Hologram imaging device

Abstract

To provide a hologram imaging device with which it is possible to improve a resolution irrespective of a subject, without having to change the NA of a light source or a lens.SOLUTION: Provided is a hologram imaging device for dividing an incoherent light wave into first and second divided light, adding mutually different phase distributions to the first and the second divided light, and thereafter causing the first and the second divided light to interfere with each other to form a hologram and capturing the image of the same, the hologram imaging device being characterized in that one of the first and the second divided light is modulated by an optical element whose focal distance has the function of a negative lens, and the other of these is modulated by an optical element whose focal distance has the function of a positive lens, then causing these to interfere on the light receiving plane of an imaging element.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a holographic imaging device, and more particularly to a holographic imaging device using incoherent digital holography. [Background technology]

[0002] Incoherent digital holography does not require a highly coherent light source such as a laser, but can capture holograms of objects by utilizing the phenomenon of self-interference using light sources with low spatial coherence, such as sunlight, LEDs, and fluorescent light (Patent Document 1). Due to this feature, incoherent digital holography, unlike active stereoscopic imaging methods such as lidar and fringe projection, does not require a special light source and can realize a passive stereoscopic imaging method in a natural light environment. Furthermore, because its principle is based on self-interference, incoherent digital holography is not subject to the constraints of Lagrange invariance and is known to have a resolution approximately 1.5 times or more than that of conventional incoherent imaging systems and twice that of conventional coherent imaging systems (Non-Patent Document 1).

[0003] As with conventional imaging systems, the resolution of incoherent digital holography is proportional to the wavelength of light and inversely proportional to the numerical aperture (NA) of the lenses that make up the optical system. Therefore, the wavelength of light and the NA of the lens must be appropriately set according to the fineness of the object to be imaged. To improve resolution, it is necessary to shorten the wavelength of the light source and increase the NA of the lens. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6416270 [Patent Document 2] Patent No. 6245551 [Patent Document 3] Japanese Patent Application Publication No. 2019-144520 [Patent Document 4] Special Publication No. 2010-127976

Non-licensed literature

[0005] [Non-licensed document 1] J. Rosen, A. Vijayakumar, M. Kumar, MR Rai, R. Kelner, Y. Kashter, A. Bulbul, and S. Mukherjee, “Recent advances in self-interference incoherent digital holography,” Advances in Optics and Photonics, Vol. 11, No. 1, pp. 1-66, (2019). [Non-licensed document 2] J. Rosen and G. Brooker, “Non-scanning motionless fluorescence three-dimensional holographic microscopy,” Nature Photonics, Vol. 2, pp. 190-195, (2008). [Non-licensed document 3] J. Hong and MK Kim, “Single-shot self-interference incoherent digital holography using off-axis configuration,” Optics Letters, Vol. 38, No. 23, pp. 5196-5199, (2013).

Non-licensed Document 4

[0006] The wavelength of light can be shortened by applying a wavelength filter with a shorter wavelength band to a white light source or by changing the light source itself to a shorter wavelength. However, shortening the wavelength of the light source beyond the blue wavelength (approximately 405 nm) limits the wavelength shortening due to the increased light absorption by optical elements. Furthermore, the former method of applying a wavelength filter requires the imaging device to be equipped with multiple wavelength filters and a mechanism for switching between them, which makes the device complex and expensive. The latter method also requires the installation of multiple light sources to change the light source, which presents similar challenges. Furthermore, when photographing ambient light such as sunlight, LEDs, or fluorescent lights, or when photographing fluorescence itself, it is difficult to improve resolution by shortening the wavelength if the subject itself contains long-wavelength red or green components.

[0007] When increasing the NA of a lens, the lens system must be constructed using high-precision alignment technology to combine multiple lenses to eliminate aberrations, and the lens system itself becomes large and expensive, which makes the imaging device complex and expensive, just as when changing the wavelength of the light source.

[0008] As described above, resolution improvement methods that change wavelength or NA tend to make imaging devices more complex and expensive, and in particular, shortening the wavelength of the light source may not be applicable depending on the subject.

[0009] Therefore, in view of the above-mentioned problems, the object of the present invention is to provide a holographic imaging device that solves the problems associated with conventional resolution improvement methods, which result in devices that are complex, large, and expensive, and that can improve resolution independently of the subject, without changing the NA of the light source or lens. [Means for solving the problem]

[0010] In order to solve the above problems, the hologram imaging device according to the present invention comprises: From the subject Incoherent a condenser lens for condensing light waves; Split the light wave into the first and second split lights an optical element having a function of a lens with a negative focal length that modulates at least one of the first divided light and the second divided light; and an optical element having a function of a lens with a positive focal length that modulates at least the other of the first divided light and the second divided light, Different phase distributions are given was causing the first divided light beam and the second divided light beam to interfere with each other to form a hologram; With image sensor In a hologram imaging device that takes ,before The distance between the subject and the condenser lens is set shorter than the focal length of the condenser lens, thereby improving the resolution more than when the subject is positioned at the focal length of the condenser lens.

[0011] In the hologram imaging device, it is desirable that the focal length of the optical element that functions as a lens with a negative focal length is greater than the focal length of the optical element that functions as a lens with a positive focal length.

[0013] Furthermore, in the hologram imaging device, it is desirable that the imaging element be positioned at a distance of 2xy / |xy| or more from the optical element having the lens function, where x is the focal length of an optical element having the lens function but with a negative focal length, and y is the focal length of an optical element having the lens function but with a positive focal length.

[0014] Furthermore, it is desirable that the hologram imaging device includes a beam splitter that splits the incoherent light wave into a first divided light and a second divided light, a convex mirror that is an optical element that functions as a lens with a negative focal length, and a concave mirror that is an optical element that functions as a lens with a positive focal length.

[0015] In addition, it is desirable that one of the convex mirror and the concave mirror of the hologram imaging device is replaced with a spatial light modulator.

[0016] Furthermore, it is desirable that the hologram imaging device comprises a first polarizer that converts incoherent light waves into linearly polarized light, a spatial light modulator that applies phase modulation to one of the polarization components whose vibration directions are orthogonal to each other using a lens with a positive focal length and converts the other polarization component into a plane wave, a lens with a negative focal length that transmits the two polarization components reflected or transmitted by the spatial light modulator, and a second polarizer that aligns the vibration directions of the two polarization components.

[0017] Furthermore, it is desirable that the hologram imaging device comprises a first polarizer that converts incoherent light waves into linearly polarized light, a spatial light modulator that applies phase modulation to one of the polarization components whose vibration directions are orthogonal to each other using a lens with a negative focal length and converts the other polarization component into a plane wave, a lens with a positive focal length that transmits the two polarization components reflected or transmitted by the spatial light modulator, and a second polarizer that aligns the vibration directions of the two polarization components. [Effects of the Invention]

[0018] The hologram imaging device of the present invention allows the optical system to be simpler and smaller than conventional resolution improvement methods, and the resolution can be improved without changing the NA of the light source or lens, and independently of the object. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a conceptual diagram of a hologram imaging device according to a first embodiment of the present invention. [Figure 2] FIG. 10 is a conceptual diagram of a holographic imaging device according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a conceptual diagram of a holographic imaging device according to a third embodiment of the present invention. [Figure 4] FIG. 10 is a conceptual diagram of a hologram imaging device according to a modified example of the third embodiment of the present invention. [Figure 5] FIG. 10 is a conceptual diagram of a holographic imaging device according to a fourth embodiment of the present invention. [Figure 6] 3 is a conceptual diagram of light propagation of the first divided light and the second divided light of the present invention. FIG. [Figure 7] 1 is a conceptual diagram for comparing the optical system of the present invention with the optical system of the prior art; [Figure 8] FIG. 10 is a diagram showing a comparison of resolution between the present invention and the prior art. [Figure 9] FIG. 1 is a diagram showing a subject used to verify the effects of the present invention. [Figure 10] 1A and 1B are diagrams showing the results of capturing and reconstructing a hologram using the hologram imaging device of the present invention and the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0021] (First embodiment) 1 is a conceptual diagram of a holographic imaging device according to a first embodiment of the present invention. The holographic imaging device includes a condenser lens 2, a beam splitter 3, a convex mirror 4, a concave mirror 5, a wavelength filter 6, an imaging element 20, and a processing device 30.

[0022] The condenser lens 2 condenses spatially and temporally incoherent light waves reflected, transmitted, or emitted from the object (subject) 1 to be photographed. As will be described later, the positional relationship between the subject 1 and the condenser lens 2 is such that the closer the subject 1 is to the condenser lens 2, the higher the resolution. It is more desirable to set the distance between the two to be shorter than the focal length (subject-side focal length) of the condenser lens 2. Note that the condenser lens 2 is effective for improving light utilization efficiency and adjusting image magnification, but is not essential. Without the condenser lens 2, it is equivalent to condensing light with a lens whose front focal length is infinite, and even in this case, the closer the subject 1 is to the optical system, the higher the resolution.

[0023] After this, beam splitter 3 splits the light wave into a first divided light and a second divided light. Beam splitter 3 also combines the first divided light and the second divided light reflected by convex mirror 4 or concave mirror 5. Here, the light directed toward convex mirror 4 is called the first divided light, and the light directed toward concave mirror 5 is called the second divided light, but the two may be reversed.

[0024] Convex mirror 4 reflects the first divided light, imparts a predetermined phase change to it, and directs it toward beam splitter 3. Here, convex mirror 4 reflects the light in a diverging direction, and acts in the same way as a concave lens when light is transmitted from the back surface, so it can be said to be an optical element that functions as a lens with a negative focal length.

[0025] Concave mirror 5 reflects the second divided light, imparting a phase change to it that differs from that of the first divided light, and directing it toward beam splitter 3. Here, concave mirror 5 reflects light in a direction that focuses it, and acts in the same way as a convex lens when light is transmitted from the back surface. Therefore, it can be said to be an optical element that functions as a lens with a positive focal length. Note that in conventional optical systems, concave mirrors with different focal lengths are used for both the first divided light and the second divided light in order to improve light utilization efficiency by focusing light.

[0026] The wavelength filter 6 improves temporal coherence by transmitting wavelengths in a specific band of the first and second split lights combined by the beam splitter 3. Note that if the temporal coherence of the light source is sufficiently high, the wavelength filter 6 does not need to be used.

[0027] The image sensor 20 receives the first and second divided lights that have passed through the wavelength filter 6. The first and second divided lights interfere with each other on the light receiving surface (sometimes referred to as the image sensor surface) of the image sensor 20, forming a hologram. The image sensor 20 captures this as a digital hologram and transfers the acquired hologram to the processing device 30.

[0028] The processing device 30 is configured, for example, by a computer equipped with a memory and a CPU, and can record captured holograms, and can also function as an image reconstructing device that reconstructs an image (three-dimensional image) from the obtained holograms.

[0029] A single hologram can be captured using the optical system shown in Fig. 1. Furthermore, to obtain a high-quality three-dimensional image, a phase shift element may be introduced into the optical system as needed to obtain multiple holograms with different phase differences between the first and second divided beams, and a phase shift method (Non-Patent Document 2) or an off-axis method (Non-Patent Document 3) may be applied. Furthermore, as shown in Patent Documents 2 and 3, a technique may be introduced in which an optical element that splits the first and second divided beams in multiple directions is used to capture multiple holograms in a single capture.

[0030] An example of image reconstruction in the processing device 30 will be described. The phase shift method or off-axis method is applied to the captured hologram or hologram group to obtain the complex amplitude distribution O(x, y) on the image sensor surface. Next, the propagation calculation shown in the following equation (1) is applied to obtain the complex amplitude distribution O(x, y) at an arbitrary distance z r It is possible to reconstruct an image of the object at

[0031]

number

[0032] where FT is the Fourier transform operator, i is the imaginary number, λ is the wavelength, (x, y) are the spatial coordinates, and u, v are the spatial frequency coordinates. r Regarding the setting of (1), the photographer may input an arbitrary value, or the value may be input based on the depth position information of the subject.

[0033] This propagation calculation itself is a calculation method commonly used in incoherent holography hologram imaging devices. The phase-shifting method and off-axis method are also calculations for removing noise from the conjugate image, direct image, and imaging element before reconstructing the image, and are common techniques in the field of holography. This embodiment is characterized by the use of a convex mirror 4 that generates light with a negative focal length, as shown in FIG. 1.

[0034] (Second embodiment) 2 is a conceptual diagram of a holographic imaging device according to a second embodiment of the present invention. The holographic imaging device includes a condenser lens 2, a beam splitter 3, a spatial light modulator 7, a concave mirror 5, a wavelength filter 6, an imaging element 20, and a processing device 30. The difference from the first embodiment is that the spatial light modulator 7 is used instead of the convex mirror 4. A description of the components common to the first embodiment will be omitted.

[0035] The spatial light modulator 7 reflects the first divided light that has passed through the beam splitter 3, and directs the first divided light toward the beam splitter 3 while imparting a predetermined phase change to the light. Here, the spatial light modulator 7 reflects light in a diverging direction, similar to the convex mirror 4, and is an optical element that functions as a lens with a negative focal length. The spatial light modulator 7 can be realized, for example, by a liquid crystal element, and a liquid crystal display type spatial light modulator with a pixel structure (matrix structure) or a spatial light modulator with a structure similar to that of a liquid crystal variable-focus lens (Patent Document 4) can be used.

[0036] Subsequent processing in the optical system is the same as in the first embodiment. The first divided light beam, which has been phase-modulated at a negative focal length by spatial light modulator 7, and the second divided light beam reflected by concave mirror 5 are combined by beam splitter 3, then pass through wavelength filter 6 and enter image sensor 20. The first divided light beam and the second divided light beam interfere with each other on the image sensor surface, forming a hologram. The image sensor 20 captures this as a digital hologram and transfers it to processing device 30.

[0037] Convex mirrors 4 are not widely available as ready-made products, and there are few options for focal length, limiting the degree of freedom when designing an optical system. On the other hand, in this embodiment, by introducing a spatial light modulator 7, it is possible to create a phase distribution of a convex mirror with any focal length, allowing for flexible design of the optical system.

[0038] In this embodiment, the convex mirror 4 of the first embodiment is replaced with a spatial light modulator 7, but the spatial light modulator 7 can also be configured as an optical element having the function of a lens with a positive focal length, and the concave mirror 5 of the first embodiment can be replaced with the spatial light modulator 7.

[0039] (Third embodiment) Figure 3 is a conceptual diagram of a holographic imaging device according to a third embodiment of the present invention. While the first embodiment (Fig. 1) and the second embodiment (Fig. 2) are devices based on a two-beam interferometer, the third embodiment is a device that uses a common-path interferometer. The holographic imaging device of this embodiment includes a condenser lens 2, a polarizer 8, a beam splitter 3, a spatial light modulator 7, a concave lens 9, a polarizer 10, a wavelength filter 6, an imaging element 20, and a processing device 30. The description of the components common to the first and second embodiments will be simplified.

[0040] The condenser lens 2 condenses spatially and temporally incoherent light reflected, transmitted, or emitted from the subject 1 to be photographed.

[0041] The first polarizer (first polarizer) 8 converts the light from the condenser lens 2 into linearly polarized light. This linearly polarized light is preferably tilted at 45 degrees with respect to the axis of the liquid crystal molecules in the spatial light modulator 7, which will be described later. The resulting linearly polarized light passes through the beam splitter 3 and enters the spatial light modulator 7.

[0042] The spatial light modulator 7 modulates the phase of the incident light and reflects it. A liquid crystal type may be used as the spatial light modulator 7, and the elliptical shape of the liquid crystal molecules allows polarization selectivity when modulating the phase with the spatial light modulator 7. In this embodiment, of two linearly polarized light components (polarized components) whose vibration directions are orthogonal to each other, the phase distribution of only one linearly polarized light component is modulated, imparting the phase of a lens with a positive focal length (convex lens). The transmission axis of the first polarizer 8 is tilted 45 degrees with respect to the major axis or minor axis of the liquid crystal molecules, so that only the phase of one of the horizontal or vertical components of the linearly polarized light is modulated. The other polarized component that is not modulated by the spatial light modulator 7 is reflected as a light wave (plane wave) having a planar phase component.

[0043] The beam splitter 3 changes the direction of the light modulated and reflected by the spatial light modulator 7 and makes it incident on the concave lens 9 .

[0044] The concave lens 9 refracts the light passing through it in a diffusing direction. Therefore, when the other polarized light component not modulated by the spatial light modulator 7 is incident on the concave lens 9, it becomes light having the phase of a lens with a negative focal length. Note that, because the concave lens 9 refracts all polarized light components, the phase of a negative focal length is also added to the polarized light component to which the phase of a lens with a positive focal length (convex lens) has been imparted by the spatial light modulator 7. That is, in the optical system of this embodiment, the convex lens of the spatial light modulator 7 and the concave lens 9 function as a composite focal lens for one polarized light component. Therefore, by making the phase modulation of the lens with a positive focal length of the spatial light modulator 7 stronger than the phase modulation of the concave lens 9, the phase modulation of the lens with a positive focal length as a composite focal lens can be imparted to one polarized light component. As a result of the above modulation, first and second split light beams (two orthogonal linearly polarized lights with different phase modulations) necessary for improving resolution are obtained.

[0045] The second polarizer (second polarizer) 10 converts two orthogonal linearly polarized lights (polarization components) into linearly polarized lights in the same direction, thereby allowing the first and second divided lights to interfere with each other on the image sensor surface.

[0046] Thereafter, similarly to the other embodiments, the first and second divided lights pass through the wavelength filter 6 and enter the image sensor 20. The image sensor 20 captures an image of the hologram formed on the image sensor surface and transfers the image to the processing device 30.

[0047] The first embodiment (Fig. 1) and the second embodiment (Fig. 2) are based on a two-beam interferometer, and are therefore susceptible to the effects of air fluctuations and vibrations, which may result in a deterioration in image quality. However, this embodiment uses a common-path interferometer, which improves robustness against external disturbances.

[0048] (Modification of the third embodiment) 4 is a conceptual diagram of a holographic imaging device according to a modification of the third embodiment. The holographic imaging device according to this modification includes a condenser lens 2, a polarizer 8, a beam splitter 3, a spatial light modulator 7, a convex lens 11, a polarizer 10, a wavelength filter 6, an imaging element 20, and a processing device 30. In this modification, the concave lens 9 of the third embodiment is changed to a convex lens 11. The description of the components common to the third embodiment will be simplified.

[0049] The spatially and temporally incoherent light reflected, transmitted, or emitted from the subject 1 to be photographed is focused by the focusing lens 2, converted into linearly polarized light by the first polarizer 8, and passes through the beam splitter 3 before entering the spatial light modulator 7.

[0050] The spatial light modulator 7 can be, for example, a liquid crystal type, and polarization selectivity can be obtained when modulating the phase with the spatial light modulator 7. In this modification, of two linearly polarized light (polarized components) whose vibration directions are orthogonal to each other, the phase distribution of only one linearly polarized light (polarized component) is modulated, and the phase of a lens with a negative focal length (concave lens) is imparted to it. The other polarized component, which is not modulated by the spatial light modulator 7, is reflected as a light wave having a planar phase component.

[0051] The beam splitter 3 changes the direction of the light modulated and reflected by the spatial light modulator 7 and makes it incident on a convex lens 11 .

[0052] The convex lens 11 refracts the light passing through it in a direction that focuses it. Therefore, when the other polarized light component not modulated by the spatial light modulator 7 is incident on the convex lens 11, it becomes light having the phase of a lens with a positive focal length. Because the convex lens 11 refracts all polarized light components, the optical system of this modification functions as a composite focal lens for one polarized light component, with the concave lens of the spatial light modulator 7 and the convex lens 11. Therefore, by making the phase modulation of the lens with a negative focal length of the spatial light modulator 7 stronger than the phase modulation of the convex lens 11, the phase modulation of the lens with a negative focal length as a composite focal lens can be imparted to one polarized light component. As a result of this modulation, the first and second split lights necessary for improving resolution are obtained.

[0053] The first and second split lights are then converted into linearly polarized lights in the same direction by the second polarizer 10, transmitted through the wavelength filter 6, and incident on the image sensor 20. The image sensor 20 captures a hologram formed on the image sensor surface and transfers it to the processing device 30. This modification also uses a common-path interferometer, which improves robustness against external disturbances.

[0054] (Fourth embodiment) 5 is a conceptual diagram of a holographic imaging device of the fourth embodiment. The holographic imaging device of this embodiment includes a condenser lens 2, a polarizer 8, a liquid crystal lens 12, a concave lens 9, a polarizer 10, a wavelength filter 6, an imaging element 20, and a processing device 30. This embodiment is an optical system in which the spatial light modulator 7 of the third embodiment is replaced with a transmissive liquid crystal lens 12, and the beam splitter 3 is omitted. The description of the components common to the third embodiment will be simplified.

[0055] The spatially and temporally incoherent light reflected, transmitted, or emitted from the subject 1 to be photographed is focused by the focusing lens 2, converted into linearly polarized light by the first polarizer 8, and then incident on the transmissive liquid crystal lens 12.

[0056] The liquid crystal lens 12 applies phase modulation to incident light in the same way as a lens. Like the spatial light modulator 7, the liquid crystal lens 12 also obtains polarization selectivity when modulating the phase due to the elliptical shape of the liquid crystal molecules. In this embodiment, of two linearly polarized light (polarized components) whose vibration directions are orthogonal to each other, the phase distribution of only one linearly polarized light (polarized component) is modulated, and the phase of a lens with a positive focal length (convex lens) is imparted to the light. The other polarized component, which is not modulated by the liquid crystal lens 12, passes through the liquid crystal lens 12 as a light wave having a planar phase component.

[0057] Concave lens 9 refracts the light that passes through it in a diffusing direction. Therefore, when the other polarized light component that is not modulated by liquid crystal lens 12 is incident on concave lens 9, it becomes light having the phase of a lens with a negative focal length. In this embodiment, too, liquid crystal lens 12 (a convex lens) and concave lens 9 function as a composite focus lens for one polarized light component. Therefore, by making the phase modulation of the lens with a positive focal length of liquid crystal lens 12 stronger than the phase modulation of concave lens 9, it is possible to impart the phase modulation of the lens with a positive focal length as a composite focus lens to one polarized light component. As a result of the above modulation, first and second split lights necessary for improving resolution are obtained.

[0058] The first and second split lights are then converted into linearly polarized lights in the same direction by the second polarizer 10, transmitted through the wavelength filter 6, and incident on the image sensor 20. The image sensor 20 captures a hologram formed on the image sensor surface and transfers it to the processing device 30. This embodiment is an optical system that uses a transmissive liquid crystal lens 12 and does not require a beam splitter 3, resulting in high light utilization efficiency.

[0059] As a modification of the holographic imaging device of the fourth embodiment, liquid crystal lens 12 may be used to modulate the phase distribution of only one of the linearly polarized lights and impart the phase of a lens with a negative focal length (concave lens), and further, an optical system may be used in which concave lens 9 is replaced with a convex lens.

[0060] With the configuration of this embodiment, liquid crystal lens 12 imparts the phase of a lens with a negative focal length (concave lens) to only one of two orthogonal linearly polarized light components (polarized light components). The other polarized light component passes through liquid crystal lens 12 as a light wave with a planar phase component, and is then imparted the phase of a lens with a positive focal length by a convex lens. Note that one of the linearly polarized light components is subjected to phase modulation by a lens with a negative focal length as a composite focal lens. As a result of this modulation, one of the two orthogonal linearly polarized light components has a phase of a positive focal length and the other has a phase of a negative focal length, thereby obtaining the required first and second divided light components. The optical system thereafter is the same as in the fourth embodiment. This modification also provides a hologram imaging device with high light utilization efficiency.

[0061] As described above, there are countless optical system configurations that can achieve improved resolution depending on the optical elements selected. However, the key point of the present invention is the generation of light beams with positive and negative focal lengths. Figure 6 shows a conceptual diagram of the light propagation of the first and second divided beams of the present invention. Here, subject 1 is used as a point light source. The first divided beam is modulated by an optical element (concave lens) 9 that functions as a lens with a negative focal length, and the light diverges due to its negative focal length. The second divided beam is modulated by an optical element (convex lens) 11 that functions as a lens with a positive focal length, and the light condenses due to its positive focal length, and then begins to diverge at that focal length. If the focal length of the first divided beam is greater than the focal length of the second divided beam, there exists a plane at a distance L from the optical element where the diameters D of the two beams coincide.

[0062] Generally, light interference occurs only at positions where two or more beams of light overlap. At the surface where the diameters of the beams match, all the beams contribute to interference, thereby improving the resolution the most. Therefore, it is desirable to position the image sensor 20 so that the diameters of the first and second divided beams match. This distance L is determined by the magnitude of the focal length |f of the optical element 9 that functions as a negative lens. d1 | and the magnitude of the focal length |f of the optical element 11 having the function of a positive lens. d2| is used to find L=2|f from an optical element that functions as a lens. d1 ||f d2 | / ||f d1 |-|f d2 It corresponds to the position of ||.

[0063] The above value of L is for when the subject 1 is placed at the focus of the focusing lens 2, and if the position of the subject 1 is closer to the focusing lens 2, the distance L at which the diameters of the first and second divided lights match becomes even larger.

[0064] (Example and verification of effects) Figure 7 is a conceptual diagram for comparing the optical system of the present invention with that of the prior art. Figure 7(a) shows a conceptual diagram visualizing the behavior of the first and second divided beams in a conventional incoherent digital holography optical system. In the conventional optical system, the first divided beam split at the splitting surface propagates as parallel beams, while the second divided beam is given a phase with a positive focal length and is focused.

[0065] 7(b) is a conceptual diagram visualizing the behavior of the first and second divided beams in the optical system of the hologram imaging device of the present invention. In the present invention, a phase of a negative focal length is imparted to one of the first and second divided beams split at the splitting surface (the first divided beam in FIG. 7(b)), and a phase of a positive focal length is imparted to the other (the second divided beam in FIG. 7(b)).

[0066] A shooting simulation was carried out using each of the optical systems shown in Fig. 7(a) and Fig. 7(b). For the simulation, a method based on light propagation calculation (Non-Patent Document 4) was used. The parameters of each optical system were set as shown in Table 1. The difference between the present invention and the prior art is the focal length f of the phase distribution given to the first divided light and the second divided light. d1 and f d2 In the prior art of FIG. 7(a), f d1 to ∞ (plane), f d2 = 400 mm, and in the present invention, f d1 =-400mm, f d2 =200mm.

[0067] [Table 1]

[0068] The distance from the condenser lens 2 to the subject 1 is recorded at position z. s The resolution was evaluated using the theoretical formula for the resolution of incoherent digital holography described in Non-Patent Document 5. Figure 8 shows a comparison of the resolution between the present invention and the prior art. In the case of the prior art shown in Figure 8(a), z s The resolution is highest at z = 400 mm, but s On the other hand, in the case of the present invention shown in FIG. 8(b), z s = 400 mm, the resolution is improved. In other words, in the present invention, the resolution is improved by moving the position of the subject 1 closer to the condenser lens 2 without changing the wavelength or the NA of the lens.

[0069] To verify the effects of the present invention, we placed object 1 at positions "A," "B," "C," and "D" in Figure 8 and performed a simulation of reconstructing an image from a hologram. Object 1 is two point light sources placed 26 μm apart, as shown in Figure 9. Figure 10 shows the results of capturing and reconstructing a hologram of object 1 using the hologram imaging devices of the present invention and the prior art. Note that a four-step phase shift method was used to capture the hologram. Figures 10(a), (b), (c), and (d) correspond to the results captured under conditions "A," "B," "C," and "D," respectively.

[0070] As can be seen from FIG. 8(a), in the conventional technology, the resolution is highest in the case of “B”, and the recording position z s It can be seen that in the case of "A" where the distance is even shorter, the resolution deteriorates. Figures 10(a) and (b), which correspond to these conditions, also show the same tendency as in Figure 8, and it can be seen that the two point light sources are better separated in "B" than in "A", and a relatively clear image is obtained. However, with conventional technology, the resolution in Figure 10(b) is the limit.

[0071] On the other hand, in the present invention, as shown in the theoretical resolution in FIG. 8(b), the recording position z s The resolution is improved for "C", where the length is shorter. Figure 10(c), which corresponds to "C", has the highest resolution of the four images, and it can be seen that the two point light sources are more resolved than in Figure 10(d). Also, for reference, Figure 8 shows that the resolution is the same under conditions "B" and "D", but this is when subject 1 is placed at the focus of condenser lens 2, and Figures 10(b) and (d) also show that this tendency is the same.

[0072] As mentioned above, the condenser lens 2 is not essential, and even if the condenser lens 2 is not used, the closer the subject 1 is to the optical system, the better the resolution. In the hologram imaging device of the present invention, by bringing the subject position closer to the optical system or the condenser lens, the high-frequency components of light can be reflected in the hologram, and it was confirmed from the simulation results that the shorter the distance, the better the resolution.

[0073] The holographic imaging device of the present invention can be used as a stereoscopic camera and is applicable to interference measurement and analysis devices such as three-dimensional microscopes.

[0074] Although the above-described embodiments have been described as representative 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 component block described in the embodiments can be rearranged so as not to be logically inconsistent, and multiple component blocks can be combined or divided into one. [Explanation of symbols]

[0075] 1. Subject 2. Condenser lens 3 Beam Splitter 4 convex mirror 5 concave mirror 6 wavelength filters 7 Spatial Light Modulator 8 Polarizer 9 Concave Lens 10 Polarizer 11 Convex Lens 12 Liquid crystal lens 20 Image sensor 30 Processing equipment

Claims

1. A focusing lens that focuses incoherent light waves from a subject, a light dividing element that divides the focused light waves into a first divided light and a second divided light, an optical element that functions as a lens with a negative focal length that modulates at least one of the first divided light and the second divided light, and an optical element that functions as a lens with a positive focal length that modulates at least the other of the first divided light and the second divided light, a hologram imaging device that causes the first divided light and the second divided light, which have been modulated and given different phase distributions, to interfere with each other to form a hologram and capture the hologram with an imaging element, A hologram imaging device characterized in that the distance between the subject and the condenser lens is made shorter than the focal length of the condenser lens, thereby improving resolution compared to when the subject is positioned at the focal length of the condenser lens.

2. 2. The hologram imaging device according to claim 1, A hologram imaging device, characterized in that the focal length of an optical element that functions as a lens with a negative focal length is greater than the focal length of an optical element that functions as a lens with a positive focal length.

3. 3. The hologram imaging device according to claim 1, A hologram imaging device, characterized in that the imaging element is positioned at a distance of 2xy / |x-y| or more from the optical element having the lens function, where x is the focal length of an optical element having the lens function but with a negative focal length, and y is the focal length of an optical element having the lens function but with a positive focal length.

4. 4. The hologram imaging device according to claim 1, A hologram imaging device comprising: a beam splitter that splits an incoherent light wave into a first divided light and a second divided light; a convex mirror that is an optical element having the function of a lens with a negative focal length; and a concave mirror that is an optical element having the function of a lens with a positive focal length.

5. 5. The hologram imaging device according to claim 4, A holographic imaging device, wherein one of the convex mirror and the concave mirror is replaced with a spatial light modulator.

6. 4. The hologram imaging device according to claim 1, A hologram imaging device comprising: a first polarizer that converts incoherent light waves into linearly polarized light; a spatial light modulator that applies phase modulation to one of polarized light components whose vibration directions are orthogonal to each other using a lens with a positive focal length and converts the other polarized light component into a plane wave; a lens with a negative focal length that transmits the two polarized light components reflected or transmitted by the spatial light modulator; and a second polarizer that aligns the vibration directions of the two polarized light components.

7. 4. The hologram imaging device according to claim 1, A hologram imaging device comprising: a first polarizer that converts incoherent light waves into linearly polarized light; a spatial light modulator that applies phase modulation to one of polarized light components having orthogonal vibration directions using a lens with a negative focal length and converts the other polarized light component into a plane wave; a lens with a positive focal length that transmits the two polarized light components reflected or transmitted by the spatial light modulator; and a second polarizer that aligns the vibration directions of the two polarized light components.

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