JPH0769482B2 - Anti-reflection film - Google Patents

Description

TECHNICAL FIELD The present invention relates to an antireflection film formed on an optical glass element produced by press-molding an optical glass material.

2. Description of the Related Art In recent years, optical lens elements such as optical glass lenses have tended to be aspherical in order to simultaneously achieve simplification, weight reduction and high performance of optical characteristics of optical devices. In the production of this aspherical glass, it is difficult to process and mass-produce it by the conventional polishing method, and a press molding method is regarded as a promising alternative manufacturing method. It has been put to practical use in pickup lenses and the like. A lens that uses a semiconductor laser, such as the pickup lens, needs to maintain necessary optical characteristics even if the wavelength of the semiconductor laser fluctuates to some extent. Therefore, recently, low-refractive index / low-dispersion glass having a refractive index of 1.48 or less and a dispersion of 80 or more is used.

In addition, in order to improve the optical characteristics of an optical glass element manufactured by either a polishing method or a press molding method,
It is known as a general technique to stack a dielectric substance on the surface of an optical glass element by a vacuum deposition method or the like to form an antireflection film. (For example, Kubota et al. "Optical Technique Handbook") Hereinafter, a conventional antireflection film of an optical glass element will be described with reference to the drawings. Figure 2 is a diagram showing the structure to form an antireflection film made of magnesium fluoride on a surface of the optical glass element, Figure 3 of 6 optical film thickness of the antireflection film is 0.25λ _0/4 (λ ₀ Shows the spectral reflection characteristics when formed to a thickness of 830 nm). In FIG. 2, 1 indicates that the refractive index and dispersion (hereinafter abbreviated as refractive index and dispersion) for the d-line are 1.
An optical glass element 4 made by pressing an optical glass material of 43,95.0 is an antireflection film made of magnesium fluoride. The antireflection film 4 is generally formed by a vacuum deposition method.

However, the refractive index as described above is 1.48 or less, the dispersion is 80
Even if a conventional antireflection film is formed on an optical glass element produced by press-molding the above-mentioned low-refractive index / low-dispersion optical glass element, the residual reflectance is high as shown in FIG. Since an altered layer is formed on the surface of the optical glass element due to the thermal effect of 1., the antireflection film has problems that the adhesion to the optical glass element is poor and the durability is low.

In view of the above problems, the present invention has a refractive index of 1.48 or less and an Abbe number of
An antireflection film having a low residual reflectance and excellent adhesion and durability is provided on the surface of an optical glass element produced by press-molding 80 or more optical glass materials.

Means for Solving the Problems The present invention is, in order to solve the above problems, an antireflection film formed on the surface of an optical glass element, the antireflection film having a two-layered structure from the optical glass element surface side. The first layer is made of a high refractive index material having a refractive index of 1.90 to 2.40, the second layer is made of a low refractive index material having a refractive index of 1.35 to 1.50, and the optical thickness of each layer is The present invention provides an antireflection film that satisfies the following conditions.

0.05λ ₀ <n ₁ d ₁ <0.25λ ₀ n ₂ d ₂ > 0.25λ ₀ where n ₁ d ₁ and n ₂ d ₂ are the optical thicknesses of the first and second layers , Λ ₀ is the design center wavelength.

Action As described above, when an antireflection film is formed on an optical glass element made by press molding an optical glass material having a low refractive index, the residual reflectance is high, and the optical glass element formed at the time of press molding There is a problem that the adhesion and durability of the antireflection film with the optical glass element are poor due to the modified layer of the surface layer, but the antireflection film has a two-layer structure, and the first layer from the optical glass element is A high-refractive-index oxide dielectric with a refractive index in the range of 1.90-2.40 is used and its optical thickness is
By setting it to 05λ _{0 to} 0.25λ ₀ , the adverse effect of the altered layer on the surface of the optical glass element is avoided, and the adhesion and durability of the antireflection film with the optical glass element are improved, and the refractive index of the second layer is increased.
An antireflection film having a low residual reflectance can be obtained by using a low-refractive index dielectric material in the range of 1.35 to 1.50 and making its optical film thickness greater than 0.25λ ₀ .

Examples Hereinafter, an antireflection film of one example of the present invention will be described with reference to the drawings.

FIG. 1 shows the structure of an antireflection film in an example of the present invention. In FIG. 1, 2 is a layer of titanium dioxide having an optical thickness of 0.0625λ ₀ , 3 is a layer of diatom dioxide having an optical thickness of 0.345λ ₀ , and λ ₀ = 830 nm. 1 is an optical glass element, n _d = 1.43, ν _d = 95.0
It is a glass material produced by press molding. In addition, each layer was formed by a vacuum vapor deposition method. Reference numeral 5 in FIG. 3 shows the spectral reflection characteristics of the antireflection film in this embodiment. As can be seen from FIG. 3, the residual reflectance of the antireflection film according to the present invention is 0.2% or less at 830 nm, which is clearly superior to the conventional example. Further, the tests conducted to compare the adhesion and durability between the antireflection film of the example of the present invention and the conventional antireflection film were as follows: (1) Adhesive tape peeling test (temperature 40 ° C., relative humidity 85%) After being left in the high temperature and high humidity atmosphere for 1000 hours, the adhesive tape is adhered to the surface of the optical glass element and peeled off.
It is left for 1000 hours in a high temperature and high humidity atmosphere), and the conventional antireflection film for comparison is a magnesium fluoride antireflection film formed on the optical glass element, which is one of the conventional examples, by a vacuum deposition method. is obtained by forming the thickness of the optical thickness _{λ 0/4 (λ 0 =} 830nm). The results of the adhesion and durability tests are shown in Table 1.

As described above, the antireflection film of this example has a two-layer structure formed on the surface of the optical glass element, and the first layer from the surface side of the optical glass element has an optical film thickness of 0.0625 made of titanium dioxide. lambda _0, the second layer is an optical film thickness 0.345Ramuda ₀ consisting of silicon dioxide, the adhesion and durability of the conventional residual reflectivity from the antireflection film is low more optical glass element by such An antireflection film having excellent properties can be obtained.

The film thickness of the antireflection film of the above-mentioned embodiment is not particularly limited to the above value, and may be changed according to the design wavelength. The substance forming the antireflection film may be ZrO ₂ or The mixture of ZrO ₂ and TiO ₂ , the first layer may be MgF ₂ .

As described above, the present invention has a refractive index of 1.48 or less and an Abbe number of
A two-layer antireflection film is formed on the surface of an optical glass element made by press molding 80 or more optical glass materials. The antireflection film is the optical glass element and the first layer has a refractive index of 1.90.
~ 2.40 made of high refractive index material, the second layer is made of low refractive index material of 1.35 ~ 1.50 range,
In addition, by satisfying the following conditions for the optical film thickness of each layer, it is possible to obtain an antireflection film having a low residual reflectance, good adhesion to an optical glass element, and excellent durability.

0.05λ ₀ <n ₁ d ₁ <0.25λ ₀ n ₂ d ₂ > 0.25λ ₀ where n ₁ d ₁ and n ₂ d ₂ are the optical thicknesses of the first layer and the second layer, respectively. Yes, λ ₀ is the design center wavelength.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an antireflection film in one embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional antireflection film, and FIG. 3 is a spectral reflection characteristic diagram. DESCRIPTION OF SYMBOLS 1 ... Optical glass element, 2 ... Layer made from titanium dioxide, 3 ... Layer made from diatom dioxide, 4 ... Layer made from magnesium fluoride, 5 ... Antireflection film in the Example of this invention, 6 ... ... Conventional antireflection film (antireflection film made of magnesium fluoride).

Claims (3)

[Claims] 1. An antireflection coating formed on the surface of an optical glass element produced by press molding an optical glass material having a refractive index (n _d ) for d-line of 1.48 or less and an Abbe number (ν _d ) of 80 or more. The antireflection film has a two-layer structure, and the first layer from the optical glass element side is made of a high refractive index material having a refractive index of 1.90 to 2.40, and the second layer is a refractive index of 1.35 to 1.
An antireflection film comprising a low refractive index material in the range of 50 and satisfying the following conditions for the optical thickness of each layer. 0.05λ ₀ <n ₁ d ₁ <0.25λ ₀ n ₂ d ₂ > 0.25λ ₀ where n ₁ d ₁ and n ₂ d ₂ are the optical thicknesses of the first layer and the second layer, respectively. Yes, λ ₀ is the design center wavelength. 2. The antireflection film according to claim 1, wherein the low refractive index substance is MgF ₂ or SiO ₂ . 3. The antireflection film according to claim 1, wherein the high refractive index substance is ZrO ₂ or TiO ₂ or a mixture thereof.