JPS6356605A - Half-mirror - Google Patents

Abstract

PURPOSE:To improve color reproducibility and to reduce light loss by providing a light translucent film of seven-layer constitution wherein the refractive index and film thickness of each layer are specified in order from one prism side to the other prism side. CONSTITUTION:A half-mirror is obtained by joining an incidence-side prism 1 which has a multilayered film 2 to a transmission-side prism 3. The multilayered film 2 is constituted by providing 1st, and 2nd-7th layers of materials with refractive indexes (ni) (i=1-7) shown by expressions II on the prism 1 of glass with a refractive index nG shown by an expression I, and the optical film thickness (nidi) (i=1, 2-7) is specified by expressions III, where lambda0 is designed wavelength. Thus, the flatness of reflectivity and transmissivity is improved and its waviness is small, so the color reproducibility is superior and the light loss is reducible.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a half mirror with excellent color reproducibility of reflected light and transmitted light.

Conventional half mirrors are made by depositing metal or non-metal on a glass surface to an appropriate thickness, and have the function of dividing incident light into reflected light and transmitted light at appropriate ratios.

Autofocus (AF) AF on video cameras, etc.
It is conceivable to use a half mirror to separate the AP system light for device operation and the imaging system light for photographing the subject, but such a half mirror can separate light of each wavelength in the visible light (400 to 700 nm) range. It must be reflected with equal reflectance (hereinafter referred to as "reflectance flatness"), and must have equal transmittance and transmission stagger (hereinafter referred to as "transmittance flatness"). . Otherwise, the reflected light and transmitted light will deviate from the natural color of the subject, causing a phenomenon called "coloration" in which certain colors stand out.

Conventionally, a half mirror with a multilayer structure in which a material with a high refractive index and a material with a low refractive index are alternately laminated on a substrate is known as a technology intended to maximize the reflectance of a half mirror. (For example, U.S. Pat. No. 3,559,090, JP-A-56-27106, JP-A-56-43601, etc.).

However, as mentioned above, a multilayer film in which materials with different refractive indexes are alternately layered is a stack of films having an optical thickness of 0.25λ relative to the designed dominant wavelength (λ). ,
A half mirror having such a multilayer film has a good increase in reflectance at the designed dominant wavelength, but no increase in reflectance can be expected around the designed dominant wavelength. Therefore, it is not possible to expect flatness of the reversal rate and flatness of transmitted light over the entire visible light range, and problems such as coloration occur.

The technology disclosed in US Pat. No. 3,559,090 relates to a half mirror laminated in a structure of glass + dielectric layer + Ag metal layer + dielectric layer and glass. The dielectric layer is a film made of a material with a high refractive index. The half mirror of the above invention minimizes the separation between the P component and the S component of polarized light, but since it contains metal (Ag), it absorbs a lot of light, making it impossible to use light effectively, and has a high reflectance. The disadvantage is that the flatness of the film and the flatness of the transmittance are not sufficient.

The technology disclosed in Japanese Patent Application Laid-Open No. 56-27106 has a high refractive index.
1 has a low refractive index and the intermediate refractive index is M, glass + dielectric (H) layer + dielectric (M) layer 10Ag or AQ metal layer + dielectric (M) layer dielectric ( I]) relates to a half mirror laminated in a structure of layer + glass.

The half mirror of the above invention suppresses p, s separation and can obtain approximately equal reflectance and transmittance, but like the half mirror described in U.S. Pat. Aff), the light absorption is large, the light cannot be used effectively, and the flatness of the reflectance and the flatness of the transmittance are not sufficient.

The technique of JP-A No. 56-43601 is that glass layer + dielectric layer (L or M) ÷ AgAg metal layer heavy dielectric I)
The present invention relates to a half mirror laminated in a structure consisting of layers and glass (H, M, and L have the same meanings as above).

The above half mirror is covered by the above-mentioned U.S. Patent No. 1355.
Although it is improved in terms of light absorption compared to the half mirror described in No. 9090, it still has the drawback that the flatness of the reflectance and the flatness of the transmittance are not sufficient.

Problems to be Solved by the Invention Conventional half mirrors have poor color reproducibility because the reflectance and transmittance of visible light (400 to 700 nm) are not sufficiently flat, and the light absorption is large, making it difficult to effectively use light. There was a problem that it could not be used.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide a half mirror with excellent flatness of reflectance and flatness of transmittance and low optical loss.

Means for Solving the Problems In order to achieve the above object, the inventors of the present invention, after repeating various trials and errors, discovered that the object can be achieved if the following conditions are satisfied.

Therefore, the present invention is characterized in that it satisfies these conditions. That is, the present invention provides a half mirror in which two prisms are joined together and a light semi-transparent film is formed on the joint surface thereof, in which the light semi-transmissive film is formed in order from one prism side to the other prism side as a first layer, It consists of a seven-layer structure consisting of a second layer, . . . , and a seventh layer, and is characterized by satisfying the following conditions.

1.50≦nG≦[,60 1,95≦n1≦2.30 0.59λ0≦n, d,≦
0.67λ.

1.38≦n, ≦1.66 0.22λ0≦nt (L≦
0.36λ01.95≦13≦2.30 0. ．． 13λ
0≦n3d3≦0, 31λ01.38≦n. ．． 66 0
．． 18λ0≦n4d4≦0.41λ.

1.95≦n,≦2.30 0.23λ0≦n5d,≦
0.37λ.

1.38=ns=1.66 0.36λo :nade
=0, 47λ.

1.953n732.30 0J7λo =n7d7=
0, 48λ0, where ni is the refractive index of the i-th layer (
i=I, 2,3°...7),...7), nidi
is the optical thickness of the i-th layer (i=1.2, 3°...7) n
G is the refractive index of the prism, λ. is the design wavelength.

A schematic cross-sectional view of the half mirror of the present invention is shown in FIG. 1st
In the figure, (1) is the entrance side prism, (2) is the prism (1)
The multilayer film laminated on top, (3) is the transmission side prism, (
4) represents an adhesive layer (4) that joins the entrance side prism (1) and the transmission side prism (3).

The incident light (5) has an incident angle of 45 degrees (
6), the reflected light (7) enters the entrance prism (1) and is reflected on the multilayer film, and the transmitted light (8) passes through the multilayer film (2).
).

The half mirror of the present invention can be used in the visible light region (400 to 660
It is effective for visible light (5) that enters at an incident angle (6) of 45 degrees, and has a good reflected light (7) with a flat reflectance and a good flat transmittance. transmitted light (
8), reflected light (7) and transmitted light (8).
), no coloring phenomenon occurs and the color reproducibility is good.

The multilayer film (2) consists of a prism (1) made of glass having a refractive index of 1.517, a layer made of a material having a high refractive index (hereinafter referred to as "high refractive layer") as the first B, and a layer having a low refractive index. (hereinafter referred to as "low refractive layer")
It has a structure in which seven layers are stacked alternately. Note that the terms "high" and "low" used here are used to express the relative relationship between the two.

The reason why the multilayer film has a seven-layer structure is that the high refractive layer has a refractive index of 2. l
The result is a design in which a reflectance of approximately 45% is obtained when a material with a refractive index of 1.385 is applied to the low refractive layer, and a material with a refractive index of 2.30 is used in the high refractive layer. This is because the 7B configuration became necessary as a result of designing so that a reflectance of about 50% can be obtained when a material with a refractive index of 1°47 is applied to the low refractive layer. However, in the present invention,
The refractive indexes of the substances applied to the high refractive index layer and the low refractive index layer, respectively, are not limited to the above values (2, 10, 1,385) or (2, 30, 1, 47).

The high refractive layer is composed of a substance having a refractive index of 1.95 to 2.30, and such substances include ZrO*, Tio
tq CeOt, Hrot, etc. can be used.

When the refractive index is lower than 1.95, the target reflectance is 50%.
This is because if the reflectance is higher than 2°30, the reflectance will be too high than 50%.

The low refractive layer is composed of a material having a refractive index of 1.38 to 1.66, and examples of such materials include MgPt, 5iO1, and A.
Q t 03 etc. can be used. The refractive index is 1.
If it is lower than 38, the reflectance will be too high than the target reflectance of 50%, and if it is higher than 1,66, the reflectance will be too low than 50%.

The high refractive layer and the low refractive layer can be formed using the above-mentioned substances by vacuum evaporation or sputtering, but in the present invention it is preferable to form them by vacuum evaporation. The electron beam method is used as the evaporation method, and the ultimate vacuum level is 3 X I.
The test is carried out under the conditions of O-'Torr and substrate temperature of 300°C.

Each of the high refractive layers constituting the odd layers and the low refractive layers constituting the even layers of the multilayer film (2) emits light (λ) with a wavelength of 550 nm.

) is adjusted to have the optical film thickness shown in Table 1 below.

table ! In the present invention, each layer constituting the multilayer film (2) has a thickness of 0.25λ as shown in Table 1. By setting the film thickness to be shifted from an integral multiple of , it is possible to achieve a flat reflectance for reflected light (7) and a flat transmittance for transmitted light (8) over a wide wavelength range of visible light. .

The half mirror of the present invention is obtained by joining an incident side prism (+) having a multilayer film (2) and a transmission side prism (3).

It is preferable to use a prism made of the same type of glass as the incident side prism (1) as the transmission side prism (3).

The entrance side prism (1) and the transmission side prism (3) are joined using an adhesive that has a refractive index equal to that of the glass that makes up the prism, and the adhesive is transparent in the visible range. If so, there are no particular limitations.

From the point of view of convenience, it is effective to use an ultraviolet curing adhesive such as Bardrop (trade name, manufactured by 'r4 Ki Kagaku Kogyo Co., Ltd.). By selecting an adhesive having the same refractive index as the prism, the loss of light amount between the prism and the adhesive and the interference in the plane between the adhesive and the multilayer film can be ignored.

The half mirror of the present invention can also be used with light entering from the transmission side prism (3) side, and the optical characteristics will not change.

The half mirror of the present invention can be effectively used as a light splitting prism for use in AF video cameras and other optical equipment.

The present invention will be explained below with reference to Examples.

The half mirror in each example is made of BK-7 glass (refractive index 1.517) and has a multilayer film in which each layer is sequentially laminated on the surface of an incident side prism as shown in each example. This is obtained by applying an ultraviolet curable resin between the two, gluing them together, and then curing them.

Example 1 Angle of incidence θ = 45° Example 2 Angle of incidence θ = 45° Example 3 Angle of incidence θ = 45° Example 4 Angle of incidence θ = 45° Example 5 Angle of incidence θ = 45° Example 6 Angle of incidence The spectral reflection characteristics of the actual length example with θ=45° are shown in FIG.

Example 7 Incident angle θ=45° As is clear from FIGS. 2 to 8, the reflectance of the light reflected by the half mirror was almost flat, and the waviness was within ±3%.

The half mirror obtained according to the present invention had a transmittance value of +00 minus reflectance in each example, and the optical loss was approximately 0.

Effects of the Invention The half mirror obtained according to the present invention has good reflectance and transmittance flatness, has small waviness of less than 3%, has excellent color reproducibility, and has no light loss. Light can be used effectively.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the half mirror of the present invention. FIGS. 2 to 8 are diagrams showing the spectral reflectance characteristics of the half mirror of the present invention. The symbols in the figure are as follows. l...Incidence side prism, 2...Multilayer film, 3...
・Transmission side prism, 4...adhesive layer, 5...incident light, 6...incident angle, 7...reflected light,
8...Transmitted light. Figure 1 Mi84-? end iz so←2 -d; 礪←2

Claims (1)

[Claims] 1. In a half mirror in which two prisms are joined together and a light semi-transparent film is formed on the joint surface, the light semi-transparent film is formed in order from the side of one prism to the side of the other prism. A half mirror consisting of a seven-layer structure consisting of a layer, a second layer, a seventh layer, and satisfying the following conditions: 1.50≦nG≦1.60 1.95≦n_1≦2 .30 0.59λ_0≦n_1
d_1≦0.67λ_0 1.38≦n_2≦1.66 0.22λ_0≦n_2
d_2≦0.36λ_0 1.95≦n_3≦2.30 0.13λ_0≦n_3
d_3≦0.31λ_0 1.38≦n_4≦1.66 0.16λ_0≦n_4
d_4≦0.41λ_0 1.95≦n_5≦2.30 0.23λ_0≦n_5
d_5≦0.37λ_0 1.38≦n_6≦1.66 0.36λ_0≦n_6
d_6≦0.47λ_0 1.95≦n_7≦2.30 0.37λ_0≦n_7
d_7≦0.48λ_0 where ni: refractive index of the i-th layer (i=1, 2, 3,...7), nidi: optical thickness of the i-th layer (i=1, 2.3 ,...
・7) nG: refractive index of the prism, λ_0: design wavelength.