JPH0526561Y2 - - 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 to a thin plastic sheet, etc., and a protective plastic sheet, etc. is adhered to the screen, 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.

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.

Therefore, a polarization conversion element has been proposed which has a high light utilization efficiency of a light source, such as the one described in Utility Model Application No. 62-073013. FIG. 2 is a diagram showing an example of the device according to the invention. In FIG. 2, the polarization conversion element includes a polarization beam splitter 34 and four right angle prisms 35, 3.
6, 37, and 38, and when the incident light 31, which is undefined polarized light, enters the polarization beam splitter 34, the linearly polarized light of the P-polarized component is directly output from the polarization conversion element as transmitted light 32. The linearly polarized light of the S-polarized component is polarized in the polarization direction 40 by four right-angle prisms 35, 36, 37, and 38.
is equal to the polarization direction 39 of the P polarized light component.
By rotating the reflected light 33 by 90 degrees and emitting it as reflected light 33, linearly polarized light can be efficiently obtained from irregularly polarized light.

[Problem that the invention attempts to solve]

However, in the above polarization conversion element, when the incident light is particularly diverging light, the linearly polarized light of the S-polarized component suffers losses at the total reflection surfaces of the four right-angle prisms and losses due to the exit surface aperture restriction due to the spread of the light flux. Then, the intensity per unit area decreases due to the spread of the light beam due to the optical path difference between the four right angle prisms.

An object of the present invention is to provide a polarization conversion element that efficiently converts unpolarized light from a light source into linearly polarized light even when the incident light is diverging light.

[Means for solving problems]

The polarization conversion element of the present invention includes a polarization beam splitter for spatially separating irregularly 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 linearly polarized light of the component and the linearly polarized light of the S-polarized component are separated by the polarizing beam splitter so that the polarization direction of one of the linearly polarized lights is equal to the polarization direction of the other linearly polarized light. The polarization direction is set in one of the two linearly polarized optical paths.
It is characterized by being comprised of two right-angle prisms that combine the two linearly polarized lights by rotating them by 90 degrees, and two right-angle prisms that maintain the polarization direction and are placed in the other optical path.

[Effect]

That is, the present invention can reduce the influence of the optical path difference by arranging an equal number of right angle prisms in the linearly polarized optical paths of the P and S polarized components separated by the polarizing beam splitter, and Since the optical path length of the right-angle prism is short, losses due to exit surface aperture limitations can be reduced.
Even if the incident light is diverging light, linearly polarized light can be efficiently obtained from undefined polarized light from the light source.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention.

This polarization conversion element is a polarization beam splitter 5.
and four right angle prisms 6, 7, 8, 9, and the incident light 3 is sent to a polarizing beam splitter 5.
P-polarized light 1 having the polarization direction 12 of the P-polarized component at
0 and S-polarized light 11 having a polarization direction 16 of the S-polarized light component. The right-angle prisms 6 and 7 are arranged so as to maintain the polarization direction 12 in the optical path of the P-polarized light 10, and the right-angle prisms 8 and 9 are arranged in the optical path of the S-polarized light 11 so as to rotate the polarization direction 16 by 90 degrees. There is. The polarizing beam splitter 5 is made by coating one of the hypotenuses of two right-angled prisms with a semi-transparent film made of a metal film, dielectric multilayer film, etc. and joining the hypotenuses together, and is particularly effective against light in the visible wavelength range. A light beam that can be effectively separated into P-polarized light 10 and S-polarized light 11 was used. The right-angle prisms 6, 7, 8, and 9 are made of optical glass, such as BK7, which has a refractive index that satisfies the total reflection condition for light in the visible wavelength range at its oblique sides. In order to bond the polarizing beam splitter 5 and the right angle prisms 6, 7, 8, and 9 together in the configuration shown in FIG. It was adhered using a suitable optical adhesive (lens bond, ultraviolet curable adhesive, etc.).
Furthermore, a light incident surface of the polarizing beam splitter 5,
The light exit surfaces of the right angle prisms 7 and 9 were coated with an antireflection film made of a dielectric multilayer film in order to reduce loss due to reflection.

In the polarization conversion element having such a configuration, undefined polarized light (represented by orthogonal components S and P in the polarization direction 4) is emitted from a light source 1 such as a xenon lamp or a halogen lamp, and after being condensed by a condenser lens 2. The light enters the polarization conversion element as incident light 3. The incident light 3 is separated by a polarizing beam splitter 5 into linearly polarized light, that is, P polarized light 10 having a polarization direction 12 and S polarized light 11 having a polarization direction 16 . The P-polarized light 10 is totally reflected by the right angle prisms 6 and 7 to obtain an output light 20. However, the polarization direction 12 is maintained in the same direction as 13, 14, and 15.
The S-polarized light 11 is totally reflected by the right angle prisms 8 and 9 to obtain an output light 21. However, the polarization direction 16 changes to 17, 18, and 19 during total reflection. Polarization direction 19 is compared to polarization direction 16.
This means it has been rotated 90 degrees. That is, polarization direction 1
5 and the polarization direction 19 are the same, and by combining the emitted lights 20 and 21, the irregularly polarized light from the light source 1 can be converted into linearly polarized light with almost no loss.

This becomes a problem when the incident light is diverging light with a slight divergence angle. The decrease in the intensity per unit area due to the loss due to the exit surface aperture limit and the beam spread due to the optical path difference between the P-polarized light 10 and the S-polarized light 11 is
The structure in which two right-angle prisms 6, 7, 8, and 9 are arranged for each of the S-polarized light 11 and the S-polarized light 11 does not cause an optical path difference, and can therefore be kept to a minimum.

Furthermore, by inserting a wedge-shaped prism into the optical path of at least one of the output lights 20 and 21, the output lights 20 and 21 can be combined at an arbitrary position. By inserting a sheet polarizer into the polarizer, linearly polarized light with an even better degree of polarization can be obtained.

In this embodiment, the incident light 3 and the output light 20, 2
1 have the same traveling direction, but right angle prisms 7 and 9
The same effect can be obtained even if the traveling direction of the emitted light beams 20 and 21 is bent by rotating the beam by 90 degrees.

By using the polarization conversion element of the present invention, a conversion efficiency of more than 75% from the irregularly polarized light of the light source to linearly polarized light can be obtained, which is approximately twice the conversion efficiency of the conventionally used sheet polarizer, which has a conversion efficiency of 40%. Utilization efficiency was achieved.

In the embodiment, the polarizing beam splitter and the right angle prisms are bonded together to make the structure compact, but the structure may be such that they are not bonded and are spaced apart from each other.

[Effect of idea]

As explained above, according to the present invention, in a polarization conversion element that obtains linearly polarized light from undefined polarized light, the light utilization efficiency of the light source is high, and even if the incident light is diverging light, the linearly polarized light can be efficiently converted. We were able to obtain a polarization conversion element that converts light into

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing an example of a conventional element. 1...Light source, 2...Condenser lens, 3...
Incident light, 4, 12, 13, 14, 15, 16, 1
7, 18, 19... Polarization direction, 5... Polarization beam splitter, 6, 7, 8, 9... Right angle prism,
10...P polarized light, 11...S polarized light, 20,2
1... Outgoing light.

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 light component and linearly polarized light having an S polarized light component; The two linearly polarized optical paths are separated by the polarizing beam splitter so that the polarization direction of one of the linearly polarized light components is equal to the polarization direction of the other linearly polarized light component. Two right-angle prisms are placed in one optical path to rotate the polarization direction by 90 degrees and combine the two linearly polarized lights, and two right-angle prisms are placed in the other optical path to maintain the polarization direction. A polarization conversion element comprising a right-angled prism.