JPH0395504A - Color separating element - Google Patents

Abstract

PURPOSE:To reduce the chromatic aberration and to receive light beams of respective separated colors at the focus position by uniting two reflecting elements with both opposite end surfaces of a columnar prism whose cross-section is a parallelogram. CONSTITUTION:The reflecting elements consisting of dichroic mirror layers D (D1 and D2), transparent layers, and total reflecting mirror layers M (M1 and M2) are provided on both the opposite end surfaces of the columnar prism whose cross-section is the parallelogram shape wherein an included angle thetaamong the internal angles is 0<theta<90 deg., and light to be separated by colors is made incident on one reflecting surface at an angle theta of incidence. Consequently, the incident light is made incident on the prism end surface at right angles, reflected twice, then projected from the end surface at right angles. Consequently, the refractive indexes before and behind the dichroic mirror layers D are equal, so the chromatic aberration is reducible. Further, even when the two reflecting elements are arranged having their reflecting surfaces at right angles, the light beams of the respective separated colors can be received at the focus position by slanting a sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a color separation element, and more particularly to a technique for improving a color separation element for separating color images.

<Prior Art> As disclosed in Japanese Patent Laid-Open No. 60-134556, for example, an apparatus equipped with a color separation element for performing color separation is used to convert a color image into a color image using a color separation element using a dichroic filter or the like. A device configured to separate into three primary colors and read each of the three primary colors is known.

The color separation element disclosed in JP-A-60-134556 uses a combination of two reflective elements each having a dichroic mirror and a total reflection mirror on the front and back sides of a transparent plate. The system separates only one of the three primary colors, and the light that is mixed with the remaining two colors is separated into two colors by the next reflective element, and the final color image is separated into parallel light rays of the three primary colors. be done.

<Problems to be Solved by the Invention> However, in the structure in which dichroic ξ mirror and total reflection mirror layers are formed on the front and back surfaces of the transparent plate as described above,
In order to narrow the distance between parallel rays after decomposition at the same incident angle, it is necessary to reduce the thickness of the transparent plate, but if the thickness of the transparent plate is made thin, there is a risk that the reflective element will warp due to film stress. There is.

Furthermore, when two reflective elements are used in combination as described above, it is necessary to perform positioning such as angle adjustment for each of the two reflective elements, making the adjustment work complicated.

Furthermore, since the media before and after the dichroic mirror layer are different, such as air and glass, there is a problem that when obliquely incident light is refracted when passing through the dichroic mirror layer, chromatic aberration becomes large.

In addition, if two reflective elements are arranged so that their reflective surfaces are perpendicular to each other and configured to separate a color image into three colors, the focal position shift due to the difference in optical path length will not be linear, and each of the three colors will be handled separately. For sensors equipped with an integrated line sensor,
Another problem occurs in that each color cannot be received at the focal position.

The present invention has been made in view of the above-mentioned problems, and when performing color separation using two sets of reflective elements each consisting of a gicroic mirror and a total reflection mirror laminated with a transparent layer interposed between them, the flatness of the reflective surface is A color separation element that can be installed with good color and angular position settings, has small chromatic aberration, and allows the sensor to read each separated color at the focal position by making the focal position shift due to the difference in optical path length linear. The purpose is to provide.

<Means for solving the problem> Therefore, in the present invention, the narrow angle θ among the interior angles is 0°〈θ〈
A columnar prism whose cross section is a 90° parallelogram has a reflective element formed by forming a dichroic ink cooler layer, a transparent layer, and a total reflection mirror layer in order from the prism side on each of the opposing end surfaces. , and the color separation element is configured such that the color-separated light is incident on one of the reflective surfaces of the reflection element at an incident angle θ.

Here, it is preferable that the transparent layer is formed of a material having substantially the same refractive index as the prism.

According to the color separation element having such a configuration, the prism is formed in the shape of a column whose cross section is a parallelogram, and in the cross section of the parallelogram, the narrow angle θ among the interior angles is 0°. θ
〈90゜, and on each of the opposite end faces of the prism having a parallelogram cross section, a dichroic ξ layer, a transparent layer, and a total reflection layer are formed from the prism side. It has an element. and,
In such a color separation element, the color-separated light is made to be incident on one reflective surface of the reflection element at an incident angle of θ, which is the same as the narrow angle.

In this way, when the incident angle is set to θ and the color-separated light is directed to the reflective element, the light that enters from the end face of the prism where the reflective element is not formed will be incident at right angles to the end face of the prism, and the light will be reflected. The light that has been reflected twice by the element and separated into colors will also be emitted at right angles to the end face of the prism.

Further, by making the refractive index of the transparent layer and the prism substantially the same, the refractive index of the medium before and after the dichroic inkler layer becomes substantially the same, thereby avoiding refraction at oblique incidence.

<Examples> Examples of the present invention will be described below. The color separation element in this embodiment is installed after the imaging lens system in an image reading device that scans and reads a color original, and is used to integrate each color-separated image with a line sensor corresponding to each color. The light shall be received by the image sensor provided.

In FIG. 1 showing Embodiment I, the prism l is columnar long in the direction penetrating the diagram, and its cross section is as follows:
The interior angles are sequentially θ, 180-θ, θ, 18〇-θ (0゜〈θ
It is a parallelogram with an angle of <90°>, and in this embodiment, the above-mentioned θ is set to 45°.

Reflection elements formed by laminating a dichroic mirror layer D, a transparent layer T, and a total reflection mirror layer M are formed on both opposing end surfaces of the prism 1 having a parallelogram cross section. A plate-shaped prism (glass plate) 2 is laminated on the outside of each color layer M.

Note that the transparent layer T has a thickness of 99 μm, and
The refractive index is set to 1.5, which is approximately the same as prism 1. The thickness of the transparent layer T is determined based on the incident angle θ, the required interval between parallel rays after decomposition, and the like.

In addition, the first dichroic ξ color layer D1 on the side where the color image first enters has a characteristic of reflecting only the cyan wavelength range and allowing the rest (red wavelength range) to pass;
The second dichroic layer D2, into which the light separated into two colors by the first dichroic mirror layer DI enters, has a characteristic of reflecting only the blue wavelength range and allowing the other wavelengths (yellow wavelength range) to pass. , As a result, the cyan light reflected by the first dichroic mirror layer D1 is separated into blue and green by the next dichroic mirror layer D2, and as a result, along with the first separated red, red R and green G. It is separated into three primary colors, blue and B.

However, the color separation process is not limited to the above, and by appropriately selecting the wavelength characteristics of the dichroic mirror layer D,
Various color separation processes and color separations can be selected.

In such a color separation element, a color image as color-separated light is incident on the first dichroic mirror layer Di and the first total reflection mirror layer M1 at an angle of 45°, which is the same as the narrow angle θ-45° of the parallelogram cross section. It is positioned so that the angle is correct, so that a color image that enters the prism 1 will be incident at right angles to the end face of the prism 1, and the color image will be refracted when it enters the prism 1. You can avoid that. Furthermore, the first dichroic layer D
Since the reflective elements are arranged in parallel, the parallel light beam reflected by the first total reflection mirror layer M1 and the first total reflection mirror layer M1 also has an angle of 45° (=θ) with respect to the next dichroic mirror layer D2. The parallel light rays that are incident at the incident angle and separated into the three primary colors are also emitted at right angles to the end face of the prism 1.

That is, if the light is incident at right angles to the end face of the prism 1,
As is clear from the figure, the angle between the end face of the first reflective element and the incident light is 90° - θ, so if you set the incident angle to be θ, it will naturally fall on the end face of the prism 1. On the other hand, it will be incident at right angles. Furthermore, the light reflected by the first dichroic mirror layer D1 and the first total reflection mirror layer M1 is reflected by the second dichroic short mirror layer D2 and the total reflection mirror layer M2 arranged in parallel thereto. Since the light is incident at an angle of θ, the light reflected by the second dichroic color layer D2 and the total reflection ξ color layer M2 is
This results in a mistake occurring at right angles to the end face of prism 1.
The light incident on the prism 1 and the light emitted after decomposition are parallel to each other.

The above explanation is not limited to θ-45° in this embodiment, but is given as a general θ, so the cross section of the prism 1 is a parallelogram, and such parallel If the narrow angle θ among the interior angles of the quadrilateral cross section is 0゜〈θ〈90゜, and if this narrow angle θ and the anatomy angle of the color-separated light with respect to the reflective element are the same, then the prism 1 end face The light can be emitted at right angles to the prism 1, and refraction of the light when entering and exiting the prism 1 can be avoided.

In addition, by making the refractive index of the medium before and after the dichroic mirror layer D approximately the same, refraction when passing through the dichroic ξ color layer D can be suppressed, and this together with the person's exit at right angles to the prism 1 can prevent the occurrence of chromatic aberration. It can be made small. Therefore, it is preferable that the transparent layer T is a prism made of the same material as the prism 1, but even if it is made of other resin, if the refractive index is similar, the dichroic mirror ND may be sandwiched between glass and air. The occurrence of chromatic aberration can be suppressed more fully than in the case of

That is, if a medium having approximately the same refractive index as the transparent layer T is placed in front of the guichroic mirror layer D, refraction when passing through the guichroic mirror layer D can be prevented and the occurrence of chromatic aberration can be avoided. This time, when the light is obliquely incident on the medium placed in front of the guichroic mirror layer D, refraction occurs due to the difference in the medium (refractive index), so as mentioned above, the end face of the prism 1 directs the light at right angles. It is necessary to input the
The angle of incidence of the color-separated light on the reflective element consisting of a guichroic mirror layer and a total reflection ξ mirror layer must be set to θ.

The color image separated into the three primary colors is separated into three primary colors by a CCD line sensor 3 that is integrally equipped with three line sensors (line sensor spacing: 168q 10 μm in this embodiment) each having a color filter corresponding to each of the three primary colors. is photoelectrically converted to
A difference in optical path length occurs because there is light reflected by the mirror layer M and light reflected by the total reflection mirror layer M, and the focal positions of the three primary colors are not lined up on the same plane perpendicular to the resolved light rays but are shifted back and forth. In the case of a configuration in which color separation is performed by arranging reflective elements in parallel as in this embodiment, the shift in focal position due to the difference in optical path length is
They are arranged on the same plane obliquely intersecting the resolved light beam (the light reflected by the second dichroic color layer D2 is at the farthest focal point). Therefore, if the CCD line sensor 3 is installed tilted to accommodate the focal position shift,
Each of the three primary colors can be received at the focal position, reducing color shift and color blurring.

If the refractive index of the prism 1 and the transparent layer T are approximately the same as in this example, the thickness of the transparent layer T is d, the refractive index of the prism 1 is n', and the outside of the color separation element (air layer) The refractive index of n
, then the optical path length difference is -2dCOSθXnl/n2, and if the line sensor spacing is S and the sensor inclination angle is α, it is necessary to set the optical path length difference = S sin α, so θ = 45°n. =
1.0, nz=1.5, S=168, czm, d=
If it is 99 μm, αξ is 33.7°, and if the sensor 3 is installed at an angle of 33.7° from a plane perpendicular to the separated light beam, each separated color can be received at the focal position.

Furthermore, in this embodiment, since the guichroic mirror layer D, the transparent layer T, and the total reflection mirror M are laminated on the prism 1,
Even if the transparent layer T is thin, the prism 1 acts as a strength member and can prevent warping of the reflective element due to film stress. Furthermore, since the reflective elements consisting of the guichroic ξ color layer D, the transparent layer T, and the total reflection mirror M are not provided individually but are integrated, simply stated, the work load for position adjustment is reduced compared to the case where they are provided separately. becomes half.

In addition, the prism 1 has a dichroic layer ND and a transparent layer T.
, total reflection ξ ray M, for example, prism 1
A dichroic ξ color layer D is formed on the end face of the prism 2, a total reflection mirror M is formed on the plate-shaped prism 2, and the prism 1 and the prism 212 are bonded together via a spacer of a predetermined thickness. It can be carried out. As the spacer, a wire or bead of a predetermined diameter can be interposed to avoid the optical path, and the adhesion can be performed by filling the gap between the prisms 1 and 2 with an ultraviolet curing resin or the like.

In addition, the plate-shaped prism 2 includes a total reflection layer M, a transparent layer T,
The dichroic layer D may be laminated in order and then adhered to the prism 1. Furthermore, without using the prism 2, a total reflection mirror M. The guichroic color layer D formed thereon may be adhered to the prism 1, and the lamination method is not limited.

Further, it is preferable that the thickness of the transparent layer T be the same in one color separation element because it is easy to manufacture and the interval between the separated color lights can be made constant, but even if it is 1:2 or 2:1,
The interval between color separations can be constant. However, since a focal shift occurs due to the difference in optical path length as described above, it is advantageous to increase the incident angle θ since this can shorten the difference in optical path length.

Next, a second embodiment in which θ is 60° will be described.

That is, in this embodiment, the narrow angle θ of the interior angles of the parallelogram cross section of the prism 1 is 60 degrees, and the interior angles are 60 degrees, 1
The angles are 20°, 60°, and 120°.

Similarly to the first embodiment, dichroic mirror layers D,
By forming a reflective element formed by laminating a transparent layer T and a total reflection mirror layer M, a color separation element for separating a color image into three primary colors is constructed.

Note that the transparent layer T has a thickness of 91 μm, and
The refractive index is set to 1.5, which is approximately the same as prism 1.

In the second embodiment as well, the angle of incidence of the color-separated light on the reflective element is set to 60 degrees, which is the same as the narrow angle θ. , the color-separated light and the color-separated light are emitted at right angles to the end face of the prism 1, thereby reducing chromatic aberration.

Furthermore, in this embodiment as well, the sensor 3 is tilted with respect to the plane perpendicular to the resolved light beams because a difference in optical path length occurs and the focal positions are lined up on a plane obliquely intersecting the resolved light beams. In this example, the sensor The inclination angle α of 3 is 21.1°.

In any of the above embodiments, the prism l may be formed by gluing two pieces together, but it is preferable to shift the prism so that the separated light passes through the joint surface at right angles. Further, θ is not limited to the angles of 45° and 60° as in the above embodiment, but it is preferable to select angles such as 45° and 60° for ease of manufacturing.

<Effects of the Invention> As explained above, according to the color separation element according to the present invention, since the two sets of reflective elements are integrally provided, the burden of position and angle adjustment is reduced, and the color separation element according to the present invention is Since the reflective element is formed, it is possible to prevent the reflective element from warping by using the prism as a strength member. Furthermore, since the refractive index of the medium before and after the guichroic mirror is substantially the same as that of the prism, refraction of light can be avoided and chromatic aberration can be reduced. Furthermore, since the focal position of each separated color shifts linearly, by tilting and installing the sensor for each separated color,
Each separated color can be received at the focal position.

[Brief explanation of drawings]

FIG. 1 is a front view showing a first embodiment of the invention, and FIG. 2 is a front view showing a second embodiment of the invention.

Claims (2)

[Claims] (1) A dichroic mirror layer, a transparent layer, a transparent layer, Color separation comprising a reflective element formed by forming a total reflection mirror layer, and configured such that color-separated light is incident on one reflective surface of the reflective element at an incident angle θ. element. (2) The color separation element according to claim 1, wherein the transparent layer is formed of a material having substantially the same refractive index as the prism.