JPH01287503A - Light beam splitter - Google Patents

Abstract

PURPOSE:To flatten optical characteristics by composing a dielectric multilayered film of seven layers in total and specifying the optical film thickness of each layer. CONSTITUTION:The light beam splitter consists of a substrate 3, the dielectric multilayered film 2 formed on the substrate, and a substrate 1 adhered thereupon. The dielectric multilayered film 2 consists of seven layers in total; and the 1st and 7th layers counted from the substrate 3 are dielectric thin film layers with intermediate refractive indexes, the 2nd, 4th, and 6th layers are dielectric thin film layers with high refractive indexes, and the 3rd and 5th layers are dielectric thin film layers with low refractive indexes. Then the 1st and 7th layers, the 3rd and 5th layers, and 2nd and 4th layers are equalized in optical film thickness respectively and the thickness of the 6th layers is larger than that of any other layer. Namely, the respective layers are made different in refractive index. Consequently, the light beam splitter which has flat optical characteristics and desired transmissivity is easily obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light beam splitter used in a viewfinder of a video camera, an imaging optical system, and the like.

A specific example of using a conventional optical beam splitter in an imaging optical system is a two-blade color video camera. A dual-blade color video camera obtains a color signal using one solid-state image sensor and a color filter, and then adds another solid-state image sensor to obtain a luminance signal, thereby achieving high resolution with a simple configuration. The purpose is to obtain.

FIG. 18 shows an example of a known optical unit for a two-plate video camera. This is a basic configuration example of this method, which consists of two prisms, a first prism 21 and a second prism 22, and separates a luminance signal and a color signal by interposing a semi-transparent film 23 at the junction of the two prisms. It is.

Image information light 25 from the camera lens enters the first prism 24 and is split by the semi-transparent film 23 into luminance signal light 26 and color signal light 27. This luminance signal light 26 is reflected by the semi-transparent film 23.

Further, it is totally reflected by the first surface 24 and becomes a luminance signal by the solid-state image sensor 28. On the other hand, the color signal light 27 that has passed through the semi-transparent film 23 is incident on the solid-state image sensor 29 . It was placed in front of this solid-state image sensor 28. color filter 30
The color signal light is decomposed into RGB components to become a color signal.

Now, as a basic type of such a semitransparent film 23, a film having optical characteristics as shown in FIG. 19 has been used. This is TlO2, ZrTl0a, ZnS, Z
A dielectric material having a relatively high refractive index such as rO*,
S10. .

Eight layers of a dielectric material having a relatively low refractive index such as Mgh are alternately formed using vacuum evaporation or the like.

Problems to be Solved by the Invention However, as an optical beam splitter for a two-panel video camera, the visible wavelength range λ = 400nm to 700nm.
It is desired that the optical characteristics be flat in the nm range, but when using an optical beam splitter such as the one shown in FIG. The distribution shapes of the color signal light as shown in FIG. 20 and the luminance signal light as shown in FIG. 21 are quite different.

As a result, it was not possible to obtain good imaging characteristics using such a light beam splitter.

In view of this point, the present invention seeks to provide an optical beam splitter with flat optical characteristics.

Means for Solving the Problems In order to solve these problems, the present invention includes a substrate, a dielectric multilayer film formed on the substrate, and a substrate bonded thereon, The total number of layers in the multilayer film is 7. Counting from the substrate, the first and seventh layers are dielectric thin film layers with a medium refractive index, and the second, fourth, and sixth layers are dielectric layers with a high refractive index. The third and fifth layers are dielectric thin film layers with a low refractive index.

The optical thickness of the first layer and the seventh layer, the optical thickness of the third layer and the fifth layer, and the optical thickness of the second layer and the fourth layer are made equal, and the optical thickness of the sixth layer is made equal. It has a structure in which the thickness is thicker than other layers.

Effects The present invention can easily realize an optical beam splitter with flat optical characteristics by employing an optical multilayer film that develops the above-described film structure.

Embodiment A first embodiment of the present invention is shown in FIG. In Figure 1,
1 is a substrate; 2 is a dielectric multilayer film formed on the substrate 1; 3 is a dielectric multilayer film formed on the substrate 1;
is the board connected on top of it.

Dielectric multilayer [2 consists of 7 layers, the 1st layer and 7th layer are AI
2's (alumina), the second, fourth and sixth layers are Ti02 (titanium dioxide), and the third and fifth layers are S
i 02 (silicon dioxide).

Table 1 Optical thickness of each layer The optical thickness of each layer is as shown in Table 1.
N, the optical thicknesses of the second layer and the fourth layer, the third layer and the fifth layer are equal, and the optical thickness of the sixth layer is relatively thick.

Here, λ indicates the design wavelength.

FIG. 2 shows the spectral optical characteristics obtained when the film has such an optical thickness. The vertical axis is transmittance (%).

The horizontal axis is the wavelength (nm).

Further, S in the figure indicates the transmittance characteristic of S-polarized light.

P indicates the transmittance characteristic of P-polarized light. The wavy line indicates the average value of S-polarized light (!-P-polarized light).

Flat optical characteristics have been achieved over the entire visible range.

Here, the design wavelength is λa=550tv.

The refractive index and angle of incidence are shown in Table 2.

TABLE 2 The present invention also has several manufacturing advantages, which are discussed in detail below.

Generally, in manufacturing an optical multilayer film, it is very difficult to accurately obtain the film thickness and refractive index as designed values. For example, a certain layer may be formed somewhat thicker than a designed value, or a certain layer may be formed thinner. Furthermore, even if the film is formed under the same conditions, it is expected that the film thickness and refractive index will vary from loft to loft or layer to layer. Therefore, somewhat
It is desirable that good optical properties can be obtained even if the film thickness or refractive index deviates from the designed values.

FIG. 3 shows the optical characteristics when the refractive index φ film thickness varies by about 1%. If the film structure according to the present invention is used, good optical characteristics can be achieved even in such cases. It can be said that it is very useful from a practical point of view.

Moreover, even if the film can be formed with very good reproducibility.

It is extremely difficult to accurately achieve the film thickness as designed, and the current situation is that desired optical characteristics are obtained through repeated trials and errors.

In other words, when a film is actually formed and the desired optical properties are not obtained, it is necessary to focus on which layer and apply feedback.
It is often difficult to decide whether to further improve optical characteristics.

Therefore, a feedback method when using the membrane structure according to the present invention will be described.

The optical beam splitter of the present invention has the following characteristics.

That is, the optical thickness of the sixth layer is 2.08Xλ74.

FIG. 4 shows the optical characteristics when the film is formed somewhat thicker than the designed value. This error can be considered as an error in initial setting of optical film thickness during actual film formation.

The optical characteristics are upward-sloping, that is, the transmittance on the long wavelength side increases and the transmittance on the short wavelength side decreases.

In addition, the optical thickness of the sixth layer is shown in Fig. 5 as 1.88Xλm/
4, which shows the optical characteristics when the thickness is made somewhat thinner than the design value. This time, on the contrary, the optical characteristics are upward-sloping to the left, that is, the transmittance on the short wavelength side increases and the transmittance on the long wavelength side decreases.

In this way, if the film structure of the present invention is used, even if the film thickness and refractive index of each layer are not obtained as expected and the optical properties have a slope, the 6th! Focusing on the optical thickness of I,
Good optical characteristics can be easily obtained by performing a correction operation.

As a specific example, as shown in Table 3, the optical thickness of each layer is as shown in Table 3. FIG. 6 shows the case using Table 2.

Since the optical thicknesses of the third and fifth layers in Table 3 are smaller than the designed values, the optical characteristics are tilted. Generally, in such a case, the layers (third layer, fifth layer) that could not be formed as designed values are focused on, a correction operation is added, and the layers are formed again. but.

It is often difficult to determine which layer has not been formed as designed.

In such a case, the film structure of the present invention is very useful, and the optical characteristics can be easily improved by focusing on the optical thickness of the sixth layer and performing a correction operation. The results are shown in FIG.

Very good optical properties have been achieved. Note that the optical thickness of the sixth layer is nd=1.90Xλa/4. This is a very useful point from the viewpoints of ease of manufacture, stability, and practicality.

Also, this does not apply only to this example;
Anything that falls within the scope of the claims of the present invention can be applied.

As a specific example, the membrane structure is shown below.

Table 4 Table 5 Table 6 Table 7 Table 8 Table 9 Table 10 Table 11 Table 12 Table 13 By using the film structure shown above, flat and good optical properties are achieved. can.

Next, the first layer and the seventh layer, the second layer and the fourth layer, the third layer and the fifth layer
A second embodiment of the present invention will now be described, in which the optical thickness of each layer is as shown in Table 4.

The film structure is the same as the seven-layer arrangement shown in FIG. 1 in the first embodiment, and the various refractive indexes and incident angles are the same as in Table 2.

The second embodiment of Table 14 is a special case of the scope of the claims of the present invention, and the optical film thickness of the first layer and the seventh layer, the second layer and the fourth layer, and the third layer and the fifth layer. are the same, but their optical thicknesses are also the same.

It is set to approximately t, ooxλ·/4.

With such an optical film thickness, the design wavelength is λ days = 550
FIG. 8 shows the optical characteristics when set to nm. Good optical characteristics equivalent to those of the first example are obtained. Further, in the second embodiment, all the optical thicknesses except for the sixth layer are equal, so it can be said that it is very useful in terms of manufacturing.

As described above, according to the present invention, the absolute accuracy of the optical thickness of each layer is not very important, and as shown in the first and second embodiments, the optical thickness of each layer has an error. Even if a film is formed, as long as the conditions set forth in the claims of the present invention are met, flat and good optical characteristics can be achieved by adjusting only the 8th Fm.

Next, the incident angle is θ=0.0°, θ=30.0”,
A third embodiment of the present invention when θ=45.0' is shown in FIGS. 9, 1O, and 11. Further, the optical thickness of each layer is shown in Tables 15, 16, and 17.

(Leaving space below) Table 15 θ=o, o@ Table 16 θ=30.0゜ Table 17 θ= 45.0 realizable.

Next, the case where different glass materials are used will be explained.

The glass material has a refractive index of n = 1. l1fl,
FIG. 12 shows the optical characteristics when the film structure is equivalent to that of the second embodiment. In addition, Fig. 13 shows the case of n: 1.81.
The case where =1.38 is shown in FIG. Even if glass materials with different refractive indexes are used, flat and good optical properties can be obtained.

It can be seen that the membrane structure of the present invention is very useful.

Up to this point, the transmittance of the optical beam splitter is approximately 50%.
Although the explanation has focused on the above, the transmittance can also be adjusted arbitrarily by adjusting the optical thickness of each layer or the refractive index of each layer.

Table 18 First, an example in which the optical film thickness was adjusted and the transmittance was set to 70% will be described.

FIG. 15 shows the optical characteristics when the optical film thicknesses shown in Table 18 are adopted.

An optical beam splitter with a transmittance of about 70%, that is, can split 70% of the image information light into color signal light and the remaining 30% into luminance signal light can be easily realized.

Note that the values shown in Table 2 were used for the refractive index or incident angle of each layer.

Next, an example in which the transmittance is changed by changing the refractive index of each layer will be described.

There are two ways to change the refractive index: by changing the substance used, and by changing the film forming conditions.

The materials used are shown in the first example.

In addition to Ties, Al2O5 and 5iOa, e Z r
O2, ZrTiO4+ ZnS+ MgF2, etc. are conceivable, but any material may be used as long as it satisfies the scope of the claims of the present invention.

Here, as a specific example, the refractive index of the high refractive index material used for the second layer, fourth layer, and sixth layer is +n=2-10, and the other layers are shown in Table 2. As shown in the figure. As a material whose refractive index is n=2.10.

ZrTi0a is mentioned.

An optical beam splitter with flat optical characteristics and a transmittance of about 65% has been realized.

Further, FIG. 17 shows the optical characteristics when the refractive index of the third layer and the fifth layer is set to n=1.38, and the other layers are made equal to those in Table 2. As a substance with a refractive index of n=1.38, @g
An example is Fx. Good optical properties with a transmittance of about 40% over a wide wavelength range have been achieved.

As described above, by adopting the film structure of the present invention, it is possible to easily realize an optical beam splitter having flat optical characteristics and a desired transmittance by simply changing the refractive index of each moon.

Effects of the Invention By adopting the film structure of the present invention, it is possible to easily realize an optical beam splitter having flat optical characteristics over a wide wavelength range. In addition, even in the film forming stage, even if the refractive index
Good optical properties can be achieved even if the optical film thickness varies.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing the film structure of the present invention, Fig. 2 is a transmittance characteristic diagram of the optical beam splitter in the first embodiment of the invention, and Fig. 3 is a refractive index and film thickness of approximately 1%. Transmittance characteristic diagram showing changes in characteristics when there are variations. Figure 4 is a transmittance characteristic diagram when the optical thickness of the 6th layer becomes thicker, Figure 5 is a transmittance characteristic diagram when the optical thickness of the 6th layer becomes thinner, and Figure 6 is a diagram of transmittance characteristics when the optical thickness of the 6th layer becomes thinner. Transmittance characteristic diagram when the optical thickness of the third and fifth layers becomes thinner. Figure 7 shows the transmission result of correcting the characteristics of Figure 6 using the optical thickness of the sixth layer. FIG. 8 is a transmittance characteristic diagram of the optical beam splitter in the second embodiment of the present invention, FIG. 9 is a transmittance characteristic diagram when the incident angle is 0 degrees, and FIG. 10 is a transmittance characteristic diagram when the incident angle is 0 degrees. Figure 11 is a transmittance characteristic diagram when the angle of incidence is 30 degrees, Figure 12 is a transmittance characteristic diagram when the incident angle is 45 degrees, and Figure 12 is a diagram when the refractive index of the glass material is n = 1.61.
Figure 13 is a transmittance characteristic diagram when a glass material with a refractive index of n = 1.81 is used, and Figure 14 is a transmittance characteristic diagram when a glass material with a refractive index of n = 1 is used. .38 is used. Figure 15 is a transmittance characteristic diagram showing a light beam splitter with a transmittance of 70%.
Figure 16 is a transmittance characteristic diagram when a material with a refractive index of approximately 2.10 is used as a high refractive index material, and Figure 17 is a diagram of transmittance characteristics when a material with a refractive index of approximately 1.38 is used as a low refractive index material. Figure 18 is a schematic diagram showing the outline of a two-plate color camera, Figure 19 is a transmittance characteristic diagram of a conventional optical beam splitter, and Figure 20 is a sensitivity characteristic diagram used as color signal light. , FIG. 21 is a sensitivity characteristic diagram used as a luminance signal light. 1.3...Substrate, 2...Dielectric multilayer film. Name of agent: Patent attorney Toshio Nakao and one other person
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Claims (2)

[Claims] (1) A substrate and a dielectric multilayer film formed on the substrate,
and a substrate bonded thereon, the total number of layers of the dielectric multilayer film is seven, the first layer and the seventh layer counting from the substrate are dielectric thin film layers with a medium refractive index, and the second layer is a dielectric thin film layer with a medium refractive index. The fourth and sixth layers are high refractive index dielectric thin film layers, the third and fifth layers are low refractive index dielectric thin film layers, and the first and seventh layers are optical films. A light beam in which the thickness, the optical thickness of the third and fifth layers, and the optical thickness of the second and fourth layers are made equal, and the optical thickness of the sixth layer is made thicker than the other layers. splitter. (2) If the design wavelength is λ_0, the optical thicknesses of the first layer, second layer, third layer, fourth layer, fifth layer, and seventh layer are approximately 1.
The optical beam splitter according to claim 1, wherein the optical beam splitter is 00×λ_0/4.