JPS63298203A - Polarization beam splitter - Google Patents

Abstract

PURPOSE:To obtain a splitter which can be manufactured easily, and by which the variation quantity of a phase characteristic and a spectral characteristic is small against a variation of an incident angle to a film layer of a light beam, a refractive index of the film layer and the film thickness, by using a film layer whose main component is Si, for a high refractive index film layer. CONSTITUTION:Between two transparent substrates 1a, 1b having a refractive index NG, a multi-layer film which has laminated a low refractive index film layer 3 having a refractive index NL of <=NG, and a high refractive index film layer 3 containing at least one layer of the film layer whose main component is Si having a higher refractive index NH than NG, alternately, and also, so that the lowest layer and the uppermost layer become the high refractive index film layer. In such a way, the manufacture can be executed easily, that is, a high polarization characteristic can be obtained with high reproducibility by a small number of laminations, and also, the variation quantity of a phase characteristic and a spectral characteristic can be reduced against a variation of an incident angle to the film layer of a light source, a refractive index of the film layer and the film thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to the field of optical measurement technology, and in particular to a polarizing beam splitter used in optical information recording and reproducing devices such as optical disks and magneto-optical disks.

[Prior art]

2. Description of the Related Art In recent years, active research and development has been conducted on optical information recording and reproducing devices that perform recording and reproducing using semiconductor laser light, with the aim of putting them into practical use as high-density recording memories.

For example, read-only optical disk devices such as video disks have already been commercialized, and magneto-optical disk devices that are erasable and rewritable are also promising. A magneto-optical disk device magnetically records information by utilizing the local temperature rise of a magnetic thin film caused by spot irradiation with laser light, and reproduces the information by the magneto-optic effect (particularly the Kerr effect). Here, the Kerr effect refers to a phenomenon in which the plane of polarization rotates when light is reflected by a magnetic recording medium.

FIG. 12 is a schematic diagram showing the configuration of a polarizing beam splitter used in a conventional magneto-optical disk device. As shown in FIG. 12, a conventional polarizing beam splitter has a high refractive index film layer 2 having a refractive index NH and a low refractive index film layer 3 having a refractive index NL alternately stacked on a prism la having a refractive index NG.
It is constructed by bonding prism 1b with an NG refractive index using adhesive 4, and as shown in Japanese Patent Publication No. 55-9683, the angle of incidence on the film surface of prism la is α0, and the refractive index of prisms la and lb is NG, refractive index of high refractive index film layer 2 NH
1. When the refractive index NL of the low refractive index film layer 3 is defined as NL, each value is satisfied. At this time, the reflectance of P-polarized light at the interface between the film layers becomes 0, and highly transmitted P-polarized light can be easily obtained. However, in order to obtain a high reflectance for S-polarized light, there is no other way than to increase the number of film layers, and usually in order to obtain a reflectance of 98% or more for S-polarized light,
The number of stacked layers is more than 1 layer. Naturally, as the number of laminated layers increases, the above equation is no longer satisfied with respect to fluctuations in the refractive index of each layer, and the characteristics deteriorate more sensitively. In cases where the angle of incidence on the film surface of the prism la is other than α=45°, the characteristics deteriorate more sensitively to an increase in the number of laminated layers. In addition, in the case of a magneto-optical disk device, due to the nature of the signal, the polarization beam splitter's P-polarization
The phase characteristics of transmission and reflection of S-polarized light become a problem. Considering the compatibility of magneto-optical disks, it is necessary that the phase difference between transmission and reflection of P-polarized light and S-polarized light has a determined value.
Generally Oo or 180°. This value is λ
A film layer equivalent to /4 film thickness.

A single wavelength and a single angle of incidence can be obtained by laminating a single layer, but if the number of laminated layers is large, the characteristics will deteriorate due to sensitivity to manufacturing errors, and furthermore, the refractive index of the film layer will deteriorate. The characteristics deteriorate more markedly due to variations in the angle of incidence on the film layer, resulting in a major problem.

[Summary of the invention]

The purpose of the present invention is to eliminate the drawbacks of the conventional polarizing beam splitter mentioned above, to be easy to manufacture, that is, to obtain high polarization characteristics with good reproducibility with a small number of laminated layers, and to improve the angle of incidence of the light beam on the film layer. Another object of the present invention is to provide a polarizing beam splitter whose phase characteristics and spectral characteristics change little with respect to changes in the refractive index and thickness of film layers.

The above object of the present invention is achieved by using a film layer containing St as a main component as a high refractive index film layer in a conventional polarizing beam splitter.

〔Example〕

FIG. 1 is a schematic diagram showing an embodiment of a polarizing beam splitter of the present invention. The polarizing beam splitter of the present invention
As shown in the figure, a film 2 mainly composed of Si with a refractive index NH = 2.9 and a MgF2 film with a refractive index NL = 1.38 are placed on a 45° right triangular prism la with a refractive index NG = 1.92. 3 and 3 alternately, and using adhesive 4, the refractive index NG=1.
．． 92 45° right triangular prisms 1b are bonded together. Here, the film thickness DI of the i-th layer is configured to satisfy the following conditions: λo1 is the center wavelength of the polarizing beam splitter, ni is the refractive index of the same film, and θI is the angle of incidence of the incident light beam on the same film. . P-polarized light due to changes in the wavelength of the incident light beam of the polarizing beam splitter in this example
The change in transmittance Tp-Ts of each component of S-polarized light is shown by a solid line in FIG. FIG. 3 also shows the phase difference δ with respect to the change in the incident angle θ of the incident light beam of the polarizing beam splitter of this example.
Figure 4 shows the change in the refractive index NH of the Si-based film 2 of the polarizing beam splitter of this example.
In FIG. 5, the change in the phase difference δ with respect to the change in the refractive index NH of the Si-based film 2 of the polarizing beam splitter of this embodiment is shown by a solid line.

FIG. 6 is a schematic diagram showing another embodiment of the polarizing beam splitter of the present invention. As shown in FIG. 6, on a 66.8° right triangular prism 5a with a refractive index NG=1.5, an St film 2 with a refractive index N=3.5 and a SiO It is constructed by alternately laminating films 3 mainly composed of and bonding them to a 66.8° right triangular prism 5b with a refractive index NG=1.5 using an adhesive 4. here,
The i-th film layer Di uses a polarizing beam splitter with a center wavelength of λ. , nl is the refractive index of the same antinode, and θi is the angle of incidence of the incident light beam on the same antinode. P-polarized light and S-polarized light with respect to changes in the wavelength of the incident light beam of the polarizing beam splitter of this example
The change in transmittance Tp-Ts of each component of polarized light is shown by a solid line in FIG. Further, FIG. 8 shows the change in the transmittance Tp of the P-polarized light component with respect to the change in the refractive index NH of the Si film 2 of the polarizing beam splitter of this embodiment, and FIG. Figure 10 shows the change in the phase difference δ with respect to the change in the refractive index NH of the polarizing beam splitter of this embodiment, and the change in the transmittance Tp of the P polarized light component with respect to the change in the incident angle θ of the incident light beam of the polarizing beam splitter of this embodiment. The solid line indicates the change in the phase difference δ with respect to the change in the incident angle θ of the light beam incident on the polarizing beam splitter of this embodiment.

The polarizing beam splitter of the present invention uses a Si film or a film containing St as a main component as a high refractive index film layer, so that the number of stacked layers of 3 layers is 96% to
It is possible to obtain highly reflected S-polarized light of approximately 99%, and because the number of laminated layers is small, there is little deterioration in phase characteristics and spectral characteristics due to changes in the angle of incidence of the light beam on the film layer and the refractive index of the film layer. There is an advantage. In particular, good phase characteristics are a great advantage for use in magneto-optical disk drives. In addition, in a configuration in which a film with a high refractive index such as St or a film with a high refractive index such as Si is used as a main component as a high refractive index film layer, the allowable range of refractive index fluctuation is It has been found that this structure has the advantage of being wider than structures using TiO2 and ZnS films. Furthermore, in a configuration in which a film having a high refractive index such as Si or a film mainly composed of a film having a high refractive index such as Si is used as a high refractive index film layer, the refractive index of the prism will inevitably be high. - When used in convergent light, the angle of incidence within the prism becomes smaller and the angular characteristics of the polarizing beam splitter can be improved.

Further, according to experiments conducted by the present inventor, it was found that the refractive index NH of the high refractive index film layer is preferably 2.6 or more. If the refractive index NH is lower than the above-mentioned value, it is impossible to obtain high reflected S-polarized light with a small number of laminated layers.
The number of laminated layers is required. According to the conventional example, refractive index NG=l
, 73 on a 45° right triangular prism with refractive index NH=2
．． The TiO□ film of No. 3 and the 5i02 film of refractive index NL = 1.45 were alternately laminated to form 7 layers, and then bonded to a 45° right triangular prism with refractive index NG = 1.73 using adhesive. Transmittance TpeT of each component of P-polarized light and S-polarized light with respect to changes in the wavelength of the incident light beam of the created polarizing beam splitter
The change in s is shown in FIG. 2 by a broken line. Furthermore, Fig. 3 shows the change in the phase difference δ with respect to the change in the incident angle θ of the incident light beam of the polarizing beam splitter mentioned above, and Fig. 4 shows the P-polarized light with respect to the change in the refractive index NH of the TiO□ film of the polarizing beam splitter mentioned above. In FIG. 5, the change in the phase difference δ with respect to the change in the refractive index NH of the TiO2 film of the polarizing beam splitter is shown by a broken line. As shown in the above-mentioned figure, if the refractive index NH of the high refractive index film layer is lower than 2.6, the angle of incidence of the light beam on the film layer, the phase characteristics and the spectral characteristics will change with respect to variations in the refractive index of the film layer. The deterioration of

In the above embodiments, the prism shape is a right triangle, but it does not necessarily have to be a right triangle depending on the optical system used, and if the film structure of the present invention is used, it can be formed on a glass plate, for example. The shape can be freely chosen, such as when joining a prism with an arbitrary angle shape using adhesive. Furthermore, any type of adhesive may be used as long as it is optically transparent and has an adhesive effect.

Furthermore, in the two examples described above, changes in the phase characteristics and spectral characteristics with respect to changes in the refractive index of the film layer were shown, but the same applies to the changes in the phase characteristics and spectral characteristics with respect to changes in the film thickness that occur in the distribution during production. It was the result.

〔Effect of the invention〕

As explained above, the present invention uses a film layer mainly composed of St as a high refractive index film layer in a conventional polarizing beam splitter, so that manufacturing is easy, that is, high polarization characteristics can be reproducibly achieved with a small number of laminated layers. It can be easily obtained, and has effects such as a small amount of change in phase characteristics and spectral characteristics with respect to variations in the angle of incidence of a light beam on a film layer, the refractive index of the film layer, and the film thickness.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the polarizing beam splitter of the present invention, FIGS. 2 to 5 are diagrams showing the characteristics of the polarizing beam splitter shown in FIG. 1, and FIG. 6 is a diagram showing the characteristics of the polarizing beam splitter of the present invention. Schematic diagrams showing other embodiments; Figures 7 to 11 are diagrams showing the characteristics of the polarizing beam splitter shown in Figure 6;
FIG. 2 is a schematic diagram showing a conventional polarizing beam splitter. la, lb・・・・・・・・・・・・・・・・・・
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・Prism 2・・・・・・・・・・・・・・・・・・
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...... High refractive index film layer 3 ...
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...Four circles...Curved low refractive index film layer 4...
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・・・・・・・・・・・・・・・・・・・・・・・・
...Adhesive Fig. 1 F Fig. 2 1E4 (? LtPLn Incident angle (degrees) Fig. 4 Fig. 5 Change factor (%) Fig. 6 Fig. 9 Fig. 10 Entry size inside & 儂) 輌11 prisoners

Claims (1)

[Claims] (1) Between two transparent substrates with refractive index N_G, N
A low refractive index film layer having a refractive index N_L of _G or less and a high refractive index film layer containing at least one film layer mainly composed of Si and having a refractive index N_H higher than N_G are alternately arranged, and the lowermost and uppermost layers are alternately arranged. A polarizing beam splitter comprising a multilayer film stacked so that the upper layer is a high refractive index film layer.