JPH02264904A - Light source for linearly polarized light - Google Patents

Abstract

PURPOSE:To obtain the light source for linearly polarized light which efficiently generates linearly polarized light by disposing a wavelength plate between the light source and a polarized beam splitter and making either one of the two luminous fluxes separated by the polarized beam splitter to a reflecting mirror. CONSTITUTION:The polarized beam splitter 34 has a slope 35 and light-emitting faces 37, 38 and separates the incident luminous flux from a light source 31 side to the two luminous fluxes having the polarization directions intersecting orthogonally with each other. A quarter-wave plate 33 is provided between the polarized beam splitter 34 and the light source 31 side. The luminous flux which is emitted from the light source 31 side and transmits the quarter-wave plate 33 and the slope 33 of the beam splitter 34 is emitted as it is as exit light from the emitting face 38. On the other hand, the luminous flux separated by the beam splitter 34 is reflected by a luminous flux reflecting element 36 via the emitting face 37, is reflected again by the slope 35 to the light source 31 side and is made incident to the reflection mirror 32 via the quarter-wave plate 33. The reflected luminous flux thereof traces again the optical path toward the quarter-wave plate 33 side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a linearly polarized light source, and particularly to a linearly polarized light source that can efficiently generate linearly polarized light.

[Conventional technology]

Some devices and other devices that use polarized light utilize linearly polarized light. An example of a device that uses linearly polarized light is a projection type liquid crystal display device that uses twisted nematic (TN) liquid crystal, as will be mentioned later.

Conventionally, when using a halogen lamp, xenon lamp, etc. as a light source in such a device, the light emitted from the light source such as a halogen lamp or xenon lamp is undefined polarized light, so it is difficult to obtain linearly polarized light. , an element is used that selects linearly polarized light by transmitting undefined polarized light from a light source through a polarizing plate or a birefringent crystal, or by reflecting it at a boundary surface.

As an example, such an element may be a sheet polarizer, which has a structure in which a polarizing film is created by aligning and adsorbing iodine, etc. to polyvinyl alcohol, etc., and a plastic sheet, glass plate, etc. is adhered to both sides for protection. , Nicol prisms, Rochon prisms, etc. are used that extract linearly polarized light from the difference in the propagation directions of ordinary and extraordinary rays in a birefringent crystal. In addition, a polarizing beam splitter is also used in which a semi-transparent film is coated on one slope of two right-angle prisms to join the slopes, and the transmitted light and reflected light are extracted as linearly polarized light whose polarization directions are orthogonal to each other. .

[Problem to be solved by the invention]

However, when using a conventional polarizing element such as a sheet polarizer or a polarizing beam splitter alone, the light utilization efficiency of the light flux from the light source is less than 50% because unnecessary polarized light components are absorbed or reflected. Since it had to be made low, there is a problem that there is a large loss of light.

For example, when the device used is a projection type liquid crystal display device, in order to secure a projection screen with the required brightness, it is necessary to use a light source with higher brightness.

That is, as mentioned above, as an example of a device that uses linearly polarized light, there is a projection type liquid crystal display device in which a liquid crystal display element using TN (twisted nematic) liquid crystal is enlarged and projected onto a screen surface using a projection lens. In such an enlarged projection, if a configuration is adopted in which a polarizing plate consisting of a sheet polarizer is placed on each of the light exit surfaces of the liquid crystal display, the transmittance of the light beam from the light source can be increased by just the polarizing plate. It becomes less than 40%. Furthermore, liquid crystal display elements are affected by absorption by the liquid crystal, reflection at interfaces, aperture ratio, and color filters, so the overall transmittance of the element has to be quite low, at a few percent. . Therefore, in order to obtain a bright projection screen, it is necessary to use a light source with high brightness.

If a high-brightness light source is required, the problem of low efficiency when obtaining linearly polarized light in the conventional way will not only increase, but also increase the power consumption of the equipment used, increase the temperature due to heat generation, and increase the polarization. This can even lead to deterioration of the board.

An object of the present invention is to provide a linearly polarized light source that can efficiently generate linearly polarized light.

[Means to solve the problem]

The linearly polarized light source of the present invention includes: a light source having a reflecting mirror; a polarizing beam splitter that separates a light beam from the light source into two light beams whose polarization directions are perpendicular to each other; and at least one light beam disposed between the light source and the polarizing beam splitter. It is characterized by comprising the above-mentioned wavelength plate, and a light beam reflecting element that causes one of the two light beams to be incident on the reflecting mirror.

[Effect]

A polarizing beam splitter separates the light beam from the light source into two light beams whose polarization directions are perpendicular to each other, and
If at least one wavelength plate is provided between the light source and the polarized beam splinter, and the light beam from either side is reflected by a light beam reflecting element and incident on the reflector on the light source side, the emitted light from the light source can be In the case of the light beam reflected between the reflector and the light beam reflecting element, a specific polarization component is transmitted to the output side, and most of the light is emitted from the polarizing beam splitter as linearly polarized light aligned in a specific polarization direction. death,
It becomes possible to realize a linearly polarized light source that efficiently generates linearly polarized light.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a plan view of a linearly polarized light source showing a first embodiment of the present invention. As shown in FIG. 1, the linearly polarized light source of this embodiment includes a light source 31, a reflecting mirror 32, and a wavelength plate.
It is composed of a /4 wavelength plate 33, a polarizing beam splitter 34, and a light beam reflecting element 36.

The light source 31 has a reflecting mirror 32 as shown in the figure, and these constitute a light source section.

The polarizing beam splitter 34 has a slope 35 and an output surface 373.
8, which is a polarizing beam splitter that separates the incident light beam from the light source 31 side into two light beams whose polarization directions are orthogonal to each other. As for the incident light flux from the light source 31 side, the light source 3
In addition to the direct light from 1, the light reflected by the reflecting mirror 32 is also included.

The quarter wavelength plate 33 is arranged between such a polarizing beam splitter 34 and the light source side, and in this embodiment,
The quarter wavelength plate 33 has one side connected to the polarizing beam splitter 3.
4 and has a glued configuration. The other surface of the quarter-wave plate 33 serves as a person exit surface 39 and faces the above-mentioned light source side.

The light flux reflecting element 36 is used to reflect one of the above-mentioned two light fluxes so that it is incident on the reflecting mirror 32. In this embodiment, as will be described later, for example, aluminum is vapor-deposited on the exit surface of one of the light beams that is reflected and separated by the slope 35 of the polarizing beam splitter 34, on the exit surface 37 side in the illustrated case. In this case, a light beam reflecting element is provided.

Emitted light from the linearly polarized light source having the above configuration is extracted from the output surface 38 side of the polarization beam splitter 34. That is, the light flux from the light source side that passes through the quarter-wave plate 33 and the slope 35 of the polarizing beam splitter 34 is emitted as output light from the output surface 38, while the other part is transmitted through the polarizing beam splitter 34. The separated luminous flux heading toward the output surface 37 is first reflected by the luminous flux reflecting element 36 and then reflected again by the slope 35 toward the light source, and enters the reflecting mirror 32 via the 1/4 wavelength plate 33. The light beam reflected by the reflecting mirror 32 is reflected again by the quarter-wave plate 3.
It is designed so that the light path toward the third side can be taken.

The linearly polarized light source of this embodiment includes a light source 31 having a reflecting mirror 32 as described above, a polarizing beam splitter 34 that separates the light beam from the light source 31 into two light beams whose polarization directions are orthogonal to each other, and a polarizing beam splitter 34 that separates the light beam from the light source 31 into two beams whose polarization directions are orthogonal to each other. A quarter-wave plate 33 serving as at least one wavelength plate disposed between the beam splitter 34 and a light beam reflecting element 36 that reflects one of the two light beams so that it is incident on the reflecting mirror 32. It is composed of.

The linearly polarized light source according to the present invention, including the linearly polarized light source having the configuration shown in FIG. 1 and other embodiments described later, is based on the following principle.

This will be explained using FIG. 2, which shows the principle of emitting p-polarized linearly polarized light as emitted light. In FIG. 2, the light emitted from the light source 1 is undefined polarized light,
It becomes an emitted light beam directly from the light source 1 or after being reflected by the reflecting mirror 2. Now, in order to simplify the explanation, we will focus on the optical path of a single emitted light 10, and the principle will be explained below using that optical path.

First, the synchrotron radiation 10 passes through the wavelength plate 3, but the synchrotron radiation 10
Since this is undefined polarized light, the transmitted light 11 also remains undefined polarized light.

Next, the transmitted light 11 enters the polarizing beam splitter 4, and the incident light 12 is split into two linearly polarized lights, a transmitted light 13 and a reflected light 15, whose polarization directions are orthogonal to each other on the slope 5 of the polarized beam splitter 4. separated into

Here, the transmitted light 13 is p-polarized linearly polarized light, and the reflected light 15
is S-polarized linearly polarized light, and the intensity ratio thereof is approximately 1:1. Of these, the transmitted light 13 is transmitted through the polarizing beam splitter 4
The output light 14, which is linearly polarized p-polarized light, is emitted as is.

On the other hand, the reflected light 15 enters the light flux reflecting element 6, and the incident light 16 is specularly reflected in the same polarization state. The reflected light 17 obtained in this way enters the polarizing beam splitter 4 again, but the incident light 18 is totally reflected at the slope 5 because it is S-polarized linearly polarized light like the reflected light 15 described above. . This reflected light 19 exits the polarizing beam splitter 4 and enters the wave plate 3.

Here, when the wavelength plate 3 is a quarter-wave plate as in the embodiment, when the incident light 20 which is linearly polarized light enters, the transmitted light 21 becomes circularly polarized light. However, it is necessary to arrange the wave plate so that the angle between the polarization direction of the incident light 20 and the optical anisotropic axis of the wave plate 3 is 45 degrees.

Now, the transmitted light 21 that is incident on the wavelength plate 3 from the polarizing beam splitter 4 side and transmitted therethrough heads toward the light source side. Since the light source 1 has a reflecting mirror 2, in this case, the incident light 22 enters the reflecting mirror 2 and is reflected by the reflecting mirror 2, thereby obtaining reflected light 23. This reflected light 23 enters the wave plate 3 again, but
Since the incident light 24 is circularly polarized, the transmitted light 25 is linearly polarized.

Moreover, not only is it converted into linearly polarized light in this way,
The polarization direction also acts as p-polarized light with respect to the polarization beam splitter 4.

That is, here, as described above, the light beam reflecting element 6
Considering the transmitted light 25 that is reflected by the light source and reflected by the reflecting mirror 2 and then enters the polarizing beam splitter 4 from the light source side, the transmitted light 25 is the same as the incident light 20 described above.
has passed through the wave plate 3 twice, and the polarization direction of the transmitted light 25 is perpendicular to the polarization direction of the incident light 20.

The incident light 20 is based on the reflected light 15 which is S-polarized linearly polarized light, and therefore, since the incident light 20 was S-polarized with respect to the polarized beam splinter 4, the transmission obtained as described above is The light 25 acts on the polarization beam splitter 4 as p-polarized light. Therefore,
Since the second incident light 26 is p-polarized light, the previous incident light 1
Similar to the component of the transmitted light 13 in case 2, the light passes through the slope 5 of the polarized beam splinter 4 as it is and becomes the emitted light 27.

As a result, the single emitted light 10 focused on in FIG. 2 is a polarized beam in which the above-mentioned emitted light 14 and the above-mentioned emitted light 27 are both linearly polarized light of P polarization, that is, linearly polarized light with the same polarization direction. The light will be emitted from the splitter 4.

The above is the same for light on optical paths other than the synchrotron radiation 10, and through the above process, the synchrotron radiation from the light source 1 is polarized as linearly polarized light with most of the light aligned in a specific polarization direction. Since the light is emitted from the beam splitter 4, according to the configuration of the present invention, it is possible to obtain a linearly polarized light source that efficiently generates linearly polarized light.

In the above, the wavelength plate 3 was explained as a 1/4 wavelength plate, but
This does not necessarily have to be a 1/4 wavelength plate; in that case, the transmitted light 25 becomes elliptically polarized light, and in the process of being repeatedly reflected between the reflecting mirror 2 and the light beam reflecting element 6, the transmitted light 25 becomes elliptically polarized light. 5, only the p-polarized light component is transmitted,
At this time as well, most of the light emitted from the light source 1 is finally emitted from the polarization beam splitter 4 as P-polarized linearly polarized light.

As described above, the wavelength plate used does not need to be a quarter-wave plate, but when higher efficiency is to be obtained, the efficiency of the negative layer can be improved by using a quarter-wave plate.

In other words, if there are many repeated reflections between the reflecting mirror and the light beam reflecting element as described above, the loss due to absorption in the element will increase and the efficiency will decrease, so it is necessary to eliminate the decrease in efficiency caused by this. In this case, it is desirable to use a quarter wavelength plate as the wavelength plate.

The configuration shown in FIG. 1 shows an example of a mode in which a quarter wavelength plate is used, and this will be explained in more detail below.

In FIG. 1, a light source 31 is a light source that emits undefined polarized light, and a direct emitted light beam from the light source 31 or an emitted light beam reflected by a reflecting mirror 32 is used as a polarized beam sub, a 34.1/4 wave plate 33 and a light beam reflecting element 36.

Here, the light source 31, polarizing beam splitter 34, 1/4 wavelength plate 33, and light beam reflecting element 36 used in the above four components are specifically as follows.

That is, as the light source 31, a xenon lamp was used as a white light source with high brightness. Although not clearly shown in the diagram, a power source is required. Furthermore, in addition to the xenon lamp, a light source such as a halogen lamp or a metal halide lamp can also be used.

Further, the quarter-wave plate 33 has the function of converting linearly polarized light into circularly polarized light or circularly polarized light into linearly polarized light, and is particularly effective in the wavelength range of the visible light region. A polyvinyl alcohol film was stretched to have the desired birefringence and sandwiched between protective glasses. 1/4
Other wavelength plates include optical crystals with birefringence,
A structure in which a liquid crystal is sandwiched between two glass substrates subjected to alignment treatment can also be used as a quarter-wave plate.

Furthermore, regarding the polarizing beam splitter 344, it is made by coating one of the slopes 35 of two right-angle prisms with a semi-transparent film made of a metal film, dielectric multilayer film, etc., and joining the slopes together. , for light with wavelengths in the visible light range, p-polarized light and S
We used polarized light that can be separated into two linearly polarized lights. The extinction ratio, that is, the strong change in the p-polarized light component and the s-polarized light component of the transmitted light, was 100:1.

The light flux reflecting element 36 is manufactured by depositing aluminum on the output surface 37 of the S-polarized light reflected by the slope 35 of the polarized beam splinter 34. Further, the quarter-wave plate 33 has its optical anisotropic axis and the S-polarized light and the P-polarized light separated by the polarization beam splitter 34.
They are arranged so that the angle formed with the polarization direction of the polarized light is 45 degrees, and are integrated by adhesive as described above.

That is, in the embodiment, in order to further reduce reflection at the light exit surface of the element, the 1/4 wavelength plate 33 and the polarizing beam splitter 34 are bonded together with their refractive indexes matched;
The light output surface 39 of the wavelength plate 33 and the output surface 38 of the polarized beam splinter 34 are coated with a non-reflection coating made of a dielectric multilayer film.

Now, in the linearly polarized light source shown in FIG. 1, if power is turned on to the light source 31, as described in the explanation of the principle above, the outgoing light beam directly from the light source 31 or reflected by the reflecting mirror 32 will be , the P-polarized light transmitted through the quarter-wave plate 33 and the slope 35 of the polarized beam splinter 34 is
The light is emitted from the light emitting surface 38, while the polarizing beam splitter 3
Regarding the S-polarized light reflected on the slope 35 of No. 4, the light flux reflecting element 36, the slope 35, the 1/4 wavelength plate 33, and the reflection m32
．． 1/4 wavelength plate 33] By taking the optical path, the polarization direction is rotated by 90 degrees, becoming P-polarized light, which passes through the slope 35,
The light is emitted from the emission surface 38. Therefore, most of the light emitted from the light source 31 is emitted from the output surface 38 of the polarization beam splitter 34 as P-polarized linearly polarized light. In the above process, the loss of light is only a small amount due to end face reflection of the element and absorption by the medium.

In this way, when obtaining linearly polarized light, the first method according to the present invention
By using the linearly polarized light source shown in the figure, it is possible to efficiently obtain linearly polarized light. Compared to the conventional example, the projection efficiency is twice as high, and when used in the aforementioned projection type liquid crystal display device, it is possible to obtain a bright projection screen with the same configuration, and therefore, the projection type liquid crystal display device When used for this purpose, it is possible to avoid an increase in the power consumption of the device and the adverse effects of heat generation.

In addition, in the description of this embodiment, the light flux reflecting element 36 is
Although it has been described that aluminum is vapor-deposited on the output surface 37, it is more effective to use an enhanced reflection mirror coated with a metal or dielectric multilayer film having a high reflectance. Also, naturally, the light flux reflecting element 36 is connected to the output surface 3 of the p-polarized light.
8, the emitted light from light #31 is mostly S
Since the polarized light is emitted from the output surface 37 as S-polarized linearly polarized light, exactly the same effect can be obtained.

FIG. 3 is a plan view of a linearly polarized light source showing a second embodiment of the present invention. In this embodiment, as shown in FIG. 3, it is composed of a light source 41 having a reflecting mirror 42, a polarizing beam splitter 44, a quarter-wave plate 43, and a right-angle prism 46 as a light beam reflecting element. , further includes an air cooling fan 50.

In this linearly polarized light source, the same light source 41 and polarized beam splitter 44 as in the first embodiment were used.

As described above, the right-angle prism 46 is used as a light beam reflecting element, and is manufactured by polishing optical glass such as BK7. This right-angle prism 46 satisfies the condition that the light incident from the output surface 47 of the polarizing beam splitter 44 is totally reflected at the interface with air, and is capable of returning and reflecting the incident light beam. Moreover, the loss can be made very small.

Furthermore, although the illustrated right-angle prism 46 and polarizing beam splitter 44 are bonded together with matching refractive indexes, this method is not limited to this method. It is also possible to do so.

In addition, when the brightness of the light source 41 is high, the 1/4 wavelength plate 4
3 and deterioration of the polarizing beam splitter 44 will occur, so in this embodiment, a cold mirror that reflects only visible light is used for the reflection of the reflection mirror 42, and a cold mirror that reflects only visible light is used for the reflection of the reflection mirror 42, and a cold mirror is used for the reflection of the 1/4 wavelength plate 43, and a A cold filter that only transmits visible light was applied to each. Furthermore, if a cooling fan 50 is provided as shown in the figure and the entire device is cooled by the air cooling fan 50, it is effective to prevent deterioration of the element.

In the case of this embodiment as well, linearly polarized light can be efficiently generated as described below. That is, in the configuration shown in FIG. 3 as well, as in the first embodiment, one of the outgoing light beams directly from the light source 41 or reflected by the reflecting mirror 42
/4 wavelength Fi 43 and slope 4 of polarizing beam splitter 44
The P-polarized light that has passed through the polarization beam splitter 44 is emitted from the exit surface 48, while the S-polarized light that has been reflected by the slope 45 of the polarization beam splitter 44
By taking the optical path of the polarized light through the right-angle prism 46, the slope 45.1/4 wavelength plate 43, and the reflecting mirror 42.1/4 wavelength plate 43, the polarization direction is rotated by 90 degrees and becomes p-polarized light, which becomes the slope 45. , and is emitted from the emission surface 48. Therefore,
Most of the light emitted from the light source 41 is emitted as p-polarized linearly polarized light from the output surface 48 of the polarizing beam splitter 44, so that linearly polarized light can be efficiently obtained from irregularly polarized light.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain a linearly polarized light source that can efficiently generate linearly polarized light, and it is possible to obtain linearly polarized light with higher efficiency than in the past.

[Brief explanation of drawings]

Fig. 1 is a plan view of a linearly polarized light source showing a first embodiment of the present invention, Fig. 2 is a diagram used to explain the principle of the present invention, and Fig. 3 is a plan view of a linearly polarized light source showing a second embodiment of the invention. FIG. 3 is a plan view of a light source. 1, 3L IH...Light source 2, 32.42...Reflector 333.43...Wave plate 4, 34.44...Polarizing beam splitter 5, 35.
45...Slope 6, 36.46...Light flux reflecting element

Claims (1)

[Claims] (1) A light source having a reflecting mirror, a polarizing beam splitter that separates the light beam from the light source into two light beams whose polarization directions are orthogonal to each other, and at least one or more wavelength plates disposed between the light source and the polarizing beam splitter. A linearly polarized light source comprising: a light flux reflecting element that reflects one of the two light fluxes so as to be incident on the reflecting mirror.