JPH07306314A - Polarizer - Google Patents

Abstract

PURPOSE:To enable both polarized light rays to be emitted at an equal optical path length to both polarized light rays and in the same direction by using a polarizer having a double prism structure obtd. by providing at least one of the stuck faces of two rectangular prisms with an optical thin-film group capable of separating the polarized light rays. CONSTITUTION:This polarizer has an isosceles triangular shape of a vertex 45 deg. formed by sticking two pieces of the rectangular prism 7a, 7b having the same size and the same shape in the shapes of the main cut faces and is constituted by forming the respective thin film groups 2a, 2b to the right parts of the second faces different from the hypotenuses of the rectangular prism 7a, 7a and joining the respective groups with adhesive layer 2c. The thin film groups 2a, 2b are multilayered films formed by combining a plurality of the thin films having a high refractive index and the thin films having a low refractive index. The light 3 emitted from a light source is made incident on the slope of the rectangular prism 7a at a certain angle with the normal of the incident face at the time of making this light incident on the slope of the prism described above. This light is refracted by the incident face and is separated into the two polarized light rays orthogonal with each other by the optical thin film groups 2a, 2b. These polarized light rays are totally reflected by the inside faces of the respective prisms and are emitted in the same direction in parallel with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizer such as a polarizing beam splitter (hereinafter referred to as "PBS") which selectively emits light having a particular vibration direction.

[0002]

2. Description of the Related Art Conventionally, PBSs shown in FIGS.
The ones shown in are known. PBS shown in FIG.
Is a pair of right-angle prisms 1a and 1b made of optical glass.
The thin film groups 2a and 2b are respectively formed on the hypotenuses and the thin film group portions 2a and 2b are joined via the joining portion 2c. The refractive index of the thin films forming the thin film group is set so as to satisfy the Brewster condition, and the light 3 from the light source enters the PBS from the side (the left side in FIG. 3) of the right-angle prism 1a, and When incident on the interface between them so that the incident angle becomes the Brewster angle, the incident light is repeatedly reflected and refracted at the interfaces between the thin films forming each thin film group, and these lights interfere with each other. By selecting the refractive index and film thickness of the film so that the reflection / refraction characteristics have polarization dependency, the PBS transmits the p-polarized light 4 to one straight side (right direction) and the s-polarized light 5 to the other side. Reflects on the immediate side (upward). In FIG. 3, the p-polarized light 4 indicates a polarized light having a vibration plane along the paper surface, and the s-polarized light 5 indicates a polarized light orthogonal to the paper surface. ) Represents the vibration direction orthogonal to the paper surface.

The PBS shown in FIG. 4 is such that a total reflection prism is arranged on top of the PBS shown in FIG. 3 to totally reflect p-polarized light and direct it in the same left direction as s-polarized light.

[0004]

However, the conventional PBS described above has the following problems. In the PBS shown in FIG. 3, p-polarized light and s-polarized light are emitted in different directions, so that one of the irradiation targets needs a reflection optical system to irradiate one irradiation target. In particular, when a total reflection prism is arranged as in the PBS of FIG. 4 and s-polarized light and p-polarized light are directed in the same direction, the optical path lengths for s-polarized light and p-polarized light are different in the prism, and both are illuminance on the irradiation surface. There is a problem that is different.

Further, when the total reflection prism is arranged outside the PBS, there is a problem that optical loss of polarized light may occur. An object of the present invention is to solve the problems of the conventional PBS as described above.

[0006]

Therefore, as a PBS which does not require a reflection optical system, two right-angled prisms are bonded together, and an optical thin film group capable of polarization separation is provided on at least one of the bonding surfaces. I decided to use a polarizer with a structure. Further, when the light from the light source is made to enter from the slope of one of the right-angled prisms, it is incident at a certain angle with respect to the normal line of the incident surface. It was set to three corners of less than 60 degrees and less than 60 degrees. As a result, it was found that the loss of incident light is reduced, and in an optical system using a polarizer, the use of such a polarizer expands the degree of freedom in design.

Therefore, the present invention uses two right-angled prisms of the same shape having a right-angled triangle cross-section consisting of three angles of a right angle, an angle of less than 30 degrees, and an angle of 60 degrees or more. Is a multi-prism structure having an isosceles triangular cross-section in which the right sides of the two are optically bonded together, and a polarization-separable optical thin film group is formed on at least one bonding surface of a right-angle prism. Is provided.

When the rectangular prism is made of optical glass, the optical thin film group is formed on the optical glass. At this time, when thermal stress or mechanical external stress is applied to the optical glass, optical anisotropy caused by the photoelastic effect is induced, and the optical anisotropy prevents the polarizer from obtaining desired performance. Sometimes. Therefore, in the present invention, it is preferable to provide a polarizer in which two right-angle prisms are made of glass whose photoelastic constant is substantially zero.

[0009]

The polarizer of the present invention has a right angle and an angle of less than 30 degrees and 60 degrees.
It is characterized in that two right-angled prisms of the same shape having a right-angled triangular cross-section consisting of three angles of more than one degree are joined by sandwiching an optical thin film group capable of polarization separation. When the light emitted from the light source is incident on the slope of one of the right-angled prisms, it is incident at an angle with the normal to the incident surface. This light is refracted at the incident surface, and is separated into two polarizations orthogonal to each other by the polarization-separable optical thin film group on the bonding surface. Then, the separated polarized lights are totally reflected on the inner surface of the prism and emitted from the emission surface in parallel with each other in the same direction, that is, in the normal direction of the emission surface.

Further, preferably, the right-angle prism is made of glass whose photoelastic constant is substantially zero, so that thermal stress or mechanical external stress due to the influence of the holder holding the polarizer or the heat of the incident light causes a right-angle prism. Even if the above occurs, the right-angle prism exhibits substantially optical isotropy and hardly causes an optical path difference in light propagating in the right-angle prism.

[0011]

[Embodiment 1] FIG. 1 is an explanatory diagram of a first embodiment of the present invention. The main cut surface of this PBS has an internal angle of 90 degrees, 6
It is a right-angled triangle with 7.5 degrees and 22.5 degrees, and the refractive index is 1.6.
An apex angle 45 of two right-angle prisms 7a and 7b of the same size and shape made of 5 light flint glass
It has an isosceles triangular shape of degrees. Each of the thin film groups 2 is formed on the right part of the second surface different from the hypotenuse of these right angle prisms.
a and 2b are formed, and these are joined by the adhesive layer 2c. These thin film groups are multilayer films in which a plurality of thin films having a high refractive index and a thin film having a low refractive index are combined, and are designed and manufactured by a conventional technique. In this example, the multilayer film was divided into 2a and 2b and formed on the prism surfaces of 7a and 7b, respectively, and the adhesive layer was formed between them, but in addition to this method, it was formed. 2a and 2 on either side
It is also possible to adopt a method in which a film group having a function of a polarization separation film is formed by one group including b and an adhesive layer is formed between the prism surface on which no film is formed and the polarization separation film group.

The light 3 from the light source is incident on the PBS at an incident angle of 39.2 degrees from the lower right side of the slope of the prism 7a, and the refraction angle is 2
The light is refracted at 2.5 degrees and is incident on the surfaces (second surfaces) of the thin film groups 2a and 2b at an incident angle of 45 degrees, and is separated into reflected s-polarized light and transmitted p-polarized light by the action of these thin film groups. The reflected s-polarized light is a prism 7
It is incident on the inclined surface of a at an incident angle of 67.5 degrees, is totally reflected, and then exits in the normal direction from the third surface. The transmitted p-polarized light ray is incident on the inclined surface of the prism 7b at an incident angle of 67.5 degrees, is totally reflected, and then exits from the third surface in the normal direction. By doing so, both s and p polarized light beams can be emitted parallel to each other and in the same direction, and the optical path lengths of the s and p polarized light beams after polarization separation in the present PBS can be made equal to each other.

[0013]

Second Embodiment FIG. 2 is an explanatory diagram of the second embodiment. First
2 is different from that of Example 1 in that the main cut surface has an angle of 90 °, 64 °, and 26 ° in the original prism of the right triangle, and is made of heavy flint glass having a refractive index of 1.90. Light 3 from the light source enters the PBS at an incident angle of 23.3 degrees, is refracted at a refraction angle of 12 degrees, and enters the surfaces (second surfaces) of the thin film groups 2a and 2b at an incident angle of 38 degrees. Is separated into reflected s-polarized light and transmitted p-polarized light. The reflected s-polarized light is a prism 7
It is incident on the inclined surface of a at an incident angle of 64 degrees, is totally reflected, and then exits in the normal direction from the third surface. The transmitted p-polarized light ray is totally reflected on the inclined surface of the prism 7b at an incident angle of 64 degrees, and then exits from the third surface in the normal direction. The subsequent operation is similar to that of the first embodiment.

[0014]

Third Embodiment Next, a third embodiment will be shown. The interior angle of the original prism having a right-angled triangular shape shown in this embodiment is 90 degrees, 6
4.8 degrees and 25.2 degrees, and the photoelastic constant having a refractive index of 1.84 is substantially zero (substantially zero means that the photoelastic constant is, for example, light incident on the PBS from the light source. This is an example in which a glass of −0.1 to 0.1 (meaning 10 ⁻⁸ cm ² / N) is used. The light from the light source is incident on the PBS at an incident angle of 27 degrees, refracted at a refraction angle of 14.3 degrees, and is incident on the thin film group at an incident angle of 39.5 degrees. Is separated into The s-polarized light enters the prism inclined surface at an incident angle of 64.8 degrees, is totally reflected, and then exits in the normal direction. The p-polarized light is incident on the prism slope surface at 64.8 degrees, is totally reflected, and is then emitted in the normal direction. In the case of this prism, since the photoelastic constant is substantially zero, the linearly polarized light produced by the action of the thin film group does not undergo birefringence in the prism, and high quality linearly polarized light can be obtained. As described above, the vertical angle (26 ° × 2 = 52 ° in the case of the second embodiment) suitable for the present PBS generally depends on the refractive index of the material of the prism and the refractive index ratio of the plurality of thin films used. However, the higher the refractive index of the material and the larger the refractive index ratio of the thin film, the larger the value, but the range of 30 to 60 degrees is suitable.

In the above embodiments, only PBS is shown, but if a ½ wavelength plate is installed in the optical path of either p or s to be emitted, p polarized light is converted to s polarized light (s polarized light is converted to p polarized light). It can be used as a polarization conversion element that emits a single polarized light.

[0016]

As described in detail above, according to the present invention, the present PBS is designed such that after the polarized light separation in the thin film group, each polarized light beam is totally reflected on the inner surface of the PBS before exiting the PBS. Since it is configured, it is possible to emit light in the same direction and in parallel in the same optical path length for both polarized lights. Further, as described in the embodiment, the incident angle to the PBS is not incident in the direction normal to the prism plane and has a predetermined angle, so that the total reflection on the inner surface of the prism is performed at a shallow angle. The allowable angle is increased and the loss is reduced. This means that the light rays actually incident on the polarizer cannot be perfectly parallel light, and non-parallel light components are mixed. In this non-parallel light ray, a light ray having an angle deviated from the law of total reflection is not totally reflected and becomes a loss. However, in the present invention, since the tolerance of this angle can be made large, the proportion of the rays totally reflected becomes large and the loss is reduced. Further, in the present invention, since the incident angle can have an angle with respect to the normal line of the surface, it is possible to emit the s-polarized light and the p-polarized light in parallel in the same direction and in the normal direction of the emission surface. it can. For this reason, the degree of freedom in the refractive index and shape of the prism increases, which facilitates designing. When the incident angle is perpendicular to the normal, the incident angle to the thin film group of the polarization splitting part is inevitably determined, and the degree of freedom in designing the polarization splitting film depends on the refractive index of the glass forming the polarizer and the polarization splitting film. 2 of the refractive index of the thin film forming the group
There is only one. In particular, when a glass having a substantially zero photoelastic constant is used as the glass forming the polarizer, the refractive index is determined to be almost 1, and there is no degree of freedom. In this case, it is an extremely difficult technique to design only with the degree of freedom of the thin film.
In the present invention, since the degree of freedom of the incident angle is increased, it is possible to have three degrees of freedom in the case of ordinary glass and two degrees of freedom even in the case of using glass having a zero photoelastic constant. It becomes easier to peel.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a PBS that is a first embodiment of the present invention.

FIG. 2 is a sectional view showing a PBS which is a second embodiment of the present invention.

FIG. 3 is a sectional view showing an example of a conventional PBS.

FIG. 4 is a sectional view showing another example of a conventional PBS.

[Explanation of symbols]

 2 polarized light separating parts 2a, 2b thin film group part 2c joint part 3 light from light source 4 p polarized light beam 5 s polarized light beam 7a, 7b right angle prism 7c right angle prism

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Katsuhiko Katano 3 2-3 Marunouchi, Chiyoda-ku, Tokyo Inside Nikon Corporation

Claims (3)

[Claims] 1. Use of two right-angle prisms of the same shape having a right-angled triangle cross-section consisting of three angles of right angles, angles less than 30 degrees and angles greater than 60 degrees, and straight sides of the two right-angle prisms. A multi-prism structure having an isosceles triangular cross-section optically bonded to each other, wherein a polarization-separable optical thin film group is formed on the bonding surface of at least one right-angle prism. 2. The polarizer according to claim 1, wherein light from a light source is incident on the slope of one of the right-angled prisms, and the incident light is two straight lines whose polarization planes are orthogonal to each other by an optical thin film group. In a method of using a polarizer that splits polarized light into two and outputs the two linearly polarized lights from an emission plane, the light from the light source is arranged so that the two linearly polarized lights are parallel to the same direction and perpendicular to the emission plane. A method of using a polarizer, characterized by setting an incident angle of. 3. The polarizer according to claim 1, wherein the two rectangular prisms are made of glass having a photoelastic constant of substantially zero.