JPH058562Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a polarization conversion element that obtains linearly polarized light from undefined polarized light.

[Conventional technology]

Conventionally, to obtain linearly polarized light from undefined polarized light,
Elements are used that select linearly polarized light by transmitting undefined polarized light through a polarizer or a birefringent crystal or reflecting it at an interface. For example, a sheet polarizer has a structure in which a polarizing film is created by orienting and adsorbing iodine, etc. to a thin plastic sheet, etc., and a protective plastic sheet, etc. is adhered to both sides, and an ordinary light beam in a birefringent crystal. Nicol prism, which extracts linearly polarized light from the difference in the traveling direction of the light and the extraordinary ray,
There are prisms, etc. There is also a polarizing beam splitter that coats one of the oblique sides of two right-angle prisms with a semi-transparent film to join the oblique sides together, and extracts transmitted light and reflected light as linearly polarized light orthogonal to each other.

[Problem that the invention attempts to solve]

However, when a conventional sheet polarizer or polarizing beam splitter is used alone, the light utilization efficiency of the light source is inevitably reduced to less than half because unnecessary polarized components of light are absorbed or reflected. As an example of a device that uses linearly polarized light, in the case of a liquid crystal display device that uses TN (twisted nematic) liquid crystal, the light from the light source is transmitted through two polarizers with 60
% or more will be lost. Furthermore, due to edge reflection, absorption, and aperture limitations of the liquid crystal display element, the light utilization efficiency of the entire device is approximately 20%, and in order to obtain a sufficient amount of light for display, the brightness of the light source must be increased. Power consumption becomes large.

An object of the present invention is to provide a polarization conversion element for obtaining linearly polarized light from irregularly polarized light, and for improving the light utilization efficiency of a light source.

[Means for solving problems]

The polarization conversion element of the present invention includes a polarization beam splitter for spatially separating undefined polarization light from a light source into linearly polarized light mainly having a P-polarized component and linearly polarized light having an S-polarized component; Either one of the linearly polarized light of the P-polarized component and the linearly polarized light of the S-polarized component such that the polarization direction of the linearly polarized light of either one is equal to the polarization direction of the other linearly polarized light. The polarization direction of the polarized light is rotated by 90 degrees, and the polarization direction of the polarized light is rotated by 90 degrees, and the polarization direction is rotated by 90 degrees, and the polarization direction of the polarized light is rotated by 90 degrees.

[Effect]

FIG. 5 is a diagram for explaining the principle of the present invention. When the incident light 50, which is linearly polarized light with a polarization direction 51, is reflected three times by the total reflection mirrors 52, 53, and 54, the polarization direction of each reflected light 55, 56, and 57 becomes the polarization direction 58, with respect to the traveling direction of the light. It changes like 59,60. As is clear from FIG. 5, the traveling direction of the reflected light 57 that has passed through the optical system is the same as that of the incident light 50, and the polarization direction is the polarization direction 5 of the incident light 50.
The polarization direction 61 is perpendicular to 1. By using a total reflection mirror in this way, it is possible to arbitrarily convert the polarization direction of linearly polarized light.

Utilizing the above principle, the present invention makes undefined polarized light from a light source enter a polarizing beam splitter, spatially separates it into transmitted light and reflected light that are linearly polarized orthogonal to each other. By reflecting one of the two lights a plurality of times with at least two or more right-angle prisms, the two lights are combined so that the polarization directions are equal, thereby obtaining a polarization conversion element with high light utilization efficiency of the light source.

〔Example〕

FIG. 1 is a diagram showing a first embodiment of the present invention. This polarization conversion element is composed of a light source 1 such as a xenon lamp or a halogen lamp, a condenser lens 2 that converts the light from the light source 1 into a parallel beam, a polarizing beam splitter 4, and two right-angle prisms 5 and 6. has been done. Note that the two right-angle prisms 5 and 6 are arranged so that their reflection normal directions are perpendicular to each other. The polarizing beam splitter 4 is made by coating one of the hypotenuses of two right-angled prisms with a semi-transparent film made of a metal film, a dielectric multilayer film, etc., and joining the hypotenuses together, and is effective especially in the visible range. A device that can be separated into polarized light and S-polarized light was used. Further, the rectangular prisms 5 and 6 satisfy the total reflection condition for light having wavelengths in the visible range at the oblique sides.

To bond the polarizing beam splitter 4 and the right-angle prisms 5 and 6 together in the configuration shown in Figure 1, an optical adhesive whose refractive index is matched to that of the glass material is used to prevent light loss at the end faces. It was attached using a material (lens bond, ultraviolet curing adhesive, etc.).

In the polarization conversion element having such a configuration, light of undefined polarization is emitted from the light source 1 and converted into a parallel light beam by the condenser lens 2 to obtain incident light 3. When the incident light 3 is made incident on the polarizing beam splitter 4, the transmitted light 7 becomes P-polarized light (polarization direction 9) and linearly polarized light, and the reflected light 8 becomes S-polarized light (polarization direction 10) linearly polarized light. The reflected light 8 is totally reflected by the right angle prisms 5 and 6, so that the polarization direction becomes polarization direction 1.
It changes like 1, 12. The reflected light 15 emitted from the right-angle prism 6 travels in the same direction as the transmitted light 7, and the polarization directions 13 and 14 are the same. Therefore, by combining the reflected light 15 and the transmitted light 7, the light utilization efficiency when converting the undefined polarized light from the light source 1 into linearly polarized light is equal to the combined reflected light 1.
I was able to increase it by 5.

FIG. 2 is a diagram showing a second embodiment of the present invention. This polarization conversion element includes a polarization beam splitter 24, four right angle prisms 25, 26, 27,
28 are pasted together as shown in the figure.

In the polarization conversion element having such a configuration, the first
When the incident light 21 obtained in the same manner as in the embodiment is made to enter the polarizing beam splitter 24, the transmitted light 22
The reflected light becomes linearly polarized P-polarized light (polarization direction 29), and the reflected light becomes linearly polarized S-polarized light. The reflected light is totally reflected four times by the four right-angle prisms 25, 26, 27, and 28, so that the polarization direction changes, and the reflected light 23 is emitted from the right-angle prism 28.
The polarization direction of is the direction indicated by 30. reflected light 23
is the same traveling direction as the transmitted light 22, and
Polarization directions 29 and 30 are equal. Therefore, similarly to the first embodiment, by combining the reflected light 23 and the transmitted light 22, the light utilization efficiency when converting the undefined polarized light from the light source into linearly polarized light is the same as that of the combined reflected light 23. I was able to increase it by that amount. Furthermore, compared to the first embodiment, the distance between the optical axes of the transmitted light 22 and the reflected light 23 could be made smaller.

FIG. 3 is a diagram showing a third embodiment of the present invention. In this embodiment, a polarizing beam splitter 34,
A structure similar to that of the second embodiment in which four right angle prisms 35, 36, 37, and 38 are bonded together as shown in the figure, and furthermore, on the output surface of the reflected light 33,
A wedge prism 39 is pasted together, and a sheet polarizer 42 is inserted into the optical system to obtain linearly polarized light with a good degree of polarization.

In the polarization conversion element having such a configuration, the first
When the incident light 31 obtained in the same manner as in the embodiment is made to enter the polarizing beam splitter 34, the transmitted light 32
The reflected light becomes linearly polarized P-polarized light (polarization direction 40), and the reflected light becomes linearly polarized S-polarized light. The reflected light is totally reflected four times by the four right-angle prisms 35, 36, 37, and 38, so that the polarization direction changes, and the reflected light 33 from the right-angle prism 38 changes its optical path by the wedge-shaped prism 39. is emitted.
The polarization direction of the reflected light 33 is the direction indicated by 41,
It is equal to the polarization direction 40 of the transmitted light 32.

In this example, the transmitted light 32 and the reflected light 33 can be combined at any position, and since the sheet polarizer 42 is inserted into the optical system, linearly polarized light with a good degree of polarization can be obtained. .

In the third embodiment, the same effect can be obtained even if the wedge prism 39 is inserted not only in the optical path of the reflected light 33 but also in the optical path of the transmitted light 32.

FIGS. 4a and 4b are diagrams for explaining the effects of the third embodiment. Figure 4a shows the light utilization efficiency when the sheet polarizer is used alone, which is 40%.
weak and low. FIG. 4b is a level diagram showing the light utilization efficiency when the polarization conversion element of the third embodiment is used. Since total reflection of the prism is used, there is little loss in the optical system, and even with the insertion of a sheet polarizer at the end, a light utilization efficiency of 76% was achieved.

[Effect of idea]

As explained above, according to the present invention, it was possible to obtain a polarization conversion element that obtains linearly polarized light from undefined polarized light and has high light utilization efficiency of a light source.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the first embodiment of the present invention, and FIG.
The figure shows a second embodiment of the present invention, Figure 3 shows a third embodiment of the present invention, and Figures 4a and b are diagrams for explaining the effects of the third embodiment. , FIG. 5 is a diagram for explaining the principle of the present invention. 1...Light source, 2...Condenser lens, 3,2
1, 31...Incoming light, 4,28,38...Polarizing beam splitter, 5,6...Right angle prism, 7,
22, 32... transmitted light, 9, 10, 11, 12,
13, 14... Polarization direction, 15, 23, 33...
Reflected light, 42...Sheet polarizer.

Claims (1)

[Scope of utility model registration request] a polarizing beam splitter for spatially separating undefined polarized light from a light source into linearly polarized light mainly having a P-polarized component and linearly polarized light having an S-polarized component; The polarization direction of one of the linearly polarized lights of the S-polarized light component is rotated by 90 degrees so that the polarization direction of one of the linearly polarized lights is equal to the polarization direction of the other linearly polarized light. , at least two or more right-angle prisms including two right-angle prisms that combine the two linearly polarized lights.