WO2011105581A1

WO2011105581A1 - Optical low-pass filter and digital camera

Info

Publication number: WO2011105581A1
Application number: PCT/JP2011/054392
Authority: WO
Inventors: 篤史小柳
Original assignee: 旭硝子株式会社
Priority date: 2010-02-26
Filing date: 2011-02-25
Publication date: 2011-09-01
Also published as: JPWO2011105581A1

Abstract

Disclosed are an optical low-pass filter and a digital camera capable of switching between two or more desired separation distances for separating incident light without a mechanical mechanism. Specifically disclosed is an optical low-pass filter which comprises a first separating element (11) and a second separating element (12) that separate incident light into a first polarized beam and a second polarized beam orthogonal to the first polarized beam, that have the same separation direction, and that have separation distances differing from each other; and a polarization control unit (20) disposed between the separating elements so as to change the polarization state of the incident light or to allow passage of the incident light therethrough without changing the polarization state by adjusting the amplitude of voltage to be applied by a voltage control unit (13). Since the first separating element (11) has a separation distance L₁ and the second separating element (12) has a separation distance L₂, two separation distances of L₁ + L₂ and |L₁ - L₂| can be obtained using the voltage of the voltage control unit (13). When the optical low-pass filter is applied to a digital camera, moiré fringes or false colors that occur in still images and moving images can be appropriately reduced.

Description

Optical low-pass filter and digital camera

The present invention relates to an optical low-pass filter and a digital camera, and more particularly to a digital camera equipped with a solid-state imaging device such as a CCD or CMOS, and more particularly to a digital camera capable of taking a moving image and a still image.

Image sensors such as CCDs and CMOSs used in imaging devices such as video cameras and digital cameras convert the amount of light and darkness that is input as external signals into the amount of electric charge, so-called photoelectric conversion, and the electrical signals are sequentially A digital image is generated by processing. In such an image sensor, it is known that distortion caused by sampling occurs in an image having a spatial frequency finer than the pixel pitch of incident light, and a pattern (moire) or false color different from the original image is generated. Yes.

In order to prevent such moire and false color, the imaging device is configured with an optical low-pass filter (OLPF: Optical Low Pass Pass Filter). A specific OLPF has a birefringent plate such as quartz and separates an incident two-dimensional image by a small distance in the horizontal direction and / or the vertical direction, thereby entering a pixel pitch incident on an image sensor (imaging device). Has a function of cutting the vicinity of the frequency (sampling frequency), and has been devised so as not to cause moiré and false color phenomena.

Such an OLPF separates an incident two-dimensional image by a specific distance in accordance with a pixel pitch necessary for imaging, but the number of pixels necessary for imaging differs between a still image and a moving image. The appropriate distance to be separated is different. Therefore, in order to support both still images and moving images, it is required to appropriately control the separation distance (hereinafter referred to as “separation distance”). In particular, for digital cameras and digital single lens reflex cameras that can shoot not only still images but also moving images, high-precision image quality is required for both still images and moving images. In digital SLR cameras, for example, still images have an image quality of 10 million pixels or more, while moving images are greatly different from about 2 million pixels even if they are compatible with Full HD (HD: High Definition). For this mode, it is required to appropriately reduce the moire and false color phenomenon.

Therefore, in order to appropriately change the separation distance between the still image and the moving image, it is possible to appropriately change the OLPF element for still images and the OLPF element for moving images having different separation distances in the optical path of the camera. An optical low-pass filter that eliminates moire has been reported (Patent Document 1).

Japanese Patent No. 4306002

However, the optical low-pass filter of Patent Document 1 needs to include two types of an OLPF element corresponding to a still image and an OLPF element corresponding to a moving image. Therefore, it is necessary to provide a mechanical mechanism for inserting or removing either one of the OLPF elements in the optical path, and since the space of the optical low-pass filter itself is required, it is difficult to obtain high reliability. There was a problem that miniaturization could not be realized.

The present invention has been made in view of the above points, and includes a first separation element, a polarization control unit, a second separation element, and a voltage control unit that controls a voltage applied to the polarization control unit. The first separation element has a separation distance between the first linearly polarized light and the second linearly polarized light orthogonal to the first linearly polarized light among the incident light. Whether the polarization control unit changes the polarization state of the incident first linearly polarized light and the second linearly polarized light according to the voltage applied by the voltage control unit, separated by L ₁ (> 0). Alternatively, the incident first linearly polarized light is modulated into the second linearly polarized light, and the incident second linearly polarized light is modulated into the first linearly polarized light, Of the incident light, the second separation element includes the first linearly polarized light and the second linearly polarized light. And light, the separation distance L _{2 (>} 0) only provides an optical low-pass filter that separates the separation distance L ₁ separating direction and the parallel direction.

The ratio between the separation distance L ₁ and the separation distance L ₂ is in the range of 1.3 to 3, and the first separation element is emitted by the voltage applied by the voltage controller. when given with _{L S} corresponding to the, | separation distance between the _light, and _{L M} corresponding to L 1 + _{L _2,} and the linear polarized light and the second linearly polarized light _| L 1 -L ₂ Provided is the above optical low-pass filter in which L _M > L _S , 10 μm ≦ L _M ≦ 32 μm, and 2 μm ≦ L _S ≦ 10 μm.

Also, providing the separation distance L ₁ between the separation distance L ₂ is equal to the above of the optical low-pass filter.

Further, the polarization control unit provides the above-described optical low-pass filter including a liquid crystal element having a liquid crystal layer.

The first separation element has a thickness d ₁ , an angle formed by the thickness direction and the extraordinary refractive index axis direction is θ ₁ , and birefringence having an ordinary refractive index no ₁ and an extraordinary refractive index _ne ₁ . The separation distance L ₁ is given by the following equation (1):

The second separation element has a thickness d ₂ , an angle formed by the thickness direction and the extraordinary refractive index axis direction is θ ₂ , and has a normal refractive index no ₂ and an extraordinary refractive index _ne ₂ . And the separation distance L ₂ is given by the following equation (2):

Provide the above optical low-pass filter.

In addition, when no voltage is applied, the liquid crystal element is aligned in a direction in which the liquid crystal molecules of the liquid crystal layer are substantially parallel to the plane of the liquid crystal layer and the major axis directions of the liquid crystal molecules of the opposing surface are substantially orthogonal. are, are about 90 ° twisted in the thickness direction to the axis, when the direction in which said theta ₁ in the thickness direction of the first separation element as a reference and positive, the second separation element, said theta ₂ of the code provides the above optical low-pass filter disposed in a direction to be negative.

Further, the optical low-pass filter is provided in which the liquid crystal layer is sandwiched and integrated by the first separation element and / or the second separation element.

The optical low-pass filter includes a first optical low-pass filter including the first separation element, a first polarization control unit that is the polarization control unit, and the second separation element;
A polarization conversion element; and a second optical low-pass filter, wherein the polarization conversion element converts the incident first linearly polarized light and the second linearly polarized light into the first linearly polarized light, respectively. The second optical low-pass filter modulates the second optical low-pass filter with light having a ratio of the linearly polarized light component to the second linearly polarized light component in a range of 3: 7 to 7: 3. a first linear polarized light and the light of the second linearly polarized light, which provides the above optical low-pass filter for separating in a direction intersecting the direction of the separation distance L ₁ and the separation distance L _2.

The optical low-pass filter includes a first optical low-pass filter including the first separation element, a first polarization control unit that is the polarization control unit, and the second separation element;
And a second optical low-pass filter, a second optical low-pass filter, said a first linear polarized light and the light of the second linearly polarized light, the separation distance L ₁ and the separating distance provides the aforementioned optical low-pass filter for separating direction intersecting at an angle not orthogonal to the direction of L _2.

The second optical low-pass filter includes a third separation element, a second polarization control unit, and a fourth separation element. The third separation element is the first linearly polarized light. And the second linearly polarized light are separated from each other by a separation distance L ₃ (> 0) in a direction intersecting the direction of the separation distance L ₁ and the separation distance L _2. The unit does not change the polarization state of the incident first linearly polarized light and the second linearly polarized light according to the voltage applied by the voltage control unit, or the incident first linearly polarized light. Is modulated into the second linearly polarized light, the incident second linearly polarized light is modulated into the first linearly polarized light, and the fourth separation element the a light of a first linear polarization, and the light of the second linearly polarized light, the separation distance L _{4 (>} 0 Only provides the above optical low-pass filter that separates the separation direction parallel direction of the separation distance L _3.

The ratio between the separation distance L ₃ and the separation distance L ₄ is in the range of 1.3 to 3, and the first separation element is emitted by the voltage applied by the voltage controller. When the separation distance between the linearly polarized light and the second linearly polarized light is L _MX corresponding to L ₃ + L ₄ and L _SX corresponding to | L ₃ −L ₄ |, Provided is the above optical low-pass filter in which L _MX > L _SX , 10 μm ≦ L _MX ≦ 32 μm, and 2 μm ≦ L _SX ≦ 10 μm.

Also, providing the separation distance L ₃ between the separation distance L ₄ equal aforementioned optical low-pass filter.

The second polarization control unit provides the optical low-pass filter including a liquid crystal element having a liquid crystal layer.

Further, the third separation element, the birefringence having a thickness d _3, the thickness direction and the extraordinary light refractive index axis direction and the angle is theta _3, and the ordinary refractive index n _o3, the extraordinary refractive index n _e3 The separation distance L ₃ is given by the following equation (3):

It said fourth separation element, the thickness d _4, the thickness direction and the extraordinary light refractive index axis direction and the angle is theta _4, and the ordinary refractive index n _o4, birefringent material having an extraordinary refractive index n _e4 And the separation distance L ₄ is given by the following equation (4):

Provide the above optical low-pass filter.

In the liquid crystal element of the second polarization controller, the liquid crystal molecules of the liquid crystal layer of the second polarization controller are substantially parallel to the plane of the liquid crystal layer of the second polarization controller when no voltage is applied. Further, the major axis direction of the liquid crystal molecules on the opposite surface is aligned in a direction substantially orthogonal to each other, twisted about 90 ° about the thickness direction, and the θ direction with respect to the thickness direction of the third separation element _{When the} direction of ₃ is positive, the fourth separation element provides the above-described optical low-pass filter arranged in a direction in which the sign of the θ ₄ is negative.

Also provided is the optical low-pass filter described above in which the liquid crystal layer of the second polarization controller is sandwiched and integrated by the third separation element and / or the fourth separation element.

The second optical low-pass filter includes a third separation element, and the third separation element separates the first linearly polarized light and the second linearly polarized light. The optical low-pass filter described above is separated by a separation distance L _{FX in} a direction crossing the separation direction of the distance L ₁ and the separation distance L ₂ .

In addition, the first separation element, the first polarization control unit, the second separation element, the second polarization control unit, the third separation element, the first polarization control unit, and the second A voltage control unit that controls a voltage applied to the polarization control unit, and the first separation element includes a first linearly polarized light and a first linearly polarized light among the incident light. The first polarization control unit and the second polarization control unit are incident on the orthogonally polarized second linearly polarized light by a voltage applied by the voltage control unit, separated by a separation distance L _A (> 0). The polarization state of the first linearly polarized light and the second linearly polarized light is not changed, or the incident first linearly polarized light is modulated into the second linearly polarized light. The second linearly polarized light incident thereon is modulated into the first linearly polarized light, and the second separation element Of the incident light, the light of the first linear polarized light, and the light of the second linearly polarized light, the separation distance L _{B (>} 0) only, the separation distance separating direction parallel direction L ₁ The third separation element is separated from the incident light by the separation distance L _C (> 0) between the first linearly polarized light and the second linearly polarized light. L ₁ is separated from the separation direction of L ₁ (L _A ≠ L _B ≠ L _C ), and any one of the separation distance L _A , the separation distance L _B, and the separation distance L _C is the remaining two Provided is an optical low-pass filter that is controlled by the voltage control unit so that the separation distance of light emitted from the third separation element is equal to a sum value and at least three values including zero.

The first polarization control unit and the second polarization control unit provide the optical low-pass filter including a liquid crystal element having a liquid crystal layer.

The first separation element has a thickness d _A , an angle formed by the thickness direction and the extraordinary refractive index axis direction is θ _A , and birefringence having an ordinary refractive index _noA and an extraordinary refractive index _neA. The separation distance L _A is given by the following equation (5):

The second separation element, the thickness d _B, the thickness direction and the extraordinary light refractive index axis direction and the angle is theta _B, and the ordinary refractive index n _oB, birefringent material having an extraordinary refractive index n _eB The separation distance L _B is given by the following equation (6):

The third separation element has a thickness d _C , an angle between the thickness direction and the extraordinary refractive index axis direction becomes θ _C , and a birefringent material having an ordinary refractive index _noC and an extraordinary refractive index _neC And the separation distance L _C is given by the following equation (7):

Provide the above optical low-pass filter.

The liquid crystal layer of the first polarization control unit is integrated with at least one of the first separation element and the second separation element, and the liquid crystal layer of the second polarization control unit is integrated with the second separation element. The optical low-pass filter is integrated with at least one of the separation element and the third separation element.

Also, a digital camera including the above-described optical low-pass filter and an image sensor is provided.

Further comprising an optical low-pass filter described above, an image sensor, when imaging a still image is the separation distance between L _S, when imaging a video to provide digital camera to the separation distance between L _M.

The present invention can provide an optical low-pass filter that can switch the separation distance between two values with accuracy or three values including zero, has no mechanical moving parts, and can be downsized, and can be added to a still image. With regard to digital cameras and digital single-lens reflex cameras that can also shoot moving images, both still images and moving images can appropriately reduce the phenomenon of moiré and false colors.

Schematic diagram showing an example of an optical low-pass filter (first embodiment) Schematic diagram showing another example of an optical low-pass filter (first embodiment) Schematic diagram showing the optical path and polarization state of light incident on and separated from an optical low-pass filter (when voltage is applied) Schematic diagram showing the optical path and polarization state of light incident on and separated from an optical low-pass filter (when no voltage is applied) Schematic diagram showing an example of an optical low-pass filter (second embodiment) Sectional drawing which shows the example of a 2nd optical low-pass filter Schematic diagram showing the optical path and polarization state of light incident on and separated from an optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the first optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the second optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the first optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the second optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the first optical low-pass filter (when no voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the second optical low-pass filter (when no voltage is applied) Schematic diagram showing an example of an optical low-pass filter (third embodiment) Schematic diagram showing the optical path and polarization state of light incident on and separated from an optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the first optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the second optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the first optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the second optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the first optical low-pass filter (when no voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the second optical low-pass filter (when no voltage is applied) Schematic diagram showing the optical path and polarization state of light incident on and separated from an optical low-pass filter (when voltage is applied) Schematic diagram showing the optical path and polarization state of light incident on and separated from an optical low-pass filter (when no voltage is applied) Schematic diagram showing the optical path and polarization state of light that enters and separates into the optical low-pass filter (when voltage is applied to both the first polarization controller and the second polarization controller) Schematic diagram showing the optical path and polarization state of light incident on and separated from the optical low-pass filter (when no voltage is applied to both the first polarization control unit and the second polarization control unit) Schematic diagram showing the optical path and polarization state of light that enters and is separated into the optical low-pass filter (when the first polarization control unit applies a non-voltage and the second polarization control unit applies a voltage) The schematic diagram which shows the example of a structure and optical characteristic of the other optical low-pass filter which concerns on 5th Embodiment. Schematic diagram illustrating an example of an optical low-pass filter (sixth embodiment) Schematic diagram showing the position and polarization state of light emitted from the second optical low-pass filter (when voltage is applied) Schematic diagram showing the position and polarization state of light emitted from the second optical low-pass filter (when no voltage is applied)

(First embodiment)
1A and 1B are conceptual diagrams illustrating a configuration example of an optical low-pass filter according to the present embodiment. Specifically, the optical low-pass filter 10 of FIG. 1A has a first separation element 11, a polarization control unit 20, and a second separation element 12, and light from the outside is incident in this order (Z direction). And As will be described later, the optical low-pass filter 10 separates first (linear) polarized light and second (linear) polarized light that are orthogonal to each other. In addition, although the light separation direction by the first separation element 11 and the second separation element 12 is parallel and is described here as the Y direction parallel to the paper surface, it may be the X direction.

The polarization controller 20 has a light modulation function that emits light without changing the polarization state of incident light or changes the polarization state depending on the magnitude of the voltage applied from the voltage controller 13. For the polarization controller 20, for example, a liquid crystal element in which the alignment state of liquid crystal molecules is changed by an applied voltage is used. FIG. 1A is an example in which the polarization control unit 20 is a liquid crystal element. As a pair of transparent substrates,

transparent electrodes

22a and 22b and

alignment films

23a and 23b are provided on the opposing surfaces of the

transparent substrates

21a and 21b, respectively. The liquid crystal layer 24 is sandwiched. And the voltage control part 13 which applies a voltage to the liquid-crystal layer 24 via

transparent electrode

22a, 22b is provided.

As long as the

transparent substrates

21a and 21b are transparent to incident light, various materials such as a resin plate and a resin film can be used. However, when an optically isotropic material such as glass or quartz glass is used, This is preferable because the transmitted light is not affected by birefringence. Further, for example, if the

transparent substrates

21a and 21b are provided with an antireflection film made of a multilayer film at the interface with air, light reflection loss due to Fresnel reflection can be reduced. Further, when the

transparent electrodes

22a and 22b are made of an oxide such as ITO (Indium で Tin Oxide), AZO (Aluminum Zinc Oxide), GZO (Gallium Zinc Oxide), for example, high transparency and conductivity Is preferable.

The polarization controller 20 is provided with

alignment films

23a and 23b for aligning the liquid crystal molecules of the liquid crystal layer 24, and between the transparent electrode 22a and the alignment film 23a, and between the transparent electrode 22b and the alignment film 23b. May have an insulating film (not shown) made of a transparent dielectric material. The

alignment films

23a and 23b are formed by rubbing a resin film such as polyimide, an oblique vapor deposition film formed by oblique vapor deposition of an inorganic material such as silicon oxide, and ultraviolet rays or the like on an organic film. A photo-alignment film that generates alignment ability by irradiation can be used. Then, as the insulating film, for _example, SiO 2, SiON or the like is used. In the optical low-pass filter 10, the first separation element 11 and / or the second separation element 12, and the transparent substrate 21a and / or the transparent substrate 21b may be integrated respectively. Although the polarization controller 20 have been described in detail configuration of a liquid crystal element is not limited thereto, using the inorganic crystal LiNbO ₃ or the like polarization controller 20 is an electro-optic crystal, the voltage control unit 13 The polarization state of the transmitted light may be controlled by the voltage applied by the above, and the same can be used in the following embodiments.

FIG. 1B shows the configuration of the optical low-pass filter 15, and the same parts as those of the optical low-pass filter 10 are denoted by the same reference numerals. The optical low-pass filter 15 has a configuration in which the first separation element 11 and the second separation element 12 include the function of the

transparent substrates

21 a and 21 b of the optical low-pass filter 10, that is, the function of sandwiching the liquid crystal layer 24. As a result, downsizing can be realized. In this case, the polarization control unit 25 is configured by a portion of the optical low-pass filter 10 excluding the transparent substrate 21a and the transparent substrate 21b of the polarization control unit 20. Although not shown, one of the first separation element 11 and the second separation element 12 may be configured to include the function of the transparent substrate 21a or the transparent substrate 21b.

Also, the optical low-pass filter is preferably as thin as possible because the thickness of the element increases when various functions are included as will be described later. For example, when an optical low-pass filter is used for a digital single lens reflex camera, the thickness may be 5 mm or less, preferably 3 mm or less, and more preferably 2 mm or less. Further, from the viewpoint of space, an optical low-pass filter may be used as a cover glass used for image sensors such as CMOS and CCD, and may be integrated with an infrared absorption filter for blocking infrared rays incident on the image sensor. .

The first separation element 11 and the second separation element 12 are made of, for example, a birefringent material, and in this case, have an extraordinary refractive index axis in an oblique direction with respect to the thickness (Z-axis) direction. In addition, as a material constituting the first separation element 11 and the second separation element 12, as a crystal material, quartz, yttrium orthovanadate (YVO ₄ ) crystal, calcite (calcite: CaCO ₃ ), rutile ( TiO ₂ ) and lithium niobate (LiNbO ₃ ). For resin materials, polyimide, polyamideimide, polyamide, polyetherimide, polyetheretherketone, polyetherketone, polyketonesulfide, polyethersulfone, polysulfone, polyphenylenesulfide, polyphenylene oxide, polyethylene terephthalate, polybutylene terephthalate , Polyethylene naphthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol, polypropylene, cellulosic plastics, polyolefin and the like. Further, it may be a liquid crystal material including a polymer liquid crystal capable of obtaining birefringence, and can be similarly used in the following embodiments.

The first separation element 11 and the second separation element 12 are not limited to those made of a birefringent material having an extraordinary refractive index axis in a direction oblique to the thickness direction. For example, the angle of refraction with respect to the second polarized light orthogonal to the first polarized light may be different, and the incident light is orthogonal to the first polarized light with respect to the thickness direction. A material in which the in-plane refractive index is uniform and the distribution of the in-plane refractive index orthogonal to the thickness direction is inclined with respect to the light of the second polarization orthogonal to the first polarization. Alternatively, it may be a separation element that refracts light of one polarized light by providing a configuration that gives such characteristics. Further, in order to control the inclination angle and thickness of the in-plane refractive index distribution, the in-plane refractive index distribution may be divided into blaze shapes so that the inclination angle is uniform in a plane orthogonal to the thickness direction. . These can be similarly used in the following embodiments.

Further, it may be a separation element composed of a polarizing diffraction grating that transmits straightly without diffracting the first polarized light and diffracts the second polarized light. As a polarizing diffraction grating, for example, a birefringence having a normal light refractive index n ₁ and an extraordinary light refractive index n ₂ (n ₁ ≠ n ₂ ) as a material corresponding to a convex portion of a diffraction grating whose cross section has periodic unevenness. The concave portion has an isotropic material with a refractive index of n _s so as to fill the material and the unevenness. For example, by making n ₁ and n _s substantially equal, light of polarized light having an ordinary refractive index is transmitted. And polarized light having an extraordinary refractive index can be diffracted. In this case, in order to increase the diffraction efficiency, the cross-sectional shape of the diffraction grating may be a blazed shape or a pseudo-blazed shape approximating the blazed shape to a staircase shape. In the following description, it is assumed that the first separation element 11 and the second separation element 12 are made of a birefringent material having an extraordinary light refractive index axis in an oblique direction.

In the optical low-pass filter 10 of FIG. 1A, the thickness of the first separation element 11 is d ₁ , the ordinary light refractive index is n _o1 , the extraordinary light refractive index is n _e1 , and the incident light enters the extraordinary light refractive index axis 11 a. When the angle formed by the Z-axis direction, which is the direction (thickness direction of the first separation element 11), is θ ₁ , the separation distance L ₁ can be expressed by Expression (1). The same applies to the optical low-pass filter 15 in FIG. 1B.

In FIG. 1A, the thickness of the second separation element 12 is d ₂ , the ordinary light refractive index is n _o2 , the extraordinary light refractive index is _{ne 2} , and the extraordinary light refractive index axis 12 a travels in the incident light direction (first). When the angle formed by the Z-axis direction, which is the thickness direction of the two separation elements 12, is θ ₂ , the separation distance L ₂ can be expressed by Expression (2). As will be described later, in this embodiment, it is set to be different values from the separation distance L ₁ and the separation distance L _2. Note that θ ₁ and θ ₂ have signs, and here, the inclination in the + Y direction is considered to be positive and the inclination in the −Y direction is considered to be negative with respect to the Z-axis direction in which light is incident.

Next, the case where the

polarization controllers

20 and 25 are liquid crystal elements will be described. As the liquid crystal of the liquid crystal layer 24, nematic phase liquid crystal is preferably used. In addition, as the alignment direction of the liquid crystal molecules, when no voltage is applied to the liquid crystal layer 24, horizontal alignment (homogeneous alignment) in which the major axis direction of the liquid crystal molecules is substantially parallel to the surfaces of the

alignment films

23a and 23b; There are two modes: vertical alignment (homeotropic alignment) in which the major axis direction of the liquid crystal molecules is substantially perpendicular to the planes of the

alignment films

23a and 23b, and either mode may be used. In the case of horizontal alignment, a liquid crystal material having positive dielectric anisotropy (Δε> 0) may be used, and in the case of vertical alignment, a liquid crystal material having negative dielectric anisotropy (Δε <0) may be used. In order to maintain a specific thickness for the liquid crystal layer 24, a spherical spacer made of an inorganic material such as SiO ₂ or an organic material such as resin may be used in the liquid crystal layer 24, for example. The voltage control unit 13 may be capable of applying a DC voltage or an AC voltage to the liquid crystal layer 24, but it is preferable that an AC voltage can be applied in order to prevent deterioration of the liquid crystal.

Here, first, consider the case where the liquid crystal molecules of the liquid crystal layer 24 are horizontally aligned when no voltage is applied. At this time, the liquid crystal is a twisted nematic (TN) liquid crystal that is aligned in a direction in which the major axis direction of the liquid crystal molecules on the surfaces of the opposing

alignment films

23a and 23b is substantially orthogonal and twisted about 90 ° about the thickness direction. To do. When a voltage of a certain value or more is applied from the voltage control unit 13 (referred to as “when voltage is applied”), the major axis direction of the liquid crystal molecules is aligned parallel to the thickness direction. In addition, a liquid crystal imparting a bistable state can be used. In this case, for example, the orientation state of the liquid crystal can be maintained even after the voltage is cut off, so that power saving can be realized.

On the other hand, when the liquid crystal molecules in the liquid crystal layer 24 are vertically aligned when no voltage is applied, the liquid crystal layer 24 operates so as to be opposite to the horizontal alignment. That is, when a voltage of a certain value or more is applied from the voltage controller 13, the liquid crystal molecules are aligned in the direction parallel to the

alignment films

23a and 23b. Here, when a voltage is applied, the liquid crystal molecules of the liquid crystal layer 24 are twisted by about 90 ° about the thickness direction by making the major axis direction of the liquid crystal molecules on the surfaces of the

alignment films

23a and 23b facing each other substantially orthogonal. Oriented. Thus, by controlling the magnitude of the voltage applied to the liquid crystal layer 24 from the voltage control unit 13 according to the alignment direction in the voltage non-applied state, the polarization direction of the incident light has a characteristic that the alignment direction is different. It is possible to control whether the light is emitted while changing the state, or the light is emitted without changing.

Next, the operation of the optical low-pass filter 10 will be described. 2A and 2B are schematic views showing the path and polarization state of light incident on the optical low-pass filter 10, where the liquid crystal molecules of the liquid crystal layer 24 are horizontally aligned when no voltage is applied and the liquid crystal molecules In the following description, it is assumed that a TN liquid crystal in which the major axis direction is twisted by 90 ° about the thickness direction is used. FIG. 2A is a schematic diagram showing a light path and a polarization state when a voltage is applied. At this time, the major axis direction of the liquid crystal molecules is aligned with the thickness direction. On the other hand, FIG. 2B is a schematic diagram showing a light path and a polarization state when no voltage is applied. At this time, the major axis direction of the liquid crystal molecules is horizontally aligned and 90 ° about the thickness direction. Twisted.

Here, first, consider the voltage application in FIG. 2A. Randomly polarized light incident on the first separation element 11 along the Z-axis direction is separated into linearly polarized light in the X-axis direction and linearly polarized light in the Y-axis direction. The separation distance is determined based on the above equation (1). In this specification, linearly polarized light in the X-axis direction may be expressed as first linearly polarized light, and linearly polarized light in the Y-axis direction may be expressed as second linearly polarized light. Specifically, it is assumed that linearly polarized light in the X-axis direction is transmitted straight through the first separation element 11, and the traveling direction of linearly polarized light in the Y-axis direction is changed. Linearly polarized light of the first separation device 11 X-axis direction of the linearly polarized light emitted from the light and the Y-axis direction enters the polarization control unit 20 at a separation distance L _1. At the time of voltage application, the major axis direction of the liquid crystal molecules is aligned in the thickness direction of the liquid crystal layer 24, so that any linearly polarized light is emitted from the polarization controller 20 without changing the polarization state.

Then, the linearly polarized light in the X-axis direction and the linearly polarized light in the Y-axis direction emitted from the polarization controller 20 are incident on the second separation element 12. In the second separation element 12, the linearly polarized light in the X-axis direction passes straight, and the linearly polarized light in the Y-axis direction passes through the first separation element 11 with reference to the optical path of the linearly polarized light in the X-axis direction. The direction of travel is changed to the direction opposite to the + Y direction separated in step 1, that is, the −Y direction, and the light is emitted. Therefore, the separation distance of the entire optical low-pass filter 10 when a voltage is applied is | L ₁ −L ₂ | (L ₁ ≠ L ₂ ).

Next, consider the case of no voltage application in FIG. 2B. Since the behavior of the linearly polarized light in the X-axis direction and the linearly polarized light in the Y-axis direction that exits the first separation element 11 is the same as when a voltage is applied, description thereof is omitted here. Then, the light of linear polarization of light and the Y-axis direction of the first separation element 11 emits the X-axis direction of the linearly polarized light is incident on the polarization control unit 20 at a separation distance L _1, the liquid crystal molecules are liquid crystal Since it is oriented so as to be twisted by 90 ° in the layer 24, linearly polarized light in the X-axis direction is converted (rotated) into linearly polarized light in the Y-axis direction, and linearly polarized light in the Y-axis direction. Is converted (rotated) into linearly polarized light in the X-axis direction. Then, the linearly polarized light in the X-axis direction and the linearly polarized light in the Y-axis direction emitted from the polarization controller 20 are incident on the second separation element 12, but the linearly polarized light in the X-axis direction is transmitted straight through. The linearly polarized light in the Y-axis direction is emitted with the traveling direction changed.

In this way, when no voltage is applied, all of the linearly polarized light incident on the polarization controller 20 is rotated by 90 ° and emitted, so that the first separation element 11 follows the trajectory shown in FIG. 2B. The separated two lights are separated by the second separation element 12 so as to be further away. Therefore, the separation distance of the entire optical low-pass filter 10 when no voltage is applied is L ₁ + L ₂ . Therefore, the separation distance can be switched between | L ₁ −L ₂ | and L ₁ + L ₂ when voltage is applied and when voltage is not applied. For example, a digital camera or a digital single lens reflex camera It is better to design to switch between video mode and still image mode.

2A and 2B are examples illustrating a configuration in which the major axis direction of the liquid crystal molecules when no voltage is applied is horizontal alignment, the liquid crystal molecules are vertically aligned when no voltage is applied. May be. The angle theta ₁ of the first extraordinary refractive index axis 11a of the separating element _11, but the sign of the angle theta ₂ of the second extraordinary refractive index axis 12a of the separating element 12 has been described different example, in this Not limited to this, θ ₁ and θ ₂ may have the same sign. In this way, taking into account the orientation state of the liquid crystal molecules at the time of voltage application / non-application of voltage and θ ₁ and θ ₂ in consideration of the sign, for example, a moving image mode of a digital camera or a digital single lens reflex camera, L ₁ and L ₂ may be designed so that the image mode can be switched according to an appropriate separation distance | L ₁ −L ₂ |, L ₁ + L ₂ . Furthermore, in a digital camera and a digital single-lens reflex camera that are frequently used in the still image mode, it is preferable in terms of power saving that the digital camera and the digital single lens reflex camera are designed to be in the still image mode when no voltage is applied.

Further, in a digital camera, a digital single lens reflex camera, or the like using an optical low-pass filter, an image sensor such as a CCD (not shown) is disposed at the subsequent stage of the second separation element 12, but when applying a voltage based on FIG. A still image mode with a large number of images and a moving image mode with a relatively small number of pixels can be obtained when no voltage is applied based on FIG. 2B. 2B, when the liquid crystal molecules of the liquid crystal layer 24 have an orientation direction twisted by 90 °, among the incident light, linearly polarized light in the X-axis direction becomes linearly polarized light in the Y-axis direction. In some cases, linearly polarized light in the direction cannot be converted 100% into linearly polarized light in the X-axis direction. That is, when no voltage is applied in FIG. 2B, linearly polarized light in the X direction is incident on the polarization controller 20 and is not converted to 100% light in the Y direction, and is slightly α% (> 0). In the case where only the component is transmitted as linearly polarized light in the X-axis direction, this α% component is transmitted straight through the second separation element 12. Similarly, when no voltage is applied in FIG. 2B, linearly polarized light in the Y direction is incident on the polarization control unit 20 and is not converted to 100% light in the X direction, and is slightly α% (> 0). When only the component is transmitted as linearly polarized light in the Y-axis direction, only the α% component is emitted by the second separation element 12 while changing the traveling direction in the −Y direction.

Further, as described above, the separation distance L ₁ + L ₂ generated by the optical low-pass filter 10 corresponds to, for example, the size of a moving image pixel of a digital camera or a digital single lens reflex camera, and | L ₁ − L ₂ | corresponds to the size of a still image pixel. Here, the α% component is generated in the moving image mode based on FIG. 2B, that is, in the case where the separation distance is L ₁ + L _2. The light of the α% component is the separation distance, L ₁ + L _2. It reaches inside, that is, within one pixel and does not reach other pixels as noise. In this way, when the liquid crystal molecules are 90 ° twist aligned, the digital camera and the digital single-lens reflex camera have a configuration of an optical low-pass filter that obtains a large separation distance that is a moving image mode. Moire and false colors can be sufficiently eliminated, which is more preferable.

In addition, even when the liquid crystal molecules of the liquid crystal layer 24 are vertically aligned when no voltage is applied and twisted 90 degrees (horizontal alignment) when a voltage is applied, the light incident on the liquid crystal layer 24 is sufficiently polarized and converted when the voltage is applied. In some cases, noise components may be generated. Similarly, in this case, the noise component does not reach other pixels in the moving image mode, which is preferable, and further, the still image mode is applied when no voltage is applied, and the moving image mode is applied when the voltage is applied. In many digital cameras and digital single-lens reflex cameras, power saving can be realized.

Next, a specific separation distance according to the number of pixels of a digital single lens reflex camera among digital cameras will be described. The digital single-lens reflex camera has an optical low-pass filter function corresponding to about 10 million pixels to about 30 million pixels for still images, and about 1 million pixels to about 2 million pixels corresponding to full HD images and HD images for moving images. It is required to reduce moire and false color by switching the optimal optical low-pass filter function. The size of image sensors (imaging devices) such as CCDs and CMOSs used in digital single-lens reflex cameras ranges from about 17.3 mm × 13.0 mm of the Four Thirds size to about 23.4 mm × 16 of the APS-C size. A size of about 36 mm × 24 mm corresponding to 0.7 mm and a 35 mm film is used.

As a result, in a digital single lens reflex camera, the pixel interval applied to a still image is in the range of about 2 μm to about 10 μm, while the pixel interval applied to a full HD image or HD image moving image is about 10 to about 10 μm. The range is about 32 μm. Thus, the first separation element 11 and the second separation element 12 are designed so that the separation distance is long and can be varied over a wide range. Here, when the separation distance for still images is L _S and the separation distance for moving images is L _M , L _M > L _S and L _S has a separation distance of about 2 to 10 μm, and L _M Preferably has a separation distance of 10 to 32 μm.

In this embodiment, the separation relationship L ₁ generated by the first separation element 11 and the separation distance L ₂ generated by the second separation element 12 are not limited in magnitude as long as they are different. That is, L ₁ > L ₂ or L ₁ <L ₂ may be satisfied. Also, of the L ₁ and L _2, when relative to the separation distance smaller, as the separation distance greater is in the range from 1.3 to 3, formula (1) and adjusting the formula (2) It is preferable to do. The first separation element 11 and the second separation element 12 are made of the same material, and the directions of the extraordinary light refractive index axes 11a and 12a are parallel (θ ₁ = θ ₂ ) or symmetrical with respect to the Z axis (| θ ₁ | = | Θ ₂ |), the ratio of the thicknesses d ₁ and d ₂ may be adjusted in the range of 1.3 to 3.

(Second Embodiment)
FIG. 3 is a conceptual diagram illustrating a configuration example of the optical low-pass filter 50 according to the present embodiment. A polarization conversion element 51 is provided between the optical low-pass filter 10 and the optical low-pass filter 30 according to the first embodiment. Have. In the present embodiment, the optical low-pass filter 10 is the first optical low-pass filter 10 having the light separation ability in the Y-axis direction, and the optical low-pass filter 30 is the second optical separation ability having the light separation ability in the X-axis direction. The optical low-pass filter 30 will be described.

FIG. 4 is a schematic cross-sectional view of the second optical low-pass filter 30 extracted from the optical low-pass filter 50, and particularly shows the XZ plane. Here, when the Z-axis direction is used as a reference, the third separation element 31 having a thickness d ₃ has an extraordinary refractive index axis that is inclined in the + X direction and has an angle θ ₃ with respect to the Z-axis direction. The fourth separation element 32 having the thickness d ₄ has an extraordinary refractive index axis having an angle θ ₄ with an inclination in the −X direction with respect to the Z-axis direction. The thickness of the third separation element 31 is d ₃ , the ordinary light refractive index is n _o3 , the extraordinary light refractive index is n _e3 , and the direction in which the incident light travels with the extraordinary light refractive index axis 31 a (third separation element). When the angle formed by the Z-axis direction (thickness direction of 31) is θ ₃ , the separation distance L ₃ can be expressed by Expression (3).

Also, the thickness of the fourth separation element 32 is d ₄ , the ordinary light refractive index is n _o4 , the extraordinary light refractive index is n _e4 , and the direction in which the incident light travels with the extraordinary light refractive index axis 32 a (fourth separation element). When the angle formed by the Z-axis direction that is the thickness direction of 32 is θ ₄ , the separation distance L ₄ can be expressed by Expression (4). Also here, the separation distance L ₃ and the separation distance L ₄ are set to be different from each other, and θ ₃ and θ ₄ also have signs, and here, the Z-axis direction in which light is incident is used as a reference. , + X direction inclination is considered as positive, and −X direction inclination is considered as negative.

Here, the thicknesses d ₃ and d ₄ and the angles θ ₃ and θ ₄ can be arbitrarily given. Here, the signs of θ ₃ and θ ₄ are different, and | θ ₃ | = | θ ₁ |, Let | θ ₄ | = | θ ₂ |. Further, d ₃ = d ₁ and d ₄ = d ₂ are set. That is, the third separation element 31 and the fourth separation element 32 have the same configuration as the first separation element 11 and the second separation element 12, and the first separation element 11 and the second separation element 12. On the other hand, the description will be made on the assumption that the Z axis direction is the same as that rotated 90 ° about the rotation axis.

The optical low-pass filter 10 according to the first embodiment provides light separation only in one direction (Y-axis direction), but the optical low-pass filter 50 according to the present embodiment has the first optical low-pass filter. By having the configuration in which the filter 10 and the second optical low-pass filter 30 overlap, light can be separated two-dimensionally. Moreover, the same part is attached | subjected to each site | part which comprises the 1st optical low-pass filter 10, and duplication of description is avoided. The second optical low-pass filter 30, between the thickness d ₃ of the third separation device 31 and the thickness d ₄ of the fourth separation device 32 includes a (second) polarization control unit 40 The polarization control unit 40 includes

transparent electrodes

42a and 42b and

alignment films

43a and 43b as opposed to the

transparent substrates

41a and 41b as a pair of transparent substrates, and the liquid crystal layer 44 is sandwiched therebetween. And the voltage control part 52 which applies a voltage to the liquid crystal layer 44 via the

transparent electrodes

42a and 42b is provided. The voltage control unit 52 can apply a voltage to the liquid crystal layer 24 in common via the

transparent electrodes

22a and 22b.

The polarization conversion element 51 is configured to transmit X-axis direction linearly polarized light (first linearly polarized light) and Y-axis direction linearly polarized light (second linearly polarized light) transmitted through the second separation element 12, respectively. The first linearly polarized light component and the second linearly polarized light component have a function of converting into substantially the same light. Specifically, it may have a function to become a broadband half-wave plate or a function to become a broadband quarter-wave plate for incident visible light. That is, in the case of a broadband ½ wavelength plate, preferably, the vibration direction of the incident linearly polarized light is converted to linearly polarized light that is rotated by an angle that is an odd multiple of 45 °. In this case, it is preferable that incident linearly polarized light is converted into circularly polarized light. The ratio of the light component in the X-axis direction and the light component in the Y-axis direction out of the light emitted from the polarization conversion element 51 is approximately the same for light in the visible light region from 7: 3 to 3: 7. Of 6: 4 to 4: 6 is preferable, and the closer to the ratio of 5: 5, the more preferable.

When the polarization conversion element 51 is a broadband ½ wavelength plate or a broadband ¼ wavelength plate, for example, the polarization conversion element 51 has an optical axis parallel to a plane orthogonal to the direction in which light enters, and the optical axis is thick. A plurality of wave plates made of birefringent materials aligned in the direction may be stacked so that the optical axes intersect. Further, one or a plurality of wave plates whose optical axis directions are spiraled about the thickness direction may be configured. Examples of the material of the wave plate include inorganic materials such as quartz and LiNbO ₃ and organic materials such as resin, liquid crystal, and polymer liquid crystal.

Next, the operation of the optical low-pass filter 50 will be described. 5A to 5C are schematic diagrams showing the path and polarization state of light incident on the optical low-pass filter 50. Here, the liquid crystal molecules of the liquid crystal layers 24 and 44 are horizontally aligned when no voltage is applied, respectively. In the following description, it is assumed that a TN liquid crystal in which the major axis direction of the liquid crystal molecules is twisted by 90 ° about the thickness direction is used. FIG. 5A is a schematic diagram showing a light path and a polarization state when a voltage is applied, and the major axis directions of the liquid crystal molecules in the liquid crystal layers 24 and 44 are aligned in the thickness direction. FIG. 5B shows the positions and polarization states of the light 10a and the light 10b on the emission surface of the first optical low-pass filter 10 when a voltage is applied. 5C shows the positions and polarization states of the light 30a, the light 30b, the light 30c, and the light 30d on the emission surface of the second optical low-pass filter 30 when a voltage is applied. This is the optical low-pass filter. It corresponds to the one showing 50 light separation states.

Next, the state of light in the optical path until incident light passes through the optical low-pass filter 50 will be described. In FIG. 5A, the light incident on the optical low-pass filter 50 is in a random polarization state and travels along the Z-axis direction. When the voltage is applied, the first optical low-pass filter 10 separates the light of the linearly polarized light in the X-axis direction (first linearly polarized light) and the light of the linearly polarized light in the Y-axis direction (second linearly polarized light). The light is transmitted by a distance _LSY . Note that 'S' in the separation distance L _SY is a still image mode, 'Y' means the separation direction is the Y-axis direction, and as will be described later, 'M' is the moving image mode, and 'X' is the separation direction X. It means the axial direction. Further, in the schematic diagram shown in FIG. 5B, the first linearly polarized light and the second linearly polarized light are separated by the first optical low-pass filter 10 and emitted from the

respective positions

10a and 10b. Corresponds to the separation distance _LSY .

Then, the light separated into the optical path 53 a of the first linearly polarized light and the optical path 54 a of the second linearly polarized light enters the polarization conversion element 51. The polarization state of the light incident on the polarization conversion element 51 is converted so that the light component of the first linearly polarized light and the light component of the second linearly polarized light are mixed. Specifically, the light corresponding to the optical path 53a follows the optical path 53b as light in which the first linearly polarized light component and the second linearly polarized light component are mixed substantially in the same manner, and the second optical low pass. The light enters the filter 30. The light corresponding to the optical path 54 a follows the optical path 54 b as light in which the first linearly polarized light component and the second linearly polarized light component are mixed substantially in the same manner, and the second optical low-pass filter 30. Is incident on.

At this time, when a voltage is applied, the second optical low-pass filter 30 is configured to emit light of linearly polarized light (first linearly polarized light) in the X-axis direction and light of linearly polarized light (second linearly polarized light) in the Y-axis direction. _Are separated by a separation distance L _SX in the X-axis direction. Note that the separation distance L _SX corresponds to | L ₃ −L ₄ |. In the schematic diagram shown in FIG. 5C, light corresponding to the optical path 53b is separated by the second optical low-pass filter 30 and is emitted from the

respective positions

30a and 30b, and the interval corresponds to the separation distance _LSX . Similarly, the light corresponding to the optical path 54b is separated by the second optical low-pass filter 30 and emitted from the

respective positions

30c and 30d, and the interval thereof also corresponds to the separation distance _LSX .

The reason for making the separation directions orthogonal in this way is that the pixels of the image sensor are two-dimensionally arranged, and therefore the pixel arrangement direction in order to reduce moiré and false colors in the two orthogonal directions arranged It is made to separate according to. Further, the separation distance varies depending on the pixel pitch and the spatial frequency to be cut. When the pixel shape is a square, it is effective to make the separation distance in the X-axis direction and the separation distance in the Y-axis direction the same. For example, in the case of an image sensor having vertically long pixels (the length of one pixel in the Y-axis direction> the length of one pixel in the X-axis direction), priority is given to the prevention of moire and false colors in the X-axis direction. For this reason, the separation distance between the X-axis direction and the Y-axis direction is different, and the quadrilateral formed by connecting the four points to be separated is not limited to a square, and may be a parallelogram.

Next, the state of light when no voltage is applied from the voltage control unit 52 and no voltage is applied will be described. When no voltage is applied, the first optical low-pass filter 10 separates the first linearly polarized light and the second linearly polarized light with a separation distance larger than that when a voltage is applied, as in the first embodiment. Separate the light. 6A to 6D are diagrams showing the light positions and polarization states of the light exit surfaces of the first optical low-pass filter 10 and the second optical low-pass filter 30 when a voltage is applied to the optical low-pass filter 50 and when no voltage is applied. is there. Specifically, FIG. 6A shows the position and polarization state of light on the exit surface of the first optical low-pass filter 10 when a voltage is applied, and FIG. 6B shows the light on the exit surface of the second optical low-pass filter 30 when a voltage is applied. 5B and FIG. 5C respectively show the same position and polarization state. Further, as compared with FIGS. 6A and 6B, FIG. 6C shows the position and polarization state of light on the exit surface of the first optical low-pass filter 10 when no voltage is applied, and FIG. 6D shows the first state when no voltage is applied. 2 shows the position and polarization state of the light on the exit surface of the second optical low-pass filter 30.

Further, in FIG. 6C, when the distance between the position 10c of the first linearly polarized light passing through the first optical low-pass filter 10 and the position 10d of the second linearly polarized light is defined as a separation distance _LMY , L _MY > L _SY . In FIG. 6D, the distance between the first linearly polarized light 30e and the second linearly polarized light position 30f on the transmission surface of the second optical low-pass filter 30, the first linearly polarized light 30g, When the distance between the second linearly polarized light and the position 30h is equal and the separation distance L _MX is set, L _MX > L _SX . The separation distance L _MX corresponds to L ₃ + L ₄ . In this way, the light incident on the optical low-pass filter 50 becomes four light beams that are two-dimensionally separated and emitted, and the separation distance can be changed depending on whether a voltage is applied or not.

Further, in the present embodiment, the voltage control unit 52 is configured to be able to apply a common voltage to the (first) liquid crystal layer 24 and the (second) liquid crystal layer 44. The voltage may be applied independently to the layer 24 and the liquid crystal layer 44. Similarly to the first embodiment, in the digital single-lens reflex camera, the separation distances L _SY , L _MY , and the separation distances L _SX , L _MX are related to the relationship of L _MY > L _SY and L _MX > L _SX . It is preferable that L _SY and L _SX have a separation distance of about 2 to 10 μm, and L _MY and L _MX have a separation distance of 10 to 32 μm. Furthermore, when the smaller separation distance of L ₁ and L ₂ is used as a reference, the larger separation distance is in the range of 1.3 to 3, and the smaller separation of L ₃ and L ₄ is smaller. When the distance is used as a reference, the birefringent material, thickness, and extraordinary refractive index axis angle of each separation element may be adjusted so that the larger separation distance is in the range of 1.3 to 3.

(Third embodiment)
FIG. 7 is a conceptual diagram illustrating a configuration example of the optical low-pass filter 60 according to the present embodiment, and includes the optical low-pass filter 10 according to the first embodiment, the polarization conversion element 51, and the optical low-pass filter 62. . In the present embodiment, the optical low-pass filter 10 is the first optical low-pass filter 10 having light separation in the Y-axis direction, and the optical low-pass filter 62 is the second optical low-pass filter having light separation in the X-axis direction. The optical low-pass filter 62 will be described. Further, the present embodiment is different from the second embodiment in that the second optical low-pass filter 62 does not include a liquid crystal layer and the separation distance is fixed. For example, the second optical low-pass filter 62 has the same configuration as that of the first separation element 11 and is arranged by being rotated 90 ° with respect to the first separation element 11 about the Z-axis direction as a rotation axis. It may be equivalent.

Next, the polarization state in the optical path through which incident light passes through the optical low-pass filter 60 will be described. 8A to 8C are schematic views showing the path and polarization state of light incident on the optical low-pass filter 60. Here, the liquid crystal layer 24 is horizontally aligned when no voltage is applied, and the major axis direction of the liquid crystal molecules is In the following description, it is assumed that a TN liquid crystal twisted by 90 ° about the thickness direction is used. FIG. 8A is a schematic diagram showing a light path and a polarization state when a voltage is applied, and the major axis direction of the liquid crystal molecules in the liquid crystal layer 24 is aligned with the thickness direction. In FIG. 8A, the light incident on the optical low-pass filter 60 is in a random polarization state and travels along the Z-axis direction. Similar to the second embodiment, in the first optical low-pass filter 10, linearly polarized light in the X-axis direction and linearly polarized light in the Y-axis direction are transmitted with a separation distance _LSY therebetween. Further, in the schematic diagram shown in FIG. 8B, the first linearly polarized light and the second linearly polarized light are separated by the first optical low-pass filter 10 and emitted from the

respective positions

10a and 10b. The interval corresponds to the separation distance _LSY .

Then, the light separated into the optical path 63 a of the first linearly polarized light and the optical path 64 a of the second linearly polarized light is incident on the polarization conversion element 51. Of the light incident on the polarization conversion element 51, the light corresponding to the optical path 63a is transmitted through the optical path 63b as light in which the first linearly polarized light component and the second linearly polarized light component are mixed substantially in the same manner. Traces and enters the second optical low-pass filter 62. The light corresponding to the optical path 64a follows the optical path 64b as light in which the first linearly polarized light component and the second linearly polarized light component are mixed substantially in the same manner, and the second optical low-pass filter 62. Is incident on.

At this time, the second optical low-pass filter 62 separates the linearly polarized light in the X-axis direction and the linearly polarized light in the Y-axis direction so as to be separated by a separation distance L _{FX in the} X-axis direction. Note that “F” in the separation distance L _FX means that the separation distance is fixed. In the schematic diagram shown in FIG. 8C, light corresponding to the optical path 63b is separated by the second optical low-pass filter 62 and emitted from the

respective positions

62a and 62b, and the interval corresponds to the separation distance L _FX . Similarly, the light corresponding to the optical path 64b is separated by the second optical low-pass filter 62 and emitted from the

respective positions

62c and 62d, and the interval thereof also corresponds to the separation distance _LFX .

This embodiment can also reduce moiré and false color two-dimensionally with respect to the image sensor as in the second embodiment. For example, moiré or false in the Y-axis direction compared to the X-axis direction can be used. When priority is given to color reduction, an optical low-pass filter 60 that varies the separation distance in the Y-axis direction and fixes the separation distance in the X-axis direction as in the present embodiment may be used. In this case, the entire optical low-pass filter can be downsized, and moire and false colors can be reduced two-dimensionally. In addition, the direction in which the separation distance is fixed is not limited to the X-axis direction, and may be the Y-axis direction. In addition, in FIG. 7, the optical low-pass filter located in the first optical low-pass filter 10 has a separation distance. The optical low-pass filter positioned in the second optical low-pass filter 62 may have a function of varying the separation distance.

Next, the state of light when no voltage is applied will be described. When no voltage is applied, the first optical low-pass filter 10 separates the first linearly polarized light and the second linearly polarized light with a separation distance larger than that when a voltage is applied, as in the first embodiment. Separate the light. 9A to 9D show the positions and polarization states of light on the exit surface of the first optical low-pass filter 10 and the exit surface of the second optical low-pass filter 62 when the voltage is applied to the optical low-pass filter 60 and when no voltage is applied. FIG. Specifically, FIG. 9A shows the position and polarization state of light on the exit surface of the first optical low-pass filter 10 when a voltage is applied, and FIG. 9B shows the light on the exit surface of the second optical low-pass filter 62 when a voltage is applied. This shows the same position and polarization state as in FIGS. 8B and 8C. 9A and 9B, FIG. 9C shows the position and polarization state of the light on the exit surface of the first optical low-pass filter 10 when no voltage is applied, and FIG. 9D shows the first state when no voltage is applied. 2 shows the position and polarization state of light on the exit surface of the second optical low-pass filter 62.

Further, in FIG. 9C, when the distance between the position 10c of the first linearly polarized light passing through the first optical low-pass filter 10 and the position 10d of the second linearly polarized light is defined as a separation distance _LMY , L _MY > L _SY . 9D, the distance between the first linearly polarized light 62e and the second linearly polarized light position 62f on the transmission surface of the second optical low-pass filter 62, the first linearly polarized light 62g, The distance between the second linearly polarized light and the position 62h is equal, and the separation distance L _FX is obtained. In this way, the light incident on the optical low-pass filter 60 becomes four light beams that are two-dimensionally separated and emitted, and the separation distance is changed in one axial direction depending on whether a voltage is applied or not. be able to.

In the present embodiment, as in the first embodiment, in the digital single-lens reflex camera, the separation distances L _SY and L _MY satisfy the relationship of L _MY > L _SY and L _SY is about 2 to 10 μm. has a _{distance, L MY} is may have a separation distance of 10 ~ 32 [mu] m. Further, the birefringent material, the thickness, and the thickness of each separation element are set so that the larger separation distance is 1.3 to 3 with reference to the smaller separation distance of L ₁ and L ₂ . The angle of the extraordinary light refractive index axis may be adjusted.

(Fourth embodiment)
10A and 10B are schematic diagrams illustrating a configuration example of the optical low-pass filter 70 according to the present embodiment, and a light path and a polarization state in the optical low-pass filter 70. The optical low-pass filter 70 includes a first separation element 71, a polarization control unit 20, and a second separation element 72, and light from the outside is incident in this order (Z direction). In the optical low-pass filter 70, the first separation element 71 and the second separation element 72 are made of the same birefringent material and have the same thickness. That is, when the thickness of the first separation element 71 is d ₁ and the thickness of the second separation element 72 is d ₂ , d ₁ = d ₂ , and the above expression (2) is the above expression. It becomes the same value as (1). Therefore, the separation distance L ₁ and the separation distance L ₂ are the same as the optical low-pass filter 10 according to the first embodiment. Even when the birefringent material of the first separation element 71 and the birefringent material of the second separation element 72 are different, L ₁ = L ₂ may be satisfied. Further, the polarization control unit 20 and the voltage control unit 13 are the same as the optical low-pass filter 10 according to the first embodiment, and a description thereof is omitted here.

The angle of the extraordinary light refractive index axis (not shown) of the first separation element 71 with respect to the thickness direction is θ ₁ , and the angle of the extraordinary light refractive index axis (not shown) of the second separation element 72 with respect to the thickness direction is θ When _2, and satisfy the relation of θ ₁ = -θ _2. FIG. 10A is a schematic diagram showing a light path and a polarization state when a voltage is applied. At this time, the major axis direction of the liquid crystal molecules is aligned with the thickness direction. On the other hand, FIG. 10B is a schematic diagram showing a light path and a polarization state when no voltage is applied. At this time, the major axis direction of the liquid crystal molecules is horizontally aligned and 90 ° with the thickness direction as an axis. ° Twisted.

Here, consider the voltage application in FIG. 10A. Randomly polarized light incident on the first separation element 71 along the Z-axis direction includes linearly polarized light in the X-axis direction and linearly polarized light in the Y-axis direction according to the above equation (1). based enters the polarization control unit 20 at a separation distance L ₁ in. At the time of voltage application, the major axis direction of the liquid crystal molecules is aligned in the thickness direction of the liquid crystal layer 24, so that any linearly polarized light is emitted from the polarization controller 20 without changing the polarization state. Then, the linearly polarized light in the X-axis direction and the linearly polarized light in the Y-axis direction emitted from the polarization controller 20 are incident on the second separation element 72. In the second separation element 72, the linearly polarized light in the X-axis direction is transmitted in a straight line, and the linearly polarized light in the Y-axis direction is transmitted through the first separation element 71 with reference to the optical path of the linearly polarized light in the X-axis direction. The direction of travel is changed to the direction opposite to the + Y direction separated in step 1, that is, the −Y direction, and the light is emitted. Therefore, the separation distance of the entire optical low-pass filter 70 when a voltage is applied is | L ₁ −L ₂ |. Here, since d ₁ = d ₂ , since L ₁ = L ₂ , the separation distance is substantially zero.

On the other hand, when the voltage is not applied in FIG. 10B, the optical action is the same as that of the optical low-pass filter 10 according to the first embodiment. That is, in the polarization controller 20, the liquid crystal molecules are aligned so as to be twisted by 90 ° in the liquid crystal layer 24, so that linearly polarized light in the X-axis direction is converted into linearly polarized light in the Y-axis direction (optical rotation). At the same time, the linearly polarized light in the Y-axis direction is converted (rotated) into linearly polarized light in the X-axis direction. As described above, when no voltage is applied, the linearly polarized light incident on the polarization controller 20 is rotated by 90 ° and emitted, so that the first separation element 71 follows the trajectory shown in FIG. 10B. The separated two lights are separated by the second separation element 72 so as to be further away. Therefore, the separation distance of the entire optical low-pass filter 70 when no voltage is applied is L ₁ + L ₂ = 2 · L ₁ .

Therefore, the separation distance can be switched between 0 and 2 · L ₁ when the voltage is applied and when the voltage is not applied. For example, in the still image mode of a digital camera, when no moiré or false color is generated as a subject to be imaged, the separation distance is set to 0 and the optical low-pass filter is substantially passed to obtain a highly accurate image. It can be in a state that does not. On the other hand, when moire or false color is generated as a subject to be imaged, the separation distance can be set to 2 · L _{1 so} that the moire or false color can be appropriately reduced. Note that, as in the optical low-pass filter 70 according to the present embodiment, switching the separation distance between 0 and 2 · L ₁ is not limited to the still image mode but may be the moving image mode. Further, the separation distance 0 may be set to the still image mode, and the separation distance 2 · L ₁ may be set to the moving image mode.

Further, switching the separation distance between 0 and 2 · L ₁ is not limited to the separation in the Y-axis direction as in the optical low-pass filter 70 shown in FIGS. 10A and 10B. For example, the present embodiment can be applied based on the optical low-pass filter 50 according to the second embodiment. That is, two optical low-pass filters 70 are arranged in the optical path, and a polarization conversion element is arranged in the optical path between the two optical low-pass filters 70. One optical low-pass filter is arranged in the Y-axis direction and the other optical low-pass filter is arranged in the optical path. The filter may have a function of separating light in the X-axis direction. In this case, one of the two optical low-pass filters 70 corresponds to a positional relationship in which the other is rotated 90 ° with the Z-axis direction as the rotation axis. In this configuration, a two-dimensional optical low-pass filter that can similarly switch the separation distance between 0 and a finite value in the X-axis direction can be obtained.

Furthermore, the present embodiment can be applied based on the optical low-pass filter 60 according to the third embodiment. That is, the optical low-pass filter 70 and the optical low-pass filter corresponding to the second optical low-pass filter 62 of the third embodiment are disposed, and the polarization conversion element is disposed therebetween, and one optical low-pass filter is disposed. Has a function of switching to two separation distance values including 0 in the Y-axis direction, and the other optical low-pass filter has a function of separating light by a certain separation distance (≠ 0) in the X-axis direction. It may be.

(Fifth embodiment)
FIGS. 11 to 13 are schematic diagrams illustrating a configuration example of the optical low-pass filter 80 according to the present embodiment, and a light path and a polarization state in the optical low-pass filter 80. The optical low-pass filter 80 includes a first separation element 81, a first polarization control unit 91, a second separation element 82, a second polarization control unit 92, and a third separation element 83. It is assumed that light is incident in this order (Z direction). Further, the first polarization control unit 91 and the second polarization control unit 92 emit light without changing the polarization state of incident light or change the polarization state depending on the voltage applied from the voltage control unit 93. It has a light modulation function that emits light by changing. Here, the first polarization control unit 91 and the second polarization control unit 92 have the same configuration as the polarization control unit 20 of the optical low-pass filter 10 according to the first embodiment, and liquid crystal is applied when no voltage is applied. The major axis direction of the molecule is assumed to be horizontally oriented and twisted by 90 ° about the thickness direction.

The first separation element 81 has a thickness d _A , an ordinary light refractive index n _oA , an extraordinary light refractive index n _eA , and an extraordinary light refractive index axis and a Z-axis direction that is a direction in which incident light travels. When the angle is θ _A , the following equation (5) can be used as the separation distance L _A. The second separation element 82, the thickness d _B, ordinary refractive index n _oB, the extraordinary refractive index n _eB, the Z-axis direction in which light travels to incident extraordinary refractive index axis There the angle of theta _B, that when the separation distance _{L B} may use a formula (6) below, the third splitting element 83, the thickness _{d C,} ordinary refractive index _{n oC,} When the extraordinary refractive index is n _eC and the angle between the extraordinary refractive index axis and the Z-axis direction, which is the direction in which incident light travels, is θ _C , the separation distance L _C is expressed by the following equation (7). Can be used.

Here, in the optical low-pass filter 80, the first separation element 81, the second separation element 82, and the third separation element 83 are made of the same birefringent material and, for example, the first separation element 81 The thickness of the element 81 is the same as the sum of the thickness of the second separation element 82 and the thickness of the third separation element 83. In other words, the thickness _{d A} of the first separation element 81, the thickness _{d B} of the second separation element 82, the third thickness relationship _{d C} separation element _83, by _d _{A =} d B + d _C There, at the same time it has a relationship of _{_{_{L a = L B + L C}}} . Even when the birefringent material of the first separating element 81, the birefringent material of the second separating element 82, and the birefringent material of the third separating element 83 are different, L _A = it may be a _L _B + L _C.

In this case, the magnitude relationship is d _A > d _B > d _C , and at the same time, L _A > L _B > L _C. The optical low-pass filter 80 having such a configuration obtains separation distances of at least three different values by the voltage control unit 93 according to the voltages applied to the first polarization control unit 91 and the second polarization control unit 92. Can do. Here, as an example, a configuration in which the signs of the extraordinary refractive index axes θ _A , θ _B and θ _C are the same is considered, but the signs of these angles can be arbitrarily set.

Next, the operation of the optical low-pass filter 80 will be described. First, FIG. 11 is a schematic diagram showing a light path and a polarization state when the first polarization control unit 91 and the second polarization control unit 92 are at the time of voltage application. The major axis direction is aligned with the thickness direction. Here, the randomly polarized light incident on the first separation element 81 along the Z-axis direction is expressed by the above formula (X-axis linearly-polarized light and Y-axis-direction linearly polarized light). It enters the first polarization control unit 91 at a separation distance L _a on the basis of 5). Then, the first polarization controller 91 emits any linearly polarized light without changing the polarization state, and enters the second separation element 82.

In the second separation element 82, the linearly polarized light in the X-axis direction is transmitted straight, and the linearly polarized light in the Y-axis direction is expressed by the above formula (6) with reference to the optical path of the linearly polarized light in the X-axis direction. based on and enters the second polarization control unit 92 at a separation distance L _B in the + Y direction. Note that the separation distance at this time is L _A + L _B. Then, the second polarization controller 92 emits any linearly polarized light without changing the polarization state and enters the third separation element 83. In the third separation element 83, linearly polarized light in the X-axis direction travels straight, and linearly polarized light in the Y-axis direction is expressed by the above formula (7) with reference to the optical path of linearly polarized light in the X-axis direction. based on, and emits at a separation distance L _C in the + Y direction. Thus, the first polarization control unit 91 and the second polarization control unit 92, at the time of any voltage applied, as the separation distance of the entire optical low-pass filter 80, it is possible to obtain the _{_{_{L A + L B + L C}}} .

FIG. 12 is a schematic diagram showing a light path and a polarization state when the first polarization control unit 91 and the second polarization control unit 92 are at the time of non-voltage application, both of which are the lengths of liquid crystal molecules. The axial direction is horizontally oriented and twisted by 90 ° about the thickness direction. Here, the randomly polarized light incident on the first separation element 81 along the Z-axis direction is expressed by the above formula (X-axis linearly-polarized light and Y-axis-direction linearly polarized light). It enters the first polarization control unit 91 at a separation distance L _a on the basis of 5). In the first polarization controller 91, the linearly polarized light in the X-axis direction is converted (rotated) into linearly polarized light in the Y-axis direction, and the linearly polarized light in the Y-axis direction is converted in the X-axis direction. The light is converted (rotated) into linearly polarized light, emitted, and incident on the second separation element 82.

In the second separation element 82, the linearly polarized light in the X-axis direction is transmitted straight, and the linearly polarized light in the Y-axis direction is expressed by the above formula (6) with reference to the optical path of the linearly polarized light in the X-axis direction. based on and enters the second polarization control unit 92 at a separation distance L _B in the + Y direction. Note that the separation distance at this time is | L _A −L _B |. In the second polarization controller 92, the linearly polarized light in the X-axis direction is converted (rotated) into linearly polarized light in the Y-axis direction, and the linearly polarized light in the Y-axis direction is converted in the X-axis direction. The light is converted (rotated) into linearly polarized light, emitted, and incident on the third separation element 83. In the third separation element 83, linearly polarized light in the X-axis direction travels straight, and linearly polarized light in the Y-axis direction is expressed by the above formula (7) with reference to the optical path of linearly polarized light in the X-axis direction. based on, and emits at a separation distance L _C in the + Y direction. Therefore, when the first polarization control unit 91 and the second polarization control unit 92 are both applied with no voltage, the separation distance of the entire optical low-pass filter 80 is obtained as | L _A −L _B + L _C |. be able to.

FIG. 13 is a schematic diagram showing a light path and a polarization state when the first polarization control unit 91 is not applying voltage and the second polarization control unit 92 is applying voltage. At this time, in the first polarization control unit 91, the major axis direction of the liquid crystal molecules is horizontally aligned and twisted by 90 ° about the thickness direction. In the second polarization control unit 92, the liquid crystal molecules Are aligned in the thickness direction. Here, the randomly polarized light incident on the first separation element 81 along the Z-axis direction is expressed by the above formula (X-axis linearly-polarized light and Y-axis-direction linearly polarized light). It enters the first polarization control unit 91 at a separation distance L _a on the basis of 5). In the first polarization controller 91, the linearly polarized light in the X-axis direction is converted (rotated) into linearly polarized light in the Y-axis direction, and the linearly polarized light in the Y-axis direction is converted in the X-axis direction. The light is converted (rotated) into linearly polarized light, emitted, and incident on the second separation element 82.

In the second separation element 82, the linearly polarized light in the X-axis direction is transmitted straight, and the linearly polarized light in the Y-axis direction is expressed by the above formula (6) with reference to the optical path of the linearly polarized light in the X-axis direction. based on and enters the second polarization control unit 92 at a separation distance L _B in the + Y direction. Note that the separation distance at this time is | L _A −L _B |. Then, the second polarization controller 92 emits any linearly polarized light without changing the polarization state and enters the third separation element 83. In the third separation element 83, linearly polarized light in the X-axis direction travels straight, and linearly polarized light in the Y-axis direction is expressed by the above formula (7) with reference to the optical path of linearly polarized light in the X-axis direction. based on, and emits at a separation distance L _C in the + Y direction. Therefore, when the first polarization control unit 91 is not applied with voltage and the second polarization control unit 92 is applied with voltage, the separation distance of the entire optical low-pass filter 80 is | L _A −L _B −L _C | Can be obtained.

Here, initially _set, so satisfy the relationship of _{_{L A = L B + L C}} , overall separation distance optical low-pass filter 80 becomes zero. _{Incidentally,} an example is described that satisfy the relation of _{_{L A = L B + L C}} , L A, L B, is one of the separation distance of the _{L C,} or if equal to the sum of the remaining two separation distance. That _may satisfy the relationship of _{_{L B = L A + L C}} . In addition, the example in which the signs of the extraordinary refractive index axes θ _A , θ _B and θ _C satisfy the same relationship has been described. In consideration, the signs of θ _A , θ _B, and θ _C can be determined.

In this way, the separation distance is set to at least three values by alternately arranging the three separation elements and the two polarization control units and controlling the voltage supplied from the voltage control unit 93 to these polarization control units. Can do. In particular, by setting the values of these three separation distances to include at least 0, for example, in the still image mode and when no moire or false color is generated as a subject to be imaged, the separation distance On the other hand, when the still image mode is used and moire or false color is generated, the separation distance L _SY = | L _A −L _B + L _C |. At this time, by further setting the separation distance L _MY = L _A + L _B + L _C in the moving image mode, the optical low-pass filter 80 can obtain a configuration with a high degree of freedom according to each mode.

In the optical low-pass filter 80 according to the present embodiment, the direction of separation for each linearly polarized light component is the Y-axis direction, but the present invention is not limited to this. For example, the present embodiment can be applied as in the second embodiment. That is, two optical low-pass filters 80 are disposed in the optical path, and a polarization conversion element is disposed in the optical path between the two optical low-pass filters 80. One optical low-pass filter is disposed in the Y-axis direction and the other optical low-pass filter is disposed in the optical path. The filter may have a function of separating light in the X-axis direction. In this case, one of the two optical low-pass filters 80 corresponds to a positional relationship in which the other is rotated by 90 ° about the Z-axis direction as a rotation axis. In this configuration, a two-dimensional optical low-pass filter that can similarly switch the separation distance to three values including 0 in the X-axis direction can be obtained.

FIG. 14 shows a configuration example of the optical low-pass filter 120 according to the present embodiment, which is a two-dimensional optical low-pass filter. Here, if the optical low-pass filter 80 described above is the first optical low-pass filter 80, the optical low-pass filter 120 includes the first optical low-pass filter 80, the polarization conversion element 51, and the second optical low-pass filter 100. It is assumed that light from the outside is incident in this order (Z direction). The second optical low-pass filter 100 includes a fourth separation element 104, a third polarization control unit 113, a fifth separation element 105, a fourth polarization control unit 114, and a sixth separation element 106. However, light from the outside enters in this order (Z direction). The polarization conversion element 51 gives the same effect as the polarization conversion element 51 of the second embodiment, and a description thereof is omitted.

The third polarization control unit 113 and the fourth polarization control unit 114 emit light without changing the polarization state of incident light or change the polarization state depending on the voltage applied from the voltage control unit 115. It has a light modulation function that emits light by changing. Note that the voltage control unit 115 is considered to include the function of the voltage control unit 93. In FIG. 14, the third polarization control unit 113 and the fourth polarization control unit 114 each indicate an optical path when a voltage is applied. It is a thing. Here, the third polarization control unit 113 and the fourth polarization control unit 114 have the same configuration as the polarization control unit 20 of the optical low-pass filter 10 according to the first embodiment, and liquid crystal is applied when no voltage is applied. The major axis direction of the molecule is assumed to be horizontally oriented and twisted by 90 ° about the thickness direction.

The fourth separation element 104 has a thickness of d _D , an ordinary light refractive index of n _oD , an extraordinary light refractive index of n _eD , and an extraordinary light refractive index axis and a Z-axis direction that is a direction in which incident light travels. When the angle is θ _D , the following equation (8) can be used as the separation distance L _D. Further, the fifth separation element 105 has a thickness d _E , an ordinary light refractive index n _oE , an extraordinary light refractive index n _eE , an anomalous light refractive index axis, and a Z-axis direction that is a direction in which incident light travels. Is an angle formed by θ _E , the following distance ( _E ) can be used as the separation distance L _E , and the sixth separation element 106 has a thickness d _F , an ordinary refractive index n _oF , When the extraordinary refractive index is n _eF and the angle between the extraordinary refractive index axis and the Z-axis direction, which is the direction in which incident light travels, is θ _F , the separation distance L _F is expressed by the following equation (10): Can be used. Θ _D , θ _E and θ _E are angles formed by the thickness direction and the extraordinary light refractive index axis direction in the XZ plane.

Here, in the second optical low-pass filter 100, the fourth separation element 104, the fifth separation element 105, and the sixth separation element 106 are made of the same birefringent material. The thickness of the fourth separation element 104 is the same as the sum of the thickness of the fifth separation element 105 and the thickness of the sixth separation element 106. In other words, the thickness _{d D} of the fourth division element 104, the thickness _{d E} of the fifth splitter 105, the relationship between the thickness _{d F} of the sixth separating element _106, be _d _{D =} d E + d _F At the same time, L _D = L _E + L _F. Even if the birefringent material of the fourth separation element 104, the birefringence material of the fifth separation element 105, and the birefringence material of the sixth separation element 106 are different, L _D = L _E + L _F may be used.

In this case, the magnitude relationship is d _D > d _E > d _F , and at the same time, L _D > L _E > L _F. The second optical low-pass filter 100 having such a configuration has at least a voltage applied to the third polarization control unit 113 and the fourth polarization control unit 114 by the voltage control unit 115 with respect to the X-axis direction. Three different values of separation distance can be obtained. Further, an example in which the signs of the extraordinary refractive index axes θ _D , θ _E, and θ _F are the same has been described, but this is not a limitation, and the orientation state of liquid crystal molecules at the time of voltage application / voltage non-application is considered. Thus, the signs of θ _D , θ _E and θ _F can be determined. _{Incidentally,} an example is described which satisfies the relation _{_{L D = L E + L F}} , L D, L E, is one of the separation distance of the _{L F,} it becomes equal to the sum of the remaining two separation distance. That _may satisfy the relationship _{_{L E = L D + L F}} .

The optical low-pass filter according to this embodiment can switch at least three separation distance values in at least the same separation direction, while at least three separation elements and at least two liquid crystal elements serving as a polarization control unit. One, and the thickness increases. Therefore, for example, based on the configuration of the low-pass filter 15 according to the first embodiment, a configuration in which the liquid crystal layer of the liquid crystal element is sandwiched by a separation element such as a crystal is preferable because the thickness can be reduced.

Furthermore, the present embodiment can be applied not only to the optical low-pass filter 120 as shown in FIG. 14 but also based on the third embodiment. That is, the optical low-pass filter 80 and the optical low-pass filter corresponding to the second optical low-pass filter 62 of the third embodiment are disposed, and the polarization conversion element is disposed therebetween, and one optical low-pass filter is disposed. Has a function of switching to three separation distance values including 0 in the Y-axis direction, and the other optical low-pass filter has a function of separating light by a certain separation distance (≠ 0) in the X-axis direction. It may be. In addition to this combination, as an optical low-pass filter that functions two-dimensionally by setting two separation directions, one separation direction can be switched between three values including a separation distance 0, and the other separation direction is It may be one that can switch between binary values including or not including the separation distance 0. And each separation distance of each separation direction can be designed suitably.

(Sixth embodiment)
FIG. 15 is a schematic diagram illustrating a configuration example of the optical low-pass filter 130 according to the present embodiment. The optical low-pass filter 130 includes a first optical low-pass filter 10 and a second optical low-pass filter 30, which are the first optical low-pass filter 10 and the second optical low-pass filter 50 in the optical low-pass filter 50 of the second embodiment. The same as the optical low-pass filter 30 of FIG. Therefore, each part which comprises the 1st optical low-pass filter 10 and the 2nd optical low-pass filter 30 attaches | subjects the same part number as 2nd Embodiment, and avoids duplication of description.

Further, the optical low-pass filter 130 according to the present embodiment does not arrange a polarization conversion element between the first optical low-pass filter 10 and the second optical low-pass filter 30. Then, when considering the separation direction of the first linearly polarized light and the second linearly polarized light, the separation direction of the first optical low-pass filter 10, the separation direction of the second optical low-pass filter 30, and Are not parallel and non-orthogonal, that is, they intersect at a non-orthogonal angle. Specifically, the relationship between the angles formed by these separation directions may be 20 ° to 70 °, preferably 30 ° to 60 °, more preferably 40 ° to 50 °, and most preferably 45 °. preferable. Thus, it is preferable that the relationship between the angles formed by the separation direction approaches 45 ° because the intensity of light separated by the second optical low-pass filter 30 becomes substantially equal. Further, in this case, there is an effect on moire generated with respect to a vertical stripe image and a horizontal stripe image. In addition, if the angle formed by the separation direction is 60 °, it can be applied to an image sensor having a honeycomb arrangement.

Here, in the optical low-pass filter 130 shown in FIG. 15, the first optical low-pass filter 10 is arranged so as to separate the first linearly polarized light and the second linearly polarized light orthogonal to each other in the Y direction. Shall be. On the other hand, the second optical low-pass filter 30 is arranged so as to separate two orthogonally polarized light beams in a direction that forms an angle of 45 ° with respect to the Y direction on the XY plane. . That is, the second optical low-pass filter 30 corresponds to a position rotated by 45 ° with respect to the position of the second optical low-pass filter 30 in the second embodiment with the Z-axis direction as the rotation axis. Here, the two linearly polarized light beams separated by the second optical low-pass filter 30 are defined as a third linearly polarized light beam and a fourth linearly polarized light beam.

Next, the operation of the optical low-pass filter 130 will be described. First, light incident on the optical low-pass filter 130 has a random polarization state and travels along the Z-axis direction. When the voltage is applied, in the first optical low-pass filter 10, the light of the first linearly polarized light (linearly polarized light in the X-axis direction) and the light of the second linearly polarized light (linearly polarized light in the Y-axis direction) are The light is transmitted through a separation distance _LSY . As described above, the two lights transmitted through the first optical low-pass filter 10 are incident on the second optical low-pass filter 30 as the first linearly polarized light and the second linearly polarized light, respectively. At this time, the position and polarization state of light on the emission surface of the first optical low-pass filter 10 correspond to those shown in FIG. 6A.

Next, when a voltage is applied, when the first linearly polarized light and the second linearly polarized light are incident on the second optical low-pass filter 30, −45 ° with respect to the Y-axis direction in the XY plane. The linearly polarized light component (referred to as “third linearly polarized light”) and the linearly polarized light in the direction forming an angle of + 45 ° with respect to the Y-axis direction (“4th Component of “linearly polarized light”) and a component separated by a certain separation distance. The specific separation distance of these light components is the same as that of _LSX described in the second embodiment, but the separation direction is 45 ° with respect to the Y-axis direction in the XY plane. It corresponds to the direction. FIG. 16A shows the

positions

130a, 130b, 130c and 130d of light on the exit surface of the second optical low-pass filter 30 and the polarization state when a voltage is applied. This is the separation of the light of the optical low-pass filter 130. It corresponds to the one indicating the state.

As described above, the first linearly polarized light transmitted through the first optical low-pass filter 10 is separated by the second optical low-pass filter 30, and is emitted from the

respective positions

130a and 130b. It corresponds to the same interval as _SX . Similarly, the second linearly polarized light transmitted through the first optical low-pass filter 10 is separated by the second optical low-pass filter 30 and emitted from the

respective positions

130c and 130d, and the distance between them is also the separation distance L _SX. Corresponds to the same interval. As described above, the optical low-pass filter 130 according to the present embodiment can be separated into four points of light without disposing a polarization conversion element.

Next, the state of light when no voltage is applied from the voltage control unit 52, that is, when no voltage is applied will be described. The first optical low-pass filter 10, the voltage at the time of non-application, as in the first embodiment, and separated by a large separation distance L _MY than when a voltage is applied, the first linear polarized light and the second linear Separates polarized light. At this time, the position and polarization state of light on the emission surface of the first optical low-pass filter 10 correspond to those shown in FIG. 6B.

Next, when no voltage is applied, when the first linearly polarized light and the second linearly polarized light are incident on the second optical low-pass filter 30, the third linearly polarized light in the XY plane is third with respect to the Y-axis direction. The linearly polarized light component and the fourth linearly polarized light component are transmitted with a predetermined separation distance therebetween. Further, the specific separation distance of these light components is the same as that of L _MX described in the second embodiment, but the separation direction is 45 ° with respect to the Y-axis direction in the XY plane. It corresponds to the direction. FIG. 16B shows the

positions

130e, 130f, 130g, and 130h of light on the exit surface of the second optical low-pass filter 30 and the polarization state when no voltage is applied. Corresponds to the separation state.

respective positions

130e and 130f. It corresponds to the same interval as _MX . Similarly, the second linearly polarized light transmitted through the first optical low-pass filter 10 is separated by the second optical low-pass filter 30 and emitted from the

respective positions

130g and 130h, and the distance between them is also the separation distance L _MX. Corresponds to the same interval. As described above, the optical low-pass filter 130 according to the present embodiment can be separated into four points of light without disposing a polarization conversion element.

The optical low-pass filter according to the present embodiment in which no polarization conversion element is disposed has been described based on the configuration of the second embodiment, but is not limited thereto. That is, if the separation direction of the first optical low-pass filter and the separation direction of the second optical low-pass filter are not parallel or orthogonal, that is, if they are arranged so that they intersect at a non-orthogonal angle, the third implementation is performed. Any one of the separation distances may be fixed based on the configuration of the form. Furthermore, it may be based on the configuration of the optical low-pass filter 120 which is the configuration of the fifth embodiment.

Example 1
In this example, the optical low-pass filter 10 according to the first embodiment will be described. A quartz glass substrate is used as the

transparent substrates

21a and 21b, and an ITO film is formed as the

transparent electrodes

22a and 22b on one surface of each quartz glass substrate. Next, on the

transparent electrodes

22a and 22b, a polyimide film formed by applying and curing polyimide is rubbed in a certain direction to form

alignment films

23a and 23b. Then, the alignment film 23a and the alignment film 23b are opposed to each other, and the alignment directions of the alignment films are arranged so as to be orthogonal to each other, and the periphery is sealed so as to have a gap of about 7 μm. Then, by filling the gap with a liquid crystal mixed with a chiral agent, the polarization controller 20 has a liquid crystal layer 24 in which the major axis direction of the liquid crystal molecules is twisted by 90 ° about the thickness direction when no voltage is applied. A liquid crystal element corresponding to is obtained.

Next, as the first separation element 11 and the second separation element 12, quartz having an extraordinary refractive index axis inclined by 45 ° with respect to the thickness direction is used. The quartz crystal used as the first separation element 11 has a thickness of about 2.05 mm, and the quartz crystal used as the second separation element 12 has a thickness of about 1.11 mm. The first separation element 11 is arranged on the transparent substrate 21a side so that the extraordinary refractive index axis is inclined 45 ° in the + Y-axis direction on the YZ plane with the thickness as the Z-axis direction. The two separation elements 12 are arranged on the transparent substrate 21b side so that the extraordinary refractive index axis is inclined by 45 ° in the −Y-axis direction on the YZ plane, thereby obtaining the optical low-pass filter 10. Quartz has an ordinary light refractive index of 1.546 and an extraordinary light refractive index of 1.555 for light having a wavelength of 546 nm. At this time, the separation distance L ₁ in the first separation element 11 is about 12.0 μm, and the separation distance L ₂ in the second separation element 12 is about 6.5 μm.

Then, randomly polarized light is incident in the visible light region along the Z-axis direction from the first separation element 11 side of the optical low-pass filter 10. When the voltage controller 13 does not apply a voltage to the liquid crystal layer 24, the first linearly polarized light and the second linearly polarized light that are orthogonal to each other are separated in the Y-axis direction, and the separation distance is about 18.5 μm. It becomes. When a rectangular AC wave of about 10V is applied to the liquid crystal layer 24, the first linearly polarized light and the second linearly polarized light are separated in the Y-axis direction, and a separation distance of about 5.5 μm is applied. Shorter than when not. By placing this optical low-pass filter in front of the image sensor of a digital camera, especially a digital single-lens reflex camera, it captures moving images when voltage is applied and images that reduce moiré and false colors in still images when voltage is not applied. can do.

(Example 2)
In this example, an optical low-pass filter 50 according to the second embodiment will be described. The first optical low-pass filter 10 and the second optical low-pass filter 30 are the same as the optical low-pass filter 10 of the first embodiment. Next, as the polarization conversion element 51, a birefringent material that generates a phase difference substantially equal to that of the quarter-wave plate for light having a wavelength in the visible light region is used. As the polarization conversion element 51, an element whose optical axis is parallel to the surface of the polarization conversion element 51 and aligned in the thickness direction is used.

Next, the first optical low-pass filter 10, the polarization conversion element 51, and the second optical low-pass filter 30 are arranged in this order with the thickness direction aligned in the Z-axis direction. The first optical low-pass filter 10 is disposed so as to correspond to a position rotated by 90 ° with the Z-axis direction as the rotation axis. Thus, the first optical low-pass filter 10 separates light in the Y-axis direction, and the second optical low-pass filter 30 separates light in the X-axis direction. The polarization conversion element 51 is arranged such that its optical axis is at an angle of 45 ° with respect to the X-axis direction (or Y-axis direction) in the XY plane.

Then, randomly polarized light is incident in the visible light region along the Z-axis direction from the first optical low-pass filter 10 side. When no voltage is applied to the liquid crystal layers 24 and 44 by the voltage controller 52, the light is separated in the X-axis direction and the Y-axis direction to become four points of light, and the separation distance in these directions is about 18. 5 μm. Further, when a rectangular AC wave of about 10 V is applied to the liquid crystal layers 24 and 44, the light is separated in the X-axis direction and the Y-axis direction to become four points of light, and the separation distance in these directions is about 5.5 μm. Become. By placing this optical low-pass filter in front of the image sensor of a digital camera, especially a digital single-lens reflex camera, it captures moving images when voltage is applied and images that reduce moiré and false colors in still images when voltage is not applied. can do.

(Example 3)
In this example, an optical low-pass filter 60 according to the third embodiment will be described. The first optical low-pass filter 10 is the same as the optical low-pass filter 10 of the first embodiment. Further, the same polarization conversion element 51 as that of the second embodiment is used. The second optical low-pass filter 62 uses a crystal having a thickness of about 0.94 mm and an extraordinary refractive index axis inclined by 45 ° with respect to the thickness direction.

Next, the first optical low-pass filter 10, the polarization conversion element 51, and the second optical low-pass filter 62 are arranged in this order with the thickness direction aligned in the Z-axis direction. The second optical low-pass filter 62 is arranged so that the extraordinary light refractive index axis is inclined by 45 ° in the + X-axis direction, and the polarization conversion element 51 has an optical axis in the X-axis direction (or Y-axis) on the XY plane. It is arranged so as to have an angle of 45 ° with respect to (direction).

Then, randomly polarized light is incident in the visible light region along the Z-axis direction from the first optical low-pass filter 10 side. When no voltage is applied to the liquid crystal layer 24 by the voltage control unit, the light is separated into the X-axis direction and the Y-axis direction to become four points of light, the separation distance in the X-axis direction is about 5.5 μm, and the separation in the Y-axis direction. The distance is about 18.5 μm. Further, when a rectangular AC wave of about 10 V is applied to the liquid crystal layer 24, the light is separated in the X-axis direction and the Y-axis direction to become four points of light, and the separation distance in these directions is about 5.5 μm. By placing this optical low-pass filter in front of the image sensor of a digital camera, especially a digital single-lens reflex camera, it captures moving images when voltage is applied and images that reduce moiré and false colors in still images when voltage is not applied. can do.

Example 4
In this example, an optical low-pass filter 70 according to the fourth embodiment will be described. The liquid crystal element corresponding to the polarization controller 20 is the same as that in the first embodiment. As the first separation element 71 and the second separation element 72, a crystal whose extraordinary refractive index axis is inclined by 45 ° with respect to the thickness direction is used. Both the quartz crystal that becomes the first separation element 71 and the quartz crystal that becomes the second separation element 72 have a thickness of about 0.46 mm. The first separation element 71 is arranged on the transparent substrate 21a side so that the extraordinary refractive index axis is inclined by 45 ° in the + Y-axis direction on the YZ plane with the thickness as the Z-axis direction. The second separation element 72 is arranged on the transparent substrate 21b side so that the extraordinary refractive index axis is inclined by 45 ° in the −Y-axis direction on the YZ plane, whereby the optical low-pass filter 70 is obtained. Quartz has an ordinary light refractive index of 1.546 and an extraordinary light refractive index of 1.555 for light having a wavelength of 546 nm. At this time, the separation distance _{L 2} in the separation distance _{L 1} and the second separation element 72 in the first separation element 71 is approximately 2.7 .mu.m.

Then, randomly polarized light is incident in the visible light region along the Z-axis direction from the first separation element 71 side of the optical low-pass filter 70. When the voltage controller 13 does not apply a voltage to the liquid crystal layer 24, the first linearly polarized light and the second linearly polarized light that are orthogonal to each other are separated in the Y-axis direction, and the separation distance is about 5.4 μm. It becomes. When a rectangular AC wave of about 10 V is applied to the liquid crystal layer 24, the separation distance in the Y-axis direction between the first linearly polarized light and the second linearly polarized light becomes about 0 μm. By placing this optical low-pass filter in front of the image sensor of the digital camera, for example, when shooting an image without moire or false color, a voltage is applied and when shooting an image with moire or false color. By not applying a voltage, it is possible to take an image in which moire and false colors are reduced.

(Example 5)
In this example, an optical low-pass filter 80 according to the fifth embodiment will be described. The liquid crystal elements corresponding to the first polarization control unit 91 and the second polarization control unit 92 are the same as the liquid crystal elements of the polarization control unit 20 of the first embodiment. As the first separation element 81, the second separation element 82, and the third separation element 83, a crystal whose extraordinary refractive index axis is inclined by 45 ° with respect to the thickness direction is used. The quartz crystal serving as the first separation element 81 is about 1.58 mm thick, the quartz crystal serving as the second separation element 82 is about 1.11 mm thick, and the quartz crystal serving as the third separation element 83 is thick. The thickness is about 0.47 mm. The first separation element 81, the second separation element 82, and the third separation element 83 all have an extraordinary refractive index axis of 45 in the + Y-axis direction on the YZ plane with the thickness as the Z-axis direction. The optical low-pass filter 80 is obtained by arranging it so as to be inclined. Quartz has an ordinary light refractive index of 1.546 and an extraordinary light refractive index of 1.555 for light having a wavelength of 546 nm. At this time, the separation distance L _A in the first separation element 81 is about 9.25 μm, the separation distance L _B in the second separation element 82 is about 6.50 μm, and in the third separation element 84 separation distance _{L C} is about 2.75.

Then, randomly polarized light is incident in the visible light region along the Z-axis direction from the first separation element 81 side of the optical low-pass filter 80. When a rectangular AC wave of about 10 V is applied to the liquid crystal layer of the first polarization control unit 91 and the liquid crystal layer of the second polarization control unit 92 by the voltage control unit 93, the first linearly polarized light and the second orthogonally crossing each other. Are separated in the Y-axis direction, and the separation distance is about 18.5 μm. When the voltage controller 93 does not apply a voltage to the liquid crystal layer of the first polarization controller 91 and the liquid crystal layer of the second polarization controller 92, the first linearly polarized light and the second linearly polarized light are applied. Are separated in the Y-axis direction, and the separation distance is about 5.5 μm. When the voltage controller 93 does not apply a voltage to the liquid crystal layer of the first polarization controller 91 and a rectangular AC wave of about 10 V is applied to the liquid crystal layer of the second polarization controller 92, the first linearly polarized light is applied. The separation distance in the Y-axis direction between this light and the second linearly polarized light is about 0 μm. And by arranging this optical low-pass filter in front of the image sensor of the digital camera, for example, when shooting a still image without moire or false color, when shooting a still image with moire or false color, and When shooting moving images with moiré or false colors, you can switch to and shoot images.

Although this application has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on Feb. 26, 2010 (Japanese Patent Application No. 2010-040555) and a Japanese patent application filed on June 2, 2010 (Japanese Patent Application No. 2010-12639). The contents are incorporated herein by reference.

As described above, the optical low-pass filter according to the present invention can accurately switch the separation distance between two values or three values including zero, has no mechanical movable part, and can be downsized. Digital cameras and digital single-lens reflex cameras using this optical low-pass filter can shoot both still images and moving images, and can appropriately reduce the moire phenomenon according to these shooting modes, as well as mechanically movable parts. And miniaturization can be realized with high accuracy.

10, 15, 50, 60, 70, 80, 120, 130 (First) optical low-

pass filter

10a, 10b Position of light on the exit surface of the first optical low-pass filter 10 (when voltage is applied)
10c, 10d Position of light on the exit surface of the first optical low-pass filter 10 (when no voltage is applied)
11, 71, 81

First separation element

11a, 12a, 31a, 32a Abnormal light

refractive index axis

12, 72, 82

Second separation element

13, 52, 93, 115

Voltage control unit

20, 25, 91 (

first Polarization controllers

21a, 21b, 41a, 41b

Transparent substrates

22a, 22b, 42a, 42b

Transparent electrodes

23a, 23b, 43a, 43b Alignment film 24 (first) liquid crystal layers 30, 62, 100 Second optical low-

pass Filters

30a, 30b, 30c, 30d, 130a, 130b, 130c, 130d The position of light on the exit surface of the second optical low-pass filter 30 (when voltage is applied)
30e, 30f, 30g, 30h, 130e, 130f, 130g, 130h The position of light on the exit surface of the second optical low-pass filter 30 (when no voltage is applied)
31, 83 Third separation element 32 Fourth separation element 40, 92 (Second) polarization controller 44 (Second) liquid crystal layer 51

Polarization conversion elements

53a, 63a X exiting the first optical low-pass filter

Optical paths

53b, 54b, 63b, 64b of linearly polarized light in the axial direction

Optical paths

54a, 64a of light exiting from the polarization controller The

optical paths

62a, 62b of linearly polarized light in the Y-axis direction exiting from the first optical low-

pass filter

62c, 62d The position of the light on the exit surface of the second optical low-pass filter 62 (when voltage is applied)
62e, 62f, 62g, 62h The position of light on the exit surface of the second optical low-pass filter 62 (when no voltage is applied)
104 4th separation element 105 5th separation element 106 6th separation element 113 3rd polarization control part 114 4th polarization control part

Claims

A first separation element;
A polarization controller;
A second separation element;
A voltage controller that controls a voltage applied to the polarization controller;
The first separation element has a separation distance L 1 (>) between incident light and first linearly polarized light and second linearly polarized light orthogonal to the first linearly polarized light. 0) apart,
The polarization controller does not change a polarization state of the incident first linearly polarized light and the second linearly polarized light according to an applied voltage of the voltage controller, or
Modulating the incident linearly polarized light into the second linearly polarized light and modulating the incident linearly polarized light into the first linearly polarized light;
The second separation element includes the separation distance L 1 of the incident light by the separation distance L 2 (> 0) between the first linearly polarized light and the second linearly polarized light. Optical low-pass filter separated in the direction parallel to the separation direction.
Wherein the ratio of the separation distance L 1 and the separation distance L 2 is in the range 1.3 to 3,
A separation distance between the first linearly polarized light and the second linearly polarized light, which is emitted from the second separation element by the voltage applied by the voltage control unit, corresponds to L 1 + L 2. M and L S corresponding to | L 1 −L 2 |
2. The optical low-pass filter according to claim 1, wherein L M > L S , 10 μm ≦ L M ≦ 32 μm, and 2 μm ≦ L S ≦ 10 μm.
The separation distance L 1 and the separation distance L 2 and the optical low pass filter according to claim 1 are equal.
The optical low-pass filter according to any one of claims 1 to 3, wherein the polarization controller comprises a liquid crystal element having a liquid crystal layer.
The first separation element has a thickness d 1 , an angle formed between the thickness direction and the extraordinary refractive index axis direction is θ 1 , and a birefringent material having an ordinary refractive index no 1 and an extraordinary refractive index ne 1 . Consists of
The separation distance L 1 is given by the following equation (1):

The second separation element has a thickness d 2 , an angle formed by the thickness direction and the extraordinary refractive index axis direction is θ 2 , and has a normal refractive index no 2 and an extraordinary refractive index ne 2 . Consists of
The separation distance L 2 is given by the following equation (2):

The optical low-pass filter according to any one of claims 1 to 4.
In the liquid crystal element, when no voltage is applied, the liquid crystal molecules of the liquid crystal layer are aligned in a direction substantially parallel to the plane of the liquid crystal layer and the major axis direction of the liquid crystal molecules on the opposite surface is substantially orthogonal, Twist about 90 ° around the thickness direction,
When the direction in which said theta 1 in the thickness direction of the first separation element as a reference and positive, the second separation element, according to claim wherein the theta 2 symbols are arranged in a direction in which a negative 5 The optical low-pass filter described in 1.
The optical low-pass filter according to any one of claims 4 to 6, wherein the liquid crystal layer is sandwiched and integrated by the first separation element and / or the second separation element.
The optical low-pass filter is
A first optical low-pass filter having the first separation element, a first polarization control unit which is the polarization control unit, and the second separation element;
A polarization conversion element;
A second optical low pass filter;
The polarization conversion element converts the incident first linearly polarized light and the second linearly polarized light into the first linearly polarized light component and the second linearly polarized light component, respectively. To a light with a ratio of 3: 7 to 7: 3,
The second optical low-pass filter separates the light of the first linear polarized light, and light of the second linearly polarized light, in a direction intersecting the direction of the separation distance L 1 and the separation distance L 2 The optical low-pass filter according to any one of claims 1 to 7.
The optical low-pass filter is
A first optical low-pass filter having the first separation element, a first polarization control unit that is the polarization control unit, and the second separation element;
A second optical low pass filter;
The second optical low pass filter, said first linear polarized light and the light of the second linearly polarized light, intersect at the separation distance L 1 and the not orthogonal to the direction of the separation distance L 2 angle The optical low-pass filter according to any one of claims 1 to 7, wherein the optical low-pass filter is separated in a direction.
The second optical low-pass filter is
A third separation element;
A second polarization controller;
A fourth separation element;
The third splitting element, the a first linear polarized light, the second and the linearly polarized light, the separation distance L 1 and the separation distance separating in a direction intersecting the direction of L 2 distance L 3 (> 0) apart,
The second polarization controller does not change a polarization state of the incident first linearly polarized light and the second linearly polarized light according to an applied voltage of the voltage controller, or
Modulating the incident linearly polarized light into the second linearly polarized light and modulating the incident linearly polarized light into the first linearly polarized light;
The fourth separation element includes the separation distance L 3 of the incident light by the separation distance L 4 (> 0) between the first linearly polarized light and the second linearly polarized light. The optical low-pass filter according to claim 8 or 9, wherein the optical low-pass filter is separated in a direction parallel to the separation direction.
Wherein the ratio of the separation distance L 3 between the separation distance L 4 is in the range 1.3 to 3,
The separation distance between the first linearly polarized light and the second linearly polarized light that is emitted from the fourth separation element by the voltage applied by the voltage control unit is L 3 corresponding to L 3 + L 4. When MX and L SX corresponding to | L 3 −L 4 | are given,
The optical low-pass filter according to claim 10, wherein L MX > L SX , 10 μm ≦ L MX ≦ 32 μm, and 2 μm ≦ L SX ≦ 10 μm.
Optical low-pass filter according to the separation distance L 3 between the separation distance L 4 are equal claim 10.
The optical low-pass filter according to any one of claims 10 to 12, wherein the second polarization controller comprises a liquid crystal element having a liquid crystal layer.
The third separation element has a thickness d 3 , an angle between the thickness direction and the extraordinary refractive index axis direction becomes θ 3 , and has a normal refractive index no 3 and an extraordinary refractive index ne 3 . Consists of
The separation distance L 3 is given by the following equation (3):

It said fourth separation element, the thickness d 4, the thickness direction and the extraordinary light refractive index axis direction and the angle is theta 4, and the ordinary refractive index n o4, birefringent material having an extraordinary refractive index n e4 Consists of
The separation distance L 4 is given by the following equation (4):

The optical low-pass filter according to any one of claims 10 to 13.
In the liquid crystal element of the second polarization controller, the liquid crystal molecules of the liquid crystal layer of the second polarization controller are substantially parallel to the plane of the liquid crystal layer of the second polarization controller when no voltage is applied. And, the major axis direction of the liquid crystal molecules on the opposite surface is aligned in a direction substantially orthogonal to each other, twisted about 90 ° about the thickness direction,
The fourth separation element is arranged in a direction in which the sign of the θ 4 is negative when the direction that becomes the θ 3 is positive with respect to the thickness direction of the third separation element. The optical low-pass filter described in 1.
The optical low-pass filter according to any one of claims 13 to 15, wherein the liquid crystal layer of the second polarization control unit is sandwiched and integrated by the third separation element and / or the fourth separation element. .
The second optical low-pass filter includes a third separation element,
The third splitting element, the a first linear polarized light, wherein the second linear polarized light, wherein the separation distance L 1 and the separation distance direction separation distance intersecting the separation direction of L 2 10. The optical low-pass filter according to claim 8, wherein the optical low-pass filter is separated by L FX .
A first separation element;
A second separation element;
A second polarization controller;
A third separation element;
A voltage controller that controls a voltage applied to the first polarization controller and the second polarization controller;
The first separation element has a separation distance L A (>) between incident light and first linearly polarized light and second linearly polarized light orthogonal to the first linearly polarized light. 0) apart,
The first polarization control unit and the second polarization control unit change a polarization state of incident first linearly polarized light and second linearly polarized light according to an applied voltage of the voltage control unit. Or
Modulating the incident linearly polarized light into the second linearly polarized light and modulating the incident linearly polarized light into the first linearly polarized light;
The second separation element includes the separation distance L 1 of the incident light by the separation distance L B (> 0) between the first linearly polarized light and the second linearly polarized light. Separated in a direction parallel to the separation direction of
The third separation element has a separation distance L 1 that is equal to a separation distance L C (> 0) between the first linearly polarized light and the second linearly polarized light among the incident light. (L A ≠ L B ≠ L C ) separated in a direction parallel to the separation direction of
Wherein the separation distance L A and the separation distance L B separation distance of L C, one is equal to the value of the remaining two sums, the separation distance of the light emitted the third separation element, An optical low-pass filter that is controlled by the voltage control unit to at least three values including zero.
The optical low-pass filter according to claim 18, wherein the first polarization control unit and the second polarization control unit are formed of a liquid crystal element having a liquid crystal layer.
The first separation element has a thickness d A , an angle formed by the thickness direction and the extraordinary refractive index axis direction is θ A , and a birefringent material having an ordinary refractive index noA and an extraordinary refractive index neA Consists of
The separation distance L A is given by equation (5) below,

The second separation element, the thickness d B, the thickness direction and the extraordinary light refractive index axis direction and the angle is theta B, and the ordinary refractive index n oB, birefringent material having an extraordinary refractive index n eB Consists of
The separation distance L B is given by the following equation (6):

The third separation element has a thickness d C , an angle between the thickness direction and the extraordinary refractive index axis direction becomes θ C , and a birefringent material having an ordinary refractive index noC and an extraordinary refractive index neC Consists of
The separation distance L C is given by (7) below,

The optical low-pass filter according to claim 18 or claim 19.
A liquid crystal layer of the first polarization control unit is integrated with at least one of the first separation element and the second separation element;
21. The optical low-pass filter according to claim 19, wherein a liquid crystal layer of the second polarization control unit is integrated with at least one of the second separation element and the third separation element.
A digital camera comprising the optical low-pass filter according to any one of claims 1 to 21 and an image sensor.
A low-pass filter according to any one of claims 2, 4 to 17, and an image sensor, wherein the separation distance is L S when capturing a still image, and the separation distance is set when capturing a moving image. digital camera to L M.