JPH06250001A - Multilayer antireflection film and optical system provided with the same - Google Patents

Abstract

PURPOSE:To provide a multilayer antireflection film which can give the required antireflection effect regardless of the refractive index of optical parts such as a lens by successively forming a specified medium refractive index layer, high refractive index layer, and low refractive index layer on a substrate. CONSTITUTION:Three layers are successively formed on a substrate comprising an optical material when lambda is the standard wavelength in the wavelength range for the antireflection effect. These layers are, from the substrate side, (a) medium refractive index layer having lambda/4 optical film thickness and refractive index (n) satisfying 1.72<=n<=1.74, (b) high refractive index layer having lambda/2 optical film thickness and satisfying 1.97<=n<=2.13, and (c) low refractive index layer of MgF2 having lambda/4 optical film thickness. The reflection characteristics are shown in the figure when layers with the following refractive indices are formed. Namely, n=1.73 in the medium refractive index layer (Al2O3/Pr2O3), n=2.03 in the high refractive index layer (TiO2/La2O3), and n=1.38 in the low refractive index layer (MgF3). The leader lines in the figure show refractive indices of- substrates. Thus, good antireflection characteristics are obtd. regardless of the refractive index of the substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system comprising a multilayer antireflection film applied to an optical lens of a camera or the like, and an optical component provided with the multilayer antireflection film.

[0002]

2. Description of the Related Art In optical parts such as lenses, prisms and filters made of optical glass having a relatively large refractive index, adverse effects such as loss of light due to surface reflection occur, resulting in a decrease in transmittance of the optical system and image defects. Cause of. for that reason,
An optical component such as a lens is generally provided with an antireflection film. A single layer film such as MgF ₂ is basically used as the antireflection film, but the antireflection effect is not always sufficient depending on the refractive index of the glass material (optical glass) of the lens, and the effective wavelength range for antireflection is narrow. Therefore, on the short wavelength side (400n
It is difficult to effectively prevent reflection in a wide range from m) to the long wavelength side (700 nm).

Therefore, in order to bring the reflection close to zero and to realize a wide antireflection effect over the entire visible range, various multilayer antireflection films are applied to lenses and the like. However, the antireflection effect differs depending on the refractive index of the glass material that is the substrate, and in general, the refractive index of optical glass is 1.49 to 1.85.
Since it is distributed over a wide range, it is necessary to design individual films according to individual lenses made of different glass materials. In an ordinary optical system such as a camera, many lenses made of different glass materials are combined to satisfy the required optical performance, and a multilayer antireflection film with different film structure should be deposited on each lens. Causes the complexity of vapor deposition management and work, leading to an increase in product cost.

Since there is often no single substance having a suitable refractive index in terms of film design, an equivalent film method for producing a pseudo-refractive index by separately vapor-depositing a substance having a high and low refractive index, or vapor-depositing a composite substance. However, in this case, it is desirable to deposit the same substance under the same conditions as possible because the refractive index of the thin film obtained by the vapor deposition conditions is likely to change. It is desirable that changes in vapor deposition conditions be small.

[0005]

SUMMARY OF THE INVENTION The present invention provides a multilayer antireflection film capable of imparting a necessary antireflection effect regardless of the refractive index of an optical component such as a lens. The present invention also provides an optical system with an antireflection film in which the amount of reflection is averaged and suppressed as a whole in the visible wavelength range.

[0006]

The first multilayer antireflection film of the present invention has the following (a) on a substrate made of an optical material, where λ is a reference wavelength within a wavelength range for antireflection. ，
Each of the layers (b) and (c) is sequentially laminated. (A) The optical film thickness is λ / 4 and the refractive index n is 1.72 ≦ n
Intermediate refractive index layer of ≤1.74. (B) The optical film thickness is λ / 2 and the refractive index n is 1.97 ≦ n
High refractive index layer of ≦ 2.13. (C) A low refractive index layer having an optical film thickness of λ / 4 and made of MgF ₂ .

The second multilayer antireflection film of the present invention has the following (a '), (b') on a substrate made of an optical material, where λ is a reference wavelength within a wavelength range for antireflection. Each of the layers (c ') and (c') are sequentially laminated. (A ′) The optical film thickness is λ / 4 and the refractive index n is 1.74 <
An intermediate refractive index layer with n ≦ 1.77. (B ′) The optical film thickness is λ / 2 and the refractive index n is 2.07 ≦
High refractive index layer with n ≦ 2.13. (C ′) A low refractive index layer having an optical film thickness of λ / 4 and made of MgF ₂ .

Further, the optical system of the present invention is an optical system comprising at least two kinds of optical components having different refractive indexes, and the surfaces of all the optical components have the same film structure as described above regardless of the refractive index. It is characterized in that a multilayer antireflection film is applied.

[0009]

EXAMPLE FIG. 1 is an explanatory view showing the film constitution of the present invention, in which an intermediate refractive index layer 2 is formed on a substrate 11 made of an optical material.
3. High refractive index layer 25 and low refractive index layer 27 to be a surface layer
Are sequentially laminated to form a multilayer antireflection film 21.
The substrate 11 is made of optical glass, optical plastic, or the like. In the case of optical glass, the refractive index is 1.49 to 1.8.
About 5 are known, and they are used properly according to the required optical characteristics. Therefore, in a lens barrel (optical system) of a camera or the like, a plurality of glass materials having different refractive indexes are used.

Therefore, in order to search for a general-purpose multilayer antireflection film for glass materials, the low refractive index layer 27 on the surface is formed with MgF ₂
Then, the intermediate refractive index layer 23 and the high refractive index layer 25 having various refractive indexes were formed, and their antireflection properties were examined. Specifically, the wavelength range for antireflection is set to 400 to 700 nm, the reference wavelength λ is set to 520 nm, and an intermediate refractive index layer having an optical film thickness of λ / 4 and a λ / 2 layer on a glass material having various refractive indices. A high refractive index layer and a λ / 4 MgF ₂ layer (n = 1.38),
It was formed by a vacuum vapor deposition method using an electron gun as a vapor deposition source.

The glass material of the substrate 11 is 1.52.1.
85 various glass materials, that is, 1.52 (BK7), 1.
62 (F3), 1.70 (SF15), 1.80 (SF
60) and 1.86 (LASF21) were used. The intermediate refractive index layer 23 is made of Al ₂ O ₃ / Pr ₂ O ₃ based composite material and has a refractive index of 1.6 by controlling the composition and vapor deposition conditions.
It was formed as a layer of 5 to 1.77. The high refractive index layer 25 is
A TiO ₂ / La ₂ O ₃ composite material was used to form a layer having a refractive index of 1.90 to 2.13 by controlling the composition and vapor deposition conditions. As a result, good antireflection characteristics were obtained for all the glass materials used in the region (including the boundary) indicated by dots in FIG. Among these, the shaded region is particularly preferable, and the crossed region is more preferable.

That is, considering the regions in which suitable antireflection characteristics can be obtained by dividing by the refractive index of the intermediate refractive index layer, it is as follows. (1) The refractive index n of the intermediate refractive index layer is 1.72 ≦ n ≦ 1.
In the case of 74 (corresponding to claim 1), the high refractive index layer: 1.97 ≤ n ≤ 2.13, preferably 2.00 ≤ n ≤ 2.10, more preferably 2.02.
≦ n ≦ 2.04 (2) The refractive index n of the medium refractive index layer is 1.74 ≦ n ≦ 1.7.
In the case of 7, high refractive index layer: 2.07 ≦ n ≦ 2.13, preferably 2.09 ≦ n ≦ 2.11

Next, an example of specific reflection characteristics will be shown. Figure 3
Is a reflection characteristic when each layer having the following refractive index is formed on the substrate. Intermediate refractive index layer: n = 1.73 (Al ₂ O ₃ / Pr ₂ O ₃ ) High refractive index layer: n = 2.03 (TiO ₂ / La ₂ O ₃ ) Low refractive index layer: n = 1.38 (MgF ₂ ) The lead line in FIG. 3 indicates the refractive index of the glass material of the substrate. From FIG. 2, it can be seen that, by combining the intermediate refractive index layer and the high refractive index layer in the cross-hatched region of FIG. 2, suitable antireflection characteristics can be obtained for all glass materials having a refractive index of 1.52 to 1.85.

Next, Table 1 shows specific examples of various combinations of the intermediate refractive index layer and the high refractive index layer. In Table 1, a matrix is assembled and the characteristics of each combination are comprehensively judged.
I showed the reason. The meaning of the abbreviations in the table will be described below with an example. nd = 1.85: more than 1.5% →
In the case of a glass material having a refractive index of 1.85, the reflectance exceeds 1.5% in the entire wavelength range or in the intermediate wavelength range. Floating at 0 points → The reflectance curve does not approach zero in the entire wavelength range of 400 to 700 nm. Appears and the reflected light looks a little whitish.

[0015]

[Table 1]  Middle refractive index layer refractive index 1.65 1.70 1.73 1.76 High refractive index layer Refractive index: 1.90 Judgment: × Judgment: × Judgment: × Judgment: × nd = 1.85, nd = 1.52,1.85 nd = 1.52 nd = 1.85,1.52 : Over 1.5%: Over 1%: Over 1%: Over 1% 2.03 Judgment: × Judgment: × Judgment: ◎ Judgment: × nd = 1.85 nd = 1.85 nd = 1.52 to nd = 1.52: Over 1%: Over 1% 1.83: All OK: Over 1% See Figure 3 2.10 Judgment: × Judgment: × Judgment: ○ Judgment: ○ nd = 1.85 nd = 1.85 nd = 1.85 nd = 1.52: over 1.5% ： more than 1% ： 0 points float ： Short wave side 0.8% nd ＝ 1.70 0 points float Total OK in general OK in general : Floating by 0 points See Fig. 4 See Fig. 5

As described above, the antireflection film of the present invention can impart good antireflection ability to substrates having a wide range of refractive indexes. Generally, in cameras, television cameras, etc., the lenses are formed from multiple optical components such as lenses, and each lens has a different refractive index. However, the same antireflection is applied to all the lenses of these optical systems. Even if a film is applied, there is no problem as long as it is the antireflection film of the present invention. As such an optical system, an optical system composed of optical components having a refractive index of 1.49 to 1.85 is preferable.

As an example, the case where the antireflection film of the present invention is applied to a lens system for a video camera will be described. This video camera lens system includes a lens 1 with a refractive index of 1.49.
One, one 1.52 lens, one 1.59 lens, 1.
It is composed of three lenses of 62, one lens of 1.64, two lenses of 1.72, two lenses of 1.80, and two lenses of 1.85, for a total of 13 lenses. For all of these lenses, the central wavelength λ is 520 nm and the refractive index is 1.
73 Al ₂ O ₃ / Pr ₂ O ₃ composite material film λ / 4, TiO ₃ / La ₂ O ₃ composite material film λ / 2 having a refractive index of 2.03, and MgF ₂ film λ / 4 having a refractive index of 1.38. Was laminated to form a multilayer antireflection film, which was incorporated into a lens barrel to prepare a lens system of the present invention.

On the other hand, instead of the above-mentioned multilayer antireflection film, MgF
A lens system of a comparative example was prepared in the same manner except that a single-layer antireflection film composed of ₂ λ / 4 film was formed. The spectral transmission characteristics of these lens systems (lens barrels) were measured, and the results are shown in FIG. It can be seen that the multi-layer antireflection film of the present invention has much more excellent spectral transmission characteristics than the conventional single-layer antireflection film. This means that the antireflection film of the present invention and the optical system on which the antireflection film is deposited have excellent antireflection properties in the entire visible region.

Also, paying attention to FIG. 2, it can be seen that when the same antireflection film of the present invention is vapor-deposited on glass materials having different refractive indexes, the reflection peak shifts depending on the glass materials. Therefore, when looking at the spectral reflection characteristics of the entire optical system using lenses made of different glass materials, it is considered that a broad antireflection characteristic is obtained that is uniform throughout and has a gentle peak.

[0020]

According to the present invention, a three-layer film having an intermediate refractive index layer having a thickness of λ / 4, a high refractive index layer having a thickness of λ / 2, and a MgF ₂ low refractive index surface layer having a thickness of λ / 4 is used. By setting the refractive index of the refractive index layer and the high refractive index layer within a predetermined range, a multilayer antireflection film having excellent properties can be obtained regardless of the refractive index of the substrate formed thereby. If this multilayer antireflection film is used, it is not necessary to successively control the refractive index of the optical component to be vapor-deposited, and it is convenient for automation and application to a continuous vapor deposition device.
Cost reduction is also possible.

Further, by forming the same multilayer antireflection film for all of the optical components having different refractive indexes that constitute the optical system, an optical system having excellent antireflection properties can be obtained at low cost.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a layer structure of a multilayer antireflection film of the present invention.

FIG. 2 is an explanatory diagram showing the suitability of the combination of the refractive indexes of the intermediate refractive index layer and the high refractive index layer in the multilayer antireflection film of the present invention.

FIG. 3 is a graph showing the spectral reflection characteristics of a multilayer antireflection coating according to an example of the present invention for each substrate refractive index.

FIG. 4 is a graph showing the spectral reflection characteristics of a multilayer antireflection coating according to an example of the present invention for each substrate refractive index.

FIG. 5 is a graph showing the spectral reflection characteristics of a multilayer antireflection coating according to an example of the present invention for each substrate refractive index.

FIG. 6 is a graph showing spectral transmission characteristics of optical systems of the present invention and a comparative example.

[Explanation of symbols]

 11 Substrate 21 Multilayer Antireflection Film 23 Intermediate Refractive Index Layer 25 High Refractive Index Layer 27 Low Refractive Index Layer

Claims (3)

[Claims] 1. When a reference wavelength within a wavelength range for antireflection is λ, (a) an optical film thickness is λ / 4 and a refractive index n is 1.72 in order on a substrate made of an optical material. ≤n
An intermediate refractive index layer of ≦ 1.74, (b) an optical film thickness of λ / 2, and a refractive index n of 1.97 ≦ n
A multilayer antireflection film comprising: a high refractive index layer of ≦ 2.13; and (c) a low refractive index layer made of MgF ₂ and having an optical film thickness of λ / 4. 2. When the reference wavelength within the wavelength range for antireflection is λ, (a ′) the optical film thickness is λ / 4 and the refractive index n is 1. 74 <
an intermediate refractive index layer having n ≦ 1.77, (b ′) an optical film thickness of λ / 2, and a refractive index n of 2.07 ≦
A multi-layer antireflection film comprising a high refractive index layer satisfying n ≦ 2.13 and (c ′) a low refractive index layer made of MgF ₂ having an optical film thickness of λ / 4. 3. An optical system comprising at least two kinds of optical components having different refractive indexes, wherein the same multilayer according to claim 1 or 2 is provided on the surface of all the optical components regardless of the refractive index. An optical system having an antireflection film.