GB2274924A

GB2274924A - Fibre optic arrangement for directional pick up of optical radiation

Info

Publication number: GB2274924A
Application number: GB9400211A
Authority: GB
Inventors: Hans Poisel; Martina Schreiber; Gert Trommer
Original assignee: Deutsche Aerospace AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1993-01-21
Filing date: 1994-01-07
Publication date: 1994-08-10
Also published as: FR2700618A1; GB9400211D0; DE4301477C1

Description

Fibre optic Arrangement f or Directional Pick Up of Optical Radiation The

invention relates to a fibre optic arrangement for directional pick up of optical radiation comprising a pluralitv of optical fibres having their end faces on the receive side arranged adjacent to one another and covering variously oriented solid angles.

An optical wide-angle sensor is known fram German Patent Specification DE 37 36 616 in which a plurality of light guides with attached individual fibres are arranged in such a way that all optical axes intersect at a point in front of the light entry ports. For this purpose, a plurality of holes are provided in a plate to accommodate the optical elements or fibres, the axes of the holes intersecting at a point in front of the plate. Although such an 'arrangement has the advantage that the entry ports of all fibres may be located very close to one another, problems of space are created inside the sensor because the optical fibres have only restricted flexibility. Moreover, manufacture of the plate with the holes placed at various angles is comparatively expensive.

Therefore, the object of the invention is to provide a fibre optic arrangement of the aforementioned type for the directional pick up or coverage of optical radiation, which is more compact and simpler to manufacture than the above-mentioned, known arrangement. This object is achieved by a fibre optic arrangement having the general features mentioned above but characterised in that the optical f ibres are arranged parallel to one another in the vicinity of their end faces on the receive side, in that surface normals of said end faces on the receive -2^ side of at least a portion of the optical f ibres extend at an angle other than zero from the fibre longitudinal axis, and in that said surface normals of at least a portion of the optical fibres have different orientations from one another.

The invention utilises the characteristic feature of optical fibres with end faces ground at an angle, as described, for 1 1% example, in "Handbook of Optics", McGraw-Hill, 1978, pages 13-7 and 13-8. in such fibres, the end face ground at an angle acts like a prism placed on a perpendicular end face, so that the optical axis of a radiated light cone, or, where the path of the rays is reversed, the central axis of the feed-in area available for the fibres deviates from the direction of the fibre longitudinal axis. In this case, the more the surface normal of the end face deviates from the direction of the fibre longitudinal axis to one side, the greater the deviation of the central receive direction is to the other side. By making use of this effect, the optical fibres may be arranged parallel to one another with their inclined end f aces having a corresponding inclination and orientation, so that they may either be arranged in a carrier plate with vertical holes and predetermined hole pattern, or directly next to one another, for exampler very closely packed, and may continue straight without any substantial curve to the rear, and may be packed into a bundle.

The invention is described in more detail below by means of the example shown partly schematically in the f iaures, in which Figure 1 is a cross-section through an optical fibre with an inclined end face; and Figure 2 is a cross-section through an arrangement for the directional coverage of optical radiation comprising optical fibres according to Figure 1.

The optical fibre 1 shown in cross-section in Figure 1 has, as known per se, a fibre core 2 with a refractive index nj and a f ibre sheath 3 with a refractive index n2 < nj. The end face 4 of the optical fibre 1 is ground at an angle so that its surf ace normal 5 is at an angle of a, to the fibre longitudinal axis 6.

The aperture angle B of the fibre corresponds in magnitude to that of a fibre with a vertical end face, however, the central direction 7 of coverage of the fibre is inclined at an angle a2 to the f ibre longitudinal axis 6. For purposes of clarity, angles a, and (12 are shown larger in the figures than is necessary or possible in practice. The following formula mentioned in the above-mentioned "Handbook of Optics" applies for small angles for a, and % with air as the ambient medium (xl = (nl - 1). (xl Figure 2 shows a cross-section through a sensor, wherein a plurality of optical fibres are arranged next to one another in a carrier plate 20.1 of a casing 20, e.g. are arranged in the form of a 4x4 matrix, the cross- section showing the second or third row of optical fibres 21 to 24. The optical fibres 21 to 24 have end faces 21.1 to 24.1 ground at an angle, their surface normals 21.2 to 24.2 intersecting at a point 25. Whilst the fibre longitudinal axes 21.3 to 24.3 all run parallel to one another, the central axes 21.4 to 24.4 of the coverage areas of the individual fibres intersect at a point 26 in front of the end faces of the optical fibres.

The angle at which the fibres 21 to 24 are ground and the orientation of their surface normals are selected in such a -S- way as to form at least partially overlapping visual fields,so that a closed solid angle is detected and from this incoming optical radiation is fed into one of the fibres, depending on direction. Evaluation of the light signals fed into the optical fibres may then occur, for example, in accordance with the above-mentioned German Patent Specification DE 37 36 616.

Claims

CLAIMS:

1. A fibre optic arrangement for directional pick up of optical radiation comprising a plurality of optical fibres having their end faces on the receive side arranged adjacent to one another and covering variously oriented solid angles, characterised in that said optical fibres are arranged parallel to one another in the vicinity of their end faces on the receive side, in that surface normals of said end faces on the receive side of at least a portion of the optical fibres extend at an angle other than zero from the fibre longitudinal axis, and in that said surface normals of at least a portion of the optical fibres have different orientations from one another.

2. A fibre optic arrangement according to Claim 1, wherein the surface normals of all of the end faces intersect at a point.

3. A fibre optic arrangement according to Claim 1 or 2, wherein the optical fibres are arranged next to one another in the form of a matrix in the vicinity of their end faces on the receive side.

4. A fibre optic arrangement according to Claim 1 or 2, wherein the optical fibres are packed very closely next to one another in the area of their end faces on the receive side.

5. A fibre optic arrangement for directional coverage of optical radiation substantially as hereinbefore described with reference to and as illustrated by Fig. 2 of the accompanying drawings.