JP2008158036A - Optical element and optical instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a spectral transmittance characteristic hard to change even when an incident angle of light changes in an optical element and an optical instrument. <P>SOLUTION: The optical element 10 comprises a substrate 11 and an optical thin film 12 which is constituted by forming two or more layers on a surface of the substrate 11. The optical thin film 12 is equipped with an optical thin film 13 which is constituted by alternately laminating a high refractive index layer 13H having a relatively high refractive index and a low refractive index layer 13L having a relatively low refractive index. The high refractive index layer 13H is made of a material having a refractive index of ≥2.0 at a wavelength of 500 nm and the low refractive index layer 13L adjoining the high refractive index layer 13H is made of a material having refractive index difference of ≤0.4 from the material of the high refractive index layer 13H. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element in which an optical thin film is formed on a substrate, and an optical apparatus including the optical element.

  Solid-state imaging devices such as CCD (Charge Coupled Device) built in digital cameras, microscopes, endoscopes, etc. are silicon semiconductor devices that convert video (light) into electrical signals, and are sensitive to the near infrared (IR) region. Have When light is incident on the CCD, near-infrared light as well as visible light is captured as an image, and a problem such as generation of a pseudo color in the obtained image occurs. Therefore, in order to make only visible light captured by the lens group enter the CCD and convert it into an electrical signal, it is common to pass an IR cut filter between the CCD and the lens group. The spectral transmittance characteristic of the IR cut filter has an important factor in determining the color reproducibility of an image obtained through a CCD such as a digital camera.

Currently, the IR cut filter used in most digital cameras is an optical low-pass filter that uses a birefringent plate such as quartz or lithium niobate as a substrate material by a generally known vacuum deposition method or sputtering method. For example, layers made of a high refractive index material such as TiO ₂ , Ta ₂ O ₅ and Nb ₂ O ₅ and layers made of a low refractive index material such as SiO ₂ and MgF ₂ are alternately laminated. An optical thin film formed is used.

Such an IR cut filter reflects near infrared rays (unnecessary light) using light interference and transmits visible light (necessary light). Further, this IR cut filter can be formed on the surface of a large number of substrates, and is suitable for miniaturization of optical equipment because of the thin film.
On the other hand, such an IR cut filter made of an optical thin film has a characteristic that the spectral transmittance characteristic changes greatly with respect to the change in the incident angle of light.
For example, TiO ₂ with a refractive index of 2.4 is adopted as a high refractive index material, and SiO ₂ with a refractive index of 1.46 is adopted as a low refractive index material with a refractive index difference of 0.94. When the incident angle is 0 °, the spectral transmittance characteristics of the IR cut filter in which 44 layers made of the respective materials are alternately laminated, as shown by the curve 200 in FIG. 9, the transmittance is substantially in the wavelength range of 400 nm to 645 nm. 100% flat change, wavelength 665 nm to 1100 nm shows a flat change of transmittance of about 0%, and wavelength 645 nm to 665 nm in the middle of these wavelength bands has a transmittance of about 100% to about 0%. It shows a characteristic that decreases almost linearly. When the incident angle of light passing through this filter is changed from 0 ° to 20 °, as shown by a curve 201 in FIG. 9, the transmittance is about 100% in the visible region and approximately 0% in the near infrared region. Although it is the same, the wavelength band in which the transmittance changes from approximately 100% to approximately 0% is shifted by 12 nm toward the short wavelength side.
In other words, the wavelength component to be transmitted differs depending on the angle of the light incident on the IR cut filter. If this IR cut filter is placed in front of a CCD such as a digital camera, the color reproducibility of the image changes. was there.

For this reason, Patent Document 1 uses an optical element in which a resin focusing lens is arranged on the incident side of a dielectric multilayer filter made of an optical thin film whose spectral transmittance characteristics change depending on the incident angle, and is incident on the optical thin film. An optical apparatus has been proposed in which the incident angle of light to be transmitted is kept as small as possible so that the influence of the angle dependency of the optical thin film is reduced and the transmitted light is guided to the fixed image sensor device.
Japanese Patent Laying-Open No. 2005-234038 (FIGS. 2 and 3)

However, such conventional optical elements and optical devices have the following problems.
In the technique described in Patent Document 1, since the influence of the angle dependency of the optical thin film is reduced by adding a focusing lens without improving the angle dependency itself with respect to the incident angle of the dielectric multilayer filter, There is a problem in that the number of points increases, leading to an increase in the cost of optical equipment.
In addition, a space in the direction of the optical axis is required to dispose the focusing lens, and there is a problem that it becomes an obstacle to miniaturization of optical equipment such as a digital camera.

  The present invention has been made in view of the above problems, and an object thereof is to provide an optical element capable of improving the angle dependency of spectral transmittance characteristics with a compact configuration and an optical apparatus including the same. To do.

In order to solve the above problems, an optical element according to one aspect of the present invention is an optical element having a base material and an optical thin film in which a plurality of layers are formed on the surface of the base material. The spectral transmittance characteristics of the optical thin film include a first wavelength band having a transmittance of 75% or more and an average transmittance of 90% or more, a second wavelength band having a transmittance of 5% or less, and the first wavelength. A third wavelength band in which the transmittance changes from 75% to 5% between the band and the second wavelength band, and changing the incident angle of light from 0 ° to 20 °, The wavelength band of 3 moves to the short wavelength side, and the movement amount is 10 nm or less.
According to the present invention, the movement amount of the third wavelength band when the incident angle of light is changed from 0 ° to 20 ° is 10 nm or less on the short wavelength side. Changes are reduced. Since the angle dependence of the spectral transmittance characteristics of the optical thin film itself is reduced in this way, the angle dependence of the spectral transmittance characteristics of the optical element is improved without changing the incident angle using, for example, a focusing lens. can do.

An optical element according to another aspect of the present invention is an optical element having a base material and an optical thin film having a plurality of layers formed on the surface of the base material, wherein the optical thin film has a relatively high height. A high refractive index layer having a refractive index and a low refractive index layer having a relative low refractive index are alternately laminated, and the high refractive index layer has a refractive index of 2.0 at a wavelength of 500 nm. The low refractive index layer made of the above material and adjacent to the high refractive index layer is made of a material having a refractive index difference of 0.4 or less from the material of the high refractive index layer.
According to the present invention, the optical thin film of the optical element is configured by alternately laminating a high refractive index layer having a relatively high refractive index and a low refractive index layer having a relatively low refractive index. The refractive index layer is made of a material having a refractive index of 2.0 or more at a wavelength of 500 nm, and the low refractive index layer adjacent to the high refractive index layer has a refractive index difference of 0. 0 with respect to the material of the high refractive index layer. Since the configuration is made of a material that is 4 or less, the difference in spectral transmittance characteristics between the S-polarized light and the P-polarized light transmitted through the optical thin film can be reduced. As a result, the angle dependence of the spectral transmittance characteristics of the optical element can be improved without changing the incident angle using, for example, a focusing lens.

In the optical element of the present invention, all or part of the optical thin film may be made of a material in which two or more kinds of substances are mixed.
According to the present invention, in a layer made of a material in which two or more kinds of substances are mixed, the refractive index value of the material can be adjusted by changing the mixing ratio of these substances. It becomes easier to set the difference in rate.

An optical apparatus according to one embodiment of the present invention includes the optical element of the above invention.
According to this invention, since the optical element of the above invention is provided, the same effect as that of the above invention is provided.
In addition, since the angle dependency of the spectral transmission characteristics of the optical element can be reduced without using a focusing lens or the like, the number of parts of the optical element can be reduced, and the cost and size can be easily reduced.

  According to the optical element and the optical apparatus of the present invention, since the optical thin film having a small change in the spectral transmittance characteristic with respect to the change in the incident angle of light is provided, the angle dependency of the spectral transmittance characteristic can be improved with a compact configuration. There is an effect that can be done.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 is a schematic cross-sectional view showing a configuration of an optical element according to the first embodiment of the present invention. FIG. 2 is a graph showing the spectral reflectance characteristics of the antireflection film of the optical element according to the first embodiment of the present invention. The horizontal axis represents wavelength (nm), and the vertical axis represents reflectance (%). FIG. 3 is a graph showing the spectral transmittance characteristics of the optical element according to the first embodiment of the present invention. The horizontal axis represents wavelength (nm) and the vertical axis represents transmittance (%). Since FIG. 1 is a schematic diagram, the dimension in the thickness direction is exaggerated (the same applies to FIG. 4).

The optical element 10 according to this embodiment is a single-plate optical low-pass filter on which a so-called IR cut filter is formed, and an optical thin film 12 is formed on a substrate 11 (base material) as shown in FIG. It has been made.
A quartz birefringent substrate having a refractive index of 1.54 at a wavelength of 500 nm is used as the substrate 11, and an antireflection film 15 composed of five layers is formed on one surface (the lower side in the drawing) of the substrate 11. ing. Further, an optical thin film 12 in which two kinds of optical thin films 13 and 14 are laminated is formed on the other surface of the substrate 11 from the substrate 11 side.
In this specification, unless otherwise specified, the refractive index at a wavelength of 500 nm is used.

The antireflection film 15 prevents visible light from being reflected and transmits it satisfactorily, and is formed by a vacuum vapor deposition method using an appropriate optical thin film vacuum film forming apparatus. In this embodiment, Al ₂ O ₃ having a refractive index of 1.64, ZrO ₂ having a refractive index of 2.0, and MgF ₂ having a refractive index of 1.38 are formed on one surface of the substrate 11 heated to 300 ° C. in a high vacuum state. The five types of Al ₂ O ₃ , ZrO ₂ , MgF ₂ , ZrO ₂ , and MgF ₂ are laminated in this order.
As shown by a curve 100 in FIG. 2, the spectral reflectance characteristics of the antireflection film 15 are as follows: a reflectance of 0.7% or less at a wavelength of 400 nm to 670 nm, and a reflectance of 1.5% or less at a wavelength of 670 nm to 700 nm. It has the characteristic which becomes.

The optical thin film 13 is a multilayer thin film provided for determining the spectral transmittance characteristics in the wavelength band of the boundary region between visible light and near infrared light. In this embodiment, in order to form a spectral transmittance characteristic (hereinafter referred to as a transmittance gradient portion) in which the transmittance decreases substantially linearly as the wavelength increases, high refraction made of a material having a refractive index n _H is formed. The refractive index layer and the low refractive index layer made of a material having a refractive index n _L (where n _H > n _L ) are alternately stacked.
The transmittance slope portion in the spectral transmittance characteristics realized by such an optical thin film configuration has a characteristic that the wavelength band moves in parallel according to the incident angle when the incident angle of light changes (hereinafter referred to as wavelength shift). It has.
Therefore, in this embodiment, in order to reduce the wavelength shift amount of the transmittance gradient portion, the refractive index of each material is set to satisfy the following expressions (1) and (2).
n _H ≧ 2.0 (1)
n _H −n _L ≦ 0.4 (2)
However, Formula (2) is applied with respect to the refractive index between the adjacent high refractive index layer and low refractive index layer.

Here, the principle of reducing the wavelength shift amount will be described.
One of the causes that the incident angle dependency of the spectral transmittance characteristics of the optical thin film becomes large is the difference in the spectral transmittance characteristics between the S-polarized component and the P-polarized component with respect to the optical thin film. The value A in the following formula (3) is an index of the difference in spectral transmittance characteristics between S-polarized light and P-polarized light.

Here, n _L and n _H are the refractive indexes of the low refractive index layer and the high refractive index layer in the optical thin film, respectively, θ is the angle of incidence of light on the optical thin film, and n _S is the refractive index of the base material. Rate.

In Formula (3), when A = 1, it is a so-called McNeill's conditional expression. When the spectral transmittance characteristics of S-polarized light and P-polarized light are completely different, that is, the S-polarized component and the P-polarized component are completely different. The relationship of the refractive index in the case of separating is shown.
In order to reduce the difference in spectral transmittance characteristics between the S-polarized light component and the P-polarized light component, the inventor of the present application only needs to make the value of A in Expression (3) as small or larger than 1 as possible. If 1) and (2) are satisfied, when θ = 20 °, the value of A becomes 2.37 or more, and the difference in spectral transmittance characteristics between S-polarized light and P-polarized light can be reduced. It has been found that the wavelength shift amount of the spectral transmittance characteristic of the optical thin film 13 with respect to the incident angle can be reduced to a favorable range.
Here, the refractive index difference of the materials of the optical thin films that are alternately stacked is preferably 0.3 to 0.4, and the preferable value of the refractive index n _H is 2.2 to 2.4. Moreover, the value of A in Formula (3) should just be 2.37 or more (preferably 2.65-3.15).
In order to make the value of A smaller than 1, for example, if n _H = 1.38, θ = 20 °, and n _S = 1.54, n _L needs to be 0.57 or less. No optical thin film material having such a refractive index exists.

In particular, the refractive index difference in the case of producing an optical thin film as an IR cut filter having about 50 film layers may be 0.2 to 0.4 (preferably 0.3 to 0.4).
Regarding the IR cut filter, the range of the first wavelength band that transmits with the transmittance of 75% or more and the average transmittance of 90% or more may be 420 nm to 630 nm (preferably 400 nm to 645 nm). The range of the second wavelength band with a transmittance of 5% or less may be 700 nm to 1100 nm (preferably 665 nm to 1200 nm).
In this case, the spectral transmittance characteristic between the first wavelength band and the second wavelength band is formed with a transmittance gradient portion in which the transmittance varies from 75% to 5%, which is the third wavelength range. The wavelength band of 630 nm to 700 nm (preferably 645 nm to 665 nm).

For example, after a high refractive index material TiO ₂ having a refractive index of 2.4 is formed on a quartz crystal birefringent substrate having a refractive index of 1.54 with a physical film thickness of 80 nm, a low refractive index material SiO ₂ having a refractive index of 1.46 is formed. The film is formed with a film thickness of 132 nm. Further, when 16 layers of TiO ₂ and SiO ₂ are alternately laminated with the same film thickness, the spectral transmittance characteristics of the optical thin film at an incident angle of 0 ° are as follows: the first wavelength band is a wavelength of 400 nm to 645 nm, and the second The third wavelength band is 645 nm to 665 nm, and the third wavelength band is 665 nm to 665 nm.
At this time, as shown in Table 1 as a comparative example, the difference between n _H and n _L is 0.94, the value of A at θ = 20 ° is 2.368, and the S-polarized light with respect to the incident angle of light of 20 ° The difference in wavelength of the spectral transmittance characteristics of P-polarized light is 6 nm, and the wavelength shift amount of the transmittance gradient portion when the incident angle of light is changed from 0 ° to 20 ° is 12 nm toward the short wavelength side.

On the other hand, when the refractive index difference between the high refractive index material and the low refractive index material is 0.4 or less, for example, Ta ₂ O ₅ having a refractive index of 2.2 and Y ₂ O ₃ having a refractive index of 1.822 are physically changed. When 32 layers are alternately laminated on a quartz crystal birefringent substrate having a film thickness of 80 nm and 96 nm and a refractive index of 1.54, the spectral transmittance characteristics of the optical thin film at an incident angle of 0 ° is the wavelength of the first wavelength band. 400 nm to 645 nm, the second wavelength band is a wavelength of 665 nm to 750 nm, and the third wavelength band is a wavelength of 645 nm to 665 nm.
At this time, as shown in Numerical Example 1 in Table 1, the difference between n _H and n _L is 0.378, the value of A at θ = 20 ° is 2.66, and S-polarized light with respect to an incident angle of light of 20 °. The difference in wavelength between the spectral transmittance characteristics of the P-polarized light and the P-polarized light is 3 nm, and the wavelength shift amount of the transmittance gradient portion when the incident angle of light is changed from 0 ° to 20 ° can be 9 nm.
Also, for example, 140 layers of a mixed film of TiO ₂ having a refractive index of 2.4 and a refractive index of 2.3 are alternately placed on a quartz crystal birefringent substrate having a thickness of 72 nm and 69 nm and a refractive index of 1.54. In the case where the optical thin film is laminated, the spectral transmittance characteristics of the optical thin film at an incident angle of 0 ° are as follows: the first wavelength band is 400 nm to 649 nm, the second wavelength band is 655 nm to 670 nm, and the third wavelength band is The wavelength is 649 nm to 655 nm.
At this time, as shown as Numerical Example 2 in Table 1, the difference between n _H and n _L is 0.1, the value of A at θ = 20 ° is 3.15, and S-polarized light with respect to an incident angle of light of 20 ° The difference in wavelength between the spectral transmittance characteristics of the P-polarized light and the P-polarized light is 1 nm, and the wavelength shift amount of the transmittance inclined portion when the incident angle of light is changed from 0 ° to 20 ° can be 6 nm.
As described above, in Numerical Examples 1 and 2 that satisfy both of the expressions (1) and (2), the amount of wavelength shift can be reduced as compared with the comparative example that does not satisfy the expression (2), and the incident angle is 20 ° or less. The wavelength shift amount is 10 nm or less.

As shown in FIG. 1, the optical thin film 13 of the present embodiment has a high refractive index of Ta ₂ O ₅ having a refractive index of 2.2 on the surface opposite to the surface on which the antireflection film 15 is formed on the substrate 11. Twenty refractive index layers 13H and 20 low refractive index layers 13L made of Y ₂ O ₃ having a refractive index of 1.822 are alternately stacked. In this case, the refractive index difference between the high refractive index material and the low refractive index material is 0.378, and the value of A in Equation (3) is 2.66.
In order to form this optical thin film 13, the substrate 11 is heated to 300 ° C. using an appropriate optical thin film vacuum film forming apparatus, and when the pressure in the vacuum chamber reaches 6 × 10 ⁻⁴ Pa, The first vapor deposition material Y ₂ O ₃ of the optical thin film 13 was formed to a physical film thickness of 49 nm. Further, a second vapor deposition material Ta ₂ O ₅ of the optical thin film 13 was formed on the surface so as to have a physical film thickness of 74 nm. Similarly, 20 layers of Y ₂ O ₃ and Ta ₂ O ₅ were alternately formed with a physical film thickness as shown in Table 2 below by vacuum evaporation.

The optical thin film 14 is a multilayer thin film provided on the uppermost surface of the optical thin film 13 in order to determine the spectral transmittance characteristics in the near-infrared wavelength band. In the present embodiment, in order to reduce the near-infrared transmittance to 5% or less, the low refractive index layer 14L made of SiO ₂ having a refractive index of 1.46 and high refraction made of Ta ₂ O ₅ having a refractive index of 2.2. 27 layers of rate layers 14H are alternately stacked.
In order to form the optical thin film 14, the 20th Ta ₂ O ₅ film of the optical thin film 13 is completed, and then the first vapor deposition material SiO ₂ of the optical thin film 14 is formed on the optical thin film 13 with a physical film thickness. The film was formed to 142 nm. Further, a second vapor deposition material Ta ₂ O ₅ of the optical thin film 14 was formed on the surface so as to have a physical film thickness of 80 nm. Similarly, 27 layers of SiO ₂ and Ta ₂ O ₅ were alternately formed with a physical film thickness as shown in Table 3 by a vacuum evaporation method.

In the optical element 10 formed according to the present embodiment, spectral transmittance characteristics at wavelengths of 400 nm to 1100 nm at an incident angle of 0 ° and an incident angle of 20 ° are measured with a spectrophotometer U-4100 (manufactured by Hitachi, Ltd.). (The same applies to the measurement of the spectral transmittance characteristics below). The result is shown in FIG.
As shown by a curve 101 in FIG. 3, the optical element 10 is approximately 100% on the short wavelength side and approximately 0% on the long wavelength side at an incident angle of 0 °, and is transmitted in the boundary region between visible light and near infrared light. The spectral transmittance characteristic is such that the rate decreases substantially linearly from approximately 100% to approximately 0%. That is, a wavelength band having a transmittance of 75% or more and an average transmittance of 90% is formed at a wavelength of 400 nm to 645 nm, a wavelength band having a transmittance of 5% or less is formed at a wavelength of 665 nm to 1100 nm, and a wavelength that is a wavelength band therebetween A transmittance slope portion that decreases from 75% to 5% transmittance is formed at 645 nm to 665 nm. These wavelength bands constitute first, second, and third wavelength bands, respectively.

  At an incident angle of 20 °, as shown by a curve 102 in FIG. 3, the transmittance slope portion of the curve 101 undergoes a wavelength shift that translates by 9 nm toward the short wavelength side, and the other transmittance hardly changes. It is a rate characteristic. That is, the first, second, and third wavelength bands are 400 nm to 636 nm, 636 nm to 656 nm, and 656 nm to 1100 nm, respectively.

  Thus, according to the optical element 10 according to the present embodiment, the optical thin film 13 composed of the high refractive index material and the low refractive index material having a refractive index difference of 0.4 or less is formed on the substrate 11. The change in the spectral transmittance characteristics in the third wavelength band with respect to the incident angle of light can be reduced to 10 nm or less.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. In the following description, the same reference numerals are given to the components described in the first embodiment, and the description thereof is omitted.
FIG. 4 is a schematic cross-sectional view showing the configuration of the optical element according to the second embodiment of the present invention. FIG. 5 is a graph showing the spectral transmittance characteristics of one optical thin film used in the optical element according to the second embodiment of the present invention. FIG. 6 is a graph showing the spectral transmittance characteristics of the other optical thin film used in the optical element according to the second embodiment of the present invention. FIG. 7 is a graph showing the spectral transmittance characteristics of the optical element according to the second embodiment of the present invention. 5 to 7, the horizontal axis represents wavelength (nm) and the vertical axis represents transmittance (%).

The optical element 20 according to the present embodiment is a single-plate optical low-pass filter on which a so-called IR cut filter is formed, and an optical thin film 23 and an optical thin film 24 are formed on a substrate 11 as shown in FIG. It has been made.
On one surface (the lower side in the drawing) of the substrate 11, an optical thin film 23 for determining the spectral transmittance characteristics in the third wavelength band is formed. Further, the optical thin film 23 is formed by mixing a substance that Si0 ₂ and _Nb 2 _{O 5} at a predetermined ratio. Further, an optical thin film 24 for determining spectral transmittance characteristics in the second wavelength band is formed on the other surface of the substrate 11.

Optical thin film 23 of the present embodiment, as shown in FIG. 4, on one surface of the substrate 11, the refractive index and SiO ₂ having a refractive index of relatively low material and 1.46 is relatively a 2.330 A high refractive index layer 23H made of a high refractive index material in which Nb ₂ O ₅ , which is a high substance, is mixed at a ratio of 10:90, and a low ratio in which SiO ₂ and Nb ₂ O ₅ are mixed at a ratio of 50:50. 30 low-refractive index layers 23L made of a refractive index material are alternately stacked. In this case, the refractive index of the high refractive index material is n _H = 2.249, the refractive index of the low refractive index material is n _L = 1.903, and the refractive index difference between the high refractive index material and the low refractive index material is 0.346. The value of A when θ = 20 ° is 2.76.
Such an optical thin film 23 can be formed by sputtering.
First, the substrate 11 of the quartz crystal birefringent plate is heated to 100 ° C. by using an appropriate optical thin film vacuum film forming apparatus, and when the pressure in the vacuum chamber reaches 6 × 10 ⁻⁴ Pa, the substrate is formed by sputtering. A high refractive index layer 23H made of a high refractive index material mixed so that the ratio of SiO ₂ and Nb ₂ O ₅ is 10:90 is formed on the surface of the first layer so as to have a physical film thickness of 101 nm. A film was formed as an eye.
Further, a low refractive index layer 23L made of a low refractive index material in which SiO ₂ and Nb ₂ O ₅ are mixed at a ratio of 50:50 is formed on the surface of the high refractive index layer 23H by a sputtering method to obtain a physical film thickness of 69 nm. As a second layer, a film was formed.
Similarly, with a physical film thickness as shown in Table 4 below, 30 layers of high refractive index layers 23H and low refractive index layers 23L composed of a mixed film of SiO ₂ and Nb ₂ O ₅ are alternately formed by a sputtering method. A film was formed.

FIG. 5 shows the result of measuring the spectral transmittance characteristics of the optical thin film 23 thus manufactured in the same manner as in the first embodiment.
As shown by a curve 103 in FIG. 5, the optical thin film 23 has a distribution of about 100% on the short wavelength side and about 0% near the wavelength of 665 nm at an incident angle of 0 °, but has a distribution on the long wavelength side. In the boundary region between visible light and near-infrared light, the transmittance has a spectral transmittance characteristic such that the transmittance decreases substantially linearly from approximately 100% to approximately 0%. That is, a wavelength band having a transmittance of 75% or more and an average transmittance of 90% is formed at a wavelength of 400 nm to 645 nm, a wavelength band having a transmittance of 5% or less is formed in the vicinity of a wavelength of 665 nm, and a wavelength band of 645 nm. A transmittance gradient portion that decreases from 75% to 5% transmittance is formed at ˜665 nm.

  At an incident angle of 20 °, as shown by a curve 104 in FIG. 5, the transmittance slope portion of the curve 103 causes a wavelength shift that translates by 7 nm toward the short wavelength side, and is similarly shifted in the near infrared region. It has spectral transmittance characteristics.

On the other hand, as shown in FIG. 4, the optical thin film 24 of the present embodiment has a high refractive index layer 24H made of Nb ₂ O ₅ and a low refractive index layer 24L made of SiO ₂ on the other surface of the substrate 11. However, 28 layers are alternately laminated.
Such an optical thin film 24 can be formed by sputtering.
First, using an appropriate optical thin film vacuum film forming apparatus, the substrate 11 is heated to 100 ° C., and when the pressure in the vacuum chamber reaches 6 × 10 ⁻⁴ Pa, the surface of the substrate 11 is sputtered by sputtering. A first layer of Nb ₂ O ₅ was deposited with a physical film thickness of 98 nm. Further, a second layer of SiO ₂ was formed on the surface with a physical film thickness of 143 nm. Similarly, 28 layers of Nb ₂ O ₅ and SiO ₂ were alternately formed by a sputtering method with a physical film thickness as shown in Table 5 below.

FIG. 6 shows the result of measuring the spectral transmittance characteristics of the optical thin film 24 thus manufactured in the same manner as in the first embodiment.
As shown by a curve 105 in FIG. 6, the optical thin film 24 is approximately 100% on the short wavelength side and approximately 0% on the long wavelength side at an incident angle of 0 °, and is transmitted in the boundary region between visible light and near infrared rays. The spectral transmittance characteristic is such that the rate decreases substantially linearly from approximately 100% to approximately 0%. That is, a wavelength band having a transmittance of 75% or more and an average transmittance of 90% is formed on the short wavelength side, a wavelength band having a transmittance of 5% or less is formed on the long wavelength side, and the transmittance is 75% in the wavelength band therebetween. A transmittance slope portion that decreases from 5% to 5% is formed.

  At an incident angle of 20 °, as shown by a curve 106 in FIG. 6, the transmittance slope portion of the curve 105 undergoes a wavelength shift that translates more than about 15 nm and more than 10 nm toward the short wavelength side, and the other transmittance is almost the same. Spectral transmittance characteristics do not change.

The measurement results of the spectral transmittance characteristics of the optical element 20 manufactured by forming the optical thin film 23 on one surface of the substrate 11 and the optical thin film 24 on the other surface in this way are shown in FIG. Shown in
As shown by a curve 107 in FIG. 7, the optical element 20 is approximately 100% on the short wavelength side and approximately 0% on the long wavelength side at an incident angle of 0 °, and is transmitted in the boundary region between visible light and near infrared rays. The spectral transmittance characteristic is such that the rate decreases substantially linearly from approximately 100% to approximately 0%. That is, a wavelength band having a transmittance of 75% or more and an average transmittance of 90% is formed at a wavelength of 400 nm to 645 nm, a wavelength band having a transmittance of 5% or less is formed at a wavelength of 665 nm to 1100 nm, and a wavelength that is a wavelength band therebetween A transmittance slope portion that decreases from 75% to 5% transmittance is formed at 645 nm to 665 nm. These wavelength bands constitute first, second, and third wavelength bands, respectively.

  At an incident angle of 20 °, as shown by a curve 108 in FIG. 7, the transmittance slope portion of the curve 107 undergoes a wavelength shift that translates by 7 nm toward the short wavelength side, and the other transmittance hardly changes. It is a rate characteristic. That is, the first, second, and third wavelength bands are 400 nm to 638 nm, 638 nm to 658 nm, and 658 nm to 1100 nm, respectively.

Thus, according to the optical element 20 according to the present embodiment, the optical thin film 23 composed of the high refractive index material and the low refractive index material having a refractive index difference of 0.4 or less is formed on one surface of the substrate 11. Thus, the change in the spectral transmittance characteristic of the third wavelength band with respect to the incident angle of light can be reduced to 10 nm or less, and the optical thin film 24 is formed on the other surface, so that unnecessary light in the near infrared region can be obtained. Can be cut effectively.
In this embodiment, since the high refractive index layer 23H and the low refractive index layer 23L of the optical thin film 23 constituting a part of the optical element 20 are manufactured by mixing two kinds of substances having different refractive indexes, mixing By changing the ratio, the refractive index value can be easily set, and the refractive index difference between the high refractive index layer 23H and the low refractive index layer 23L can be easily set.
In addition, since the optical thin film is formed on both surfaces of the optical element 20, the stress of the substrate 11 can be relaxed. Furthermore, since the optical thin film is formed on both surfaces of the substrate 11, the antireflection film 15 can be omitted, and it is not necessary to use expensive vapor deposition materials such as MgF ₂ , Al ₂ O ₃ , ZrO ₂ , Material costs can be reduced.

[Third Embodiment]
Next, an optical apparatus according to a third embodiment of the present invention will be described with reference to FIG. In the following description, the same reference numerals are given to the components described in the above embodiment, and the description thereof is omitted.
FIG. 8 is a schematic cross-sectional view showing a schematic configuration of an optical apparatus according to the third embodiment of the present invention.

A digital camera (optical apparatus) 40 according to the present embodiment is an optical apparatus using the optical element 20 according to the second embodiment.
As shown in FIG. 8, the digital camera 40 includes an imaging module 41, a processing circuit 42, a memory card 43 that records image data from the imaging module 41, and an electric board 44 that electrically connects them. Yes.
The imaging module 41 includes an imaging lens 45, an optical element 20, a microlens array 46, and a solid-state imaging element 47. The optical image condensed by the imaging lens 45 is condensed on each pixel of the solid-state imaging element 47 by the microlens array 46 via the optical element 20.

Next, the operation of the digital camera 40 of the present embodiment having the above configuration will be described.
The optical image incident on the imaging lens 45 is condensed by the imaging lens 45 and enters the optical element 20. Here, of the light incident on the imaging lens 45, the light in the near infrared region is reflected by the optical element 20, and only the light in the visible light region is transmitted and enters the microlens array 46. The light incident on the microlens array 46 is condensed on each pixel of the solid-state image sensor 47, and becomes an image data in which the optical image is converted into an electric signal. The image data can be displayed on a display device (not shown) such as a display by the processing circuit 42 or recorded on the memory card 43.

According to the digital camera 40 according to the present embodiment, the spectral transmittance characteristic when light is incident on the optical element 20 has little change in the spectral transmittance characteristic with respect to the incident angle change. Even when the incident angle is large, image quality deterioration due to a change in spectral transmittance characteristics can be reduced. Therefore, the degree of freedom with respect to the incident angle when optically designing a digital camera, a small imaging module, or the like is widened, and application to a wide range of optical devices becomes possible.
Further, since the influence of the change in the spectral transmittance characteristic with respect to the change in the incident angle can be reduced without using an optical element such as a condenser lens for reducing the change in the incident angle with respect to the optical element 20, the number of parts can be reduced. The configuration can reduce the cost. In addition, since no optical element such as a condenser lens is disposed between the imaging lens 45 and the microlens array 46, an optical device having a space-saving configuration can be obtained, and the size can be reduced.

As a modification of the present embodiment, the optical thin films 23 and 24 may be formed using the imaging lens 45 as a base material instead of the substrate 11. Alternatively, the optical thin film 12 may be formed using the imaging lens 45 as a base material.
In these cases, since the substrate 11 can be omitted, the cost can be reduced and the size can be further reduced by reducing the number of parts.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

  For example, in the first embodiment, the vacuum deposition method is used when producing the optical thin film, and the sputtering method is used when producing the optical thin film in the second embodiment. However, the present invention is not limited thereto. Alternatively, an ion plating method, an ion assist deposition method, or a plasma assist deposition method may be used.

In the second embodiment, the optical thin film 23 is formed by mixing SiO ₂ and Nb ₂ O ₅ at a predetermined ratio. At this time, the two kinds of substances are separately sputtered to form a substrate. A film may be formed on the substrate 11 so as to be mixed at a predetermined ratio, or a material obtained by mixing two kinds of materials at a predetermined ratio in advance may be formed on the substrate 11 by sputtering.

The material for the optical thin film formed on the optical element is limited to Ta ₂ O ₅ , SiO ₂ , Nb ₂ O ₅ , and Y ₂ O ₃ used in the first and second embodiments. It is not a thing. For _{example, TiO 2, ZrO 2, Al} 2 O 3, WO 3, SiO, Hf0 2, CeO 2, may be used materials of MgF ₂ or the like.
Alternatively, an optical thin film in which two or more kinds of substances are mixed from substances containing these may be used. In this case, the optical thin film in which two or more kinds of substances are mixed may be a part of the optical thin film of the optical element or the entire layer.

  In addition, although a quartz crystal birefringent substrate is used as the substrate of the optical element according to the first and second embodiments, an appropriate material and shape can be adopted as the material and shape of the substrate. Therefore, the optical element may also serve as a transmission optical element such as a lens, a prism, or a beam splitter.

  Moreover, although the optical apparatus of said 3rd Embodiment demonstrated by the example of the digital camera as an example, you may apply to other optical apparatuses, such as a microscope and an endoscope, for example.

  Moreover, although the optical element of said 1st, 2nd embodiment demonstrated in the example in the case of IR cut filter, since the conditions of a wavelength are not included in Formula (3), arbitrary wavelengths are cut. It can be applied to an optical filter having an on wavelength or a cutoff wavelength. Further, it may be a low-pass filter or a high-pass filter.

It is typical sectional drawing which shows the structure of the optical element which concerns on the 1st Embodiment of this invention. It is a graph which shows the spectral reflectance characteristic of the anti-reflective film of the optical element which concerns on the 1st Embodiment of this invention. It is a graph which shows the spectral transmittance characteristic of the optical element which concerns on the 1st Embodiment of this invention. It is typical sectional drawing which shows the structure of the optical element which concerns on the 2nd Embodiment of this invention. It is a graph which shows the spectral transmittance characteristic of one optical thin film (optical thin film 23 of FIG. 4) used for the optical element which concerns on the 2nd Embodiment of this invention. It is a graph which shows the spectral transmittance characteristic of the other optical thin film (optical thin film 24 of FIG. 4) used for the optical element which concerns on the 2nd Embodiment of this invention. It is a graph which shows the spectral transmittance characteristic of the optical element which concerns on the 2nd Embodiment of this invention. It is typical sectional drawing which shows schematic structure of the optical instrument which concerns on the 3rd Embodiment of this invention. It is a graph which shows an example of the spectral transmittance characteristic of IR cut filter concerning a prior art.

Explanation of symbols

10, 20 Optical element 11 Substrate (base material)
12, 13, 14, 23, 24 Optical thin film 15 Antireflection film 13H, 14H, 23H, 24H High refractive index layer 13L, 14L, 23L, 24L Low refractive index layer 40 Digital camera (optical apparatus)
45 Imaging lens 46 Micro lens array 47 Solid-state imaging device

Claims (4)

An optical element having a substrate and an optical thin film having a plurality of layers formed on the surface of the substrate,
Spectral transmittance characteristics of the optical thin film are
A first wavelength band having a transmittance of 75% or more and an average transmittance of 90% or more;
A second wavelength band having a transmittance of 5% or less;
A third wavelength band between which the transmittance changes from 75% to 5% between the first wavelength band and the second wavelength band;
An optical element characterized in that the third wavelength band moves to the short wavelength side by changing the incident angle of light from 0 ° to 20 °, and the amount of movement is 10 nm or less. An optical element having a substrate and an optical thin film having a plurality of layers formed on the surface of the substrate,
The optical thin film is
It is configured by alternately stacking a high refractive index layer having a relative high refractive index and a low refractive index layer having a relative low refractive index,
The high refractive index layer is made of a material having a refractive index of 2.0 or more at a wavelength of 500 nm, and the low refractive index layer adjacent to the high refractive index layer is refracted from the material of the high refractive index layer. An optical element comprising a material having a difference in rate of 0.4 or less.   3. The optical element according to claim 1, wherein all or a part of the optical thin film is made of a material in which two or more kinds of substances are mixed.   An optical apparatus comprising the optical element according to any one of claims 1 to 3.

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