JPH04116504A - Half mirror - Google Patents

Abstract

PURPOSE:To obtain an optically flat characteristic by composing the half mirror of the five layers of dielectric multilayered films and lowering the refraction factor of either the first or fifth high refraction factor layer a little rather than that of the other high refraction factor layer. CONSTITUTION:This prism type half mirror is composed of an incident side prism 1, dielectric multilayered films 2, emissive side prism 3 and adhesive agent layer 4 for bonding the two prisms 2 and 3, and an incident beam 5 made incident to a prism 1 is splitted into a reflected beam 6 and a transmitted beam 7 by the interference effect of the multilayered films 2. By laminating a high refraction factor layer H having the film thickness of 1/4lambda0 for comparatively easily executing film thickness control and a low refraction factor layer L, a fifth high refraction factor layer H' to be the top layer has the film thickness of 1/2lambda0 lowering the value of the refraction factor a little rather than that of the H layer. In such a case, the lambda0 is a design wavelength for designing the film constitution. Thus, the optically flat characteristic can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used to separate subject light into reflected light and transmitted light, such as an autofocus optical system, an imaging optical system, a finder optical system, and an imaging optical system. This invention relates to improving the optically flat characteristics of a half mirror.

[Conventional technology]

Conventionally, when a semi-transparent film is formed on the prism surface and then two prisms are glued together and used as a half mirror,
The semi-transparent film may be a metal film, a dielectric film, or a combination of a metal film and a dielectric film, and a half mirror having the structure shown below has been proposed.

That is, as a combination of a metal film and a dielectric film, US Pat. No. 3,559,090 discloses a combination of glass/dielectric layer/
Ag metal layer/dielectric layer/glass, JP-A-56-2710
In No. 1, glass/high refractive index dielectric layer H/low refractive index dielectric layer L/metal layer/H /L/glass, in JP-A-56-43601, glass/L/Ag metal layer/
A layered structure of H/glass (H and L have the same meanings as above) is described.

In addition, as a combination of only dielectric layers, JP-A-63
-56604, JP-A-63-56605, JP-A-63-
56606, both of which have a high refractive index dielectric layer H layer,
It is described as forming an alternating multilayer film consisting of 7 to 11 layers including a low refractive index dielectric layer.

[Problem to be solved by the invention]

When a metal film is used as a semi-transparent film, light absorption occurs inside the film, and the sum of reflected light and transmitted light is 100%.
Therefore, the light cannot be used effectively. Furthermore, the transmittance or reflectance is not constant depending on the wavelength, and optically flat characteristics cannot be obtained. Further, even when a metal film and a dielectric film are combined as described above, the problem of absorption and the problem of optically flat characteristics are somewhat improved, but this is not sufficient.

Furthermore, when a dielectric multilayer film is used, there is no absorption and optically flat characteristics can be obtained, but the total number of films is as large as 7 to 11, and the film thickness is also strictly limited. Because of this, it is technically difficult, takes a long time to manufacture, and has poor productivity.

In the prism type /\-7 mirror, which consists of a semi-transparent film on the prism surface and two prisms glued together, this /1-fmirror prism is used to operate an AF device such as an autofocus (AF) video camera. When used to separate the AF optical system and the imaging system for photographing the subject,
It is necessary to have a reflectance and transmittance in the entire visible light range (400 nm to 700 nm), especially in the range from 450 nm to 650 nm, where colors are easily noticeable.

If the reflectance differs depending on the wavelength, the reflected light or transmitted light will be biased depending on the wavelength, resulting in a phenomenon called coloring.

The present invention uses a dielectric multilayer film as a multilayer film forming a half mirror, provides a nof mirror that has no absorption and has optically flat characteristics, and furthermore provides a half mirror that has optically flat characteristics. - by stacking a small number of dielectric multilayer films, and the objective is to make it possible to manufacture it at low cost.

[Means to solve the problem]

This objective is achieved by one of the following technical means 1, 2.3.

(1) In a prism ffi mirror in which two prisms are bonded together and a dielectric multilayer film is formed on the bonded surface, the dielectric multilayer film is formed into a first layer, a second layer, etc. from the prism surface. In the case of One of the high refractive index layers is a layer having a slightly lower refractive index than the other high refractive index layer./S-7 mirror (2) The refractive index of the high refractive index vapor deposited material layer. is nH, then the refractive index n of either the first layer or the fifth layer is
The half mirror according to item 1, wherein 18 is in the following range: nHI>n'->0.75nH (3) Vapor deposition having a refractive index n'o of the first layer or the fifth layer. H-7 mirror according to item 1 or 2, characterized in that a mixture of titanium oxide and praseodymium oxide is used as the material [Function] The structure of the present invention is shown below. A semitransparent film made of a dielectric multilayer film is formed on the joining surface of one of the two prisms using a method such as vacuum evaporation, and then another layer is applied to the surface of the film via an adhesive layer. A prism-type half mirror is constructed by bonding prism substrates, and the multilayer film that functions as a semitransparent film is as shown below. is the desired value range to obtain . Here H
is a high refractive index vapor deposition material, L is a low refractive index vapor deposition material, and H layer is H.
nl (i = 1 to 5) means the refractive index of the i-th layer film n1d4 means the optical thickness of the i-th layer film do. λ.

is the design wavelength when designing the film configuration.

The characteristic that the amount of reflected light and the amount of transmitted light have a constant ratio over the visible wavelength region is called optically flat characteristic, but in order to improve this characteristic, the nHnd of each layer must be within a certain range. desirable.

The basic thickness of each layer is 1/4λ, which is relatively easy to control.
. However, by adjusting the film thickness according to the refractive index of the selected vapor deposition material, it is possible to achieve even more optically flat characteristics.
It becomes possible to do so.

Furthermore, the refractive index nM' of the H' layer must be limited to the range of 0.75nH≦nH' (nH) relative to the refractive index nH of the H layer.As nH' is gradually lowered from nH, the optical Optically flat characteristics can be obtained, but the wavelength range becomes narrower.If nHl is lower than 0.75 This is because it ends up cutting you off.

Furthermore, by using the film structure of the present invention, by setting nH and nMl to appropriate values, the ratio of reflectance R and transmittance T can be set to R:T-50%=50%, R:T-5Q. %=40%,
It is also possible to set it arbitrarily.

The basis of the present invention is a relatively simple method for controlling film thickness.
/4λ. The refractive index of the fifth high refractive index layer H', which is the top layer, is l, which has a slightly lower value than the H layer. /・2λ. It is characterized by a film thickness of . Here, even if the values of the refractive index and the optical film thickness of the first layer and the fifth layer are switched, there is no problem because they exhibit exactly the same effect.

The vapor deposition materials for each layer include, for example, T1 sail for the H layer;
It can be selected from mixtures of C, O, , Z, O, , T, O, and P r * Oy, and the H'' layer can be selected from the same material group as the H layer, or YwOy, AlxOy. You can choose from among them.Here, X and Y are 1≦X≦2,
This value is arbitrarily selected from l≦Y≦2.

Further, as the L layer, M, F, , S, 0. ,AlwOY・
You can choose from...etc. Even if the H'' layer is made of the same vapor deposition material as the H layer, the refractive index can be adjusted by arbitrarily selecting the vaporization conditions, for example by changing the amount of oxygen gas introduced during vapor deposition. I don't mind.

〔Example〕

An embodiment of the present invention will first be described with reference to FIG.

The prism-type half mirror includes a prism 1 on the entrance side, a dielectric multilayer film 2 formed on the prism 1, and a prism 3 on the exit side.
．． It is composed of an adhesive layer 4 for joining two prisms 2.3, and the incident light 5 entering the prism 1 is divided into reflected light 6 and transmitted light 7 due to the interference effect of the dielectric multilayer film 2. Ru.

The material of the prism i3 may be glass or plastic, but it is preferable to use glass BK7, which is relatively widely used.

Further, since the adhesive 4 is made of a material having a refractive index equivalent to that of the prism substrate, it does not affect the film characteristics of the dielectric multilayer film. Possible adhesives include thermosetting or ultraviolet curable resins, but considering ease of handling,
It is desirable to use an ultraviolet curable resin.

The dielectric multilayer film 2 can be formed by vacuum evaporation, sputtering, or the like.

Specific examples and comparative examples of the present invention will be described below.

Example 1 The configuration of the half mirror of Example 1 is as shown in the following table *MER
(Manufactured by J company product name: Substance Incident angle 45″ λ. = 700 nm As the high refractive index layer (H layer), titanium oxide T, O as the low refractive index layer (L layer) Magnesium fluoride M□F0, H
A mixture of substance (1) was selected as a high refractive index layer (one H layer) having a slightly lower refractive index than the other layers, and five layers were laminated on a BK7 glass prism using a vacuum evaporation method. The film thickness nd of each layer is 0.25λ to achieve optically flat characteristics.・0.
5λ. It's more of a shift than that.

During vapor deposition, the inside of the vacuum chamber was heated to 350℃, and 2.0×1
Vapor deposition was carried out while introducing oxygen gas up to 0"' mbar. After the vapor deposition was completed, it was taken out into the atmosphere and an ultraviolet curable adhesive No. manufactured by Norland Co., Ltd. having a refractive index almost the same as BK7 was used.
61 was used to perform the bonding. When the spectral reflectance of 45° incident light was measured, the curve looked like the one shown in FIG. 2. In the visible light region, especially in the range of 450 nm to 650 nm, the reflectance could be suppressed to within 50%±3%.

On the other hand, as a comparative example, a case is given in which a high refractive index layer and a low refractive index layer are simply stacked on top of each other.

Comparative Example 1 is a case in which titanium oxide T is selected as a high refractive index material, and magnesium fluoride M and F are selected as low refractive index materials, and five layers are laminated with a film thickness of 1/4 wavelength. In this case, the reflectance has a chevron-shaped characteristic due to the interference effect of each layer. The spectral reflectance characteristics in this case are shown in FIG.

Comparative Example 2 includes the structure of Comparative Example I in which the thickness of the fifth layer is changed to 1/2 wavelength.

The spectral reflectance characteristics in this case are shown in FIG. Although the characteristics are slightly improved compared to Comparative Example 1, they are not sufficient. Film thickness is 0.25λ. , 0.5λ. No improvement in characteristics was observed even if the distance was shifted further. These examples and Example 1
You can also compare the refractive index of the 5th layer with that of the 1st layer and 3rd layer.
It can be seen that optically flat characteristics can be obtained by making the thickness lower than the thickness of the layer. Incidentally, the data for Comparative Examples 1 and 2 are as shown in the following table.

λ. −700 nm *The data in parentheses is for Comparative Example 2, and data other than * are common to Comparative Example 1 and Comparative Example 2.

Example 2 The configuration of the half mirror of Example 2 is as shown in the following table.

λ. -700 nm That is, titanium oxide T, O, as the H layer, magnesium fluoride M, F, as the L layer, and itrium oxide y, oY as the H' layer. A layer with a refractive index of n)I' -0,766 nH was chosen as the H' layer.

The spectral reflectance characteristics in this case are shown in FIG. Looking at this characteristic, although the reflectance R decreases on the short wavelength side and long wavelength side of the visible light region, in the range of 450 nm to 650 nm, R is suppressed to within 50%±3%.

However, if the value of the H' layer is made lower than this, the decrease in reflectance on the short wavelength side and the long wavelength side becomes large, making it impossible to obtain optically flat characteristics, which is the object of the present invention.

Therefore, the refractive index of the H' layer is 0.75nH<nH'<1. You will need to choose within the range.

Example 3 As Example 3, the ratio of reflected light R and transmitted light T is R:T=
An example of 40%:60% is shown. The configuration of the half mirror is shown in the following table.

This has a structure in which Substance (described above), which is a mixture of titanium oxide and praseodymium oxide, is used as the H layer, magnesium fluoride is used as the L layer, and yttrium oxide is used as the H1 layer.

The spectral reflectance characteristics in this case are shown in FIG. 6, and it can be seen that good optical characteristics are exhibited in the visible region, particularly in the range from 450 nm to 650 nm.

In all the cases of the examples, it does not matter even if the first layer and the fifth layer are exchanged because the same characteristics can be obtained.

However, since it is known that titanium oxide has the property of reacting with ultraviolet curable resin and absorbing light, it is preferable not to use it as the fifth layer, that is, the layer in contact with the adhesive layer.

By using the configuration of the present invention as described above, a half mirror with optically flat characteristics can be realized by stacking five layers of films.

〔Effect of the invention〕

According to the present invention, the number of dielectric multilayer films deposited on the prism substrate can be kept to five layers, and the optically flat characteristics of a half mirror can thereby be satisfied. As a result, a high-performance half mirror can now be provided with technically easier technical means and manufacturing time.

[Brief explanation of drawings]

Figure 1 is a structural diagram of a half mirror. FIG. 2 is a spectral reflectance curve of Example 1 of the present invention. 3 and 4 are spectral reflectance curves of comparative examples, respectively. FIG. 5 is a spectral reflectance curve of Example 2 of the present invention. FIG. 6 is a spectral reflectance curve of Example 3 of the present invention. ■・・・Incidence side prism 2...Dielectric multilayer film 3... Output side prism 4...Adhesive layer 5...Incoming light 6...Reflected light 7...Transmitted light

Claims (1)

[Claims] (1) In a prism-type half mirror in which two prisms are bonded together and a dielectric multilayer film is formed on the bonded surface, the dielectric multilayer film is arranged in a first layer, a second layer, and so on from the prism surface.
In the case of A half mirror characterized in that one of the high refractive index layers has a slightly lower refractive index than the other high refractive index layer. (2)
If the refractive index of the high refractive index vapor deposition material layer is n_H, then the refractive index of either the first layer or the fifth layer is n'_
The half mirror according to claim 1, wherein H has a relationship of n_H>n'_H>0.75n_H. (3)
3. The half mirror according to claim 1, wherein the first layer uses a mixture of titanium oxide and praseodymium oxide as a vapor deposition material having the refractive index n'_H of the fifth layer.