GB2108283A - Optical path folding system - Google Patents

Abstract

An optical path folding system includes a first mirror (12) and a second mirror (10) opposing the first mirror and forming an acute angle therewith, the mirrors being separated by a predetermined distance, whereby one end of the mirrors is more open than the other end of the mirrors. An input light ray (16) enters at the more open end of the mirrors and is incident upon the first mirror at a predetermined angle. The ray is reflected off each mirror a plurality of times and exits the mirrors at the more open end by reflecting off the second mirror at the same predetermined angle the input ray makes with the first mirror. <IMAGE>

Description

SPECIFICATION Optical path folding system This invention relates to an optical path folding system or apparatus and more particularly the utilization of a pair of mirrors forming an acute angle there-between to obtain a compact arrangement of the parts of scanning devices or line imaging optical systems.

There are many applications in which it is desirable to decrease the length of an optical path, the primary reason being to reduce the space needed for an optical system ensconced in a larger piece of equipment. One example of the need for conserving space is the modern electrophotocopier, in which a complex and bulky optical system is utilized to project an image of an original document onto a photoconductive surface. Photocopiers can be made considerably smaller if their optical systems can be reduced in size.

It is similarly desirable to shorten the required separation between a scanning mechanism such as a laser scanner, and a scanned surface, or between a lens and a line image or object.

While the folding of an optical path is not a new concept, it is desirable to have a relatively simple device, which, when positioned properly, will decrease the required separation between elements in an optical system.

According to the present invention there is provided an optical path folding system, comprising: a first mirror; a second mirror opposing said first mirror and forming an acute angle therewith, said mirrors being separated by a predetermined distance, whereby one end of said mirrors is more open than the other end of said mirrors; and an input light ray entering at the more open end of said mirrors and incident upon said first mirror at a predetermined angle, wherein said ray is reflected off each of said mirrors a plurality of times and exits said mirrors at the more open end by reflecting off said second mirror at the same predetermined angle the input ray makes with said first mirror.

In this specification, the phrase "one end of the mirrors being more open than the other end" is intended to indicate that the mirrors are located substantially in planes that intersect at an acute angle.

The single Figure of the accompanying drawing is a schematic, side elevation view of one example of optical path folding system according to the invention.

In the single Figure, there is seen a first mirror 10 and a second mirror 12 opposing the first mirror 10 and separated therefrom by a predetermined distance. A centre line 14 is indicated between the opposing mirrors 10 and 12, and each of the mirrors 10 and 12 forms an acute angle 0 with the centre line 14.

An input light ray 16 from a bundle of light rays (not shown) is provided by any conventional means at a predetermined angle 0 which is the angle between the input ray 16 and a plane perpendicular to the centre line 14. The relationship between angles 0 and 0 is as follows: 0= n where n represents the total number of times the input ray 16 bounces offthetwo mirrors 10 and 12.

For the arrangement illustrated in the single drawing Figure, n is 6, p is 45 degrees, and 0 is 7.5 degrees.

The lower limit for n is 4, inasmuch as the input ray 16 must bounce off each of the mirrors 10 and 12 at least twice in order to take advantage of the unique and useful compacting characteristics of the folding system described. The practical upper limit for n is primarily determined by the acceptable reflective losses and optical degradations associated with the optical quality of the mirrors 10 and 12.

The lower limit for the angle ,0 is determined by the interference caused by the mirror 12 and the input ray 16 which, in actual use, will be a bundle of rays.

As angle ,0 is reduced, the input ray 16 approaches the edge of the mirror 12 until some angle at which the edge of mirror 12 intersects the input bundle causing unacceptable loss. Angle may be as large as 90 degrees, at which point the input and output rays shown would be parallel. The user of the folding system described would determine the degree of deviation a acceptable or desirable between the input rays 16 and the exit rays 20.

The input light ray 16 enters the space between the mirrors 10 and 12 at the more open end 18 and also exitsthe mirror 10 and 12 atthe more open end 18 as illustrated by the exit light ray 20. The exit ray 20 exits the more open end 18 at the same angle 0 as the input ray 16, but on the opposite side of the centre line 14, with the exit ray 20 forming an angle with the input ray 16 such that a = 180" - 2.

It will be apparent that various changes may be made in the form, construction and arrangement of the parts without departing from the invention; the particular embodiment hereinbefore described and illustrated being merely a preferred and non-limiting embodiment.

1. An optical path folding system, comprising: a first mirror; a second mirror opposing said first mirror and forming an acute angle therewith, said mirrors being separated by a predetermined distance, whereby one end of said mirrors is more open than the other end of said mirrors; and an input light ray entering at the more open end of said mirrors and incident upon said first mirror at a predetermined angle, wherein said ray is reflected off each of said mirrors a plurality of times and exits said mirrors at the more open end by reflecting off said second mirror at the same predetermined angle the input ray makes with said first mirror.

2. A system according to claim 1, wherein the input light ray is reflected off each of said mirrors three times.

3. A system according to claim 1 or claim 2,

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Optical path folding system This invention relates to an optical path folding system or apparatus and more particularly the utilization of a pair of mirrors forming an acute angle there-between to obtain a compact arrangement of the parts of scanning devices or line imaging optical systems. There are many applications in which it is desirable to decrease the length of an optical path, the primary reason being to reduce the space needed for an optical system ensconced in a larger piece of equipment. One example of the need for conserving space is the modern electrophotocopier, in which a complex and bulky optical system is utilized to project an image of an original document onto a photoconductive surface. Photocopiers can be made considerably smaller if their optical systems can be reduced in size. It is similarly desirable to shorten the required separation between a scanning mechanism such as a laser scanner, and a scanned surface, or between a lens and a line image or object. While the folding of an optical path is not a new concept, it is desirable to have a relatively simple device, which, when positioned properly, will decrease the required separation between elements in an optical system. According to the present invention there is provided an optical path folding system, comprising: a first mirror; a second mirror opposing said first mirror and forming an acute angle therewith, said mirrors being separated by a predetermined distance, whereby one end of said mirrors is more open than the other end of said mirrors; and an input light ray entering at the more open end of said mirrors and incident upon said first mirror at a predetermined angle, wherein said ray is reflected off each of said mirrors a plurality of times and exits said mirrors at the more open end by reflecting off said second mirror at the same predetermined angle the input ray makes with said first mirror. In this specification, the phrase "one end of the mirrors being more open than the other end" is intended to indicate that the mirrors are located substantially in planes that intersect at an acute angle. The single Figure of the accompanying drawing is a schematic, side elevation view of one example of optical path folding system according to the invention. In the single Figure, there is seen a first mirror 10 and a second mirror 12 opposing the first mirror 10 and separated therefrom by a predetermined distance. A centre line 14 is indicated between the opposing mirrors 10 and 12, and each of the mirrors 10 and 12 forms an acute angle 0 with the centre line 14. An input light ray 16 from a bundle of light rays (not shown) is provided by any conventional means at a predetermined angle 0 which is the angle between the input ray 16 and a plane perpendicular to the centre line 14. The relationship between angles 0 and 0 is as follows: 0= n where n represents the total number of times the input ray 16 bounces offthetwo mirrors 10 and 12. For the arrangement illustrated in the single drawing Figure, n is 6, p is 45 degrees, and 0 is 7.5 degrees. The lower limit for n is 4, inasmuch as the input ray 16 must bounce off each of the mirrors 10 and 12 at least twice in order to take advantage of the unique and useful compacting characteristics of the folding system described. The practical upper limit for n is primarily determined by the acceptable reflective losses and optical degradations associated with the optical quality of the mirrors 10 and 12. The lower limit for the angle ,0 is determined by the interference caused by the mirror 12 and the input ray 16 which, in actual use, will be a bundle of rays. As angle ,0 is reduced, the input ray 16 approaches the edge of the mirror 12 until some angle at which the edge of mirror 12 intersects the input bundle causing unacceptable loss. Angle may be as large as 90 degrees, at which point the input and output rays shown would be parallel. The user of the folding system described would determine the degree of deviation a acceptable or desirable between the input rays 16 and the exit rays 20. The input light ray 16 enters the space between the mirrors 10 and 12 at the more open end 18 and also exitsthe mirror 10 and 12 atthe more open end 18 as illustrated by the exit light ray 20. The exit ray 20 exits the more open end 18 at the same angle 0 as the input ray 16, but on the opposite side of the centre line 14, with the exit ray 20 forming an angle with the input ray 16 such that a = 180" - 2. It will be apparent that various changes may be made in the form, construction and arrangement of the parts without departing from the invention; the particular embodiment hereinbefore described and illustrated being merely a preferred and non-limiting embodiment. CLAIMS

1. An optical path folding system, comprising: a first mirror; a second mirror opposing said first mirror and forming an acute angle therewith, said mirrors being separated by a predetermined distance, whereby one end of said mirrors is more open than the other end of said mirrors; and an input light ray entering at the more open end of said mirrors and incident upon said first mirror at a predetermined angle, wherein said ray is reflected off each of said mirrors a plurality of times and exits said mirrors at the more open end by reflecting off said second mirror at the same predetermined angle the input ray makes with said first mirror.

2. A system according to claim 1, wherein the input light ray is reflected off each of said mirrors three times.

3. A system according to claim 1 or claim 2, wherein the acute angle between mirrors is about 15 degrees.

4. An optical path folding system substantially as herein described and illustrated.