JPH09218308A - Polarized light separating element, and solid image pikcup device and light emitting element array printer using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarized light separating element which can easily obtain the image of high resolution without causing blur due to defocusing, and the solid image pickup device and light emitting element array printer which use the polarized light separating element. SOLUTION: The polarized light separating element 19 is constituted by arranging a 1st birefringent element 11 and a 2nd birefringent 13 which is equal in separation width to the 1st birefringent element 11 so that the separating direction of the 2nd birefringent element 13 is opposite firom that of the 1st birefringent element 11, and installing a polarized light rotating element 12 which rotates the polarizing direction of output polarized light from the 1st birefringent element 1 by 90 deg. between the two birefringent elements 11 and 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization separation element, a solid-state image pickup device and a light-emitting element array printer using the same, and in the solid-state image pickup device, a video camera device which is particularly required to have high image quality is used. It is suitable, and is suitable for high resolution in the light emitting element array printer.

[0002]

2. Description of the Related Art Conventionally, as a prior art in such a field, there has been one disclosed in, for example, Japanese Patent Laid-Open No. 6-82846. There is a demand for high image quality in an image input device using a solid-state image sensor or the like. Further, among the high image quality, in particular, higher resolution is desired, and in order to meet such demand, solid-state image pickup devices with a high pixel count are being developed, but the cost is high in terms of yield and the like. There was a problem.

Further, a method of increasing the resolution without increasing the number of pixels of the solid-state image pickup device is described in the above-mentioned document. The solid-state imaging device includes an imaging lens that forms an image of a subject on an imaging surface, and a solid-state imaging device that photoelectrically converts the image formed by the imaging lens. In the optical path between
A control for providing a polarization element, a voltage control polarization element, and a birefringence element, and applying a voltage to the voltage control polarization element at a predetermined timing to control the polarization state of light passing through the voltage control polarization element at a predetermined timing. A circuit and a signal processing device for performing image synthesis according to the control state of the control circuit are provided.

The voltage control polarization element is, for example, a TN liquid crystal element or the like, which does not rotate the polarization plane of light passing therethrough when a voltage is applied, but passes through here when no voltage is applied. Since the plane of polarization of light is rotated by 90 °, when a voltage is applied to the voltage control polarization device at a predetermined timing, the light beam reaching the solid-state imaging device via the birefringence element is displaced by the separation width of the birefringence element. Therefore, the optical paths can be separated without providing a mechanical drive mechanism.

FIG. 6 is a schematic configuration diagram of a conventional solid-state image pickup device. As shown in this figure, light 1 from a subject passes through a lens 2, a polarizing element 3, a voltage control polarizing element 4, and a birefringent element 5 and reaches a solid-state image sensor 6. The output signal from the solid-state image pickup device 6 is output as a video signal Sv after being subjected to necessary processing by the signal processing device 7. The voltage-controlled polarization element 4 is subjected to voltage control for each frame by the control circuit 8, and the polarization plane is rotated by 90 °. Control circuit 8
Controls its output voltage based on the output of the synchronization signal generator 9.

FIG. 7 is an operation explanatory view of the conventional solid-state image pickup device. First, the case where no voltage is applied to the voltage control polarization element 4 will be described with reference to FIG. The light 1 reaching the polarizing element 3 is natural light and is not polarized. The polarizing element 3 is arranged, for example, so as to transmit polarized light in a direction parallel to the paper surface. In this case, the voltage control polarization element 4
Since no voltage is applied to the transmitted light, the transmitted light becomes polarized light in the direction perpendicular to the paper surface and enters the birefringent element 5.

The birefringent element 5 is, for example, a parallel plate made of quartz, calcite, etc., and a predetermined surface normal is set on the incident side so as to form an angle φ with the crystal axis. When natural light is incident, it is separated into ordinary rays and extraordinary rays and output. FIG. 8 is a diagram schematically showing the separation of light when natural light is incident on the birefringent element. At this time, the ordinary ray incident on the birefringent element 5 is the light polarized in the direction perpendicular to the separation direction (in this case, the polarized light is perpendicular to the paper surface and shown by black dots), and is transmitted as it is. Birefringent element 5
The extraordinary ray incident on is a light polarized in a direction parallel to the separation direction (in this case, it is a polarization parallel to the paper surface and is shown by a double-headed arrow) and is output with a predetermined separation width.

Therefore, when no voltage is applied to the voltage control polarization element 4, the polarized light incident on the birefringence element 5 is an ordinary ray, and as shown in FIG. 7A, it is transmitted without displacement. Next, the case where a voltage is applied to the voltage control polarization element 4 will be described with reference to FIG. In this case, the light transmitted through the voltage control polarization element 4 does not undergo rotation of the polarization plane. Therefore, it enters the birefringent element 5 as it is as the polarized light in the direction parallel to the paper surface.

In this case, the polarized light incident on the birefringent element 5 is an extraordinary ray, which is output after being shifted by a predetermined separation width. Therefore, when a voltage is applied to the voltage control polarization element 4, the polarized light entering the birefringence element 5 is an extraordinary ray, which is displaced by a predetermined distance and transmitted. Therefore, the light beam reaching the solid-state imaging device 6 is displaced by the separation width of the birefringent element 5 when the voltage is applied to the voltage control polarization element 4 and when the voltage is not applied. Therefore, if the separation width is set to a width (1/2) P that is 1/2 of the pitch P of the photoelectric conversion photodiodes PD of the solid-state image sensor 6, the sampling interval is equivalently 1/2 times (sampling). This means that the number of points is doubled, and a high-resolution image can be obtained.

A method of synthesizing and restoring images that have been optically deviated is, for example, to turn on / off the voltage to the voltage control polarization element for each frame according to the synchronization signal given from the synchronization signal generator, Control is performed so that the optical image shifts for each frame. Then, in the subsequent signal processing device, 1 /
Perform offset correction for 2 minutes.

[0011]

However, the above-mentioned conventional device has the following problems. That is,
Since the ordinary ray and the extraordinary ray separated by the birefringent element are the displaced light and the undisplaced light, the photoelectric conversion photodiode PD of the solid-state imaging element is used by the imaging lens.
When an image is formed on a surface, there is a problem that defocus occurs between the displaced optical image and the non-displaced optical image, causing blurring. This has been a serious problem in image pickup devices that are trying to obtain high resolution images.

In view of the above problems, the present invention provides a polarization beam splitting element which can easily obtain a high resolution image without causing blurring due to defocusing, a solid-state imaging device using the same, and a light emitting element array printer. The purpose is to

[0013]

In order to achieve the above-mentioned object, the present invention provides: (1) a polarization separation element having birefringence and having a predetermined angle with respect to its optical axis, By setting a predetermined surface normal on the incident side, the first birefringent element formed as a parallel plate and the same material as the first birefringent element, having the same crystal axis angle and the same thickness, In the first birefringent element,
Between the second birefringent element set and arranged at the same distance as the separation width of the extraordinary ray with respect to the ordinary ray and arranged in the opposite direction, and between the first birefringent element and the second birefringent element. An ordinary ray component that is installed and is not displaced and that is output from the first birefringent element, and an extraordinary ray component that is separated and displaced and is output from the first birefringent element Abnormality output from the first birefringent element as an extraordinary ray in the second birefringent element by rotating the ordinary ray component output from the first birefringent element by an odd multiple of 90 ° A polarization rotation element that causes the light ray component to enter the second birefringent element as an ordinary ray component in the second birefringent element is provided.

Therefore, of the incident natural light, "x
“Polarized light having a plane of polarization in the z plane” is displaced by a distance S in the first birefringent element, and “polarized light having a plane of polarization in the yz plane” is distanced in the opposite direction in the second birefringent element. Displace by S. Since both polarizations are displaced by the same distance, there is no optical path difference or propagation time difference between both light rays, and even if both light rays are imaged by a lens, no focus shift occurs between the formed optical images.

(2) In the polarization beam splitting element described in (1) above, the polarization rotating element satisfies the half-wave plate condition at the transmitted light wavelength. Therefore, in addition to the effect described in (1) above, the polarized light can be easily rotated by the phase difference by the half-wave plate. (3) In the polarization beam splitting element described in (1) above, the polarization rotating element is an optical rotatory element that rotates polarized light by an odd multiple of 90 °.

Therefore, in addition to the effect described in the above item (1), the polarization rotating element can rotate the polarized light by an odd multiple of 90 ° with a simple structure. Further, as the element having the optical rotatory power, a TN liquid crystal element or a liquid crystal film in which the twisted orientation of liquid crystal molecules is fixed may be used. Moreover, you may use the optical crystal (crystal etc.) which has optical activity.

(4) In the polarization beam splitting element described in the above (3), the polarization rotating element is arranged so that the substrate subjected to the parallel alignment treatment is twisted by 90 ° in the alignment treatment direction.
It is a TN liquid crystal element in which a nematic liquid crystal is enclosed. As described above, since the TN liquid crystal element is used as the polarization rotating element, the polarized light can be rotated by the twisted alignment of the liquid crystal molecules. Therefore, in addition to the effect described in the above (3), optical rotatory power can be given in a wide wavelength range by determining the element condition so as to satisfy the Morgan condition.

(5) In a solid-state image pickup device having an image pickup lens for forming an image of a subject on an image pickup surface and a solid-state image pickup device for photoelectrically converting the image formed by the image pickup lens, the image pickup lens and the solid-state image pickup device are provided. A polarization element, a voltage control polarization element, and a polarization separation element according to any one of claims 1 to 4 are provided in an optical path between the imaging element and a voltage is applied to the voltage control polarization element at a predetermined timing. Then, a control circuit for controlling the polarization state of the light passing through the voltage control polarization element at a predetermined timing, and a signal processing device for performing image combination according to the control state of the control circuit are provided. is there.

Therefore, the light beam reaching the solid-state image pickup device is displaced by the separation width (2S) of the polarization separation element between when the voltage is applied to the voltage control polarization element and when the voltage is not applied. Therefore, the separation width 2S of the polarization separation element is set to be half the width (1/2) P of the pitch P of the photoelectric conversion photodiode PD of the solid-state image pickup element, that is, the separation width of each birefringent element. S is the width of the pitch P of the photodiodes PD for photoelectric conversion of the solid-state image sensor (1
/ 4) When set to P, the sampling interval is equivalently 1
/ 2 times (sampling points are doubled),
A high resolution image can be obtained.

(6) Light emitting element array for turning on / off according to print data for generating print data, rod lens array for focusing light from the light emitting element array on a photosensitive medium, and light from the light emitting element array In the electrophotographic light-emitting element array printer having a photosensitive medium for forming an electrostatic latent image by forming a polarizing element and a voltage-controlled polarizing element in an optical path between the light-emitting element array and the photosensitive medium. The polarization separating element according to any one of claims 1 to 4 is provided, and a voltage is applied to the voltage control polarizing element at a predetermined timing to set a polarization state of light passing through the voltage control polarizing element to a predetermined value. A control circuit for controlling the timing is provided.

Therefore, when the polarization separation element of the present invention is used in the exposure optical system of a light emitting element array printer, the exposure resolution is twice the light emitting element density, a high-resolution image is obtained, and the rod lens array is used. Even in the case of an image, there is no focus shift, and good image formation can be obtained.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of a polarization beam splitting element of a first embodiment of the present invention.
Is a structural diagram thereof, and FIG. 1B is a diagram schematically showing transmission of the light. As shown in these figures, the polarization splitting element 19 of the present invention includes a first birefringent element 1 from the light incident side.
1 is preferably transparent at the wavelength of incident light, and for example, calcite, rutile crystal, etc. are used, but here calcite is used. The polarization rotation element 12 is an element that rotates polarized light by 90 ° at the wavelength of incident light, and uses, for example, a half-wave plate.

The second birefringent element 13 uses the same element as the first birefringent element 11 and has the same separation width as the separation width set in the first birefringent element 11 described later. The second birefringent element 13 has its optical axis direction set in the first birefringent element 11
Install in the opposite direction, and so that the separation direction of the light rays is opposite. Next, the operation of this polarization separation element will be described.

As shown in FIG. 1 (b), polarized light is indicated by a double-headed arrow and represents polarized light having a plane of polarization in the xz plane and polarized light having a plane of polarization in the yz plane. Since unpolarized natural light can be represented by polarized lights that are orthogonal to each other, an arrow showing a polarized light having a polarization plane in the xz plane and an arrow showing a polarized light having a polarization plane in the yz plane are overlapped. Here, unpolarized natural light is incident.

The first birefringent element 11 is a parallel plate having birefringence and has a predetermined surface normal on the incident side so as to form an angle φ with the crystal axis. Here, the crystal axis direction is in the xz plane. When light is incident in the z-axis direction, "polarized light having a polarization plane in the xz plane", which is an extraordinary ray component, advances in the z-axis direction while being displaced by a distance S,
"Polarized light with a plane of polarization in the yz plane" which is an ordinary ray component
Penetrates without any displacement.

When the thickness of the first birefringent element 11 is D, the displacement amount s can be expressed by the following equation. s = [D (b ² −a ² ) / 2c ² ] sin2φ (1) a = 1 / n _e b = 1 / n _O c ² = a ² sin ² φ + b ² cos ² φ the refractive index n _e of the crystal axis direction and the refractive index of the crystal axis direction perpendicular to the n _O.

The separated light enters the polarization rotation element 12. The polarization rotation element 12 is an element that rotates linearly polarized light by 90 °. In the first embodiment of the present invention, a half wave plate is used. The half-wave plate is a birefringent parallel plate having a crystal axis 14 in the incident plane (here, the xy plane), and rotates polarized light in the 45 ° direction by 90 ° with respect to the crystal axis direction. Therefore, in the first embodiment of the present invention, the half-wave plate is arranged so that the crystal axis of the half-wave plate is on the xy plane and at a direction of 45 ° from the x-axis and the y-axis.

The light passing through the half-wave plate has its polarization direction rotated by 90 ° and is incident on the second birefringent element 13.
Therefore, in the first birefringent element 11, the “polarized light having the polarization plane in the xz plane” transmitted while being displaced by the distance S becomes “polarized light having the polarization plane in the yz plane”, and In the first birefringent element 11, “polarized light having a polarization plane in the yz plane” transmitted without being displaced is “x-
The polarized light has a polarization plane in the z-plane and is incident on the second birefringent element 13.

The second birefringent element 13 uses the same element as the first birefringent element 11, and has the same separation width S as the separation width set by the first birefringent element 11. The second birefringent element 13 is installed so that its optical axis direction is opposite to that of the first birefringent element 11, and the light separating directions are opposite. That is, if the same crystal material is used, the crystal axis angle may be −φ and the thickness D may be the same.

The crystal axis direction is in the xz plane. When light is incident in the z-axis direction, the “polarized light having a polarization plane in the xz plane”, which is an extraordinary ray component, is displaced by the distance S in the direction opposite to the case of the first birefringent element 11. The “polarized light having a plane of polarization in the yz plane”, which is an ordinary ray component and proceeds in the z-axis direction, is transmitted without being displaced. To summarize the above,
In the first embodiment of the present invention, of the incident natural light,
The “polarized light having the polarization plane in the xz plane” is displaced by the distance S in the first birefringent element 11, and the “polarized light having the polarization plane in the yz plane” is generated in the second birefringent element 13. It is displaced by the distance S in the opposite direction. That is, both polarizations
They are displaced in the opposite directions by the same distance S. Therefore, the separation width is 2S.

As described above, according to the first embodiment, "polarized light having a polarization plane in the xz plane" among incident natural light is displaced by the distance S in the first birefringent element 11, The “polarized light having a polarization plane in the yz plane” is displaced by the distance S in the opposite direction in the second birefringent element 13. Since both polarizations are displaced by the same distance, there is no optical path difference or propagation time difference between both light rays, and even if both light rays are imaged by a lens, no focus shift occurs between the formed optical images.

Next, a second embodiment of the present invention will be described. 2A and 2B are configuration diagrams of a polarization beam splitting element according to a second embodiment of the present invention. FIG. 2A is a structural diagram thereof, and FIG. 2B is a diagram schematically showing transmission of light thereof. In the second embodiment, an optical rotation element 15 is used as the polarization rotation element 12 in the first embodiment. The optical rotation element 15 is an element that rotates linearly polarized light by a predetermined angle. Here, since it is necessary to rotate 90 °, a TN liquid crystal element is used.

In this TN liquid crystal element, an alignment film (not shown) is formed on the surface, and two glass substrates (16, 17) that have been subjected to parallel alignment treatment such as rubbing are twisted so that the rubbing directions thereof are twisted by 90 °. The nematic liquid crystal (for example, ZLI-5 manufactured by Merck & Co., Inc.).
No. 081 is suitable) and the periphery is sealed. No electrodes are needed because no voltage needs to be applied. It is effective to arrange the polarization rotating element so that the rubbing direction is the above-mentioned x-axis direction or y-axis direction.

Next, the operation of the polarization separation element will be described. In the second embodiment, the principle of polarization rotation in the polarization rotating element is different from that in the first embodiment. That is, the polarized light is polarized by the twisted orientation of the liquid crystal molecules in the TN liquid crystal element used as the polarization rotation element.
It is supposed to rotate 0 °.

Only the principle of polarization rotation in the polarization rotator is different, and the separation of the light rays is the same as in the first embodiment, so a detailed description will be omitted. As described above, there is no optical path difference or propagation time difference between the two light rays separated by the second embodiment, and even if both light rays are imaged by a lens, no focus shift occurs between the formed optical images. The effect is similar to that of the first embodiment.

In the half-wave plate in the first embodiment, the polarized light is rotated by the phase difference, whereas in the second embodiment using the TN liquid crystal element, the polarized light is rotated by the twisted orientation of the liquid crystal molecules 18. They differ in points.
Therefore, strictly speaking, in the first embodiment, the polarized light can be rotated by 90 ° only within a predetermined wavelength, whereas when the TN liquid crystal device of the second embodiment is used, the device should satisfy the Morgan condition. By determining the conditions, there is also an advantage that the compound has optical activity in a wide wavelength range.

Further, as the element having optical rotatory power, a liquid crystal film in which the twisted orientation of liquid crystal molecules is fixed may be used. Moreover, you may use the optical crystal (crystal etc.) which has optical activity. Therefore, in the first and second embodiments, when a predetermined displacement amount S is obtained, only one "polarized light having a polarization plane in the xz plane" is obtained in the conventional separation element including only the birefringent element. Since only S changes, an optical path difference and a time difference occur between the separated lights, and a focus shift occurs when an image is formed by the lens system.

On the other hand, in the polarization beam splitting element of the present invention, in order to obtain a predetermined displacement amount S, both "polarization having a polarization plane in the xz plane" and "polarization having a polarization plane in the yz plane" are used. Since the polarizations of the two are equally displaced by a distance (1/2) S to obtain a predetermined displacement amount S, the optical path difference and the time difference between the separated lights are compensated, and the focus shift occurs when the image is formed by the lens system. Does not occur.

In FIGS. 1 and 2 for explaining the first and second embodiments, the ray splitting direction in the first birefringent element 11 is upward and the ray bundle in the second birefringent element 13 is upward. The separation direction is set downward, but conversely, the first
The ray separating direction in the birefringent element 11 may be downward and the ray separating direction in the second birefringent element 13 may be upward. In this case as well, the light splitting directions in the first and second birefringent elements are opposite to each other and the splitting widths are equal, so that the same polarization splitting characteristics as in the first and second embodiments are obtained. It becomes an element that can be used. However, in this case, the displacement directions of the incident light with respect to the polarization plane are also opposite to each other. That is, “polarized light having a polarization plane in the xz direction” is displaced downward, and “polarized light having a polarization plane in the yz direction” is displaced upward.

Next, a third embodiment of the present invention will be described. As a third embodiment of the present invention, an embodiment in which an image pickup device is configured by using a polarization separation element will be described. This uses the polarization separation element of the present invention in the image pickup apparatus described as a conventional example. FIG. 3 is a block diagram of an image pickup apparatus using a polarization beam splitting element showing a third embodiment of the present invention.

Light 1 from a subject reaches a solid-state image pickup device 6 through a lens 2, a polarizing element 3, a voltage control polarizing element 4 and a polarization separating element 19 of the present invention. The output signal from the solid-state image pickup device 6 is output as a video signal Sv after being subjected to necessary processing by the signal processing device 7. The voltage-controlled polarization element 4 is subjected to voltage control, for example, for each frame by the control circuit 8 to rotate the polarization plane by 90 °. The control circuit 8
The output voltage is controlled based on the output of the synchronizing signal generator 9.

Next, the operation of the image pickup apparatus will be described. FIG. 4 is a diagram for explaining the operation of the image pickup apparatus using the polarization beam splitting element of the present invention. First, the case where no voltage is applied to the voltage control polarization element will be described with reference to FIG. The light 1 reaching the polarizing element 3 is natural light and is not polarized. The polarizing element 3 is arranged, for example, so as to transmit polarized light in a direction parallel to the paper surface. In this case, since no voltage is applied to the voltage control polarization element 4, the transmitted light becomes polarized light in the direction perpendicular to the paper surface and enters the polarization separation element 19.

In this case, the polarized light is the first birefringent element 11
Is an ordinary ray and becomes an extraordinary ray with respect to the second birefringent element 13. Therefore, the light is transmitted while being displaced by a predetermined separation width S in the lower part of the figure. Next, the case where a voltage is applied to the voltage control polarization element will be described with reference to FIG.

In this case, the light transmitted through the voltage control polarization element 4 is not rotated by the polarization plane. Therefore, the polarized light in the direction parallel to the plane of the paper is incident on the polarization separation element 19 as it is. In this case, the polarized light is an extraordinary ray with respect to the first birefringent element 11 and an ordinary ray with respect to the second birefringent element 13. Therefore, the output is shifted upward by a predetermined separation width S in the figure.

As described above, according to the third embodiment, the light beam reaching the solid-state image pickup device 6 is reflected by the polarization separation element 19 when the voltage is applied to the voltage control polarization element 4 and when it is not applied. The position is displaced by the separation width (2S). Therefore, the separation width 2S of the polarization separation element 19 is set to be 1/2 the width (1/2) P of the pitch P of the photoelectric conversion photodiodes PD of the solid-state imaging element 6, that is, each birefringence element (11, 13). ) Is the width (1/4) of the pitch P of the photoelectric conversion photodiodes PD of the solid-state image sensor.
When set to P, the sampling interval is equivalently halved (sampling points are twice), and a high-resolution image can be obtained.

The method of synthesizing and restoring the optically displaced image is, for example, according to the synchronization signal given from the synchronization signal generator 9, for example, the voltage control polarization element 4 for each frame.
Then, the voltage is turned on and off, and the optical image is controlled to shift for each frame. Then, the signal processing device 7 in the subsequent stage performs 1 / 2-minute offset correction. Further, although the image switching timing is set for each frame, the image may be switched for each field. In the embodiment of the present invention, the spatial separation direction of the image is not specified. For example, separation in the horizontal direction can improve the horizontal resolution, and separation in the vertical direction can improve the vertical resolution. Furthermore, by using multiple stages,
The vertical resolution can be improved. Also in this case, the signal processing device 7 in the subsequent stage may be slightly improved.

Therefore, when an image pickup device is constructed using the polarization beam splitting element of the present invention, a high resolution image is obtained,
Further, the focus shift as in the conventional example is eliminated. FIG. 5 is a configuration diagram of a light emitting element array printer using a polarization separation element according to the fourth embodiment of the present invention. In this embodiment, the polarization separation element of the present invention is used in the exposure optical system of a light emitting element array printer, and the exposure resolution is set to the light emitting element density of 2.
An example of doubling will be described.

As shown in FIG. 5, the light 23 emitted from each light emitting element 22 of the light emitting element array 21 is the rod lens array 2.
4, polarization element 3, voltage control polarization element 4, polarization separation element 1
An image is formed on the photosensitive medium 25 (photosensitive drum) via
Reference numeral 26 is a print data generator. In addition, the voltage-controlled polarization element 4 is subjected to voltage control by the control circuit 8 at every 1/2 line cycle, for example, and the polarization plane is rotated by 90 °. Here, a ferroelectric liquid crystal element or the like is suitable as an element that can perform polarization rotation operation by voltage. in this case,
The rotation of the polarization direction can be controlled by the polarity of the voltage. The control circuit 8 controls its output voltage based on the output of the synchronization signal generator 9.

Next, the operation of the light emitting element array printer will be described. First, the case where the voltage in one case is applied to the voltage control polarization element 4 to rotate the polarized light will be described. Light 23 from the light emitting element up to the polarizing element 3
Is unpolarized because it is natural light. The polarizing element 3 is arranged, for example, so as to transmit polarized light in a direction parallel to the paper surface. In this case, the light transmitted through the voltage control polarization element 4 becomes polarized light in the direction perpendicular to the paper surface and enters the polarization separation element 19.

In this case, the polarized light is an ordinary ray for the first birefringent element 11 and an extraordinary ray for the second birefringent element 13. Therefore, the light is transmitted while being displaced to the left in the main scanning direction by the predetermined separation width S. Next, the case where the voltage in the other case is applied to the voltage control polarization element 4 and the polarized light is not rotated will be described. Therefore, the polarized light in the direction parallel to the paper surface is incident on the polarization beam splitting element 19 of the present invention.

In this case, the polarized light is an extraordinary ray for the first birefringent element 11 and an ordinary ray for the second birefringent element 13. Therefore, the output is shifted to the right in the main scanning direction by the predetermined separation width S. Therefore, the exposure position of the light beam reaching the photoconductor drum 25 is shifted by 2S corresponding to the separation width of the polarization separation element depending on the polarity of the electric field applied to the voltage control polarization element 4. Therefore, the separation width 2S of the polarization splitting element 19 is set to a width (1/2) N that is 1/2 of the pitch N of the light emitting elements in the light emitting element array, that is, each birefringent element (11, When the separation width S of 13) is set to (1/4) N, the exposure interval is equivalently halved (the exposure point is doubled), and a high-resolution image can be obtained. it can.

The optically shifted optical images are combined on the photosensitive drum 25, and after exposing one line, the photosensitive drum 2 is exposed.
5 is rotated in the sub-scanning direction by a predetermined distance, and printing of the next line is continued. As described above, according to the fourth embodiment, the exposure resolution is twice the light emitting element density, a high-resolution image is obtained, and there is no focus shift when forming an image with the rod lens array, which is good. An excellent image can be obtained.

The present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0054]

As described above, according to the present invention, the following effects can be obtained. (1) According to the invention described in claim 1, of the incident natural light, “polarized light having a polarization plane in the xz plane” is displaced by the distance S in the first birefringent element, and the “yz plane”. The polarized light having the plane of polarization "is displaced in the opposite direction by the distance S in the second birefringent element. Since both polarizations are displaced by the same distance, there is no optical path difference or propagation time difference between both rays,
Even if both light rays are imaged by the lens, no focus shift occurs between the formed optical images.

(2) According to the second aspect of the invention, in addition to the effect of the first aspect of the invention, the half-wave plate can easily rotate the polarized light by the phase difference. (3) According to the invention of claim 3, in addition to the effect of the invention of claim 1, the polarization rotating element
With a simple structure, polarized light can be rotated by an odd multiple of 90 °.

As an element having optical rotatory power, TN
A liquid crystal film or a liquid crystal film in which the twisted orientation of liquid crystal molecules is fixed may be used. Moreover, you may use the optical crystal (crystal etc.) which has optical activity. (4) According to the invention described in claim 4, in addition to the effect of the invention described in claim 3, as a polarization rotation element,
Since the TN liquid crystal element is used, the polarized light can be rotated by the twisted alignment of the liquid crystal molecules. Therefore, by determining the element condition so as to satisfy the Morgan condition, it is possible to provide the optical activity in a wide wavelength range.

(5) According to the fifth aspect of the present invention, the light beam reaching the solid-state image pickup device is divided by the separation width of the polarization separation element when the voltage is applied to the voltage control polarization element and when the voltage is not applied. The position will be displaced by 2S). Therefore, the separation width 2S of the polarization separation element is set to be 1/2 the width (1/2) P of the pitch P of the photoelectric conversion photodiode PD of the solid-state image pickup element, that is, the separation width S of each birefringence element. Is a photodiode P for photoelectric conversion of a solid-state image sensor.
When the width of the pitch P of D is set to (1/4) P, the sampling interval is equivalently halved (sampling point is doubled).
Therefore, it is possible to obtain a high resolution image.

(6) According to the sixth aspect of the present invention, when the polarization separation element of the present invention is used in the exposure optical system of the light emitting element array printer, the exposure resolution is twice the light emitting element density, resulting in high resolution. An image is obtained, and even when an image is formed by the rod lens array, there is no focus shift, and a good image is obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a polarization beam splitting element according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a polarization beam splitting element according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of an image pickup apparatus using a polarization beam splitting element showing a third embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the image pickup apparatus using the polarization beam splitting element of the present invention.

FIG. 5 is a configuration diagram of a light emitting element array printer using a polarization beam splitting element according to a fourth embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a conventional solid-state imaging device.

FIG. 7 is an operation explanatory diagram of a conventional solid-state imaging device.

FIG. 8 is an explanatory diagram of light transmission of a birefringent element of a conventional solid-state imaging device.

[Explanation of symbols]

 1, 23 light 2 lens 3 polarizing element 4 voltage control polarizing element 6 solid-state image sensor 7 signal processing device 8 control circuit 9 synchronization signal generator 11 first birefringent element 12 polarization rotator 13 second birefringent element 14 crystal Axis 15 Optical rotation element 16,17 Glass substrate 18 Liquid crystal molecule 19 Polarization separation element 21 Light emitting element array 22 Light emitting element 24 Rod lens array 25 Photosensitive medium (photosensitive drum)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H04N 5/335 (72) Inventor ▲ Takahashi Wataru Toranomon 1-chome 12-12 Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (6)

[Claims] (A) A first parallel plate having birefringence and having a predetermined plane normal on the incident side so as to form a predetermined angle with respect to its optical axis. A birefringent element, (b)
The same material as that of the first birefringent element, the same crystal axis angle and the same thickness, the same distance as the separation width of the extraordinary ray from the ordinary ray in the first birefringent element, and the direction is opposite. The second birefringent element set and arranged as described above, and (c) is disposed between the first birefringent element and the second birefringent element, and is displaced from the first birefringent element. The extraordinary ray component which is separated from the ordinary ray component and is displaced and output from the first birefringent element is output from the first birefringent element by rotating each polarization plane by an odd multiple of 90 °. The non-displaced ordinary ray component is the extraordinary ray component in the second birefringent element, and the extraordinary ray component output from the first birefringent element is the ordinary ray component in the second birefringent element. And a polarization rotation element for making the light incident on the birefringent element. Polarization separating element characterized. 2. The polarization separation element according to claim 1, wherein
A polarization separation element, wherein the polarization rotation element is an element that satisfies a half-wave plate condition at a transmitted light wavelength. 3. The polarization separation element according to claim 1, wherein
A polarization separation element, wherein the polarization rotation element is an optical rotation element that rotates polarization by an odd multiple of 90 °. 4. The polarized light separating element according to claim 3,
A polarization separation element, wherein the polarization rotation element is a TN liquid crystal element in which a substrate subjected to a parallel orientation treatment is arranged so that the orientation treatment direction is twisted by 90 °, and nematic liquid crystal is sealed. 5. A solid-state image pickup device comprising: an image pickup lens for forming an image of a subject on an image pickup surface; and a solid-state image pickup device for photoelectrically converting the image formed by the image pickup lens. In the optical path between the element,
A polarization element, a voltage control polarization element, and a polarization separation element according to any one of claims 1 to 4 are provided, and a voltage is applied to the voltage control polarization element at a predetermined timing,
A solid-state imaging device, comprising: a control circuit for controlling the polarization state of light passing through the voltage-controlled polarization element at a predetermined timing; and a signal processing device for performing image synthesis according to the control state of the control circuit. apparatus. 6. A light emitting element array for turning on and off according to print data for generating print data, a rod lens array for focusing light from the light emitting element array on a photosensitive medium, and light from the light emitting element array. In an electrophotographic light emitting element array printer having a photosensitive medium which forms an electrostatic latent image by forming an image, in an optical path between the light emitting element array and the photosensitive medium,
A polarization element, a voltage control polarization element, and a polarization separation element according to any one of claims 1 to 4 are provided, and a voltage is applied to the voltage control polarization element at a predetermined timing,
A light emitting element array printer comprising a control circuit for controlling a polarization state of light passing through the voltage control polarization element at a predetermined timing.