Patent Application
20050024725
The present application claims priority to Japanese Patent Application No. 2003-284722 filed Aug. 1, 2003, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a polarizing beam splitter, more particularly to a polarizing beam splitter capable of a high-level performance suitable for, for example, a light pickup optical system using blue laser, a projection optical system, or the like, and a polarizing, beam splitter film as a component thereof.
2. Description of the Related Art
In a light pickup optical system for a blue region requires a polarizing beam splitter having such polarization separation characteristics that a transmissivity of a polarized light p and a reflectivity of a polarized light s in a wavelength region of around 405 nm both mark nearly 100%. Currently, however, a divergence angle of blue laser is significantly large. Therefore, when an ordinary polarizing beam splitter film is used, the transmissivity of the polarized light p is largely decreased due to a variation of an incidence angle.
Japanese Unexamined Patent Publication Nos. 08-146218 and 09-184916 disclose, in order to solve such a problem, polarizing beam splitters having predetermined polarization separation characteristics with respect to even a broad angle region, where a divergence angle of an incident light is ±5° or above. For example, a polarizing beam splitter film disclosed in No. 09-184916 comprises, when a central wavelength of a split light is λ, an optical film thickness of a film made of a high-refractivity material is H, and an optical film thickness of a film made of a low-refractivity material is L, a first stack constituting 0.8×λ/4≦H≦1×λ/4 and 0.7×λ/4≦L≦1×λ/4, and a second stack constituting 1.3×λ/4≦H≦1.5×λ/4 and 1.2×λ/4≦L≦1.5×λ/4.
However, in the case of polarizing beam splitter films disclosed in No. 08-146218 and No. 9-184916, an angle dependency of the polarized light s can only be controlled at approximately 20% in terms of the transmissivity, which shows insufficient polarization separation characteristics thereof. Therefore, when the polarizing beam splitter film is used in the light pickup optical system using the blue laser, projection optical system, or the like, such a problem as an decreased quantity of light is generated.
A main object of the present invention is to provide a polarizing beam splitter and a polarizing beam splitter film capable of preventing a transmissivity of a polarized light p from decreasing while maintaining a reflectivity of a polarized light s at nearly 100% with respect to even a broad angle region, where a divergence angle of an incident light is ±5° or above.
In order to achieve the foregoing object and other objects as well, in an stage of the present invention, a polarizing beam splitter having a multilayer structure, wherein a film made of a high-refractivity material and a film made of a low-refractivity are alternately stacked on a substrate, satisfies the following conditional expressions 1A and 1B in an entire range of 40≦θ≦50 (°) when an incidence angle with respect to a film surface in a particular wavelength is set to be θ (°).
0.99≦Rs(45)/Rs(θ)≦1.04 1A
0.96≦Tp(45)/Tp(θ)≦1.05 1B
Rs(θ): reflectivity of polarized light s at an incidence angle of θ
Tp(θ): transmissivity of polarized light p at an incidence angle of θ
Rs(45): reflectivity of polarized light s at the incidence angle of 45°.
Tp(45): transmissivity of polarized light p at the incidence angle of 45°.
The invention itself, together with further objects and attendant advantages, will best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
In the following description, like components are designated by like reference numbers throughout the several drawings.
Hereinafter, a polarizing beam splitter and a polarizing beam splitter film executed by the present invention are described referring to the drawings. Tables 1 and 2 respectively show multilayer films according to embodiments 1 and 2 (QWOT=4·n·d/λ, d: physical film thickness, n: refractivity, λ: wavelength) as the polarizing beam splitter film according to the present invention. In the embodiment 1, a film made of a high-refractivity material: TiO2 (titanium oxide) and a film made of a low-refractivity material: SiO2 (silicon oxide) are alternately stacked to thereby form 33 layers on a glass substrate having the refractivity of 1.64 in the order of layer numbers. In the embodiment 2, a film made of a blended material TX including a high-refractivity material: TiO2 (titanium oxide) and a film made of a low-refractivity material: MgF2 (magnesium fluoride) or SiO2 (silicon oxide) are alternately stacked to thereby form 25 layers on a glass substrate having the reflectivity of 1.64 in the order of the layer numbers.
In the case of the polarizing beam splitter film comprised of the film made of the high-refractivity material and the film made of the low-refractivity material alternately stacked as in the embodiments 1 and 2, it is preferable to satisfy the following conditional expressions 1A and 1B in an entire range of 40≦θ≦50 (°) when an incidence angle with respect to a film surface in a particular wavelength is set to be θ (°).
0.99≦Rs(45)/Rs(θ)≦1.04 1A
0.96≦Tp(45)/Tp(θ)≦1.05 1B
Rs(θ): reflectivity of polarized light s at an incidence angle of θ
Tp(θ): transmissivity of polarized light p at an incidence angle of θ
Rs(45): reflectivity of polarized light s at the incidence angle of 45°
Tp(45): transmissivity of polarized light p at the incidence angle of 45°
Tables 3 and 4 show data according to respective embodiments in the case of wavelength λ=405 nm and 40≦θ≦50 (°): reflectivity Rs (θ) of polarized light s and transmissivity Tp (θ) of polarized light p, and data corresponding to parameters regulated in the conditional expressions 1A and 1B. As learnt from the tables 3 and 4, the embodiments 1 and 2 satisfy the conditional expressions 1A and 1B in the entire range of 40≦θ≦50 (°). Thus, when the conditional expressions 1A and 1B are satisfied in the entire range of 40≦θ≦50 (°), the transmissivity of the polarized light p can be prevented from decreasing while maintaining the reflectivity of the polarized light s at nearly 100% with respect to even a broad angle region, where a divergence angle of an incident light is ±5° or above.
As described, in order to satisfy the conditional expressions 1A and 1B in the entire range of 40≦θ≦50 (°), it is preferable to have at least a stack comprised of a film made of a high-refractivity material satisfying the following conditional expression 2A and a film made of a low-refractivity material satisfying the following conditional expression 2B alternately stacked in two or more repetitive cycles, providing that a pair of a layer of the film made of the high-refractivity material and a layer of the film made of the low-refractivity material constitutes a cycle.
0.7×λ/4≦H≦1×λ/4 2A
1×λ/4≦L≦2×λ/4 2B
providing that,
H: optical film thickness of film made of high-refractivity material
L: optical film thickness of film made of low-refractivity material
λ: central wavelength of split light
In the embodiment 1, a multilayer structure comprised of layers from a 16th layer through a 27th layer (layer No. 16-27) constitutes a stack. The stack is comprised of a film made of TiO2 satisfying the conditional expression 2A and a film made of SiO2 satisfying the conditional expression 2B alternately stacked in six repetitive cycles. In the embodiment 2, a multilayer structure comprised of layers from a 3rd layer through a 14th layer (layer No. 3-14) constitutes a stack. The stack is comprised of a film made of TX satisfying the conditional expression 2A and a film made of SiO2 or MgF2 satisfying the conditional expression 2B alternately stacked in six repetitive cycles. The adoption of such a configuration having a discriminative stack is capable of arranging an angle dependency of the polarized light s to invariably lead to the transmissivity of approximately 0%. Therefore, in an optical system, in which the polarized lights p and s are required to be sufficiently polarized and separated despite the divergence angle of the incident light being large (for example, light pickup optical system using blue laser, projection optical system, or the like), a quantity of light and optical performance can be dramatically improved.
Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Therefore, unless such changes and modifications depart from the scope of the present invention, they should be construed as being included therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-284722 | Aug 2003 | JP | national |
