JP2017207431A - Polarization sensor, polarization information acquisition device and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To acquire polarization information without requiring a movement of rotation of a phase plate and the like.SOLUTION: A polarization sensor 101 has: a phase adjustment unit 102 that gives a polarization component of a fast axis direction of incident light 105 and a polarization component of a slow axis direction thereof a phase difference; a light detection unit 103 that transmits polarized light having a polarization direction in one direction of the polarized light emitted from the phase adjustment unit; and a photoelectric conversion unit 104 that photoelectrically converts the polarized light transmitting the light detection unit, in which a thickness in a light advancement direction of the phase adjustment unit is equal to or less than 10 μm. Let λ be a wavelength of the incident light, and m be a natural number, an optical path length d in the fast axis direction of the phase adjustment unit satisfies a specific condition (1).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a polarization sensor capable of acquiring polarization information.

  A polarization sensor that acquires polarization information of light from an object is used for evaluating or inspecting the object. Patent Document 1 discloses a polarization imaging apparatus in which a dielectric multilayer film is laminated on a pixel. A fine periodic structure is provided in the lowermost layer of the dielectric multilayer film, and the dielectric multilayer film is laminated thereon, thereby functioning as a polarizer that transmits polarized light according to the periodic direction of the fine periodic structure. Thereby, polarization information such as the polarization state and light intensity of incident light can be acquired two-dimensionally.

  Patent Document 2 discloses a polarization conversion device that changes the polarization state of incident light to an arbitrary polarization state. Specifically, a λ / 2 plate and a λ / 4 plate, which are phase plates, are arranged in series, and each is rotated so that a desired polarization state can be reproduced.

Japanese Patent No. 4974543 JP 2005-221620 A

  However, in the polarization imaging apparatus disclosed in Patent Document 1, since the polarizer transmits only linearly polarized light, the amount of phase difference when incident light is divided into orthogonal polarization cannot be detected. Further, in the polarization conversion device disclosed in Patent Document 2, since it is necessary to rotate the phase plate, it takes time to reproduce a desired polarization state.

  The present invention provides a polarization sensor capable of acquiring information on the light intensity and phase of polarized light without requiring driving such as rotation of a phase plate, and further improving the detection accuracy of linearly polarized light. An imaging device used is provided.

  The polarization sensor as one aspect of the present invention acquires polarization information of incident light. The polarization sensor includes a phase adjustment unit that gives a phase difference between a polarization component in a fast axis direction and a polarization component in a slow axis direction of incident light, and a polarization direction in one direction of polarized light emitted from the phase adjustment unit. And a photoelectric conversion unit that photoelectrically converts the polarized light that has passed through the light detection unit. When the thickness of the phase adjusting unit in the light traveling direction is 10 μm or less, λ is the wavelength of the incident light, and m is a natural number, the optical path length d in the fast axis direction of the phase adjusting unit is The condition shown in (1) is satisfied.

  The polarization information acquisition device including the polarization sensor and the imaging device including the polarization information acquisition device also constitute another aspect of the present invention.

  According to the present invention, polarization information such as the light intensity and phase of polarized light can be acquired in a lump without requiring movement such as rotation of the phase plate, and linearly polarized light can be detected with high detection accuracy. A polarization sensor and a device using the same can be realized.

The figure which shows the structure of the polarization sensor which is an Example of this invention. The figure which shows the linearly polarized light which injects into a phase adjustment part. The figure which shows the propagation of the light before a phase difference is given in a phase adjustment part. The figure which shows the left circularly polarized light radiate | emitted from a phase adjustment part. The figure which shows the propagation of the light after a phase difference is given in the phase adjustment part. The figure which shows the vibration of a linearly polarized light. The figure which shows the propagation of linearly polarized light. The figure which shows 1 set of phase adjustment area | regions of the phase adjustment part in an Example. FIG. 3 is a diagram showing the amplitude transmittance of the λ / 4 plate in Example 1. The figure which shows the polarization state in the conventional (lambda) / 4 board. FIG. 3 is a diagram showing a polarization state on a λ / 4 plate in Example 1. FIG. 6 is a diagram showing the amplitude transmittance of a λ / 2 plate in Example 2. The figure which shows the polarization state in the conventional (lambda) / 2 board. FIG. 6 is a diagram showing a polarization state on a λ / 2 plate in Example 2. FIG. 9 is a diagram showing polarization detection when the phase adjustment unit shown in FIG. 8 is configured as a conventional phase plate. The figure which shows the polarization detection when the phase adjustment part shown in FIG. 8 is comprised as a phase plate of an Example. The figure which shows the amplitude transmittance | permeability of (lambda) / 4 board in the wavelength range different from the wavelength range shown in FIG. The figure which shows the fine periodic structure which has the structure anisotropy in Example 1, 2, and its refractive index. FIG. 6 is a diagram illustrating a configuration of a digital camera that is Embodiment 3 of the present invention.

Embodiments of the present invention will be described below with reference to the drawings.
First, prior to the description of a specific embodiment to be described later, the premise items of the embodiment will be described. In the embodiment, the wavelength used (λ of incident light: also referred to as incident wavelength) λ is mainly the wavelength of visible light or near infrared light. FIG. 1 schematically shows a configuration of a polarization sensor (hereinafter simply referred to as a sensor) according to an embodiment. The sensor 101 includes a phase adjustment unit 102, a light detection unit 103, a photoelectric conversion unit 104, and a substrate (not shown) in order from the incident side of the incident light 105. The incident light 105 is light in which polarized light in various polarization directions is mixed, and the sensor 101 is configured to acquire polarization information such as light intensity for each polarization direction. Reference numeral 120 denotes a calculation unit configured by a microcomputer (CPU, MPU, etc.) or a personal computer, and calculates polarization information using an output from the sensor 101 (photoelectric conversion unit 104). The sensor 101 and the calculation unit 120 constitute a polarization information acquisition device.

  The phase adjustment unit 102 has a phase adjustment function that divides incident linearly polarized light into two orthogonally polarized lights and changes the phase difference between the polarized lights (gives a phase difference between the polarized lights). For example, when the phase adjustment unit 102 is configured as a λ / 4 plate as a phase plate, linearly polarized light incident on the phase adjustment unit 102 is converted into circularly polarized light by passing through it. In FIG. 2, as shown in FIG. 3, light 201 and 202 that enter the phase adjustment unit 102 while oscillating in the x-axis direction and the y-axis direction with a phase difference of 0 are obtained by combining these lights 201 and 202. Linearly polarized light 203 is shown. The vibration direction of the linearly polarized light 203 is 45 ° with respect to the x-axis. In FIG. 4, the phase adjustment unit 102 gives a phase difference of π / 2 (90 °) as shown in FIG. 5, and is emitted from the phase adjustment unit 102 while vibrating in the x-axis direction and the y-axis direction. 401 and 402, and circularly polarized light (left circularly polarized light) 403 obtained by combining these lights 401 and 402 are shown.

  The light analysis unit 103 is configured by a polarizing plate that transmits only linearly polarized light that vibrates in one direction among incident light. Polarized light that vibrates in a direction different from the transmitted polarized light is reflected or absorbed. The linearly polarized light emitted from the light detection unit 103 is converted into an electric signal by the photoelectric conversion unit 104.

  The sensor 101 is divided into a plurality of pixels arranged one-dimensionally or two-dimensionally within the unit region, and can calculate (acquire) polarization information of the incident light 105 from an electric signal output for each pixel. it can.

  Here, the light incident on one pixel of the phase adjustment unit 102 (here, assumed to be configured as a λ / 4 plate) is the linearly polarized light 203 shown in FIG. 3, and the light emitted from the pixel is shown in FIG. The case of the left circularly polarized light 403 shown in FIG. When the light analyzer 103 transmits only linearly polarized light that vibrates in the y-axis direction, both the linearly polarized light 203 and the left circularly polarized light 403 are light having the same size and vibrating in the y-axis direction. The linearly polarized light 203 and the left circularly polarized light 403 are out of phase by π / 2. However, since the general photoelectric conversion element 104 cannot acquire phase information, only the intensity of incident light is recorded. Cannot be separated into circularly polarized light and linearly polarized light.

  Therefore, in the embodiment, the thickness of the phase adjusting unit 102 in the light traveling direction (light transmission direction) is set to 10 μm or less. If the thickness of the phase adjustment unit 102 is 10 μm or less, the light incident on the phase adjustment unit 102 interferes in the phase adjustment unit 102, and thus the emitted polarized light becomes light affected by the interference. In the embodiment, the optical path length d in the fast axis direction of the phase adjusting unit 102 satisfies the condition expressed by the following formula (1).

However, (lambda) is a use wavelength and m is a natural number. When this condition is satisfied, the transmittance of the light of the wavelength λ used that vibrates along the fast axis of the phase adjustment unit 102 in the phase adjustment unit 102 has a maximum value or a minimum value due to interference in the phase adjustment unit 102. Have. Further, when the phase adjusting unit 102 is configured as a λ / 4 plate or a λ / 2 plate, the light oscillating along the slow axis of the phase adjusting unit 102 also has a maximum value or a minimum value in the transmittance. . By utilizing this, it is possible to give an amplitude intensity difference to the light that passes through the phase adjusting unit 102 and vibrates in the fast axis direction and the slow axis direction.

  Examples (simulation results) will be described below with specific numerical examples. Here, the use wavelength λ is 550 nm.

  First, the case where the refractive index in the fast axis direction of one pixel of the phase adjusting unit 102 is 1.08, the refractive index in the slow axis direction is 1.34, and the physical thickness is 515 nm will be described. Here, light is incident on the phase adjustment unit 102 from the air, and the refractive index of the substrate constituting the phase adjustment unit 102 is 1.53. At this time, the phase adjustment unit 102 functions as a λ / 4 plate for light having a working wavelength of 550 nm, depending on the refractive index difference and the thickness. The optical path length d in the fast axis direction is 556 nm, and when m is 4, the condition of the formula (1) is satisfied.

  FIG. 9 shows the amplitude transmittance with respect to the wavelength in the fast axis direction and the slow axis direction at this time. A solid line indicates the amplitude transmittance in the fast axis direction, and a broken line indicates the amplitude transmittance in the slow axis direction. In order to satisfy the condition of Formula (1), the amplitude transmittance in the fast axis direction has a minimum value at a wavelength of 550 nm. On the other hand, since the phase adjustment unit 102 functions as a λ / 4 plate, the amplitude transmittance in the slow axis direction also has a maximum value. The difference in transmittance was 10%, which is the difference between 90% and 80% at a wavelength of 550 nm. FIGS. 10 and 11 schematically show the state of polarization in the phase adjustment unit 102 functioning as such a λ / 4 plate.

  FIG. 10 shows the polarization state on the conventional λ / 4 plate, and FIG. 11 shows the polarization state on the λ / 4 plate in this embodiment. In these figures, 1000 and 1100 indicate the polarization state of light incident on the λ / 4 plate, and 1010 and 1110 indicate the polarization state of light emitted from the λ / 4 plate. Reference numerals 1001 and 1101 denote light oscillating in the x-axis direction among incident light, and reference numerals 1002 and 1102 denote light oscillating in the y-axis direction among incident light. Reference numerals 1003 and 1103 denote linearly polarized light incident on the λ / 4 plate. Reference numerals 1004 and 1104 denote light that oscillates in the x-axis direction among the emitted light, and reference numerals 1005 and 1105 denote light that oscillates in the y-axis direction among the emitted light. Reference numerals 1006 and 1106 denote circularly polarized light (left circularly polarized light) emitted from the λ / 4 plate.

  The λ / 4 plate converts linearly polarized light into circularly polarized light when incident. When the y-axis is the slow axis, the incident linearly polarized light 1003 and 1103 is converted to left circularly polarized light 1006 and 1106 which is counterclockwise circularly polarized light. In the conventional λ / 4 plate, the outgoing circularly polarized light 1006 becomes left circularly polarized light because there is little difference in amplitude transmittance between the x-axis direction and the y-axis direction. On the other hand, the phase adjustment unit 102 in this embodiment can give a large difference between the amplitude transmittances in the x-axis direction and the y-axis direction as shown in FIG. 9, and thus the circularly polarized light 1106 has a difference in amplitude intensity. It becomes elliptically polarized light.

  When the circularly polarized light 1006 is made incident on the light detection unit 103 made of a polarizing plate that transmits only linearly polarized light, there is no difference in intensity regardless of which direction of linearly polarized light is transmitted. Since the scraping phenomenon is the same as when unpolarized light is incident, it is difficult to detect the polarization state of incident light from linearly polarized light. On the other hand, when the elliptically polarized light 1106 is incident on the light detection unit 103, an intensity difference is generated between linearly polarized light whose polarization direction is the x-axis direction and linearly polarized light whose polarization direction is the y-axis direction. For this reason, it is possible to easily detect that the incident light is the linearly polarized light 1103 from the intensity difference between the linearly polarized light emitted from the light detecting unit 103.

Next, a case where the refractive index in the fast axis direction of one pixel of the phase adjustment unit 102 is 1.34, the refractive index in the slow axis direction is 1.85, and the physical thickness is 515 nm will be described. Also in the following description, it is assumed that light enters the pixel from the air, and the refractive index of the substrate constituting the phase adjustment unit 102 is 1.53. At this time, the pixel of the phase adjustment unit 102 functions as a λ / 2 plate with respect to light having a working wavelength of 550 nm, depending on the refractive index difference and the thickness. The optical path length d in the fast axis direction is 690 nm, and when m is 5, the condition of the formula (1) is satisfied.

  FIG. 12 shows the amplitude transmittance with respect to the wavelength in the fast axis direction and the slow axis direction at this time. A solid line indicates the amplitude transmittance in the fast axis direction, and a broken line indicates the amplitude transmittance in the slow axis direction. In order to satisfy the condition of formula (1), the amplitude transmittance in the fast axis direction has a maximum value at a wavelength of 550 nm. On the other hand, since the phase adjusting unit 102 functions as a λ / 2 plate, the amplitude transmittance in the slow axis direction also has a minimum value. The difference in transmittance was 30%, which is the difference between 92% and 62% at a wavelength of 550 nm. FIG. 13 and FIG. 14 schematically show the state of polarization in the phase adjustment unit 102 functioning as such a λ / 2 plate.

  FIG. 13 shows the polarization state on the conventional λ / 2 plate, and FIG. 14 shows the polarization state on the λ / 2 plate in the second embodiment. In these drawings, 1300 and 1400 indicate polarization states of light incident on the λ / 2 plate, and 1310 and 1410 indicate polarization states of light emitted from the λ / 2 plate. Reference numerals 1301 and 1401 denote light oscillating in the x-axis direction among incident light, and reference numerals 1302 and 1402 denote light oscillating in the y-axis direction among incident light. Reference numerals 1303 and 1403 denote linearly polarized light incident on the λ / 2 plate. Reference numerals 1304 and 1404 denote light that oscillates in the x-axis direction, and 1305 and 1405 denote light that oscillates in the y-axis direction. Reference numerals 1306 and 1406 denote linearly polarized light emitted from the λ / 4 plate.

  The λ / 2 plate converts linearly polarized light having a different polarization direction when linearly polarized light is incident. When the y-axis is the slow axis, the incident clockwise linearly polarized light 1303 and 1403 is converted into counterclockwise linearly polarized light 1306 and 1406. In the conventional λ / 2 plate, the emitted linearly polarized light 1306 becomes light that vibrates in the 45-degree direction with respect to the x-axis because there is little difference in amplitude transmittance between the x-axis direction and the y-axis direction. On the other hand, the phase adjustment unit 102 in this embodiment can give a large difference in the amplitude transmittance in the x-axis direction and the y-axis direction as shown in FIG. Vibrate in the direction of 34 degrees.

  Thus, when the amplitude transmittance is adjusted, the amplitude intensity can be adjusted in addition to the phase adjustment by a general phase plate. This makes it possible to identify the incident polarized light 105 by taking into account not only the polarization rotation by simple phase adjustment but also the intensity modulation, and the detection accuracy can be improved.

  In this embodiment, in order to efficiently detect polarized light, the phase adjustment unit 102 has a plurality of phase adjustment amounts (that is, phase differences) and phase adjustment directions (that is, slow axis directions) that are different from each other. It is comprised so that the area | region may be included.

  For example, a case where one pixel of the phase adjustment unit 102 is configured as a λ / 2 plate having a slow axis in the y-axis direction will be described. FIGS. 6 and 7 show the state of polarized light emitted when the incident light is the linearly polarized light 203 shown in FIG. Reference numeral 601 denotes light that vibrates in the x-axis direction, and reference numeral 602 denotes light that vibrates in the y-axis direction. Reference numeral 603 denotes linearly polarized light. Of the light emitted from the pixels of the phase adjustment unit 102, the phase of the light oscillating in the y-axis direction is shifted by π (180 °). For this reason, the phase of the light 602 oscillating in the y-axis direction of the outgoing light is shifted by π from the light 202 oscillating in the y-axis direction of the incident light. Therefore, the linearly polarized light 603 is generated by combining the light 601 that vibrates in the x-axis direction and the light 602 that vibrates in the y-axis direction.

  Thus, when the phase adjustment amount in the phase adjustment unit 102 is different, the type of polarized light that is emitted differs from the type of incident polarized light (linearly polarized light, circularly polarized light, etc.). When the light analyzing unit 103 is composed of a polarizing plate that transmits only light that vibrates in the direction of 45 degrees with respect to the x axis, the linearly polarized light 203 incident on the phase adjusting unit 102 and the phase adjusting unit 102 emit light. Thus, there is a large difference in transmission intensity with the linearly polarized light 603 that passes through the light detection unit 103. This polarization intensity difference makes it possible to detect the polarization state of incident light.

  FIG. 8 shows a configuration example of a phase adjustment unit 800 in which a plurality of pixels (phase adjustment regions) of the phase adjustment unit 102 having the characteristics described with reference to FIGS. 9 and 12 are combined. In this example, the phase adjustment unit 800 is provided with a plurality (four in this case) of regions 801 to 804 in which at least one of the phase adjustment amount and the phase adjustment direction is different. Reference numerals 805 to 808 denote the direction of the slow axis in these regions 801 to 804. Further, the regions 801 and 802 having the slow axes 805 and 806 indicated by the one-dot chain line function as λ / 4 plates, and the regions 803 and 804 having the slow axes 807 and 808 indicated by the dotted lines are λ / 2. Functions as a board. A region 801 is a λ / 4 plate region having a slow axis in the direction of 135 degrees with respect to the a axis, and a region 802 is a λ / 4 plate region having a slow axis in the direction of 45 degrees with respect to the a axis. On the other hand, the region 803 is a λ / 2 plate region having a slow axis in the direction of 45 degrees with respect to the a axis, and the region 804 is a λ / 2 plate region having a slow axis in the direction of 135 degrees with respect to the a axis. is there.

  Even if the same polarized light enters these regions 801 to 804, the polarization state of the emitted light is different. For example, when light oscillating in the b-axis direction is incident, the light emitted from the region 801 is left circularly polarized light, and the light emitted from the region 802 is right circularly polarized light. Further, the light emitted from the regions 803 and 804 is linearly polarized light that vibrates in the a-axis direction. Thus, even when the same light is incident, by using the phase adjusting unit 800 that changes the polarization state of the emitted light for each incident region, the light detecting unit 103 is a polarizing plate that transmits uniform polarized light. When configured, polarized light having different intensities from the respective regions can be detected.

  Examples of polarization detection are shown in FIGS. 15 and 16. FIG. 15 shows an example of polarization detection when a conventional phase adjustment unit that functions as a phase plate with a small amount of anisotropy is used. On the other hand, FIG. 16 shows an example of polarization detection when the phase adjustment unit 800 of the present embodiment is used. In these figures, the types of polarized light (incident polarized light) incident on the phase adjustment unit (longitudinal polarized light, lateral polarized light, left circularly polarized light, right circularly polarized light, 45 degree polarized light, and 135 degree polarized light) are shown in FIG. The type of polarized light (outgoing polarized light) emitted from the regions 801 to 804 is shown. In addition, the amplitude intensity of the polarized light emitted from the regions 801 to 804 when 100% of the polarized light in the b-axis direction is transmitted by the analyzer is shown. The amplitude of the incident polarization is shown below the type of incident polarization. The outgoing polarized light from the regions 801 to 804 is shown in association with the positions of the regions 801 to 804 shown in FIG. In addition, since the numerical values shown in these figures are amplitudes, they are the square root of the intensity acquired by the photoelectric conversion unit 104.

  The computing unit 120 calculates the correlation value of the amplitude intensity of the output polarized light from the regions 801 to 804 using outputs from the plurality of pixels of the sensor 101 (photoelectric conversion unit 104) corresponding to each of the regions 801 to 804. The polarization information of the incident polarized light can be calculated from the correlation value. When the same incident polarized light enters the regions 801 to 804, the polarization state of the outgoing polarized light differs in the regions 801 to 804. The light analyzing unit 103 is composed of a polarizing plate, and basically only extracts the amplitude intensity of linearly polarized light having a certain direction as a polarization direction. When the photoelectric conversion unit 104 is configured by a conventional photodiode or the like, the exposure time for performing photoelectric conversion is very long with respect to the frequency of light. In such a photoelectric conversion unit 104, the incident light is integrated within the exposure time, and thus it is not possible to acquire information on the phase amount (phase difference) between polarized light in the incident light.

  Therefore, the calculation unit 120 calculates the polarization information of the incident polarized light from the correlation value of the amplitude intensity of the output polarized light from the regions 801 to 804. Specifically, the computing unit 120 calculates the vibration direction and the light intensity of the incident polarized light from the correlation value of the amplitude intensity of the polarized light transmitted through the light analyzing unit 103. Further, the phase amount of the incident polarized light is also calculated by correlating the amplitude intensity of the outgoing polarized light from the regions 801 to 804 having different phase adjustment amounts. Thus, in this embodiment, information on the phase amount of incident polarized light (phase information) can also be acquired. The polarization information referred to in this embodiment includes the vibration direction, light intensity, and phase information.

  In the example shown in FIGS. 15 and 16, when the incident polarized light is longitudinally polarized light, laterally polarized light, right circularly polarized light, and left circularly polarized light, the correlation of the amplitude intensity of the polarized light emitted from the regions 801 to 804 is different. For example, when the incident polarized light is longitudinally polarized light, the amplitude intensity of the outgoing polarized light from the areas 801 and 802 is the same, and the amplitude intensity of the outgoing polarized light from the areas 803 and 804 is the same with a smaller intensity. The polarization state of the incident polarized light can be detected from the correlation of the amplitude intensity of the emitted polarized light from the regions 801 to 804.

  However, since the difference in refractive index in the phase adjusting unit functioning as the conventional phase plate shown in FIG. 15 is small, there is almost no influence on the amplitude of the outgoing polarized light. Therefore, for example, even if 45-degree polarized light that oscillates in the 45-degree direction and 134-degree polarized light that oscillates in the 135-degree direction with respect to the a-axis direction are incident, no modulation is performed in the regions 801 to 804. For this reason, even if the polarized light in the b-axis direction is analyzed, the same intensity is obtained without causing an amplitude intensity difference. On the other hand, in the phase adjustment unit 800 of this embodiment shown in FIG. 16, the amplitude intensity difference as shown in FIGS. 9 and 12 occurs. For this reason, an amplitude intensity difference corresponding to the vibration direction is generated. In contrast to the 45-degree polarized light and 135-polarized light as the incident polarized light, there is no change in the output of the output polarized light from the regions 801 to 804 in the light detection unit 103 in FIG. 15, but in FIG. There is a change in the output of the polarized light detector 103. For this reason, it is possible to separate 45-degree polarized light and 135-degree polarized light, which was impossible even by using a conventional phase adjusting unit. Thus, the detection accuracy of linearly polarized light can be improved by using the phase adjustment unit 800 of the present embodiment.

  Further, the refractive index of the base material adjacent to the phase adjustment unit 102 and through which the light entering or exiting from the phase adjustment unit 102 is transmitted is the refractive index in the fast axis direction of the phase adjustment unit 102 and the slow axis direction. It is desirable that the refractive index be in the middle of the refractive index at. Example 2 satisfies the condition. By satisfying this condition, the difference in amplitude transmittance can be increased as shown in FIG. Since the difference in amplitude transmittance can be increased as compared with the case shown in FIG. 9 that does not satisfy this condition, the detection accuracy of polarized light can be further improved.

  Further, when the set of the plurality of regions 801 to 804 shown in FIG. 8 is referred to as a set of phase adjustment regions (800), the set of phase adjustment regions 800 is used as the phase adjustment unit 102 of the sensor 101 shown in FIG. It is desirable to use one periodically arranged in a two-dimensional direction. The sensor 101 can detect an in-plane polarization distribution by periodically arranging a pair of phase adjustment regions including regions 801 to 804 for performing different phase adjustments in a two-dimensional direction.

  Further, it is desirable that the calculation unit 120 performs electronic intensity correction on the polarization information (amplitude intensity) acquired by the sensor 101 according to the polarization direction. In the example shown in FIG. 16, the maximum amplitude detected by the light detection unit 103 when the incident polarized light is longitudinally polarized light is 6.0, whereas the maximum amplitude when the incident polarized light is right circularly polarized light. Is 12.0. On the other hand, the amplitude of incident polarized light is 10 for both. The detected amplitude intensity varies depending on the phase adjustment direction of the regions 801 to 804. For this reason, the detected amplitude intensity varies greatly depending on the type of incident polarized light. Therefore, by performing electronic intensity correction on the detected amplitude intensity, it is possible to obtain the converted amplitude intensity when the incident polarized light is circularly polarized light when the incident polarized light is longitudinally polarized light. The electronic intensity correction can be calculated according to the reflectance characteristics of the phase plate used in the phase adjustment unit 102 and the direction of the slow axis.

Further, the difference between the refractive index in the fast axis or slow axis direction of one region of the phase adjustment unit 800 and the refractive index in the fast axis or slow axis direction of another region adjacent to the one region is , 0.1 or less is desirable. For example, the difference between the refractive index n _TM for the TM wave in the region 801 and the refractive index n _TE for the TE wave in the region 803 is 0.01. When this condition is satisfied, the polarization component that vibrates in the slow axis direction of the region 801 and the fast axis of the region 803 when the polarized light is transmitted through the phase adjusting unit 102 are small. There is little difference in transmittance from the polarization component that vibrates in the direction. This makes it easier to compare the output between the regions 801 to 804 when performing electronic intensity correction.

  Moreover, when calculating the polarization information using the output from the sensor 101, the calculation unit 120 preferably changes the calculation method of the polarization intensity and the phase amount between the polarizations for each wavelength. As shown in FIGS. 9 and 12, the amplitude transmittance characteristic of the phase adjustment unit 102 changes depending on the wavelength. For example, FIG. 17 shows amplitude transmittance in a wavelength region different from the wavelength region shown in FIG. The relationship between the amplitude transmittance in the slow axis direction and the fast axis direction is reversed, and the absolute value of each changes. As described above, since the characteristics of the phase plate change depending on the wavelength, the polarization of incident polarized light can be accurately changed by changing the calculation method of the intensity of polarized light and the phase amount between polarized lights according to the amplitude transmittance at each wavelength. The state can be detected.

Furthermore, it is desirable that the phase adjustment unit 102 has a fine periodic structure finer than the wavelength of visible light. In a structure finer than the wavelength of incident visible light, it is known that the light behaves as if it was incident on a homogeneous medium without recognizing the structure. Such a phenomenon is called structural anisotropy, and light behaves in accordance with the structure interval, material filling rate, and refractive index. An example of structural anisotropy is shown in FIG. In a rectangular lattice [filling rate f = a / (a + b)] in which two media having a refractive index of n1, n2 and a width ratio of a: b are repeatedly arranged, the refractive index in the direction parallel to the lattice is n _{// Assuming} that the refractive index in the direction orthogonal to the grating is n _⊥ , n _// and n _⊥ are expressed by equations (2) and (3), respectively.

  Thus, the apparent refractive index can be changed by changing the structure depending on the direction.

_TiO 2 with _(n 1 = 2.335) in the structure of the width a, showing the effective refractive index n _// for filling rate when using the air to the structure b of width b, and n _⊥ in FIG 18 (B) . The solid line indicates n _// and the broken line indicates n _⊥ . When filling factor _{f = 0.17, n // = 1.34} , the n _⊥ = 1.08. On the other hand, when the filling rate f = 0.52, n _// = 1.85 and n _⊥ = 1.34. Thus, by using a structure finer than the wavelength, very large anisotropy can be obtained.

  As another means for obtaining such anisotropy, there is a method using a crystalline material having high anisotropy. For example, calcite or titanium dioxide crystals can be used. However, it is difficult to cut out such a crystal with various orientations in the plane like the phase adjusting unit 800 shown in FIG. For this reason, it is desirable to use the structural anisotropy by the fine periodic structure as shown in FIG.

  Various methods are known for manufacturing an element having a fine periodic structure. For example, formation and transfer of a mask pattern using two-beam interference and injection molding using nanoimprinting can be mentioned. The element having the fine periodic structure described in this embodiment is not limited to these manufacturing methods, and can be manufactured by various methods.

  When the transmittances in the fast axis and slow axis directions of the phase adjustment unit 102 (800) are A and B, respectively, the angle α of the polarization axis of the light detection unit 103 with respect to the slow axis direction is as follows: It is desirable to satisfy the condition shown in Formula (4).

In the present embodiment, as described above, the polarization is detected using the difference in transmittance between the fast axis direction and the slow axis direction of the phase adjustment unit 102 (800). This is because the polarization rotation based on the amplitude intensity ratio is added in addition to the polarization rotation by the phase plate. For this reason, the light detection rate in the light detection part 103 improves more by making it the arrangement | positioning which satisfy | fills the conditions of Formula (4) rather than the arrangement | positioning which assumed using the conventional phase plate. Thereby, the detection accuracy of polarized light can be further improved.

  FIG. 19 shows a digital camera that is an image pickup apparatus according to a third embodiment of the present invention including the polarization information acquisition apparatus (the sensor 101 and the calculation unit 120) described in the first or second embodiment.

  Reference numeral 1900 denotes a camera body, and 1901 denotes an imaging optical system. Reference numeral 1902 denotes an image sensor corresponding to the sensor 101 described in the first embodiment built in the camera body 1900, and receives an object image formed by the image pickup optical system 1901. The arithmetic unit 120 may be provided integrally with the image sensor 1902 or may be provided as part of an arithmetic processing unit (not shown) built in the camera body 1900. Reference numeral 1903 denotes a memory that records information corresponding to a subject image photoelectrically converted by the image sensor 1902, and 1904 denotes a display device provided on the back of the camera body 1900.

  By using the sensor 101 described in the first embodiment, the polarization state of the subject image formed by the imaging optical system 1901 can be detected with high accuracy.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

101 Polarization sensor 102 Phase adjustment unit 103 Light detection unit 104 Photoelectric conversion unit

Claims (11)

A polarization sensor that acquires polarization information of incident light,
A phase adjustment unit that gives a phase difference between the polarization component in the fast axis direction and the polarization component in the slow axis direction of the incident light;
An analyzer that transmits polarized light having a polarization direction in one direction out of the polarized light emitted from the phase adjustment unit;
A photoelectric conversion unit that photoelectrically converts the polarized light transmitted through the light detection unit;
The thickness of the phase adjusting unit in the light traveling direction is 10 μm or less,
And λ is the wavelength of the incident light, and m is a natural number, the optical path length d in the fast axis direction of the phase adjusting unit is

A polarization sensor characterized by satisfying the following conditions.   The polarization sensor according to claim 1, wherein the phase adjustment unit includes a plurality of regions in which at least one of the phase difference and the slow axis direction is different from each other.   Among the plurality of regions in the phase adjustment unit, the refractive index in the fast axis or slow axis direction of one region and the fast axis or slow axis direction of another region adjacent to the one region The polarization sensor according to claim 2, wherein a difference between the refractive index and the refractive index is 0.1 or less.   4. The polarization sensor according to claim 2, wherein the phase adjusting unit is configured such that when the plurality of regions are set as one set, the set is periodically arranged. 5.   5. The polarization sensor according to claim 1, wherein the phase adjustment unit has a periodic structure finer than a wavelength of visible light as the incident light. Adjacent to the phase adjustment unit, and having a base material through which light incident on the phase adjustment unit or emitted from the phase adjustment unit is transmitted,
The refractive index of the base material is an intermediate refractive index between the refractive index in the fast axis direction and the refractive index in the slow axis direction of the phase adjusting unit. The polarization sensor according to claim 1. When the transmittances in the fast axis direction and the slow axis direction of the phase adjusting unit are respectively A and B,
The angle α of the polarization axis of the analyzer with respect to the slow axis direction of the phase adjuster is

The polarization sensor according to claim 1, wherein the following condition is satisfied. The polarization sensor according to claim 1, comprising a plurality of pixels,
An operation for calculating a correlation value of polarization intensity in the incident light using outputs from the plurality of pixels, and calculating a phase difference between polarizations oscillating in a direction orthogonal to the polarization intensity from the correlation value. A polarization information acquisition apparatus characterized by comprising a unit.   The polarization information acquisition apparatus according to claim 8, wherein the calculation unit changes a method of calculating the intensity of the polarized light and a phase difference between the polarized lights for each wavelength of the incident light.   The polarization information acquisition apparatus according to claim 8 or 9, wherein the arithmetic unit performs electronic intensity correction on the intensity of the polarized light according to a polarization direction of the polarized light. The polarization information acquisition device according to any one of claims 8 to 10,
An image pickup apparatus that picks up a subject image using the polarization sensor.