JP3584257B2 - Polarizing beam splitter - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a polarizing beam splitter used for separating and combining both S and P polarization components.
[0002]
[Comparison technology]
Generally, a polarizing beam splitter is used in which a dielectric multilayer film in which dielectric thin films of a high refractive index material and a low refractive index material are alternately stacked is interposed between two 45 ° prisms. The material selection of the dielectric multilayer film is within a wavelength range where the reflectance of the P-polarized light component of the incident light incident from the optical axis of the 45 ° prism is the smallest and the reflectance of the S-polarized light component is the highest. It is done as follows.
[0003]
2. Description of the Related Art A polarizing beam splitter is used in an optical disk device, a projection display device, and the like in order to efficiently separate incident light into P and S polarization components. From the comparison, various proposals have been made on the configuration of the dielectric multilayer film in order to widen the usable wavelength bandwidth of the polarizing beam splitter. For example, in JP-A-61-141402, an intermediate layer is provided on a dielectric multilayer film having a basic period of two layers of a high refractive index material and a low refractive index material, and the thickness of this layer is adjusted. Broadening the bandwidth. Further, in the configuration example of the conventional polarizing beam splitter disclosed in Japanese Patent Application Laid-Open No. 3-284705, a combination of a high refractive index material and a low refractive index material is the same in two dielectric multilayer films having different design reference wavelengths. It is a combination. With this configuration, the bandwidth of the used wavelength is widened and the polarization separation ratio is improved.
[0004]
[Problems to be solved by the invention]
However, in the conventional polarization beam splitter having a dielectric multilayer structure, although the bandwidth is widened with respect to the design incident angle, even if the incident angle of the light beam is slightly deviated, the P / S polarization separation ratio is deteriorated, and the bandwidth is reduced. Is very narrow.
SUMMARY OF THE INVENTION An object of the present invention is to provide a polarization beam splitter which has a small incident angle dependence of a light beam incident on a polarization separation multilayer film surface, a high polarization separation ratio, and a wide use bandwidth.
[0005]
[Means for Solving the Problems]
According to the present invention, there is provided a polarizing beam splitter having a dielectric multilayer film formed on a light-transmitting substrate, wherein the dielectric multilayer film has a first dielectric layer having two different design reference wavelengths λ1. And a second dielectric multilayer film having a design reference wavelength λ2, wherein the first and second dielectric multilayer films each include alternating layers of a high refractive index material and a low refractive index material. And the incident angle satisfying the Brewster condition of the alternate layer of the first dielectric multilayer film and the incident angle satisfying the Brewster condition of the alternate layer of the second dielectric multilayer film are different. A combination of the refractive index values of the high-refractive index material and the low-refractive index material forming the alternating layers in the alternating layers of the first dielectric multilayer film and the alternating layers of the second dielectric multilayer film Are characterized in that they differ from each other.
[0006]
[Action]
The polarizing beam splitter according to the present invention has a configuration in which the bandwidth of the used wavelength region is not narrowed even if the angle of incidence of the light beam on the dielectric multilayer film slightly changes, and a high refractive index of the alternating layers of the dielectric multilayer film. The material used for the layer and the low refractive index layer is selected. In order to separate the polarized light over a wide band, it is necessary to increase the wavelength band separating the P-polarized component and the S-polarized component from the wavelength of the light beam incident on the polarization separating film. To this end, according to Snell's law, the vicinity of the Brewster angle, at which the polarization separation of the P-polarized light component and the S-polarized light component is the largest, is set as the design incident angle and the light is incident on the polarization splitting film.
[0007]
The dielectric multilayer structure of the present invention includes first and second dielectric multilayer films having different design reference wavelengths. The incident angles of the light beams incident on the first and second dielectric multilayer films are set to be different. The high refractive index and low refractive index substances of the first and second dielectric multilayer films were selected so that the following Brewster conditions (1) and (2) were different. For example, one of the alternate layers of the dielectric multilayer film is a combination of TiO ₂ and a low-refractive-index material SiO ₂ as a high-refractive-index material, and the other alternating layer of the dielectric multilayer film is a combination of TiO _{2 and a} high-refractive-index material. Alternatively, a combination in which Al ₂ O ₃ is used as the low refractive index substance may be used.
[0008]
The design reference wavelengths λ1 and λ2 (λ1 ≠ λ2) and the design reference incident angle θ are the incident angles θ1 and θ2, respectively. The Brewster conditions in each case are represented by the following equations (1) and (2).
λ1> λ2
λ1, θ1; nH1 / COSθH1 = nL1 / COSθL1 (1)
λ2, θ2; nH2 / COSθH2 = nL2 / COSθL2 (2)
θ1; the angle θ2 from the light-transmitting substrate 1 to the boundary surface between the first dielectric multilayer film and the light-transmitting substrate 1; Angles nH1 and nL1 incident on the boundary surface with the refractive index nH2 and nL2 of the high refractive index layer and the low refractive index layer in the alternating layers of the first dielectric multilayer film at the design reference wavelength λ1; High refractive index layers and low refractive index layers in the alternate layers of the second dielectric multilayer film θH1 and θL1; high refractive index layers in the first dielectric multilayer film at the design reference wavelength λ1 ΘH2, θL2 incident on the interface from each layer of the low-refractive-index layer and the interface between the high-refractive-index layer and the low-refractive-index layer at the design reference wavelength λ2. FIG. 3 shows that the luminous flux incident on the dielectric multilayer film has a high refractive index layer and It is a state diagram enters the boundary surface from the refractive index layer. In the figure, θi, θHi, and θLi correspond to the first and second dielectric multilayer films i = 1 and 2, respectively.
[0009]
The thicknesses of the high refractive index layer, the low refractive index layer, and the adjustment layer used for the alternating layers of the dielectric multilayer film of the present invention are λ / 4, λ / 4, and λ / 8, respectively. However, the actually formed film thickness is determined experimentally through trial and error, and may slightly deviate from the designed value.
Further, the adjustment layer of the present invention is provided to reduce a ripple generated in the transmittance of the P-polarized light component. If there is a large ripple, the wavelength range that can be used as the polarizing beam splitter is limited, which is not preferable.
[0010]
For comparison with the embodiment of the present invention, the configuration of the polarizing beam splitter is basically the same as that of FIG. 1, and the high refractive index layer TiO ₂ and the low refractive index used for the alternating layers of the first and second dielectric multilayer films are used. The transmittance characteristics in which the combination of the substance with the rate layer SiO ₂ is the same will be examined. FIG. 10 shows the incident angle dependence of the transmittance characteristics.
At a design reference angle of incidence of 45 °, the band having a high P / S polarization separation ratio is 160 nm, but if the angle of incidence is shifted by ± 2.5 °, the bandwidth becomes 90 nm. A polarization beam splitter using a dielectric multilayer film composed of only one type can obtain a wide usable wavelength range in which S and P polarization components can be separated. However, even if the angle of incidence on the surface of the dielectric multilayer film is slightly shifted, the desired wavelength bandwidth becomes very narrow.
[0011]
On the other hand, the working bandwidth of the embodiment of the present invention is very wide while maintaining the separation ratio between the P-polarized light component and the S-polarized light component even if the angle at which the light beam enters the dielectric multilayer film is slightly shifted. Further, the degree of freedom in the arrangement of the optical system incorporating the polarizing beam splitter is increased.
Next, a method of forming the dielectric multilayer film of the polarizing beam splitter of the present invention will be described.
[0012]
FIG. 1 shows that first and second dielectric multilayer films 3 and 4 of the present invention are formed on a prism 1 which is a translucent substrate, and each of them is bonded via an adhesive layer 5. Configuration.
FIG. 8 shows that a first dielectric multilayer film and a second dielectric multilayer film are continuously formed on a transparent substrate 1. Further, the translucent base 12 is bonded thereon.
[0013]
In FIG. 9, the same performance can be obtained even when the transparent substrate is formed by applying a dielectric multilayer film on both sides of the flat glass 2 and immersing it in a liquid medium 6 having a refractive index similar to that of the glass.
[0014]
【Example】
A first embodiment of the polarizing beam splitter according to the present invention will be described.
FIG. 1 shows a prism 1 in which an adjustment layer 1C and an alternating layer 13 of the first dielectric multilayer film 3 are stacked, and an adjustment layer 2C and an alternating layer 23 of the second dielectric multilayer film 4 stacked. This is a configuration of a polarizing beam splitter in which a prism 2 and an optical adhesive 5 are joined. The prism 1 and the prism 2 have a refractive index nS of 1.84. The refractive index nb of the optical adhesive is 1.52. The drawing shows the reflected light R and the transmitted light T when the light beam is incident at 45 °. The transmitted light T has an S-polarized component TS and a P-polarized component TP.
[0015]
The alternating layers 13 of the first dielectric multilayer film are composed of TiO ₂ 11 having a high refractive index material nH1 = 2.38 and Al ₂ O ₃ 12 having a low refractive index material nL1 = 1.65 at a design reference wavelength λ1 = 680 nm. Are configured with an optical film thickness λ1 / 4.
The alternating layers 23 of the second dielectric multilayer film are composed of TiO ₂ 21 having a high refractive index material nH2 = 2.38 and SiO ₂ 22 having a low refractive index material nL2 = 1.47 at a design reference wavelength λ2 = 420 nm. It has an optical film thickness λ2 / 4.
Further, between each alternate layer of the first and second dielectric multilayer films and the prism 1 and the prism 2, adjustment layers having a film thickness of λ1 / 8 and λ2 / 8, respectively, are provided.
[0016]
Consider a case where the light beam has an incident angle shifted by ± 2.5 ° from the design reference incident angle of 45 °. The high-refractive-index material 11 and the low-refractive-index material 12 used for the alternating layers 13 of the first dielectric multilayer film corresponding to the high angle side (corresponding to the short wavelength side in the used wavelength region) transmit light. Is selected so as to satisfy the Brewster condition (1) at an angle θ1 = 47.5 ° from the transparent substrate 1 to the interface between the transparent substrate 1 and the first dielectric multilayer film. In this embodiment, TiO ₂ was selected for the high refractive index layer 11 and Al ₂ O ₃ was selected for the low refractive index layer 12 as a material combination of the alternating layers of the first dielectric multilayer film.
[0017]
The high-refractive-index substance 21 and the low-refractive-index substance 22 used for the alternating layer 23 of the second dielectric multilayer film corresponding to the low angle side (corresponding to the long wavelength side in the used wavelength range) transmit light. It is selected so as to satisfy the Brewster condition (2) at an angle θ2 = 42.5 ° at which the light enters the interface between the light-transmitting substrate 2 and the second dielectric multilayer film from the light-transmitting substrate 2. In this embodiment, as the substance a combination of alternating layers of the second dielectric multilayer film, TiO 2 in the high refractive index layer _21, was chosen SiO ₂ for the low refractive index layer 22.
[0018]
FIG. 4 shows the transmittance characteristics Tp and TS of the P and S polarization components and the respective transmittance characteristics of the incident angles 42.5 °, 45 °, and 47.5 ° of the dielectric multilayer structure of the first embodiment. .
The dependence of the transmittance of the P and S polarization components of the polarization beam splitter having the dielectric multilayer structure of the first embodiment of the present invention on the incident angle will be compared with the comparative example of FIG.
[0019]
In the multilayer film configuration of the comparative example, when the incident angle deviates from the design reference angle by several degrees in the wavelength range of 480 nm to 550 nm, the bandwidth X becomes 70 nm, and the used band becomes very narrow.
In contrast, the first embodiment of the present invention has a high polarization separation (TS / TP) of 0.1% or less over the wavelength range of 460 nm to 620 nm. Even if it deviates from the design standard incident angle by ± 2.5 °, the bandwidth X maintains a wide band of 160 nm.
[0020]
FIG. 5 shows the dependency of the transmittance of the P-polarized light component on the long wavelength side λ = 620 nm in the incident angle according to the first embodiment of the present invention.
This embodiment is different from the comparative example of FIG. 10 in which the combination of the alternating layers of the first dielectric multilayer film and the alternating layers of the second dielectric multilayer film uses the same type of substance TiO ₂ and SiO ₂ . The bandwidth of the transmittance characteristics could be greatly expanded even if the incident angle dependence was taken into consideration.
[0021]
This is because the alternating layer of the first dielectric multilayer film, which causes the drop of the P-polarized light transmittance on the long wavelength side, satisfies the Brewster condition (1) at 47.5 °, and the drop on the short wavelength side does not. This is because the film material of each dielectric multilayer film is selected so that the alternate layer of the second dielectric multilayer film which causes the problem satisfies the Brewster condition (2) at 42.5 °.
[0022]
As described above, by using the polarization beam splitter having the configuration of the present invention, the wavelength band to be used can be significantly widened as compared with the conventional example, and a polarization beam splitter having a high degree of freedom with respect to the incident angle of light can be obtained. .
Next, a second embodiment of the present invention will be described.
The structure of the dielectric multilayer film of the second embodiment is basically the same as that of the first embodiment, and the combination of substances used for the dielectric multilayer film is different. The structure is such that the light-transmitting substrate 1 in which the adjustment layer 1C and the alternating layer 13 of the first dielectric multilayer film 3 are stacked, the adjustment layer 2C and the alternating layer 23 of the second dielectric multilayer film 4 are stacked. This is a configuration of a polarization beam splitter in which a transparent substrate 2 is bonded with an optical adhesive 5. The translucent substrate 1 and the translucent substrate 2 have a refractive index nS of 1.52.
[0023]
Alternating layers of the first dielectric multilayer film is a design wavelength .lambda.1 = 700 nm, the high refractive index material nH1 = 2.38 TiO ₂ and the low refractive index material n1 = 1.47 SiO ₂ and an optical membrane of It has a thickness of λ1 / 4.
The alternate layers of the second dielectric multilayer film are optical films of ZrO ₂ having a high refractive index material nH2 = 2.02 and MgF ₂ having a low refractive index material nL2 = 1.37 at a design reference wavelength λ2 = 430 nm. It has a thickness of λ2 / 4.
Further, between the alternating layers of the first and second dielectric multilayer films and the prisms 1 and 2, adjustment layers having a film thickness of λ1 / 8 and λ2 / 8, respectively, are provided.
[0024]
When the luminous flux is deviated by ± 4 ° in the vicinity of the design reference incident angle of 52 °, the luminous flux is used as an alternate layer of the first dielectric multilayer film corresponding to the higher angle side (corresponding to the shorter wavelength side in the used wavelength range). The high-refractive-index substance and the low-refractive-index substance are selected so as to satisfy the Brewster condition (1) at an incident angle of 56 ° with respect to the normal to the film surface of the light beam. Substance combination of the first dielectric multilayer film of this example, TiO _2, the low refractive index layer 12 was selected SiO ₂ in the high refractive index layer 11.
[0025]
The high-refractive index material and the low-refractive index material used for the alternating layers of the second dielectric multilayer film corresponding to the low angle side (corresponding to the long wavelength side in the used wavelength range) have a light flux of an incident angle of 48 °. Is selected so as to satisfy the Brewster condition (2). Substance combination of the second dielectric multilayer film of this example, ZrO 2 in the high refractive index layer _21, was chosen MgF ₂ for the low refractive index layer 22.
[0026]
FIG. 6 shows the transmittance characteristics of the P and S polarization components and the transmittance characteristics at incident angles of 48 °, 52 ° and 56 ° in the second embodiment of the dielectric multilayer structure.
The incident angle dependence of the transmittance of the P and S polarization components of the polarizing beam splitter having the dielectric multilayer structure according to the second embodiment of the present invention will be compared with the comparative example of FIG.
In the multilayer structure of the comparative example, in the wavelength range of 480 nm to 550 nm, if the incident angle deviates from the design reference angle by several degrees, the bandwidth becomes 70 nm, and the used band becomes very narrow.
[0027]
On the other hand, the second embodiment of the present invention shows high polarization separation of the S-polarized component and the P-polarized component over the wavelength range of 460 nm to 620 nm. Even if it deviates from the design standard incident angle by ± 4 °, the bandwidth X maintains a wide band of 170 nm.
As described above, the embodiment of the present invention uses TiO ₂ and SiO _{2 in} which the alternating layers of the first dielectric multilayer film and the alternating layers of the second dielectric multilayer film are the same kind of substance combination. Compared with the comparative example, the bandwidth of the transmittance characteristics could be greatly increased even when the incident angle dependency was taken into consideration.
[0028]
This is because the alternating layers of the first dielectric multilayer film, which cause the drop in the transmittance of P-polarized light on the long wavelength side, satisfy the Brewster condition (1) at 56 °, and cause the drop on the short wavelength side. This is because the material of the dielectric multilayer film is selected so as to satisfy the Brewster condition (2) at 48 ° in the alternate layer of the second dielectric multilayer film.
As described above, by changing the design reference wavelength of each of the first dielectric multilayer film and the second dielectric multilayer film and the combination of the low refractive index material and the high refractive index material, the degree of freedom with respect to the incident angle is increased. It is possible to obtain a high-bandwidth polarization beam splitter having a high polarization separation ratio S / P.
[0029]
7 and 8 show a third embodiment.
This embodiment is a modified example regarding the arrangement of the polarizing beam splitter of the present invention.
A first dielectric multilayer film 3 and a second dielectric multilayer film 4 are continuously laminated on a light-transmitting substrate 1, and the light-transmitting substrate 2 is formed via an adhesive layer 5.
According to this configuration, there is an advantage that the deposition of the low refractive index layer and the high refractive index layer can be performed in one batch.
[0030]
FIG. 9 shows a fourth embodiment of the polarizing beam splitter according to the present invention.
The polarizing beam splitter of this embodiment uses a transparent flat substrate 2 as a light-transmitting substrate, and includes a first and a second dielectric multilayer film filled with a liquid medium 6 having substantially the same refractive index as the flat substrate. It is configured. The first dielectric multilayer film 3 and the second dielectric multilayer film 4 are arranged on both sides of the transparent flat substrate. Examples of the liquid medium include ethylene glycol (refractive index: 1.43) and benzene (refractive index: 1.51).
[0031]
In general, when a prism is used for a light-transmitting substrate, birefringence occurs due to unevenness of the material in the prism. It is known that when a light beam passes through a substrate, the state of polarization changes and linear polarization characteristics deteriorate. In such a case, the problem of birefringence of the light-transmitting substrate can be avoided by the structure using the liquid medium.
With the polarization beam splitter having the configuration and arrangement as in the third embodiment, the formation of the dielectric multilayer film is completed in one batch, and an improvement in productivity can be expected.
[0032]
The polarization beam splitter having the configuration and arrangement of the fourth embodiment does not need to use an expensive prism, so that cost reduction can be expected.
[0033]
【The invention's effect】
As described above, according to the polarizing beam splitter of the present invention, a configuration in which a combination of a low-refractive index substance and a high-refractive index substance and first and second dielectric multilayer films having different design reference wavelengths are used. Accordingly, the degree of freedom with respect to the incident angle is high, and the S-polarized component and the P-polarized component can be separated or synthesized in a wide wavelength range.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view showing a configuration of a polarizing beam splitter according to the present invention.
FIG. 2 is a configuration sectional view of first and second dielectric multilayer films of the present invention.
FIG. 3 is an explanatory diagram of a state of a light beam incident on a dielectric multilayer structure of the present invention.
FIG. 4 is a transmittance characteristic diagram of a dielectric multilayer structure according to the first embodiment of the present invention.
FIG. 5 is an incident angle dependence of transmittance characteristics of the dielectric multilayer structure of the first embodiment of the present invention.
FIG. 6 is a transmittance characteristic diagram of a P-polarized light component having a dielectric multilayer structure according to a second embodiment of the present invention.
FIG. 7 is a configuration sectional view of a polarization beam splitter according to a third embodiment of the present invention.
FIG. 8 is a configuration sectional view of first and second dielectric multilayer films according to a third embodiment of the present invention.
FIG. 9 is a configuration sectional view of a polarization beam splitter according to a fourth embodiment of the present invention.
FIG. 10 is a graph showing a comparison of transmittance characteristics based on the configuration of a conventional polarizing beam splitter.
[Explanation of symbols]
1 First translucent substrate (prism)
2 Second translucent substrate (prism)
3 First Dielectric Multilayer Film 4 Second Dielectric Multilayer Film 5 Adhesive Layer 6 Liquid Medium 11 High Refractive Index Material with Optical Thickness λ1 / 4 Low Refractive Index Material with Optical Thickness λ1 / 4 13 Alternating layer 1C made of a high-refractive-index substance and a low-refractive-index substance each having an optical thickness of λ1 / 4 Adjusting layer 21 having an optical thickness of λ1 / 8 High-refractive index having an optical thickness of λ2 / 4 Substance 22 Low-refractive-index substance having an optical film thickness of λ2 / 4 23 Alternating layer 2C composed of high-refractive-index substance and low-refractive-index substance having an optical film thickness of λ2 / 4, respectively. Adjustment layer

Claims (7)

In a polarizing beam splitter having a dielectric multilayer film formed on a transparent substrate,
  The dielectric multilayer has two different design reference wavelengths λ. One A first dielectric multilayer film having Two And a second dielectric multilayer film having
  The first and second dielectric multilayer films each include alternating layers of a high refractive index material and a low refractive index material,
The second dielectric multilayer film is formed such that the incident angle satisfying the Brewster condition of the alternating layer and the incident angle satisfying the Brewster condition of the alternating layer of the second dielectric multilayer film are different from each other. The combination of the refractive indices of the high-refractive index material and the low-refractive index material forming the alternating layer is made different between the alternating layer of the first dielectric multilayer film and the alternating layer of the second dielectric multilayer film. A polarizing beam splitter. 2. The polarization beam splitter according to claim 1, wherein the high refractive index material of the first dielectric multilayer film, the high refractive index material of the second dielectric multilayer film, and the first dielectric multilayer film. A polarizing beam splitter, wherein at least one set of the low refractive index material and the low refractive index material of the second dielectric multilayer film has different refractive indexes. 2. The polarization beam splitter according to claim 1, wherein the high refractive index material of the first dielectric multilayer film, the high refractive index material of the second dielectric multilayer film, and the first dielectric multilayer film. A polarizing beam splitter, wherein at least one pair of the low refractive index material and the low refractive index material of the second dielectric multilayer film is different from each other. The high refractive index material TiO ₂ and the low refractive index material SiO ₂ are provided in the alternating layers of the first dielectric multilayer film, and the high refractive index material TiO ₂ and the low refractive index material Al are provided in the alternating layers of the second dielectric multilayer film. 4. The polarization beam splitter according to claim 3, wherein the polarization beam splitter is a combination using ₂ O ₃ . A high refractive index material TiO ₂ and a low refractive index material SiO ₂ are provided in the alternate layers of the first dielectric multilayer film, and a high refractive index material ZrO ₂ and a low refractive index material MgF are provided in the alternate layers of the second dielectric multilayer film. polarization beam splitter according to claim 3, characterized in that a combination with the _2. The first and second dielectric multilayer films have respective reference wavelengths λ One , Λ Two At the optical film thickness λ One / 4, λ Two 4. An alternating layer in which two layers composed of a high-refractive-index substance and a low-refractive-index substance of / 4 are stacked with n periods (n is an arbitrary integer) as a basic period. One The polarizing beam splitter according to 1. The polarizing beam splitter according to claim 6, further comprising an optical thin film λ formed on both sides of the alternating layer. One / 8, λ Two / 8. A polarizing beam splitter comprising a thin film layer made of either the high refractive index material or the low refractive index material.

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