GB2110413A

GB2110413A - Gradient index fiber optic array

Info

Publication number: GB2110413A
Application number: GB08232929A
Authority: GB
Inventors: David Kleinschmitt
Original assignee: Pitney Bowes Inc
Current assignee: Pitney Bowes Inc
Priority date: 1981-11-20
Filing date: 1982-11-18
Publication date: 1983-06-15
Also published as: JPS58184108A; DE3240928A1; FR2517075A1

Abstract

A gradient index fiber optic array 12 has at least one row of image transmitting optical fibers, the fibers having input and output ends. The improvement comprises a pair of opposing mirrored surfaces 16, 18; 20, 22 adjacent both the row input and output ends of the fibers, whereby the light gathering capacity of the array is increased. <IMAGE>

Description

SPECIFICATION Gradient index fiber optic array The present invention relates to an image transmission means, and more particularly to a means of increasing the light throughput from a radiating line or point source on the axis of a gradient index fiber optic array while maintaining the integrity of the image.

Image transmitting optical fibers, such as that produced by the Nippon Sheet Glass Co., Ltd.

under the trade name of Selfoc, are employed in many applications, such as photocopying machines, transfer optics for LED printers, or CRT scanners and printers. A Selfoc lens, or image transmitting optical fiber, is made of glass or synthetic resin having a refractive index distribution in a cross section thereof that varies parabolically outwardly from the center of the fiber, and is defined by the equation n=nO (1-ar2) where nO is the refractive index at the center, n is the refractive index at a distance r from the center, and a is a positive constant of proportionality. The Selfoc lens and the image transmitter formed by a bundle of Selfoc lenses are described in U.S. Patent No. 3,658,407, issued April 25, 1972, and reference may be made thereto for the details thereof.

A practical image transmitter consists of a plurality of said image-transmitting optical fibers, which are held closely bundled together, in a staggered file arrangement, for example, by synthetic resin or other suitable binder, the corresponding opposite ends of which constitute an image receiving surface and an image emitting surface. When a line source such as might be traced on a cathode ray tube or a point source such as a light emitting diode is imaged by a gradient index fiber optic array, the amount of light collected is maximized by increasing the number of fiber rows in the array up to the point where the limitations imposed by the fiber field angle prevent further improvement. Typically, two or three rows of fibers provide the greatest practical light gathering ability.Increasing the number of rows, however, increases the cost, size and manufacturing complexity of the array.

The present invention accordingly aims to increase the light gathering ability of an array of gradient index optic fibers, and is applicable in electrostatic printers where the imaged light source is a cathode ray tube (CRT) or LED array.

The invention may also be used in any image transfer system where a line from a cathode ray tube or LED array is to be imaged, such as photographic CRT recorders.

According to the invention, there is provided a gradient index fiber optic array having at least one row of image transmitting optical fibers, said fibers having input and output ends, the array including a pair of opposing mirrored surfaces adjacent both the row input and output ends of said fibers, arranged in such a manner that the light gathering capacity of said gradient index fiber optic array is increased.

The invention will be better understood from the following non-limiting description of examples thereof given with reference to the accompanying drawings in which: Fig. 1 is a side view of a line or point source on the axis of a single row array of gradient index fibers in accordance with the prior art; Fig. 2 is a view similar to Fig. 1 except it shows the addition of mirrored surfaces adjacent to the row input and output ends in accordance with this embodiment of the invention; Fig. 3 is a perspective view, partiany broken away, of a double row array of gradient index fibers having mirrored surfaces adjacent the row input and output ends, in accordance with another embodiment of the invention.

Fig. 1 shows a point or line source of light A located on the axis of a single row array of gradient index fibers 12 in accordance with the prior art. It can be seen that the image 14 contains the light radiated only within the angle a, while all the rays outside this angle a are lost.

Fig. 2 shows how the addition of mirrored surfaces placed adjacent the row input and output ends increases the light gathering capacity of the fibers 12. A pair of input mirrors 16 and 18 placed as shown in Fig. 2 generate apparent sources of light at B and C, the rays of which are collected by the fiber 12. It is important to note that those rays appearing to emanate from B and C would not be collected if it were not for the mirrored surfaces 16 and 18. A pair of mirrors 20 and 22 are located at the output end of the fiber 12. The exiting rays which would otherwise that is to say if only mirrors 1 6 and 1 were present) form images at B' and C' are reflected by the second pair of mirrors 20 and 22 and superimposed at A'.

Since the image at A' contains the light from A, B, and C, the throughput of the array has been increased. Since the light apparently emanating from the notional sources at B and C suffers some loss in reflection, the image at A' is not three times as bright as it would be without the inclusion of the mirrors 1 6, 18, 20 and 22, but rather about 2.5 times as bright as it would be without the mirrors, 1 6, 1 8, 20 and 22 for the single row array of fibers 12 seen in Fig. 2. In other words the light gathering ability of the array has been more than doubled by the present invention.

Fig. 3 shows a plurality of gradient index optic fibers 12 arranged in two rows 24 and 26 in staggered file arrangement and held together by a synthetic resin or other suitable binder 28. On either side of the fibers 1 2 are a pair of support blocks 30 and 32 for supporting a pair of input mirrors 34 and 36 and a pair of output mirrors 38 and 40.

Tests results have shown that the increase in light throughput with the two row array, as seen in Fig. 3, is almost the same as with the single row array seen in Fig. 2. Generally, however, there is a decrease in the enhancement of the light gathering capacity of a gradient index fiber optic array as the number of rows of fibers is increased, but this decrese is very slight.

It will be understood by those skilled in the art that the present invention can be carried into effect in other ways, and the protection hereby obtained is not to be regarded as limited to the specific details illustrated herein.

Claims

1. A gradient index fiber optic array having at least one row of image transmitting optical fibers, said fibers having input and output ends, the array including a pair of opposing mirrored surfaces adjacent both the row input and output ends of said fibers, arranged in such a manner that the light gathering capacity of said gradient index fiber optic array is increased.

2. An array according to claim 1, wherein the gradient index fiber optic array includes two rows of optical fibers, said rows being adjacent to one another in a staggered file arrangement.

3. An array according to claim 2, wherein the rows of optical fibers are located between a pair of support blocks which also serve to support or provide the mirrored surfaces.

4. A gradient index fiber optic array substantially as herein described with reference to and as illustrated in the accompanying drawings.