JP6694008B2 - Total reflection type polarizer - Google Patents

Description

  The present invention relates to a polarizer, and more particularly to a total reflection type polarizer that removes one of two polarization components of an incident light ray by total reflection.

  Polarizers with a high extinction ratio are used in high-precision measurement and analysis equipment such as polarization analysis, but high extinction ratio performance is required for polarizers used in imaging optical systems such as cameras. There weren't many.

Glan-Thomson prisms made of calcite or α-BaB ₂ O ₄ (α-BBO) are commonly used high extinction ratio polarizers. However, ordinary refractive index of the prism material _{(n o)} is the extraordinary refractive index _{(n e)} more negative uniaxial crystal _(n o> n _e) a is calcite or alpha-BBO common ground with - In the Thomson prism, since the extraordinary light becomes transmitted light inside the prism material, the aberration is affected by the incident angle dependence of the extraordinary light. Therefore, when the condensed light is incident on the conventional Glan-Thompson prism, the condensing point is not reduced due to the influence of the astigmatic aberration.

  FIG. 19 shows the calculation result of the condensing size at the condensing point when the condensed light having the incident angle of ± 2 ° is incident on the Calcite-Gran-Thompson prism. As shown in FIG. 19, the size of the condensing point is about 200 μm or more, which is large. As described above, the Glan-Thompson prism, which is a normal total reflection type high extinction ratio polarizer, is not suitable for use in which high resolution is required due to large influence of aberration.

  As described above, most conventional high-extinction-ratio polarizers including Calcite-Glan-Thomson prisms and Glan-Taylor prisms have large aberrations and thus have poor imaging performance, and are used in imaging optical systems such as cameras. Not suitable for.

  On the other hand, the Rochon prism, which is a polarization splitting type polarizer, is a rare polarizer with a high extinction ratio and low aberration, and can convert ordinary rays into transmitted light regardless of whether the uniaxial crystal used is positive or negative. It is possible to reduce the size of condensed light. However, since the Rochon prism is a polarization separation type that removes one of the two polarization components of the incident light by refraction, when using condensed light, it is necessary to make the separation angle larger than the collection angle. Depending on the size of the incident light beam, a long space is required after the Rochon prism in order to separate the separated light, which causes an increase in size of the device. Further, since the Rochon prism has a feature that the transmittance changes depending on the incident angle and direction of the incident light, when condensed light or divergent light is transmitted, it gives a luminance distribution (luminance unevenness) to the transmitted light. Not suitable for use in systems.

  Patent Document 1 relates to a polarizing prism in which two uniaxial crystal prisms and a uniaxial crystal plate are arranged between two uniaxial crystal prisms, and the positive and negative polarities of the uniaxial crystal used for the prism material and the crystal plate material are opposite. Indicates that the viewing angle is widened.

  Patent Document 2 discloses a first triangular prism and a second triangular prism formed of a first material which is the same anisotropic crystal material, and a flat plate interposed between the first and second triangular prisms. Regarding the provided polarizer, it is described that the flat plate is formed of a second material which is an anisotropic crystal material different from the first material, an isotropic crystal material, or an optical glass.

  In Patent Document 3, a plurality of uniaxial crystal prisms are arranged such that their optical axes are alternately orthogonal to each other, and the gap between the crystal prisms is made small, whereby the aberration is reduced. Is listed.

  Non-Patent Document 1 shows an example of reducing the chromatic aberration by setting the air gap of a calcite Gran-Taylor prism to 15 μm. To make the size of the same size.

JP-A-4-208901 JP, 2006-153913, A Special table 2016-517040 gazette

WuHai-Ying et al., “Analysis and evaluation of Glan-Taylor prism's image qualityin a new polarization interference imaging spectrometer”, Acta Physica Sinica, vol.57, no.6, pp.3499-3505 (2008).

  In recent years, along with the high precision and high density of semiconductors and the like, polarization analysis of minute areas and analysis of high resolution in-plane information have become more important. Since such analyzes have been made possible, there is a need for a polarizer having a high extinction ratio even when used in an imaging optical system, and having excellent wavelength characteristics and viewing angle characteristics.

  The present inventors examined the conditions necessary for reducing the aberration of a total reflection type polarizer showing a high extinction ratio using a birefringent crystal, and found that (condition 1) a light beam that passes through the polarizer (emitted light beam). It has been found that there are two conditions: that is an ordinary ray, and that (condition 2) a ray incident on the polarizer (incident ray) travels straight in the polarizer.

  Specifically, since the light ray that passes through the polarizer (outgoing light ray) is an ordinary ray, it does not undergo a change in the refractive index due to the difference in the incident angle, and the light ray that enters the polarizer (incident light ray) is inside the polarizer. By going straight on, low aberration is realized.

  Patent Document 1 discloses a structure in which the positive and negative polarities of the uniaxial crystal used for the prism material and the crystal plate material are reversed so that the light ray (exiting light ray) that passes through the polarizer becomes an ordinary ray. It is also disclosed and suggested that a light beam (incident light beam) travels straight in the polarizer, that is, to reduce the thickness of the crystal plate material in order to suppress refraction at the interface between the prism material and the crystal plate material. Absent.

  Patent Document 2 also discloses a structure in which the positive and negative polarities of the uniaxial crystal used in the crystal plate material and the prism material in which the light ray (emitted light ray) that passes through the polarizer becomes an ordinary ray are made to enter, but are incident on the polarizer. There is no disclosure or suggestion of reducing the thickness of the crystal plate material so that the light ray (incident light ray) goes straight in the polarizer, that is, in order to suppress the refraction at the interface between the prism material and the crystal plate material. ..

  In the polarizer assembly described in Patent Document 3, the transmitted light always repeats the ordinary ray and the extraordinary ray in each prism, so that the transmitted light is not the ordinary ray. Further, in the polarizer assembly described in Patent Document 3, an isotropic material such as air is arranged between the prisms, or the prisms are directly bonded but a uniaxial crystal is arranged between the prisms. There is no mention of what to do. The polarizer assembly described in Patent Document 3 is intended to widen the viewing angle, and may have no air gap. When an air gap is provided, a thinner thickness does not increase aberrations. It has been shown to be preferred. Therefore, the polarizer assembly described in Patent Document 3 does not positively reduce the aberration by reducing the thickness of the air gap. Since the basic structure of the polarizer assembly described in Patent Document 3 is a Wollaston prism, the aberration is similar to that of a general Wollaston prism, and the aberration is not small.

  The calcite Gran-Taylor prism described in Non-Patent Document 1 is not intended to reduce aberrations. Specifically, since the calcite-Glan-Taylor prism described in Non-Patent Document 1 has a large condensing point size at each wavelength, the condensing point size should be reduced to realize a two-dimensional image with high resolution. I can't. Further, since calcite, which is a negative uniaxial crystal, is used for the prism material, the transmitted light is an extraordinary ray within the prism. Further, in the polarizer of Non-Patent Document 1, there is an air gap between the prisms, and it is not described that a crystal material or the like is provided between the prisms.

  There is a Foisner prism as a total reflection type polarizer having a basic structure with a high extinction ratio and little aberration. The Feusner prism is a polarizer having a structure in which a plate material of uniaxial crystal having a large birefringence is arranged between two glass prisms and bonded. When a negative uniaxial crystal with large birefringence such as calcite or α-BBO is used as the plate material in the Feusner prism, the transmitted polarized light becomes an ordinary ray in the element, so that the change in the refractive index due to the difference in the incident angle is changed. I do not receive it. Further, in the Feusner prism, since it is possible to select the glass that is the prism material according to the ordinary refractive index of the calcite, it is not affected by the astigmatism and coma aberration caused by the plate material portion.

  However, the Foisner prism may be distorted by the stress generated in the glass prism used at the time of molding, polishing, and joining with a plate material. As a result, the extinction ratio performance may be deteriorated. Therefore, the Feusner prism was never actually used as a polarizer.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a total reflection type polarizer having a high extinction ratio and low aberration.

  As a result of earnest research to solve the above problems, the present inventors have made a dramatic difference by using a uniaxial crystal as the prism material and a thin uniaxial crystal as the flat plate between the prisms in the Feusner prism. It was found that the aberration was reduced, and the present invention was completed.

According to the total reflection type polarizer of the present invention, the above-mentioned problem is a total reflection type polarizer that removes one of two polarization components of an incident light ray by total reflection, and a first prism and a first prism formed of sapphire. comprising a secondary prism, and a flat plate formed of a negative uniaxial crystal larger than the refractive index (n _o) is the extraordinary refractive index (n _e) ordinary between the first prism and the second prism, The first prism includes a first incident optical surface on which the incident light beam is incident, and a first emission optical surface on which one polarized light of the incident light beam is totally reflected and the other polarized light is emitted. The prism includes a second incident optical surface on which one of the separated incident light beams is incident, and a second outgoing optical surface on which one of the separated incident light beams is emitted as an emitted light beam. , the thickness of the plate is at 20μm or less, before The first optical axis that is the optical axis of the first prism, the second optical axis that is the optical axis of the second prism, the third optical axis that is the optical axis of the flat plate is parallel to each other, the first optical axis, The second optical axis and the third optical axis are orthogonal to the optical axis of the incident light beam, and the ordinary refractive index of sapphire forming the first prism and the second prism is n _pro , and the extraordinary refractive index is was a n _pre, the ordinary refractive index of the negative uniaxial crystal that forms the flat n _o, the extraordinary refractive index and n _e, the first outgoing optical surface and the first incidence optical surface in the first prism And the wedge angle, which is the angle between the second incident optical surface and the second output optical surface in the second prism, is defined as α, the following equation (1) is satisfied.
sin ⁻¹ (n _e / n _pre ) ≦ α <sin ⁻¹ (n _o / n _pro ) Expression (1)

As described above, in the total reflection type polarizer, since the flat plate formed of the thin negative uniaxial crystal is provided between the two prisms formed of sapphire, the interface between the first prism and the flat plate is In (1), the extraordinary ray of the incident ray is totally reflected and separated, and the refraction occurring in the ordinary ray of the incident ray is suppressed small. Therefore, it is possible to provide a totally reflective polarizer sufficient aberration is more is further reduced with a high extinction ratio.

At this time, the first optical axis, the second optical axis, and the third optical axis may be arranged parallel to the incident optical surface of the first prism.
According to this structure, the viewing angle becomes wide, and the reflection between the first prism and the flat plate and between the second prism and the flat plate is reduced, so that the transmittance is improved and the ghost can be reduced. It will be possible.

At this time, an antireflection film may be provided on at least one of the first prism and the flat plate or the second prism and the flat plate.
According to this structure, the transmittance can be improved and the ghost can be reduced.

At this time, an antireflection film may be provided both between the first prism and the flat plate and between the second prism and the flat plate.
According to this structure, the transmittance can be further improved and the ghost can be further reduced.

In this case, it is preferable prior SL flat _calcite, Li ₂ B 4 _{O 7,} and is formed by one selected from _α-BaB 2 _{O 4.}

  According to the present invention, in a total reflection type polarizer, a flat plate formed of a thin negative uniaxial crystal is provided between two prisms formed of a uniaxial crystal, and a light beam emitted is Since it is an ordinary ray and the ordinary ray travels straight in the polarizer, it is possible to have a high extinction ratio and sufficiently reduce aberrations.

1 is a schematic configuration diagram of a total internal reflection type polarizer according to Embodiment 1 of the present invention. 4 is a spot diagram showing a condensed size of a light beam that has passed through the total internal reflection type polarizer according to the first embodiment of the present invention. It is a graph which shows the thickness of a flat plate, and the relationship of spot size. It is a schematic block diagram of the total reflection type polarizer which concerns on Embodiment 2 of this invention. 1 is a schematic configuration diagram showing a configuration of a total internal reflection type polarizer according to Example 1. FIG. 3 is a spot diagram showing the condensed size of light rays that have passed through the total internal reflection type polarizer according to Example 1. FIG. 5 is a graph showing the relationship between the wavelength and the transmittance of the total internal reflection type polarizer according to Example 1. 6 is a schematic configuration diagram showing a configuration of a total reflection type polarizer according to Example 2. FIG. 5 is a spot diagram showing the size of light collected through a total reflection type polarizer according to Example 2; 5 is a graph showing the relationship between the wavelength and the transmittance of the total internal reflection type polarizer according to Example 2. 6 is a graph showing the reflectance of an antireflection film formed on the inclined surface of the total reflection type polarizer according to Example 2. 5 is a graph showing the reflectance of an antireflection film formed on the end surface of the total reflection type polarizer according to Example 2. 6 is a schematic configuration diagram showing a configuration of a total reflection type polarizer according to Example 3. FIG. 9 is a spot diagram showing a condensed size of a light beam that has passed through a total internal reflection type polarizer according to Example 3; 9 is a graph showing the relationship between the wavelength and the transmittance of the total reflection type polarizer according to Example 3. 7 is a schematic configuration diagram showing a configuration of a total reflection type polarizer according to Example 4. FIG. 9 is a spot diagram showing a condensed size of a light beam transmitted through a total reflection type polarizer according to Example 4. 9 is a graph showing the relationship between the wavelength and the transmittance of the total internal reflection type polarizer according to Example 4. It is a spot diagram which shows the condensing size of the condensing light which permeated the Glan-Thompson prism made from calcite.

Hereinafter, a total reflection type polarizer according to an embodiment of the present invention will be described with reference to FIGS. 1 to 18.
The total internal reflection type polarizer according to the present invention is a total internal reflection type polarizer having a high extinction ratio and low aberration, which eliminates the drawbacks of the Foisner prism.
In the present specification, the term “contact” means that a pair of adjacent prisms are arranged in contact with each other, and includes not only optical contact directly bonded but also bonding by adhesion.
Further, in the present specification, “opposing” the prisms includes a case of an optical contact that is directly bonded and a case of bonding that is bonded by interposing something such as an adhesive.

The "birefringence" means a property that when a light ray enters a material having optical anisotropy, refracted light is divided into two. When light is incident on the birefringent crystal material, an incident ray is separated into an ordinary ray (O line: Ordinary Wave) and an extraordinary ray (E line: Extraordinary Wave).
An "ordinary ray" is a ray that oscillates so as to be orthogonal to the plane formed by the optical axis of the birefringent crystal material and the optical axis of the incident ray, and is birefringent without being affected by the optical axis. Travels on the same straight line as the optical axis of the incident ray in the crystalline material.
An "extraordinary ray" is a ray that oscillates so as to be parallel to the plane formed by the optical axis of the birefringent crystal material and the optical axis of the incident ray. In the crystalline material, it travels separately from the ordinary rays.
The ordinary ray and the extraordinary ray are rays having a linear polarization component, and the vibration directions of the electric fields of the ordinary ray and the extraordinary ray are orthogonal to each other.

  Isotropic materials, such as glass, are prone to anisotropic strain during processing, but uniaxial anisotropic crystals already have anisotropy, so they occur during processing. It has the feature that anisotropic strain is less likely to occur due to stress. In the present invention, by utilizing this characteristic, the material forming the prism is replaced with a uniaxial crystal to solve the problem of distortion.

However, unlike glass in which the refractive index can be controlled relatively freely, it is difficult to set the refractive index freely, and therefore the uniaxial crystal can be made to have the refractive index of the material forming the prism freely. I can't choose. Actually, in the wavelength band practically used, in the ultraviolet region to the near infrared region, calcite, α-BaB ₂ O ₄ (α-BBO), which is a negative uniaxial crystal having large anisotropy used for a flat plate, For practical prisms, the refractive index of ordinary light is almost the same as that of crystals such as Li ₂ B ₄ O ₇ (LB4), and the refractive index of extraordinary light is larger than that of a flat plate in order to totally reflect extraordinary light. There are no uniaxial crystals.

  Therefore, it is necessary to use a uniaxial crystal having an ordinary refractive index different from that of a flat plate as the material forming the prism. Here, sapphire is a practical uniaxial crystal having a larger extraordinary light refractive index than the negative uniaxial crystal having a large birefringence and being transparent from the ultraviolet region to the near infrared region. Even with sapphire, the ordinary refractive index and the ordinary refractive index of a negative uniaxial crystal having a large birefringence are different.

  When the material that makes up the prism and the material that makes up the flat plate have different refractive indices, the light is refracted when the light beam passes from the prism to the flat plate, and the light also refracts when the light passes from the flat plate to the prism. To do. Therefore, in the condensed light or the divergent light, aberration occurs when the light is refracted and the condensing performance is deteriorated. Therefore, in the present invention, by reducing the thickness of the flat plate, the aberration that occurs when transmitting from the prism (first prism) to the flat plate and from the flat plate to the prism (second prism) is reduced.

(Embodiment 1)
As shown in FIG. 1, the total reflection type polarizer P1 of the present embodiment has a first prism 10 and a second prism 20 having the same shape of a triangular prism having a right-angled cross section, and a first prism 10 and a second prism 20. And a flat plate 30 arranged between them. Further, as shown in FIG. 1, the total reflection type polarizer P1 of the present embodiment is configured such that the first prism 10, the flat plate 30, and the second prism 20 are arranged in this order along the optical axis X of the incident light ray I. Has been done.

The first prism 10 includes a first incident optical surface 12 on which the incident light ray I is incident, and a first outgoing optical surface 14 on which one polarized light of the incident light ray I is totally reflected and the other polarized light is emitted. ..
The second prism 20 has a second incident optical surface 22 on which one polarized light of the separated incident light I is incident and a second outgoing optical surface 24 on which one polarized light of the separated incident light I is emitted as an outgoing light ray E. And are equipped with.

  The flat plate 30 includes a first cemented surface 32 that faces the first exiting optical surface 14 of the first prism 10, and a second cemented surface 34 that faces the second incident optical surface 22 of the second prism 20. The first joint surface 32 and the second joint surface 34 are formed to be parallel to each other.

  In the total reflection type polarizer P1 of the present embodiment, as shown in FIG. 1, the first exit optical surface 14 of the first prism 10 is joined to the first joint surface 32 of the flat plate 30, and the second joint surface of the flat plate 30 is formed. 34 is joined to the second incident optical surface 22 of the second prism 20. At this time, the first exit optical surface 14 of the first prism 10, the first joint surface 32 of the flat plate 30, the second joint surface 34, and the second incident optical surface 22 of the second prism 20 are parallel to each other.

The first prism 10 and the second prism 20 are formed of a uniaxial crystal. Here, it is preferable to use sapphire as a practical uniaxial crystal that is transparent from the ultraviolet region to the near infrared region and has a higher extraordinary refractive index than the negative uniaxial crystalline of the negative uniaxial crystal forming the flat plate 30. Is. The refractive index of sapphire is such that the ordinary light refractive index (n _o ) is larger than the extraordinary light refractive index (n _e ), that is, n _o > n _e , and it is a negative uniaxial crystal.

The refractive index of sapphire is n _o = 1.966, n _e = 1.954 at the wavelength λ = 180 nm, and n _o = 1.878, n _e = 1.868 at the wavelength λ = 220 nm. At the wavelength λ = 500 nm, n _o = 1.774 and n _e = 1.766, at the wavelength λ = 1700 nm, n _o = 1.744 and n _e = 1.736, and at the wavelength λ = 2000 nm, n _o = 1.738 and n _e = 1.730, and at the wavelength λ = 2300 nm, n _o = 1.731 and n _e = 1.723.

The flat plate 30 is a negative uniaxial crystal with a large birefringence in which the ordinary light refractive index (n _o ) is larger than the extraordinary light refractive index (n _e ), that is, n _o > n _e , for example, calcite (CaCO ₃ ). , Α-BaB ₂ O ₄ (barium borate; α-BBO) and Li ₂ B ₄ O ₇ (lithium tetraborate; LB4) are preferable.

Refractive index of the calcite, the wavelength _{λ = 220nm, n o = 1.829} , is n e = 1.554 at a wavelength _{λ = 500nm, n o = 1.666} , is n e = 1.490, At the wavelength λ = 1700 nm, n _o = 1.630 and n _e = 1.477.

refractive index of the alpha-BBO at a wavelength _{λ = 220nm, n o = 1.832} , is n e = 1.661 at a wavelength _{λ = 500nm, n o = 1.677} , with n e = 1.557 Then, at the wavelength λ = 2000 nm, n _o = 1.639 and n _e = 1.522.

The refractive index of LB4 is n _o = 1.790, n _e = 1.712 at the wavelength λ = 180 nm, and n _o = 1.616, n _e = 1.558 at the wavelength λ = 500 nm, At the wavelength λ = 2300 nm, n _o = 1.570 and n _e = 1.523.

  As shown in FIG. 1, the first entrance optical surface 12 and the first exit optical surface 14 of the first prism 10 form a wedge angle α, and similarly, the second entrance optical surface 22 and the second entrance optical surface 22 of the second prism 20 are the same. The dual emission optical surface 24 also forms a wedge angle α. Here, the wedge angle α can be set in accordance with the intended use and the used wavelength within the range of the angle at which only the extraordinary ray of the incident ray I entering the total reflection type polarizer P1 is reflected. ..

Specifically, in the total internal reflection type polarizer P1 of the present embodiment, the ordinary light refractive index of the uniaxial crystal forming the first prism 10 and the second prism 20 is n _pro , and the extraordinary light refractive index is n _pre. When the ordinary light refractive index of the negative uniaxial crystal forming 30 is n _o , the extraordinary light refractive index is n _e, and the wedge angles of the first prism 10 and the second prism 20 are α, the following formula (1) is obtained. Fulfill.
sin ⁻¹ (n _e / n _pre ) ≦ α <sin ⁻¹ (n _o / n _pro ) Expression (1)

The derivation of equation (1) is as follows. The uniaxial crystal has an ordinary light refractive index (n _pro ) and an extraordinary light refractive index (n _pre ). The ordinary light in the prism becomes the ordinary light in the flat plate 30, and the extraordinary light in the prism becomes the abnormal light in the flat plate 30. Therefore, the total reflection type polarizer P1 of the present embodiment has a pair of different total reflections (critical angles), that is, the critical angle θ _c1 and the critical angle θ, as shown in the following formulas (2) and (3). has _c2 .
The critical angle ^{_{θ c1 = sin -1 (n o}} / n pro) formula (2)
Critical angle θ _c2 = sin ⁻¹ ( _ne / n _pre ) Formula (3)

The range in which the function as a total reflection polarizer is obtained is when incident light is incident at an angle between the critical angle θ _c1 and the critical angle θ _c2 . In this case, the wedge angle α of the prism satisfies Expression (4).
θ _c2 ≦ α <θ _c1 Formula (4)
The expression (1) is obtained by substituting the critical angle θ _c1 and the critical angle θ _c2 of the expression (2) and the expression (3) into the expression (4).

As described above, in order to totally reflect the extraordinary light, the extraordinary light refractive index n _{pre of} the uniaxial crystal forming the first prism 10 and the second prism 20 is a negative uniaxial crystal forming the flat plate 30. since the extraordinary refractive index must be greater than _{n e,} a _{n e <n pre.}

  The optical axes (crystal axes) of the prisms (first prism 10 and second prism 20) and the flat plate 30 need to be arranged on the same plane because the transmitted light is an ordinary ray. However, when the optical axes of the prisms (the first prism 10 and the second prism 20) and the flat plate 30 are arranged in the ray axis direction of the incident ray, they do not function as a polarizer and are therefore excluded.

  The preferred arrangement of the optical axis (crystal axis) is such that the optical axes of the prisms (the first prism 10 and the second prism 20) and the flat plate 30 are arranged in the same direction, and the optical axis X of the incident ray I is orthogonal. Is. This arrangement is the arrangement shown in FIG. 1 and FIG. 4 described later, and is suitable because it is effective for widening the viewing angle and widening the wavelength band. Further, as shown in FIG. 1, the first optical axis A1 of the first prism 10, the second optical axis A2 of the second prism 20, and the third optical axis A3 of the flat plate 30 are arranged perpendicular to the paper surface, in other words, Then, when the first optical axis A1, the second optical axis A2, and the third optical axis A3 are arranged in parallel with the first incident optical surface 12 and the first outgoing optical surface 14 of the first prism 10, Since the reflection between the one prism 10 and the flat plate 30 and between the second prism 20 and the flat plate 30 is reduced, it is effective because it is effective in improving the transmittance and reducing the ghost.

  The first prism 10 and the flat plate 30 and the second prism 20 and the flat plate 30 are preferably joined together by direct contact by optical contact, but they may be adhered and fixed by using an adhesive. is there. When joining is performed using an adhesive, the refractive index of the adhesive is preferably equal to or higher than the ordinary refractive index of the negative uniaxial crystal forming the flat plate 30.

  The thickness d of the flat plate 30 is preferably thin in order to reduce aberrations, more preferably 20 μm or less, and particularly preferably 10 μm or less. Further, from the viewpoint of preventing the light tunnel effect, the thickness d of the flat plate 30 is preferably 0.5 μm or more.

The manner in which the polarized light of the incident light is separated by using the total reflection type polarizer P1 of the present embodiment will be described with reference to FIG.
When the incident light ray I is incident on the total reflection type polarizer P1 of the present embodiment from the first incident optical surface 12 of the first prism 10, the incident light ray I is incident on the first exiting optical surface 14 of the first prism 10 and the flat plate 30. At the interface with the first bonding surface 32, one polarized component (extraordinary ray) is totally reflected and separated (removed) as a reflected ray R, and the other polarized component (ordinary ray) is flat plate 30 and the second prism 20. And is emitted from the second emission optical surface 24 of the second prism 20 as an emission ray E. That is, the interface between the first emission optical surface 14 of the first prism 10 and the first bonding surface 32 of the flat plate 30 functions as a total reflection section. Although not shown in FIG. 1, the ordinary ray is mixed in the reflected ray R, although it is a part.

The first prism 10 and second prism 20 satisfy equations (1), the ordinary refractive index (n _o) is the extraordinary refractive index (n _e) because it is formed by the negative uniaxial crystal is greater than At the interface between the first exit optical surface 14 of the first prism 10 and the first joint surface 32 of the flat plate 30, the extraordinary ray of the incident ray I is totally reflected and separated (removed) as a reflected ray R.

  The ordinary ray that is the other polarization component passes through the flat plate 30 and the second prism 20, and is emitted from the second emission optical surface 24 of the second prism 20. At this time, there is some difference between the ordinary refractive index of the uniaxial crystal forming the first prism 10 and the second prism 20 and the ordinary refractive index of the uniaxial crystal forming the flat plate 30. When d is thin, the refraction generated at the interface between the first prism 10 and the flat plate 30 and at the interface between the flat plate 30 and the second prism 20 is suppressed to be small. Therefore, in the total reflection type polarizer P1, the ordinary ray travels straight with the deviation from the optical axis X of the incident ray I suppressed, and the aberration is reduced.

  As described above, according to the total internal reflection type polarizer P1 of the present embodiment, the light rays emitted from the total internal reflection type polarizer P1 are ordinary rays, and the refraction within the total internal reflection type polarizer P1 is suppressed to be small. Since the vehicle is driven and goes straight, it is possible to sufficiently reduce the aberration.

  When the first prism 10 and the second prism 20 are made of sapphire, and the flat plate 30 is a calcite having a plate thickness of 20 μm, the total reflection type polarizer P1 is made to collect light at an incident angle of ± 2 °. The shape and size of the dots are shown in FIG. As shown in FIG. 2, it can be seen that the size of the focal point is as small as several μm. Even when compared with a calcite Glan-Taylor prism that can relatively reduce the focusing point among general polarizers, the focusing point size under the same condition is 40 μm or more. From this, it can be seen that even when the plate thickness of the flat plate 30 is 20 μm, the aberration is sufficiently reduced as compared with the conventional polarizer. By making the plate thickness of the flat plate 30 thinner, it is possible to further reduce the size of the focal point.

  FIG. 3 is a graph showing the relationship between the thickness of the flat plate 30 and the spot size. The thick line in FIG. 3 indicates a spot diameter of about 45 μm when the spacer thickness is 100 μm, which minimizes the spot diameter in a calcite Gran-Taylor prism. As shown in FIG. 3, when the thickness d of the flat plate 30 is 20 μm or less, the spot diameter becomes half or less of the spot diameter of about 45 μm of the calcite-Glan-Taylor prism, that is, 20 μm or less, and the aberration is sufficiently reduced. The straight line in FIG. 3 of the flat plate 30 has a substantially common relationship in the combination of the sapphire prism and the LB4, the calcite, and the α-BBO plate.

The total reflection type polarizer P1 of the present embodiment has a high extinction ratio. Here, the extinction ratio is, when the intensity of one polarization (ordinary ray) is P _O and the intensity of the other polarization (extraordinary ray) is P _E with respect to the outgoing ray E emitted from the polarizer, Extinction ratio / dB = −10 log (P _E / P _O ). The extinction ratio of the total reflection type polarizer P1 is preferably 50 dB or more, and particularly preferably 60 dB or more.

Further, an antireflection film is formed on the prism slopes of the first prism 10 and the second prism 20 (the first output optical surface 14 and the second input optical surface 22), or the first bonding surface 32 and the second bonding surface 34 of the flat plate 30. It is more preferable to apply the (AR film) because the transmittance can be improved and the ghost can be reduced. A known material is used for the antireflection film. For example, titanium film, titanium oxide film, titanium nitride film, chromium oxide film, carbon film, magnesium fluoride (MgF ₂ ) film, silicon oxide film, zirconium oxide film, aluminum oxide film, hafnium oxide film, H4 (Merck Co. Product name: lanthanum titanate film, M2 (Merck company product name: lanthanum aluminate) film, M3 (Merck company product name: lanthanum aluminate) film, Ta ₂ O ₅ film and other inorganic films are vacuum deposited, CVD, Examples thereof include those formed by a method such as sputtering and those formed by a method such as coating an organic film such as methacrylic resin. Also, these films may be appropriately laminated.

(Embodiment 2)
A total reflection type polarizer P2 according to another embodiment of the present invention will be described with reference to FIG.
The total internal reflection type polarizer P2 of this embodiment has a first optical axis A1 of the first prism 10, a second optical axis A2 of the second prism 20, and a third optical axis of the flat plate 30 with respect to the optical axis X of the incident light ray I. Except that the direction of A3 is different, the structure is the same as that of the total reflection type polarizer P1 of the first embodiment.

  When the incident light ray I is incident on the total reflection type polarizer P2 from the first incident optical surface 12 of the first prism 10, the incident light ray I is joined to the first exit optical surface 14 of the first prism 10 and the flat plate 30 by the first joining. At the interface with the surface 32, one polarized component (extraordinary ray) is totally reflected and separated (removed) as a reflected ray R, and the other polarized component (ordinary ray) passes through the flat plate 30 and the second prism 20. , Is emitted from the second emission optical surface 24 of the second prism 20. That is, the interface between the first emission optical surface 14 of the first prism 10 and the first bonding surface 32 of the flat plate 30 functions as a total reflection section. Although not shown in FIG. 4, the ordinary ray is mixed in the reflected ray R although it is a part.

  In the total reflection type polarizer P2, the directions of the first optical axis A1 of the first prism 10, the second optical axis A2 of the second prism 20, and the third optical axis A3 of the flat plate 30 with respect to the optical axis X of the incident light ray I are all directions. Since it is different from the reflective polarizer P1 (because the first optical axis A1, the second optical axis A2, and the third optical axis A3 are arranged parallel to the paper surface), in the case of the total reflective polarizer P1 (first Compared with the arrangement in which the one optical axis A1, the second optical axis A2, and the third optical axis A3 are perpendicular to the paper surface), the components of the extraordinary ray and the ordinary ray are opposite to each other.

  In the example shown in FIGS. 1 and 4, the upper surface of the first prism 10 and the lower surface of the second prism 20 are grained in order to scatter reflected light rays R reflected by total reflection between the prism and the flat plate 30. It is common to shape the surface of the first prism 10 and to apply a black paint for absorption, but the upper surface of the first prism 10 and the lower surface of the second prism 20 are optically polished, and the reflected light rays reflected by total reflection are reflected. R may be taken out of the polarizer.

  Hereinafter, the total reflection type polarizer of the present invention will be described in more detail based on Examples, but the present invention is not limited to the following Examples.

<Example 1: Sapphire prism + LB4 plate + Sapphire prism>
In the total reflection type polarizer P3 of Example 1, the first prism 10 and the second prism 20 were formed of sapphire, and the flat plate 30 was formed of LB4.
As shown in FIG. 5, the total reflection polarizer P3 includes a first prism 10 and a second prism 20 made of sapphire, and a flat plate 30 made of LB4 between the first prism 10 and the second prism 20. And the first optical axis A1 of the first prism 10, the second optical axis A2 of the second prism 20, and the third optical axis A3 of the flat plate 30 are parallel to each other. The axis A2 and the third optical axis A3 are perpendicular to the paper surface (that is, parallel to the first entrance optical surface 12, the first exit optical surface 14, the second entrance optical surface 22, and the second exit optical surface 24). The first optical axis A1, the second optical axis A2, and the third optical axis A3 are arranged so as to be orthogonal to the optical axis X of the incident light ray I.

  Table 1 shows the materials of the first prism 10, the second prism 20, and the flat plate 30, the wedge angle α of the first prism 10 and the second prism 20, and the thickness d of the flat plate 30. The values shown in Table 1 are examples, and can be set as appropriate according to the required performance of the polarizer. Further, Table 2 shows the usable wavelength band, the viewing angle, and the extinction ratio of the total reflection type polarizer P3. Hereinafter, as the wavelength band to be used, the wavelength band in which the length of the polarizer is 40 mm and the transmittance is reduced by about 50% is adopted.

  FIG. 6 shows the shape and size of the condensing point of the outgoing light ray when the condensed light of ± 2 ° is incident on the total reflection type polarizer P3. As shown in FIG. 6, it was found that the size of the focal point was as small as about 10 μm.

  FIG. 7 shows the wavelength dependence of the transmittance of the total reflection type polarizer P3. It can be seen that the transmission characteristics are flat between wavelengths λ = 180 to 2300 nm. In addition, the decrease of the transmittance is achieved by the end faces of the first prism 10 and the second prism 20 (the first incident optical surface 12 and the second output optical surface 24), the prisms (the first prism 10 and the second prism 20) and the flat plate. This is due to reflection at the 30-bonded surface.

<Example 2 Sapphire prism + LB4 plate + Sapphire prism + Antireflection film>
In the total reflection type polarizer P4 of Example 2, the first prism 10 and the second prism 20 are formed of sapphire, the flat plate 30 is formed of LB4, and the first incident optical surface 12 and the first exit of the first prism 10 are formed. An antireflection film AR is applied to the optical surface 14, the second incident optical surface 22 and the second output optical surface 24 of the second prism 20.

  As shown in FIG. 8, the total reflection type polarizer P4 includes a first prism 10 and a second prism 20 formed of sapphire, and a flat plate 30 formed of LB4 between the first prism 10 and the second prism 20. And the first optical axis A1 of the first prism 10, the second optical axis A2 of the second prism 20, and the third optical axis A3 of the flat plate 30 are parallel to each other. The axis A2 and the third optical axis A3 are orthogonal to the optical axis X of the incident light ray I.

The first incident optical surface 12 of the first prism 10 and the second outgoing optical surface 24 of the second prism 20 are provided with a MgF 2 single-layer antireflection film AR (film thickness = about 0.05 μm). Further, between the first incident optical surface 12 of the first prism 10 and the first joining surface 32 of the flat plate 30, and between the second joining surface 34 of the flat plate 30 and the second incident optical surface 22 of the second prism 20, An antireflection film AR (film thickness = about 0.3 μm) in which five layers of M2 / SiO ₂ are laminated is provided.

  Table 3 shows the materials of the first prism 10, the second prism 20, and the flat plate 30, the wedge angle α of the first prism 10 and the second prism 20, the thickness d of the flat plate 30, and the material of the antireflection film AR. Further, Table 4 shows the usable wavelength band, the viewing angle, and the extinction ratio of the total reflection type polarizer P4.

  Practical uniaxial crystal materials that transmit ultraviolet light to near infrared light and have large birefringence are limited. Further, in order to have a practical performance as a Foisner prism type polarizer, the prism material needs to have a large refractive index. There are not many materials that have such physical properties. If the material that forms the prism and the material that forms the flat plate have the same refractive index, less light will be reflected at the cemented surface, but with a limited combination of materials, look for a material combination that also has the same refractive index. Is difficult.

  It is also difficult to develop new materials. Therefore, in order to manufacture a polarizer with low aberration and high extinction ratio, it is inevitable to combine materials whose refractive indices do not match, but in that case, due to reflection at the junction between the prism and the flat plate, The transmittance is reduced. Therefore, in order to improve the transmittance, it is preferable to improve the performance of the polarizer by interposing the antireflection film AR at the joint between the prism and the flat plate.

  FIG. 9 shows the shape and size of the condensing point of the outgoing ray when the condensed light of ± 2 ° is incident on the total reflection type polarizer P4. As shown in FIG. 9, it was found that the size of the condensing point was as small as about 10 μm.

  FIG. 10 shows the wavelength dependence of the transmittance of the total reflection type polarizer P4 including the antireflection film AR. Compared to the total reflection type polarizer P3 (Example 1, FIG. 7) which does not include the antireflection film AR, the transmittance is improved by 20% or more in the ultraviolet to visible light region and 10% or more in the infrared region. Has been.

  FIG. 11 is a graph showing the reflectance of the antireflection film AR formed on the inclined surface of the prism, that is, the first exit optical surface 14 of the first prism 10 and the second incident optical surface 22 of the second prism 20. FIG. 12 is a graph showing the reflectance of the antireflection film AR applied to the end surface of the prism, that is, the first incident optical surface 12 of the first prism 10 and the second outgoing optical surface 24 of the second prism 20.

  As shown in FIGS. 11 and 12, it can be seen that the reflectance is reduced when the antireflection film AR is applied, as compared with the case where the antireflection film AR is not applied. Therefore, by interposing the antireflection film AR on the end surface of the prism or on the joint surface between the prism and the flat plate 30, a ghost is generated when an image is formed like the total reflection type polarizer P4 including the antireflection film AR. It is more preferable because it is reduced.

<Example 3: Sapphire prism + calcite plate + sapphire prism>
In the total reflection type polarizer P5 of Example 3, the first prism 10 and the second prism 20 were made of sapphire, and the flat plate 30 was made of calcite.
As shown in FIG. 13, the total reflection type polarizer P5 includes a first prism 10 and a second prism 20 made of sapphire, and a flat plate 30 made of calcite between the first prism 10 and the second prism 20. And the first optical axis A1 of the first prism 10, the second optical axis A2 of the second prism 20, and the third optical axis A3 of the flat plate 30 are parallel to each other. The axis A2 and the third optical axis A3 are orthogonal to the optical axis X of the incident light ray I.

  Table 5 shows the materials of the first prism 10, the second prism 20, and the flat plate 30, the wedge angle α of the first prism 10 and the second prism 20, and the thickness d of the flat plate 30. Further, Table 6 shows the usable wavelength band, the viewing angle, and the extinction ratio of the total reflection type polarizer P5.

  FIG. 14 shows the shape and size of the condensing point of the outgoing light beam when the condensed light of ± 9 ° is incident on the total reflection type polarizer P5. As shown in FIG. 14, it was found that the size of the focal point was as small as about 10 μm.

FIG. 15 shows the wavelength dependence of the transmittance of the total reflection polarizer P5 at λ = 220 to 1700 nm. The total reflection type polarizer P5 has a narrower transmission wavelength band but higher transmittance than the total reflection type polarizer P3 of Example 1 using sapphire. This is from the ordinary refractive index of LB4 _{(n o),} towards the _{n o} calcite is due to proximity to sapphire _{n o.}

  The total internal reflection type polarizer P5 has a wide viewing angle and can be incorporated in a bright optical system. The spot diameter appears to be slightly larger than in the case of Example 1 and Example 2, but this is because the viewing angle is large and the aberration is large. Even if a light beam of ± 9 ° is incident, the spot diameter can be condensed to about 10 μm with the configuration of the total reflection type polarizer P5.

  As in the case of the second embodiment, it is possible to improve the transmittance and reduce the ghost by providing the antireflection film AR on the inclined surface of the prism. It is also possible to improve the transmittance by providing the antireflection film AR on the end surface of the prism.

<Example 4: Sapphire prism + α-BBO plate + Sapphire prism>
In the total reflection type polarizer P6 of Example 4, the first prism 10 and the second prism 20 were made of sapphire, and the flat plate 30 was made of α-BBO.
As shown in FIG. 16, the total reflection polarizer P6 is formed of α-BBO between the first prism 10 and the second prism 20 formed of sapphire and between the first prism 10 and the second prism 20. The flat plate 30 is provided, and the first optical axis A1 of the first prism 10, the second optical axis A2 of the second prism 20, and the third optical axis A3 of the flat plate 30 are parallel to each other. The two optical axes A2 and the third optical axis A3 are orthogonal to the optical axis X of the incident light ray I.

  Table 7 shows the materials of the first prism 10, the second prism 20, and the flat plate 30, the wedge angle α of the first prism 10 and the second prism 20, and the thickness d of the flat plate 30. Further, Table 8 shows the usable wavelength band, the viewing angle, and the extinction ratio of the total reflection type polarizer P6.

  FIG. 17 shows the shape and size of the condensing point of the outgoing ray when the condensed light of ± 7 ° is incident on the total reflection type polarizer P6. As shown in FIG. 17, it was found that the size of the focal point was as small as about 10 μm.

FIG. 18 shows the wavelength dependence of the transmittance of the total reflection polarizer P6 at λ = 220 to 2000 nm. The total reflection type polarizer P6 has a narrower transmission wavelength band but higher transmittance than the total reflection type polarizer P3 of Example 1 using sapphire. This is from the ordinary refractive index of LB4 _{(n o),} towards the alpha-BBO of _{n o} is due to proximity to sapphire _{n o.} Most of the calcite is natural stone, while α-BBO can be artificially synthesized, and thus stable production is possible, which is preferable.

  The configuration of the total reflection type polarizer P6 has a wide viewing angle and can be incorporated in a bright optical system. Note that the spot diameter appears to be slightly larger than those in Examples 1 and 2, but this is because the viewing angle is large and the aberration is large. Even if a light beam of ± 7 ° is incident, the spot diameter can be condensed to about 10 μm with the configuration of the total reflection type polarizer P6.

  As in the case of the second embodiment, it is possible to improve the transmittance and reduce the ghost by providing the antireflection film AR on the inclined surface of the prism. It is also possible to improve the transmittance by providing the antireflection film AR on the end surface of the prism.

P1 Total reflection type polarizer P2 Total reflection type polarizer P3 Total reflection type polarizer P4 Total reflection type polarizer 10 First prism (negative uniaxial crystal)
12 1st incident optical surface 14 1st outgoing optical surface A1 1st optical axis (alpha) Wedge angle 20 2nd prism 22 2nd incident optical surface 24 2nd outgoing optical surface A2 2nd optical axis 30 Flat plate (negative uniaxial crystal)
32 first bonding surface 34 second bonding surface A3 third optical axis d flat plate thickness AR antireflection film X optical axis I incident light ray R reflected light ray E outgoing light ray

Claims (5)

A total reflection type polarizer that removes one of two polarization components of an incident light ray by total reflection,
A first prism and a second prism made of sapphire,
An ordinary light refractive index between the first prism and the second prism, and a flat plate formed of a negative uniaxial crystal larger than the extraordinary light refractive index, and,
The first prism comprises a first incident optical surface on which the incident light beam is incident, and a first exiting optical surface on which one polarized light of the incident light beam is totally reflected and the other polarized light is emitted,
The second prism has a second incident optical surface on which one of the separated incident light beams is incident, and a second outgoing optical surface on which one of the separated incident light beams is emitted as an outgoing light beam. Is equipped with
The thickness of the flat plate is 20 μm or less ,
The first optical axis that is the optical axis of the first prism, the second optical axis that is the optical axis of the second prism, the third optical axis that is the optical axis of the flat plate is parallel to each other,
The first optical axis, the second optical axis, the third optical axis is orthogonal to the optical axis of the incident light beam,
The ordinary light refractive index of sapphire forming the first prism and the second prism is n _pro , the extraordinary light refractive index is n _pre, and the ordinary light refractive index of the negative uniaxial crystal forming the flat plate is n _o , and the extraordinary light is The refractive index is n _e, and the angle formed by the first incident optical surface and the first output optical surface of the first prism and the angle formed by the second incident optical surface and the second output optical surface of the second prism. The following formula (1) is satisfied, where the wedge angle is α.
sin ⁻¹ (n _e / n _pre ) ≦ α <sin ⁻¹ (n _o / n _pro ) Expression (1) The total reflection type polarizer according to claim 1, wherein the first optical axis, the second optical axis, and the third optical axis are arranged in parallel with an incident optical surface of the first prism. .. The total reflection type polarizer according to claim 1 or 2 , wherein an antireflection film is provided on at least one of the first prism and the flat plate or between the second prism and the flat plate. The total reflection type polarizer according to claim 3 , wherein an antireflection film is provided both between the first prism and the flat plate and between the second prism and the flat plate. The total reflection type according to any one of claims 1 to 4 , wherein the flat plate is formed of one kind selected from calcite, Li ₂ B ₄ O ₇ , and α-BaB ₂ O _4. Polarizer.

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