Light width controller and image projector employing the same

A light width controller is disclosed including a light width controlling mirror of a refractive index n2, the mirror having: a first surface of an angle a1 with respect to horizontal; a second surface of a different angle a2 with respect to horizontal; and a reflection layer for reflecting light incident on the second surface. The first and second surfaces are not parallel. Light that has passed through a medium of a refractive index of n1 smaller than n2 and then has passed through the first surface is incident upon, and then reflected from, the second surface. Also, an image projector utilizing such a light width controller is disclosed.

BACKGROUND OF THE INVENTION 
The present invention relates to a light width controller and an image 
projector employing the same, and more particularly, to a light width 
controller and an image projector employing the same, in which efficient 
illumination of light is enabled even when the vertical and horizontal 
sizes of a target position are different. 
Generally, a conventional light width controller reduces the width of light 
by coupling or combining prisms or lenses. FIG. 1 shows a method for 
controlling the width of light in a prism-coupled mode. As shown in the 
drawing, when light of incidence angle of i and width h is incident on a 
first prism p1 of angle a and refractive index n, the light is refracted 
and bent by prism p1. The bent light is re-incident on second prism p2 of 
angle a and refractive index n at incidence angle i. The incident light is 
re-refracted by second prism p2 and converted to have width h'. 
Meanwhile, FIG. 2 shows a method for controlling the width of light by 
combining lenses according to Kepler's method. As shown in the drawing, 
when light of width h is incident on a first lens L1, the light is 
refracted by first lens L1 and travels toward a focus F. When a second 
lens L2 having its focus at the same position as that of first lens L1 is 
placed in parallel with the first lens, the refracted light is converted 
to have width h'. 
However, the conventional light width controller which reduces the width of 
light in such a method uses a plurality of components. For this reason, 
their relative positions must be precisely located, which complicates 
their configuration. Even if the configuration is enabled, the production 
cost is undesirably raised. 
In case that lenses are combined in the Kepler's mode, first lens L1 and 
second lens L2 must ensure a predetermined distance therebetween. If the 
whole system is formed with them, its set size becomes larger or reduces 
the light utilizing efficiency. 
SUMMARY OF THE INVENTION 
Therefore, it is a first object of the present invention to provide a light 
width controller which simplifies its components and facilitates reducing 
the width of light. 
It is a second object of the present invention to provide an image 
projector employing such a light width controller. 
In order to accomplish the first object, there is provided a light width 
controller including a light width controlling mirror of a refractive 
index n2, the mirror having: 
a first surface formed to have a predetermined angle a1 with respect to 
horizontal; a second surface formed to have a different predetermined 
angle a2 with respect to horizontal and a reflection layer formed against 
the second surface for reflecting light incident on the second surface, 
the light having passed through a medium of a refractive index of n1 
smaller than n2 and then having passed through the first surface prior to 
being incident on the second surface. 
In order to accomplish the second object, there is provided an image 
projector utilizing a light width controller, including: 
a light source; 
light width controller having a light width controlling mirror of a 
refractive index of n2 having a first surface of an angle a1 with respect 
to horizontal and a second surface of a different angle a2 with respect to 
horizontal and a reflection layer formed against the second surface for 
reflecting light incident on the second surface, the light having passed 
through a medium of a refractive index of n1 smaller than n2 and then 
having passed through the first surface prior to being incident on the 
second surface; 
image display means for displaying an image with a light width controlled 
by the light width controller; 
a projection lens for enlarging an image formed in the image display means; 
and 
a screen for projecting the image focused by the projection lens.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Hereinafter, preferred embodiments of the present invention will be 
described below with reference to the attached drawings. 
Referring to FIGS. 3 and 4, the light width controller of the present 
invention is comprised of a light width controlling mirror 100 of a 
refractive index of n2, having a first surface 10 formed to have a 
predetermined angle a1 with respect to the surface of land, i.e., 
horizontal, and a second surface 20 formed to have a predetermined angle 
a2 with respect to horizontal. The second surface 20 has a reflecting 
layer formed against it for reflecting light incident thereto that has 
passed through the first surface 10 and, before that, through a medium of 
a refractive index n1. 
The slope angle a1 of the first surface 10 is smaller than the angle a2 of 
the second surface 20 having the reflecting layer. There is relation of 
n2&gt;n1 in each refractive index, and n2 is in the range of 1.4 to 2.0. 
When light is incident to the light width controller at an angle a3, it 
advances to second surface 20 at an angle a4 according to the refraction 
principle. On the second surface, the incident angle is a8. At this angle, 
the light is reflected to be incident on first surface 10. 
Here, the incident angle at first surface 10 is a10. In this state, the 
light radiates with an angle of a11 according to the refraction principle. 
In other words, the incident light gets out after turning perpendicularly. 
Second and third lights also get out perpendicularly but the width that 
they define is reduced from H to H', as shown in FIG. 4. This effect will 
be explained in detail, as follows. 
Given that a1: slope angle of the first surface; 
a2: slope angle of the second surface; 
a3: incident angle (=a1) on the first surface; 
a4: outgoing angle (=sin.sup.-1 (n1*sin (a3)/n2) on the first surface; 
EQU a5=a3-a4; 
EQU a6=n/2-a2; 
EQU a7=n/2-a1; 
EQU a8=n/2-a6-a7=a2-a1+a4; 
EQU a9=n-a2-a7-a8 =n/2+2*(a1-a2)-a4; 
EQU a10=n/2-a9=2*(a2-a1)+a4; and 
EQU a11=sin.sup.-1 (n2*sin (a10)/n1), 
conditions to let light advance perpendicularly, a11=n/2-a1, and n1=1.0. If 
n2 equals n, a2 equals a1+1/2*arcsin {cos a1*(n.sup.2 -sin.sup.2 
a1).sup.1/2 -sin a1*(n.sup.2 -cos.sup.2 a1)!/n.sup.2 }. 
In the above equation, n1 and n2 indicate a refractive index of air and a 
refractive index of glass, respectively. When it comes to n1, a medium 
having a refractive index smaller than n2, other than the refractive index 
of air, may be applied to this invention. 
For instance, if n1=1, n2=8K7(1.5168), 
a2=37.78.degree. in case that a1=30.degree., and a2=52.22.degree. in case 
that a1=60.degree.. 
Here, width H of light is reduced into H'. 
EQU H'=H*tan(a1)+dL{sin (2*a8)/sin (a9)}*sin (a1). 
This result can be applied even in case that light is incident slantingly 
on the light width controller. 
In case that first surface 10 and second surface 20 are disposed oppositely 
to their former position, light of width H' that is incident on first 
surface 10 formed to have an angle a1 with respect to the surface of land, 
is produced to be light of width H, after passing through second surface 
20, the second surface being formed to an angle a2 to the surface of land 
and having the reflecting layer. Thus, the inventive light width 
controller may be employed for enlargement of light in width, e.g., a 
video signal having an aspect ratio of 4:3 can be changed to an aspect 
ratio of 16:9. 
This controller can be employed even in case of enlarging the width of 
light. In addition, it can be made to transmit a portion of light not 
required to form a visible image (for instance, ultraviolet or infrared 
rays), i.e., which is not required to be reflected by second surface 20. 
Such light width controller can be adapted even in case that the vertical 
and horizontal sizes of image display means such as LCD panel or film are 
different. FIG. 5 shows an image projector according to the second 
embodiment of the present invention to which the light width controller is 
attached. 
Referring to FIG. 5, the image projector of the present invention comprises 
a light source 40, that is, a light emitting portion, a light width 
controller means having a light width controlling mirror 100 for receiving 
light of width H projected from the light source to control width H to 
width H' and a condensing lens 50 for collecting light of width H' emitted 
via the light width controller, image display device having a liquid 
crystal panel 60 disposed on the back of the condensing lens, a projection 
lens 70 for enlarging an image formed on liquid crystal panel 60, and a 
screen 80 for projecting an image focused by the projection lens. 
The above-mentioned condensing lens 50 may be excluded from the light width 
controller. The light width controlling mirror 100, as mentioned above 
referring to FIG. 3, has a refractive index of n2, has a first surface 10 
formed to have a predetermined angle a1 to the surface of land and a 
second surface 20 formed to have a predetermined angle a2 larger than a1 
to the surface of land, and has a reflection layer for reflecting the 
light incident on the second surface 20 after having passed through the 
first surface 10, and before that, through a medium of a refractive index 
of n1. In the above occasion, each refractive index is in the relation of 
n2&gt;n1 and a2&gt;a1. 
When light of width H projected from light source 40, it is reflected via a 
reflection mirror 30, and this reflected light is incident on a light 
width controlling mirror 100. The light width controlling mirror 100 
receives light of width H and then emits light of width H' which is 
reduced from width H. 
The light of width H' emitted via the light width controlling mirror is 
collected by condensing lens 50 and then projected to liquid crystal panel 
60, an image forming portion, placed on the back. Here, the liquid crystal 
may be replaced with films. 
The light emitted from liquid crystal panel 60 enlarges an image formed in 
the liquid crystal via a projection lens 70, an image enlarging portion. 
An image focused by the projection lens is projected onto screen 80, a 
display. 
As a result, even in case that the vertical and horizontal sizes of a 
target position have a large difference, illumination can be performed 
efficiently by the light width controller in accordance with them. 
As described above, the present invention simplifies its components and 
easily reduces the width of light from H to H'. In addition, in case that 
the light width controller of the present invention is adapted to an image 
projector, illumination can be performed efficiently by easily controlling 
the width of light even in case that the vertical and horizontal sizes of 
the liquid crystal panel are different.