JP2007333806A - Antireflection film and optical member - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antireflection film that is suitable for an optical substrate having a relatively high refractive index, and has a lower reflectance in a broad wavelength range. <P>SOLUTION: The antireflection film C1 comprises first layer 1 to fifth layer 5 successively laminated on the surface 100S of an optical substrate 100 having a refractive index of 1.75 to 2.10 to d-line. The first layer and the third layer 3 are made of an intermediate refractive index material having a refractive index of 1.53 to 2.50 to d-line, the second layer 2 and the fourth layer 4 are made of a high refractive index material having a refractive index of 1.90 to 2.50 to d-line, and the fifth layer 5 is made of a low refractive index material having a refractive index of 1.35 to 1.50 to d-line. The first layer 1 to the fifth layer 5 have optical film thicknesses satisfying conditional expressions (1) to (5). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an antireflection film that is formed on one surface of an optical member such as a lens or a filter and exhibits an antireflection effect on light of a predetermined wavelength band, and an optical member including the same.

  In general, in an imaging apparatus such as a photographic camera or a broadcast camera, a large number of optical members such as lenses, prisms, or filters are arranged on the optical path. On the surface of each optical member, when light is incident, a part of the light becomes reflected light. Here, when the total number of optical members increases, the total amount of reflected light increases accordingly. For example, in a broadcast camera, a failure such as flare or ghost appears in an image. In addition, the reflectance on the surface of each optical member has a distribution with respect to the wavelength of incident light, and the wavelength dependence of various reflectances varies depending on the constituent material of each optical member. Deteriorating and it is necessary to adjust the white balance of the entire imaging apparatus.

For these reasons, conventionally, an antireflection film is provided on the surface of each optical member. The antireflection film is a multilayer film in which dielectric films having different refractive indexes are combined, and the configuration thereof is disclosed, for example, in Non-Patent Document 1 below. Non-Patent Document 1 discloses an antireflection film having a five-layer structure, and attempts have been made to obtain a low reflectance over a wider band.
“Optical / Thin Film Manual”, Optronics, October 9, 1989, p. 246-247

  The antireflection film disclosed in Non-Patent Document 1 exhibits relatively good low reflectance characteristics when provided on an optical substrate that exhibits a refractive index lower than 1.70 with respect to d-line, for example. However, when provided on an optical substrate exhibiting a high refractive index exceeding 1.75, the flatness of the reflectance distribution is lost as described below, and the reflectance increases at a specific wavelength. It turned out that there is a tendency to end.

  Tables 1 and 2 show basic data (constituent materials, refractive index, optical film thickness) of antireflection films (conventional examples 1 and 2) having a laminated structure corresponding to the antireflection film disclosed in Non-Patent Document 1. FIG. 14 shows the reflectance distribution of the antireflection film having the basic data of Tables 1 and 2.

  Conventional Example 1 in Table 1 is a configuration example when the refractive index of the optical substrate on which the antireflection film is formed is relatively low, and Conventional Example 2 in Table 2 is a case where the refractive index of the optical substrate is relatively high. It is a structural example. In FIG. 14, a curve 20A indicates the reflectance distribution of Conventional Example 1, and a curve 20B indicates the reflectance distribution of Conventional Example 2. As described above, in the conventional example 2 in which the refractive index of the optical substrate is 1.8830, the reflectance distribution is not flat, and peaks are generated in the vicinity of 420 nm, 510 nm, and 650 nm. For these reasons, an antireflection film having good reflectance characteristics suitable for formation on an optical substrate having a high refractive index exceeding 1.75, for example, is desired while having a relatively small number of layers.

  The present invention has been made in view of such problems, and a first object of the present invention is to provide an antireflection film having a lower reflectance in a wider wavelength band, suitable for an optical substrate having a relatively high refractive index. There is to do. A second object of the present invention is to provide an optical member provided with such an antireflection film.

The antireflection film of the present invention is formed on a substrate exhibiting a refractive index of 1.75 or more and 2.10 or less with respect to the d line, and is laminated in order from the substrate side to the fifth. And the following conditional expression (1) is satisfied when the refractive index with respect to the center wavelength λ0 in the first layer is N1 and the physical film thickness in the first layer is d1. It has been done. The d line is a light beam having a wavelength of 587.56 nm.
0.45 × λ0 ≦ N1 × d1 ≦ 0.55 × λ0 (1)
The optical member of the present invention is provided with the antireflection film as described above.

  In the antireflection film and the optical member of the present invention, the first film having an optical film thickness N1 × d1 satisfying the conditional expression (1) is provided on a substrate exhibiting a refractive index of 1.75 to 2.10 with respect to the d line. Since one layer is provided, a sufficiently low reflectance characteristic is exhibited in a wider wavelength band.

In the antireflection film and the optical member of the present invention, it is further preferable that the following conditional expressions (2) to (5) are all satisfied. However, (lambda) 0 is a center wavelength, N2-N5 is a refractive index with respect to center wavelength (lambda) 0 in a 2nd layer-a 5th layer, d2-d5 is a physical film thickness in a 2nd layer-a 5th layer. It is.
0.45 × λ0 ≦ N2 · d2 ≦ 0.55 × λ0 (2)
0.45 × λ0 ≦ N3 · d3 ≦ 0.55 × λ0 (3)
0.45 × λ0 ≦ N4 · d4 ≦ 0.55 × λ0 (4)
0.20 × λ0 ≦ N5 · d5 ≦ 0.30 × λ0 (5)

  In the antireflection film and the optical member of the present invention, the first layer and the third layer are made of an intermediate refractive index material having a refractive index of 1.53 or more and 1.85 or less with respect to the d line, and the second layer And the fourth layer is made of a high refractive index material having a refractive index of 1.90 or more and 2.50 or less with respect to the d line, and the fifth layer is 1.35 or more and 1.50 or less with respect to the d line. It may be made of a low refractive index material exhibiting a refractive index.

As a constituent material (low refractive index material) of the fifth layer, a material containing at least one of magnesium fluoride (MgF ₂ ), silicon dioxide (SiO ₂ ), and aluminum fluoride (AlF ₃ ) is used. Can do. As the constituent material (intermediate refractive index material) of the first layer and the third layer, praseodymium aluminate (PrAlO ₃ ), lanthanum aluminate (La _2X Al _2Y O _{3 (X + Y)} , La ₂ O _3. 3.3Al ₂ O _3), aluminum oxide (Al ₂ O _3), it can be used those containing at least one of germanium oxide (GeO ₂₎ and yttrium oxide (Y ₂ O _3). Further, the constituent materials (high refractive index materials) of the second layer and the fourth layer include lanthanum titanate (LaTiO ₃ ), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ ). O ₅ ), niobium oxide (Nb ₂ O ₅ ), hafnium oxide (HfO ₂ ), and cerium oxide (CeO ₂ ) may be used.

  According to the antireflection film and the optical member of the present invention, including the first to fifth layers sequentially laminated on the substrate exhibiting a refractive index of 1.75 to 2.10 with respect to the d-line, and Since the optical film thickness n1 × d1 that is the product of the refractive index n1 and the physical film thickness d1 in the first layer satisfies the predetermined conditional expression (1), the number of stacked layers is relatively small. The reflectance can be sufficiently reduced over a wider wavelength band. Therefore, when the antireflection film or optical member of the present invention is applied to an optical system in an imaging apparatus such as a photographic camera or a broadcast camera, the occurrence of flare and ghost is suppressed, and more excellent chromaticity balance. Can be obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing the configuration of an optical member provided with an antireflection film C1 as one embodiment of the present invention. The antireflection film C1 in FIG. 1 corresponds to numerical examples (Examples 1 to 11) described later.

  The antireflection film C1 is a multilayer film composed of a total of five layers provided on the surface 100S of the optical substrate 100, and the layers from the first layer 1 to the fifth layer 5 are laminated in order from the optical substrate 100 side. It is a thing. Although the surface 100S is a plane here, it is not limited to this and may be a curved surface. That is, a lens having a spherical surface or an aspheric surface may be used as the optical substrate 100, and the antireflection film C1 may be provided on the spherical surface or the aspheric surface.

  The optical substrate 100 is made of a transparent material such as glass or a crystal material. Specifically, for example, SF11, LASF-N21, S-LAH58, and FDS1 that show a refractive index of 1.75 to 2.10 with respect to the d-line (wavelength λ = 587.56 nm) It is desirable to use an optical glass such as a German company Schott.

  The first layer 1 and the third layer 3 are intermediate refractive index layers made of an intermediate refractive index material exhibiting a refractive index of 1.53 or more and 1.85 or less with respect to the d line. The second layer 2 and the fourth layer 4 are high refractive index layers made of a high refractive index material exhibiting a refractive index of 1.90 or more and 2.50 or less with respect to the d line. Further, the fifth layer 5 is a low refractive index layer made of a low refractive index material exhibiting a refractive index of 1.35 or more and 1.50 or less with respect to the d-line.

As the low refractive index material, for example, magnesium fluoride (MgF ₂ ), silicon dioxide SiO ₂ and aluminum fluoride (AlF ₃ ), and mixtures and compounds thereof can be used. Examples of the intermediate refractive index material include praseodymium aluminate (PrAlO ₃ ), lanthanum aluminate (La _2X Al _2Y O _{3 (X + Y)} ), aluminum oxide (Al ₂ O ₃ ), germanium oxide (GeO ₂ ), and oxide. Yttrium (Y ₂ O ₃ ), and mixtures and compounds thereof can be used. Further, examples of the high refractive index material include lanthanum titanate (LaTiO ₃ ), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), Hafnium oxide (HfO ₂ ) and cerium oxide (CeO ₂ ), and mixtures and compounds thereof can be used.

  Further, it is desirable that the first layer 1 to the fifth layer 5 are configured to satisfy all of the following conditional expressions (1) to (5). However, (lambda) 0 is a center wavelength (unit: nm), N1-N5 is the refractive index with respect to center wavelength (lambda) 0 in the 1st layer 1 to the 5th layer 5, and d1-d5 is the 1st layer 1 to the 5th layer 5. Is the physical film thickness (unit: nm).

0.45 × λ0 ≦ N1 × d1 ≦ 0.55 × λ0 (1)
0.45 × λ0 ≦ N2 · d2 ≦ 0.55 × λ0 (2)
0.45 × λ0 ≦ N3 · d3 ≦ 0.55 × λ0 (3)
0.45 × λ0 ≦ N4 · d4 ≦ 0.55 × λ0 (4)
0.20 × λ0 ≦ N5 · d5 ≦ 0.30 × λ0 (5)

  As described above, according to the antireflection film C1 of the present embodiment, the optical that satisfies the conditional expression (1) on the optical substrate 100 that exhibits a refractive index of 1.75 to 2.10 with respect to the d line. Since the first layer 1 having the film thickness N1 × d1 is provided, the reflectivity can be sufficiently reduced over a wider wavelength band while the number of layers is relatively small as a five-layer structure. Specifically, the reflectance can be suppressed to 0.5% or less in a wavelength band having a width of at least 350 nm.

  In particular, since the refractive index in the first layer 1 to the fifth layer 5 is optimized and the optical film thickness N · d is optimized so as to satisfy the conditional expressions (2) to (5), The above effects can be further enhanced. Therefore, when this antireflection film C1 is applied to an optical system in a photographic camera or a broadcast camera, the reflection of incident light is reduced, thereby suppressing the occurrence of flare and ghost and more excellent color. Degree of balance can be obtained.

  Next, specific numerical examples of the antireflection film according to the present embodiment will be described.

  Here, first to fourth numerical examples (Examples 1 to 4) corresponding to the antireflection film C1 shown in FIG. 1 will be described together. Tables 3 to 6 show basic data of Examples 1 to 4, respectively. 2 to 5 show the reflectance distributions of Examples 1 to 4, respectively.

Tables 3 to 6 show the constituent materials of each layer, the refractive index N with respect to the d-line, and the optical film thickness N · d (unit: nm), respectively. “Sub-M1” in the column of the constituent material represents substance M1 (Merck, Germany) mainly composed of PrAlO ₃ , and “Sub-M2” represents lanthanum aluminate (La ₂ O ₃ .3.3Al ₂ O _3). ) Represents the substance M2 (Merck, Germany), and “Sub-M3” represents the substance M3 (Merck, Germany) whose main component is lanthanum aluminate (La _2X Al _2Y O _{3 (X + Y)} ). “Sub-H4” represents substance H4 (Merck, Germany) whose main component is LaTiO ₃ . The center wavelength λ0 shown in the column of the optical film thickness N × d was all set to 500 nm. As is clear from each table, the value of the optical film thickness N × d of each layer satisfies all of the conditional expressions (1) to (5). Further, the refractive index N of each layer is also a numerical value within a predetermined range.

  On the other hand, FIGS. 2 to 5 show the wavelength dependence of the reflectance (%) in each example. In each figure, the horizontal axis is the wavelength λ (nm) at the time of measurement, and the vertical axis is the reflectance (%). As is clear from each figure, it was confirmed that the reflectance was within 0.5% or less in a wavelength band of approximately 350 nm to 700 nm.

  Further, in Table 7 and FIG. 6, as the fifth to eleventh numerical examples (Examples 5 to 11) corresponding to the antireflection film C1, the first to fifth layers corresponding to the refractive index N100 of the optical substrate are shown. The optimal refractive indexes N1-N5 in each layer of the layers are shown. Table 7 shows specific numerical values, and FIG. 6 shows a graph of the numerical values of Table 7. In FIG. 6, the horizontal axis represents the refractive index N100 of the optical substrate, and the vertical axis represents the respective refractive indexes N1 to N5 in the first to fifth layers. The optical film thickness N × d in the first to fifth layers is also shown in Table 7. Here, the center wavelength λ0 is set to 500 nm.

  The reflectance distribution corresponding to the configurations of Table 7 and FIG. 6 is shown in FIGS. As in FIGS. 2 to 5, the horizontal axis is the wavelength λ (nm) at the time of measurement, and the vertical axis is the reflectance (%). As is apparent from the results of FIGS. 7 to 13, it was confirmed that in Examples 5 to 11 as well, the reflectance was within 0.5% or less in the wavelength band of approximately 350 nm to 700 nm.

  As is clear from the above basic data and each reflectance distribution diagram, a very good reflectance distribution is exhibited in each embodiment. That is, according to the antireflection film of the present invention, it was confirmed that the reflectance in a predetermined wavelength band can be sufficiently reduced and the reflectance distribution can be sufficiently flattened.

  The present invention has been described with reference to the embodiment and examples. However, the present invention is not limited to the above embodiment and example, and various modifications can be made. For example, the values of the refractive index and the optical film thickness of each layer and each substrate are not limited to the values shown in the above numerical examples, and can take other values. Also, the material types constituting each layer and each substrate are not limited to those shown in the above numerical examples, and other material types can be used.

  Furthermore, each layer may be composed of a plurality of films based on the equivalent film theory. That is, it may be configured to behave optically as a single layer by stacking two types of refractive index films symmetrically.

It is sectional drawing of the optical member as one embodiment in this invention. It is a reflectance distribution map corresponding to basic data of Example 1 of the present invention. It is a reflectance distribution map corresponding to basic data of Example 2 of the present invention. It is a reflectance distribution map corresponding to basic data of Example 3 of the present invention. It is a reflectance distribution map corresponding to basic data of Example 4 of the present invention. It is explanatory drawing showing each basic data of Examples 5-11 of this invention. FIG. 6 is a reflectance distribution diagram corresponding to the basic data of Example 5 shown in FIG. 5. FIG. 7 is a reflectance distribution diagram corresponding to the basic data of Example 6 shown in FIG. 5. It is a reflectance distribution map corresponding to the basic data of Example 7 shown in FIG. It is a reflectance distribution map corresponding to the basic data of Example 8 shown in FIG. It is a reflectance distribution map corresponding to the basic data of Example 9 shown in FIG. It is a reflectance distribution map corresponding to the basic data of Example 10 shown in FIG. It is a reflectance distribution map corresponding to the basic data of Example 11 shown in FIG. It is a reflectance distribution figure of prior art examples 1 and 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1-5 ... 1st layer-5th layer, C1 ... Antireflection film, 100 ... Optical substrate, 100S ... Surface.

Claims (5)

an antireflection film formed on a substrate having a refractive index of 1.75 or more and 2.10 or less with respect to a d-line,
When the first to fifth layers stacked in order from the substrate side are included, the refractive index with respect to the center wavelength λ0 in the first layer is N1, and the physical film thickness in the first layer is d1 And an antireflection film characterized by satisfying the following conditional expression (1).
0.45 × λ0 ≦ N1 × d1 ≦ 0.55 × λ0 (1) Furthermore, all the following conditional expressions (2)-(5) are satisfied, The antireflection film of Claim 1 characterized by the above-mentioned.
0.45 × λ0 ≦ N2 · d2 ≦ 0.55 × λ0 (2)
0.45 × λ0 ≦ N3 · d3 ≦ 0.55 × λ0 (3)
0.45 × λ0 ≦ N4 · d4 ≦ 0.55 × λ0 (4)
0.20 × λ0 ≦ N5 · d5 ≦ 0.30 × λ0 (5)
However,
λ0: Center wavelength N2 to N5: Refractive index with respect to the center wavelength λ0 from the second layer to the fifth layer d2 to d5: Physical film thickness from the second layer to the fifth layer The first layer and the third layer are made of an intermediate refractive index material exhibiting a refractive index of 1.53 or more and 1.85 or less with respect to the d-line,
The second layer and the fourth layer are made of a high refractive index material exhibiting a refractive index of 1.90 or more and 2.50 or less with respect to the d-line,
The antireflection film according to claim 1, wherein the fifth layer is made of a low refractive index material having a refractive index of 1.35 or more and 1.50 or less with respect to the d-line. The fifth layer includes at least one of magnesium fluoride (MgF ₂ ), silicon dioxide (SiO ₂ ), and aluminum fluoride (AlF ₃ ),
The first layer and the third layer are composed of praseodymium aluminate (PrAlO ₃ ), lanthanum aluminate (La _2X Al _2Y O _{3 (X + Y)} , La ₂ O ₃ .3.3Al ₂ O ₃ ), oxidation Including at least one of aluminum (Al ₂ O ₃ ), germanium oxide (GeO ₂ ), and yttrium oxide (Y ₂ O ₃ ),
The second layer and the fourth layer include lanthanum titanate (LaTiO ₃ ), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), tantalum oxide (Ta ₂ O ₅ ), niobium oxide (Nb ₂ O _5). ), Hafnium oxide (HfO ₂ ), and cerium oxide (CeO ₂ ). The antireflection film according to claim 1, wherein the antireflection film includes at least one selected from the group consisting of hafnium oxide (HfO ₂ ) and cerium oxide (CeO ₂ ). a substrate having a refractive index of 1.75 or more and 2.10 or less with respect to the d-line, and an antireflection film formed on the substrate,
The antireflection film is
When the first to fifth layers stacked in order from the substrate side are included, the refractive index with respect to the center wavelength λ0 in the first layer is N1, and the physical film thickness in the first layer is d1 The optical member is characterized by satisfying the following conditional expression (1).
0.45 × λ0 ≦ N1 × d1 ≦ 0.55 × λ0 (1)

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