Optical element and projection lens

文档序号：1631616 发布日期：2020-01-14 浏览：32次中文

阅读说明：本技术 光学元件以及投影透镜 (Optical element and projection lens ) 是由中野喜博高原浩滋寺本美雪于 2018-03-09 设计创作，主要内容包括：光学元件在光学元件基板上具有防反射膜。防反射膜具有从空气侧起依次交替地层叠八层以上的由SiO2构成的低折射率膜和由TiO2、Nb2O5或者Ta2O5构成的一种以上的高折射率膜而成的构造。在防反射膜中,若将设计主波长设为550nm,则从空气侧起数而得的第一层～第六层的1/4波长光学膜厚为：在第一层的低折射率膜中为0.94±0.05,在第二层的高折射率膜中为1.29±0.25,在第三层的低折射率膜中为0.08±0.05,在第四层的高折射率膜中为0.45±0.20,在第五层的低折射率膜中为2.05±0.20,在第六层的高折射率膜中为0.45±0.20。(The optical element has an antireflection film on an optical element substrate. The antireflection film has eight or more layers of SiO alternately laminated in this order from the air side 2 Low refractive index film composed of TiO 2 、Nb 2 O 5 Or Ta 2 O 5 And one or more high refractive index films. In the antireflection film, when the design dominant wavelength is 550nm, the 1/4-wavelength optical film thicknesses of the first to sixth layers counted from the air side are: 0.94 + -0.05 in the low refractive index film of the first layer, 1.29 + -0.25 in the high refractive index film of the second layer, and0.08 + -0.05 in the low refractive index film of the third layer, 0.45 + -0.20 in the high refractive index film of the fourth layer, 2.05 + -0.20 in the low refractive index film of the fifth layer, and 0.45 + -0.20 in the high refractive index film of the sixth layer.)

1. An optical element having an antireflection film on an optical element substrate,

the antireflection film has eight or more layers of SiO alternately laminated in this order from the air side₂Low refractive index film composed of TiO₂、Nb₂O₅Or Ta₂O₅A structure comprising at least one high refractive index film,

in the antireflection film, when the design dominant wavelength is 550nm, the 1/4-wavelength optical film thicknesses of the first to sixth layers counted from the air side are:

0.94 + -0.05 in the low refractive index film of the first layer,

1.29 + -0.25 in the high refractive index film of the second layer,

0.08 + -0.05 in the low refractive index film of the third layer,

0.45 + -0.20 in the high refractive index film of the fourth layer,

2.05 + -0.20 in the low refractive index film of the fifth layer,

0.45 ± 0.20 in the high refractive index film of the sixth layer.

2. The optical element of claim 1,

the total number of layers of the antireflection film is ten,

in the antireflection film, when the design dominant wavelength is 550nm, the 1/4-wavelength optical film thicknesses of the seventh to tenth layers counted from the air side are:

0.19 + -0.10 in the low refractive index film of the seventh layer,

1.03 + -0.35 in the high refractive index film of the eighth layer,

0.24 + -0.15 in the low refractive index film of the ninth layer,

0.30 + -0.10 in the high refractive index film of the tenth layer,

the maximum reflectance at a wavelength of 420 to 680nm is 0.2% or less.

3. The optical element of claim 1,

the total number of layers of the anti-reflection film is thirteen,

in the antireflection film, when the design dominant wavelength is 550nm, the 1/4-wavelength optical film thicknesses of the seventh to thirteenth layers counted from the air side are:

0.11 + -0.10 in the low refractive index film of the seventh layer,

1.32 + -0.10 in the high refractive index film of the eighth layer,

0.42 + -0.10 in the low refractive index film of the ninth layer,

0.31 + -0.10 in the high refractive index film of the tenth layer,

1.05 + -0.35 in the low refractive index film of the eleventh layer,

0.21 + -0.15 in the high refractive index film of the twelfth layer,

0.38 + -0.10 in the low refractive index film of the thirteenth layer,

the maximum reflectance at a wavelength of 420 to 780nm is 0.4% or less.

4. The optical element according to any one of claims 1 to 3,

when the optical element substrate is left at 300 ℃ or higher for one hour or more and the antireflection film is applied, an increase in absorption loss of light of 1% or more occurs at a wavelength of 430 nm.

5. The optical element according to any one of claims 1 to 4,

in the optical element substrate, the refractive index to the d-line is 1.80809 + -0.001, and the Abbe number is 22.76 + -0.36.

6. A projection lens for a projector, wherein,

having the optical element of any one of claims 1 to 5 as a lens element.

Technical Field

The present invention relates to an optical element and a projection lens, and more particularly to an optical element having an antireflection film and a projection lens for a projector including the optical element.

Background

With the progress of higher precision of projection lenses for projectors, optical glasses having various refractive indices and relatively low dispersion or optical glasses having relatively high dispersion have been used as lens materials for projection lenses. However, in products provided by optical glass manufacturers, when heating is performed by a conventional method for producing an antireflection film, absorption loss of light inside the glass increases. For example, in an optical glass such as FD225 provided by HOYA and S-NPH 1W provided by OHARA, when coating is performed by heating at 300 ℃ in a conventional production method, an increase in absorption loss of light of about 1.5% occurs at a wavelength of 430 nm. Therefore, when light of a large quantity of light of 1 ten thousand lumens or more passes through the optical glass, heat is generated even with a slight absorption, and the change in refractive index of the optical glass due to the heat affects the projection performance.

In order to avoid an increase in absorption loss of light inside the glass substrate, it is necessary to perform coating under low temperature conditions. Therefore, MgF, which has been used frequently in the past, cannot be used from the viewpoint of reliability such as strength₂. Therefore, it is desirable not to use MgF₂The antireflection film of (1). As without MgF₂The antireflection film of (3) is described in, for example, patent document 1. The antireflection film described in patent document 1 is formed of Nb₂O₅Film with equal refractive index and made of SiO₂Is formed ofThe refractive index film is composed of thirteen alternating layers, and the reflectivity in the visible light wavelength band is suppressed to be less than 3%.

Patent document 1: japanese patent laid-open publication No. 2010-217445

However, in the optical element having an antireflection film described in patent document 1, the number of film layers is large, but the antireflection performance is rather low, and stable antireflection performance cannot be obtained over the entire visible light wavelength band.

Disclosure of Invention

The present invention has been made in view of such circumstances, and an object thereof is to provide an optical element having an antireflection film which has high antireflection performance even if the number of film layers is small, and which has stable antireflection performance over the entire visible light wavelength band, and in which absorption loss of light inside an optical element substrate is small, and a projection lens provided with the optical element.

In order to achieve the above object, an optical element of the present invention is an optical element having an antireflection film on an optical element substrate,

the anti-reflection film comprises eight or more layers of SiO alternately laminated in order from the air side₂Low refractive index film composed of TiO₂、Nb₂O₅Or Ta₂O₅A structure comprising at least one high refractive index film,

in the antireflection film, when the design dominant wavelength is 550nm, the 1/4-wavelength optical film thicknesses of the first to sixth layers counted from the air side are:

0.94 + -0.05 in the low refractive index film of the first layer,

1.29 + -0.25 in the high refractive index film of the second layer,

0.08 + -0.05 in the low refractive index film of the third layer,

0.45 + -0.20 in the high refractive index film of the fourth layer,

2.05 + -0.20 in the low refractive index film of the fifth layer,

0.45 ± 0.20 in the high refractive index film of the sixth layer.

The projection lens for a projector according to the present invention is characterized by having the optical element according to the present invention as a lens element.

According to the present invention, since the antireflection film in which eight or more layers are laminated has a characteristic film structure in the first to sixth layers, high antireflection performance can be obtained even with a small number of film layers, and stable antireflection performance can be obtained over the entire visible light wavelength band. For example, an antireflection film composed of ten layers can realize antireflection performance with a reflectance of 0.2% or less. Further, since the antireflection film is formed of a material that can be applied under low temperature conditions, absorption loss of light inside the optical element substrate can be reduced, and since optical element substrates having various refractive indices can be used, high versatility can be obtained. Therefore, an optical element having an antireflection film which has high antireflection performance even if the number of film layers is small and which has stable antireflection performance over the entire visible light wavelength band and in which light absorption loss inside the optical element substrate is small, and a projection lens including the optical element can be realized.

Drawings

Fig. 1 is a cross-sectional view schematically showing one embodiment of an optical element having an antireflection film.

Fig. 2 is an optical configuration diagram showing an embodiment of a projection lens having the optical element of fig. 1 as a lens element.

FIG. 3 is a graph showing the antireflection characteristics of example 1 in terms of spectral reflectance.

FIG. 4 is a graph showing the antireflection characteristics of example 2 in terms of spectral reflectance.

FIG. 5 is a graph showing the antireflection characteristics of example 3 in terms of spectral reflectance.

FIG. 6 is a graph showing the antireflection characteristics of example 4 in terms of spectral reflectance.

FIG. 7 is a graph showing the antireflection characteristics of example 5 in terms of spectral reflectance.

FIG. 8 is a graph showing the antireflection characteristics of example 6 in terms of spectral reflectance.

FIG. 9 is a graph showing the antireflection characteristics of example 7 in terms of spectral reflectance.

Fig. 10 is a graph showing the antireflection characteristics of comparative example 1 in terms of spectral reflectance.

Fig. 11 is a graph showing the antireflection characteristics of comparative example 2 by spectral reflectance.

FIG. 12 is a graph showing spectral characteristics of example 6 and comparative example 2 by increasing the absorption loss with light.

Detailed Description

Hereinafter, an optical element, a projection lens, and the like according to an embodiment of the present invention will be described with reference to the drawings. Fig. 1 schematically shows a laminated structure of an antireflection film AR in an optical cross section, in an embodiment of an optical element having the antireflection film.

The optical element DS shown in FIG. 1 has an antireflection film AR on an optical element substrate SU, the antireflection film AR having eight or more layers of SiO alternately laminated in this order from the Air (Air) side₂Low refractive index film composed of TiO₂、Nb₂O₅Or Ta₂O₅And one or more high refractive index films. If the i-th (i is 1, 2, 3, …, n) layer counted from the air side is the i-th layer Ci, odd-numbered layers such as the first layer C1, the third layer C3, the fifth layer C5, and the seventh layer C7 are formed of SiO₂The even number layers of the low refractive index film, such as the second layer C2, the fourth layer C4, the sixth layer C6 and the eighth layer C8, are made of TiO₂、Nb₂O₅Or Ta₂O₅A high refractive index film. Therefore, one low refractive index film is one of the films included in one anti-reflection film AR, but two or three high refractive index films may be used.

In the antireflection film AR, the dominant wavelength λ is designed₀When the Thickness is 550nm, the 1/4 wavelength Optical film Thickness (QWOT: quick Wave Optical Thickness) of the first layer C1 to the sixth layer C6 counted from the air side is:

0.94 + -0.05 in the low refractive index film of the first layer C1,

1.29 + -0.25 in the high refractive index film of the second layer C2,

0.08 + -0.05 in the low refractive index film of the third layer C3,

0.45 + -0.20 in the high refractive index film of the fourth layer C4,

2.05 + -0.20 in the low refractive index film of fifth layer C5,

0.45 ± 0.20 in the high refractive index film of the sixth layer C6. Further, the 1/4 wavelength optical film thickness is represented by the formula: QWOT ═ 4. n.d/lambda₀Expressed (in the formula, d: physical film thickness, n: refractive index, λ)₀: the dominant wavelength is designed. ).

Examples of the material constituting the optical element substrate SU include a glass substrate having a refractive index nd of 1.80809 ± 0.001 with respect to d-line and an abbe number ν d of 22.76 ± 0.36. In such a glass substrate, as described above, the absorption loss of light is increased by heating at the time of film formation. In other words, when the optical element substrate SU assumed here is left at 300 ℃ or higher for one hour or more and coated with the antireflection film AR, an increase in absorption loss of light of 1% or more occurs at a wavelength of 430 nm. In order to avoid this increase in absorption loss, film formation at low temperature is required. Therefore, in the present embodiment, the antireflection film AR is configured to satisfy the above conditions in order to perform film formation at a low temperature.

According to the above configuration, since the antireflection film AR laminated in eight or more layers has a characteristic film structure in the first to sixth layers C1 to C6, high antireflection performance can be obtained even if the number of film layers is small, and stable antireflection performance can be obtained over the entire visible light wavelength band. For example, the antireflection film AR composed of ten layers can realize antireflection performance with a reflectance of 0.2% or less. Further, since the antireflection film AR is made of a material that can be applied under low temperature conditions, absorption loss of light inside the optical element substrate SU can be reduced, and since optical element substrates SU having various refractive indices can be used, high versatility can be obtained. Therefore, it is possible to realize the optical element DS having the antireflection film AR having high antireflection performance even if the number of film layers is small and stable antireflection performance over the entire visible light wavelength band, and having small absorption loss of light inside the optical element substrate SU.

With regard to the film thicknesses of the seventh layer C7 and thereafter, in the antireflection film AR, if the first layer C1 to the sixth layer C6 are defined according to the above conditions, it can be easily obtained by optimization calculation using optical thin film design software or the like. Further, the film structure of the seventh layer C7 and thereafter can achieve the above-described effects in a well-balanced manner, and can achieve further excellent antireflection performance and the like.

For example, it is preferable that: in the antireflection film AR having ten total film layers, the dominant wavelength λ is designed₀When 550nm is set, the 1/4-wavelength optical film thicknesses of the seventh layer C7 to the tenth layer C10 counted from the air side are:

0.19 + -0.10 in the low refractive index film of the seventh layer C7,

1.03 + -0.35 in the high refractive index film of the eighth layer C8,

0.24 + -0.15 in the low refractive index film of the ninth layer C9,

0.30 + -0.10 in the high refractive index film of the tenth layer C10,

the maximum reflectance at a wavelength of 420 to 680nm is 0.2% or less.

For example, it is preferable that: in the antireflection film AR having thirteen total film layers, the dominant wavelength λ is designed₀When 550nm is set, the 1/4-wavelength optical film thicknesses of the seventh layer C7 to the thirteenth layer C13 counted from the air side are:

0.11 + -0.10 in the low refractive index film of the seventh layer C7,

1.32 + -0.10 in the high refractive index film of the eighth layer C8,

0.42 + -0.10 in the low refractive index film of the ninth layer C9,

0.31 + -0.10 in the high refractive index film of the tenth layer C10,

1.05 + -0.35 in the tenth layer of the low refractive index film of C11,

0.21 + -0.15 in the high refractive index film of the twelfth layer C12,

0.38 + -0.10 in the low refractive index film of the thirteenth layer of C13,

the maximum reflectance at a wavelength of 420 to 780nm is 0.4% or less.

Each layer of the antireflection film AR is formed by, for example, a vacuum deposition method under heating at 150 ℃. By using ion-assisted deposition, it is possible to reduce variations in film density of the antireflection film AR, roughness of the film surface, and the like caused by variations in the degree of vacuum in the vacuum deposition method. This can suppress the occurrence of color unevenness and the deterioration of characteristic reproducibility due to a change in film density (in other words, a change in refractive index of the film). Further, when the formation of the antireflection film AR is performed by ion-assisted deposition, a high refractive index material which has been difficult to use in the past can be used for the layer constituting the antireflection film AR.

For example, in a projector lens, a large amount of light passes through a lens element constituting the projector lens, and therefore, even if the absorption loss of light in the lens element is small, heat generation occurs. If the refractive index of the lens element changes due to this heat generation, the optical performance of the projection lens may be degraded. Therefore, if the antireflection film AR having the above-described structure is provided on the lens substrate serving as the optical element substrate SU, a lens element having a small absorption loss of light inside the lens substrate and a good antireflection performance can be obtained. Further, if a lens element having such an antireflection film AR is used for a projection lens, high optical performance and antireflection effect can be stably and highly reliably obtained, and therefore, a projector in which the lens element is mounted can be provided with high image quality. Hereinafter, an embodiment of a projection lens for a projector in which the optical element DS is applied as a lens element having the antireflection film AR will be described.

Fig. 2 is an optical configuration diagram of a projection lens LN for a projector, and shows a lens cross-sectional shape, a lens arrangement, and the like of the projection lens LN as a zoom lens in optical cross-sections for the wide-angle end (W) and the telephoto end (T), respectively. On the reduction side of the projection lens LN, a prism PR (e.g., a TIR (Total Internal Reflection) prism, a color separation/synthesis prism, etc.) and a cover glass CG of the image display element are disposed.

The projection lens LN is configured as follows: the first optical system LN1 (from the first surface to the front of the intermediate image plane IM 1) and the second optical system LN2 (from the rear of the intermediate image plane IM1 to the final lens surface) are arranged in this order from the enlargement side, the second optical system LN2 forms an intermediate image IM1 of an image (reduction-side image plane) displayed on the image display surface IM2 of the image display device, and the first optical system LN1 enlarges and projects the intermediate image IM 1. Further, the aperture stop ST is located near the center of the second optical system LN2 (the most enlarged side in the 2 c-th lens group Gr2 c).

The projection lens LN is a spherical lens system including no aspherical surface and composed of 30 lens elements as a whole, 17 lenses on the enlargement side are the first optical system LN1 for performing enlarged projection of the intermediate image IM1, and 13 lenses on the reduction side are the second optical system LN2 for forming the intermediate image IM 1. The first optical system LN1 is constituted by the 1 st lens group Gr1 which is positive overall, and the second optical system LN2 is constituted by the positive 2a lens group Gr2a, the positive 2b lens group Gr2b, the positive 2c lens group Gr2c, and the positive 2d lens group Gr2d in this order from the magnification side, and the position of the intermediate image IM1 at the time of zooming is fixed and magnification is performed only by the second optical system LN2 (5-group zoom lens structure which is positive).

Arrows m1, m2a, m2b, m2c, and m2d in fig. 2 schematically illustrate movement or fixation of the 1 st lens group Gr1 and the 2a to 2d lens groups Gr2a to Gr2d, respectively, upon zooming from the wide-angle end (W) to the telephoto end (T). In other words, it is constituted that: the 1 st lens group Gr1 and the 2d lens group Gr2d form a fixed group, the 2a to 2c lens groups Gr2a to Gr2c form a moving group, and the 2a to 2c lens groups Gr2a to Gr2c are moved along the optical axis AX, respectively, to zoom. When zooming from the wide angle end (W) to the telephoto end (T), the 2a lens group Gr2a moves in a locus convex toward magnification (U-turn movement), and the 2b lens group Gr2B and the 2c lens group Gr2c each move monotonously toward magnification.

As described above, the projection lens LN is configured to perform magnification change (i.e., zooming) from the wide angle end (W) to the telephoto end (T) by moving the moving group relative to the image display surface IM2 and changing the group interval on the axis. Since the zoom positions of the 1 st lens group Gr1 and the 2d lens group Gr2d are fixed, there is no change in the overall length of the optical system due to magnification change, and moving parts are reduced, thereby simplifying the magnification change mechanism. Further, the zoom positions of the prism PR and the cover glass CG on the reduction side of the 2 d-th lens group Gr2d are also fixed.

The intermediate image IM1 formed by the second optical system LN2 is an image obtained by enlarging the image display surface IM2 in the vicinity of the center of the entire projection lens LN. This can increase the off-axis light passing position in the lens near the intermediate image IM1, and can realize high optical performance without using an aspherical surface. The seventeenth lens element L17 from the magnified side, which is disposed adjacent to the magnified side of the intermediate image IM1, is a positive lens having a concave meniscus shape on the side of the intermediate image IM1, and the antireflection film AR (fig. 1) described above is provided on at least one surface thereof. The substrate material of the lens element L17 is assumed to be as follows: the refractive index nd of the d-line is 1.80809 + -0.001, the Abbe number vd is 22.76 + -0.36, and when the coating of the antireflection film AR is performed while being left at 300 ℃ or more for one hour, the absorption loss of light of 1% or more at a wavelength of 430nm increases.

In the projection lens LN with a large field angle, when the lens diameter is reduced as shown in fig. 2, off-axis aberrations such as field curvature and chromatic aberration of magnification tend to occur. However, when a substrate material having a high refractive index and a large anomalous dispersion is used for the lens element L17 located immediately before the intermediate image IM1 where the off-axis light beam passing position is high as described above, it is possible to efficiently correct the field curvature and the chromatic aberration of magnification. Further, since the antireflection film AR of the lens element L17 is made of a material that can be coated under low temperature conditions, it is possible to obtain good antireflection performance while avoiding an increase in absorption loss of light inside the lens element L17.

As is clear from the above description, the above-described embodiment and the examples described later include the following characteristic configurations (#1) to (#6), and the like.

(# 1): an optical element having an antireflection film on an optical element substrate,

the anti-reflection film comprises eight or more layers of SiO alternately laminated in order from the air side₂Constructed low refractionFilm and film made of TiO₂、Nb₂O₅Or Ta₂O₅A structure comprising at least one high refractive index film,

in the antireflection film, when the design dominant wavelength is 550nm, the 1/4-wavelength optical film thicknesses of the first to sixth layers counted from the air side are:

0.94 + -0.05 in the low refractive index film of the first layer,

1.29 + -0.25 in the high refractive index film of the second layer,

0.08 + -0.05 in the low refractive index film of the third layer,

0.45 + -0.20 in the high refractive index film of the fourth layer,

2.05 + -0.20 in the low refractive index film of the fifth layer,

0.45 ± 0.20 in the high refractive index film of the sixth layer.

(# 2): the optical element according to (#1), wherein,

the total number of layers of the antireflection film is ten,

in the antireflection film, when the design dominant wavelength is 550nm, the 1/4-wavelength optical film thicknesses of the seventh to tenth layers counted from the air side are:

0.19 + -0.10 in the low refractive index film of the seventh layer,

1.03 + -0.35 in the high refractive index film of the eighth layer,

0.24 + -0.15 in the low refractive index film of the ninth layer,

0.30 + -0.10 in the high refractive index film of the tenth layer,

the maximum reflectance at a wavelength of 420 to 680nm is 0.2% or less.

(# 3): the optical element according to (#1), wherein,