JPH05188220A - Three color separating prism - Google Patents

Abstract

PURPOSE:To provide the three color-separating prism which has a high degree of freedom in shape and design and has good color separating performance in the constitution of the three color-separating prism having no air gaps. CONSTITUTION:The prism has three pieces of prism members 1, 2, 3, a 1st dichroic mirror 4 which reflects a green wavelength band at <=30 deg. incident angle and a 2nd dichroic mirror 5 which reflects a red wavelength band at >=30 deg. incident angle. The half-value wavelength width of the P polarized light and S polarized light of the reflection wavelength band of the 2nd dichroic mirror 5 is set narrower than the half-value wavelength width of the P polarized light of the reflection wavelength band of the 1st dichroic mirror 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-color separation prism used in a color solid-state image pickup device such as a television camera.

[0002]

2. Description of the Related Art In recent years, a three-plate color camera (hereinafter referred to as a three-plate camera) that uses three solid-state image pickup devices has been developed. In this type of camera, an image pickup light flux is divided into three primary colors of blue, green and red. A three-color separation prism for color separation is used.

FIG. 4 is a cross-sectional view of a three-color separating prism which has been widely used in the past, which is described in Japanese Patent Publication No. 38-23724 and is hereinafter referred to as a gap type prism.

In FIG. 4, reference numerals 41, 42 and 43 are prism members, and 44 is a first reflection member for reflecting a light beam in the blue wavelength band.
Is a second dichroic mirror that reflects a light beam in the red wavelength band, and an air gap 46 is provided between the prism members 41 and 42 at intervals of several tens of microns. Reference numeral 47 denotes the optical axis of the incident light beam.

On the other hand, a three-color separation prism (hereinafter referred to as a gapless prism) having a simple structure in which all the prism members are adhered and joined and no air gap is provided has been proposed in, for example, Japanese Patent Laid-Open No. 50-159618. ..

FIG. 5 shows a sectional view of the three-color separation prism having the gapless structure. In the figure, 61, 62, 6
Reference numeral 3 is a prism member, all of which are closely joined, 64 is a first dichroic mirror, 65 is a second dichroic mirror, and 66 is a light beam incident on a gapless prism.

The incident light beam 66 is color-separated into a blue light beam 67a by the first dichroic mirror, is totally reflected by the incident surface 68, and is then emitted from the light beam emitting surface 69a. The light flux transmitted through the first dichroic mirror 64 is red light flux 67b and green light flux 67 at the second dichroic mirror 65.
The color is separated into c and. Red luminous flux 67b, green luminous flux 67c
Are not totally reflected, and are emitted from the light flux emission surfaces 69b and 69c. The dotted line in FIG. 5 is a region through which the imaging light flux passes, and the imaging light flux must not be eclipsed. 70a, 70
b indicates the incident angle on the first and second dichroic mirrors 64 and 65.

[0008]

Generally, the spectral characteristic of a dichroic mirror has an incident angle dependency, and the behavior is such that the half-value wavelength position changes depending on the incident angle and the characteristic changes depending on the polarization state of the incident light. ..

The former can be corrected in the design of the spectral characteristics if the incident angle is known in advance, but the latter is difficult to solve. This change in the spectral characteristic due to the polarization state is represented by the characteristics of the P-polarized light and the S-polarized light, and the influence on the color can be quantitatively grasped by the width of the half-value wavelength of both characteristics.

In the gapless prism of FIG. 5, since the incident angle 70b is larger than that of the gap type prism of FIG. 4, the influence of the incident angle dependency of the second dichroic mirror 65 is large, so that a large polarization characteristic is obtained. Will have. On the contrary, if the incident angle 70b is reduced, the position of the light flux 67b on the exit surface 69b will be too close to the prism member 64, and as a result, the outgoing light flux will be eclipsed or the image pickup element, especially the one having a large package size. Will not be installed.

That is, in the gapless prism,
A large incident angle 70b is convenient for the design of a compact prism shape and mounting of the image pickup device, but it is inconvenient for the polarization characteristic of the second dichroic mirror 65.

In view of the above points, the present invention has a gapless structure, but the incident angle of the second dichroic mirror can be set to a large value, and it is less affected by the polarization characteristics, thus achieving good color separation performance. It is an object of the present invention to provide a realizable three-color separation prism.

[0013]

According to the present invention, at least three first, second, and third prism members are provided from the incident side, and the green wavelength band of the light beam incident on the first prism member is A first dichroic mirror, which is reflected at an incident angle of 30 ° or less on the optical axis and then is totally reflected by an incident surface to be emitted from the first prism member, and a blue or red light beam transmitted through the first dichroic mirror. Second dichroic in which the wavelength band of is reflected at an incident angle of the optical axis of 30 ° or more and then straightly travels to be emitted from the second prism member, and the transmitted light flux is straightly traveled to be emitted from the third prism member. And a half-value wavelength width of the characteristics of P-polarized light and S-polarized light at the reflection / transmission boundary of the second dichroic mirror, which is equal to P of the reflection wavelength band of the first dichroic mirror. It is narrower than the half-value wavelength width of polarized light.

[0014]

By the above means, in the first dichroic mirror having a relatively small incident angle, it is possible to set the spectral characteristic for sufficiently reflecting the green wavelength band while suppressing the polarization characteristic, and in the second dichroic mirror having a large incident angle. The spectral characteristic is set so that the polarization characteristic generated there is within the range of the green wavelength band. As a result, the influence of the polarization characteristic of the second dichroic mirror does not appear,
Stable color separation performance can be obtained regardless of the polarization state of incident light. As a result, a prism shape without an air gap, which makes the incident angle of the second dichroic mirror larger, becomes possible.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a three-color separation prism in the embodiment, in which 1, 2, 3 are prism members, 4 is a first dichroic mirror, and 5 is a second dichroic mirror. The prism members 1, 2 and 3 are closely joined and no air gap is provided. 6 is an imaging lens (not shown)
Which is an incident light beam that has passed through the first dichroic mirror 4 and is separated into a green light beam 7a by the first dichroic mirror 4 and emitted from the emission surface 8a.

The light beam transmitted through the first dichroic mirror is color-separated by the second dichroic mirror 5, and the blue light beam 7b is emitted from the emission surface 8b and the red light beam 7c is emitted from the emission surface 8.
It is emitted from c.

The incident angle of the dichroic mirror is preferably 30 degrees or less so that the polarization characteristic does not matter, and the incident angle 9a of the first dichroic mirror 4 is set to 30 degrees or less. However, if the incident angle 9b of the second dichroic mirror 5 is larger than 30 degrees,
This is advantageous in designing the prism shape and securing the mounting surface of the solid-state imaging device package 10b.
8 degrees.

10a and 10c are also solid-state image pickup device packages, and 11a, 11b and 11c respectively indicate image pickup devices in the package.

FIG. 2 is a spectral characteristic diagram of the first dichroic mirror 4 of the present embodiment. In the figure, 21 is a P polarization characteristic, 22 is an S polarization characteristic, and 23 is a characteristic of an average value of P polarization and S polarization. (Hereinafter, referred to as (P + S) / 2 characteristic), 24 is a ripple. The dotted line arrow indicates the wavelength region in which the dichroic mirror reflects and separates.

In this embodiment, in the curve 23 showing the (P + S) / 2 characteristic, the position of the half value wavelength is about 48 on the short wavelength side.
6 nm and the long wavelength side are set to about 577 nm, and the half-value wavelength width of the P-polarization characteristic is 70 nm.

This spectral characteristic serves to determine the characteristic on the long wavelength side of blue, both the characteristic on the short wavelength side of green and the characteristic on the long wavelength side of green, and the characteristic on the short wavelength side of red. The structure will be a film.

That is, it is an alternating multilayer film of 19 or more and 25 or less layers composed of a high-refractive index material and a low-refractive index material, and the odd-numbered layers counted from the adherend side are low-refractive-index materials and even-numbered layers. The layers are composed of high refractive index materials, and the optical thickness n of each layer
_i d _i is the following condition; n _i d _i = 1.57λ / 4 (even layer within the range of i = 2 to (n-1)) n _i d _i = 2.85λ / 4 (i = 1, 3, n-th layer) n _i d _i = 0.32λ / 4 (i = 5, (n-3) -th layer) n _i d _i = 0.41λ / 4 (i: 1 to n An optical multilayer film satisfying the following: (odd layer other than the above in the range) (n _i : refractive index of constituent material of i-th layer) (λ: design reference wavelength in visible light) (n: number of dichroic mirror layers) do it.

As a specific example, the refractive index (n _d ) of the prism glass material with respect to the d-line is 1.59, and the design reference wavelength λ is 53.
0 nm, the incident angle is 26.5 degrees, the number of multilayer layers is 19, the refractive index of the high refractive index material is 2.20, and the refractive index of the low refractive index material is 1.46. The optical film thickness n _i d _i of each layer at this time is as follows: n _i d _i = 208.0 nm (i = 2, 4, 6, 8, 10, 12, 14, 16, 18 layers) _{n i d i = 377.6nm (i} = 1,3,19 _{layer) n i d i = 42.4nm (} i = 5,17 _{layer) n i d i = 54.3nm (} i = 7,9,11 , 13, 15 layers) In the present dichroic mirror, adjustment is performed by changing only the optical film thickness of the odd-numbered layer, that is, the low refractive index material layer. It will be easy. The optical film thickness n of the dichroic mirror
_i d _i shows good spectral characteristics in the range of about ± 10% with the above value as a reference value. The optical film thickness of the outermost layer may be the above optical film thickness.

In FIG. 2, the ripple 2 in the long wavelength region is
No. 4 has appeared, but in an image pickup apparatus using a three-color separation prism, an infrared light cut filter is usually used to suppress the amount of transmitted near-infrared light on the long wavelength side.
The effect of No. 4 is extremely small, and there is no practical problem.

FIG. 3 is a spectral characteristic diagram of the second dichroic mirror 5 of this embodiment. In the figure, 31 is a P polarization characteristic, 32 is an S polarization characteristic, and 33 is an average value of P polarization and S polarization. It is a characteristic. The dotted arrow indicates the half-value wavelength width of the characteristics of P-polarized light and S-polarized light. The position of the half-value wavelength of the P-polarization characteristic 31 is about 500 nm, and the half-value wavelength position of the S-polarization characteristic 32 is about 56 nm.
5 nm.

The half-value wavelength width of the characteristics of P-polarized light and S-polarized light is 65.
nm, and the half-value wavelength width of the P-polarized light of the first dichroic mirror 4 is suppressed to 70 nm or less. Then, it is set so as to have sufficient reflection characteristics in the blue wavelength region and sufficient transmission characteristics in the red wavelength region, and the following optical multilayer film is formed.

That is, it is an alternating multi-layered film of 17 or more and 23 or less layers composed of a high-refractive index material and a low-refractive index material, and the odd-numbered layers counted from the adherend side are low-refractive-index materials and even-numbered layers. The layers are composed of high refractive index materials, and the optical thickness n of each layer
_i d _i is the following condition; n _i d _i = 0.56λ / 4 (i = 2, (m-1) th layer) n _i d _i = 0.92λ / 4 (i = 5, (m- 4) th layer) n _i d _i = 1.00λ / 4 (i: layers other than the above in the range of 1 to m) (n _i : refractive index of constituent material of i th layer) (λ: visible light The design reference wavelength in (): (m: number of layers of dichroic mirror).

As a specific example, the refractive index (n _d ) of the prism glass material for the d-line is 1.59, and the design reference wavelength λ is 52.
The incident angle was 0 nm, the incident angle was 38.0 degrees, the number of layers of the multilayer film was 17, the refractive index of the high refractive index substance was 2.20, and the refractive index of the low refractive index substance was 1.46. The optical film thickness n _i d _i of each layer is as follows: n _i d _i = 73.2 nm (i = 2, 16 layers) n _i d _i = 119.7 nm (i = 5, 13 layers) n _i d _i = 130.0 nm (i = 1, 3, 4, 6 to 12, 14, 15, 17 layers) The optical film thickness n _i d _i of the dichroic mirror is ± 10 with the above value as a reference value. In the range of about%, good spectral characteristics are exhibited. The optical film thickness of the outermost layer may be the above optical film thickness. In general, in the dichroic mirror, if the incident angles of the light beams are the same, the influence of the incident angle dependency is reduced when the wavelength region in which the light is reflected and separated is set to the short wavelength region. Therefore, in this embodiment, the second dichroic mirror has a characteristic of reflecting the blue light beam and transmitting the red light beam.

As described above, in the first dichroic mirror having a relatively small incident angle, the spectral characteristic is set so as to sufficiently reflect the green wavelength band while suppressing the polarizing characteristic to be small. Next, in the second dichroic mirror with a large incident angle,
The spectral characteristic is set so that the polarization characteristic generated there is within the range of the green wavelength band.

As a result, the influence of the polarization characteristic of the second dichroic mirror is less likely to appear, and stable color separation performance can be obtained regardless of the polarization state of incident light. A large exit surface 8a of the prism member 2 can be secured, mounting of the image sensor becomes easy, and the degree of freedom in designing the prism shape increases. That is, in the three-color separation prism having no air gap, the three-color separation prism is more compact, the image pickup element can be easily mounted, and good color separation performance can be obtained.

[0032]

Although the three-color separation prism of the present invention has the gapless structure, the incident angle of the second dichroic mirror can be set to a large value and the influence of the polarization characteristic is lessened. The three-color separation prism capable of facilitating mounting and prism shape design related to the prism size and realizing good color separation performance can be obtained, and the industrial value of the present invention is high.

[Brief description of drawings]

FIG. 1 is a sectional configuration diagram of a three-color separation prism in an embodiment of the present invention.

FIG. 2 is a spectral characteristic diagram of a first dichroic mirror in the example.

FIG. 3 is a spectral characteristic diagram of a second dichroic mirror in the example.

FIG. 4 is a cross-sectional configuration diagram of a gap type prism which is an example of a conventional three-color separation prism.

FIG. 5 is a cross-sectional configuration diagram of a gapless prism that is an example of a conventional three-color separation prism.

[Explanation of symbols]

 1, 2 and 3 Prism member 4, 5 Dichroic mirror 6 Imaging light flux (incident light) 7a, 7b, 7c Color separation light flux 8a, 8b, 8c Light flux exit surface 9a, 9b Incident angle 10a, 10b, 10c Solid-state imaging device package 21 Spectral characteristics of P-polarized light 22 Spectral characteristics of S-polarized light 23 Average spectral characteristics of P-polarized light and S-polarized light 24 Ripple 31 Spectral characteristics of P-polarized light 32 Spectral characteristics of S-polarized light 33 Average spectral characteristics of P-polarized light and S-polarized light 41, 42, 43 Prism member 44, 45 Dichroic mirror 46 Air gap 47 Imaging light flux (incident light) 61, 62, 63 Prism member 64, 65 Dichroic mirror 66 Imaging light flux (incident light) 67a, 67b, 67c Color separated light flux 68 Total reflection surface 69a, 69b, 69c Luminous flux exit surface 70a, 70b Incident angle

Claims (3)

[Claims] 1. At least three prism members, first, second and third, are provided from the incident side, and a green wavelength band of a light beam incident on the first prism member is set at an optical axis incident angle of 30 ° or less. A first dichroic mirror that is reflected and then totally reflected on an incident surface to be emitted from the first prism member, and a blue or red wavelength band of a light flux transmitted through the first dichroic mirror is an optical axis incident angle. A second dichroic mirror is provided which, after being reflected at 30 ° or more, advances straight to be emitted from the second prism member, and advances the transmitted light flux straight to be emitted from the third prism member. The half-value wavelength width of the characteristics of P-polarized light and S-polarized light at the reflection / transmission boundary of the dichroic mirror is made narrower than the half-value wavelength width of P-polarized light in the reflection wavelength band of the first dichroic mirror. A three-color separation prism characterized by that. 2. A first dichroic mirror is composed of a low refractive index layer and a high refractive index layer with the inner adjusting layer group, the basic periodic layer group and the outer adjusting layer group as a basic structure from the substrate side. Is a two-layered structure in which the optical length (nd) of the low refractive index layer is smaller than the optical length of the high refractive index layer, and the number of layers of the inner adjusting layer group is smaller than that of the outer adjusting layer group. The three-color separation prism according to claim 1, wherein the optical multi-layer film is increased. 3. A second dichroic mirror is composed of a low refractive index layer and a high refractive index layer with an inner adjusting layer group, a basic periodic layer group and an outer adjusting layer group as a basic structure from the substrate side. Is a laminated structure of two types in which the optical lengths of the low refractive index layer and the high refractive index layer are equal, and the inner adjustment layer group and the outer adjustment layer group have the same number of layers and are symmetrical to each other. The three-color separation prism according to claim 1, wherein the three-color separation prism is formed of the optical multilayer film.