JPH04321001A - Polarized light separating element - Google Patents

Abstract

PURPOSE:To inexpensively attain the improvement of polarized light separating efficiency. CONSTITUTION:This polarized light separating element consists of a square prism 4 in which angles formed between a pair of side faces and a bottom face are equal and a triangular prism 3 arranged so as to be stuck to the bottom face the prism 4 through a polarized light separating film, one of angles formed between the bottom face of the prism 3 contacting with the separating film and side faces is equal to the angle formed between each side face and the bottom face of the prism 4 and the face of the prism 3 which is opposed to the stuck face through the separating film is parallel with one of inclined faces of the prism 4. Since the polarized light separating efficiency of the polarized light separating element is high, dielectric multi-layer films can be reduced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to orthogonal natural polarized light.
The present invention relates to a structure of a polarization separation element that separates light into two linearly polarized lights, and the emission directions of the linearly polarized lights are perpendicular to each other.

0002

2. Description of the Related Art A conventional polarization separation element has a structure in which the slopes of a pair of right-angled prisms are glued together, as shown in FIG. Naturally polarized light incident on the outer surface of this polarization separation element at 0° and at 45° to the polarization separation film present on the adhesive surface is divided into two linearly polarized lights whose polarization planes are perpendicular to each other by the polarization separation film. It is divided into S polarized light and P polarized light (
Most of the S-polarized light is reflected, and most of the P-polarized light is transmitted unchanged), and is emitted from two adjacent outer surfaces of the polarization splitting element with a separation angle of 90°.

0003

However, in the above-mentioned polarized light splitting element, the incident angle of naturally polarized light to the polarized light splitting element is 45 degrees, so that there is a limit to the separation efficiency. One way to increase separation efficiency is to increase the number of layers in the polarization separation film, but increasing the number of layers increases cost, and the hotter the film, the greater the aberrations. Furthermore, even with methods such as using a plurality of polarization separation elements or providing polarization separation films at a plurality of locations within the same element, it has not been possible to achieve both cost reduction and improvement in separation efficiency, as described above.

The present invention aims to solve these problems at low cost and with a simple structure, and the object thereof is to provide a polarization separation element that can obtain high polarization separation efficiency. be.

[0005]

Means for Solving the Problems The present invention provides a polarization separation element in which two prisms are arranged in close contact with each other through a polarization separation film, including at least one pair of square prisms whose side faces and bottom faces are at equal angles; a triangular prism disposed in close contact with the bottom surface of a prism through the polarization separation film, and at least one of the angles between the bottom surface and the side surface of the triangular prism in contact with the polarization separation film is at least one pair of the square prism. is equal to the angle between the side surface and the bottom surface of the triangular prism, and the opposing surface of the surface of the triangular prism that is closely arranged through the polarization separation film is parallel to one slope of the quadrangular prism, and the quadrangular prism The angle between at least one pair of side faces and the bottom face is 45
The angle of incidence of polarized light from the polarized light source on the polarized light separation film is greater than 45° and less than 90°, and the two prisms are coated with an antireflection film on their light input and output surfaces. Since the polarization separation film is made of a dielectric multilayer film, high polarization separation efficiency can be obtained.

[0006]

[Operation] When light is incident on the interface between two media with different refractive indexes, the relationship between the reflectance and phase of the reflected light relative to the incident light at the interface is explained by Fresnel's law of reflection, and is expressed by the following equation. It is expressed as follows.

[0007]

[Formula 1] rs={sin(θ1-θ2)/sin(θ1+θ2)
}2

[0008]

[Formula 2] rp={tan(θ1-θ2)/tan(θ1+θ2)
}2 Here, rS is the reflectance of S-polarized light, rp is the reflectance of P-polarized light, θ1 is the incident angle, and θ2 is the refraction angle.

The incident angle of rp is 0% at the Brewster angle, and the separation efficiency of P-polarized light and S-polarized light is maximum at this angle. Brewster's angle is determined by the following formula.

0010

[Math 3] θ1=arctan(n1/n2) n1 and n2 are the respective refractive indices of the two media.

That is, in the present invention, polarized light incident on the polarization separation film at Brewster's angle is separated into P-polarized light and S-polarized light according to Fresnel's law of reflection. P-polarized light travels straight without being reflected by the polarization separation film, and almost 100% of S-polarized light is reflected by the polarization separation film.

0012

Embodiment FIG. 1 is a three-dimensional view of an embodiment of the present invention, and FIG. 2 is a sectional view.

Light from the polarized light source enters the polarization separation element from ab to ab in FIG. The angle of incidence of polarized light on ab is set from 0° to 80°.

The incident polarized light is separated into P polarized light and S polarized light on the bd plane. The angle of incidence on the polarization separation film on the bd plane is preferably greater than 45° and less than 90°.

[0015] Also, the angle abd, the angle bde, and the angle bdc
The angle should preferably be between 50° and 90°.

The P-polarized light passes through the polarization separation film without being reflected by the polarization separation film, and is emitted from the side surface dc of the triangular prism. Since the AB plane and the DC plane are parallel, the incident light and the outgoing light are parallel.

FIG. 3 shows the relationship between the incident angle and the reflectance of S-polarized light when the incident angle of polarized light on the polarization separation film is the Brewster angle. According to this, the reflectance of S-polarized light increases as the incident angle increases.

FIG. 4 shows one embodiment of the structure of an optical system comprising the polarization separation element of the present invention and polarization direction conversion means. By installing a λ/2 plate as a polarization direction converting means on the optical path of the P-polarized light separated by the polarization separation element, the plane of polarization is rotated by 90 degrees, and the P-polarized light travels straight as S-polarized light. On the other hand, S
The traveling direction of the polarized light is changed by a reflecting mirror, and both polarized lights are converted into the same polarization direction and emitted in parallel.

When using P-polarized light as the polarized light component,
A λ/2 plate is installed on the optical path of S-polarized light, and a reflecting mirror is installed on the optical path of P-polarized light.

[0020] If the separation angle between the S-polarized light and the P-polarized light is too small, the size of the apparatus required to convert the polarization direction will become large. If the separation angle is too large, aberrations between polarized lights in the same direction emitted in parallel will become large. Considering these, the separation angle between S-polarized light and P-polarized light is larger than 0°, and 13
0° or less is good. More preferably from 10° to 110°
It is.

As described above, the angle of incidence on the polarization separation film, the angles abd, bde, and bcd of the polarization separation film, the angle of incidence on the polarization separation element, and the separation angle of S-polarized light and P-polarized light are , are each set to take the optimum value.

Furthermore, anti-reflection films were provided on the incident surface of polarized light from the polarized light source to the polarized light splitting element and on the exit surfaces of S-polarized light and P-polarized light, respectively. Note that the number of layers and the material of the polarization separation film made of a dielectric multilayer film are set so that the polarization separation efficiency is maximized.

[0023]

[Effects of the Invention] As explained above, the present invention has a structure in which the angle of incidence of polarized light on the polarized light separation film is increased, so there is no need to increase the number of layers of the polarized light separation film in order to increase separation efficiency. Aberrations can be minimized. Furthermore, since it is not necessary to use a plurality of polarization separation elements, it is possible to provide a polarization separation element that is inexpensive, has a simple structure, and can obtain high polarization separation efficiency.

[Brief explanation of drawings]

FIG. 1 is a three-dimensional diagram of a polarization separation element of the present invention.

FIG. 2 is a cross-sectional view of the polarization splitting element of the present invention.

FIG. 3 is a diagram showing the relationship between the incident angle and the reflectance of S-polarized light when the incident angle of polarized light to the polarization separation film is the Brewster angle.

FIG. 4 is a diagram showing the structure of an optical system including a polarization separation element of the present invention and polarization direction conversion means.

FIG. 5 is a cross-sectional view of a conventional polarization splitting element.

[Explanation of symbols]

1 Polarization separation element 2　Anti-reflection film 3 Triangular prism 4 Square prism 5　S polarized light 6 P polarized light 7 Polarized light source 8 λ/2 plate 9 Incident light

Claims (5)

[Claims] 1. A polarization separation element in which two prisms are arranged in close contact with each other with a polarization separation film interposed therebetween, comprising: a square prism having at least one pair of side surfaces and a bottom surface having equal angles; and a polarization separation film on the bottom surface of the square prism. and a triangular prism arranged in close contact with each other through a prism, and at least one of the angles between the bottom surface and the side surface of the triangular prism in contact with the polarization separation film is the angle between at least one pair of side surfaces and the bottom surface of the quadrangular prism. 1. A polarized light separating element characterized in that opposing surfaces of the triangular prism which are arranged in close contact with each other via the polarized light separating film are parallel to one slope of the quadrangular prism. 2. The polarization separation element according to claim 1, wherein the angle between the at least one pair of side surfaces and the bottom surface of the quadrangular prism is greater than 45 degrees and less than 90 degrees. 3. The polarized light separating element according to claim 1, wherein the incident angle of the polarized light from the polarized light source onto the polarized light separating film is greater than 45° and smaller than 90°. 4. The polarized light separation element according to claim 1, wherein the two prisms have an antireflection film coated on their light input/output surfaces. 5. The polarized light separating element according to claim 1, wherein the polarized light separating film is made of a dielectric multilayer film.