JPH1066096A - Optical image pickup device and optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute an optical image pickup system having no chrominance abberation and to reduce the size of the device by arranging a plate-like diffractive lens provided with a diffractive lens surface on the same optical path as a refractive lens having power. SOLUTION: The plate-like diffractive lens 1 and the refractive lens 2 are arranged on the optical path successively from the light incidence side and a solid state image pickup element 3 is arranged on the light projection side of the lens 2. The lens 1 to be an optical element is provided with a diffractive lens surface 1a on its light projection surface side, the grating pattern of the lens surface 1a is a concentric phase diffractive element and the amplitude of phase modulation applied by the lens 1 is 2π radians. The variation of the phase is determined by the phase terms u<1> , u<2> ,... of a phase function expressed by an equation. The lens 2 has positive power and forms an image of a subject on the position of the element 3. An infrared-ray cutting filter 4 and a low-pass filter 5 are arranged on the optical path of the lens 1 as necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging optical device constituting an optical system or the like using a solid-state imaging device such as a CCD and an optical element used for the same.

[0002]

2. Description of the Related Art FIG. 9 shows an optical system configuration diagram of a conventional imaging optical device. In FIG. 9, an infrared cut filter 10, a low-pass filter 11, and one refraction lens 12 are disposed on the optical path, and a solid-state imaging device 13 is disposed on the light exit side of the refraction lens 12. The infrared cut filter 10 absorbs or reflects infrared light in the incident light, and corrects the sensitivity characteristic of the solid-state imaging device 13 having high sensitivity in a long wavelength range. The low-pass filter 11 cuts a high frequency range in the incident light, and removes a signal such as moire that appears when a subject having a high spatial frequency is photographed. The refractive lens 13 has a positive power and forms an image of a subject at the position of the solid-state imaging device 13.

[0003] According to the above configuration, a total of three lenses including one refraction lens and two filters can be used, and an imaging system using a solid-state imaging device can be configured with a minimum number of parts. However, if one ordinary refractive lens is given power, chromatic aberration occurs, and good optical performance cannot be obtained.

Therefore, generally, as shown in FIG. 10, an infrared cut filter 10 and a low-pass filter 11 are used.
In addition, two or more refractive lenses 14 and 15 are arranged to constitute an optical system having almost no chromatic aberration.

[0005]

However, according to the above configuration, two or more refractive lenses 14, 15 having a thickness much larger than that of the filter must be arranged, so that the apparatus becomes large in size. was there.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image pickup optical system which constitutes an image pickup optical system free from chromatic aberration and which is used for downsizing the apparatus, and an optical element used for the same.

[0007]

According to the present invention, there is provided an imaging optical apparatus comprising: a refracting lens having power; and a flat plate having a diffractive lens surface disposed on the same optical path as the refracting lens. And a diffraction lens.

The optical element of the present invention is a flat diffractive lens which is disposed on the same optical path as a refractive lens having power and has a diffractive lens surface on one side.

That is, since the chromatic aberration opposite to the chromatic aberration of the refractive lens is generated by the diffractive lens surface of the flat diffractive lens, chromatic aberration hardly occurs in the entire image pickup optical system. It can be constructed with a much smaller thickness compared to.

[0010]

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

FIG. 1 shows an optical system configuration diagram of an image pickup optical apparatus according to the first embodiment. In FIG. 1, a flat diffractive lens 1 and a refraction lens 2 are arranged on the optical path from the light incident side, and a solid-state imaging device 3 is arranged on the light exit side of the refraction lens 1.

The flat diffractive lens 1 as an optical element has a diffractive lens surface 1a on the light exit surface side. The grating pattern on the diffraction lens surface 1a is a concentric phase type diffraction element, and the amplitude of the phase modulation given by the diffraction lens 1 is 2π radians. The amount of phase change is determined by the following phase terms u ₁ , u ₂ ,.

[0013]

(Equation 1)

The refracting lens 2 has a positive power and forms an image of a subject at the position of the solid-state image sensor 3.

The following Table 1 shows design data of an image pickup optical system composed of the flat diffractive lens 1 (one piece) and the refraction lens 2 (one piece) having the above-mentioned structure, and FIG. 2 shows aberration diagrams. For comparison, design data of a conventional imaging optical system including one flat plate and one refraction lens is shown in Table 2 below, and each aberration diagram is shown in FIG.

[0016]

[Table 1]

[0017]

[Table 2]

2 and 3 show that the spherical aberration, astigmatism, and distortion are almost the same, while FIG.
As shown in FIG. 3D and FIG. 3D, the coma aberration characteristics of each color are different. In FIG. 3D of the conventional type, each line (g, e,
Although there is a large difference (chromatic aberration) in the coma aberration of c), there is not much difference (chromatic aberration) in the coma aberration of each line (g, e, c) in FIG.

That is, in the above configuration, since the chromatic aberration for canceling the chromatic aberration of the refractive lens 2 is generated by the diffractive lens surface 1a of the flat diffractive lens 1, chromatic aberration hardly occurs in the entire image pickup optical system. Further, since the flat diffractive lens 1 can be configured to be very thin as compared to the refractive lens 2, the imaging optical device can be configured to be smaller than when a plurality of refractive lenses are arranged.

As shown by a virtual line in FIG. 1, in an actual image pickup optical system, an infrared cut filter 4 and a low-pass filter 5 are arranged as necessary.

In the first embodiment, the flat diffractive lens 1 is arranged on the light incident side of the refracting lens 2. It may be arranged on both the side and the light exit side.

FIG. 4 shows an optical system configuration diagram of an image pickup optical apparatus according to the second embodiment. In FIG. 4, a flat diffraction lens 6 and a refraction lens 2 are arranged on the light path from the light incident side, and a solid-state imaging device 3 is arranged on the light exit side of the refraction lens 2.

The flat diffractive lens 6 as an optical element has a diffractive lens surface 6a on the light exit side, and the configuration of the diffractive lens surface 6a is the same as that of the first embodiment (FIG. 1). Description is omitted. The flat diffractive lens 6 has an aspheric surface 6b having an infinite radius of curvature, which is an optical low-pass filter, on the light incident side. The aspheric surface 6b positively generates aberrations to provide an optical low-pass filter effect.

In the second embodiment, the same operation and effect as those in the first embodiment can be obtained, and a signal due to moire or the like can be removed without adding a low-pass filter. Further, since the flat diffractive lens can be configured to be very thin, it is used for downsizing the imaging optical device.

As shown by a virtual line in FIG. 4, in the actual imaging optical system, only the infrared cut filter 4 has to be arranged as required, so that it is provided for further downsizing as compared with the first embodiment. . The patterns on both sides of the flat diffractive lens 6 can be formed by glass molding technology.

FIG. 5 is an optical system configuration diagram of an image pickup optical device according to the third embodiment. In FIG. 5, since the third embodiment is substantially the same as the configuration of the second embodiment, the same components are denoted by the same reference numerals in the drawings, and description thereof will be omitted. Only different configurations will be described. .
That is, the flat diffractive lens 7 as an optical element has a diffractive lens surface 7a on its light exit surface side as in the second embodiment, but has a phase grating pattern as optical low-pass filter means on its light incident surface side. It has a surface 7b. The phase grating pattern surface 7b has a plurality of protruding line portions arranged at equal intervals in the horizontal direction, a plurality of protruding line portions arranged at equal intervals in the vertical direction, or an equal interval in both the horizontal and vertical directions. It is constituted by a plurality of arranged protruding line portions, and positively generates aberration to have an optical low-pass filter effect.

The third embodiment has the same functions and effects as those of the second embodiment. Diffraction lens 7
Can be formed by the same patterning technology as photolithography or the like.

FIG. 6 is an optical system configuration diagram of an image pickup optical apparatus according to the fourth embodiment. In FIG. 6, the fourth embodiment is substantially the same as the configuration of the third embodiment. Therefore, the same components are denoted by the same reference numerals in the drawings, and the description thereof will be omitted. Only different configurations will be described. .
That is, the flat diffractive lens 8 as an optical element is configured by mixing the diffractive lens surface 8a and the phase grating pattern surface 8b on the light exit surface side. Incidentally, it may be configured on the light incident surface side of the flat diffraction lens 8.

The fourth embodiment has the same functions and effects as the third embodiment. Further, since the diffractive lens surface 8a and the phase grating pattern surface 8b of the flat diffractive lens 8 are formed on the same plane, the die cost can be reduced as compared with the third embodiment.

FIG. 7 shows an optical system configuration diagram of an image pickup optical apparatus according to the fifth embodiment. In FIG. 7, the fifth embodiment differs from the third embodiment (FIG. 5) only in the material of the flat diffractive lens 7 '.
Since other configurations are the same, the same reference numerals are given to the drawings and description thereof will be omitted. That is, the flat diffractive lens 7 'of the fifth embodiment is made of a material that absorbs infrared rays.

The fifth embodiment has the same functions and effects as those of the third embodiment. In addition, there is no need to provide an infrared cut filter 4 as shown by a virtual line in FIG. 5, further reducing the number of parts, improving mass productivity,
The cost can be reduced.

In the fifth embodiment, the flat diffractive lens 7 'is made of a material that absorbs infrared rays as the infrared ray cut filter means. A thin film that reflects infrared rays may be formed by vapor deposition or the like. With this configuration, the same operation and effect as those of the fifth embodiment can be obtained.

FIG. 8 shows an example in which the image pickup optical device of the present invention is applied to a notebook personal computer.
8, a lid 2 is provided at one end of the upper surface of the personal computer main body 20.
1 is rotatably supported, and a liquid crystal display section 21 a is provided on the inner surface side of the lid section 21. An imaging optical device 22 is buried in the upper center of the liquid crystal display section 21a, so that an image can be obtained from the imaging optical device 22. The content of a document or the like is captured and recorded as video data by the imaging optical device 22.

That is, since the imaging optical device 22 of the present invention can be made compact as described above, it can also be incorporated in a thin portion such as the lid 21.

[0035]

As described above, according to the present invention, a refractive lens having power and a flat diffractive lens having a diffractive lens surface disposed on the same optical path as the refractive lens are provided. Thus, there is an effect that an imaging optical system having no chromatic aberration is formed and the apparatus is downsized.

[Brief description of the drawings]

FIG. 1 is an optical system configuration diagram of an imaging optical device (first embodiment).

2A is a characteristic diagram of spherical aberration, FIG. 2B is a characteristic diagram of astigmatism, FIG. 2C is a characteristic diagram of distortion aberration, and FIG. One embodiment).

3A is a characteristic diagram of a spherical aberration, FIG. 3B is a characteristic diagram of an astigmatism, FIG. 3C is a characteristic diagram of a distortion aberration, and FIG. type).

FIG. 4 is an optical system configuration diagram of an imaging optical device (second embodiment).

FIG. 5 is an optical system configuration diagram of an imaging optical device (third embodiment).

FIG. 6 is an optical system configuration diagram of an imaging optical device (fourth embodiment).

FIG. 7 is an optical system configuration diagram of an imaging optical device (fifth embodiment).

FIG. 8 is a perspective view of a notebook personal computer incorporating the imaging optical device of the present invention.

FIG. 9 is an optical system configuration diagram of an imaging optical device (conventional example).

FIG. 10 is an optical system configuration diagram of an imaging optical device (another conventional example).

[Explanation of symbols]

1, 6, 7, 7 ', 8: flat diffractive lens (optical element), 1a, 6a, 7a, 8a: diffractive lens surface, 2: refractive lens, 6b: aspherical surface, 7b, 8b: phase grating Pattern surface.

Claims (14)

[Claims] 1. An imaging optical device comprising: a refractive lens having power; and a flat diffractive lens having a diffractive lens surface disposed on the same optical path as the refractive lens. 2. The imaging optical device according to claim 1, wherein the flat diffraction lens has optical low-pass filter means. 3. The imaging optical device according to claim 2, wherein the optical low-pass filter has an aspheric surface. 4. The image pickup optical device according to claim 2, wherein said optical low-pass filter means is a phase grating pattern surface. 5. The imaging optical device according to claim 4, wherein the phase grating pattern surface is formed on the same surface by being mixed with the diffraction lens surface. 6. The imaging optical device according to claim 1, wherein the flat diffraction lens has an infrared cut filter. 7. The imaging optical device according to claim 6, wherein the infrared cut filter means uses a material that absorbs infrared rays as a material of the flat diffractive lens. 8. An optical element characterized by being a flat diffractive lens disposed on the same optical path as a refractive lens having power and having a diffractive lens surface on one surface. 9. The optical element according to claim 8, wherein the plate-like diffraction lens has an optical low-pass filter. 10. The optical low-pass filter means,
The optical element according to claim 9, wherein the optical element has an aspheric surface. 11. The optical low-pass filter means includes:
The optical element according to claim 9, wherein the optical element is a phase grating pattern surface. 12. The optical element according to claim 11, wherein the phase grating pattern surface is formed on the same surface by being mixed with the diffraction lens surface. 13. The optical element according to claim 8, wherein the flat diffraction lens has an infrared cut filter. 14. The optical element according to claim 13, wherein the infrared cut filter means uses a material that absorbs infrared rays as a material of the flat diffractive lens.