JP3795152B2 - Imaging device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an imaging apparatus having a polarization function, and more particularly to an imaging apparatus that can remove unnecessary polarized light and extract a desired optical image in real time.
[0002]
[Summary of Invention]
The present invention relates to an imaging apparatus having a polarization control function, and a polarization control unit capable of changing a polarization direction is disposed in front of an imaging unit, and the polarization control unit is provided on the basis of a video electric signal from the imaging unit. By controlling the drive, it is possible to instantaneously remove various incident polarization components and obtain a desired optical image free from unnecessary polarization.
[0003]
[Prior art]
In outdoor video shooting, strong reflected light (reflection) from a water surface or a glass plate becomes an obstacle, and an imaging apparatus having a polarization control function is required to remove the polarized reflected light. Conventionally, an image pickup apparatus having a polarization control function is known as shown in FIG.
[0004]
An imaging apparatus 100 shown in FIG. 5 includes a polarizing film 102 made of polyvinyl alcohol resin containing iodine molecules that absorb light and absorbing polarized light of incident light 101, and a polarizing film 102 made of a lens, a mirror, etc. An imaging optical system 103 that emits the absorbed incident light 101 as an optical image 104, and an imaging unit 105 that receives the optical image 104 from the imaging optical system 103, converts it into an electrical video signal 106, and outputs it. The polarizing film 102 is rotated, thereby removing an arbitrary polarization component contained in the incident light 101, and then an electric video signal is obtained via the imaging optical system 103 and the imaging unit 105.
[0005]
However, in this imaging apparatus 100, in order to change the polarization direction, the polarizing film 102 must be mechanically rotated, and since the operation speed is slow, in image shooting in which the incident light 102 changes at high speed, The polarized reflected light cannot be removed and cannot be applied.
[0006]
[Problems to be solved by the invention]
As described above, the conventional imaging apparatus 100 needs to mechanically rotate the polarizing film 102 and has a slow operation speed. Therefore, in the image shooting in which the incident light 102 changes at a high speed, the polarized reflected light is used. There is a problem that it cannot be removed.
[0007]
In addition, as an imaging device having a polarization control function, a “solid-state imaging device” described in Japanese Patent Application Laid-Open No. 63-175586 is known, but the “solid-state imaging device” described in this publication is In this configuration, the polarizing plate is simply provided on the surface of the solid-state imaging device, and the polarization direction of the device cannot be changed in various ways at high speed. Further, there are “an optical head of an imaging device” described in JP-A-3-135276 and “infrared imaging device” described in JP-A-6-51921. Therefore, it is impossible to cope with various polarized light at high speed.
[0008]
The present invention has been made in view of the above circumstances, and an object of the present invention is to remove unnecessary polarized light in real time by changing the polarization direction at high speed and variously, and to obtain a desired optical image. It is to provide an image pickup apparatus.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, in claim 1, an imaging unit that converts an optical image into an electric video signal, and a polarization control unit that is disposed in front of the imaging unit and changes a polarization direction of incident light, A drive unit that drives and controls the polarization control unit. The polarization control unit includes a polarization rotation unit including a plurality of twisted nematic liquid crystal cells that rotate the polarization plane of the incident light, and the polarization rotation unit. A polarization absorbing unit that absorbs polarized light in a certain direction from the light emitted from the unit and emits the polarized light to the imaging unit side, and the driving unit is a part or the whole of the electric video signal output from the imaging unit The reflected light is removed by controlling the voltage of the twisted nematic liquid crystal cell of the polarization rotation unit by setting a control voltage that minimizes the image level .
[0010]
According to the above configuration, since the polarization controller can be driven and controlled from the outside, it is possible to deal with various types of polarized light and to obtain an optical image from which unnecessary polarization components are removed. In addition, unnecessary polarized components such as reflected light can be removed automatically and at high speed, and a desired optical image can be obtained.
[0017]
The imaging device according to claim 1 , wherein the polarization absorption unit is a polarizing film or a guest-host liquid crystal cell in which a homogeneous alignment liquid crystal material including a dichroic dye is sandwiched between transparent electrodes. It is characterized by comprising.
[0018]
According to said structure, polarized light can be absorbed and selected with the polarizing film of a simple structure. When a guest host liquid crystal cell is used, the polarization intensity of the guest host liquid crystal cell can be controlled by controlling the voltage applied to the transparent electrode. In this case, when the polarization function becomes unnecessary, a voltage may be applied to the guest-host liquid crystal cell.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the overall configuration of an imaging apparatus according to the present invention. The imaging apparatus 1 includes a polarization control unit 3 that controls the polarization of incident light 2, an imaging optical system 4 that is configured by a lens, a mirror, and the like and that emits incident light that is polarization-controlled by the polarization control unit 3 as an optical image 5. The image pickup unit 6 that receives the optical image 5 from the image pickup optical system 4 and converts the light image 5 into an electric video signal 7 and outputs it, and the electric video signal 7 output from the image pickup unit 6 are input to control the polarization controller 3. And a voltage driver 8 that generates and outputs a voltage 9. In addition, as long as the arrangement position of the polarization control unit 2 is in front of the imaging unit 6, it may be incorporated in the imaging optical system 4 regardless of whether it is before or after the imaging optical system 4.
[0020]
In the above configuration, the polarization control unit 3 is controlled based on the electric video signal 7 output from the imaging unit 6, and thereby a desired optical image can be extracted. For example, when there is a strong reflection due to reflected light from a glass plate or water surface and it is difficult to shoot a video, the control voltage is set so that the level of a part or the whole of the electric video signal 7 from the imaging unit 6 is minimized. And the polarization controller 3 is driven, unnecessary reflected light (polarized light) can be automatically removed at high speed.
[0021]
<First Embodiment>
2 and 3 show the configuration of the first embodiment of the imaging apparatus according to the present invention. The polarization control unit 3 includes a polarization rotation unit 30 that rotates the polarization plane of the incident light 2 and a polarization absorption unit 40 that is laminated and integrated with the polarization rotation unit 30 to absorb a certain amount of polarized light. The incident light 2 incident from the polarization rotating unit 30 side is polarized by the polarization absorbing unit 40 and then emitted to the imaging optical system 4. The polarization rotation unit 30 is configured by stacking two twisted nematic liquid crystal cells 10A and 10B.
[0022]
As shown in detail in FIG. 3, the twisted nematic liquid crystal cell 10A constituting the polarization rotation unit 30 includes a first transparent substrate 11A, a first transparent electrode 12A, a liquid crystal 13A, and a second transparent electrode 14A. The second transparent substrate 15A is laminated in order. Similarly, the twisted nematic liquid crystal cell 10B is configured by sequentially laminating a first transparent substrate 11B, a first transparent electrode 12B, a liquid crystal 13B, a second transparent electrode 14B, and a second transparent substrate 15B. ing.
[0023]
The first transparent substrates 11A and 11B and the second transparent substrates 15A and 15B are each formed of a flat glass substrate or the like. The first transparent electrodes 12A and 12B and the second transparent electrodes 14A and 14B are both ITO transparent electrodes having a thickness of about 0.07 μm formed by adding 5% Sn to In ₂ O ₃ , for example. It consists of a membrane.
[0024]
The liquid crystals 13A and 13B constituting the twisted nematic liquid crystal cells 10A and 10B have a low viscosity such as nematic liquid crystal or cholesteric liquid crystal in which the material itself has a twisted orientation in order to realize the polarization controller 3 having a high-speed response. A liquid crystal material is advantageous. Further, a chiral agent that induces twist in molecular orientation may be mixed in nematic liquid crystal and used.
[0025]
The optical rotatory power of the twisted nematic liquid crystal cells 10A and 10B becomes remarkable when the plane of polarization of light is parallel or perpendicular to the liquid crystal molecular arrangement on the substrate surface on the incident side. Therefore, in order to efficiently rotate the polarization plane of the incident light 2 using two or more twisted nematic liquid crystal cells, the molecules (liquid crystal molecules 17, 18) of the twisted nematic liquid crystal cells 10A, 10B adjacent to each other are rotated. , 19, 20) It is desirable that the arrangement direction is parallel or vertical. In the configuration of FIG. 3, the alignment direction of the liquid crystal molecules 17 on the substrate surface is parallel to the alignment direction of the liquid crystal molecules 18. However, even when the molecular alignment directions are not parallel or perpendicular, the polarization intensity is reduced, but the plane of polarization can be rotated.
[0026]
Also, in order to control the alignment direction of the liquid crystal molecules 17, 18, 19, and 20 on the substrate surface of the liquid crystal molecules, between the first transparent electrode 12A and the liquid crystal 13A, and between the liquid crystal 13A and the second transparent electrode 14A. , Between the first transparent electrode 12B and the liquid crystal 13B, and between the liquid crystal 13B and the second transparent electrode 14B, respectively, as an alignment film, a polymer thin film made of a synthetic resin such as polyimide or polyvinyl alcohol, SiO, SiO ₂ It is also possible to form an inorganic thin film made of or the like.
[0027]
The twisted nematic liquid crystal cells 10 </ b> A and 10 </ b> B constituting the polarization rotating unit 30 are individually controlled by an AC voltage from the voltage driving unit 8. That is, an AC power source 23A is connected between the first transparent electrode 12A and the second transparent electrode 14A of the twisted nematic liquid crystal cell 10A via the switch 21A and the lead wire 22A, and the second power supply of the twisted nematic liquid crystal cell 10B. An AC power source 23B is connected between the first transparent electrode 12B and the second transparent electrode 14B via a switch 21B and a lead wire 22B.
[0028]
The polarizing film 16 constituting the polarization absorbing portion 40 is made of a polyvinyl alcohol resin containing iodine molecules that absorb light. Further, it is desirable that the optical direction that absorbs the most light is arranged parallel to or perpendicular to the molecular arrangement direction of the substrate surface of the adjacent twisted nematic liquid crystal cell 10B.
[0029]
In the imaging device 1 having the polarization controller 3 configured as shown in FIG. 2 and FIG. 3, the incident light 2 incident on the polarization rotation unit 30 is rotated by 45 ° or 90 ° twisted nematic liquid crystal cells 10A and 10B. Thereafter, the light is absorbed by the polarizing film 16 of the polarization absorbing unit 40 and emitted to the imaging optical system 4. Since the two twisted nematic liquid crystal cells 10A and 10B of the polarization rotating unit 30 are arranged so that the liquid crystal molecules are continuously twisted, the polarization plane of the incident light 2 is rotated by 135 ° at the maximum. On the other hand, the optical rotatory power of the individual twisted nematic liquid crystal cells 10A and 10B is eliminated by applying a voltage between the first transparent electrodes 12A and 12B and the second transparent electrodes 14A and 14B. For this reason, the control voltage 9 is output from the voltage drive unit 8 to the polarization rotation unit 30 of the polarization control unit 3 based on the level of the electric video signal 7 output from the imaging unit 6. At this time, the polarization angle of the polarization controller 3 is the sum of the optical rotation angles of the twisted nematic liquid crystal cells 10A and 10B that are individually voltage controlled. Therefore, the polarization rotation can be controlled in four ways of 0 ° (180 °), 45 °, 90 °, and 135 ° by switching the switches 21A and 21B.
[0030]
Various polarization components of the incident light 2 are absorbed and selected by the polarization film 16 after the polarization plane is controlled by the polarization rotation unit 30 constituted by the twisted nematic liquid crystal cells 10A and 10B. Therefore, the polarization controller 3 can cover all directions in units of 45 °. Since the polarization direction of the polarization control unit 3 depends on the rotation function of the polarization plane by the polarization rotation unit 30, the twisted nematic liquid crystals 10A and 10B may have various twisted polarities other than 45 ° and 90 °. Function is obtained.
[0031]
<Example of prototype>
The imaging device 1 shown in the first embodiment shown in FIGS. 2 and 3 was prototyped as follows.
[0032]
First, the twisted nematic liquid crystals 10A and 10B constituting the polarization rotation unit 30 were manufactured as follows. First, In ₂ O ₃ : A polyimide film (manufactured by Nippon Synthetic Rubber Co., Ltd., AL-1254, 0.05 μm thick) is applied on a transparent substrate made of 1.1 mm thick soda glass with a 0.07 μm thick transparent electrode made of Sn. After that, an alignment film was produced by rubbing with a rayon roll, so-called rubbing treatment. Next, the transparent electrode 12 coated with an alignment film is bonded through a spherical spacer, and nematic liquid crystals 17 and 18 containing a chiral agent in the gap (manufactured by Chisso Corporation, JB-4002LA, refractive index anisotropy Δn = 0.137). By changing the rubbing direction of the alignment film, twisted nematic liquid crystal cells 10A and 10B having twist angles of 45 ° and 90 ° were produced. The areas of the produced twisted nematic liquid crystal cells 10A and 10B are 10 cm × 10 cm. Here, the thickness d is 10 μm so that the thickness d of the twisted nematic liquid crystal cells 10A and 10B and the wavelength λ of the incident light satisfy the Morgan condition (Δn · d> 2λ) and sufficient optical rotatory power is obtained. It was.
[0033]
A polarization controller 3 in which a polarizing film 19 (manufactured by Luceo) is bonded to two twisted nematic liquid crystal cells 10A and 10B is disposed on the front surface of the optical system of a CCD three-plate TV imaging device (manufactured by Sony, CCD-VX1). The individual twisted nematic liquid crystal cells 10A and 10B were individually driven by the voltage driving unit 8 having AC voltage sources 23A and 23B (frequency 1 kHz) of 10 V or higher. Thereby, the polarization rotation angle can be controlled to 0 ° (180 °), 45 °, 90 °, and 135 °. As a result, it has been found that polarized light in all directions can be selectively removed by 80% or more. Further, the time required for the control is several tens of ms.
[0034]
Normally, in the case of oblique reflection on a glass plate or water surface, the reflected light is polarized in a direction parallel to the surface of the reflector. Therefore, as a result of driving the twisted nematic liquid crystal cells 10A and 10B so as to pick up an image of the water surface using the above-described imaging device 1 and to remove the horizontally polarized incident light 2, 0 ° (that is, horizontal polarization) It has been found that the reflected light can be removed significantly. In addition, most of the reflected light from building window glass and vehicle tilted windows can be removed by 90 ° (ie, vertical depolarization) and 45 ° (or 135 °) depolarization, respectively. Has been confirmed experimentally.
[0035]
In particular, when the reflected light is strong, the drive state of the twisted nematic liquid crystal cells 10A and 10B is controlled so that part or all of the level of the video signal captured by the imaging unit 6 is minimized. The reflected light can be removed.
[0036]
<Second Embodiment>
FIG. 4 shows the configuration of the second embodiment. The polarization controller 3 of this embodiment uses two twisted nematic liquid crystal cells 10A and 10B as the polarization rotator 30 as in the first embodiment, and replaces the polarizing film 16 as the polarization absorber 40. The guest-host liquid crystal cell 36 is used. The same components as those in the first embodiment shown in FIG.
[0037]
The guest host liquid crystal cell 36 constituting the polarization absorbing unit 40 includes a first transparent substrate 31, a first transparent electrode 32, a guest host liquid crystal 33, a second transparent electrode 34, and a second transparent substrate 35 stacked in order. Configured. The first and second transparent substrates 31 and 35 and the first and second transparent electrodes 32 and 34 are the same as the first and second transparent substrates 11A and 15A of the twisted nematic liquid crystal cell 10A described above. The two transparent electrodes 12A and 14A can be formed by laminating the same material with the same thickness.
[0038]
The polarization absorber 40 is driven and controlled by the voltage driver 8. That is, an AC power supply 44 is connected between the first transparent electrode 32 and the second transparent electrode 34 via a switch 42 and a lead wire 43, and the guest host liquid crystal 33 is driven and controlled by the applied AC voltage. It has come to be.
[0039]
The guest host liquid crystal 33 is obtained by mixing a dichroic dye 37 having light absorption anisotropy into a nematic liquid crystal 38. Various colors can be used as the dichroic dye 37, but in order to maintain white balance in video shooting, the guest host liquid crystal 33 is added by adding one or more kinds of dichroic dyes. It is desirable to make it black.
[0040]
Further, the optical direction in which the dichroic dye 37 of the guest-host liquid crystal 33 absorbs the most light is parallel or perpendicular to the molecular arrangement direction of the substrate surface (liquid crystal molecules 20) of the adjacent twisted nematic liquid crystal cell 10B. It is desirable to be arranged.
[0041]
In the polarization control unit 3 having the configuration shown in FIG. 4, when no voltage is applied to the guest-host liquid crystal cell 36, unnecessary polarization components in the incident light 2 rotated by the polarization rotation unit 30 are dichroic dye 37. Is absorbed by. On the other hand, when an AC voltage from the AC power supply 44 is applied between the first transparent electrode 32 and the second transparent electrode 34 of the guest host liquid crystal cell 36 via the switch 42 and the lead wire 43, the guest host liquid crystal 32 The molecules of the dichroic dye 37 and the nematic liquid crystal 38 are aligned in the voltage application direction, the light absorptance of the guest-host liquid crystal 32 is lowered and the polarization intensity is lowered.
[0042]
That is, when a sufficient voltage is applied to the guest-host liquid crystal cell 36, the polarization controller 3 does not exhibit a polarization operation. Thus, the polarization intensity can be controlled by controlling the voltage applied to the guest-host liquid crystal cell 36.
[0043]
Therefore, in the photographing apparatus 1 equipped with the polarization controller 3, if the polarization function becomes unnecessary, it is not necessary to remove the polarization controller 3 if a voltage is applied to the guest-host liquid crystal cell 36.
[0044]
<Modification>
In each embodiment shown in FIGS. 2 and 4, the polarization rotating unit 30 is composed of two twisted nematic liquid crystal cells 10A and 10B. However, one or more twisted nematic liquid crystal cells having a small twist angle are also provided. You may make it laminate | stack. With this configuration, a more precise rotation operation of the polarization plane can be obtained.
[0045]
In each of the embodiments shown in FIGS. 2 and 4, the twisted nematic liquid crystal cells 10A and 10B having the same twisted orientation in the rotational direction are used. However, the twisted nematic liquid crystal cells having different rotational directions in the twisted orientation are used. It is also possible to use in combination.
[0046]
Furthermore, instead of the twisted nematic liquid crystals 10A and 10B, liquid crystal cells in which liquid crystal materials such as ferroelectric liquid crystals, smectic liquid crystals, nematic liquid crystals, and cholesteric liquid crystals are aligned in various ways such as homogeneous alignment and homeotropic alignment are provided. It can also be used. In that case, since the electric field control type birefringence effect is used instead of the optical rotatory power, the plane of polarization can be rotated by 90 °. The optical rotation of twisted nematic liquid crystal can be controlled in various ways with respect to the rotation angle of the polarization plane compared to the electric field control type birefringence effect, and is also suitable for video shooting because the effect of coloring transmitted light is extremely small.
[0047]
【The invention's effect】
As described above, according to the present invention, in claim 1, an imaging unit that converts an optical image into an electric video signal, a polarization control unit that is disposed in front of the imaging unit and changes the polarization direction of incident light, A drive unit that drives and controls the polarization control unit , and the polarization control unit includes a polarization rotation unit including a plurality of twisted nematic liquid crystal cells that rotate the polarization plane of the incident light, and the polarization rotation unit. A polarization absorbing unit that absorbs polarized light in a certain direction from the light emitted from and emits the polarized light to the imaging unit side, and the driving unit is configured to include a part or the whole of the electric video signal output from the imaging unit The control voltage is set to minimize the image level and the reflected light is removed by controlling the voltage of the twisted nematic liquid crystal cell of the polarization rotation unit. A fast, can remove unnecessary polarized light components such as reflection light, it is possible to obtain a desired light image.
[0051]
In claim 2 , polarized light can be absorbed and selected by a polarizing film having a simple structure. When a guest host liquid crystal cell is used, the polarization intensity of the guest host liquid crystal cell can be controlled by controlling the voltage applied to the transparent electrode. In this case, when the polarization function becomes unnecessary, a voltage may be applied to the guest-host liquid crystal cell.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an imaging apparatus according to the present invention.
FIG. 2 is a configuration diagram illustrating a first embodiment of an imaging apparatus according to the present invention.
FIG. 3 is a detailed configuration diagram illustrating a first embodiment of an imaging apparatus according to the present invention.
FIG. 4 is a detailed configuration diagram showing a second embodiment of the imaging apparatus according to the present invention.
FIG. 5 is a configuration diagram illustrating an example of a conventional imaging apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Imaging device 2 Incident light 3 Polarization control part 4 Imaging optical system 5 Optical image 6 Imaging part 7 Electrical video signal 8 Voltage drive part 9 Control voltage 10A, 10B Twisted nematic liquid crystal cell 11A, 11B, 31 1st transparent substrate 12A, 12B, 32 First transparent electrodes 13A, 13B Liquid crystals 14A, 14B, 34 Second transparent electrodes 15A, 15B, 35 Second transparent substrate 16 Polarizing films 17, 18, 19, 20 Liquid crystal molecules 21A, 21B, 42 Switches 22A, 22B , 43 Lead wires 23A, 23B, 44 AC power supply 30 Polarization rotation unit 35 Guest host liquid crystal 36 Guest host liquid crystal cell 37 Dichroic dye 38 Nematic liquid crystal 40 Polarization absorption unit

Claims (2)

An imaging unit that converts an optical image into an electrical video signal;
A polarization controller that is arranged in front of the imaging unit and changes the polarization direction of incident light;
A drive unit that drives and controls the polarization control unit;
The polarization control unit includes a polarization rotation unit including a plurality of twisted nematic liquid crystal cells that rotate a polarization plane of the incident light, and absorbs polarized light in a certain direction from light emitted from the polarization rotation unit. It is composed of a polarization absorber that emits to the imaging unit side,
The driving unit sets a control voltage that minimizes the image level of a part or the whole of the electric video signal output from the imaging unit, and controls the voltage of the twisted nematic liquid crystal cell of the polarization rotating unit. To remove the reflected light,
An imaging apparatus characterized by that. The imaging device according to claim 1 ,
The imaging apparatus, wherein the polarization absorbing section is configured by either a polarizing film or a guest-host liquid crystal cell in which a homogeneous alignment liquid crystal material including a dichroic dye is sandwiched between transparent electrodes.

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