. The housing is generally cylindrical and includes at one end a flange 12. The housing includes a pair of sprung members 13 that can be bent upwards to allow the housing 10, once the holder 1 is threaded onto the end of the bundle [not shown], to be moved up through the hole [not shown] in the wall or ceiling through which the bundle protrudes. Once the housing 10 is sitting in the hole, the members 13 can be allowed to move downwards so that the housing 1 is held firmly in position.

Referring now to Figure 3, which shows an embodiment of the present invention, there is shown a lens holder comprising a generally cylindrical housing 10, defining a cylindrical cavity 20 sized to receive a generally spherical lens mount 15, which includes a lens 2 at one end. The housing includes an internal flange 16 against which can sit a circular rubber O-ring 17. The purpose of the O-ring is to ensure that the lens holder does not provide a means for liquid to pass from one side of the support to the other. This is particulalry important where the device is used in the wall of a swimming pool or on the deck of a boat.

At one end, the housing includes a flange 12. In use, the housing is first screwed into a fitting [not shown] already installed by conventional means into the wall, ceiling or other support means by engaging the screw thread 18 on the external face of the housing 10 with a co-operating screw thread of the fitting. The flange will then abut against the support wall/deck etc into which the holder has been placed. The fibre optic bundle [not shown] is passed through the housing 10 and past the O-ring 17.

The screw threaded head of the bundle is then screwed into a threaded section 4 protruding from the end of the lens mount 15 opposite to the lens 2. The lens mount 15 is then placed into the cavity 20, abutting against the O-ring 17. By turning the lens mount 15, it is possible to vary the amount that the head of the bundle is screwed into the thread section 18 to effect changes in focus. Once the lens is properly focused and oriented in the desired direction, a locking member 20 is screwed onto the housing 10 by screwing the locking member onto the internal screw thread 21 of the housing 10.

Claims (7)

Claims

1. A lens holder, for a fibre optic cable which terminates in a threaded portion, comprising: a housing arranged to be fixed in or adjacent to an aperture in a support means and defining a cavity for receiving a lens mounted into a lens mount, the lens mount comprising a threaded section sized to engage the threaded portion of the fibre optic cable, wherein the housing is arranged so that the lens mount can be engaged with the fibre optic cable and positioned in the housing after the housing is fixed in or adjacent to the aperture of the support means.

2. The lens holder as claimed in Claim 1 wherein the lens mount is not attached to the housing prior to the housing being fixed in or adjacent to the aperture.

3. The lens holder of either Claims 1 or 2 wherein the lens mount when received into the cavity of the housing can be rotated to vary the amount of cable engaged by the threaded section in order to vary the distance between the lens and the end face of the bundle.

4. The lens holder as claimed in any preceding Claim wherein the housing comprises an externally threaded chamber arranged to engage a receiving means that has been positioned in or adjacent to the aperture in the support means such that the housing is fixed in or adjacent to the aperture when engaged with the receiving means.

5. The lens holder as claimed in any preceding Claim, wherein the housing is a cylindrical housing and the lens mount is substantially spherical in shape to be rotatable in the housing to provide an illuminating beam of predetermined direction.

6. The lens holder as claimed in Claim 4 wherein there is provided a sealing ring to prevent liquid from passing through the housing when fixed in the aperture from one side of the support means to the other.

7. The lens holder as claimed in Claim 5 further comprising a locking member to lock the lens mount with respect to the housing once inserted into the cavity of the housing.