Optical filter, method of manufacturing optical filter, optical filter unit, method of manufacturing optical filter unit, and optical measurement device

Abstract

To provide an optical filter and an optical filter unit capable of reducing polarization dependence of transmittance for vertical incident light, a method of manufacturing them, and an optical measurement device capable of reducing measurement errors that depend on a polarization direction of light to be measured.SOLUTION: An optical filter having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range includes a first optical function layer and a second optical function layer each having a transmittance that varies in a polarization direction of linearly polarized light at vertical incidence. The first optical function layer and the second optical function layer each have a high transmittance axis determined by a polarization direction in which transmittance of linearly polarized light at vertical incidence is greatest. The first optical function layer and the second optical function layer are arranged such that an angle formed by the high transmittance axis is within a range of 90°±30° .SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to an optical filter, a method for manufacturing an optical filter, an optical filter unit, a method for manufacturing an optical filter unit, and an optical measurement device. [Background technology]

[0002] An optical measurement device is known as a device capable of measuring the luminance, chromaticity, etc. of light emitted from an object to be measured (such as a smartphone display or LCD monitor) (Patent Document 1). In this optical measurement device, the light to be measured from the object to be measured is split into multiple beams and measured.

[0003] Recent smartphones and other devices use displays with a wide dynamic range of brightness. Therefore, optical measurement devices are required to have the ability to measure brightness ranging from dark to bright when performing gamma testing and adjustments. In order to expand the dynamic range of an optical measurement device, it is necessary to control the amount of light received. A known method for controlling the amount of light received is to use a thin-film filter that has spectral flatness and little change in transmittance due to ambient temperature (Patent Document 2).

[0004] Thin film filters are inserted into the optical path of the light to be measured as needed. When a thin film filter is inserted into the optical path, the measured value must take into account the transmittance of the thin film filter. For this reason, the transmittance of the thin film filter is measured during calibration (factory calibration) by the measuring instrument manufacturer and saved as a correction coefficient in the optical measurement device. By appropriately correcting the measured value, linear continuity can be obtained in the measured value when switching from a state where a thin film filter is not inserted into the optical path to a state where it is inserted. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5454675 [Patent Document 2] Japanese Patent Publication No. 2022-36766 Summary of the Invention [Problem to be solved by the invention]

[0006] It is known that the transmittance of a thin film filter has polarization dependency depending on the angle of incidence of the light to be measured, but theoretically there is no polarization dependency at normal incidence. However, recent research has revealed that there is a slight polarization dependency even at normal incidence.

[0007] In the past, in many optical measurement instruments, this minute polarization dependency was considered to be within the range of measurement error and was either not noticed or not considered a problem. However, in high-precision optical measurement instruments, a discrepancy occurs between the stored filter correction coefficient and the actual transmittance, resulting in a non-negligible error in the measurement results.

[0008] The problem to be solved by the present invention is to provide an optical filter and optical filter unit that enable more accurate optical measurement, a method for manufacturing the same, and an optical measurement device that reduces measurement errors that depend on the polarization direction of the light to be measured. [Means for solving the problem]

[0009] In order to solve the above problems, the optical filter of the present invention comprises: An optical filter having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, a first optical functional layer and a second optical functional layer whose transmittance varies in the polarization direction when linearly polarized light is perpendicularly incident; the first optical functional layer and the second optical functional layer each have a high transmittance axis determined from a polarization direction in which the transmittance is highest when linearly polarized light is perpendicularly incident, The first optical functional layer and the second optical functional layer are arranged so that the angle at which the high transmittance axes intersect is within a range of 90°±30°.

[0010] The invention described in claim 2 is the invention described in claim 1, a substrate supporting the first optical functional layer and the second optical functional layer; The first optical function layer is disposed on one surface of the substrate, and the second optical function layer is disposed on the other surface of the substrate.

[0011] The invention described in claim 3 is the invention described in claim 1, a substrate supporting the first optical functional layer and the second optical functional layer; The first optical functional layer and the second optical functional layer are laminated on either surface of the substrate.

[0012] The invention described in claim 4 is the invention described in any one of claims 1 to 3, When the layer with the larger difference between the maximum transmittance and the average transmittance is the first optical functional layer and the layer with the smaller difference is the second optical functional layer, the following formula (1) is satisfied. Equation (1) (T2 max -T2 ave ) / (T1 max -T1 ave )≧1 / 2 In the formula, T1 max and T1 ave represent the maximum transmittance and the average transmittance of the first optical functional layer, respectively, and T2 max and T2 ave represent the maximum transmittance and the average transmittance of the second optical functional layer, respectively.

[0013] The invention described in claim 5 is the invention described in any one of claims 1 to 3, The optical filter is a neutral density filter.

[0014] The invention described in claim 6 is the invention described in any one of claims 1 to 3, The optical filter is a wavelength filter.

[0015] The invention described in claim 7 is the invention described in any one of claims 1 to 3, The minimum transmittance when the polarization direction is changed for linearly polarized light perpendicular to the incident light is T min , the maximum value is T max When this is the case, the following formula (2) is satisfied. Equation (2) (T min / T max ) × 100 [%] ≥ 95 [%]

[0016] The filter according to claim 8 comprises: An optical filter having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, a first optical functional layer and a second optical functional layer whose reflectance varies in the polarization direction when linearly polarized light is perpendicularly incident; a substrate supporting the first optical functional layer and the second optical functional layer, the first optical functional layer is disposed on one surface side of the substrate, and the second optical functional layer is disposed on the other surface side of the substrate; the first optical functional layer and the second optical functional layer each have a high reflectance axis determined by a polarization direction in which the reflectance is highest when linearly polarized light is perpendicularly incident, The first optical functional layer and the second optical functional layer are arranged so that the angle at which the high reflectance axes intersect is within a range of 90°±30°.

[0017] The invention described in claim 9 is a method for producing the optical filter according to claim 1 or 2, comprising: a first layering step of forming the first optical functional layer on a surface of a substrate moving in a specific direction relative to a target that is a material of the first optical functional layer; a rotation step of rotating the substrate around the center of the substrate as a rotation center within a range of 90°±30° with respect to the specific direction when the substrate is inverted so that the rear surface thereof faces the target which is the material of the second optical functional layer; and a second layering step of forming the second optical functional layer on the rear surface of the substrate.

[0018] The invention described in claim 10 is a method for producing the optical filter according to claim 1 or 3, comprising: a first layering step of forming the first optical functional layer on a surface of a substrate moving in a specific direction relative to a target that is a material of the first optical functional layer; a rotating step of rotating the substrate around the center of the substrate as a rotation center so that the angle is within a range of 90°±30° with respect to the specific direction; and a second layering step of forming the second optical functional layer on the first optical functional layer.

[0019] The method for producing an optical filter according to claim 11 is a method for producing an optical filter including a fifth optical functional layer having light transmittance characteristics or light reflectance characteristics in a predetermined wavelength range, The method includes a third layering step in which a substrate moving in a specific direction relative to a target that is the material of the fifth optical functional layer is rotated in the specific direction with the center of the substrate as the center of rotation, while the fifth optical functional layer is formed on the surface of the substrate.

[0020] The filter unit according to claim 12 is an optical filter unit including a first optical filter and a second optical filter having light transmittance characteristics or light reflectance characteristics for a predetermined wavelength range, the first optical filter includes a first substrate and a first optical function layer supported by the first substrate, the first optical function layer having a transmittance that varies in a polarization direction when linearly polarized light is perpendicularly incident; the second optical filter includes a second substrate and a second optical function layer supported by the second substrate, the second optical function layer having a transmittance that varies in a polarization direction when linearly polarized light is perpendicularly incident, the first optical functional layer and the second optical functional layer each have a high transmittance axis determined from a polarization direction in which the transmittance is highest when linearly polarized light is perpendicularly incident, The first optical filter and the second optical filter are arranged so that the angle at which the high transmittance axes intersect is within a range of 90°±30°.

[0021] The invention described in claim 13 is a method for manufacturing an optical filter unit according to claim 12, comprising: a first optical filter fabrication step of forming the first optical functional layer on a surface of a first substrate that moves in a specific direction relative to a target that is a material of the first optical functional layer, thereby fabricating the first optical filter; a second optical filter fabrication step of forming the second optical functional layer on a surface of a second substrate that moves in a specific direction relative to a target that is a material of the second optical functional layer, thereby fabricating the second optical filter; and an arrangement step of arranging the first optical filter and the second optical filter so that the angle between the specific direction moved on the first substrate and the specific direction moved on the second substrate is within a range of 90°±30°.

[0022] The optical measurement device described in claim 14 is equipped with the optical filter described in any one of claims 1 to 3 or the optical filter unit described in claim 12.

[0023] The invention described in claim 15 is the invention described in claim 14, The optical filter or the optical filter unit is provided with an insertion / removal device for inserting or removing the optical filter or the optical filter unit into or from the optical path of the light to be measured.

[0024] The invention described in claim 16 is the invention described in claim 14, Measure the luminance or chromaticity of the object to be measured. [Effects of the Invention]

[0025] According to the present invention, the polarization dependency of the transmittance for perpendicularly incident light can be reduced. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a block diagram showing an example of the configuration of a tristimulus value type optical measurement device 10 of the present embodiment. [Figure 2]FIG. 10 is a diagram illustrating a method for measuring the polarization dependency of transmittance for perpendicularly incident light. [Figure 3] 10 is a graph showing an example of measurements of the polarization dependence of transmittance for perpendicularly incident light through a filter with an average transmittance of approximately 4.7%. [Figure 4] 10 is a graph showing an example of measurements of the polarization dependence of transmittance for perpendicularly incident light through a filter with an average transmittance of approximately 4.7%. [Figure 5] FIG. 2 is a schematic cross-sectional view of an example of a filter 40 of the present embodiment. [Figure 6] FIG. 2 is a schematic cross-sectional view of an example of a filter 40 of the present embodiment. [Figure 7] FIG. 10 is a perspective view of a measurement filter 50 at a rotation angle of 0° when measuring the polarization dependency of transmittance. [Figure 8] FIG. 10 is a perspective view of a measurement filter 50 rotated at an angle of 45° when measuring the polarization dependency of transmittance. [Figure 9] FIG. 10 is a perspective view of a measurement filter 50 rotated at an angle of 90° when measuring the polarization dependency of transmittance. [Figure 10] 10 is a graph showing an example of an optical function layer in which the transmittance varies in the polarization direction when linearly polarized light is perpendicularly incident. [Figure 11] 1 is a diagram showing the relationship between a first high transmittance axis 61 and a second high transmittance axis 62 in a filter 40 of the present embodiment. [Figure 12] 10 is a graph showing the rate of change in the transmittance of the filter when the amplitude A1=A2=1.0% and the angle α=0°. [Figure 13] 10 is a graph showing the rate of change in the transmittance of a filter when the amplitude A1=A2=1.0% and the angle α=90°. [Figure 14] 10 is a graph showing the rate of change in the transmittance of a filter when the amplitude A1 is 1.0%, A2 is 0.5%, and the angle α is 90°. [Figure 15] 10 is a graph showing the rate of change in the transmittance of a filter when the amplitude A1=A2=1.0% and the angle α=105°. [Figure 16]10 is a graph showing the rate of change in the transmittance of a filter when the amplitude A1=A2=1.0% and the angle α=120°. [Figure 17] FIG. 2 is a schematic cross-sectional view of a measuring device 70 used to set a high reflectance axis in the optical function layer of the filter 40. [Figure 18] FIG. 2 is a schematic cross-sectional view of an example of a filter unit 44 of the present embodiment. [Figure 19] 10 is a diagram showing the relationship between a third high transmittance axis 63 and a fourth high transmittance axis 64 in a filter unit 44 of the present embodiment. FIG. [Figure 20] FIG. 1 is a schematic cross-sectional view of a drum-type film-forming apparatus 80 for the RAS method, as viewed from above. [Figure 21] FIG. 1 is a flow diagram of each step in manufacturing methods (1) and (2). [Figure 22] FIG. 10 is a view of the substrate 41 held by the drum 81 as viewed from the opposing target during the first layer-forming step S1. [Figure 23] FIG. 10 is a view of the substrate 41 held by the drum 81 after the rotation step S2, as viewed from the opposing target. [Figure 24] FIG. 10 is a schematic cross-sectional view of an example of a filter 92 manufactured by the manufacturing method (3). [Figure 25] FIG. 10 is a view of the substrate 41 held by the drum 81 during the third layer-forming step, as viewed from the opposing target. [Figure 26] FIG. 1 is a flow diagram of each step of the manufacturing method (4). [Figure 27] 1 is a graph showing the relationship between the rotation angle of the filter (a) and the rate of change in reflectance. [Figure 28] 10 is a graph showing the relationship between the rotation angle of the filter (b) and the rate of change in reflectance. DETAILED DESCRIPTION OF THE INVENTION

[0027] One or more embodiments of the present invention will now be described with reference to the drawings, however, it is not intended that the scope of the present invention be limited to the disclosed embodiments.

[0028] [Configuration of optical measurement device] The optical measurement device of this embodiment is equipped with an optical filter or optical filter unit, which will be described later. The optical measurement device may be any device that measures a physical quantity using light. In this embodiment, a photometric device will be described. The photometric device is a device that measures the intensity of light emitted from an object to be measured, such as luminance or chromaticity.

[0029] Fig. 1 is a block diagram showing an example of the configuration of a tristimulus value type optical measurement device 10 of this embodiment. In Fig. 1, the optical measurement device 10 is a photometric device that measures the luminance or chromaticity of an object under test 1. The optical measurement device 10 is used, for example, in an inspection process on a manufacturing line for smartphone displays, and measures the brightness, chromaticity, etc. of the display surface of the display.

[0030] The optical measurement device 10 includes an objective optical system 11 , a branching optical system 12 , a colorimetric optical system 13 , an electrical processing unit 14 , and a control unit 15 .

[0031] The objective optical system 11 includes a convex lens 11a having a positive power, an optical filter 4, and an aperture stop 11b. The splitting optical system 12 includes a diffuser plate 20 having splitting and diffusing functions.

[0032] Aperture stop 11b is disposed at the rear focal position of convex lens 11a. By adopting a front telecentric optical arrangement, it is possible to capture components within ±2.5 degrees of the normal to the measurement surface, which is the display surface of object 1. Diffuser 20 is disposed behind aperture stop 11b. Optical filter 4 is disposed between convex lens 11a and diffuser 20, in front of aperture stop 11b.

[0033] The optical filter 4 is driven by an insertion / removal device 5. The insertion / removal device 5 inserts the optical filter 4 into or removes it from the optical path of the light under measurement 2. The insertion / removal device 5 is formed, for example, by a linear actuator. When the optical filter 4 is inserted into the optical path of the light under measurement 2, the amount of the light under measurement 2 incident on the diffuser plate 20 is reduced by the optical filter 4. When the optical filter 4 is removed from the optical path of the light under measurement 2, the light under measurement 2 is incident on the diffuser plate 20 without any reduction in its amount. The optical filter 4 is also called a "neutral density (ND) filter."

[0034] The optical filter 4 is inserted or removed depending on the brightness of the object under test 1. Specifically, when the object under test 1 is dark, the optical filter 4 is removed from the optical path. When the object under test 1 is bright, the optical filter 4 is inserted into the optical path to reduce the amount of light, thereby preventing saturation of the light-receiving sensors 132a, 132b, and 132c. This allows the intensity of the light under test 2 to be within the dynamic range of the light-receiving sensors 132a, 132b, and 132c, and as a result, the dynamic range of the optical measurement device 10 is expanded.

[0035] It is important that the optical filter 4 has spectral flatness (uniformity) and that its transmittance does not change with the ambient temperature. This is because flatness affects the spectral response whether the optical filter 4 is inserted or removed (whether the optical filter 4 is present or not). If the optical filter 4 is not flat, the received light spectral sensitivity when the optical filter 4 is not present will change from the received light spectral sensitivity when the optical filter 4 is present. If the received light spectral sensitivity deviates from the color matching function, errors in luminance and chromaticity will occur.

[0036] Glass absorption filters have poor spectral flatness and their transmittance varies greatly depending on the ambient temperature. Furthermore, glass absorption filters offer relatively low flexibility in designing the transmission spectrum. Perforated plates have spectral flatness, but measurement unevenness occurs in the light-receiving angle. Furthermore, perforated plates require strict positional repeatability.

[0037] On the other hand, thin film filters have spectral flatness and little change in transmittance due to environmental temperature, so it is preferable to use a thin film filter as the optical filter 4. Thin film filters have a relatively high degree of freedom in designing the transmission spectrum, little change in transmittance due to environmental temperature and humidity, and are relatively stable.

[0038] The colorimetric optical system 13 includes color filters 131a, 131b, and 131c and light-receiving sensors 132a, 132b, and 132c. The color filters 131a, 131b, and 131c are wavelength filters and color-matching function filters corresponding to the tristimulus values ​​of X, Y, and Z. The light-receiving sensors 132a, 132b, and 132c are light-receiving elements used in combination with the color-matching function filters.

[0039] The color filters 131a, 131b, and 131c may be constructed by stacking multiple light-absorbing filters to achieve transmittance corresponding to desired spectral characteristics, such as the tristimulus values ​​of X, Y, and Z. However, with such a configuration, it is difficult to design a filter that has transmittance peaks in two wavelength ranges, meaning that the degree of freedom in filter design is limited. Furthermore, light-absorbing filters have low transmittance and suffer from significant light loss. Furthermore, film-type color filters are subject to significant aging and low stability due to factors such as heat, light (ultraviolet rays), and humidity.

[0040] Therefore, it is preferable to use interference-type interference filters for the color filters 131a, 131b, and 131c. Interference filters are obtained by laminating several dozen layers of dielectrics, oxides, etc. on a glass substrate using methods such as vacuum deposition and sputtering. In interference filters, wavelengths that are transmitted or reflected are selected by the interference of light.

[0041] Compared to light-absorption filters, interference filters are easier to design and offer greater design flexibility, making it easier to achieve the desired transmittance. It is also possible to create filters with two peaks, like the color-matching function X. Interference filters also have high transmittance. For example, the peak transmittance of an interference filter is close to 100%, while that of a light-absorption filter is 50% or less. Furthermore, interference filters experience less change in transmittance over time due to temperature, humidity, and exposure to light.

[0042] For example, silicon sensors are used as the light-receiving sensors 132a, 132b, and 132c. The light received by each of the light-receiving sensors 132a, 132b, and 132c is converted into an electrical signal, and the electrical processing units 14a, 14b, and 14c perform processes such as I / V conversion and amplification on the electrical signals. The processed electrical signals are then input to the control unit 15 as numerical data. The control unit 15 performs calculations based on the input numerical data to calculate a measurement value.

[0043] When the optical filter 4 is inserted into the optical path, a correction is made when calculating the measurement value. The correction is calculated using a correction coefficient held in the control unit 15. The correction coefficient is set, for example, during factory calibration at the measuring instrument manufacturer. Specifically, the correction coefficient is set by using a reference light source to obtain measurement values ​​when the optical filter 4 is inserted into the optical path and when it is removed, so that these measurement values ​​match.

[0044] The slight polarization dependency of the transmittance of a thin film filter serving as the optical filter 4 for perpendicularly incident light can be measured using the method shown in Figure 2. Light L from a light source 202 (LED, laser, lamp, etc.) is passed through a polarizing plate 203 to become linearly polarized light with a fixed polarization direction. The linearly polarized light is made to enter the thin film filter 204 perpendicularly, and the light at an angle of approximately 0° is measured by a photodetector 205. By measuring the transmittance when the thin film filter 204 is rotated, the polarization dependency of the transmittance for perpendicularly incident light can be measured.

[0045] Figures 3 and 4 show actual measurement examples of the polarization dependence of transmittance for perpendicularly incident light of a thin film filter with an average transmittance of approximately 4.7%. In the graphs shown in Figures 3 and 4, the horizontal axis represents the rotation angle [°] of the filter relative to the linear polarization direction. In the graph shown in Figure 3, the vertical axis represents transmittance [%]. In the graph shown in Figure 4, the vertical axis represents the fluctuation rate of transmittance [%].

[0046] As can be seen from Figure 3, the transmittance of this thin film filter fluctuates slightly within a range of 4.686 to 4.714% depending on the polarization direction. Figure 4 is a graph that focuses on this slight variation. As can be seen from Figure 4, the transmittance of this thin film filter fluctuates within a range of ±0.3% depending on the polarization direction, indicating slight polarization dependency.

[0047] This slight polarization dependency is within the range of measurement error, so it has not been noticed or considered a problem in many optical measurement instruments. However, in high-precision optical measurement instruments, a discrepancy occurs between the stored filter correction coefficient and the actual transmittance, resulting in large errors in the measurement results.

[0048] In the optical measurement device 10, it is assumed that the thin-film filter serving as the optical filter 4 has polarization-dependent transmittance for perpendicularly incident light. If the reference light source used during calibration is configured with a diffuser, the light emitted from the reference light source is randomly polarized. In this case, the correction coefficient is set to the average value of the polarization-dependent transmittance of the optical filter 4. Subsequently, in measurements using the optical measurement device 10, if the measured light 2 is randomly polarized or perfectly circularly polarized, no measurement error occurs with the set correction coefficient. However, if the measured light 2 is linearly polarized or elliptically polarized, the optical filter 4 is affected by polarization dependency, resulting in a change in transmittance from the time of calibration and a measurement error. Note that if the measured object 1 is a smartphone display, LCD monitor, or the like, the light emitted from these devices is often linearly polarized or elliptically polarized.

[0049] When the DUT 1 itself is used as the reference light source during calibration, the polarization direction of the light emitted from the reference light source during calibration matches that of the light under measurement 2, eliminating measurement errors. However, if the installation angle of the DUT 1 shifts between calibration and measurement, the polarization direction of the light emitted from the reference light source during calibration will shift from that of the light under measurement 2, resulting in measurement errors. On the other hand, if calibration and a correction coefficient can be set each time a measurement is performed, the installation position of the DUT 1 can be kept the same between calibration and measurement. However, calibration is typically performed only at the measurement instrument manufacturer's factory. From this perspective, using an optical filter or optical filter unit with reduced polarization dependency of transmittance for perpendicularly incident light as the optical filter 4 can reduce measurement errors and improve accuracy.

[0050] [Configuration of optical filter] The optical filter of this embodiment has light transmittance characteristics or light reflectance characteristics for a predetermined wavelength range. Hereinafter, the "optical filter" may also be simply referred to as "filter." In addition, the filter of this embodiment has a minimum value of the transmitted light amount when the polarization direction is changed for linearly polarized light perpendicularly incident thereon, which is T min , the maximum value is T max When this is the case, the target is one that satisfies the following formula (2). Equation (2) (T min / T max ) × 100 [%] ≥ 95 [%]

[0051] In other words, the filter used in this embodiment is an optical filter that has almost no polarization function. Examples of filters include wavelength filters and neutral density (ND) filters. Examples of wavelength filters include bandpass filters, highpass filters, lowpass filters, notch filters, and color-matching function filters corresponding to the XYZ tristimulus values. A polarizing filter (polarizing plate), for example, that does not satisfy the above formula (2) is not applicable as the filter of this embodiment.

[0052] Fig. 5 is a schematic cross-sectional view of an example of a filter 40 of this embodiment. As shown in Fig. 5, the filter 40 has a first optical functional layer 42, a second optical functional layer 43, and a substrate 41 that supports these.

[0053] The first optical functional layer 42 is disposed on one side of the substrate 41, and the second optical functional layer 43 is disposed on the other side of the substrate 41. The surfaces of the substrate 41 on which the optical functional layers are disposed are the two largest opposing surfaces, and correspond to the light entrance and exit surfaces. In Fig. 5, as an example, the first optical functional layer 42 and the second optical functional layer 43 are disposed on the light entrance surface 41a side and the light exit surface 41b side of the substrate 41, respectively, but the surfaces on which they are disposed may be opposite.

[0054] Fig. 6 is a schematic cross-sectional view of an example of the filter 40 of this embodiment. In Fig. 6, the first optical functional layer 42 and the second optical functional layer 43 are laminated on the exit surface 41b side of the substrate 41. Note that, although the first optical functional layer 42 and the second optical functional layer 43 are laminated on the exit surface 41b side of the substrate 41 in Fig. 6, they may also be laminated on the entrance surface 41a side.

[0055] The first optical functional layer 42 and the second optical functional layer 43 may have the same film configuration or different film configurations.

[0056] The first optical functional layer 42 and the second optical functional layer 43 may be formed of the same material or different materials. The first optical functional layer 42 and the second optical functional layer 43 may be interference films using a dielectric material such as SiO2 or MgF2. The first optical functional layer 42 and the second optical functional layer 43 may be metal oxide films using a metal oxide material such as Al2O3, TiO2, Nb2O5, or NbO. The first optical functional layer 42 and the second optical functional layer 43 may be films using a metal material such as Cr or Nb.

[0057] The substrate 41 is made of a transparent optical material, and the optical material can be appropriately selected depending on the wavelength range of the light to be measured 2. Examples of optical materials include glass, plastic, quartz, and sapphire.

[0058] [Polarization Dependence of Optical Functional Layer] In this embodiment, the "high transmittance axis determined from the polarization direction in which the amount of transmitted light is highest when linearly polarized light is perpendicularly incident" is set by the following procedure.

[0059] The polarization dependency of the transmittance of the optical functional layer for perpendicularly incident light is measured by the method shown in Fig. 2. In this measurement, a measurement filter having only one optical functional layer is used as a sample.

[0060] 7 is a perspective view of measurement filter 50 at a rotation angle of 0° when measuring the polarization dependence of transmittance. Linearly polarized light L transmitted through polarizing plate 203 is incident on measurement filter 50. Before measurement filter 50 is rotated, that is, at a rotation angle of 0°, an axis parallel to the reference direction is set as position 51 at a rotation angle of 0°.

[0061] Fig. 8 is a perspective view of the measurement filter 50 rotated at a rotation angle of 45° when measuring the polarization dependence of transmittance. In Fig. 8, the measurement filter 50 is rotated 45° clockwise from the position shown in Fig. 7, with the center of the measurement filter 50 as the rotation center. At a rotation angle of 45°, the axis parallel to the reference direction is set to position 52 at a rotation angle of 45°.

[0062] Fig. 9 is a perspective view of the measurement filter 50 rotated 90° when measuring the polarization dependency of transmittance. In Fig. 9, the measurement filter 50 is rotated 90° clockwise from the position shown in Fig. 7, with the center of the measurement filter 50 as the rotation center. At a rotation angle of 90°, the axis parallel to the reference direction is set to position 53 at a rotation angle of 90°.

[0063] Figure 10 is a graph showing an example of an optical functional layer whose transmittance varies in the polarization direction when linearly polarized light is perpendicularly incident. The horizontal axis of the graph represents the rotation angle [°] of the optical functional layer (measurement filter), and the vertical axis represents the variation rate [%] of the transmittance of the optical functional layer (measurement filter). The variation rate of the transmittance of the optical functional layer can be calculated as a ratio value with the average transmittance as a reference value, as shown in the following formula. As shown in Figure 10, the relationship between the rotation angle [°] of the optical functional layer and the variation rate [%] of the transmittance can be fitted with a sine curve. Formula: Transmittance fluctuation rate [%] = {(Transmittance at a specific rotation angle - average transmittance) / average transmittance} x 100

[0064] In the example shown in Fig. 10, the amplitude of the sine curve of the fluctuation rate is 0.5%, and the transmittance fluctuates by a maximum of 1.0%. Also, in the example shown in Fig. 10, the fluctuation rate is maximum, i.e., the transmittance is highest, when the rotation angle is 0° and 180°. Therefore, the positions of the rotation angle of 0° and the rotation angle of 180° are referred to as "high transmittance axes determined from the polarization direction with the highest transmittance for perpendicular incidence of linearly polarized light." Hereinafter, they will also be referred to simply as "high transmittance axes."

[0065] FIG. 11 is a diagram showing the relationship between the first high transmittance axis 61 and the second high transmittance axis 62 in the filter 40 of this embodiment. The first high transmittance axis 61 is the high transmittance axis of the first optical functional layer 42, and the second high transmittance axis 62 is the high transmittance axis of the second optical functional layer 43. The first optical functional layer 42 and the second optical functional layer 43 are arranged so that the angle at which the first high transmittance axis 61 and the second high transmittance axis 62 intersect is within a range of 90°±30°. This reduces the polarization dependency of the filter 40. Note that in FIG. 11, the intersecting angle is set to 90°, as an example.

[0066] The relationship between the angle at which the first high transmittance axis 61 and the second high transmittance axis 62 intersect and the transmittance of the filter will be described below. Here, it is assumed that the fluctuation rate T of the transmittance is a sine wave.

[0067] The variation rate T1(θ) of the transmittance in the first optical functional layer 42 is expressed by the following formula (I). Formula (I) T1(θ)=A1×cos2θ Here, the angle θ represents the polarization angle of the incident linearly polarized light when the first high transmittance axis 61 is set to 0°. The amplitude A1 represents the difference between the maximum transmittance and the average transmittance.

[0068] The variation rate T2(θ) of the transmittance in the second optical functional layer 43 is expressed by the following formula (II). Formula (II) T2(θ)=A2×cos2(θ-α) where angle θ represents the polarization angle of the incident linearly polarized light when the first high transmittance axis 61 is set to 0°. Amplitude A2 represents the difference between the average transmittance and the maximum transmittance. Angle α represents the angle at which the first high transmittance axis 61 and the second high transmittance axis 62 intersect.

[0069] The variation rate T(θ) of the transmittance of the filter including the first optical functional layer 42 and the second optical functional layer 43 is expressed by the following formula (III). Equation (III) T(θ)=T1(θ)+T2(θ)

[0070] Figure 12 is a graph showing the variation rate of the transmittance of the filter when the amplitude A1 = A2 = 1.0% and the angle α = 0°. The horizontal axis of the graph represents the polarization angle θ [°] of the linearly polarized light incident on the filter. The vertical axis of the graph represents the variation rate T [%] of the transmittance of the filter. Note that in the graph of Figure 12, T1(θ) and T2(θ) completely overlap.

[0071] At this time, the amplitude of T(θ) is larger than T1(θ) and T2(θ), as shown in Fig. 12. In other words, by using the first optical functional layer 42 and the second optical functional layer 43 together, the polarization dependencies of the layers are strengthened, and the fluctuation in the transmittance of the filter becomes larger than when each layer is used alone.

[0072] Figure 13 is a graph showing the variation rate of the filter's transmittance when the amplitude A1 = A2 = 1.0% and the angle α = 90°. The horizontal axis of the graph represents the polarization angle θ [°] of the linearly polarized light incident on the filter. The vertical axis of the graph represents the variation rate T [%] of the filter's transmittance.

[0073] At this time, T(θ) is a constant value, as shown in Fig. 13. In other words, by using the first optical functional layer 42 and the second optical functional layer 43 together, the polarization dependencies cancel each other out, and the transmittance of the filter does not fluctuate.

[0074] Figure 14 is a graph showing the variation rate of the filter's transmittance when the amplitude A1 is 1.0%, A2 is 0.5%, and the angle α is 90°. The amplitude A2 is half the amplitude A1. The horizontal axis of the graph represents the polarization angle θ [°] of the linearly polarized light incident on the filter. The vertical axis of the graph represents the variation rate T [%] of the filter's transmittance.

[0075] At this time, the amplitude of T(θ) is smaller than T1(θ), as shown in Fig. 14. In other words, by using the first optical functional layer 42 and the second optical functional layer 43 together, the polarization dependency of the first optical functional layer 42 is partially canceled out by the second optical functional layer 43, and the fluctuation in the transmittance of the filter is half that of the first optical functional layer 42.

[0076] Figure 15 is a graph showing the variation rate of the filter's transmittance when the amplitude A1 = A2 = 1.0% and the angle α = 105°. The horizontal axis of the graph represents the polarization angle θ [°] of the linearly polarized light incident on the filter. The vertical axis of the graph represents the variation rate T [%] of the filter's transmittance.

[0077] At this time, the amplitude of T(θ) is smaller than T1(θ) and T2(θ), as shown in Fig. 15. In other words, by using the first optical functional layer 42 and the second optical functional layer 43 together, the polarization dependency of the first optical functional layer 42 is partially canceled out by the second optical functional layer 43, and the fluctuation in the transmittance of the filter is half that of the first optical functional layer 42.

[0078] Figure 16 is a graph showing the variation rate of the filter's transmittance when the amplitude A1 = A2 = 1.0% and the angle α = 120°. The horizontal axis of the graph represents the polarization angle θ [°] of the linearly polarized light incident on the filter. The vertical axis of the graph represents the variation rate T [%] of the filter's transmittance.

[0079] 16, the amplitude of T(θ) is equal to T1(θ) and T2(θ). In other words, by using the first optical functional layer 42 and the second optical functional layer 43 together, the polarization characteristics of the first optical functional layer 42 are partially canceled out by the second optical functional layer 43, and the fluctuation in the transmittance of the filter becomes equal to that of the first optical functional layer 42.

[0080] By setting the angle α within the range of 90°±30°, the variation in the transmittance of the filter can be made smaller than the variation in the transmittance of only the first optical functional layer 42 or only the second optical functional layer 43. Furthermore, the angle α is preferably within the range of 90°±15°, and more preferably 90°.

[0081] As mentioned above, the relationship between the rotation angle of the optical functional layer and the rate of change in transmittance can be fitted with a sine curve. The amplitude A of the sine curve can be expressed as the difference between the maximum transmittance and the average transmittance of the optical functional layer. When the layer with the larger difference between the maximum transmittance and the average transmittance is the first optical functional layer 42 and the layer with the smaller difference is the second optical functional layer 43, it is preferable that the following formula (1) is satisfied: Equation (1) (T2 max -T2 ave ) / (T1 max -T1 ave )≧1 / 2 In the formula, T1 max and T1 ave represent the maximum transmittance and the average transmittance of the first optical functional layer, respectively, and T2 max and T2 ave represent the maximum transmittance and the average transmittance of the second optical functional layer, respectively.

[0082] That is, when the amplitude A1 is larger than A2, the amplitude A2 is preferably larger than half the amplitude A1, so that the second optical functional layer 43 effectively cancels out the polarization dependency of the first optical functional layer 42, thereby further reducing fluctuations in the transmittance of the filter.

[0083] In particular, it is preferable that the amplitudes A1 and A2 are equal and the angle α is 90°, which can eliminate fluctuations in the transmittance of the filter.

[0084] The filter 40 may have three or more optical functional layers as long as the polarization dependency of transmittance is canceled out between the multiple optical functional layers used in combination. For example, in the configuration shown in Fig. 6, the filter 40 may have a first optical functional layer 42 and a second optical functional layer 43 on the incident surface 41a side as well, making the number of optical functional layers four.

[0085] [Method for detecting high transmittance axis of optical functional layer] If the first optical functional layer 42 and the second optical functional layer 43 cannot be separated in the filter 40, it is relatively difficult to detect the first high transmittance axis 61 and the second high transmittance axis 62 from transmittance measurements. If the filter 40 has the configuration shown in FIG. 5 and the first optical functional layer 42 and the second optical functional layer 43 are both exposed, the first high transmittance axis 61 and the second high transmittance axis 62 may be detected by the following method.

[0086] It has been found that the optical functional layer formed by the method described below exhibits polarization dependence in both transmitted and reflected light, and that the phases of these polarization dependencies are generally the same. In other words, it has been found that the high transmittance axis and the low reflectance axis are generally oriented in the same direction, and that the angle at which the high transmittance axis and the high reflectance axis intersect is generally 90°. Therefore, by detecting the high reflectance axis of the first optical functional layer 42 and the high reflectance axis of the second optical functional layer 43, it is possible to determine the approximate angle at which the first high transmittance axis 61 and the second high transmittance axis 62 intersect. The "high reflectance axis" here is set using the same procedure as for setting the high transmittance axis, except that reflectance is measured instead of transmittance.

[0087] 17 is a schematic cross-sectional view of a measurement device 70 used to set the high reflectance axis in the optical function layer of the filter 40. The measurement device 70 includes an optical measuring instrument 71, a flat light source 72, a polarizing plate 73, and a rotation stage 74.

[0088] First, the filter 40 to be measured is placed on the rotation stage 74. At this time, the filter 40 is placed so that either the first optical functional layer 42 or the second optical functional layer 43 faces the optical measuring instrument 71. In addition, it is preferable to mark the placed filter 40 at a position corresponding to the 0° direction of the rotation stage 74.

[0089] Next, diffused light is emitted from the planar light source 72. An example of the planar light source 72 is a surface-emitting light source using a light-emitting diode (LED). The diffused light emitted from the planar light source 72 is incident on the polarizing plate 73. The illumination light 75, which is linearly polarized uniformly diffused light emitted from the polarizing plate 73, illuminates the filter 40. The polarization direction of the illumination light 75 is the depth direction of the paper in FIG. 17, and the light illuminates the filter 40 as S-polarized light.

[0090] The amount of reflected light 76 reflected by the surface of filter 40 is measured using optical measuring instrument 71. During measurement, it is preferable to adjust the positions of each part so that the axis of illumination light 75 passes through intersection P between stage rotation axis 77 and the surface of filter 40. This reduces measurement errors that depend on the measurement position. It is preferable that the optical measuring instrument 71 be capable of measuring the amount of light with high precision, and examples include a power meter, a luminance meter, etc.

[0091] While rotating the rotation stage 74, the amount of reflected light 76 is measured and the reflectance is calculated. The polarization dependence of the reflected light can be confirmed by observing the rate of change in reflectance relative to the average reflectance. Once the polarization dependence has been confirmed, the filter 40 is turned over and placed on the rotation stage 74 so that the mark corresponds to the 0° direction of the rotation stage 74. The same procedure is used to confirm the polarization dependence of the reflected light on the back side of the filter 40. The high reflectance axis is set using the same procedure as for setting the high transmittance axis, and the high reflectance axis is treated as an approximation of the high transmittance axis. The angle at which the high transmittance axis intersects is determined from the angle at which the high reflectance axis intersects. Note that while the method for measuring reflectance at oblique incidence has been described here, it is preferable to measure reflectance at normal incidence using a coaxial illumination configuration using a beam splitter or the like.

[0092] [Filter unit configuration] The optical filter unit of this embodiment includes a first optical filter and a second optical filter that have light transmittance characteristics or light reflectance characteristics for a predetermined wavelength range.

[0093] That is, the filter unit of this embodiment is an optical filter unit that has almost no polarization function. Examples of the filter unit include a wavelength filter unit and a neutral density (ND) filter unit.

[0094] Fig. 18 is a schematic cross-sectional view of an example of a filter unit 44 of this embodiment. As shown in Fig. 18, the filter unit 44 includes a first filter 45 and a second filter 46. The first filter 45 includes third optical function layers 51a and 51b and a first substrate 47 that supports them. The second filter 46 includes fourth optical function layers 52a and 52b and a second substrate 48 that supports them.

[0095] 18, the third optical functional layers 51a, 51b of the first filter 45 are shown as having a two-layer structure, but may instead be a single-layer structure or a structure of three or more layers. The third optical functional layers 51a, 51b are provided on the incident surface 47a side and the exit surface 47b side of the first substrate 47, respectively, but may instead be provided only on the incident surface 47a side or the exit surface 47b side. Similarly, the fourth optical functional layers 52a, 52b of the second filter 46 are shown as having a two-layer structure, but may instead be a single-layer structure or a structure of three or more layers. The fourth optical functional layers 52a, 52b are provided on the incident surface 48a side and the exit surface 48b side of the second substrate 48, respectively, but may instead be provided only on the incident surface 48a side or the exit surface 48b side.

[0096] FIG. 19 is a diagram showing the relationship between the third high transmittance axis 63 and the fourth high transmittance axis 64 in the filter unit 44 of this embodiment. The third high transmittance axis 63 is the high transmittance axis in the first filter 45 and the high transmittance axis in the entire third optical functional layers 51a and 52b. The fourth high transmittance axis 64 is the high transmittance axis in the second filter 46 and the high transmittance axis in the entire fourth optical functional layers 52a and 52b. The first optical filter 45 and the second optical filter 46 are arranged so that the angle between the third high transmittance axis 63 and the fourth high transmittance axis 64 is within a range of 90°±30°. This reduces the polarization dependency of the filter unit 44. Note that in FIG. 19, the intersection angle is set to 90° as an example.

[0097] The filter unit 44 must be designed taking into account the use of multiple filters in combination. For example, if an ND filter unit with a transmittance of 4% is used, the first filter 45 and the second filter 46 each have a transmittance of 20%. In addition, the transmittance varies due to front-surface reflection, back-surface reflection, or inter-surface reflection, so these effects must be taken into account.

[0098] The filter unit 44 may have three or more filters as long as the polarization dependency of the transmittance is cancelled out between the multiple filters used in combination.

[0099] [Method for manufacturing a filter and a filter unit] The method for manufacturing a filter according to the present embodiment is not particularly limited, but will be described using a drum-type film-forming apparatus based on the Radical Assisted Sputtering (RAS) method as an example. The RAS method involves repeating a film-forming process for forming a metal or incomplete oxide of a metal and a complete oxidation process using an oxygen radical source, thereby forming a high-density oxide film at high speed and low temperature. A film-forming method using a general drum-type RAS film-forming apparatus will be described.

[0100] 20 is a schematic cross-sectional view of a drum-type film forming apparatus for the RAS method as seen from above. The film forming apparatus 80 includes a drum 81, a radical source 82, a first target 83, and a second target 84. The film forming apparatus 80 may be divided into regions by walls 85. The region near the first target 83, which is divided by the wall 85, is referred to as a first region 86. The region near the second target 84, which is divided by the wall 85, is referred to as a second region 87. The region near the radical source 82, which is divided by the wall 85, is referred to as a third region 88. A material for an optical function layer is disposed on the first target 83 and the second target 84.

[0101] The drum 81 rotates in the direction of the arrow in FIG. 20 while holding the plurality of substrates 41. As a result, the substrates 41 are transported to a first region 86. In the first region, for example, argon gas is supplied, and the first targets 83 are sputtered, and a film of the first targets 83 is formed on the substrates 41. As the drum 81 rotates, the substrates 41 are transported to a second region 87. As in the first region, for example, argon gas is supplied in the second region as well, and the second targets 84 are sputtered, and a film of the second targets 84 is formed on the substrates 41. Note that sputtering may be performed only in the first region 86, and only the first targets 83 may be formed on the substrates 41.

[0102] Thereafter, by the rotation of drum 81, substrate 41 is transported to third region 88. In the third region, for example, argon gas, oxygen gas, nitrogen gas, etc. are supplied as needed. When plasma comes into contact with the film on substrate 41, oxidation, nitridation reactions, etc. proceed, and a film of oxide, nitride, etc. of the target is formed on substrate 41.

[0103] However, as mentioned above, it was found that the filter fabricated using this film formation method exhibits polarization dependence of transmittance for perpendicularly incident light. This is thought to be because, during film formation, the substrate 41 moves only in a specific direction as the drum 81 rotates, which creates directionality in the film that is formed. In contrast, as mentioned above, it is thought that the polarization dependence of the filter's transmittance for perpendicularly incident light can be reduced by arranging the two films so that the directionality cancels out. Furthermore, it is thought that the polarization dependence of the filter's transmittance for perpendicularly incident light can be reduced by eliminating the movement of the substrate 41 only in a specific direction during film formation.

[0104] Next, the method for producing the filter or filter unit shown below will be described in order. (1) Manufacturing method of the filter 40 shown in FIG. 5 (2) Manufacturing method of the filter 40 shown in FIG. 6 (3) A manufacturing method of a filter 92 having only one fifth optical function layer 93 on a substrate 41 (4) Manufacturing method of the filter unit 44 shown in FIG. 18

[0105] (1) Manufacturing method of the filter 40 shown in FIG. 5 21 is a flow diagram of each step of the manufacturing methods (1) and (2). The manufacturing method (1) includes a first layering step S1, a rotating step S2, and a second layering step S3.

[0106] In the first layer-forming step S1, the first optical functional layer is formed on the surface of a substrate 41 that moves in a specific direction relative to a target that is the material of the first optical functional layer .

[0107] 22 is a view of the substrate 41 held by the drum 81 as seen from the opposing target during the first layering step S1. The straight arrow in FIG. 22 indicates the direction of movement of the substrate 41 as the drum 81 rotates. At this time, a mark 90 indicating the direction of movement is attached to the substrate 41. A first optical function layer 42 is formed on the surface of the substrate 41.

[0108] In the rotation process S2, when the back surface of the substrate 41 is inverted to face the target, which is the material of the second optical functional layer 43, the substrate is rotated so that the center of the substrate 41 is the rotation center 91 and is within a range of 90°±30° relative to a specific direction.

[0109] FIG. 23 is a view of the substrate 41 held by the drum 81 after the rotation step S2, as viewed from the opposing target. The straight arrow in FIG. 23 indicates the movement direction of the substrate 41 as the drum 81 rotates. In the rotation step S2, first, the substrate 41 is turned over so that the back surface of the substrate 41 faces the target. Then, the substrate 41 is rotated within a range of 90°±30° in the movement direction, with the center of the substrate 41 as the rotation center 91. Note that in FIG. 23, the substrate 41 is rotated by 90° as an example.

[0110] However, the direction of the high transmittance axis 61 of the first optical functional layer 42 formed in the first layering process may vary depending on the layering (film-forming) conditions, the mounting method of the substrate 41, and other factors. Specifically, there may be a variation of approximately ±20° between the direction of the high transmittance axis 61 and the rotation direction of the drum 81. If this variation occurs, even if the substrate 41 is rotated by, for example, 90°, the angle at which the high transmittance axis 61 and the high transmittance axis 62 intersect will not be 90°. Therefore, in the rotation process S2, the rotation angle may be adjusted as appropriate. By adjusting the rotation angle, a filter 40 can be manufactured in which the first high transmittance axis 61 and the second high transmittance axis 62 intersect at a desired angle. Specifically, first, the transmittance or reflectance is measured using the method described above, and the high transmittance axis 61 of the first optical functional layer 42 formed in the first layering process is set (high transmittance axis setting process). Next, the rotation angle of the substrate 41 after being turned over is calculated from the relationship between the high transmittance shaft 61 and the rotation direction of the drum 81 (rotation angle calculation step). The substrate 41 is turned over and rotated by the calculated angle (rotation step S2).

[0111] In the second layering step S3, the second optical functional layer 43 is formed on the back surface of the substrate 41. This makes it possible to manufacture the filter 40 having the first optical functional layer 42 on the front surface of the substrate 41 and the second optical functional layer 43 on the back surface.

[0112] (2) Manufacturing method of the filter 40 shown in FIG. 6 The manufacturing method (2) includes a first layering step S1, a rotating step S2, and a second layering step S3.

[0113] In the first layering step S1, similar to the first layering step S1 of manufacturing method (1), the first optical functional layer 42 is formed on the surface of the substrate 41 which moves in a specific direction relative to a target which is the material of the first optical functional layer 42.

[0114] In the rotation step S2, the substrate 41 is rotated within a range of 90°±30° with respect to a specific direction, with the center of the substrate 41 serving as the rotation center 91. In other words, in the rotation step S2 of the manufacturing method (2), unlike the rotation step S2 of the manufacturing method (1), the substrate 41 is not flipped over. Other than not being flipped over, the rotation step S2 is the same as the rotation step S2 of the manufacturing method (1), and the rotation angle may be adjusted as appropriate as described above.

[0115] In the second layering process S3, the second optical functional layer 43 is formed on the first optical functional layer 42. This makes it possible to manufacture the filter 40 having the first optical functional layer 42 and the second optical functional layer 43 stacked on one surface of the substrate 41.

[0116] (3) A method for manufacturing a filter having only one fifth optical function layer 93 on a substrate 41 24 is a schematic cross-sectional view of an example of a filter 92 manufactured by manufacturing method (3). The filter 92 manufactured by manufacturing method (3) does not correspond to the filter 40 having the above configuration, but can reduce the polarization dependency of the transmittance for perpendicularly incident light. The filter 92 has a fifth optical function layer 93 on either the incident surface 41a side or the exit surface 41b side of the substrate 41.

[0117] The manufacturing method (3) includes a third layering step in which the substrate 41, which moves in a specific direction relative to a target that is the material of the fifth optical functional layer 93, is rotated in a specific direction around the center of the substrate 41 as the rotation center 91, thereby forming the fifth optical functional layer 93 on the surface of the substrate 41.

[0118] FIG. 25 is a view of the substrate 41 held by the drum 81 during the third layering step, as viewed from the opposing target. The straight arrow in FIG. 25 indicates the movement direction of the substrate 41 as the drum 81 rotates. The circular arrow in FIG. 25 indicates the rotation direction of the substrate 41. In the third layering step, the substrate 41 is rotated at a constant speed in the movement direction, with its center serving as the rotation center 91, to form a fifth optical functional layer 93 on the surface of the substrate 41. In other words, the substrate 41 moves in the direction of the straight arrow while rotating in the direction of the circular arrow. As a result, the formed fifth optical functional layer 93 does not have a high transmittance axis, and therefore, even if it is only one layer, the polarization dependence of the transmittance for perpendicularly incident light can be reduced.

[0119] (4) Manufacturing method of the filter unit 44 shown in FIG. 18 26 is a flow diagram of each step of the manufacturing method (4). The manufacturing method (4) includes a first optical filter manufacturing step S4, a second optical filter manufacturing step S5, and an arrangement step S6.

[0120] In the first optical filter manufacturing process S4, third optical functional layers 51a, 51b are formed on the surface of a first substrate 47 that moves in a specific direction relative to a target, which is the material of the first optical functional layer 42, to manufacture a first filter 45.

[0121] In the second optical filter manufacturing process S5, fourth optical functional layers 52a, 52b are formed on the surface of a second substrate 48 that moves in a specific direction relative to a target, which is the material of the second optical functional layer 43, to manufacture a second filter 46.

[0122] In the first optical filter fabrication step S4 and the second optical filter fabrication step S5, the first substrate 47 and the second substrate 48 are marked with marks indicating the movement direction, as in the first layering step S1 of the manufacturing method (1).

[0123] In the arrangement step S6, the first filter 45 and the second filter 46 are arranged so that the angle between the mark indicating the movement direction of the first substrate 47 and the mark indicating the movement direction of the second substrate 48 is within the range of 90°±30°. This allows the manufacture of a filter unit 44 including the first filter 45 having the first optical functional layer 42 and the second filter 46 having the second optical functional layer 43. Note that, from the viewpoint of more effectively canceling out the polarization dependency, it is preferable that the first filter 45 and the second filter 46 are manufactured in the same batch. Alternatively, the transmittance or reflectance may be measured using the above-described method, and the high transmittance axis 63 of the first filter 45 and the high transmittance axis 64 of the second filter 46 may be set, and the filters may be arranged so that the angle between the high transmittance axis 63 and the high transmittance axis 64 is a desired angle.

[0124] This embodiment can also be applied to sputtering methods or vacuum deposition methods other than the RAS method, since it is believed that directionality occurs in the film formed in an apparatus that moves or rotates the substrate in a specific direction during film formation. [Example]

[0125] A filter (a) of a comparative example and a filter (b) having the configuration shown in FIG. 5 were fabricated. In both filters (a) and (b), a first optical functional layer 42 was disposed on the incident surface 41a side and a second optical functional layer 43 was disposed on the exit surface 41b side, with a substrate 41 interposed therebetween. The first optical functional layer 42 and the second optical functional layer 43 were layers having the same configuration. Filter (a) was fabricated using the same procedure as manufacturing method (1) above, except that in the rotation step S2, the substrate 41 was simply inverted but not rotated. Filter (b) was fabricated using manufacturing method (1) above. Note that in the rotation step S2 for filter (b), after the substrate 41 was inverted, it was rotated 90° in the moving direction with the center of the substrate 41 as the rotation center 91.

[0126] (Confirmation of polarization dependency in filters) The polarization dependence of transmittance for perpendicularly incident light was measured for filters (a) and (b) using the procedure described above. As a result, for filter (a), the transmittance varied when the rotation angle of filter (a) was changed, and a sinusoidal curve was obtained for the relationship between the rotation angle of filter (a) and the rate of change in transmittance. For filter (b), the transmittance varied when the rotation angle of filter (b) was changed, but the rate of change was smaller than that of filter (a).

[0127] (Confirmation of polarization dependence in the optical functional layer only) In addition to filters (a) and (b), a measurement filter was fabricated by forming only the first optical functional layer 42 on a separate substrate. The polarization dependence of the transmittance of the measurement filter for perpendicularly incident light was measured using the procedure described above. As a result, the transmittance varied as the rotation angle of the first optical functional layer 42 was changed, and a sine curve was obtained for the relationship between the rotation angle of the first optical functional layer 42 and the rate of change in transmittance. When the obtained sine curve was superimposed on a sine curve with a phase angle shifted by 90°, it was confirmed that the sine waves canceled each other out. Therefore, in filter (b), the first optical functional layer 42 and the second optical functional layer 43 were positioned so that the high transmittance axes determined from the sine curves intersected at 90°, which is thought to have canceled out the sine waves and reduced polarization dependence.

[0128] The reflectances of the front surface (surface of the first optical functional layer 42) and back surface (surface of the second optical functional layer 43) of the filters (a) and (b) were measured using the procedure described above.

[0129] Figure 27 is a graph showing the relationship between the rotation angle of filter (a) and the rate of change in reflectance. Each point on the graph represents an actual measurement, and the dotted line represents a fitting curve applied to the actual measurement. As shown in Figure 27, the fitting curve for the front surface and the fitting curve for the back surface are nearly identical, and it can be seen that the high reflectance axis set from the curves also nearly coincides.

[0130] Figure 28 is a graph showing the relationship between the rotation angle of filter (b) and the rate of change in reflectance. Each point on the graph is an actual measurement value, and the dotted line is a fitting curve applied to the actual measurement values. As shown in Figure 28, the fitting curve for the front surface and the fitting curve for the back surface are out of phase with each other by approximately 90°, and when they are superimposed, they almost cancel each other out. It can also be seen that the angle at which the high reflectance axis set from the curves intersects is approximately 90°.

[0131] In this embodiment, an optical filter 40 having optical transmittance characteristics or optical reflectance characteristics for a predetermined wavelength range includes a first optical functional layer 42 and a second optical functional layer 43 whose transmittance varies depending on the polarization direction when linearly polarized light is perpendicularly incident. The first optical functional layer 42 and the second optical functional layer 43 each have a high transmittance axis determined from the polarization direction in which the transmittance is highest when linearly polarized light is perpendicularly incident. The first optical functional layer 42 and the second optical functional layer 43 are arranged so that the angle between the high transmittance axes is within a range of 90°±30°. This cancels out the polarization dependency of the transmittance of perpendicularly incident light in the optical function layer, thereby reducing the polarization dependency of the filter 40.

[0132] This embodiment includes a substrate 41 that supports a first optical functional layer 42 and a second optical functional layer 43, with the first optical functional layer 42 disposed on one surface of the substrate 41 and the second optical functional layer 43 disposed on the other surface of the substrate 41. This cancels out the polarization dependence of the transmittance of perpendicularly incident light in the optical functional layers, thereby reducing the polarization dependence of the filter 40.

[0133] This embodiment includes a substrate 41 that supports the first optical functional layer 42 and the second optical functional layer 43, and the first optical functional layer 42 and the second optical functional layer 43 are laminated on either side of the substrate 41. This allows the polarization dependence of the transmittance of perpendicularly incident light in the optical functional layers to cancel each other out, thereby reducing the polarization dependence of the filter 40.

[0134] In this embodiment, when the layer with the larger difference between the maximum transmittance and the average transmittance is the first optical functional layer 42 and the layer with the smaller difference is the second optical functional layer 43, the following formula (1) is satisfied. Equation (1) (T2 max -T2 ave ) / (T1 max -T1 ave )≧1 / 2 In the formula, T1 max and T1 ave represent the maximum transmittance and the average transmittance of the first optical functional layer, respectively, and T2 max and T2 ave represent the maximum transmittance and the average transmittance of the second optical functional layer, respectively. This more effectively cancels out the polarization dependency of the transmittance of perpendicularly incident light in the optical function layer, thereby reducing the polarization dependency of the filter 40.

[0135] In this embodiment, the filter 40 is a neutral density filter, which can reduce the influence of polarization dependency in a device equipped with the filter 40.

[0136] In this embodiment, the filter 40 is a wavelength filter, which can reduce the influence of polarization dependency in a device equipped with the filter 40.

[0137] In this embodiment, the minimum value of the transmittance when the polarization direction is changed in the case of vertical incidence of linearly polarized light is T min , the maximum value is T max When this is the case, the above formula (2) is satisfied. Equation (2) (T min / T max ) × 100 [%] ≥ 95 [%] This makes it possible to reduce the influence of polarization dependency in an apparatus equipped with a filter 40 that does not have polarization characteristics.

[0138] In this embodiment, an optical filter 40 having optical transmittance or reflectance characteristics for a predetermined wavelength range includes a first optical functional layer 42 and a second optical functional layer 43 whose reflectance varies with the polarization direction for linearly polarized light perpendicularly incident thereon, and a substrate 41 supporting the first optical functional layer 42 and the second optical functional layer 43. The first optical functional layer 42 is disposed on one side of the substrate 41, and the second optical functional layer 43 is disposed on the other side of the substrate 41. The first optical functional layer 42 and the second optical functional layer 43 each have a high-reflectance axis determined by the polarization direction with the highest reflectance for linearly polarized light perpendicularly incident thereon. The first optical functional layer 42 and the second optical functional layer 43 are disposed such that the angle between the high-reflectance axes is within a range of 90°±30°. This cancels out the polarization dependence of the transmittance for perpendicularly incident light in the optical functional layers, thereby reducing the polarization dependence of the filter 40.

[0139] In this embodiment, the method for manufacturing the filter 40 includes a first layering step S1, a rotation step S2, and a second layering step S3. The first layering step S1 forms the first optical functional layer 42 on the surface of the substrate 41, which moves in a specific direction relative to a target, which is the material for the first optical functional layer 42. The rotation step S2 rotates the substrate 41 around the center of the substrate 41 as a rotation center 91, rotating it within a range of 90°±30° relative to the specific direction when the back surface of the substrate 41 is inverted to face the target, which is the material for the second optical functional layer 43. The second layering step S3 forms the second optical functional layer 43 on the back surface of the substrate 41. This cancels out the film directionality caused by the substrate 41 moving only in the specific direction, thereby reducing the polarization dependency of the filter 40.

[0140] In this embodiment, the method for manufacturing the filter 40 includes a first layering step S1, a rotation step S2, and a second layering step S3. The first layering step S1 forms the first optical functional layer 42 on the surface of a substrate 41 that moves in a specific direction relative to a target, which is the material of the first optical functional layer 42. The rotation step S2 rotates the substrate 41 around the center of the substrate 41 as a rotation center 91 so that the angle is within a range of 90°±30° relative to the specific direction. The second layering step S3 forms the second optical functional layer 43 on the first optical functional layer 42. This allows the film directionality caused by the substrate 41 moving only in the specific direction to be canceled out, thereby reducing the polarization dependency of the filter 40.

[0141] In this embodiment, a method for manufacturing a filter 92 including a fifth optical functional layer 93 having light transmittance or light reflectance characteristics for a predetermined wavelength range includes a third layering step. In the third layering step, the fifth optical functional layer 93 is formed on the surface of the substrate 41 while the substrate 41, which moves in a specific direction relative to a target that is the material of the fifth optical functional layer 93, is rotated in a specific direction around the center of the substrate 41 as the rotation center 91. This prevents the substrate 41 from moving only in a specific direction during film formation, and reduces the polarization dependency of the filter 92.

[0142] In this embodiment, the optical filter unit 44 includes a first filter 45 and a second filter 46, each having optical transmittance or reflectance characteristics for a predetermined wavelength range. The first filter 45 includes a first substrate 47 and a first optical functional layer 42 supported by the first substrate 47, whose transmittance varies with the polarization direction for linearly polarized light perpendicularly incident thereon. The second optical filter 46 includes a second substrate 48 and a second optical functional layer 43 supported by the second substrate 48, whose transmittance varies with the polarization direction for linearly polarized light perpendicularly incident thereon. The first optical functional layer 42 and the second optical functional layer 43 each have a high transmittance axis determined by the polarization direction with the highest transmittance for linearly polarized light perpendicularly incident thereon. The first filter 45 and the second filter 46 are positioned so that the intersecting angle of the high transmittance axes is within a range of 90°±30°. This cancels out the polarization dependence of the transmittance for perpendicularly incident light in the optical functional layers, thereby reducing the polarization dependence of the filter unit 44.

[0143] In this embodiment, the method for manufacturing the filter unit 44 includes a first optical filter fabrication step S4, a second optical filter fabrication step S5, and an arrangement step S6. In the first optical filter fabrication step S4, the first optical functional layer 42 is formed on the surface of a first substrate 47, which moves in a specific direction relative to a target, the material of the first optical functional layer 42, to produce a first filter 45. In the second optical filter fabrication step S5, the second optical functional layer 43 is formed on the surface of a second substrate 48, which moves in a specific direction relative to a target, the material of the second optical functional layer 43, to produce a second filter 46. In the arrangement step S6, the first filter 45 and the second filter 46 are arranged so that the angle between the specific direction of movement of the first substrate 47 and the specific direction of movement of the second substrate 48 is within a range of 90°±30°. This allows the film directionality caused by the movement of the first substrate 47 and the second substrate 48 only in the specific direction to be canceled out, thereby reducing the polarization dependency of the filter unit 44.

[0144] In this embodiment, the optical measurement device 10 is equipped with a filter 40 or a filter unit 44. This makes it possible to reduce measurement errors that depend on the polarization direction of the light to be measured.

[0145] In this embodiment, the optical measurement device 10 has an insertion / removal device that inserts or removes the filter 40 or filter unit 44 into or from the optical path of the light to be measured, thereby reducing measurement errors that occur due to insertion or removal.

[0146] In this embodiment, the optical measurement device 10 measures the luminance or chromaticity of the object to be measured, thereby reducing measurement errors that depend on the polarization direction of the light to be measured.

[0147] In addition, the detailed configuration and operation of each device constituting the optical characteristic measuring device can be modified as appropriate without departing from the spirit of the present invention. [Explanation of symbols]

[0148] 1 Object to be measured 2 Light to be measured 4 Optical Filters 5 Insertion / extraction device 10 Optical measurement device 11 Objective optical system 11a Convex lens 11b Aperture diaphragm 12 Branching optical system 13 Colorimetric optical system 131a, 131b, 131c color filters 132a, 132b, 132c Light receiving sensors 14 Electrical processing section 15 Control Unit 20 Diffuser 40 Optical Filters 41 PCB 41a Incidence plane 41b Output surface 42 1st optical functional layer 43 Second optical functional layer 44 Optical filter unit 45 First Optical Filter 46 Second Optical Filter 47 First board 47a Entrance plane 47b Exit surface 48 Second board 48a Entrance plane 48b Output surface 50 Measurement filter 51a,51b Third optical functional layer 52a,52b 4th optical functional layer 61 High transmittance axis of the first optical functional layer 62 High transmittance axis of the second optical functional layer 63 High transmittance axis of the third optical functional layer 64 High transmittance axis of the fourth optical functional layer 70 Measuring Equipment 71 Optical Measuring Instruments 72 Planar light source 73 Polarizing Plate 74 Rotating Stage 75 Illumination 76 Reflected light 77 Stage rotation axis 80 Film deposition equipment 81 Drums 82 Radical Source 83 First Target 84 Second Target 85 Wall 86 First area 87 Second area 88 Third area 90 Movement direction mark 91 Center of rotation 92 filters 93 5th optical functional layer 202 Light source 203 Polarizing Plate 204 Thin Film Filter 205 Receiver L light P intersection

Claims

1. An optical filter having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, a first optical functional layer and a second optical functional layer whose transmittance varies in the polarization direction when linearly polarized light is perpendicularly incident; the first optical functional layer and the second optical functional layer each have a high transmittance axis determined from a polarization direction in which the transmittance is highest when linearly polarized light is perpendicularly incident, An optical filter, wherein the first optical functional layer and the second optical functional layer are arranged so that the angle at which the high transmittance axes intersect is within a range of 90°±30°.

2. a substrate supporting the first optical functional layer and the second optical functional layer; The optical filter according to claim 1 , wherein the first optical function layer is disposed on one surface of the substrate, and the second optical function layer is disposed on the other surface of the substrate.

3. a substrate supporting the first optical functional layer and the second optical functional layer; The optical filter according to claim 1 , wherein the first optical functional layer and the second optical functional layer are laminated on either one surface of the substrate.

4. An optical filter described in any one of claims 1 to 3, wherein when the layer with a larger difference between the maximum transmittance and the average transmittance is the first optical functional layer and the layer with a smaller difference is the second optical functional layer, the following formula (1) is satisfied. Formula (1) (T2 ｍａｘ -T2 ａｖｅ ) / (T1 ｍａｘ -T1 ａｖｅ )≧1 / 2 In the formula, T1 ｍａｘ and T1 ａｖｅ represent the maximum transmittance and the average transmittance of the first optical functional layer, respectively, and T2 ｍａｘ and T2 ａｖｅ represent the maximum transmittance and the average transmittance of the second optical functional layer, respectively.

5. The optical filter according to claim 1 , wherein the optical filter is a neutral density filter.

6. The optical filter according to claim 1 , wherein the optical filter is a wavelength filter.

7. The minimum transmittance when the polarization direction is changed for linearly polarized light perpendicular to the incident light is T ｍｉｎ , the maximum value is T ｍａｘ 4. The optical filter according to claim 1, which satisfies the following formula (2): Formula (2) (T ｍｉｎ / T ｍａｘ )×100[%]≧95[%]

8. An optical filter having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, a first optical functional layer and a second optical functional layer whose reflectance varies in the polarization direction when linearly polarized light is perpendicularly incident; a substrate supporting the first optical functional layer and the second optical functional layer, the first optical functional layer is disposed on one surface side of the substrate, and the second optical functional layer is disposed on the other surface side of the substrate; the first optical functional layer and the second optical functional layer each have a high reflectance axis determined from a polarization direction in which reflectance is highest when linearly polarized light is perpendicularly incident, An optical filter, wherein the first optical functional layer and the second optical functional layer are arranged so that the angle at which the high reflectance axes intersect is within a range of 90°±30°.

9. A method for producing the optical filter according to claim 1 or 2, comprising the steps of: a first layering step of forming the first optical functional layer on a surface of a substrate that moves in a specific direction relative to a target that is a material of the first optical functional layer; a rotation step of rotating the substrate around a center of the substrate as a rotation center within a range of 90°±30° with respect to the specific direction when the substrate is inverted so that the rear surface thereof faces a target which is the material of the second optical functional layer; a second layering step of forming the second optical functional layer on the rear surface of the substrate.

10. A method for producing the optical filter according to claim 1 or 3, comprising the steps of: a first layering step of forming the first optical functional layer on a surface of a substrate that moves in a specific direction relative to a target that is a material of the first optical functional layer; a rotating step of rotating the substrate around the center of the substrate as a rotation center so that the angle is within a range of 90°±30° with respect to the specific direction; a second layering step of forming the second optical functional layer on the first optical functional layer.

11. A method for manufacturing an optical filter including a fifth optical functional layer having a light transmittance characteristic or a light reflectance characteristic for a predetermined wavelength range, A method for manufacturing an optical filter, comprising a third layering step of forming the fifth optical functional layer on a surface of a substrate while rotating the substrate, which moves in a specific direction relative to a target that is the material of the fifth optical functional layer, with the center of the substrate as the center of rotation, in the specific direction.

12. An optical filter unit including a first optical filter and a second optical filter having light transmittance characteristics or light reflectance characteristics for a predetermined wavelength range, the first optical filter includes a first substrate and a first optical function layer supported by the first substrate, the first optical function layer having a transmittance that varies in a polarization direction when linearly polarized light is perpendicularly incident; the second optical filter includes a second substrate and a second optical function layer supported by the second substrate, the second optical function layer having a transmittance that varies in a polarization direction when linearly polarized light is perpendicularly incident, the first optical functional layer and the second optical functional layer each have a high transmittance axis determined from a polarization direction in which the transmittance is highest when linearly polarized light is perpendicularly incident, An optical filter unit, wherein the first optical filter and the second optical filter are arranged so that the angle at which the high transmittance axes intersect is within a range of 90°±30°.

13. A method for manufacturing the optical filter unit according to claim 12, comprising the steps of: a first optical filter fabrication step of forming the first optical functional layer on a surface of a first substrate that moves in a specific direction relative to a target that is a material of the first optical functional layer, thereby fabricating the first optical filter; a second optical filter fabrication step of forming the second optical functional layer on a surface of a second substrate that moves in a specific direction relative to a target that is a material of the second optical functional layer, thereby fabricating the second optical filter; and arranging the first optical filter and the second optical filter so that an angle between a specific direction moved in the first substrate and a specific direction moved in the second substrate is within a range of 90°±30°.

14. An optical measurement device equipped with the optical filter according to any one of claims 1 to 3 or the optical filter unit according to claim 12.

15. 15. The optical measurement device according to claim 14, further comprising an insertion / removal device that inserts the optical filter or the optical filter unit into or removes the optical filter or the optical filter unit from the optical path of the light to be measured.

16. The optical measurement device according to claim 14, which measures luminance or chromaticity of an object to be measured.

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