JPH08146218A - Polarizing beam splitter - Google Patents

Abstract

PURPOSE: To obtain desired polarizing characteristics in a wide angle range over ±5 deg. and to increase latitude of design for an optical system. CONSTITUTION: This polarizing beam splitter is produced by alternately laminating high refractive index layers and low refractive index layers. The polarizing beam splitter has a first stack and a second stacks satisfying the following relations for the center wavelength λ of light to be divided and optical film thicknesses H and L of the high refractive index material and the low refractive index material, respectively. In the first stack, H, and L satisfy 0.8×λ/4<H<1.0×λ/4 and 0.8×λ/4<L<1.0×λ/4, while in the second stack, 1.3×λ/4<H<1.5×λ/4 and 1.3×λ/4<L<1.5×λ/4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing beam splitter in which, when a light beam having a predetermined wavelength is incident, the direction of branching differs depending on the polarization state at a predetermined ratio.

[0002]

2. Description of the Related Art Generally, in a laser application device such as an optical disk device, a laser printer, a laser processing machine, and a measuring device, a polarization beam splitter is one of optical components for dividing an optical path from a light source and an optical path to a detector. It is used as a department. This polarization beam splitter is usually constructed by laminating a high refractive index layer and a low refractive index layer each having an optical film thickness of ¼ times the design wavelength. Further, in order to widen the wavelength region functioning as a beam splitter, various adjustment layers may be provided on the laminated film, or the layers may be formed by using various adjustment layers.
As disclosed in the publication, the film thickness is an integral multiple of 1/4 times the design wavelength, or the inverse multiple of the integer is used as the reference film thickness.

[0003]

However, in these conventionally used polarization beam splitters, the angle of incidence of light rays is very limited, and most of them are only 45 °.
Or any other single angle, at best about the central angle ±
The desired polarization characteristics could be obtained only in the angle range of about 1 °.

Therefore, the arrangement of the elements constituting the optical system is fixed to some extent, and the range of the optical design is narrowed. Therefore, it is attempted to downsize and simplify the device and reduce the number of parts. It was a case limitation.

The present invention has been made in view of such conventional problems. The invention according to claim 1 has a desired polarization characteristic in a very wide angle range of ± 5 ° or more, and an optical system design. An object of the present invention is to provide a polarization beam splitter that can improve the degree of freedom.

In addition to the above object, the invention according to claim 2 provides
The purpose is to provide the best polarization beam splitter.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 is a polarizing beam splitter in which high-refractive index layers and low-refractive index layers are alternately laminated. Where .lambda. Is the central wavelength of the high refractive index layer and the low refractive index layer has optical thicknesses H and L of 0.8 * [lambda] / 4 <H <1.0 * [lambda] / 4 and 0. 8 x λ
A first stack with /4<L<1.0×λ/4, and
1.3 × λ / 4 <H <1.5 × λ / 4 and 1.3 × λ /
And a second stack with 4 <L <1.5 × λ / 4.

The invention according to claim 2 is the polarization beam splitter according to claim 1, wherein the high refractive index layer is Ti.
It is characterized in that it is made of O ₂ and the low refractive index layer is made of SiO ₂ .

[0009]

The film of only the first stack reflects light having a wavelength shorter than λ (both P and S polarized light) and also reflects light having a wavelength near λ and a wavelength somewhat longer than λ. Then, the S-polarized light reflects light having a longer wavelength than the P-polarized light. On the contrary, the film of only the second stack reflects light having a wavelength longer than λ (both P and S polarized light) and reflects light having a wavelength near λ and a wavelength somewhat shorter than λ. Then, the S-polarized light reflects light having a shorter wavelength than the P-polarized light.

A multi-layer film having these two stacks at the same time has a characteristic which is a combination of the characteristics of the above two films, and is a polarization beam splitter that transmits P-polarized light and reflects S-polarized light in a wavelength range around λ. Is obtained. And
Especially when the film thickness of the present invention is as described above, a very good film can be obtained in terms of the angle dependence of the characteristics.

H and L constituting each stack
(H and L of the first stack, or H and L of the second stack) may have the same film thickness or different film thicknesses.

With such a structure, it is possible to obtain a polarization beam splitter having desired polarization characteristics in a wide angle range of ± 5 ° or more. Further, by using this polarization beam splitter, the degree of freedom in designing the optical system can be increased, the optical system can be made small and the number of parts can be reduced, and the configuration can be simplified.

[0013]

【Example】

Example 1 In this example, lithium niobate (LiN
bO ₃ ) An example in which a polarization beam splitter is provided on the substrate so that the reflectance of S-polarized light of the wavelength of 785 nm is 80% and the reflectance of P-polarized light is 0% in the angle range of 45 ± 5 °. Show.

First, after setting the LiNbO ₃ substrate in a vacuum chamber, the substrate is heated to 300 ° C. and the degree of vacuum is 5 × 1.
When reaching 0 ⁻⁴ Pa, a 21-layer beam splitter having an optical film thickness as shown in Table 1 was formed by a vacuum evaporation method. As a film material, T is a high refractive index material.
SiO ₂ was used as the low refractive index material for iO ₂ . In this embodiment, the first stack is 0.887 × λ / 4 for both TiO ₂ and SiO ₂ , and the second stack is TiO ₂ and S.
iO _{2 is} 1.385 × λ / 4 (where λ =
785 nm).

[0015]

[Table 1]

785 nm of this polarization beam splitter
When the transmittance characteristic at 45 is measured, as shown in FIG.
The reflectance of S-polarized light is within 80 ± 1% in the angle range of ± 5 °, P
The reflectance of polarized light is 2.8% or less, the reflectance of S-polarized light is within 80 ± 1%, and the reflectance of P-polarized light is 1 within 45 ± 4 °.
% Or less.

[Embodiment 2] In this embodiment, LiNbO ^{3 is used.}
On the substrate, the reflectance of S-polarized light of the wavelength of 785 nm is 40% and the reflectance of P-polarized light is 10% in the angle range of 40 to 55 °.
An example in which a polarization beam splitter that satisfies

First, after setting the LiNbO ₃ substrate in a vacuum chamber, the substrate was heated to 300 ° C. and the degree of vacuum was 5 × 1.
When reaching 0 ⁻⁴ Pa, a 21-layer beam splitter having an optical film thickness as shown in Table 2 was formed by a vacuum evaporation method. As a film material, T is a high refractive index material.
SiO ₂ was used as the low refractive index material for iO ₂ . In this example, the first stack contains 0.896 × λ / TiO ₂
4, SiO ₂ is 0.917 × λ / 4, and the second stack is TiO ₂ 1.461 × λ / 4 and SiO ₂ is 1.4.
69 × λ / 4 (where λ = 785 nm).

[0019]

[Table 2]

785 nm of this polarization beam splitter
When the transmittance characteristics at 40 are measured, as shown in FIG.
The reflectance of S-polarized light in the angle range of ˜55 ° is 76.6-80.
4% and the reflectance of P polarized light were 9.3 to 13.6%.

[Embodiment 3] In this embodiment, LiNbO _{3 is used.}
An example is shown in which a polarization beam splitter is provided on the substrate so that the reflectance of S-polarized light of the wavelength of 785 nm is 80% and the reflectance of P-polarized light thereof is 5% in the angle range of 45 ± 5 °.

First, after setting the LiNbO ₃ substrate in a vacuum chamber, the substrate was heated to 300 ° C. and the degree of vacuum was 5 × 1.
When reaching 0 ⁻⁴ Pa, a 23-layer beam splitter having an optical film thickness as shown in Table 3 was formed by a vacuum evaporation method. As a film material, T is a high refractive index material.
SiO ₂ was used as the low refractive index material for iO ₂ . In this example, the first stack contains TiO ₂ of 0.995 × λ /
4, SiO ₂ is 0.904 × λ / 4, and the second stack is TiO ₂ 1.380 × λ / 4 and SiO ₂ is 1.3.
27 × λ / 4 (where λ = 785 nm).

[0023]

[Table 3]

785 nm of this polarization beam splitter
The transmittance characteristics at 45 are measured, and as shown in FIG.
The reflectance of S-polarized light was 78 to 81%, and the reflectance of P-polarized light was 3.7 to 7.6% in an angle range of ± 5 °.

[Embodiment 4] In this embodiment, the refractive index is 1.5.
785nm in the 45 ± 7 ° angle range on the 2nd glass substrate
An example will be shown in which a polarization beam splitter is provided so that the reflectance of S-polarized light of light of wavelength is 80% and the reflectance of P-polarized light is 0%.

First, after setting the glass substrate in a vacuum chamber, the substrate is heated to 300 ° C. and the degree of vacuum is 5 × 10 ⁻⁴ P.
When reaching a, a 26-layer beam splitter having an optical film thickness as shown in Table 4 was formed by a vacuum evaporation method. As film material, Ti with high refractive index material
O ₂ and SiO ₂ were used as the low refractive index material. In this embodiment, the first _stack, TiO 2, SiO ₂ are 0.
902 × λ / 4, the second stack is TiO ₂ , SiO
Both ₂ are 1.338 × λ / 4 (where λ = 78
5 nm).

[0027]

[Table 4]

785 nm of this polarization beam splitter
When the transmittance characteristic at 45 is measured, as shown in FIG.
The reflectance of S-polarized light is 76 to 82% in the angle range of ± 7 °, the reflectance of P-polarized light is 5.5% or less, and the reflectance of S-polarized light is 45% in the angle range of ± 5 °.
The polarized light reflectance is 76 to 82%, and the P polarized light reflectance is 2.2.
% Or less.

[Embodiment 5] In this embodiment, the refractive index is 1.5.
785nm on the glass substrate of 2 in the angle range of 45 ± 5 °
An example will be shown in which a polarization beam splitter is provided so that the reflectance of S-polarized light of light of wavelength is 80% and the reflectance of P-polarized light is 0%.

First, after setting a glass substrate in a vacuum chamber, the substrate is heated to 300 ° C. and the degree of vacuum is 5 × 10 ⁻⁴ P.
When reaching a, a 24-layer beam splitter having an optical film thickness as shown in Table 5 was formed by a vacuum evaporation method. As film material, Ti with high refractive index material
O ₂ and SiO ₂ were used as the low refractive index material. In this embodiment, the first _stack, TiO 2, SiO ₂ are 0.
900 × λ / 4, the second stack is TiO ₂ , SiO
Both ₂ are 1.385 × λ / 4 (where λ = 78
5 nm).

[0031]

[Table 5]

785 nm of this polarization beam splitter
The transmittance characteristics at 45 are measured, and as shown in FIG.
The reflectance of S polarized light is 78.5 to 80.5 in an angle range of ± 5 °.
%, The reflectance of P-polarized light was 2.2% or less, and the reflectance of S-polarized light was 80 ± 0.5% and the reflectance of P-polarized light was 0.8% or less in the angle range of 45 ± 4 °.

[Embodiment 6] In this embodiment, the refractive index is 1.5.
785nm on the glass substrate of 2 in the angle range of 45 ± 5 °
An example will be shown in which a polarization beam splitter is provided so that the reflectance of S-polarized light of light of wavelength is 90% and the reflectance of P-polarized light is 0%.

First, after setting a glass substrate in a vacuum chamber, the substrate is heated to 300 ° C. and the degree of vacuum is 5 × 10 -4 P.
When reaching a, a 27-layer beam splitter having an optical film thickness as shown in Table 6 was formed by a vacuum evaporation method. As the film material, TiO2 is added to the high refractive index material.
, SiO2 was used as the low refractive index material. In the present embodiment, the first stack has TiO2 and SiO2 of less than 0.
903 × λ / 4, the second stack is TiO2, SiO
2 is 1.345 × λ / 4 (where λ = 78)
5 nm).

[0035]

[Table 6]

785 nm of this polarization beam splitter
When the transmittance characteristics at 45 are measured, as shown in FIG.
The reflectance of S-polarized light is 87 to 91% in the angle range of ± 5 °, the reflectance of P-polarized light is 4.4% or less, and the reflectance of the S-polarized light is 45% in the angle range of ± 4 °.
The reflectance of polarized light was 87.5 to 91%, and the reflectance of P polarized light was 1.7% or less.

[0037]

As described above, according to the invention of claim 1, a desired polarization characteristic can be obtained in a wide angle range of ± 5 ° or more or more, and the polarization beam splitter is used. As a result, it is possible to obtain an optical system that is compact, has a small number of parts, and has a simple configuration. According to the invention of claim 2, in addition to the above effects, the polarization beam splitter is the best.

[Brief description of drawings]

FIG. 1 is a graph showing reflectance characteristics of a polarization beam splitter of Example 1.

FIG. 2 is a graph showing reflectance characteristics of the polarization beam splitter of Example 2.

FIG. 3 is a graph showing reflectance characteristics of the polarization beam splitter of Example 3.

FIG. 4 is a graph showing reflectance characteristics of the polarization beam splitter of Example 4.

FIG. 5 is a graph showing reflectance characteristics of the polarization beam splitter of Example 5.

FIG. 6 is a graph showing reflectance characteristics of the polarization beam splitter of Example 6.

Claims (2)

[Claims] 1. A polarizing beam splitter comprising a high-refractive index layer and a low-refractive index layer, which are alternately laminated, wherein each of the high-refractive index layer and the low-refractive index layer has a central wavelength of λ. Optical film thicknesses H and L are 0.8 × λ /
4 <H <1.0 × λ / 4 and 0.8 × λ / 4 <L <1.
The first stack is 0 × λ / 4 and 1.3 × λ / 4 <
H <1.5 × λ / 4 and 1.3 × λ / 4 <L <1.5 ×
A polarizing beam splitter having a second stack of λ / 4. 2. The high refractive index layer is made of TiO ₂ and the low refractive index layer is made of SiO _2.
The described polarizing beam splitter.