JPS62187802A - Beam splitter - Google Patents

Abstract

PURPOSE:To prevent transmitted light in the visible light range from coloring by forming a multilayered film having alternate laminate constitution of high- refractive-index layers and low-refractive-index layers and allowing layers which contact the 1st and the 2nd prisms to have a high refractive index and meet specific requirements. CONSTITUTION:The multilayered film 3 has the alternate laminate constitution of the high-refractive-index dielectric layers H made of a high-refractive-index dielectric with a 1.90-2.30 refractive index and the low-refractive-index dielectric layers L made of a low-refractive-index dielectric with a 1.47-1.80 refractive index. The outermost layers of the multilayered film 3 which contact the 1st prism 1 and the 2nd prism 2 are both formed of the high-refractive-index dielectric layers H. Then, the optical film thickness of each high-refractive-index dielectric layer H is 0.25lambda when reference wavelength is denoted as lambda, and the optical film thickness of each low-refractive-index dielectric layer L is 0.27lambda-0.35lambda. Consequently, a ripple in the visible light range is eliminated and a beam splitter which has uniform spectral transmissivity over the entire visible light range is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a beam splitter that transmits visible light and reflects infrared light for distance measurement.

(Prior Art) In an active autofocus video camera that uses a lens system, a beam transmits visible light and reflects infrared light (for example, monochromatic light with a wavelength of 880 nm) for distance measurement. Using a splitter simplifies the configuration of the optical system.

A filter made of a dielectric multilayer film can be used for this beam splitter. This multilayer film is made up of alternating layers of high refractive index and low refractive index, and the thickness of each layer is set to I/4 of the reference wavelength in order to strengthen reflection at the boundary between each layer. Of the light incident on this dielectric multilayer film, many components of wavelengths near the reference wavelength are reflected, but many other components are transmitted.

Therefore, the dielectric material, reference wavelength, etc. may be designed to transmit visible light and reflect infrared light for distance measurement.

(Problems to be Solved by the Invention) By the way, when using a beam splitter using a dielectric multilayer film at an incident angle of 45°, the balance between the S component and the P component of polarized light becomes poor, resulting in a decrease in reflection. It becomes less efficient. To explain this in more detail, generally, the refractive index of the base material constituting the prism is 18, the refractive index of the high refractive index dielectric layer is '11, and the refractive index of the low refractive index dielectric layer is n. In a beam splitter having a structure in which dielectric layers are alternately laminated with an optical thickness of λ/4 (λ: reference wavelength), ns'/2-(n-n)"/(no' +n%
) I L , the separation of the S component and the acid component of the polarized light becomes maximum. For this reason, once the refractive index of the base material constituting the prism and the constituent material of one dielectric layer are determined,
The refractive index of the other dielectric layer needs to take a value far from the refractive index determined by the above conditions, and therefore, the refractive index is determined to a certain extent.

Furthermore, in a beam splitter in which high refractive index dielectric layers and low refractive index dielectric layers, both of which have an optical thickness of 1/4 of the reference wavelength λ, are laminated alternately, A depression in transmittance occurs.

These depressions are called "ripples," and the light transmitted through a beam splitter that causes such ripples becomes colored.

Therefore, an object of the present invention is to suppress the separation of the S component and the P component of polarized light in a prism type beam splitter that is used at an incident angle of about 45 degrees and transmits visible light and reflects infrared light. Another object of the present invention is to provide a beam splitter that has uniform spectral transmittance without the ripples in the visible light region.

(Means for Solving the Problems) In order to achieve the above object, the inventors of the present invention have discovered that the above ripples can be eliminated in an alternately laminated structure of high and low dielectric layers having an optical thickness of λ/4. Since it was not possible to do this, we repeatedly changed the optical thickness of each dielectric layer through trial and error.
By slightly shifting the optical thickness of the low refractive index dielectric layer from λ/4 without shifting the optical thickness of the high refractive index dielectric layer from λ/4, it is possible to eliminate the bipedal ripple. They realized that it could be done and came up with the present invention.

Therefore, the present invention provides a multilayer film formed on the joint surface of a first prism made of glass having a refractive index of about 1.52 and a second prism made of glass having a refractive index of about 1.52. In the beam splitter, the multilayer film has an alternate lamination structure of high refractive index layers made of a high refractive index dielectric material and low refractive index layers made of a low refractive index dielectric material, and the above-mentioned first and second The layers in contact with the prism are all high refractive index layers, and are further characterized by satisfying the following conditions.

1.90≦nH≦2.30 1.47≦nI, ≦1.80 n,,d,,=0,25λ 0.27λ≦nL9≦0.35λ However, here, 'II is the refractive index of each high refractive index layer, and J is the refractive index of each high refractive index layer.

is the refractive index of each low refractive index layer, nItdll is the optical thickness of each high refractive index layer, n+, db is the optical thickness of each low refractive index layer, and λ is the reference wavelength.

(Function) By setting the refractive index and optical thickness of the high refractive index dielectric layer and the refractive index and optical thickness of the low refractive index dielectric layer within the above-mentioned ranges, By eliminating ripples, a beam splitter with uniform spectral transmittance over the entire visible light region is obtained. Furthermore, in the present invention, since the above refractive index condition is not satisfied, the polarized light S
Separation between the component and the P component can be suppressed.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

A beam splitter used in an autofocus video camera that uses an active method through a lens system.
As shown in FIG. A second two rectangular prisms 1.2 are manufactured by gluing them together on an inclined surface using an ultraviolet curing resin 4 via a multilayer film 3. This multilayer film 3 reflects infrared light (here, monochromatic light with a wavelength of 880 nm) used for distance measurement, which is incident at an incident angle of 0 at 45°, and reflects light in the visible range of 400 to 700 ni. Transmit.

As the prism 1.2, a prism made of glass having a refractive index of about 1.52 is used. As shown in FIG. 2, the multilayer film 3 includes a high refractive index dielectric layer 1-1 made of a high refractive index dielectric having a refractive index of 1.90 to 2.30. , 47~
It has an alternate lamination structure with a low refractive index dielectric layer made of a low refractive index dielectric having a refractive index of 1.80, and when the number of times the alternate lamination is repeated is N, N is 3 or more.

The outermost layer of the multilayer film 3, which is in contact with the first prism l side and the second prism 2 side, respectively, is formed of a high refractive index dielectric layer 12. The optical film thickness of each high refractive index dielectric layer H is 0.25λ, respectively, where J, li W, and 11 wavelengths are λ, and the optical film thickness of each low refractive index dielectric layer H is 0.25λ, respectively. are within the range of 0.27λ to 0°35λ, respectively. Thus, according to the present invention, the high refractive index dielectric layer 1-
The ratio of the optical film thickness nIt dl+ of 1 to the optical film thickness nb9 of the low refractive index dielectric layer is expressed as the conventional rlJ (0,25λ:
By increasing C from 0.25λ), ripples in transmittance that conventionally occur in the visible light region can be eliminated.

Examples of the present invention will be described in detail below. In Examples 1 to 3 below, the high refractive index dielectric is Alx0
t (refractive index 1.62) is used. Here, as the high refractive index dielectric constituting the high refractive index dielectric layer 1, in addition to the above, Zr0y, TiCL, Cent, H'0. In addition to the above, the low refractive index dielectric constituting the dielectric layer includes MgO.
t, Y t Os, etc. are applicable.

Example 1 The structure of Example I is shown in Table 1. This embodiment is an embodiment in which the number N of repetitions of alternate lamination is IO.

Here, the configuration of Example 1 is as follows: glass + [0,251-1・0.29L]”・Q, 25
It can be expressed as 11+ glass. However, [0,251
-1・0.29L]" is a high refractive index dielectric layer H with an optical thickness of 0.25λ and a low refractive index dielectric layer ■7 with an optical thickness of 0.29λ, alternately 10ff each. The spectral transmittance characteristics of the beam splitter of Example 1 are shown in FIG.

Below is the margin Table 1 (λ; I020nIn) Example 2 In this example, Glass + [0,2514・0.29L]3・0.251
It is represented by 4+glass, so N=3. The constituent materials of each dielectric layer are the same as in Example 1. The spectral transmittance characteristics of this example are shown in FIG.

Example 3 In this example, Glass+[0,25H・0°29L]”・0.25H+
It is represented by glass and therefore N;22. The constituent materials of each dielectric layer are the same as in Example I. The spectral transmittance characteristics of this example are shown in FIG.

Example 4 The configuration of this embodiment is shown in Table 2.

Therefore, the configuration of this example is: Glass + [0,25H・0.29L] Ward 0・0.25H
+Glass, N=IO. In this example, the low refractive index dielectrics include Y, 0. MgO instead of
You can also use The spectral transmittance characteristics of this example are shown in FIG.

Table 2 (λ=100 Onm) Example 5 The configuration of this embodiment is shown in Table 3.

Therefore, the configuration of this example is as follows: glass + [0,25H・083 ratio 1°・0.25I (
+glass, and N=10. The spectral transmittance characteristics of this example are shown in FIG.

Margin below Table 3 (λ=1050nm) Example 6 Table 4 shows the configuration of this embodiment.

Therefore, the configuration of this example is as follows: glass + [0.25N・0.32L]”・0.2511
+Glass, N=IO. The spectral transmittance characteristics of this example are shown in FIG.

Table 4 below with margins (λ=IO00os) The beam splitters of each of the embodiments described above are manufactured in the following manner. First, each layer of the multilayer film 3 is sequentially vacuum-deposited using the first prism 1 as a substrate by an electron beam method. The vapor deposition materials for each layer are as described above. The degree of vacuum during vapor deposition was approximately 3XlO'Torr, and the substrate was
It is heated to 0° C., and both deposition materials are alternately deposited until a predetermined optical film thickness is reached. Next, apply ultraviolet curing resin 4 to the opposing surfaces of the second prism, and
After pasting them together, cure the ultraviolet curing resin 4.

The refractive index of this ultraviolet curing resin 4 is approximately 1.51,
Since the refractive index is almost the same as that of the prism 1.2, it is considered that there is no loss in the amount of light between the second prism 2 and the ultraviolet curing resin 4.

As can be seen from the graphs in Figures 3 to 8, 400 to 7
Most of the visible light of 00r++n is transmitted, so the ripple in the transmittance curve is small, and the wavelength dependence of the transmittance is small. On the other hand, the transmittance of infrared light for distance measurement (wavelength = 880 nm) is about 50% when N=3, decreases as N increases, and becomes almost 0 when N-22. That is, by increasing the number of layers, more reflected light at 880 nm can be extracted. From the above measurement results,
If the number of times N of alternate lamination of the high refractive index dielectric layer tr and the low refractive index dielectric JPiL is set to 3 or more, 400 to 70
It can transmit light in the visible range of 0 nm and reflect infrared light for distance measurement. If N is less than 3, the transmittance of infrared light for distance measurement becomes large and the reflection pre-order is insufficient. Also,
Even if N is set to 23 or more, no improvement in infrared light reflection characteristics can be expected, so N is desirably 22 or less.

(Effect of the invention) In the beam splitter of the present invention, the incident n145
When used at In the optical region, uniform transmittance can be obtained by suppressing ripples in the spectral transmittance curve. For this reason, there is no possibility that the transmitted light in the visible light region will be colored.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a beam splitter according to an embodiment of the present invention. FIG. 2 is a diagram showing the structure of a dielectric multilayer film. 3 to 8 are graphs of transmittance curves of beam splitters according to embodiments of the present invention, respectively. 1.2... Prism, 3... Multilayer dielectric film, r-
t...High refractive index dielectric layer, L...Low refractive index dielectric layer. Patent applicant: Minolta Camera Co., Ltd. Agent: Patent attorney: Aobai Ao and two others Figure 1 (IT% Tato Yu) Figure 2 Figure 3 IJS Figure 4 Growth (nm) Figure 5
Shift A (nm) Liquid length (nm) Figure 6 Growth (nm) Figure 7 Figure 8 Branch length (nm) Procedural amendment (self-control April 3, 1986)

Claims (2)

[Claims] (1) A first made of glass having a refractive index of about 1.52.
In a beam splitter having a multilayer film formed on the joint surface of a prism of 1.0 and a second prism made of glass having a refractive index of about 1.52, the multilayer film has a high refractive index made of a dielectric material with a high refractive index. The prism has an alternate laminated structure of index layers and low refractive index layers made of a low refractive index dielectric, and the layers in contact with the first and second prisms are both high refractive index layers, and further satisfy the following conditions. A beam splitter characterized by: 1.90≦n_H≦2.30 1.47≦n_L≦1.80 n_Hd_H=0.25λ 0.27λ≦n_Ld_L≦0.35λ where, n_H: each height refractive index of the refractive index layer, n_L: refractive index of each low refractive index layer, n_Hd_H: optical thickness of each high refractive index layer, n_Ld_
L: optical thickness of each low refractive index layer, λ: reference wavelength. (2) The beam splitter according to claim 1, wherein the number of repetitions of the alternate lamination structure of high refractive index layers and low refractive index layers is 3 or more.