JP2009031406A - Nonpolarization beam splitter and optical measuring instrument using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide a nonpolarization beam splitter which has nonpolarization in a wide wavelength band. <P>SOLUTION: The nonpolarization beam splitter comprises a multilayer film which is inserted between two sheets of transparent base materials, the multilayer film being formed by laminating a layer (a layer of high refractive index), which has a refractive index which is higher than the refractive index Ns of the transparent base materials, and a layer (a layer of low refractive index) which has a refractive index which is lower than the refractive index Ns of the transparent base materials. In addition, an expression θ<SB>0</SB>°-3.5°≤sin<SP>-1</SP>(Nl/Ns)≤θ<SB>0</SB>°+ 3.5° is satisfied, wherein Ns represents the refractive index of the transparent base materials, and Nl represents the refractive index of a layer having the lowest refractive index in the multilayer film, and θ<SB>0</SB>° represents a light-beam incident angle to the multilayer film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical element that separates one light beam into two light beams, each of which relates to a non-polarizing beam splitter having non-polarization properties in a wide wavelength region, and an optical measuring instrument using the same.

  The non-polarizing beam splitter is used in an optical measuring instrument such as a laser planar, and is an optical element that separates one light beam into two light beams. As shown in FIG. 2, the laser planar (horizontal plane setting machine) includes a laser light source 2, a beam splitter 4 that separates the laser light L emitted from the laser light source 2 into reflected light L1 and transmitted light L2, and a beam splitter 4 And a disk 3 that is rotatably supported. When the disk 3 rotates horizontally, the reflected light L1 from the beam splitter 4 is irradiated in the horizontal direction to form a horizontal plane, and the transmitted light L2 is applied to the ceiling surface to mark a vertical point. Since the laser light source 2 is electrically wired, the laser light source 2 does not rotate with the disk 3. Since the polarized light component of the laser light L emitted from the laser light source 2 is normally biased, the brightness of the reflected light L1 from the beam splitter 4 depends on the rotation of the disk 3 if the polarization characteristics of the beam splitter 4 are biased. It will change. For this reason, it is necessary to use a non-polarized beam splitter for the beam splitter 4.

  In recent years, semiconductor lasers have been used as laser light sources, and semiconductor lasers in the visible range are often used particularly for laser planars. Visible semiconductor lasers include those with a red wavelength of 630 to 690 nm, a green wavelength of 532 nm, and a blue wavelength of 405 to 410 nm. It is desirable that various lasers can share a non-polarizing beam splitter. That is, a non-polarizing beam splitter that can be shared at a wavelength of 400 to 700 nm is desired.

JP-A-9-184908 (Patent Document 1) discloses a flat plate type non-polarizing beam splitter. The non-polarizing beam splitter described in Japanese Patent Application Laid-Open No. 9-184908 (Patent Document 1) is formed by laminating and integrating a plurality of dielectric layers having different refractive indexes from a first layer to a twentieth layer on a transparent optical glass substrate. As a first layer, a mixture of ZrO ₂ and TiO ₂ (refractive index 2.07) is formed to a thickness of λ / 2, and MgF ₂ (refractive index 1.37) is λ // as the _second , eighth and tenth layers. 4 and a third, fifth, seventh, ninth, eleventh, thirteenth, fifteenth and nineteenth layer of Al ₂ O ₃ (refractive index 1.61) with a thickness of λ / 4. as 4 and 6 layers, a mixture of the ZrO ₂ and TiO ₂ was formed to a thickness of lambda / 4, as a 12, 14, 16 and 18 layers, the thickness of the TiO ₂ (refractive index 2.27) a lambda / 4 The MgF ₂ is formed to a thickness of λ / 2.4 to λ / 1.9 as the twentieth layer that is the outermost layer. However, in the case of a flat plate type non-polarizing beam splitter, the transmission optical path shifts by the thickness of the substrate, and the vertical point cannot be accurately marked on the ceiling surface.

Japanese Patent Laid-Open No. 1-92702 (Patent Document 2) discloses a non-polarizing beam splitter that does not cause a deviation of a transmission optical path, a dielectric layer such as TiO ₂ and a metal layer such as Ag on a joint surface of a right isosceles triangular prism. A non-polarizing beam splitter is disclosed. However, the non-polarizing beam splitter described in Japanese Patent Laid-Open No. 1-92702 (Patent Document 2) has a problem of a decrease in light amount due to absorption of the metal layer.

Japanese Patent Application Laid-Open No. 64-35402 (Patent Document 3) discloses a multi-layer composed of three or more kinds of dielectric materials on the joint surface of a right-angled isosceles triangular prism as another non-polarizing beam splitter that does not cause a deviation of the transmitted light path. A non-polarizing beam splitter with a film is disclosed. However, the non-polarizing beam splitter described in JP-A-64-35402 (Patent Document 3) is manufactured by forming a multilayer film of nine or more layers using three or more kinds of dielectric materials. There is a problem that it is expensive. In addition, when trying to widen the usable wavelength range, more layers are required.
JP-A-9-184908 JP-A-1-92702 Japanese Unexamined Patent Publication No. 64-35402

  Accordingly, an object of the present invention is to provide a non-polarizing beam splitter having non-polarization properties in a wide wavelength range at a low cost.

  As a result of diligent research in view of the above problems, the present inventors have developed a beam splitter having a multilayer film in which two or more transparent films having different refractive indexes are laminated between two transparent substrates. When the refractive index and the refractive index of the film having the lowest refractive index in the multilayer film are in the range defined by the incident angle of light to the multilayer film, it was discovered that the film has non-polarization properties in a wide wavelength range. I came up with the invention.

That is, the non-polarizing beam splitter of the present invention includes a layer (high refractive index layer) having a refractive index higher than the refractive index Ns of the transparent substrate and the refractive index Ns of the transparent substrate between two transparent substrates. A non-polarizing beam splitter in which a multilayer film formed by laminating a layer having a lower refractive index (a layer having a low refractive index) is inserted, the refractive index Ns of the transparent substrate being the highest among the multilayer films A refractive index Nl of a layer having a low refractive index is expressed by the following formula with respect to a light incident angle θ ₀ ° on the multilayer film:
θ ₀ ° −3.5 ° ≦ sin ⁻¹ (Nl / Ns) ≦ θ ₀ ° + 3.5 °
It is a value satisfying.

The material forming the high refractive index layer is Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , HfO ₂ , CeO ₂ , SnO ₂ , In ₂ O ₃ , ZnO, ZnS, La ₂ O ₃ and The group consisting of NaF, CaF ₂ , LiF, MgF ₂ , SiO ₂ , YF ₃ and Al ₂ O ₃ , which is at least one selected from the group consisting of Sb ₂ O ₃ , and the material forming the low refractive index layer It is preferable that the multilayer film is composed of 5 to 21 layers.

  The multilayer film preferably has a five-layer structure in which the high refractive index layers and the low refractive index layers are alternately stacked.

  It is preferable that at least one of the low refractive index layers has a nanoporous structure.

  The non-polarizing beam splitter of the present invention preferably has a non-polarizing characteristic in which the difference in transmittance between S-polarized light and P-polarized light is 10% or less in the wavelength range of 300 to 700 nm.

  The optical measuring instrument of the present invention uses the non-polarizing beam splitter.

  The non-polarizing beam splitter according to the present invention can divide the reflected light and transmitted light at an equal ratio in a wide wavelength range regardless of the ratio of the S-polarized component and the P-polarized component. It is not necessary to consider the polarization ratio of incident light. Therefore, the degree of freedom in optical design of the optical measuring instrument is widened, which is very useful.

[1] non-polarizing beam splitter
(1) Configuration A non-polarizing beam splitter has a configuration in which the slopes of two right-angled isosceles triangular prisms are bonded together (Fig. 1 (a)), or a configuration in which two trapezoidal prisms are bonded (Fig. 1 (b) And a layer (high refractive index layer) having a refractive index higher than the refractive index Ns of the transparent substrate and a refractive index Ns of the transparent substrate on the bonding surface 5 between the two transparent prism substrates. A multilayer film formed by laminating a layer having a low refractive index (a layer having a low refractive index) is inserted. The light Lin incident on the beam splitter is divided into transmitted light Lt and reflected light Lr by a multilayer film provided on the bonding surface. The refractive index Ns of the transparent substrate and the refractive index Nl of the layer having the lowest refractive index among the multilayer films are expressed by the following formula (1) with respect to a light incident angle θ ₀ ° on the multilayer film:
θ ₀ ° −3.5 ° ≦ sin ⁻¹ (Nl / Ns) ≦ θ ₀ ° + 3.5 ° (1)
It is a value that satisfies More preferably, the following formula:
θ ₀ ° −1.7 ° ≦ sin ⁻¹ (Nl / Ns) ≦ θ ₀ ° + 1.7 °
It is a value that satisfies The refractive index Nh of the layer having the highest refractive index in the multilayer film is
It is preferable to satisfy the relationship of Nh> Ns.

  The multilayer film is preferably composed of 5 layers or more, more preferably 5 layers to 21 layers, and further preferably 5 layers to 9 layers.

Examples of the high refractive index material constituting the layer having a refractive index higher than the refractive index Ns of the transparent substrate (high refractive index layer) include Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , and HfO _{2. , CeO 2, SnO 2, In} 2 O 3, ZnO, ZnS, and La ₂ O ₃ and Sb ₂ O ₃ or the like can be used. Particularly preferred are Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , and HfO ₂ . Examples of materials for forming a layer having a refractive index lower than the refractive index Ns of the transparent substrate (low refractive index layer) include NaF, CaF ₂ , LiF, MgF ₂ , SiO ₂ , YF _3, and Al ₂ O _3. Can be used. Particularly preferred are MgF ₂ , SiO ₂ , and Al ₂ O ₃ .

  Each layer can be formed by an existing method. For example, vacuum deposition method, ion-assisted deposition method, ion plating method, sputtering method, chemical vapor deposition method (CVD) and other vapor phase deposition methods (dry plating method), wet plating method, dip coating method, ultrasonic mist coating Method, spin coating method, spray coating method and inkjet coating method. For the vapor deposition method, for example, the methods described in JP-A-2001-59172 and JP-A-2001-81548 can be used, and the ultrasonic mist coating method is described in Japanese Patent No. 3159780. The method currently used can be used. In particular, it is preferable to use a vacuum deposition method, an ion assist deposition method, an ion plating method, a sputtering method, a dip coating method, an ultrasonic mist coating method, a spray coating method, and a spin coating method. Although all layers may be formed by the same method, an optimum method may be selected for each layer.

When the refractive index Ns of the substrate is low, a film having a low refractive index that cannot be obtained by a film formed by a method such as vapor deposition is required. For example, when the refractive index Ns of the substrate is 1.73 and the light incident angle to the multilayer film is 45 °, the refractive index Nl of the layer having the lowest refractive index in the multilayer film is 1.15 to 1.30 from the equation (1). There must be. In order to obtain such a low refractive index film, it is preferable to use a nanostructured porous film. In particular, it is preferable to use a nanostructured porous film using a sol-gel method. Specifically, a nanostructured porous MgF ₂ film having a refractive index of 1.15 to 1.25 described in Japanese Patent No. 3509804, a nanostructured porous film having a refractive index of 1.10 described in Japanese Patent Application Laid-Open No. 2006-151800, and the like can be used.

  Such a non-polarizing beam splitter can be commonly used in an optical measuring instrument such as a laser planar using lasers of various wavelengths.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
On the slopes of isosceles right triangular prisms of slope 1mm by OHARA made of optical glass S-LAL18 (Nd = 1.73) , as a high refractive index material ZrO ₂ (Nd = 2.05) and a low refractive index material as the SiO ₂ Using a nanostructured porous film (Nd = 1.21), a film having a five-layer structure shown in Table 1 was formed. A non-polarizing beam splitter was constructed by bringing the slope of another isosceles right triangular prism of the same size into close contact with the slope of this prism. FIG. 3 shows the spectral transmittances (wavelength range 400 to 700 nm) of S-polarized light and P-polarized light measured at a light incident angle of 45 ° to the bonding surface. This beam splitter showed an excellent non-polarization property with a maximum transmittance difference of about 4.5% between S-polarized light and P-polarized light.

Example 2
Nb ₂ O ₅ (Nd = 2.25) as a high refractive index material and MgF ₂ (as a low refractive index material) on the slope of a right isosceles triangular prism with a 1 mm slope by optical glass TAFD40 (Nd = 2.00) manufactured by HOYA Corporation. Nd = 1.39) was used to form a five-layer film shown in Table 2. A non-polarizing beam splitter was constructed by closely contacting the slope of another right-angled isosceles triangular prism of the same size with the slope of this prism. FIG. 4 shows the spectral transmittances of S-polarized light and P-polarized light measured at a light incident angle of 45 ° on the joint surface.

Example 3
ZrO ₂ (Nd = 2.05) as the high refractive index material and MgF ₂ (Nd = 1.39) as the high refractive index material on the slope of the trapezoidal prism with a slope of 1 mm by synthetic quartz glass SUPERASIL (Nd = 1.46) manufactured by Shin-Etsu Quartz Co., Ltd. ) Was used to form a five-layer film shown in Table 3. A non-polarizing beam splitter was constructed by bringing the slope of another uncoated trapezoidal prism into close contact with the slope of this prism. FIG. 5 shows the spectral transmittances of S-polarized light and P-polarized light measured at a light incident angle of 72 ° on the joint surface.

Example 4
ZrO ₂ (Nd = 2.05) as the high refractive index material and MgF ₂ (Nd = 1.39) as the high refractive index material on the slope of the trapezoidal prism with a slope of 1 mm by synthetic quartz glass SUPERASIL (Nd = 1.46) manufactured by Shin-Etsu Quartz Co., Ltd. ) Was used to form a five-layer film shown in Table 4. A non-polarizing beam splitter was constructed by bringing the slope of another uncoated trapezoidal prism into close contact with the slope of this prism. FIG. 6 shows the spectral transmittances of S-polarized light and P-polarized light measured at a light incident angle of 72 ° on the joint surface.

Example 5
HOYA's optical glass TAFD40 (Nd = 2.00) has a right isosceles triangular prism slope with a slope of 1 mm, Nb ₂ O ₅ (Nd = 2.25) as the high refractive index material, and MgF ₂ (Nd = 1.39) was used to form a 9-layer film shown in Table 5. An unpolarized beam splitter was constructed by bringing the slope of another right-angled isosceles triangular prism of the same size into close contact with the slope of this prism. FIG. 7 shows the spectral transmittances of S-polarized light and P-polarized light measured at a light incident angle of 45 ° to the joint surface.

Comparative Example 1
In accordance with the embodiment described in JP-A-64-35402, an optical glass S-LAH55 (Nd = 1.84) manufactured by OHARA INC. Is used as a high refractive index material on the inclined surface of a right-angled isosceles triangular prism. ₂ O ₅ (Nd = 2.25), Al ₂ O ₃ (Nd = 1.64) as the intermediate refractive index material, and MgF ₂ (Nd = 1.39) as the low refractive index material, and a nine-layer film shown in Table 6 Formed. A non-polarizing beam splitter was constructed by bringing the slope of another isosceles right triangular prism of the same size into close contact with the slope of this prism. FIG. 8 shows the spectral transmittances of S-polarized light and P-polarized light measured at a light incident angle of 45 ° to the joint surface.

Comparative Example 2
Following the design example described on the website of Hulinks (http://www.hulinks.co.jp/software/tfcalc/design_04.html), optical glass S-BSL7 (Nd = 1.52) manufactured by OHARA INC. On the slope of a right isosceles triangular prism with a slope of 1 mm, TiO ₂ (Nd = 2.35) as the high refractive index material, Y ₂ O ₃ (Nd = 1.90) as the intermediate refractive index material, and MgF ₂ (as the low refractive index material) Nd = 1.35) was used to form a 97-layer film as shown in Table 7-1 to Table 7-3. A non-polarizing beam splitter was constructed by bringing the slope of another isosceles right triangular prism of the same size into close contact with the slope of this prism. FIG. 9 shows the spectral transmittances of S-polarized light and P-polarized light measured at a light incident angle of 45 ° to the joint surface.

  As is clear from comparison between Examples 1 to 4 and Comparative Examples 1 and 2, the non-polarizing beam splitter of the present invention has fewer film materials than conventional ones (conventional two types compared to three or more types). In addition, it can be seen that it has a non-polarization characteristic in a wavelength range of 300 nm or more which cannot be achieved even with a 97-layer film with a small number of layers (conventionally 5 layers compared with 9 layers or more). Furthermore, according to Example 5, it has non-polarization characteristics at 700 nm or more, which is a wider wavelength range, with less film material (previously two kinds than three kinds) compared with the conventional non-polarization beam splitter. I understand. Therefore, the non-polarizing beam splitter of the present invention is very useful when applied to an optical measuring instrument such as a laser planar.

It is a schematic diagram which shows an example of the non-polarization beam splitter using a right-angled isosceles triangle prism. It is a schematic diagram which shows an example of the non-polarization beam splitter using a trapezoid prism. It is a schematic diagram which shows an example of the laser planar using a non-polarizing beam splitter. 3 is a graph showing spectral transmittances of S-polarized light and P-polarized light of the non-polarizing beam splitter manufactured in Example 1. FIG. 6 is a graph showing spectral transmittances of S-polarized light and P-polarized light of the non-polarizing beam splitter produced in Example 2. FIG. 6 is a graph showing spectral transmittances of S-polarized light and P-polarized light of the non-polarizing beam splitter produced in Example 3. 6 is a graph showing spectral transmittances of S-polarized light and P-polarized light of the non-polarizing beam splitter produced in Example 4. 6 is a graph showing spectral transmittances of S-polarized light and P-polarized light of the non-polarizing beam splitter produced in Example 5. FIG. 4 is a graph showing spectral transmittances of S-polarized light and P-polarized light of the non-polarizing beam splitter produced in Comparative Example 1. 6 is a graph showing spectral transmittances of S-polarized light and P-polarized light of the non-polarizing beam splitter produced in Comparative Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser planar 2 ... Laser light source 3 ... Disk 4 ... Beam splitter
L ... Laser light
L1 ... Reflected light
L2: Transmitted light

Claims (6)

Between two transparent substrates, a layer having a refractive index higher than the refractive index Ns of the transparent substrate (high refractive index layer) and a layer having a refractive index lower than the refractive index Ns of the transparent substrate (low refractive index). A non-polarizing beam splitter in which a multilayer film formed by laminating a refractive index layer is inserted, the refractive index Ns of the transparent substrate and the refractive index Nl of the layer having the lowest refractive index among the multilayer films , With respect to the light incident angle θ ₀ ° on the multilayer film:
θ ₀ ° −3.5 ° ≦ sin ⁻¹ (Nl / Ns) ≦ θ ₀ ° + 3.5 °
A non-polarizing beam splitter characterized by satisfying 2. The non-polarizing beam splitter according to claim 1, wherein the material forming the high refractive index layer is Ta ₂ O ₅ , TiO ₂ , Nb ₂ O ₅ , ZrO ₂ , HfO ₂ , CeO ₂ , SnO ₂ , In _2. At least one selected from the group consisting of O ₃ , ZnO, ZnS, La ₂ O ₃ and Sb ₂ O ₃ , and the material for forming the low refractive index layer is NaF, CaF ₂ , LiF, MgF ₂ , SiO _2. A non-polarizing beam splitter, which is at least one selected from the group consisting of YF ₃ and Al ₂ O ₃ , wherein the multilayer film is composed of 5 to 21 layers.   3. The non-polarizing beam splitter according to claim 1, wherein the multilayer film has a five-layer structure in which the high refractive index layers and the low refractive index layers are alternately stacked. .   The non-polarizing beam splitter according to any one of claims 1 to 3, wherein at least one of the low refractive index layers has a nanoporous structure.   The non-polarizing beam splitter according to any one of claims 1 to 4, wherein the non-polarizing property is that the difference in transmittance between S-polarized light and P-polarized light is 10% or less in a wavelength range of 300 to 700 nm. Polarizing beam splitter.   An optical measuring instrument using the non-polarizing beam splitter according to claim 1.

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