Imaging device and imaging method

Abstract

To obtain a high-quality hologram image / reconstruction image by improving utilization efficiency of light.SOLUTION: An imaging device comprises: a first polarizing plate which converts an incoherent light wave into linearly polarized light; a polarizing beam splitter which divides the light wave passing through the first polarizing plate into the first divided light and the second divided light in the polarization direction; first and second mirrors having the mutually-different curvatures; first and second 1 / 4 wavelength plates which are arranged between the polarizing beam splitter and the first and second mirrors; and a third 1 / 4 wavelength plate which converts the first divided light reflected by the first mirror and the second divided light reflected by the second mirror into the circularly polarized light. The imaging device images the first divided light and the second divided light passing through the third 1 / 4 wavelength plate via the polarizing plate and simultaneously acquires a plurality of interference fringes.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an imaging device and an imaging method, and more particularly to an imaging device and an imaging method for incoherent digital holography. [Background technology]

[0002] Incoherent digital holography is being investigated as a method for acquiring 3D information without using special lighting such as lasers. Incoherent object light from a subject is split into two optical paths, and a concave mirror or lens is placed in one of the optical paths to create a slight optical path difference. These lights are then combined and interfered with, capturing the subject as interference fringes. By acquiring and calculating multiple interference fringe images (holograms) with different phases, complex amplitude information of the subject on the image sensor surface can be obtained. By performing backpropagation calculations of light from this complex amplitude information, a 2D image at any depth distance, i.e., 3D image information, can be obtained.

[0003] To capture moving images containing three-dimensional information, it is necessary to acquire the complex amplitude information of the subject for each frame, and to do so, it is necessary to simultaneously acquire interference fringes of different phases, for example.As a method for this, a method has been proposed in which polarization is used to simultaneously generate and acquire interference fringe images of different phases (Patent Document 1, Non-Patent Document 1).

[0004] Figures 7 and 8 show examples of conventional incoherent digital holography imaging devices. The imaging device in Figure 7 is configured with an optical system using a birefringent lens. Object light from subject 1 passes through lens 2 and wavelength filter 3, and polarizer 4 filters out only linearly polarized components in a desired direction. Birefringent lens 5 is provided with different focal lengths for polarization directions that are ±45° from this polarization direction. The object light passing through birefringent lens 5 is converted into clockwise and counterclockwise circularly polarized light by quarter-wave plate 6. This light is captured by polarization camera 20, in which polarizers are provided at 45° intervals for each pixel, and images for each polarization direction (images constructed by aggregating pixel data for each polarization direction) are generated, allowing interference fringe images with different phases to be simultaneously acquired. Complex amplitude information is obtained from these interference fringe images, and a reconstructed image at any depth can be obtained by performing a light backpropagation calculation. It has been reported that this optical system can capture video at a frame rate of 25 fps (Non-Patent Document 1).

[0005] On the other hand, an optical system using a reflective liquid crystal panel instead of a birefringent lens has also been proposed, as shown in Figure 8. Object light from a subject 1 becomes a linearly polarized light wave after passing through a lens 2, a wavelength filter 3, and a polarizing plate 4. This linearly polarized light is incident on a reflective liquid crystal panel 8 via a beam splitter (BS) 7. The reflective liquid crystal panel 8 imparts a different spherical phase distribution to the polarization directions that are ±45° from the original polarization direction.

[0006] The object light reflected by the reflective liquid crystal panel 8 and the beam splitter (BS) 7 passes through the quarter-wave plate 9 to become right- and left-handed circularly polarized light, which is then split into four directions by the diffraction grating 21 (since FIG. 8 is a plan view, only two directions of light are depicted, but in reality, the light is diffracted in four directions). Note that this diffraction grating 21 may be, for example, a checkered diffraction grating in which two types of phase objects (objects that change only the phase of light) are arranged in a checkered pattern. Due to its periodic structure, a checkered diffraction grating (phase grating) can diffract light in four directions (up, down, left, and right), which has the effect of propagating light of the same quality as the incident light in four directions.

[0007] Next, the light waves diffracted in four directions are incident on the polarizing plate array 22. FIG. 9 shows an example of the transmission axes of the polarizing plate array 22. The polarizing plate array 22 is composed of, for example, four types (four regions) of linear polarizers with transmission axes at 0°, 45°, 90°, and 135°. When the polarizers are installed so that their transmission axes form an angle of η with respect to the x-axis, right-handed circularly polarized light and left-handed circularly polarized light undergo a phase shift of +η and −η, respectively, and are output from the linear polarizer as two linearly polarized lights with the same polarization state but a relative phase difference of 2η. In other words, different phase shifts of 0, π / 2, π, and 3π / 2 [rad] are imparted to each pair of linearly polarized light in each region depending on the angle of the transmission axis of the linear polarizer.

[0008] Interference fringe images with different phases can be obtained simultaneously by using cameras 23 and 24 (actually, four cameras) to capture pairs of linearly polarized light that have passed through the polarizer array 22. Complex amplitude information is obtained from these interference fringe images, and a reconstructed image at any depth distance can be obtained by performing a backpropagation calculation of light (Patent Document 1).

[0009] The imaging device of Figure 8 is capable of simultaneously acquiring interference fringes in the same way as Figure 7 by capturing the object light after it has passed through the quarter-wave plate 9 using the polarizing plate array 22 and cameras 23 and 24. Furthermore, this method can acquire interference fringes in each polarization direction with high resolution, so the resolution of the interference fringe image is twice as high in both the vertical and horizontal directions as that of Figure 7. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent Publication No. 2021-131457 [Non-patent literature]

[0011] [Non-Patent Document 1] KiHong Choi, Kyung-Il Joo, Tae-Hyun Lee, Hak-Rin Kim, Junkyu Yim, Hyeongkyu Do, and Sung-Wook Min, “Compact self-interference incoherent digital holographic camera system with real-time operation,” Optics Express, Vol. 27, No 4, pp. 4818-4833, (2019) Summary of the Invention [Problem to be solved by the invention]

[0012] The optical system of the imaging device shown in Figure 7 uses a birefringent lens 5. However, when constructing a lens from a birefringent material, it is difficult to obtain a material large enough to form a lens and with a birefringence large enough to be used in incoherent digital holography. Furthermore, a diffractive birefringent lens 5 generates unnecessary diffracted light, which causes degradation of the reconstructed image.

[0013] The optical system of the imaging device shown in Figure 8 uses a beam splitter (BS) 7. In this optical system, the object light passes through the beam splitter twice, reducing the light utilization efficiency to 1 / 4. Furthermore, if the object light is incident on a reflective liquid crystal panel at an angle without using a beam splitter, the light utilization efficiency does not decrease, but the angle dependency of the liquid crystal panel makes it impossible to provide an accurate spherical phase distribution.

[0014] Therefore, in consideration of the above-mentioned problems, the object of the present invention is to provide an imaging device and imaging method that can improve the light utilization efficiency and obtain high-quality hologram images / reconstructed images compared to conventional incoherent digital holography imaging devices. [Means for solving the problem]

[0015] In order to solve the above problems, the imaging device of the present invention includes a first polarizing plate that converts incoherent light waves into linearly polarized light, a polarizing beam splitter that splits the light waves that have passed through the first polarizing plate into first and second divided lights according to the polarization direction, first and second mirrors that reflect the first and second divided lights, respectively, and have different curvatures, a first quarter-wave plate that is arranged between the polarizing beam splitter and the first mirror, a second quarter-wave plate that is arranged between the polarizing beam splitter and the second mirror, and a third quarter-wave plate that converts the first divided light that has been reflected by the first mirror and passed through the first quarter-wave plate and the second divided light that has been reflected by the second mirror and passed through the second quarter-wave plate into circularly polarized light, and is characterized in that the first divided light and the second divided light that have passed through the third quarter-wave plate are photographed through the polarizing plate, and multiple interference fringes are obtained simultaneously.

[0016] It is also preferable that the imaging device captures the first and second split lights transmitted through the third quarter-wave plate with a polarization camera, and simultaneously obtains interference fringes of different phases.

[0017] Furthermore, it is desirable that the imaging device diffracts the first and second split lights that have passed through the third quarter-wave plate in multiple directions using a diffraction grating, and photographs the diffracted lights in each direction using a camera through polarizing plates with different polarization directions, thereby simultaneously obtaining interference fringes of different phases.

[0018] Furthermore, it is desirable that the imaging device splits the first and second split lights that have passed through the third quarter-wave plate into two optical paths using a beam splitter through a polarizing plate, and photographs the first and second split lights with cameras placed on each optical path at different distances from the beam splitter, thereby simultaneously obtaining interference fringes at different optical path distances.

[0019] Furthermore, it is desirable that the imaging device further obtains complex amplitude information from a plurality of interference fringes of different phases by a phase shift method, and performs a back propagation calculation of light to obtain a reconstructed image at any depth distance.

[0020] Furthermore, it is desirable that the imaging device further obtains phase information by phase retrieval from amplitude information of interference fringes obtained at different distances, and performs back propagation calculation of light using the obtained amplitude information and the obtained phase information, thereby obtaining a reconstructed image at any depth distance.

[0021] In order to solve the above problems, the incoherent digital holography imaging method of the present invention is characterized in that it splits a light wave transmitted through a polarizing plate into first and second split lights using a polarizing beam splitter, reflects the first and second split lights through mirrors with different curvatures after passing them through a quarter-wave plate, and combines them again using the polarizing beam splitter after passing them through a polarizing plate with a polarization direction different from that of the quarter-wave plate, thereby simultaneously obtaining interference fringes of different phases.

[0022] In order to solve the above problems, the incoherent digital holography imaging method of the present invention is characterized in that it splits a light wave transmitted through a polarizing plate into first and second split lights using a polarizing beam splitter, reflects the first and second split lights each through a quarter-wave plate on mirrors with different curvatures, and then combines them using the polarizing beam splitter again after passing through the quarter-wave plate, splits the combined first and second split lights into two optical paths using a beam splitter after passing through the quarter-wave plate and a polarizing plate, and photographs the combined lights with cameras positioned on each optical path at different distances from the beam splitter, thereby simultaneously obtaining interference fringes with different optical path lengths. [Effects of the Invention]

[0023] The imaging device and imaging method of the present invention can improve the light utilization efficiency and obtain a high-quality hologram image / reconstructed image compared to conventional incoherent digital holography imaging devices. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a diagram illustrating the principle of an interferometer used in an imaging device of the present invention. [Figure 2]1 is a schematic diagram of an imaging device according to a first embodiment of the present invention. [Figure 3] FIG. 4 is a schematic diagram of an imaging device according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a schematic diagram of an imaging device according to a third embodiment of the present invention. [Figure 5] 10 is an example of four interference fringes with different phases when a point object is photographed by the imaging device of the present invention. [Figure 6] 10 is an example of a reconstructed image of one frame when a moving grayscale object is captured as a video by the imaging device of the present invention. [Figure 7] 1 is an example of a conventional incoherent digital holography imaging device. [Figure 8] 1 is an example of a conventional incoherent digital holography imaging device. [Figure 9] 1A and 1B are diagrams illustrating examples of transmission axes of a polarizing plate array. DETAILED DESCRIPTION OF THE INVENTION

[0025] Figure 1 shows the principle of an interferometer used in the imaging device of the present invention. The interferometer is composed of a polarizing plate 11, a polarizing beam splitter (PBS) 12, quarter-wave plates 13, 15, and 17, a concave mirror 14, and a plane mirror 16. Furthermore, the imaging device is equipped with a polarizing plate 18 and a camera 19 to capture interference fringes. Each component will be explained below.

[0026] Polarizing plate 11 (first polarizing plate) converts object light from a subject into linearly polarized light. For example, polarizing plate 11 is installed so that only linearly polarized light at an angle of 45° to the horizontal plane is transmitted.

[0027] Polarizing beam splitter (PBS) 12 splits the object light transmitted through polarizing plate 11 into first and second split lights according to polarization components. PBS 12 reflects the s-polarized light component (referred to as the first split light) of the object light transmitted through polarizing plate 11, changing its traveling direction (upward in the drawing), and transmits the p-polarized light component (referred to as the second split light) of the object light transmitted through polarizing plate 11. As will be described later, after reflection by the mirror, the first split light enters PBS 12 as p-polarized light, and the second split light enters PBS 12 as s-polarized light. Therefore, PBS 12 transmits the first split light after reflection by the mirror and reflects the second split light, changing its traveling direction (downward in the drawing), and combines the first and second split lights.

[0028] The quarter-wave plate 13 (first quarter-wave plate) transmits the s-polarized object light (first split light) reflected by the PBS 12 and converts it into circularly polarized light. Furthermore, the quarter-wave plate 13 transmits the circularly polarized light reflected by the concave mirror 14 and inputs it, converting it into p-polarized light, which is then guided to the PBS 12.

[0029] The quarter-wave plate 15 (second quarter-wave plate) transmits the p-polarized object light (second split light) that has passed through the PBS 12, converting it into circularly polarized light. Furthermore, the quarter-wave plate 15 transmits the circularly polarized light that is reflected by the mirror 16 and incident thereon, converting it into s-polarized light, and directs it to the PBS 12.

[0030] Concave mirror 14 (first mirror) gives a phase distribution of a predetermined focal length (curvature) to the circularly polarized light that has passed through quarter-wave plate 13 , and reflects it toward quarter-wave plate 13 .

[0031] Plane mirror 16 (second mirror) gives a planar (infinite focal length) phase distribution to the circularly polarized light that has passed through quarter-wave plate 15, and reflects it toward quarter-wave plate 15. Note that in this principle diagram, mirror 16 is described as a plane mirror, but it may be any mirror with a focal length (curvature) different from that of concave mirror 14.

[0032] The quarter-wave plate 17 (third quarter-wave plate) transmits the first and second split beams that have been reflected by the mirror and transmitted / reflected by the PBS 12, and converts them into clockwise and counterclockwise circularly polarized light, respectively.

[0033] In this interferometer, the first and second split lights interfere with each other due to a slight difference in optical path caused by reflections from the concave mirror 14 and the plane mirror 16. Interference fringes can be obtained by capturing images of the first and second split lights after they pass through the quarter-wave plate 17 using a camera 19 via a polarizing plate 18. For example, multiple interference fringes with different phases can be simultaneously captured using a polarization camera. Complex amplitude information on the imaging plane can then be obtained from these interference fringe images, and a reconstructed image at any depth distance can be obtained by performing a backpropagation calculation of the light.

[0034] In this description, the s-polarized component of the object light is the first split light, and the p-polarized component of the object light is the second split light, but the first and second split lights may be reversed.

[0035] According to the interferometer (optical system) of the imaging device of the present invention, the s-polarized component of the object light incident on the PBS 12 is reflected by the concave mirror 14, passes through the quarter-wave plate 13 again, becomes p-polarized, and then passes through the PBS 12. That is, all of the s-polarized components of the object light incident on the PBS 12 become p-polarized and pass through the PBS 12, so there is no attenuation of light, as occurs in an interferometer configured with a beam splitter (BS) 7, as in the prior art. Similarly, the p-polarized component of the object light that passes through the PBS 12 is reflected by the plane mirror 16, passes through the quarter-wave plate 15 again, becomes s-polarized, and is reflected by the PBS 12. Because all of the p-polarized components of the object light incident on the PBS 12 become s-polarized and are reflected by the PBS 12, there is no attenuation of light, as occurs in an interferometer configured with a beam splitter (BS) 7. Therefore, the light utilization efficiency can be improved.

[0036] Furthermore, the PBS 12, concave mirror 14, and plane mirror 16 that make up this interferometer are common optical components, and the size of the interference fringes can be easily adjusted to suit the resolution required for the reconstructed image by changing the focal length of the concave mirror 14 or replacing the plane mirror 16 with a concave mirror. Furthermore, because a diffractive birefringent lens is not used, noise caused by harmonic components due to diffraction can be suppressed. Furthermore, unlike birefringent materials or diffractive lenses, concave and plane mirrors are not affected by chromatic aberration.

[0037] Hereinafter, an embodiment of an incoherent digital holography imaging device will be described, which improves the efficiency of light utilization by configuring an interferometer using a polarizing beam splitter (PBS) without using a birefringent lens or a reflective liquid crystal panel.

[0038] (First embodiment) 2 is a schematic diagram of an imaging device according to a first embodiment of the present invention. The imaging device includes an interferometer made up of a polarizing plate 11, a polarizing beam splitter (PBS) 12, quarter-wave plates 13, 15, and 17, a concave mirror 14, and a flat mirror 16, and further includes a lens 2, a wavelength filter 3, and a polarization camera 20. The configuration of the interferometer is the same as in FIG. 1, so a description of each optical element that makes up the interferometer will be omitted.

[0039] The object light from the subject 1 is an incoherent light wave and enters the lens 2. Note that the object light may be reflected light, transmitted light, or light emitted from the subject 1.

[0040] Lens 2 collects the object light and makes it incident on wavelength filter 3. Like a normal camera lens, lens 2 has the function of adjusting the image magnification, wide angle, etc. Note that subject 1 can be placed at any position regardless of the focal position of lens 2.

[0041] The wavelength filter 3 is a bandpass filter that transmits light waves of a predetermined wavelength width (for example, 3 nm to 20 nm), and improves the temporal coherence of the light waves. Note that narrowing the wavelength width improves image quality but reduces the amount of light in the image, so an appropriate wavelength filter 3 is selected depending on the desired image. The light waves that have passed through the wavelength filter 3 are incident on the polarizing plate 11 of the interferometer.

[0042] The lens 2 and the wavelength filter 3 are not essential components of the imaging device, and the object light may be input directly to the polarizing plate 11 .

[0043] The behavior of the object light after entering polarizing plate 11 and the function of each optical element are as explained in the principle diagram in Figure 1. The object light that passes through polarizing plate 11 becomes linearly polarized at 45° to the horizontal plane, and the s-polarized component is reflected by PBS 12, while the p-polarized component is transmitted. The s-polarized component of the object light passes through quarter-wave plate 13 and becomes circularly polarized light, is reflected by concave mirror 14, passes through quarter-wave plate 13 again and becomes p-polarized light, and is transmitted through PBS 12. The p-polarized component of the object light passes through quarter-wave plate 15 and becomes circularly polarized light, is reflected by plane mirror 16, passes through quarter-wave plate 15 again and becomes s-polarized light, and is reflected by PBS 12. These two beams (the first and second split beams) are converted to right- and left-handed circularly polarized light by quarter-wave plate 17. A slight difference in the optical path between the beams occurs due to reflections by concave mirror 14 and plane mirror 16, causing interference between them.

[0044] This interference light is captured by a polarization camera 20 in which polarizing plates are installed at 45° intervals for each pixel. For example, a polarization camera 20 can be used in which each pixel has a pitch of 3.75 μm and four types of polarizing plates are installed at 45° intervals for every four adjacent 2 × 2 pixels. By constructing an image from pixels with different polarization directions, interference fringes can be captured with a resolution of 6.5 μm pitch in both the vertical and horizontal directions, and four interference fringes with different phases can be obtained.

[0045] The imaging device may further include an information processing device (not shown). The information processing device obtains complex amplitude information of the subject 1 on the imaging plane of the polarization camera 20 from the four acquired interference fringes using a phase shift method or the like. Furthermore, an image at any depth distance can be reconstructed from this complex amplitude information using wavefront backpropagation calculations (see Patent Document 1). According to this embodiment, light utilization efficiency is higher and exposure time can be shortened compared to conventional methods, making it possible to easily obtain moving images.

[0046] (Second embodiment) 3 is a schematic diagram of an imaging device according to a second embodiment of the present invention. The imaging device includes an interferometer made up of a polarizing plate 11, a polarizing beam splitter (PBS) 12, quarter-wave plates 13, 15, and 17, a concave mirror 14, and a flat mirror 16, as well as a lens 2, a wavelength filter 3, a diffraction grating 21, a polarizing plate array 22, and cameras 23 and 24.

[0047] The object light from the subject 1 is an incoherent light wave and enters the lens 2. The functions of the lens 2 and the wavelength filter 3 are the same as those in the first embodiment. Furthermore, since the configuration of the interferometer is the same as that in FIG. 1, a description of each optical element that constitutes the interferometer will be omitted. The object light is split into a first split light and a second split light within the interferometer, which are reflected by the concave mirror 14 and the plane mirror 16, respectively, and become clockwise and counterclockwise circularly polarized light by the quarter-wave plate 17.

[0048] The object light (first split light and second split light) that has passed through the interferometer is split into four directions by the diffraction grating 21 (although light in two directions is depicted in FIG. 3, in reality it is diffracted in four directions). For this diffraction grating 21, for example, a checkered diffraction grating in which two types of phase objects (objects that change only the phase of light) are arranged in a checkered pattern is used.

[0049] Next, the diffracted light beams branched into four directions are incident on each region of the polarizing plate array 22. The polarizing plate array 22 is configured with four types (four regions) of linear polarizers with transmission axes at 0°, 45°, 90°, and 135°, as shown in Fig. 9. Depending on the angle of the transmission axis of the linear polarizer, different phase shift amounts of 0, π / 2, π, and 3π / 2 [rad] are imparted to each set of linearly polarized light for each region.

[0050] Four interference fringe images with different phases can be simultaneously obtained by using cameras 23 and 24 (actually, four cameras) to capture pairs of linearly polarized light that have passed through polarizer array 22. Although four cameras are used here, four interference fringe images can also be simultaneously obtained using a single camera (image sensor) with a large light-receiving area.

[0051] The imaging device may further include an information processing device (not shown). The information processing device obtains a complex amplitude distribution of the subject 1 on the imaging plane from the four acquired interference fringes using a phase shift method or the like, and then reconstructs an image at an arbitrary depth distance from this complex amplitude distribution using a wavefront backpropagation calculation, just like in the first embodiment.

[0052] In the above embodiment, a checkerboard diffraction grating is used to split the light into four directions. However, a linear diffraction grating may be used to split the light into three directions. For example, if a diffraction grating (light modulation element) that periodically changes the incident light in one axial direction (x direction) and imparts a constant two-level phase distribution in the direction perpendicular to the x direction (y direction) is used as the diffraction grating 21, the first and second split light beams, which are left-handed and right-handed circularly polarized light beams, that have passed through the quarter-wave plate 17 are each split into three beams (center and left and right). The polarizer array 22 is a three-area split polarizer (a polarizer consisting of three linear polarizers with different transmission axis directions at the center and left and right), and the three split diffracted light beams are incident on each of the three areas of the three-area split polarizer. Three cameras capture the light that has passed through each area, allowing three interference fringe images with different phases to be simultaneously acquired.

[0053] Furthermore, the information processing device can obtain the complex amplitude distribution on the imaging plane from the three acquired interference fringes using a phase shift method or the like, and from this complex amplitude distribution, an image at any depth distance can be reconstructed using wavefront backpropagation calculations.

[0054] As described above, in the first embodiment (FIG. 2), the polarization components are separated using the polarization camera 20, but in the second embodiment (FIG. 3), the polarization components are separated and interference fringes of different phases are simultaneously acquired by using the diffraction grating 21, the polarizing plate array 22, and the cameras 23 and 24. In this embodiment, interference fringes can be acquired at high density by each camera, and therefore the resolution of the interference fringes can be improved compared to the first embodiment.

[0055] (Third embodiment) Figure 4 shows a schematic diagram of an imaging device according to a third embodiment of the present invention. The imaging device according to the third embodiment is an incoherent digital holography imaging device that acquires complex amplitude information of interference fringes by phase retrieval. The imaging device includes an interferometer consisting of a polarizing plate 11, a polarizing beam splitter (PBS) 12, quarter-wave plates 13, 15, and 17, a concave mirror 14, and a flat mirror 16, as well as a lens 2, a wavelength filter 3, a polarizing plate 25, a beam splitter (BS) 26, and cameras 27 and 28.

[0056] The object light from the subject 1 is an incoherent light wave and enters the lens 2. The functions of the lens 2 and the wavelength filter 3 are the same as those in the first embodiment. Furthermore, since the configuration of the interferometer is the same as that in FIG. 1, a description of each optical element that constitutes the interferometer will be omitted. The object light is split into a first split light and a second split light within the interferometer, which are reflected by the concave mirror 14 and the plane mirror 16, respectively, and become clockwise and counterclockwise circularly polarized light by the quarter-wave plate 17.

[0057] The object light (first and second split lights) transmitted through the quarter-wave plate 17 passes through a polarizing plate 25 and becomes linearly polarized light. Then, the light is split into two optical paths by a beam splitter (BS) 26.

[0058] The cameras 27 and 28 for each optical path are installed at different distances from the beam splitter (BS) 26. By capturing the split object light (including the first split light and the second split light) with the cameras 27 and 28, respectively, interference fringes with different optical path distances (and therefore magnification ratios) can be simultaneously obtained.

[0059] The imaging device may further include an information processing device (not shown). The information processing device can obtain phase information from the intensity distributions (amplitude information) of two interference fringes obtained at different distances by phase retrieval using the TIE (Transport of Intensity Equation) method or the GS (Gerchberg-Saxton) algorithm. An image at any depth distance can be reconstructed by performing a backpropagation calculation of light using the obtained amplitude information and the obtained phase information.

[0060] In this embodiment, complex amplitude information is obtained by phase retrieval, which is a method different from the phase shift method. However, as in the first and second embodiments, the efficiency of light utilization can be improved by configuring an interferometer using a polarizing beam splitter (PBS).

[0061] (Experimental results and verification of effects) FIG. 5 shows an example of four interference fringes with different phases when a point object is photographed by the imaging device according to the first embodiment of the present invention.

[0062] Figure 5(a) shows interference fringes when the polarization direction of the polarizer provided in the pixel is 0° relative to the horizontal direction. Figure 5(b) shows interference fringes when the polarization direction is 135°, Figure 5(c) shows interference fringes when the polarization direction is 45°, and Figure 5(d) shows interference fringes when the polarization direction is 90°. Each image in Figure 5 is an image of 1024 x 1024 pixels. An image at any depth distance can be reconstructed from the four acquired interference fringes by wavefront backpropagation calculation. It has been confirmed that the present invention can capture clearer interference fringes with higher light utilization efficiency than conventional methods.

[0063] 6 shows an example of a reconstructed image of one frame when a moving grayscale image is captured by the imaging device according to the first embodiment of the present invention. The image shows a grayscale chart with different brightness levels in the horizontal direction (the upper side is bright on the right and dark on the left, the center is a black line, and the lower side is dark on the right and bright on the left), which is moved horizontally.

[0064] Figure 6(a) shows a reconstructed image of one frame taken in grayscale at a frame rate of 10 fps, but the boundaries between each brightness level are unclear at 10 fps. On the other hand, Figure 6(b) shows a reconstructed image of one frame taken at a frame rate of 60 fps, where the image is not blurred and the boundaries between each brightness level are clear.

[0065] The imaging device of the present invention has high light utilization efficiency and can shorten exposure time, making it easy to capture moving images. Therefore, it has been confirmed that it is possible to capture moving images (reconstructed images) at a frame rate of 60 fps.

[0066] Although the configuration and operation of the imaging device have been described in the embodiments of the present invention, the present invention is not limited thereto and may be configured as an imaging method for incoherent digital holography. That is, the present invention may be configured as an imaging method in which, following the flow of object light (light waves) in each figure, a light wave transmitted through a polarizing plate is split into first and second split lights by a polarizing beam splitter, the first and second split lights are each passed through a quarter-wave plate and reflected by mirrors with different curvatures, passed through the quarter-wave plate again and combined by the polarizing beam splitter, and the combined first and second split lights are photographed by a camera through the quarter-wave plate and polarizing plate, thereby simultaneously acquiring multiple interference fringes.

[0067] Although the above-described embodiments have been described as typical examples, it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications or alterations are possible without departing from the scope of the claims. For example, the functions included in each block, step, etc. described in the embodiments can be rearranged so as not to be logically inconsistent, and multiple constituent blocks, steps, etc. can be combined or divided into one. [Explanation of symbols]

[0068] 1. Subject 2 lenses 3 wavelength filters 4 Polarizing Plate 5. Birefringent lenses 6 1 / 4 wave plate 7 Beam Splitter 8 Reflective LCD panel 9 1 / 4 wave plate 11 Polarizing plate 12 Polarizing beam splitter 13 1 / 4 wave plate 14 Concave mirror 15 1 / 4 wave plate 16 Plane mirror 17 1 / 4 wave plate 18 Polarizing Plate 19 Camera 20 Polarization Camera 21 Diffraction Grating 22 Polarizer Array 23 Camera 24 Camera 25 Polarizing Plate 26 Beam Splitter 27 Camera 28 Camera

Claims

1. a first polarizer for converting incoherent light waves into linearly polarized light; a polarizing beam splitter that splits the light wave transmitted through the first polarizing plate into a first split light and a second split light according to the polarization direction; first and second mirrors having different curvatures that reflect the first divided light and the second divided light, respectively; a first quarter-wave plate disposed between the polarizing beam splitter and the first mirror; a second quarter-wave plate disposed between the polarizing beam splitter and the second mirror; a third quarter-wave plate that converts the first split light reflected by the first mirror and transmitted through the first quarter-wave plate and the second split light reflected by the second mirror and transmitted through the second quarter-wave plate into circularly polarized light; Equipped with an imaging device, characterized in that the first split light and the second split light that have passed through the third quarter-wave plate are photographed through a polarizing plate, and a plurality of interference fringes are simultaneously obtained.

2. 2. The imaging device according to claim 1, an imaging device, characterized in that the first split light and the second split light that have passed through the third quarter-wave plate are photographed by a polarization camera, and interference fringes of different phases are simultaneously obtained.

3. 2. The imaging device according to claim 1, an imaging device characterized in that the first divided light and the second divided light that have passed through the third quarter-wave plate are diffracted in a plurality of directions by a diffraction grating, and the diffracted light in each direction is photographed by a camera through a polarizing plate of a different polarization direction, thereby simultaneously obtaining interference fringes of different phases.

4. 2. The imaging device according to claim 1, an imaging device, characterized in that the first split light and the second split light that have passed through the third quarter-wave plate are split into two optical paths by a beam splitter through a polarizing plate, and the first split light and the second split light are photographed by cameras arranged on each optical path at different distances from the beam splitter, thereby simultaneously obtaining interference fringes at different optical path distances.

5. 4. The imaging device according to claim 2, Furthermore, the imaging device is characterized in that it obtains complex amplitude information from a plurality of interference fringes of different phases by a phase shift method, and performs a back propagation calculation of light to obtain a reconstructed image at any depth distance.

6. 5. The imaging device according to claim 4, Furthermore, the imaging device is characterized in that it obtains phase information by phase retrieval from amplitude information of interference fringes acquired at different distances, and performs back propagation calculations of light using the acquired amplitude information and the obtained phase information, thereby obtaining a reconstructed image at any depth distance.

7. An incoherent digital holography imaging method comprising: splitting a light wave transmitted through a polarizing plate into first and second split lights by a polarizing beam splitter; passing the first and second split lights through a quarter-wave plate, reflecting them off mirrors with different curvatures, and then combining them by the polarizing beam splitter after passing them through the quarter-wave plate again; and photographing the combined first and second split lights with a camera through a polarizing plate having a polarization direction different from that of the quarter-wave plate, thereby simultaneously obtaining interference fringes of different phases.

8. An incoherent digital holography imaging method comprising: splitting a light wave transmitted through a polarizing plate into first and second split lights by a polarizing beam splitter; reflecting the first and second split lights by mirrors with different curvatures after passing through a quarter-wave plate; combining the first and second split lights by the polarizing beam splitter after passing through the quarter-wave plate again; splitting the combined first and second split lights into two optical paths after passing through a quarter-wave plate and a polarizing plate by a beam splitter; and photographing the combined first and second split lights with cameras positioned on each optical path at different distances from the beam splitter, thereby simultaneously obtaining interference fringes at different optical path lengths.

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