JP2005276306A - Polarizing beam splitter, its manufacturing method, and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing beam splitter having a film structure capable of reducing a ripple in a transmission bandpass of a P polarization. <P>SOLUTION: This polarizing beam splitter has a multi-layer film (polarizing beam splitter film 4) formed by being alternatively laminated with high refractive films 2 and low refractive films 3 on an optical substrate 1, and it reflects a light of a 1st light source 6 incident to a surface having the multi-layer film from an air face and transmits a light of a 2nd light source 7 incident to an optical substrate surface opposite to the above surface having the multi-layer film. Further, the number of laminated layers N of the polarizing beam splitter film 4 is in the range of 16≤N≤40, and a distribution of a ratio of optical film thickness D/M (M: average thickness of optical films of all laminated layer films, D: thickness of optical film of each layer) is in the range of 0.5≤D/M≤2.5, and an average surface roughness is settled to ≤0.50nm, which is obtained by measuring such measuring points that a distance between the measuring points is ≤100nm with respect to a surface of the side arranging the polarizing beam splitter film 4 of the optical substrate 1 thereon. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polarizing beam splitter made of a dielectric multilayer film, a method for manufacturing the same, and an optical pickup device.

  There are two general types of polarizing beam splitters: a prism type in which a dielectric multilayer film is sandwiched between inclined surfaces of two right-angle prisms, and a plate type in which a dielectric multilayer film is provided on a flat optical substrate. Known. These polarizing beam splitters can efficiently separate incident light into P-polarized light and S-polarized light by using interference of the dielectric multilayer film. Further, the wavelength band to be used can be changed by combining a high refractive index film and a low refractive index film constituting the dielectric multilayer film of the polarization beam splitter.

  Since the polarization beam splitter can be used as an edge filter or a bandpass filter, it is used for optical devices such as optical disk pickups, projection display devices, communication devices using wavelength multiplexing technology, and the like. For example, as an application of a plate-type polarizing beam splitter, there is an optical pickup device disclosed in Patent Document 1. This is because the signal light reflected from the optical disk is incident on the polarization beam splitter at a predetermined incident angle, and the recorded signal is compared by comparing the light transmitted through the polarization beam splitter with the reflected light amount. It is to play.

  In such an optical pickup device, a wavelength in the vicinity of 780 nm for CD and a wavelength in the vicinity of 660 nm for DVD have been used. However, in order to improve the recording density, it is necessary to make the pickup wavelength shorter. In the future, it is expected that the number using a wavelength band near 400 nm, which is shorter than the wavelength of 660 nm used for a DVD pickup light source, will increase. Along with this, the polarizing beam splitter used in the optical pickup needs to have a shorter target wavelength, and preferably has a wider usable wavelength band. Therefore, as the characteristics of the polarizing beam splitter, the smaller the ripple generated in the reflection band and the transmission band, the better, and the wider the transmission band and the reflection band, the more desirable.

In general, the optical thin film constituting the polarizing beam splitter has a wavelength dispersion characteristic in which the rate of change in the refractive index increases as the wavelength becomes shorter, so that the ripple increases as the wavelength becomes shorter. It is known that flat transmission characteristics tend to be difficult to obtain. For this reason, conventionally, as means for reducing the ripple, not only the selection of the material of the optical thin film but also the smoothing of the average surface roughness of the optical substrate on which the thin film is laminated has been considered.
Japanese Patent Laid-Open No. 5-266501

  However, the problem that the reduction in ripple is insufficient only by the above-described smoothing of the surface roughness is required for a severe condition such as an optical pickup device that changes the light intensity of the laser wavelength at the time of temperature change. was there.

  Further, unlike the prism-type polarizing beam splitter, the plate-type polarizing beam splitter does not have a light incident medium to the polarizing beam splitter film as an optical substrate, and the incident medium to the polarizing beam splitter film is air. As described above, when the light incident medium is different, even if a film having the same configuration as that of the conventional prism-type polarization beam splitter film is laminated on the planar optical substrate, the characteristics are not the same as those of the prism-type polarization beam splitter.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a polarizing beam splitter having a film structure that can reduce ripple in the transmission band of P-polarized light.

  The polarizing beam splitter according to the present invention has a multilayer film formed by alternately laminating at least two types of optical thin films having different refractive indexes on an optical substrate, and enters the surface having the multilayer film from the air surface. A polarizing beam splitter that reflects light of a first wavelength and transmits light of a second wavelength that is incident on an optical substrate surface opposite to the surface having the multilayer film, wherein the number N of the multilayer films is The distribution of the optical film thickness ratio D / M is 16 ≦ N ≦ 40, where M is the average optical film thickness of all the laminated films constituting the multilayer film, and D is the optical film thickness of each layer. The average surface roughness obtained by measuring the measurement points within the range of 0.5 ≦ D / M ≦ 2.5 and having a distance between measurement points of 100 nm or less with respect to the surface on the side where the optical thin film is provided. It is 0.50 nm or less. With this configuration, it is possible to reduce ripple in the transmission band of P-polarized light.

  The polarization beam splitter described above includes an angle formed between the reflected light of the first wavelength light and the normal of the surface by the multilayer film, and the transmitted light of the second wavelength and the surface method by the multilayer film. It is desirable that the angle formed by the line is 40 degrees or more and 60 degrees or less.

  Moreover, you may make it have the antireflection film from which the reflectance of the light of the said 1st wavelength and the light of the said 2nd light becomes substantially zero on the back surface of the said optical board | substrate. Thereby, it is possible to prevent an increase in insertion loss that occurs when incident light is reflected by the back surface of the optical substrate 1.

  On the other hand, an optical pickup device according to the present invention includes at least two light sources having different wavelengths and polarized light that reflects light from at least one of the light sources and transmits light from at least one other light source. An optical pickup device having a beam splitter, wherein the polarization beam splitter includes an angle formed by the reflected light and a normal line of a filter surface of the polarization beam splitter, and a filter surface of the transmission light and the polarization beam splitter. The polarizing surfaces of the polarizing beam splitter are alternately arranged with at least two types of optical thin films having different refractive indexes on a planar optical substrate. A multilayer film formed by laminating, and the number N of the multilayer films is in a range of 16 ≦ N ≦ 40, and all of the multilayer films are formed. When the average optical film thickness of the layer film is M and the optical film thickness of each layer is D, the distribution of the optical film thickness ratio D / M is within the range of 0.5 ≦ D / M ≦ 2.5, The average surface roughness obtained by measuring a measurement point having a distance between measurement points of 100 nm or less with respect to the surface on the side where the optical thin film is provided is 0.50 nm or less. Thereby, in an optical pickup device having two or more light sources having different wavelengths for performing optical pickup for two or more recording methods, the usable wavelength band can be expanded.

  Furthermore, the polarizing beam splitter manufacturing method according to the present invention has an average surface roughness of 0.50 nm obtained by measuring a measurement point having a distance between measurement points of 100 nm or less with respect to at least one surface of a planar optical substrate. The first step of smoothing to the following, and the total lamination of the optical thin film when alternately laminating at least two types of optical thin films having different refractive indexes on the surface of the optical substrate smoothed in the first step The number N falls within the range of 16 ≦ N ≦ 40. When the average optical film thickness of all the laminated films is M and the optical film thickness of each layer is D, the distribution of the optical film thickness ratio D / M is 0.5 ≦. And a second step of laminating the multilayer film so as to be within the range of D / M ≦ 2.5. By this method, it is possible to manufacture a polarization beam splitter having a film structure in which the ripple in the transmission band of P-polarized light is reduced.

  According to the present invention, it is possible to provide a polarizing beam splitter having a film structure that can reduce ripple in the transmission band of P-polarized light.

Embodiment 1 of the Invention
FIG. 1 is a schematic diagram showing a cross section of a polarizing beam splitter 100 according to the present embodiment. The polarizing beam splitter film 4 is obtained by alternately laminating a high refractive index film 2 and a low refractive index film 3 on a parallel plane optical substrate 1, and by laminating N thin films, desired optical characteristics are obtained. The film thickness of each layer is adjusted so as to satisfy the conditions. Note that FIG. 1 is a schematic diagram for ease of understanding of the present invention, and therefore the size and the like are different from actual ones.

  As shown in FIG. 1, it is preferable that the refractive index of the planar optical substrate 1 and the refractive index of the film disposed immediately above the refractive index difference be large. In FIG. 1, the high refractive index film 2 is formed immediately above the planar optical substrate 1 and the final layer is the low refractive index film 3. However, the structure directly below the planar optical substrate 1 is low. The refractive index film 3 may be used, and the final layer may have a high refractive index film 2.

  The antireflection film 5 is formed by alternately laminating a plurality of high refractive index films 2 and low refractive index films 3 on the back surface of the optical substrate 1 on which the polarizing beam splitter film 4 is formed. The antireflection film 5 can prevent an increase in insertion loss that occurs when light transmitted through the polarizing beam splitter film 4 is reflected by the back surface of the optical substrate 1. When the insertion loss caused by the back surface reflection does not become a problem, the antireflection film 5 may not be provided.

  Next, the manufacturing method of the polarization beam splitter according to the present embodiment and the material of each part will be described.

As the optical substrate 1, amorphous glass, crystallized glass, or another optical substrate can be used. Specifically, oxide single crystals such as LiNbO ₃ , LiTaO ₃ , TiO ₂ , SrTiO ₃ , Al ₂ O ₃ and MgO, polycrystalline substrates, fluoride single crystal substrates such as CaF ₂ , MgF ₂ BaF ₂ and LiF, Polycrystalline substrates, chlorides such as NaCl, KBr, KCl, bromide single crystals, polycrystalline substrates, and the like can be applied. The optical substrate 1 preferably has a high transmittance. For example, the optical substrate 1 desirably has a transmittance of 99.8% or more.

  Various methods can be used as a method for producing the optical substrate 1. In consideration of productivity and the like, for example, there is a method by polishing. Examples of the polishing method include mechanical polishing. In this method, the surface of the optical substrate 1 can be smoothed by performing lapping, intermediate polishing, and final polishing in this order.

  First, in the lapping process, the optical substrate 1 is pressed against a glass plate with a predetermined shape and both surfaces roughened against a metal surface plate with a weight of 49 to 245 N, and a diamond slurry (diamond abrasive particle size: 1 to 1) as a polishing liquid is pressed. 10 μm), and polishing is performed while rotating the surface plate at 10 to 100 rpm. The lapping is stopped when a rough cut mark is made on the entire surface of the substrate and a diamond slurry mark has entered.

  Next, the intermediate polish presses the lapped glass substrate against a ceramic surface plate with a load of 49 to 245 N, and drops a cerium oxide solution (particle size: 0.1 μm to 1.0 μm) as a polishing solution (drop amount: 10). Polishing is performed by rotating the surface plate at a rotation speed of 10 to 100 rpm. The polishing time is 10 to 30 minutes.

  Finally, final polishing is performed on the surface on which the dielectric multilayer film is formed. An intermediate polished glass substrate is pressed with a weight of 49 to 245 N on a surface plate with a urethane foam pad on a flat plate, and a polishing liquid containing colloidal silica (particle size: 0.06 to 1.0 μm) is dropped ( The final polishing is performed by rotating the padded platen at 10 to 100 rpm while the dropping amount is about 10 to 300 ml / h. The final polishing is performed for about 3 to 10 minutes.

  In addition, you may make it further grind | polish using the polishing liquid with a particle size smaller than the polishing liquid used by the last polish after the last polish.

Examples of the material for the high refractive index film 2 include Ta _x O _y , TiO _x , ZnS, ZnSe, GaP, InP, Si, Ge, SiGe _x , SiN _x , SiC _x , ZrO _x , NbO _x , YO _x , and CeO _x. , HfO _x , ZrO _x , and the like, and mixed materials thereof are selected. Further, _SiO x as the low refractive index film 3 _{materials, MgF 2, AlO x, SiO} x C y, SiO x N y, MgO x , etc., and at least one of these admixtures selected. Note that the same kind of film is preferably used for each film, but it is possible to replace a part of the film with a film made of another material as long as the material has an approximate refractive index.

  The dielectric multilayer filter 4 can be manufactured by, for example, a vacuum film forming method. As the vacuum film forming method, various film forming methods such as a vacuum deposition method, a sputtering method, a chemical vapor deposition method, and a laser brazing method can be used. When using a vacuum deposition method, ion deposition is performed by ionizing a part of the deposition air flow and applying a bias to the substrate side in order to improve the film quality, cluster ion beam method, or ion irradiation to the substrate using an ion gun. It is effective to use an ion-assisted deposition method. As the sputtering method, a DC reactive sputtering method, an RF sputtering method, an ion beam sputtering method, or the like can be used. Further, as the chemical vapor phase method, a plasma polymerization method, a light-assisted vapor phase method, a thermal decomposition method, a metal organic chemical vapor phase method, or the like can be used. In addition, the film thickness of each thin film can be made into a desired film thickness by changing the vapor deposition time etc. at the time of film formation.

  The surface roughness Ra of the optical substrate 1 in the present embodiment is 0.5 nm or less, preferably 0.45 nm or less, and the lower limit is not particularly limited, but considering the difficulty in manufacturing. It is 0.20 nm or more.

  In addition, said surface roughness uses an atomic force microscope (AFM), makes a measurement area | region into a square area of 10 micrometers x 10 micrometers, this area is a 256 point x 256 point scanning line, and a tip radius is 5-10 nm. An average of the maximum and minimum values of the profile curve of the surface shape obtained by each scanning line using a Si needle is measured as a center line L, and the area surrounded by the center line L and the profile curve is the scanning line length. The value divided by the thickness is the average surface roughness Ra. According to the measurement method according to this example, the distance between adjacent measurement points is about 39 nm. The resonance frequency in the tapping mode is 200 to 400 Hz, and the scanning frequency is 0.3 Hz.

  Next, the structure of the polarizing beam splitter film 4 according to the present embodiment will be described in detail below. As described above, ripples may not be sufficiently reduced by simply smoothing the surface of the planar optical substrate on the side where the polarizing beam splitter film is provided with an average surface roughness Ra of 0.50 nm or less. It became clear. The inventor has found that the occurrence of this ripple is caused by the film structure of the polarizing beam splitter film. Furthermore, as a result of examining the number of layers of the film and the film thickness of each layer, the inventor has determined that the number of stacked films is N, the average optical film thickness of all the stacked films at the design wavelength λ is M, and the optical film thickness of each layer is D. In this case, the number N of stacked layers is set to 16 ≦ N ≦ 40, and the ratio of each film thickness represented by D / M is set to 0.5 ≦ D / M ≦ 2.5, thereby reducing the generation of ripples. I found out that I can. Here, the design wavelength λ means the wavelength at the center of the reflection band of S-polarized light when the spectral characteristic is measured at an incident angle of 0 degree.

  According to the study, when the number N of layers is smaller than 16, the bandwidth of the P-polarized transmission band and the S-polarized reflection band tends to be narrowed. Therefore, an attempt is made to obtain a sufficient bandwidth for the characteristics of the polarizing beam splitter. In this case, ripples are generated in the transmission band of P-polarized light and the reflection band of S-polarized light. Accordingly, the number N of stacked layers is preferably 16 or more. In general, it is known that higher-order edge filters tend to generate ripples in the transmission band as the order increases. When the number N of layers is larger than 40, a large number of oscillating ripples are generated at narrow wavelength intervals in the transmission band, and therefore the number N of layers is preferably 40 or less. Therefore, the number N of stacked films should be 16 ≦ N ≦ 40, and preferably 18 ≦ N ≦ 25.

  Furthermore, if the polarizing beam splitter film includes a layer having an optical film thickness ratio D / M smaller than 0.5, the inclination between the transmission band and the reflection band is small in the transmission characteristics of P-polarized light and the reflection characteristics of S-polarized light. It was clarified that ripples occurred due to this. In addition, when a layer having a D / M in a range smaller than 0.5 is included, if an attempt is made to obtain sufficient characteristics as a polarizing beam splitter, it is necessary to increase the number of stacked layers N, and the manufacturing cost increases. It is preferable that M ≧ 0.5.

  On the other hand, when the polarizing beam splitter film includes a layer having an optical film thickness ratio D / M larger than 2.5, a large number of vibrations are formed in a narrow wavelength interval in the transmission band as in the case where the number N of stacked layers is larger than 40. Therefore, it is preferable to satisfy D / M ≦ 2.5. From the above, the ratio of the optical film thickness of each layer in the polarization beam splitter film 4 according to the present embodiment is preferably 0.5 ≦ D / M ≦ 2.5, and preferably 0.6 ≦ D. /M≦2.0.

  Next, the effect of ripple reduction by the polarization beam splitter 100 according to the present embodiment will be described. Although specific examples will be described below, the present invention is not limited to these specific examples. Note that λ is a design wavelength, H is a high refractive index film, and L is a low refractive index film. The refractive index of the material used for the polarizing beam splitter described in Example 1, Comparative Example 1 and Comparative Example 2 includes a light refractive index film H: 2.30, a low refractive index film L: 1.467, air: 1, A planar optical substrate: 1.51 was used. In addition, the layer numbers used in Tables 1 to 3 are given in ascending order toward the optical substrate, with the interface side with air set to 1.

(Example 1)
The refractive index is different on a planar optical substrate having an average surface roughness Ra of 0.40 nm obtained by measuring a measurement point having a distance between measurement points of 100 nm or less on the surface on which the polarizing beam splitter film is provided. Two types of optical thin films (high refractive index film H and low refractive index film L) are alternately laminated, P-polarized light is transmitted in a band near 785 nm, S-polarized light is reflected in a band near 660 nm, and a polarized beam A polarizing beam splitter film was designed in which the angle formed between the normal of the splitter film and incident light was 45 degrees. The optical characteristics were such that the reflectance of S-polarized light was 97% or more in the wavelength range of 640 to 680 nm, the transmittance of P-polarized light was 97% or more in the wavelength range of 765 to 805 nm, and the design wavelength λ was 675 nm.

  An example of the result is a polarizing beam splitter film in which the number of layers is 22 and the thickness of each layer is defined in Table 1. The value of the film thickness in Table 1 is a value normalized with λ / 4 set to 1. As shown in Table 1, when the average optical film thickness of all the laminated films is M and the optical film thickness of each layer is D, the ratio of the optical film thickness expressed by D / M is 0.5 ≦ D / Distribution is in a range of M ≦ 2.5. A graph of the reflectance Rs of S-polarized light and the transmittance Tp of P-polarized light at this time is shown in FIG. In the graph, Rs and Tp are both expressed as percentages, the reflectance Rs of S-polarized light is indicated by a thick line, and the transmittance Tp of P-polarized light is indicated by a thin line.

(Comparative Example 1)
An example of a polarizing beam splitter film including a layer in which the number N of layers is 14 and the ratio D / M of the optical film thickness of each layer is smaller than 0.5 is shown. The incident angle of light was 45 degrees, and the design wavelength λ was 685 nm. The film configuration is shown in Table 2. As in Table 1, the value of the film thickness is a value normalized with λ / 4 set to 1. As shown in Table 2, a layer having a D / M smaller than 0.5 exists in the layer number 11. A graph of the reflectance Rs of S-polarized light and the transmittance Tp of P-polarized light at this time is shown in FIG. In the graph, Rs and Tp are both expressed as percentages, the reflectance Rs of S-polarized light is indicated by a thick line, and the transmittance Tp of P-polarized light is indicated by a thin line.

  2 and FIG. 3, when the transmission characteristics of P-polarized light of Example 1 and Comparative Example 1 are compared, the number N of thin films is 16 ≦ N ≦ 40, and the optical film thickness expressed by D / M of each layer In the first example in which the ratio is 0.5 ≦ D / M ≦ 2.5, the ripple in the transmission band of P-polarized light is clearly reduced, and good optical characteristics as a polarizing beam splitter can be obtained. I understand that

(Comparative Example 2)
An example of a polarizing beam splitter film including layers in which the number N of stacked layers is 50 and the ratio D / M of the optical film thickness of each layer is larger than 2.5 is shown. The film configuration is shown in Table 3. As in Table 1, the value of the film thickness is a value normalized with λ / 4 set to 1. As shown in Table 3, a layer having a D / M greater than 2.5 exists in layer number 2. The incident angle of light was 45 degrees and the design wavelength was 680 nm. A graph of the reflectance Rs of S-polarized light and the transmittance Tp of P-polarized light at this time is shown in FIG. In the graph, Rs and Tp are both expressed as percentages, the reflectance Rs of S-polarized light is indicated by a thick line, and the transmittance Tp of P-polarized light is indicated by a thin line.

  2 and FIG. 4, when the S-polarized light reflection characteristics and the P-polarized light transmission characteristics of Example 1 and Comparative Example 2 are compared, the ratio of the optical film thickness expressed by D / M of each layer is 0.5 ≦ D. In Example 1 where /M≦2.5, the ripple in the transmission band of P-polarized light is clearly reduced, and it can be seen that good optical characteristics are obtained as a polarizing beam splitter.

  As described above, the reduction of ripple was insufficient only by setting the average surface roughness Ra of the surface of the flat optical substrate on the side where the polarizing beam splitter film is provided to 0.50 nm or less. By suppressing the generation of ripple in the transmission band by adopting a configuration in which the ratio of the number of polarizing beam splitter films to be formed and the ratio of each film thickness has a distribution in the range of 0.5 ≦ D / M ≦ 2.5. Can do.

Embodiment 2 of the Invention
Next, FIG. 5 shows an example of an optical pickup device 200 using the polarizing beam splitter 100 according to the first embodiment of the invention. The optical pickup device 200 has two light sources, a first light source 6 and a second light source 7. For example, the first light source 6 is a light source that emits laser light having a wavelength of about 660 nm for DVD, and the second light source 7 is a light source that emits laser light having a wavelength of about 780 nm for CD. As described above, the optical pickup device 200 is an optical pickup device that can be used for two recording methods such as CD and DVD.

  In FIG. 5, light of a predetermined wavelength generated from the first light source 6 is reflected by the plate-type polarization beam splitter 100 described in the first embodiment of the present invention, and is generated from the second light source 7. Light having a predetermined wavelength different from that of the one light source 6 passes through the same plate-type polarization beam splitter 100. The reflected light from the first light source 6 and the transmitted light from the second light source 7 are converted into parallel light fluxes by the coupling lens 9 and enter the prism-shaped polarizing beam splitter 10. The light reflected by the prismatic polarization beam splitter 10 is collected by the objective lens 11 and forms a spot on the recording surface of the optical disk 12. Then, the reflected light reflected by the optical disk 12 becomes parallel light by the objective lens 11, passes through the prism-like polarization beam splitter 10, is condensed by the condenser lens 13, and reaches the photodetector 14.

  In the polarization beam splitter 100, in the optical pickup device 200, the reflected light of the first light source 6 and the transmitted light of the second light source 7 are both 40 degrees or more and 60 degrees with respect to the normal of the surface of the polarization beam splitter film 4. They are arranged in the following range. FIG. 6 is an enlarged view for explaining the arrangement of the polarization beam splitter 100. As shown in the figure, the angle θ formed by the light from the first light source 6 reflected by the polarizing beam splitter 100 and the normal of the surface of the polarizing beam splitter film 4 (broken arrow in FIG. 6) is the predetermined angle. The polarization beam splitter 100 is disposed so as to be incident at the angle. At the same time, an angle Φ formed by the transmitted light of the second light source 6 that is transmitted through the polarizing beam splitter 100 and is emitted from the filter surface, and the normal line (dashed line arrow in FIG. 6) of the surface of the polarizing beam splitter film 4. The polarizing beam splitter 100 is arranged so that is at the predetermined angle.

  In the above example, the case where there are two light sources of the optical pickup device 200 is shown. However, when there are three or more light sources, the same configuration may be made using two or more polarization beam splitters.

  Thus, by using the polarization beam splitter 100 having a film structure that reduces the ripple in the transmission band of P-polarized light, an optical pickup having two or more light sources having different wavelengths for performing optical pickup for two or more recording systems. In the apparatus, the usable wavelength band can be expanded.

Other embodiments.
The effect of the present invention occurs with respect to a polarizing beam splitter in which the interface on one side of the polarizing beam splitter film laminated on the optical substrate is an air surface. Therefore, in the first and second embodiments of the invention described above, the case where the polarizing beam splitter film is formed on the planar optical substrate has been described. However, the shape of the optical substrate on which the polarizing beam splitter film is laminated is limited to a plane. However, the present invention can be applied to the case of generating on an optical substrate having any other shape.

It is sectional drawing which shows the polarizing beam splitter in Embodiment 1 of invention. 6 is a graph showing S-polarized light reflection characteristics and P-polarized light transmission characteristics of the polarization beam splitter in Example 1. FIG. 5 is a graph showing S-polarized light reflection characteristics and P-polarized light transmission characteristics of the polarizing beam splitter in Comparative Example 1. FIG. 10 is a graph showing S-polarized light reflection characteristics and P-polarized light transmission characteristics of the polarizing beam splitter in Comparative Example 2. It is a figure which shows the optical pick-up apparatus using the polarization beam splitter concerning this invention. It is a conceptual diagram which shows the relationship between the reflected light and transmitted light from a light source, and a polarizing beam splitter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Polarizing beam splitter 200 Optical pick-up apparatus 1 Optical substrate 2 High refractive index film 3 Low refractive index film 4 Polarizing beam splitter film 5 Antireflection film 6 First light source 7 Second light source

Claims (5)

It has a multilayer film formed by alternately laminating at least two types of optical thin films having different refractive indexes on an optical substrate, and reflects light of the first wavelength incident from the air surface onto the surface having the multilayer film. A polarizing beam splitter that transmits light of a second wavelength incident on an optical substrate surface opposite to the surface having the multilayer film,
The multilayer number N of the multilayer film is in the range of 16 ≦ N ≦ 40,
The distribution of the optical film thickness ratio D / M is 0.5 ≦ D / M ≦ 2.5, where M is the average optical film thickness of all the laminated films constituting the multilayer film and D is the optical film thickness of each layer. Within the range of
A polarizing beam splitter having an average surface roughness of 0.50 nm or less obtained by measuring a measurement point having a distance between measurement points of 100 nm or less with respect to the surface of the optical substrate on which the optical thin film is provided.   The angle between the reflected light of the first wavelength light and the normal of the surface by the multilayer film, and the angle of the transmitted light of the second wavelength and the normal of the surface by the multilayer film are both The polarizing beam splitter according to claim 1, wherein the polarizing beam splitter is used in a state of 40 degrees or more and 60 degrees or less.   The polarizing beam splitter according to claim 1, further comprising an antireflection film that prevents reflection of light having the first wavelength and light having the second light wavelength on a back surface of the optical substrate. An optical pickup device comprising: at least two light sources having different wavelengths; and a polarizing beam splitter that reflects light from at least one of the light sources and transmits light from at least one other light source. ,
In the polarizing beam splitter, both the angle formed by the reflected light and the normal line of the filter surface of the polarizing beam splitter and the angle formed by the transmitted light and the normal line of the filter surface of the polarizing beam splitter are both 40 degrees or more and 60 degrees. Arranged to be less than
The filter surface of the polarizing beam splitter is a multilayer film formed by alternately laminating at least two types of optical thin films having different refractive indexes on a planar optical substrate,
The multilayer number N of the multilayer film is in the range of 16 ≦ N ≦ 40,
The distribution of the optical film thickness ratio D / M is 0.5 ≦ D / M ≦ 2.5, where M is the average optical film thickness of all the laminated films constituting the multilayer film and D is the optical film thickness of each layer. Within the range of
An optical pickup device having an average surface roughness of 0.50 nm or less obtained by measuring a measurement point having a distance between measurement points of 100 nm or less with respect to the surface of the optical substrate on which the optical thin film is provided. A first step of smoothing until an average surface roughness of 0.50 nm or less obtained by measuring a measurement point having a distance between measurement points of 100 nm or less with respect to at least one surface of a planar optical substrate;
When alternately laminating at least two types of optical thin films having different refractive indexes on the surface of the optical substrate smoothed in the first step, the total number N of the optical thin films is in the range of 16 ≦ N ≦ 40. When the average optical film thickness of all the laminated films is M and the optical film thickness of each layer is D, the distribution of the optical film thickness ratio D / M is in the range of 0.5 ≦ D / M ≦ 2.5. A second step of laminating a multilayer film,
A manufacturing method of a polarization beam splitter including:

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