JP3251798B2 - Deflection device and image shift type imaging device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deflecting device used for a TV camera or an image scanner and an image shift type image pickup device using the same, and more particularly, to a deflecting device having a structure in which an electro-optic crystal is sandwiched between transparent electrodes. The present invention relates to a deflecting device including an element and a driving unit thereof, and an image shift type imaging apparatus that uses the deflecting device to relatively shift an image formed on an image sensor with respect to the image sensor.

[0002]

2. Description of the Related Art In the world of video, high definition is typified by HDTV, and image sensors such as CCDs are required to be smaller and have higher resolution. However, high-definition CCD image sensors require advanced semiconductor microfabrication technology, which increases costs due to an increase in capital investment and a decrease in yield. In addition, the density of the CCD image pickup device becomes extremely small, and the volume of one cell becomes extremely small.

For this reason, techniques for improving the resolution while maintaining the degree of integration of the image sensor have been studied. The most effective method is to increase the resolution by modulating the relative position between the image sensor and the subject image. First, image information when the relative position is not shifted is stored in a memory, and then the image information is fetched by shifting the subject image on the image sensor by half the image pitch. Image information having twice the resolution can be obtained from both image information. A deflection device is used to shift the imaging position.

[0004] Conventional deflection devices include mechanical systems and non-mechanical systems. The mechanical system applies mechanical vibration to the optical system using a voltage element or the like, and includes a system that changes an optical path in the optical system, a system that moves an image sensor such as a CCD, and a system that moves a subject. As shown in FIG. 12, a device that changes an optical path in an optical system inserts a transparent glass plate 51 into an optical system including a lens 50 and an image pickup device 52, and forms an image by tilting the glass plate 51. Displacement method (see JP-A-63-284980) A prism having a structure in which a transparent liquid having a refractive index is filled between two transparent flat plates, and the periphery of the prism is configured as a bellows to change the apex angle. A method of disposing in the optical path, a method of shifting the reflection direction by oscillating a mirror and shifting the image
No. 93678). As a method for moving the image pickup device itself, there is a method of moving the image pickup device 52 by placing the image pickup device 52 on a piezoelectric actuator 53 as shown in FIG. 13 (see Japanese Patent Publication No. 2-45874). The method of moving the subject is a method of vibrating the original with a diaphragm (Japanese Patent Laid-Open No. 3-1732).
No. 77 gazette) has been proposed.

[0005] The non-mechanical method does not apply a mechanical force, and two methods are roughly considered. One uses the difference between the propagation directions of ordinary light and extraordinary light in a birefringent plate, as shown in FIG. The incident light is converted into parallel light by a lens 50, the polarization plane of the light is aligned in one direction by a polarizing plate 53, then passes through an element 54 whose polarization plane is rotatable, and further forms an image on an imaging element 52 through a birefringent plate 55. The optical path of the birefringent plate 55 differs depending on the ordinary light and the extraordinary light. That is, when the polarization plane is rotated by 90 degrees, the optical path changes, and the image can be displaced. In order to rotate the polarization plane, an element capable of electrically changing the anisotropy of the refractive index is used, and a case using a liquid crystal and a case using an electro-optic effect have been proposed. Since the mechanical system can continuously displace the image, n
It is possible to increase the definition by n times by displacing it by a factor of 1. However, the non-mechanical method using the rotation of the polarization plane uses ordinary light to make use of the optical path difference of extraordinary light. It is possible (see JP-A-62-157482). Another method uses an element 56 in which an electro-optic crystal is attached in a wedge shape with crystal axes opposite to each other as shown in FIG.
A continuous change in the refractive index is induced in the vertical direction by applying an electric field perpendicular to the optical axis to change the propagation direction of light (Japanese Patent Application Laid-Open Nos. 62-15977 and 62-159581). Gazette).

[0006]

The mechanical system is disadvantageous in that mechanical vibration applied to an optical system, a mechanical system, and an electronic circuit system adversely affects long-term reliability or generates vibration noise. Have been. In addition, since the piezoelectric element has hysteresis, it is difficult to determine the timing of extracting the image signal.

In the non-mechanical system, since the displacement of the rotation of the polarization plane using an electro-optic crystal or liquid crystal is constant, it is impossible to increase the resolution twice or more in one direction. The disadvantage is that the cost is high because a plate is required. The method using a device in which the crystal axes are bonded in opposite directions to each other in a wedge shape without using a birefringent plate has a problem that a high voltage is required because the voltage application direction is perpendicular to the optical axis. Was.

It is an object of the present invention to provide an inexpensive deflection device which deflects light without using mechanical vibration, is driven at low voltage, and is inexpensive. It is another object of the present invention to provide an image shift type image pickup apparatus that can obtain a high-definition image without increasing the resolution of an image pickup element by using the deflection device.

[0009]

In order to achieve the above object, the present invention provides an electro-optic crystal in which the opposing surfaces of both sides are sandwiched by a transparent electrode, and the electro-optic crystal is laminated with an odd-numbered electro-optic crystal.
The crystal axes of even-numbered electro-optic crystals are mirror images of each other
Deflecting element with adjacent structure and adjacent odd-numbered transparent element
Apply a voltage between the electrode and the even-numbered transparent electrode, respectively.
Driving means for applying an opposite electric field to the adjacent electro-optic crystal, and arranging the deflecting element so that the direction of the optical axis and the electric field are parallel to each other. A deflecting device characterized in that the refractive index ellipsoid is rotated to change the traveling direction of the light to deflect the light.

The present invention further comprises the deflecting device, an image pickup device, and control means for controlling the operation of the driving means of the deflecting device in accordance with the timing of image pickup. An image shift type imaging apparatus characterized in that an image is formed on the image sensor when no voltage is applied to the electrode and when an electrode is applied, and the image is relatively shifted with respect to the image sensor.

[0011]

[0012]

[0013]

In the deflecting device according to the first aspect, an electric field parallel to the direction of the optical axis is applied to the electro-optic crystal of the deflecting element by the driving means to rotate the refractive index ellipsoid. This changes the light propagation direction and shifts the imaging position in proportion to the applied voltage. In addition, the voltage can be reduced as compared with the conventional method in which a voltage is applied perpendicular to the optical axis.

The deflecting device according to claim 3, wherein the deflecting element has a structure in which the electro-optic crystal is stacked so as to be sandwiched between transparent electrodes.
The crystal axes of the odd-numbered electro-optic crystal and the even-numbered electro-optic crystal are arranged in a mirror image relationship with each other, and a voltage is applied between adjacent odd-numbered transparent electrodes and even-numbered transparent electrodes, respectively. The deflection element is arranged so as to apply an electric field parallel to the direction to the electro-optic crystal. Therefore, in each electro-optic crystal, the index ellipsoid rotates in the same direction. That is, the light incident on each of the electro-optic crystals is displaced in the same direction, and a large amount of displacement is obtained as compared with the case where one electro-optic crystal is used.
Therefore, in order to obtain the same displacement, a low voltage application is required.

In the image shift type image pickup apparatus according to claim 2 or 4, the control means controls the image shift type image pickup apparatus.
The image is taken when a voltage is not applied to the deflecting device, and the image is taken when a voltage is applied to the deflecting device. The image forming position of the deflection device is displaced depending on whether or not a voltage is applied. Therefore, the relative position between the image formed on the image sensor and the image sensor can be displaced, and a higher resolution can be achieved without increasing the resolution of the image sensor itself. In addition, the imaging position can be freely displaced by the applied voltage, and the applied voltage can be reduced.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments with reference to the drawings. FIG. 1 is a schematic view showing one embodiment of the deflection device according to the present invention. This deflecting device comprises a deflecting element 1 comprising a parallel-plate electro-optic crystal C ₁ and transparent electrodes T ₁ and T ₂ formed sandwiching the electro-optic crystal C ₁ , a transparent electrode T ₁ having a high potential and a transparent electrode T ₂ having a low potential. A direct-current drive voltage 2 for applying a voltage to a potential. Where the electro-optic crystal C
₁ is, for example, LiNbO ₃ (hereinafter LN), BaTiO
₃ (hereinafter referred to as BaT), KTa _0.35 Nb _0.65 O ₃ (hereinafter referred to as KT
N) or a single crystal of KD ₂ PO ₄ (hereinafter DKDP: D at the beginning means deuteration). And LN, Ba
In the case of a single crystal of T or KTN, for example, a rectangular parallelepiped having a crystal axis of 1 mm in the a-axis direction, 10 mm in the b-axis direction, and 10 mm in the c-axis direction is cut out.
A TO film is formed by a sputtering method. In the case of a single crystal of DKDP, for example, 1 mm in the c-axis direction, 10 mm in the a-axis direction, b
A rectangular parallelepiped of 10 mm in the axial direction is cut out, and an ITO film is formed as a transparent electrode on both cut surfaces perpendicular to the c-axis by a sputtering method.

The principle of operation in which the image forming position is displaced by the deflecting device will be described below. The electro-optic effect is a kind of second-order nonlinear optical effect. When a voltage is applied to a crystal exhibiting the electro-optic effect, a change occurs in the refractive index of the crystal and its anisotropy. As described in the section of the prior art, a method of applying an electric field perpendicular to the traveling direction of light in polarization by the electro-optic effect has been studied. However, when used in an imaging device, the electro-optic crystal needs to have an area larger than the light receiving surface of the CCD, and a high voltage is required to apply an electric field perpendicular to this surface. On the other hand, the present invention applies an electric field in parallel to the optical axis direction to displace the optical path. By changing the refractive index ellipsoid of the crystal by applying an electric field, in particular, by inducing the rotation of the refractive index ellipsoid,
The propagation direction of the extraordinary light or the ordinary light is changed, and the image formation position on the image sensor is shifted in proportion to the applied voltage.

FIG. 2 is an explanatory diagram showing the rotation of the refractive index ellipsoid. (a) is when no voltage is applied to the crystal,
(b) is a case where a voltage is applied to the crystal. The polarization plane dependence on the phase velocity of light traveling through the crystal is expressed as an index ellipsoid. First, consider a case where the orthogonal coordinate axes are x, y, and z, and no voltage is applied. If the x direction is the optical axis direction,
Refractive index ellipsoid can be expressed as ^{_{η xx · x 2 + η yy}} · y 2 + η zz · z 2 + η yz · yz + η xz · xz + η xy · xy = 1 (1).

As shown in FIG. 2, the refractive index ellipsoid is cut on a plane perpendicular to the direction (x direction) of the wavefront vector k of light traveling in the crystal and passing through the origin. At this time, the directions of the major axis and the minor axis of the cut surface of the refractive index ellipsoid become the polarization plane, and the direction perpendicular to the tangent plane at the point where the major axis and the minor axis contact the refractive index ellipse becomes the electric field vector E of light. . The magnetic field vector H of the light is perpendicular to the electric field vector E and the wavefront vector k of the light, and the traveling direction of the light is a pointing B
(The cross product of the electric field vector and the magnetic field vector). The fourth, fifth, and sixth terms in equation (1) represent the inclination of the refractive index ellipsoid with respect to the main axis.

When an electric field E _k is applied in the direction of the wavefront vector k of light, the following equation is established. η _ii (E) = 1 / n _i ² + r _ik E _k (i, k = x, y, z) (2) η _ij (E) = r _ijk E _k (i ≠ j) (3) where n _i is the refractive index in the main axis direction. When the electric field is applied, the value of the expression (3) causes the index ellipsoid to rotate and tilt with respect to the main axis ((b) in FIG. 2).

For example, if η _xz (E) = r _xzx E _x ≠ 0, the application of an electric field in the x direction causes the index ellipsoid to rotate in the xz plane, and has a wavefront vector in the x direction and in the xz plane. In light having a polarization plane, the wavefront vector k 'is tilted in the xz plane, and the direction of the pointing belt S' is tilted. Accordingly, since the traveling direction of light can be changed by applying an electric field in parallel to the traveling direction of light, the electro-optic crystal can be made thinner and the voltage can be reduced.

The displacement of the image was measured using the deflection device shown in FIG. FIG. 3 shows an explanatory diagram of the displacement measuring system. A first lens 3 is arranged before the deflecting element 1, and a knife edge 4, a piezo drive device 5 for moving the knife edge 4 up and down, a second lens 6, and a photodetector 7 are arranged after the first lens 3. First
After passing through the deflecting element 1 by the lens 3, the parallel light beam is once converged at the focal point set at the tip of the knife edge 4. After being converged, the light that is diffused is converged on the photodetector 7 by the second lens 6. Depending on the voltage applied to the electro-optic crystal C ₁ ,
As described above, as the refractive index ellipsoid rotates and the traveling direction of light changes, the focal position of the first lens 3 shifts up and down. The knife edge 4 is moved up and down by a piezo driving device 5, and the light amount is detected by a photodetector 7.
Detects the displacement of the focal point.

The above-described electro-optic crystal LN, BaT, KT
FIGS. 4 to 7 show the relationship between the applied voltage and the displacement of the focal position measured by the above-mentioned knife edge method by passing a laser through a deflection device composed of N and DKDP. It was confirmed that the displacement amount of each crystal increased almost in proportion to the applied voltage. L
In the case of N, a displacement of about 5.4 μm by applying a voltage of 20 kV using a HeNe laser (633 nm) (see FIG. 4), and in the case of BaT, a displacement of about 6.4 μm at 400 V using an argon ion laser (514 nm) (See Fig. 5), HeNe for KTN
7. Applying a voltage of 100 V using a laser (633 nm) to about 8.
A displacement of 3 μm was obtained (see FIG. 6). DKDP is about 6.5 at 10 kV using an argon ion laser (514 nm).
A displacement of μm was obtained (see FIG. 7). In this embodiment, the same effect can be obtained even if the crystal axes a and b are exchanged.

FIG. 8 is a schematic diagram showing another embodiment of the deflecting device. This deflecting device comprises a deflecting element 1 having transparent electrodes T ₁ , T ₂ , T ₃ sandwiching electro-optic crystals C ₁ , C _2.
1 and a drive voltage 12 for applying a voltage to the transparent electrodes T ₁ , T ₂ , and T ₃ . Here, the electro-optic crystals C ₁ and C ₂ are, for example, a single crystal of KTN having an a-axis direction of 1 mm, b
It is cut out into a rectangular parallelepiped of 10 mm in the axial direction and 10 mm in the c-axis direction. Then an ITO film is formed by sputtering as a transparent electrode on both sides was cut perpendicular to the a-axis in the electro-optical crystal C _1. The electro-optic crystals C ₁ and C ₂ are overlapped so that the a-axes are opposite to each other and sandwich the transparent electrode T ₂ , and are bonded by hot pressing. Forming a transparent electrode T ₃ on opposite surface to the transparent electrode T ₂ of the electro-optical crystal C ₂ and the deflection element. A voltage is applied so that the transparent electrodes T ₁ and T ₃ have a high potential and the transparent electrode T ₂ has a low potential.

The electro-optic crystals C ₁ and C ₂ are arranged such that the a-axes are arranged in opposite directions and an electric field is applied in opposite directions. Therefore, in the electro-optic crystals C ₁ and C ₂ , the index ellipsoid rotates in the same direction. That is, the light incident parallel to the a-axis is displaced by the same distance in the same direction, so that the displacement amount is twice as large as when only one electro-optic crystal is used. Therefore, in order to obtain the same displacement, it is sufficient to apply a voltage of 1/2.

FIG. 9 shows the relationship between the applied voltage and the amount of displacement of the focal position measured by the knife-edge method measuring system shown in FIG. When a voltage of 50 V is applied by using a HeNe laser (633 nm), a displacement of about 8.3 μm is obtained.
/ 2, and the voltage can be reduced.

Although the case of two layers has been described above, the present invention is not limited to this, and three or more layers can be used. FIG. 10 shows a schematic diagram of this embodiment. In this deflection device, transparent electrodes T _{1 to} T _{n + 1} are formed so as to sandwich each of the electro-optic crystals C _{1 to} C _n , and these are laminated and integrated. Where the electro-optic crystal C
₁ -C _n is the same material and shape as FIG. 8, the transparent electrodes T ₁
To T _{n + 1} are similar materials. The crystal axes of the odd-numbered electro-optic crystal and the even-numbered electro-optic crystal are arranged in a mirror image relationship with each other. That is, they are arranged such that the a-axes of adjacent electro-optical crystals are opposite to each other. A voltage is applied from the drive voltage 22 so that the odd-numbered transparent electrodes have a high potential and the even-numbered transparent electrodes have a low potential.

Each adjacent electro-optic crystal is arranged so that the a-axis is opposite to each other, and the electric field is applied in the opposite direction. Therefore, the electro-optic crystal C ₁
At ~ C _n , the index ellipsoid will rotate in the same direction. That is, the light incident parallel to the a-axis is displaced by the same distance in the same direction, and a displacement amount n times as large as that obtained when only one electro-optic crystal is provided is obtained. Therefore, in order to obtain the same displacement, it is only necessary to apply 1 / n of the voltage.

FIG. 11 shows an embodiment of an image shift type image pickup apparatus using the deflection device shown in FIG. CCD image sensor 33
A 1/4 inch pixel having 410,000 pixels and a pixel pitch in the horizontal direction of 4.8 μm is used. CCD image sensor 33
A deflecting device is installed just before. This deflecting device uses KTN
A deflection element 31 comprising a crystal C ₁ and transparent electrodes T ₁ and T ₂ ;
And a drive unit 32 for applying a voltage to the transparent electrode.
The polarizer 34 is placed on the incident light side of the deflecting element 31 and transmits light having a polarization plane parallel to the c-axis. Further, a lens 35 is arranged on the incident light side of the polarizer to convert the light into parallel light. The timing control unit 36 outputs detection signals of the image sensor 33 when no voltage is applied to the drive unit 32 and when the voltage is applied to the drive unit 32 via an image processing unit 39 via a first image memory 37 and a second image memory 38.
Output to It is output as a video signal.

The CCD passes through the deflecting element without applying a voltage.
The image is captured by the image sensor 33 and the image information is stored in the first image memory 3.
7 is accumulated. Next, a voltage of 28 V is applied to the deflecting element 31, the image forming position of the image is shifted by 2.4 μm in the horizontal direction, the image is picked up by the CCD image pickup element 33, and the image information is stored in the second image memory 38. By alternately cylinder-outputting the horizontal direction data of the first and second image memories 37 and 38 by the image processing unit 39, a high-resolution video output twice as high in the horizontal direction can be obtained.

The resolution in the horizontal direction is important for increasing the resolution for a standard television. Even if the resolution is increased in the horizontal direction, the effect is sufficient, but the resolution can be increased in the vertical direction at the same time. I have never done it. In order to increase the resolution in both the horizontal and vertical directions using the present deflection element, after the horizontal deflection element, a vertical element whose crystal axis is rotated by 90 ° with respect to the optical axis as the rotation axis with respect to the horizontal deflection element is used. Deploy. In this case, a vertical displacement requires application of a voltage of about 1 kV. However, a half-wave plate is inserted between the horizontal deflection element and the vertical deflection element, and the deflection surface is set at 90 °.
By rotating, it can be displaced by the same voltage application in the horizontal direction. In this embodiment, the vertical pixel pitch is 5.6 μm, and 2.8 μm by applying a voltage of 32 V.
Of vertical shift was obtained. Thereby, the horizontal direction 2
The resolution is twice as high and twice as high in the vertical direction.

The present invention is not limited to the above configuration. The deflecting device of the image shift type image pickup device has a single-layer electro-optic crystal, but may have a multi-layer type as shown in FIGS. The material of the electro-optic crystal is
Not limited to KTN, LN, BaT, DKDP, etc. may be used.

[0033]

The deflecting device according to the present invention is characterized in that the electro-optic crystal is sandwiched between transparent electrodes, a voltage is applied between the transparent electrodes, and an electric field parallel to the optical axis direction is applied to the electro-optic crystal. Is arranged, by rotating the refractive index ellipsoid, the amount of displacement of the image can be continuously varied according to the applied voltage, and the applied voltage is also compared to the conventional method in which the applied voltage is applied perpendicular to the optical axis. It can be done with low voltage. In addition, since mechanical vibration is not used, there is an advantage that the reliability is high, no vibration noise is generated, and the structure is simple, so that it is inexpensive. Further, the wavelength dependency can be reduced as compared with the conventional apparatus using the rotation of the polarization plane.

Further, in the deflecting device of the present invention , the deflecting element is formed by laminating an electro-optic crystal between transparent electrodes, and arranging the crystal axes of the odd-numbered electro-optic crystal and the even-numbered electro-optic crystal in a mirror image relationship with each other. By applying a voltage between the adjacent odd-numbered transparent electrodes and the even-numbered transparent electrodes and applying an opposite electric field to the adjacent electro-optical crystals, the structure in each electro-optical crystal is in the same direction. Since the imaging is displaced, the voltage can be reduced as compared with one electro-optic crystal.

The image shift type image pickup apparatus of the present invention, because provided a control means for controlling the operation of the polarization direction device according to the timing of the imaging, the imaging element and the imaging by the presence or absence of voltage applied to the transparent electrode A high-definition image can be obtained without relatively shifting the position and increasing the resolution of the image sensor.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of a deflection device according to the present invention.

FIGS. 2A and 2B are explanatory diagrams showing rotation of a refractive index ellipsoid of an electro-optic crystal.

FIG. 3 is an explanatory schematic diagram showing an imaging displacement amount measuring system.

FIG. 4 is a graph showing a relationship between an image forming displacement amount and an applied voltage of a deflecting device using LN as a deflecting element.

FIG. 5 is a graph showing a relationship between an image forming displacement amount and an applied voltage of a deflection device using a BAT as a deflection element.

FIG. 6 is a graph showing a relationship between an image forming displacement amount and an applied voltage of a deflecting device using KTN as a deflecting element.

FIG. 7 is a graph showing a relationship between an image forming displacement amount and an applied voltage of a deflecting device using DKDP as a deflecting element.

FIG. 8 is a schematic view showing another embodiment of the deflecting device according to the present invention.

FIG. 9 is a graph showing a relationship between an image forming displacement amount and an applied voltage of the deflection apparatus using KTN as a deflection element.

FIG. 10 is a schematic view showing still another embodiment of the deflecting device according to the present invention.

FIG. 11 is a schematic diagram showing an embodiment of an image shift type imaging apparatus according to the present invention.

FIG. 12 is a schematic view showing a conventional deflecting device using a method of tilting a glass plate.

FIG. 13 is a schematic diagram showing a conventional deflecting device based on a method in which an imaging element is moved by a piezoelectric actuator.

FIG. 14 is a schematic diagram showing a conventional deflection device using an electro-optic crystal and a birefringent plate.

FIG. 15 is a schematic view showing a conventional deflection device to which a wedge-shaped electro-optic crystal is bonded.

[Explanation of symbols]

First deflecting element 2 driving voltage C ₁ electrooptic crystal R _1, R _2, R ₃ transparent electrode

Continuation of the front page (56) References JP-A-62-289065 (JP, A) JP-A-62-194221 (JP, A) JP-A-1-1666021 (JP, A) JP-A-63-116832 (JP) JP-A-4-115786 (JP, A) JP-B-52-3310 (JP, B1) U.S. Pat. No. 4,432,901 (US, A) Research Report, Faculty of Engineering, Nippon Institute of Technology Vol. 20, No. 2, pp. 301-304 (1990) Yoshiharu Nakayama (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/03-1/295 H04N 5/225-5/335 INSPEC (DIALOG) JICST file (JOIS) WPI (DIALOG)

Claims (2)

(57) [Claims] 1. An electro-optic crystal according to claim 1, wherein the opposing surfaces of the opto-electric crystal are laminated with a transparent electrode therebetween.
The crystal axes of even-numbered electro-optic crystals are mirror images of each other
Between the odd-numbered transparent electrode and the even-numbered transparent electrode
And a driving unit for applying a voltage to each of the adjacent electro-optic crystals to apply a reverse electric field to the electro-optic crystal, and arranging the deflection element so that an optical axis direction is parallel to the electric field, and applying the electric field. A deflector for rotating a refractive index ellipsoid of the electro-optic crystal to change a traveling direction of light to deflect light. 2. The deflecting device according to claim 1, further comprising: an image sensor; and a control unit for controlling an operation of a driving unit of the deflecting device according to an imaging timing. An image is formed on the image sensor when no voltage is applied to the electrode and when a voltage is applied,
An image shift type image pickup apparatus, wherein the image formation is shifted relative to an image pickup device.