JP2000056268A - Optical low-pass filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cost and to obtain optical characteristic having no wavelength dependency by combining separate double refraction plates in specified directions and separating a light beam to specified number of luminous fluxes having equal intensity and positioned at the corners of a square. SOLUTION: This filter is constituted by disposing the separation double refraction plates 11, 12 and 13 in a zero-degree direction, a 90-degree direction and a +45-degree direction from an incident light side and integrally sticking them with optical adhesive. By arranging the filter in a specified optical path, the incident light beam is separated to four luminous fluxes having equal brightness, which are positioned at the corners of the square. In such a case, by setting the bases of the respective double refraction plates 11, 12 and 13 as reference, the square where the luminous fluxes separated to four are positioned is rotated by 45 deg. and positioned. By arranging the filter on the incident side of a solid-state image pickup element such as a CCD, etc., a pseudo signal is removed and a distinct image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical low-pass filter having no wavelength dependence in light transmission characteristics.

[0002]

2. Description of the Related Art Conventionally, in an electronic optical apparatus such as a video camera and an electronic still camera, for example, an optical low-pass filter is used in an optical system in order to prevent reflection of an incident light beam and perform color correction. I have. When such an optical low-pass filter is used, a pseudo signal generated by the solid-state imaging device can be removed. If such a pseudo signal cannot be removed, problems occur such as horizontal lines appearing jagged or black and white grid stripes are colored.

In particular, recent high-pixel electro-optical devices require an optical low-pass filter having a square separation or a rhombus separation pattern. As such an optical low-pass filter having a square separation or a rhombus separation pattern, a filter provided with a wave plate for shifting the phase is used.

However, in such a case, when a wave plate and a birefringent plate are cut out from, for example, an artificial quartz rough, at least two types of rough need to be prepared because the cutting directions are different from each other, and the cost of the product is required. Rises. In particular, the cost of a rough used for a wave plate having a large area is extremely high because the rough itself is expensive, for example, about three times as expensive as a birefringent plate having the same area.

Further, in a wave plate, the phase difference of a transmitted light essentially depends on the wavelength of an incident light. For this reason, in the case of an electro-optical device that mainly uses light having a wavelength of 400 nm to 700 nm, which is a visible region, there is a problem that optically constant characteristics cannot be obtained in all wavelength regions.

For example, 550 nm using quartz crystal
The wavelength plate having a phase difference of 90 degrees at a wavelength of about 0.5 mm has a thickness of about 0.5 mm. When 700 nm light passes through this wave plate, a phase difference of 130 degrees is generated. With a wavelength plate having a phase difference of 90 degrees, linearly polarized light becomes circularly polarized light and can be separated into light beams of uniform intensity. On the other hand, when the phase difference is 130 degrees, the linearly polarized light becomes elliptically polarized light, and the intensity of the separated light beam is not uniform.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an optical low-pass filter capable of reducing costs and obtaining optical characteristics independent of wavelength. It is intended for.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to a method using 0 degree, +45 degrees.
An optical low-pass filter, which combines three types of birefringent plates having different directions of -45 degrees, -45 degrees, and 90 degrees to separate transmitted light into four light beams having equal intensity and located at the corners of a square. The three types of direction-separating birefringent plates use, for example, respective direction-separating birefringent plates at 0, 90, and +45 degrees from the incident light side.

[0009]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described in detail with reference to the assembly perspective view shown in FIG. From the incident light side, a 0-degree direction separating birefringent plate 11, a 90-degree direction separating birefringent plate 12, and a + 45-degree direction separating birefringent plate 13 are provided. Each of these direction-separating birefringent plates 1
Reference numerals 1, 12, and 13 are, for example, artificial quartz crystals cut at a predetermined angle with respect to the crystal axis and molded.

Note that the 0-degree direction separating birefringent plates 11 and 90
The 90 degree direction separating birefringent plate 12 may be arranged on the incident light side and the 0 degree direction separating birefringent plate 11 may be arranged on the outgoing light side by exchanging the positions of the 90 degree direction separating birefringent plate 12 with each other. Then, these birefringent plates 11, 12, and 13 are integrally bonded with an optical adhesive to constitute an optical low-pass filter.

By arranging the optical low-pass filter in a predetermined optical path, the light beams incident on the optical low-pass filter can be converted into four light beams 14a to 14e having the same brightness.
14d, and these four light fluxes 14a to 14a
d is located at the corner of the square as shown in the projection view of the light beam shown in FIG. In this case, for example, with reference to the bottom sides of the angular sub refraction plates 11, 12, and 13, the square where the four separated light beams are located is rotated by 45 degrees.

With this arrangement, for example, if this optical low-pass filter is arranged on the incident side of a solid-state image pickup device such as a CCD, a pseudo signal can be removed and a clear image can be obtained.

It should be noted that the present invention is not limited to the above-described embodiment, and the present invention is applicable to 0 degree, +45 degree, -45 degree, 90 degree,
What is necessary is just to combine the three kinds of birefringent plates in each direction of the degree, and to separate the transmitted light into four light beams having the same intensity and located at the corners of the square. Therefore, for example, 9
A direction-separating birefringent plate of 0 °, 0 ° and + 45 ° may be used, or 0 °, + 45 ° and -45 ° from the incident light side.
Alternatively, bidirectional birefringent plates having different directions may be used.

Further, according to the present invention, there is provided an optical system comprising:
Each of -45 degree and 0 degree directional separation birefringent plates may be used, -45 degree, +45 degree and 0 degree directional separation birefringent plates may be used from the incident light side, and the incident light side may be used. From -4
A 5-degree, + 45-degree and 0-degree direction-separating birefringent plate may be used.

Further, in the present invention, for example, as shown in FIG. 3, each of direction-separating birefringent plates 11, 13, and 15 at 0, +45, and -45 degrees from the incident light side may be used.
In this case, for example, when the bottom sides of the angular sub refraction plates 11, 13, and 15 are set as a reference, a square where the light beam divided into four is located, as shown in a projection view in FIG. Be parallel.

As described in detail above, according to the present invention,
It is possible to provide an optical low-pass filter that has no wavelength dependence in light transmission characteristics and is inexpensive.

[Brief description of the drawings]

FIG. 1 is an assembled perspective view of an optical low-pass filter according to an embodiment of the present invention.

FIG. 2 is a projection view showing positions of four light beams of the optical low-pass filter shown in FIG.

FIG. 3 is an assembled perspective view of an optical low-pass filter according to another embodiment of the present invention.

FIG. 4 is a projection view showing positions of four light beams of the optical low-pass filter shown in FIG.

[Explanation of symbols]

 11 ··· 0 degree direction separating birefringent plate 12 ··· 90 degree direction separating birefringent plate 13 ·· +45 degree direction separating birefringent plate 14a to 14d ··· luminous flux

Claims (8)

[Claims] 1. Combination of three types of birefringent plates of each direction of 0 degree, +45 degrees, -45 degrees, and 90 degrees to separate transmitted light into four light beams having equal intensity and located at the corners of a square. An optical low-pass filter. 2. The method according to claim 1, wherein the three types of direction-separating birefringent plates are at 0 degree and 90 degrees from the incident light side.
An optical low-pass filter, which is a birefringent plate having a direction separation of +45 degrees and +45 degrees. 3. The device according to claim 1, wherein the three types of direction-separating birefringent plates are at 0 degree, 90 degrees from the incident light side.
An optical low-pass filter, which is a birefringent plate separated in directions of -45 degrees and -45 degrees. 4. The device according to claim 1, wherein the three types of direction-separating birefringent plates are 90 degrees from the incident light side and 0 degrees.
An optical low-pass filter, which is a birefringent plate having a direction separation of +45 degrees and +45 degrees. 5. The apparatus according to claim 1, wherein the three types of direction-separating birefringent plates are at 90 degrees from the incident light side and at 0 degrees.
An optical low-pass filter, which is a birefringent plate separated in directions of -45 degrees and -45 degrees. 6. The device according to claim 1, wherein the three kinds of direction-separating birefringent plates are at 0 degree and +4 degrees from the incident light side.
An optical low-pass filter, comprising a birefringent plate having a direction separation of 5 degrees and -45 degrees. 7. The device according to claim 1, wherein the three types of direction-separating birefringent plates are at +45 degrees from the incident light side,
An optical low-pass filter, which is a birefringent plate separated at -45 degrees and 0 degrees. 8. The device according to claim 1, wherein the three kinds of direction-separating birefringent plates are at -45 degrees from the incident light side,
An optical low-pass filter comprising a birefringent plate separated at +45 degrees and 0 degrees.