JPH10227912A - Polarization beam splitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen a wavelength range wherein demultiplexing or multiplexing is possible within the visible range, to improve the steepness from a reflection band to a transmission band, and to make incidence angle dependency small by providing a center layer consisting of a low and a high refractive index layer having their chemical film thicknesses specified and a couple of adjusting layers consisting of a low and a high refractive index layer. SOLUTION: The polarization beam splitter is formed by joining an optical base 1, having the center layer 3 having the low refractive index layer of fluororesin with optical film thickness λ/4 and a refractive index 1.2 to 1.4 and a high refractive index layer with optical film thickness λ/4 and a refractive index 2.0 to 2.4 laminated by turns and the couple of adjusting layers 4 consisting of the low refractive index layer and high refractive index layer formed of fluororesin across the center layer 3 (where the center layer 3 and adjusting layers 4 are called a polarization splitting film 6), with a transparent base body 2 having a reflection preventive film 5 with an adhesive 7. Here, the optics film thickness λ/4 is ndcos θ=λ, where (n) is a refractive index, (d) is mechanical film thickness, and θ is an angle of incidence.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polarizing beam splitter.

[0002]

2. Description of the Related Art A polarizing beam splitter transmits a P-polarized light component of light incident on a dielectric alternating multilayer film and reflects an S-polarized light component to split the light into two polarized light components. A general polarizing beam splitter has a configuration in which a dielectric alternating multilayer film including a high refractive index layer and a low refractive index layer is interposed between two 45 ° prisms. The material of the dielectric alternating multilayer film is such that the reflectance of the P-polarized component of the incident light incident from the optical axis of the 45 ° prism is the smallest and the reflectance of the S-polarized component is the largest in the desired wavelength range. To choose.

[0003] Polarizing beam splitters are used in optical disk devices, projection display devices, and the like to efficiently separate incident light into P-polarized light components and S-polarized light components. Conventionally, various proposals have been made on the configuration of the dielectric alternating multilayer film in order to extend the wavelength band used by the polarizing beam splitter. For example, in Japanese Patent Application Laid-Open No. 61-141402, an intermediate layer is provided in an alternate multilayer film having a basic period of two layers of a high refractive index layer and a low refractive index layer, and the bandwidth is adjusted by adjusting the thickness of this layer. Is spreading. The configuration of the conventional polarizing beam splitter disclosed in Japanese Patent Application Laid-Open No. 3-284705 has a structure in which two dielectric multilayer films having different center wavelengths are sequentially laminated on a substrate.

[0004]

However, these polarization beam splitters cannot be said to have a sufficiently wide wavelength range in which S-polarized light and P-polarized light can be separated or combined.
When a light beam having a certain spread is incident, there is a problem that the spectral characteristics of the S-polarized light and the P-polarized light change significantly.

Further, when a polarizing beam splitter having no steepness from the reflection band to the transmission band is used in an optical system such as a projection display device, color bleeding occurs, and it is difficult to see an image of a projector or the like without sharpness. Problems arise. Accordingly, the present invention has been made in view of these problems,
The wavelength range in which polarized or P-polarized light can be separated or synthesized is wide in the visible region, and the steepness from the reflection band to the transmission band is good,
It is an object of the present invention to provide a polarization beam splitter having small incident angle dependence with respect to S-polarized light and P-polarized light.

[0006]

SUMMARY OF THE INVENTION The present invention firstly provides "at least a low refractive index layer made of a fluororesin having an optical film thickness of λ / 4, and a high refractive index layer having an optical film thickness of λ / 4. And a pair of adjustment layers consisting of a high refractive index layer and a low refractive index layer made of a fluororesin, each of which is disposed at a substantially symmetrical position with respect to the central layer. A polarizing beam splitter (Claim 1).

[0007] The present invention also provides a second aspect of the invention: "a low refractive index layer made of a fluororesin having an optical thickness of λ / 4 on at least one surface of a substrate in a liquid medium; A high refractive index layer of No. 4, a central layer, a low refractive index layer made of a fluororesin, and a pair of adjustment layers composed of a high refractive index layer, each of which is disposed substantially symmetrically with respect to the central layer; A polarizing beam splitter (claim 2) provided with an optical member formed with (1).

The present invention also relates to a third aspect, wherein the material of the low refractive index layer made of the fluororesin is an ethylene tetrafluoride resin (P
TFE), methylene trifluoride chloride resin (PCTFE),
3. The method according to claim 1, wherein the resin is a polyvinyl fluoride resin (PVF), an ethylene tetrafluoride-propylene hexafluoride copolymer (FEP), a vinylidene fluoride resin (PVDF), or a polyacetal (POM). A polarizing beam splitter (Claim 3) is provided.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1A shows a first embodiment according to the present invention.
It is a schematic sectional drawing of the polarization beam splitter of Embodiment 1, and (b) is a schematic sectional drawing of the structure of a polarization separation film.
The polarizing boom splitter according to the first embodiment of the present invention has a low refractive index layer made of a fluororesin having an optical thickness of λ / 4 and a refractive index of 1.2 to 1.4, and an optical thickness of λ. / 4, a central layer 3 in which high refractive index layers having a refractive index of 2.0 to 2.4 are alternately laminated, and a low refractive index layer and a high refractive index layer made of a fluororesin sandwiching the central layer 3. A transparent substrate 1 on which a pair of adjusting layers 4 (the central layer 3 and the adjusting layer 4 are referred to as a polarization separating film 6) are formed, and a transparent substrate 2 on which an anti-reflection film 5 is formed.
Are joined by the adhesive 7.

Here, the optical film thickness λ / 4 is ndcos
θ = λ / 4, n is the refractive index, d is the mechanical film thickness, and θ is the incident angle. Incident angle on the polarizing beam splitter,
When sin ² θ _G = n _H ² n _L ² / [n _G ² (n _H ² + n _L ² )] is satisfied in relation to the glass material and the film material, the incident light is completely separated into P-polarized light and S-polarized light. It is possible.

Here, θ_GTo the polarizing beam splitter
Incident angle, n_HIs the refractive index of the high refractive index layer, n_LIs the low refractive index layer
Index of refraction, n_GIs the refractive index of the glass material. θ_G= 45 ° (light
Is the optimal angle of incidence for the geometry), n_H= 2.0-2.
4, n _G= 1.5 to 1.7 (there are many types of glass materials in this range)
Optimizing by applying the above equation, n_L=
1.2-1.4 are derived.

As a material of the low refractive index layer satisfying the above conditions, tetrafluoroethylene resin (P) having a refractive index of 1.2 to 1.4 is used.
TFE), methylene trifluoride chloride resin (PCTFE),
Examples include vinyl fluoride resin (PVF), ethylene tetrafluoride-propylene hexafluoride copolymer (FEP), vinylidene fluoride resin (PVDF), and polyacetal (POM).

As materials for the high refractive index layer, TiO ₂ , Ce
O ₂ , HfO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , ZrO ₂ , ZnS
And the like. By adjusting the thickness of the adjustment layer, the ripple that temporarily reduces the transmittance of the P-polarized component can be reduced. This is because large ripples limit the wavelength range that can be used as a polarizing beam splitter.

In the polarization beam splitter according to the second embodiment of the present invention, one surface of the substrate 11 has an optical film thickness of λ.
/ 4, a central layer in which a low refractive index layer made of a fluororesin having a refractive index of 1.2 to 1.4 and a high refractive index layer having an optical film thickness of λ / 4 are alternately laminated; A pair of adjustment layers (a central layer and an adjustment layer are referred to as a polarization separation film 6) including a low-refractive-index layer and a high-refractive-index layer made of a sandwiched fluororesin are formed,
This is a liquid polarization beam splitter in which an optical member having an antireflection film 5 formed on the other surface is provided in a liquid cell medium 12.

As the medium, a general standard refraction liquid is used, and a medium having a desired refractive index can be used.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A polarization beam splitter according to the present invention will be described below with reference to the drawings. FIG. 1A is a schematic sectional view of a polarizing beam splitter according to the present invention,
(B) is a schematic sectional view of the configuration of the polarization splitting film.

[0017] The polarizing beam splitter according to the present invention comprises:
The center where 21 layers of tetrafluoroethylene resin (PTFE) having an optical film thickness of １ ／ λ and a refractive index of 1.29 and TiO ₂ having an optical film thickness of λλ and a refractive index of 2.38 are alternately laminated. Layer 3
And a tetrafluoroethylene resin (PTF) sandwiching the central layer 3
E) and a pair of adjusting layers 4 made of TiO ₂ and a 45 ° prism 1 having a refractive index of 1.51 on which a central layer 3 and an adjusting layer 4 are hereinafter referred to as a polarization separating film 6, and anti-reflection. Membrane 5
Is formed by bonding the 45 ° prism 2 formed with the adhesive 7 with an adhesive 7 having a refractive index of 1.58.

The antireflection film 5 and the polarization separation film 6 formed on the prism are formed by a physical film forming method such as a vacuum evaporation method, a sputtering method, an ion plating method, or a chemical film forming method such as a CVD method. It is possible. FIG. 2 shows the spectral transmittance of S-polarized light and P-polarized light when light is incident on the polarizing beam splitter at 45 °.

From this, it can be seen that S-polarized light and P-polarized light can be separated in a wide wavelength range from 580 nm to 740 nm, and that the steepness from the reflection band to the transmission band is good. FIG. 3 shows that the polarization beam splitter has λ = 650.
FIG. 4 is an incident angle characteristic diagram of S-polarized light and P-polarized light when light of nm is incident. The transmittance of P-polarized light is 0%.

It can be seen that P-polarized light and S-polarized light can be completely separated in a range of 45 ± 5 ° around an incident angle of 45 °. Therefore, even when there is a range in the incident angle to be used due to the condensed light beam or the like, it is possible to separate or combine S-polarized light and P-polarized light in a wide wavelength range. [Comparative Example 1] The polarizing beam splitter of Comparative Example 1 is composed of SiO ₂ having an optical thickness of λ / 4 and a refractive index of 1.47 and TiO ₂ having an optical thickness of λ / 4 and a refractive index of 2.38. In this configuration, a 45 ° prism having a refractive index of 1.51 on which alternate layers are formed and a 45 ° prism on which an antireflection film is formed are joined by an adhesive.

FIG. 4 shows a case where light is supplied to a polarizing beam splitter for 45 minutes.
分光 is the spectral transmittance of S-polarized light and P-polarized light when incident. This indicates that the wavelength range in which the S-polarized light and the P-polarized light can be separated is 630 nm to 700 nm, which is narrower than that of the polarization beam splitter of the first embodiment. FIG.
FIG. 9 is an incident angle characteristic diagram of S-polarized light and P-polarized light when light of λ = 650 nm is incident on a polarization beam splitter.

The P-polarized light and the S-polarized light can be completely separated in a range of 45 ± 2 ° around the incident angle of 45 °. It can be seen that the incident angle range is narrower than that of the polarization beam splitter of the first embodiment. Embodiment 2 FIG. 6 is a schematic sectional view of a second polarizing beam splitter according to the present invention.

The second polarizing beam splitter according to the present invention has an optical thickness of λ / 4 and a refractive index of 1.28 on one surface of a glass substrate 11 having a refractive index of 1.47. PTFE), the optical film thickness is λ / 4, and the refractive index is 2.3.
And a TiO ₂ and TiO ₂ sandwiching a central layer made of 21 layers of TiO _2
A pair of adjustment layers made of ₂ are formed (polarization separation film 6),
This is a liquid polarization beam splitter in which an optical member having an antireflection film 5 formed on the other surface is provided in a standard refractive liquid 12 having a refractive index similar to that of glass and having a refractive index of 1.48.

Since this polarizing beam splitter does not use an adhesive, it does not deteriorate or change with time even when irradiated with a high-power laser.

[0025]

As described above, the polarizing beam splitter according to the present invention has a wide wavelength range (580 nm to 740 n) at which S-polarized light and P-polarized light can be separated or combined.
m), the steepness from the reflection band to the transmission band is good, and even when a light beam having a certain spread is incident, the spectral characteristics of the S-polarized light and the P-polarized light do not change significantly.

Therefore, even when the polarizing beam splitter according to the present invention is used in an optical system such as a projection display device using light in a wide wavelength range in the visible region, the colors are clear and sharp and easy to see in an image of a projector or the like. There are benefits.

[Brief description of the drawings]

FIG. 1A is a schematic sectional view of a polarizing beam splitter according to a first embodiment and an example 1 according to the present invention;
(B) is a schematic sectional view of the configuration of the polarization splitting film.

FIG. 2 shows an incident angle of 4 to the polarizing beam splitter of the first embodiment.
FIG. 9 is a spectral characteristic diagram of S-polarized light and P-polarized light when entering at 5 °.

FIG. 3 shows that the polarization beam splitter according to the first embodiment has λ = 650.
FIG. 4 is an incident angle characteristic diagram of S-polarized light and P-polarized light when light of nm is incident.

FIG. 4 shows an incident angle of 4 on the polarizing beam splitter of Comparative Example 1.
FIG. 5 is a spectral characteristic diagram of S-polarized light and P-polarized light when incident at 5 °.

FIG. 5 shows that the polarization beam splitter of Comparative Example 1 has λ = 650.
FIG. 4 is an incident angle characteristic diagram of S-polarized light and P-polarized light when light of nm is incident.

FIG. 6 is a schematic sectional view of a polarizing beam splitter according to a second embodiment and an example 2 according to the present invention.

[Explanation of symbols]

 1, 2 Prism 3 Central layer 4 Adjusting layer 5 Antireflection film 6 Polarization separating film 7 Adhesive 8 Transmitted light 9 P-polarized light 10 S-polarized light 11 Glass substrate 12 Medium

Claims (3)

[Claims] 1. A central layer comprising at least a low refractive index layer made of a fluororesin having an optical thickness of λ / 4, a high refractive index layer having an optical thickness of λ / 4, and A polarizing beam splitter comprising: a pair of adjusting layers each including a low refractive index layer made of a fluororesin and a high refractive index layer, each of which is disposed at a substantially symmetrical position therebetween. 2. A low refractive index layer made of a fluororesin having an optical thickness of λ / 4 on at least one surface of a substrate in a liquid medium, and a high refractive index layer having an optical thickness of λ / 4. And a pair of adjustment layers composed of a high refractive index layer and a low refractive index layer made of a fluororesin, each of which is disposed at a substantially symmetrical position with respect to the central layer. Polarization beam splitter. 3. The low refractive index layer made of a fluororesin is made of a material selected from the group consisting of ethylene tetrafluoride resin (PTFE), methylene trifluoride chloride resin (PCTFE), and vinyl fluoride resin (PV).
F), ethylene tetrafluoride-propylene hexafluoride copolymer (FEP), vinylidene fluoride resin (PVDF), and polyacetal (POM).
Or the polarizing beam splitter according to 2.