WO2012039087A1 - Imaging element and imaging device - Google Patents

Abstract

This imaging device comprises: multiple polarizer units (140) each of which comprises a single polarizer (14) or N pieces (wherein N represents an integer of 2 or more) of polarizers (14) having different polarization transmission axis direction from each other; a photosensor cell array (120) on which multiple photosensor cells (12) are arranged along the image plane and which is so adopted that linear polarized light that passes through the polarizers (14) can enter each of the photosensor cells (12); and an MEMS rotation element (16) which can rotate each of the polarizer units (140) about the center axis of each of the polarizer units (140) so as to cause the rotation of a polarization plane of the linear polarized light that enters each of the photosensor cells (12).

Description

Imaging device and imaging apparatus

The present invention relates to an imaging device that can acquire polarization information and an imaging device including the imaging device.

Polarized imaging that can acquire information that cannot be obtained with luminance images alone has attracted attention. In order to perform polarization imaging, it is necessary to arrange a polarizer or a polarizing plate in front of the imaging surface of the imaging device. Patent Document 1 discloses an image sensor in which fine polarizers are arranged at a pitch of about 100 μm, for example. Patent Document 2 discloses an imaging apparatus having a mechanism for rotating a polarizing plate. Patent Document 3 discloses an endoscope that acquires a polarization image by alternately using two polarizing plates having a polarization transmission axis orthogonal to each other.

JP 2007-86720 A US Patent Application Publication No. 2007-79982 JP 2003-47588 A

According to the prior art described in Patent Document 1, the polarizer is fixed, the problem of pixel displacement does not occur, and a mechanism for rotating the polarizing plate is unnecessary. However, since only light transmitted through the polarization transmission axis in a certain direction is incident from each pixel, it is necessary to use signals from a plurality of pixels in order to obtain polarization information such as the degree of polarization and the polarization phase angle. The resolution decreases.

According to the conventional technique described in Patent Document 2, there is a problem of pixel shift due to a large rotating polarizing plate, and resolution and SN ratio are lowered. Moreover, it is difficult to reduce the size of an apparatus for rotating the polarizing plate.

According to the prior art described in Patent Document 3, the moving distance of the polarizing plate is large, and it is difficult to reduce the size of the apparatus for changing the position of the polarizing plate.

The present invention has been made in order to solve the above-described problems, and has as its main purpose an imaging that does not require a device for rotating or moving a large polarizing plate and can acquire polarization information from each pixel. It is to provide an element.

Another object of the present invention is to provide an imaging device that includes the imaging device described above and can output polarization information.

The imaging device of the present invention includes a plurality of polarizer units each including one polarizer or N polarizers (N is an integer of 2 or more) having different polarization transmission axis directions, and a plurality of photosensitive cells. And a photosensitive cell array arranged such that linearly polarized light transmitted through the polarizer is incident on each photosensitive cell, and each polarizer unit is rotated about the central axis of each polarizer unit. And a MEMS rotating element for rotating the polarization plane of linearly polarized light incident on each photosensitive cell.

In one embodiment, each polarizer unit includes four polarizers having different polarization transmission axis directions, and each polarization transmission axis direction is different by 45 °.

In one embodiment, the MEMS rotating element rotates each polarizer unit by rotating the polarizer unit by an angle that is a multiple of 45 ° in synchronization with a timing at which charge accumulation in the photosensitive cell array is reset. The plane of polarization of linearly polarized light incident on the cell is changed.

In one embodiment, the MEMS rotating element temporarily changes a polarization plane of linearly polarized light incident on each photosensitive cell by quiescing the polarizer unit during a period in which charge accumulation is performed in the photosensitive cell array. Fix it.

In one embodiment, one polarizer faces one photosensitive cell during the period in which the charge accumulation is performed in the photosensitive cell array.

In one embodiment, the MEMS rotating element includes a rotating unit that supports each polarizer unit, and a fixed unit that rotates the rotating unit by electrostatic force.

The imaging apparatus of the present invention includes a plurality of polarizer units each including one polarizer or N polarizers (N is an integer of 2 or more) having different polarization transmission axis directions, and a plurality of photosensitive cells. And a photosensitive cell array arranged such that linearly polarized light transmitted through the polarizer is incident on each photosensitive cell, and each polarizer unit is rotated about the central axis of each polarizer unit. Thus, an imaging device including a MEMS rotating element that rotates a polarization plane of linearly polarized light incident on each photosensitive cell, a driving circuit that drives the MEMS rotating element, and imaging for forming an image on the imaging device And a lens.

According to the present invention, since each of a plurality of polarizer units each including one or several polarizers is rotated by a MEMS rotating element, a large apparatus for rotating or replacing a large polarizing plate is provided. It is unnecessary. In addition, since light having a different polarization main axis can be incident on each pixel, it is possible to obtain a polarized image with high resolution.

It is a figure which shows schematic structure of the imaging part in embodiment of the imaging device by this invention. (A) is a figure which shows typically the one part plane structure of the rotating polarizer array 160 in 1st Embodiment, (b) is a figure which shows the cross-sectional structure typically. (A) is a figure which shows typically the plane structure for 1 pixel of the rotating polarizer array 160, (b) is a figure which shows typically the cross section and the cross section of the photosensitive cell array 120 corresponding. In a 1st example, it is a figure which shows the relationship between polarizer 14A, 14B, 14C, 14D in an initial state, and photosensitive cell 12a, 12b, 12c, 12d. In a 1st example, it is a figure which shows the relationship between polarizer 14A, 14B, 14C, 14D in a 2nd state, and photosensitive cell 12a, 12b, 12c, 12d. In a 1st example, it is a figure which shows the relationship between polarizer 14A, 14B, 14C, 14D in a 3rd state, and photosensitive cell 12a, 12b, 12c, 12d. In a 1st example, it is a figure which shows the relationship between polarizer 14A, 14B, 14C, 14D in a 4th state, and photosensitive cell 12a, 12b, 12c, 12d. In a 2nd example, it is a figure which shows the relationship between polarizer 14A, 14B, 14C, 14D in an initial state, and photosensitive cell 12a, 12b, 12c, 12d. In a 2nd example, it is a figure which shows the relationship between polarizer 14A, 14B, 14C, 14D in a 2nd state, and photosensitive cell 12a, 12b, 12c, 12d. In a 2nd example, it is a figure which shows the relationship between polarizer 14A, 14B, 14C, 14D in a 3rd state, and photosensitive cell 12a, 12b, 12c, 12d. In a 2nd example, it is a figure which shows the relationship between polarizer 14A, 14B, 14C, 14D in a 4th state, and photosensitive cell 12a, 12b, 12c, 12d. (A) is a figure which shows typically the plane structure for 4 pixels of the rotating polarizer array 160 in 2nd Embodiment, (b) is a figure which shows the cross section and the cross section of the corresponding photosensitive cell array 120 typically. FIG. It is a figure which shows typically the plane structure for 36 pixels of the rotating polarizer array 160 in 2nd Embodiment. (A) to (d) is a diagram showing the rotation of the polarizer unit 140 in the second embodiment. It is a top view which shows the relationship between one polarizer unit and several photosensitive cell. 1 is a block diagram illustrating a schematic configuration of an imaging apparatus according to an embodiment of the present invention. It is a block diagram which shows an example of the main components of the signal processing part 200 in embodiment of this invention. A graph showing light intensities (pixel values or luminances) I ₁ to I ₄ transmitted through four types of polarizers having polarization transmission axes (ψi = 0 °, 45 °, 90 °, 135 °) having different directions. is there. It is a graph which shows the amplitude, phase, and average value of the fluctuation curve of polarization luminance.

(Embodiment 1)
First, refer to FIG. FIG. 1 is a diagram illustrating a schematic configuration of an imaging unit in an embodiment of an imaging apparatus according to the present invention.

The imaging unit includes an imaging element (image sensor) 10 and a photographing lens 20 for forming an image on the imaging surface of the imaging element 10. The imaging element 10 includes a photosensitive cell array 120 in which a plurality of photosensitive cells (photoelectric conversion elements) are arranged along the imaging surface, a rotating polarizer array 160 that controls a polarization plane of light incident on each photosensitive cell, and the like. It has. Since each photosensitive cell corresponds to a pixel, the photosensitive cell array 120 may be referred to as a pixel array 120. The photographic lens 20 is schematically described as a single lens in FIG. 1, but is usually an optical system in which a plurality of lenses are combined, and has a known configuration.

Next, a configuration example of the rotating polarizer array 160 will be described with reference to FIGS. 2 and 3. 2A schematically shows a part of the planar configuration of the rotating polarizer array 160, and FIG. 2B shows a cross section thereof. In FIG. 2A, for simplicity, only a region corresponding to the size of four pixels in the rotating polarizer array 160 is shown. The actual rotating polarizer array 160 has a size that covers all the photosensitive cells (all pixels) included in the opposing photosensitive cell array 120. FIG. 3A is a plan view of a region for one pixel in the rotating polarizer array 160, and FIG. 3B schematically shows a cross section thereof and a cross section of one corresponding photosensitive cell 12. As shown in FIG. Show.

As shown in FIG. 2, the rotating polarizing element 160 of the present embodiment includes a plurality of polarizer units 140 and a MEMS rotating element 16 that rotates each polarizer unit 140 around the central axis of each polarizer unit 140. I have. In the second embodiment to be described later, each polarizer unit 140 includes four polarizers 14 having different polarization transmission axis directions. However, in this embodiment, each polarizer unit 140 includes one polarizer 14. Contains. As shown in FIG. 3B, the polarizer 14 covers one corresponding photosensitive cell 12, and linearly polarized light polarized in the direction of the polarization transmission axis of the polarizer 14 is incident on the photosensitive cell 12. Let As shown in FIGS. 3A and 3B, the MEMS rotating element 16 has a rotating portion 16b that supports each polarizer unit 140 and a fixing portion 16a that rotates the rotating portion 16b by electrostatic force. is doing. The fixing unit 16a may be separated for each polarizer unit 140, or integrated with the fixing unit 16a of another polarizer unit 140 and continuously in one rotating polarizer array 160 as shown in FIG. You may do it. The MEMS rotating element 16 can be manufactured by a micromachining technique using a known semiconductor manufacturing technique. The fixed portion 16a and the rotating portion 16b can be formed by preparing a single crystal silicon substrate and performing fine processing by a thin film deposition process, a photolithography process, and an etching process. The fixed portion 16a and the rotating portion 16b can be formed of, for example, a polycrystalline silicon thin film or a silicon dioxide film. An example of a method for manufacturing such a MEMS rotating element 16 is disclosed in Non-Patent Document 1, for example.

The diameter of the rotating unit 16b can be determined according to the pixel size. When the pixel size is, for example, 25 μm × 25 μm, the diameter of the rotating unit 16b can be set to, for example, 14 μm. The size of the polarizer 14 is limited by the rotating unit 16b.

As shown in FIG. 3A, the MEMS rotating element 16 includes electrodes 15a and 15b that generate an electrostatic force for rotating the rotating portion 16b, and wiring (not shown). When an electrostatic force is generated between the electrode 15a of the fixed portion 16a and the electrode 15b of the rotating portion 16b due to the potential applied to the wiring, the rotating portion 16b rotates by a desired angle. Since the rotation unit 16b rotates together with the polarizer unit 140, the polarization transmission axis direction of the polarizer 14 included in the polarizer unit 140 can be rotated by a predetermined angle.

In a preferred embodiment, the movement of the rotating unit 16b can be controlled so as to rotate in a state where the polarization transmission axes of all the polarizers 14 are aligned in the same direction. However, the present invention is not limited to such an example. The directions of the polarization transmission axes of the individual polarizers 14 do not need to match. Each polarizer 14 is preferably rotated by the same angle (for example, 45 °) by one rotation operation.

Refer to FIG. 1 again. The imaging unit of FIG. 1 includes a MEMS driving circuit 40 that drives the MEMS rotating element 16 of the rotating polarizer array 160. The MEMS drive circuit 40 may be incorporated in the image sensor 10 or may be mounted as another component. The electrodes 15a and 15b in FIG. 3A are connected to the MEMS drive circuit 40 through the wiring described above.

Next, the rotation operation of the polarizer 14 will be described with reference to FIGS. 4A to 4D. In this specification, in order to distinguish the four polarizers 14 corresponding to the four pixels, the letters A, B, C, and D are appended to the end of the reference numerals. Similarly, in order to distinguish the four photosensitive cells 12 corresponding to the four pixels, letters a, b, c and d are appended to the end of the reference numerals.

An arrow is described on each polarizer 14A, 14B, 14C, 14D in the drawing. This arrow indicates the direction (main axis direction) of the polarization transmission axis of the polarizer. Of the light incident on the polarizer 14, light in which the vibration direction of the electric field vector coincides with the polarization transmission axis can pass through the polarizer. The light transmitted through the polarizer 14 is linearly polarized light polarized in the direction of the polarization transmission axis of the polarizer 14. 4A to 4D show four polarizers 14A, 14B, 14C, and 14D in which the directions of polarization transmission axes are aligned in the same direction.

In FIG. 4A to FIG. 4D, 2 rows × 2 columns = 4 photosensitive cells 12a, 12b, 12c, and 12d are shown for simplicity, but in an actual photosensitive cell array 120, for example, 1 million is shown. A greater number of photosensitive cells are arranged. The arrangement pitch of the photosensitive cells in the photosensitive cell array 120 matches the arrangement pitch of the polarizers 14 in the rotating polarizer array 160. These arrangement pitches are sometimes referred to as “pixel pitches”. The actual photosensitive cell array 120 is disposed at a position to receive light transmitted through each polarizer 14 of the rotating polarizer array 160 as described above. The photosensitive cell array 120 is composed of photosensitive cells 12 arranged in rows and columns.

FIG. 4A shows the relationship between the polarization transmission axis directions of the four polarizers 14A, 14B, 14C, and 14D included in the rotating polarizer array 160 in the initial state and the photosensitive cells 12a, 12b, 12c, and 12d. ing. The light transmitted through the four polarizers 14A, 14B, 14C, and 14D is linearly polarized light that is polarized in the Y-axis direction, and is incident on the photosensitive cells 12a, 12b, 12c, and 12d, respectively. At this time, in the photosensitive cells 12a, 12b, 12c, and 12d, charges corresponding to the amount of incident light are generated and accumulated by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charges accumulated in each of the photosensitive cells 12a, 12b, 12c, and 12d are read out as pixel signals. After the charge reading is completed, the accumulated charge is reset. In general, the charge accumulation period is defined by the reciprocal of the signal reading frame rate (fps: frame per second).

Next, refer to FIG. 4B.

FIG. 4B shows a state in which the polarizers 14A, 14B, 14C, and 14D are rotated by 45 ° by the action of the individual MEMS rotating elements 16, respectively. In this state, the light transmitted through the four polarizers 14A, 14B, 14C, and 14D is polarized in a direction rotated by 45 ° clockwise from the Y axis, and the photosensitive cells 12a, 12b, and 12c, respectively. , 12d. While in the state of FIG. 4B, in the photosensitive cells 12a, 12b, 12c, and 12d, charges corresponding to the amount of incident light are generated and accumulated by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charges accumulated in each of the photosensitive cells 12a, 12b, 12c, and 12d are read out as pixel signals. After the charge reading is completed, the accumulated charge is reset.

The rotation of the polarizers 14A, 14B, 14C, and 14D is performed in synchronization with the charge accumulation reset timing. The time during which the polarizers 14A, 14B, 14C, and 14D are rotating is excluded from the charge accumulation period. For this reason, the polarization direction of light incident on each photosensitive cell does not change during the charge accumulation period. As a result, it is possible to obtain polarization information of light incident on the photosensitive cell based on the read pixel signal. Acquisition of polarization information in pixel units will be described in detail later.

Next, refer to FIG. 4C.

FIG. 4C shows a state in which the polarizers 14A, 14B, 14C, and 14D are further rotated by 45 ° by the action of the individual MEMS rotating elements 16, respectively. In this state, the light transmitted through the four polarizers 14A, 14B, 14C, and 14D is polarized in a direction (X-axis direction) rotated by 90 ° clockwise from the Y-axis, and each of the photosensitive cells. It enters 12a, 12b, 12c, 12d. While in the state of FIG. 4C, in the photosensitive cells 12a, 12b, 12c, and 12d, charges corresponding to the amount of incident light are generated and accumulated by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charges accumulated in each of the photosensitive cells 12a, 12b, 12c, and 12d are read out as pixel signals. After the charge reading is completed, the accumulated charge is reset.

Next, refer to FIG. 4D.

FIG. 4D shows a state in which the polarizers 14A, 14B, 14C, and 14D are further rotated by 45 ° by the action of the individual MEMS rotating elements 16, respectively. In this state, the light transmitted through the four polarizers 14A, 14B, 14C, and 14D is polarized in a direction rotated by 135 ° clockwise from the Y axis, and the photosensitive cells 12a, 12b, and 12c, respectively. , 12d. While in the state of FIG. 4D, in the photosensitive cells 12a, 12b, 12c, and 12d, charges corresponding to the amount of incident light are generated and accumulated by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charges accumulated in each of the photosensitive cells 12a, 12b, 12c, and 12d are read out as pixel signals. After the charge reading is completed, the accumulated charge is reset.

Thereafter, the polarizers 14A, 14B, 14C, and 14D are further rotated by 45 ° by the action of the individual MEMS rotating elements 16, and return to the state shown in FIG. 4A.

Thus, in this embodiment, each polarizer 14 returns from the state of FIG. 4A to the original state (the state of FIG. 4A) through the state of FIG. 4B, the state of FIG. 4C, and the state of FIG. 4D. When this periodic operation is repeated, light transmitted through a polarizer having a different polarization transmission axis is sequentially incident on each photosensitive cell during one period. Since the pixel signal is read out in synchronization with the rotational motion of the polarizer 14, polarization information can be acquired.

When acquiring polarization information, while the polarizer 14 rotates 180 °, charges are accumulated with the polarization transmission axis facing at least three different directions, and at least three photoelectric conversion signals are sequentially output. preferable. In the above example, the polarization transmission axis direction is set to four directions. However, for example, when the polarization transmission axis direction is set to three directions, pixel signals may be acquired in a state where the polarization transmission axis directions are different by 60 °.

The rotation angle of the polarizer 14 is not limited to 45 ° or 60 °. Any other angle can be set. Two types of pixel signals may be output in a state where the polarization transmission axis directions are different by 90 °. In this case, the polarizer 14 may repeat this operation with one cycle of the operation of rotating 90 ° clockwise and then rotating 90 ° counterclockwise. Although complete polarization information cannot be obtained, it is possible to detect polarization components whose polarization directions are orthogonal.

The planar shapes of the polarizer 14 and the photosensitive cell 12 shown in FIGS. 4A to 4D are both circular. However, the planar shapes of the polarizer 14 and the photosensitive cell (light receiving region) 12 are not limited to a circular shape. The planar shape and size of the polarizer 14 and the photosensitive cell 12 are such that light transmitted through the polarizer 14 efficiently enters each photosensitive cell 12 and light that does not transmit through the corresponding polarizer 14 corresponds to each light. It is designed not to enter the sensing cell 12.

As long as the entire photosensitive cell 12 is always covered by the polarizer 14, the planar shape of the photosensitive cell 12 does not have to be circular, and may be an ellipse or a polygon. Further, the planar shape of the polarizer 14 is not necessarily circular, and may be an ellipse or a polygon. For example, the planar shape of each polarizer 14 may be a square or an octagon. In general, when the polarization transmission axis faces N different directions due to rotation, the planar shape of the polarizer 14 preferably has a symmetrical shape with a rotation of (360 / N) degrees around the central axis.

The light sensing cell 12 may be covered with a microlens. The photosensitive cell array 120 may be realized by a backside illuminated image sensor. When the photosensitive cell array 120 is realized by a normal surface irradiation type image sensor, a wiring (not shown) exists between the photosensitive cell 12 and the photosensitive cell 12.

Next, another example of the rotation operation of the polarizer 14 will be described with reference to FIGS. 5A to 5D. In this example, the polarization transmission axis directions of the four polarizers 14A, 14B, 14C, and 14D shown in the figure are different by 45 °, but the other points are the same as the examples shown in FIGS. 4A to 4D. Are the same.

First, refer to FIG. 5A.

FIG. 5A shows the relationship between the polarization transmission axis directions of the four polarizers 14A, 14B, 14C, and 14D included in the rotating polarizer array 160 in the initial state and the photosensitive cells 12a, 12b, 12c, and 12d. ing. The light transmitted through the four polarizers 14A, 14B, 14C, and 14D is linearly polarized light that is polarized in different directions by 45 °, and is incident on the photosensitive cells 12a, 12b, 12c, and 12d, respectively. At this time, in the photosensitive cells 12a, 12b, 12c, and 12d, charges corresponding to the amount of incident light are generated and accumulated by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charges accumulated in each of the photosensitive cells 12a, 12b, 12c, and 12d are read out as pixel signals. After the charge reading is completed, the accumulated charge is reset. In this example, four polarizers 14A, 14B, 14C, and 14D form one basic configuration. This basic configuration is two-dimensionally and periodically arranged in one rotating polarizer array 160. The four polarizers 14A, 14B, 14C, and 14D can rotate independently, but in the present embodiment, they rotate by the same angle in the same direction.

Next, refer to FIG. 5B.

FIG. 5B shows a state in which the polarizers 14A, 14B, 14C, and 14D are rotated by 45 ° by the action of the individual MEMS rotating elements 16, respectively. In this state, the light transmitted through the four polarizers 14A, 14B, 14C, and 14D is polarized in a direction rotated by 45 ° clockwise from the polarization transmission axis direction shown in FIG. 5A. The light enters the sensing cells 12a, 12b, 12c, and 12d. While in the state of FIG. 5B, in the photosensitive cells 12a, 12b, 12c, and 12d, charges corresponding to the amount of incident light are generated and accumulated by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charges accumulated in each of the photosensitive cells 12a, 12b, 12c, and 12d are read out as pixel signals. After the charge reading is completed, the accumulated charge is reset.

Next, refer to FIG. 5C.

FIG. 5C shows a state in which the polarizers 14A, 14B, 14C, and 14D are further rotated by 45 ° by the action of the individual MEMS rotating elements 16, respectively. In this state, the light transmitted through the four polarizers 14A, 14B, 14C, and 14D is incident on the photosensitive cells 12a, 12b, 12c, and 12d, respectively. While in the state of FIG. 5C, in the photosensitive cells 12a, 12b, 12c, and 12d, charges corresponding to the amount of incident light are generated and accumulated by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charges accumulated in each of the photosensitive cells 12a, 12b, 12c, and 12d are read out as pixel signals. After the charge reading is completed, the accumulated charge is reset.

Next, refer to FIG. 5D.

FIG. 5D shows a state in which the polarizers 14A, 14B, 14C, and 14D are further rotated by 45 ° by the action of the individual MEMS rotating elements 16. In this state, the light transmitted through the four polarizers 14A, 14B, 14C, and 14D is incident on the photosensitive cells 12a, 12b, 12c, and 12d, respectively. While in the state of FIG. 5D, in the photosensitive cells 12a, 12b, 12c, and 12d, charges corresponding to the amount of incident light are generated and accumulated by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charges accumulated in each of the photosensitive cells 12a, 12b, 12c, and 12d are read out as pixel signals. After the charge reading is completed, the accumulated charge is reset.

Thereafter, the polarizers 14A, 14B, 14C, and 14D are further rotated by 45 ° by the action of the individual MEMS rotating elements 16, and return to the state shown in FIG. 5A.

Even in such an example, each polarizer 14 rotates by 45 °. When this periodic operation is repeated, light transmitted through four polarizers having different polarization transmission axes is sequentially incident on each photosensitive cell 12 during one period. Since pixel signals are read out in synchronization with the rotational movement of the polarizer 14, polarization information can be acquired.

In order to allow only light transmitted through the polarizer 14 corresponding to each photosensitive cell 12 to enter, it is preferable to set the interval between the photosensitive cell array 120 and the rotating polarizer array 160 to 1 mm or less. In a more preferred embodiment, they are in contact.

(Embodiment 2)
In the above embodiment, one polarizer unit 140 includes one polarizer 14, but the present invention is not limited to such an example. The number of the polarizers 14 included in one polarizer unit 140 may be N (N is an integer of 2 or more).

FIG. 6 is a plan view showing a planar configuration example of one polarizer unit 140 including four polarizers 14 having different polarization transmission axis directions. FIG. It is a top view of the area | region for 4 pixels, FIG.6 (b) has shown typically the cross section and the cross section of the photosensitive cell array 120 corresponding. An arrow is described on each polarizer 14 in FIG. This arrow indicates the direction (main axis direction) of the polarization transmission axis of the polarizer. In this example, the polarization transmission axis directions of the polarizers 14 included in one polarizer unit 140 are different by 45 °.

The MEMS rotating element 16 in this example also includes a rotating portion 16b that supports the polarizer unit 140 and a fixing portion 16a that rotates the rotating portion 16b by electrostatic force, as shown in FIG. These configurations are basically the same as those shown in FIGS. 3A and 3B. The difference is that one rotating unit 16b supports four polarizers 14A, 14B, 14C, and 14D.

As described above, since the rotation unit 16b rotates together with the polarizer unit 140, the polarization transmission axis directions of the four polarizers 14A, 14B, 14C, and 14D included in the polarizer unit 140 are rotated by a predetermined angle. Can do. The four polarizers 14A, 14B, 14C, 14D rotate about the center O of the polarizer unit 140, not the center of each.

Next, the rotation operation of the polarizer unit 140 will be described with reference to FIGS.

FIG. 7 is a plan view showing nine polarizer units 140. The nine polarizer units 140 cover a total of 6 rows × 6 columns = 36 photosensitive cells. In the example of FIG. 7, the polarizers 14A, 14B, 14C, and 14D in the individual polarizer units 140 have the same arrangement pattern. The actual rotating polarizer array 160 includes a number of polarizer units 140.

Next, an example of the rotation operation of one polarizer unit 140 will be described with reference to FIG.

First, when the polarizer unit 140 in the state shown in FIG. 8A is rotated clockwise by 90 °, the polarizer unit 140 is in the state shown in FIG. 8B. For example, paying attention to the polarizer 14A, in the state of FIG. 8A, it has a polarization transmission axis parallel to the Y-axis direction, but in the state shown in FIG. 8B, polarization transmission parallel to the X-axis direction. Has an axis. That is, when the polarizer unit rotates 90 °, the polarizer 14A rotates 90 ° around the rotation center of the polarizer unit 140 and rotates the polarization transmission axis direction by 90 °. The same applies to the other polarizer units 14B, 14C, and 14D included in the same polarizer unit 140.

In the state of FIG. 8B, the photosensitive cell covered with the polarizer 14A was covered with the polarizer 14B in the state of FIG. 8A. For this reason, in this state shown in FIG. 8A, light that is polarized in a direction rotated by 45 ° clockwise from the Y-axis direction is incident on this photosensitive cell. However, in the state shown in FIG. Light polarized in the direction will be incident. Note that when the polarizer unit 140 is rotated 90 ° clockwise, the polarization direction of light incident on one photosensitive cell 12 is rotated 45 °. The same is true for all four photosensitive cells 12 covered by the polarization unit 140.

Next, when the polarizer unit 140 further rotates 90 ° clockwise, the state changes to the state shown in FIG. When the polarizer unit 140 further rotates 90 ° in the clockwise direction, the state transitions to the state shown in FIG. When the polarizer unit 140 further rotates 90 ° in the clockwise direction, it returns to the state shown in FIG.

In this way, when the polarizer unit 140 is rotated by 90 °, the polarization plane of the light incident on each light sensing cell 12 is rotated by 45 °. In the present embodiment, unlike the above-described embodiment, the polarizer 14 itself covering each photosensitive cell 12 is sequentially changed by the rotation of the polarizer unit 140. That is, also in this embodiment, the polarization plane of the light incident on each photosensitive cell 12 can be rotated.

As described with reference to FIGS. 4A to 5D, when light polarized in a specific direction is incident, each photosensitive cell 12 generates and accumulates a charge corresponding to the amount of incident light by photoelectric conversion. When a predetermined charge accumulation period has elapsed, the charge accumulated in each of the photosensitive cells 12 is read out as a pixel signal. After the charge reading is completed, the accumulated charge is reset. The rotation of the polarizer unit 140 is performed in synchronization with the timing at which the accumulated charge is reset. When charge accumulation is performed, the rotation of the polarizer unit 140 is stopped.

FIG. 9 shows an example of a configuration in which one polarizer unit 140 covers the photosensitive cells 12 having a larger number than the polarizers 14 included therein. In the state shown in FIG. 9, the polarizer 14A covers the photosensitive cells 12a, 12b, 12c, and 12d. Similarly, the polarizer 14B covers the photosensitive cells 12e, 12f, 12g, and 12h. The polarizer 14C covers the photosensitive cells 12i, 12j, 12k, and 12l. The polarizer 14D covers the photosensitive cells 12m, 12n, 12o, and 12p.

When the polarizer unit 140 rotates 90 ° clockwise, for example, the polarization transmission axis direction of the polarizer 14A rotates 90 °, and the polarizer 14A moves to a position covering the photosensitive cells 12e, 12f, 12g, and 12h. . The other polarizers 14B, 14C, and 14D move their positions while rotating the polarization transmission axis direction in the same manner as the polarizer 14A.

In this embodiment, since the polarizer unit 140 is rotated by 90 °, the shape of each polarizer 14 does not have to be a circle, and may be a square as shown in FIG. The number of photosensitive cells 12 covered by one polarizer 14 is not limited to four. The number of photosensitive cells 12 covered by one polarizer 14 is preferably n × n. Here, n is an integer of 2 or more. Note that n = 1 corresponds to the first embodiment.

<Imaging device>
Hereinafter, the configuration of the imaging apparatus according to the present embodiment will be described.

FIG. 10 is a block diagram illustrating a schematic configuration of the imaging apparatus according to the present embodiment.

The imaging apparatus of the present embodiment includes an imaging unit 100, a signal processing unit 200 that performs various signal processing, an imaging display unit 300 that displays an image acquired by imaging, a recording medium 400 that records image data, and each unit And a system control unit 500 for controlling the system.

The imaging unit 100 according to the present embodiment includes an imaging element (image sensor) 10 having the rotating polarizer array 160 having each configuration described above, and a photographing lens 20 for forming an image on the imaging surface of the imaging element 10. is doing. The photographic lens 20 in the present embodiment has a known configuration, and is actually a lens unit that includes a plurality of lenses. The photographing lens 20 is driven by a mechanism (not shown), and necessary operations for optical zooming, automatic exposure (AE) and automatic focus (AF) are performed as necessary.

Furthermore, the imaging unit 100 includes an imaging element driving unit 30 and a MEMS driving circuit 40 that drive the imaging element 10. The image sensor driving unit 30 is composed of, for example, a driver LSI. The image sensor drive unit 30 drives the image sensor 10 to read an analog signal from the image sensor 10 and convert it into a digital signal. The MEMS driving circuit 40 rotates the polarization transmission axis direction of the polarizer in a plane parallel to the imaging area by driving the MEMS rotating element 16 of the rotating polarizer array 160 described above.

The signal processing unit 200 in the present embodiment includes an image processing unit (image processor) 220, a memory 240, and an interface (IF) unit 260. The signal processing unit 200 is connected to a display unit 300 such as a liquid crystal display panel and a recording medium 400 such as a memory card.

The image processing unit 220 performs various signal processes necessary for operations such as color correction, resolution change, automatic exposure, automatic focus, and data compression, and executes polarization information acquisition processing according to the present invention. The image processing unit 220 is preferably realized by a combination of hardware such as a known digital signal processor (DSP) and software that executes image processing including polarization information processing according to the present invention. The memory 240 is configured by a DRAM or the like. The memory 240 records the image data obtained from the imaging unit 100 and temporarily records the image data subjected to various image processing by the image processing unit 220. These image data are converted into analog signals and then displayed on the display unit 300 or recorded on the recording medium 400 via the interface unit 260 as digital signals.

The above-described components are controlled by a system control unit 500 including a central processing unit (CPU) (not shown) and a flash memory. Note that the imaging apparatus of the present embodiment may include known components such as a viewfinder, a power source (battery), and a flashlight, but a description thereof is omitted because it is not particularly necessary for understanding the present invention.

FIG. 11 is a block diagram illustrating an example of main components of the signal processing unit 200 in the present embodiment. In this embodiment, polarization image information can be acquired from a subject and output as two types of polarization images (polarization degree image ρ and polarization phase image φ).

The signal output from the imaging unit 100 is sent to the image processing unit 220, processed by the image processing unit 220, and then stored in the polarization degree image frame memory 222 and the polarization phase image frame memory 224. Polarization degree image frame memory 222 outputs polarization degree image (ρ) data, and polarization phase image frame memory 224 outputs polarization phase image (φ) data.

<Polarization information>
FIG. 12 shows the intensity (pixel value or luminance) I ₁ to I _{4 of} light transmitted through a polarizer directed in four directions (Ψi = 0 °, 45 °, 90 °, 135 °) having different polarization transmission axes. Is shown. Here, I _i is the luminance observed when the rotation angle ψ of the polarization transmission axis is ψ _i . However, “i” is an integer from 1 to N, and “N” is the number of samples. In this embodiment, since N = 4, i = 1, 2, 3, and 4. FIG. 12 shows luminances I ₁ to I ₄ corresponding to four samples (ψ _i , I _i ) obtained from one pixel. The relationship between the polarization transmission axis angle ψi and the luminance I _i is expressed by a sine function with a period = π (180 °). There are only three unknowns in the sine function with a fixed period: amplitude, phase, and average. By observing at least three luminances I _i at different angles Ψ, one sine function curve is completely determined. The

The observed luminance with respect to the angle ψ of the polarization main axis of the polarizer unit is expressed by the following equation.

Here, as shown in FIG. 13, A, B, and C are unknown constants, and represent the amplitude, phase, and average value of the polarization luminance fluctuation curve, respectively.

In the present specification, “polarization information” means amplitude modulation degree (modulation degree) ρ and phase information φ in a sine function curve indicating the dependence of luminance on the polarization principal axis angle. When the three parameters A, B, and C of the sine function are determined for each pixel by the above processing, a polarization degree image indicating the polarization degree ρ in each pixel and a polarization phase image indicating the polarization phase φ in each pixel are obtained. The degree of polarization ρ represents the degree to which the light of the corresponding pixel is polarized, and the polarization phase φ represents the angular position that takes the maximum value of the sine function. The angle of the polarization main axis is the same between 0 ° and 180 ° (π).

The values ρ and φ (0 ≦ φ ≦ π) are calculated by the following (formula 2) and (formula 3), respectively.

Thus, in the present embodiment, polarization information can be acquired from all pixels based on the pixel signal (pixel value) to be read even if the polarization transmission axis of the polarizer is changed by driving the MEMS rotating element 16. .

The effect of the present invention can also be obtained, for example, by adopting a configuration in which light sequentially transmitted through a polarizer in which the polarization transmission axis has two different directions enters each photosensitive cell. In this case, it is not possible to specify three parameters for determining a luminance variation curve as shown in FIG. However, for example, orthogonal polarization components can be detected, which is also useful in technical fields such as endoscopes.

The imaging device and imaging apparatus of the present invention can be applied to various fields of polarization imaging technology. For example, the imaging device and imaging apparatus of the present invention are useful as key devices for security, medical care, communication, and analysis.

10 Image sensor (image sensor)
DESCRIPTION OF SYMBOLS 12 Photosensitive cell 12a-12d Photosensitive cell 12e-12p Photosensitive cell 14 Polarizer 14A-14D Polarizer 15a Electrode 15b Electrode 16 MEMS rotating element 16a Fixed part 16b Rotating part 20 Shooting lens 30 Imaging element drive part 40 Drive circuit 100 Imaging unit 120 Photosensitive cell array 140 Polarizer unit 160 Rotating polarizer array 200 Signal processing unit 220 Image processing unit (image processor)
222 Polarization image frame memory 224 Polarization phase image frame memory 226 Luminance image frame memory 240 Memory 260 Interface (IF) section 300 Imaging display section 400 Recording medium 500 System control section

Claims (7)

1. A plurality of polarizer units each including one polarizer or N polarizers (N is an integer of 2 or more) having different polarization transmission axis directions;
   A photosensitive cell array in which a plurality of photosensitive cells are arranged along the imaging surface and linearly polarized light transmitted through the polarizer is incident on each photosensitive cell;
   A MEMS rotating element that rotates the plane of polarization of linearly polarized light incident on each photosensitive cell by rotating each polarizer unit around the central axis of each polarizer unit;
   An imaging device comprising:
2. The imaging device according to claim 1, wherein each polarizer unit includes four polarizers having different polarization transmission axis directions, and each polarization transmission axis direction is different by 45 °.
3. The MEMS rotating element is configured to rotate the polarizer unit by an angle that is a multiple of 45 ° in synchronization with a timing at which charge accumulation in the photosensitive cell array is reset. The imaging device according to claim 1, wherein a polarization plane of polarized light is changed.
4. The MEMS rotating element temporarily fixes a polarization plane of linearly polarized light incident on each photosensitive cell by quiescing the polarizer unit during a period in which charge accumulation is performed in the photosensitive cell array. The imaging device according to any one of 1 to 3.
5. The imaging device according to any one of claims 1 to 4, wherein one polarizer faces one photosensitive cell during a period in which the charge accumulation is performed in the photosensitive cell array.
6. The imaging element according to claim 1, wherein the MEMS rotating element includes a rotating part that supports each polarizer unit and a fixing part that rotates the rotating part by electrostatic force.
7. A plurality of polarizer units each including one polarizer or N polarizers (N is an integer of 2 or more) having different polarization transmission axis directions, and a plurality of photosensitive cells are arranged along the imaging surface, A photosensitive cell array arranged so that linearly polarized light transmitted through the polarizer enters each photosensitive cell, and by rotating each polarizer unit around the central axis of each polarizer unit, An imaging device comprising a MEMS rotating element that rotates a polarization plane of incident linearly polarized light;
   A drive circuit for driving the MEMS rotating element;
   A photographic lens for forming an image on the image sensor;
   An imaging apparatus comprising:

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