TECHNICAL FIELD

The invention relates to an optical cable intended to be used in reading an optical information carrier, the cable containing a light conductor for transferring light from the information carrier to a light-sensitive receiver.

BACKGROUND ART

Light conductors have different properties with relation to flexibility, light divergence angle, and reception angle depending on what material they are made from. These angles are equally as great for a given light conductor and represent the angle within which the light can be spread from, or collected by, the end of the light conductor. A plastics optical fibre is thus relatively pliant and generally has a comparatively large light divergence angle. Fibres having a comparatively small light divergence angle are usually manufactured from glass or quartz. However, such fibres are not as pliant as plastics fibres and furthermore, they are more easily damaged by bending. As an example of the magnitude of the light divergence and light reception angle it may be stated that in a plastics fibre this is usually between 45 and 90°, while the corresponding angle for a glass or quartz fibre is usually only about 15 to 40°.

In the G. B. specification 1375963 there is described an optical cable intended for use in reading an optical information carrier. The cable contains a plurality of fibre conductors, of which the majority are utilised for illuminating the information carrier, and one for transmitting the light reflected from the carrier to a light-sensitive receiver.

If the information carrier is a display screen, no further illumination thereof is necessary, and thus no fibres which lead light to it. Irrespective of how the information carrier is illuminated, however, it is desirable that the so-called reading fibre, i.e. the fibre which transmits light from ^' the information carrier to the light-sensitive receiver, has a small light reception angle. Good resolution is obtained in such a case, which is important for reading such as bar

codes. .

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DISCLOSURE OF INVENTION

The object of the present invention is to provide an optical cable of the kind mentioned in the introduction, which is easy to bend, while at the same time the light conductor for transmitting light to the light-sensitive receiver will only be able to take up light from the information carrier within a comparatively small angle. This is achieved by the cable having been given the characterising features disclosed in the claims.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in detail with reference to the accompanying drawing, on which Figure 1 is a side elevation fo an optical cable, Figure 2 is an end elevation of the light conductors in an optical cable comprising several light conductors, and Figure 3 is a side elevation of certain of the light conductors in the cable according to Figure 2.

BEST MODES FOR CARRYING OUT THE INVENTION

A side elevation of an optical cable is shown in Figure 1. The cable is intended for use in reading such as a display screen and comprises a light conductor denoted by the numberal 5 for transmitting light from the screen to a light- sensitive receiver. The light conductor 5 mainly comprises an optical fibre made from an easily bendable material with a comparatively large light reception angle. The conductor end portion 6 facing towards the screen comprises a fibre from a material with a comparatively small light reception angle ^ . The easily bendable and major portion of the light conductor 5 can be made from plastics, e.g. polymethyl methacrylate, and the end portion 6 from glass or quartz.

The illustrated cable can thus be easily bent and wound into a helix shape. Since the end portion 6 of the light conductor 5 has a small light reception angle, there is obtained better resolution in reading than if this had also been made from a more easily bendable material with a greater light reception angle.

Figure 2 is an end elevation of the light condμctors in an optical cable containing several light conductors, and Figure 3 is a side elevation of certain of these conductors. They comprise fibre optical fibres 1-5, of which the fibres 2 and 4 have been left out in Figure 3, for the sake of clarity. The fibre 5 with its end portion 6 corresponds to the fibre according to Figure 1. The fibres 1-4 are manufactured from an easily bendable material with a comparatively large light divergence angle. These fibres extend along the sides of the fibre 5 and are utilised for illuminating an optical information carrier, which does not generate light itself. The fibre 5 thus catches the reflected light at its end portion 6 and transmits it to a light-sensitive receiver at the other end of the fibre. Light directions and approximate light angles are indicated by arrows and dashed lines in Figure 3.

Since the cable according to Figures 2 and 3 also contains light conductors of an easily bendable material, except the end portion 6, the same advantages are obtained with reference to flexibility and resolution as with the embodiment according to Figure 1. The fibres 1-4, intended for illumination, also spread the light relatively uniformly on the information carrier, as a result of their comparatively large light divergence, angles.

With the illustrated embodiments there is thus obtained a cable which is durable and easy to bend, while having good optical properties at the same time. Of course, the invention can be further varied within the scope of the following claims. For example, the number of the light conductors and thus their interrelating dimensions may be varied. Fabrication material other than those given above is also conceivable.