Hologram recording method, hologram reproduction method, and holography apparatus
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- CHIBA UNIV
- Filing Date
- 2025-01-24
- Publication Date
- 2026-08-05
Smart Images
Figure 2026126729000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a method for recording holograms using incoherent light, a method for reproducing holograms, and a holography apparatus. [Background technology]
[0002] Holography is a technology that uses the interference phenomenon of light to record and reproduce light waves from a three-dimensional object as a hologram. Traditionally, coherent light has been used to enhance the coherence of light waves when recording holograms. However, coherent light sources such as lasers are not only expensive, but in digital holography, where a reconstructed image is created in a computer from a hologram captured on an image sensor using coherent light, the high coherence of coherent light causes speckle-like noise in the reconstructed image, severely limiting the subjects that can be photographed.
[0003] Therefore, in recent years, research has been progressing on incoherent digital holography, which uses inexpensive incoherent light sources such as LEDs and halogen lamps to capture holograms on an image sensor by utilizing the self-interference of incoherent light, and then reconstructs a reconstructed image from that hologram in a computer, in order to eliminate the limitations on what can be photographed.
[0004] As shown in Patent Document 1, in incoherent digital holography, a phase shift method has been established as a technique to remove unwanted light such as direct light and conjugate light from the reconstructed image in order to improve the image quality of the reconstructed image. Specifically, in the digital holography apparatus of Patent Document 1, the phase of one of the two orthogonal directional components in a single optical path is spatially linearly modulated to generate multiple types of phase shift amounts in that directional component. Specifically, for example, a polarizer array is used to generate a spatially and periodically changing distribution of the phase shift amount of the phase-modulated light relative to the wavefront-modulated light, which is part of the object light incident on the image sensor. A hologram having multiple interference fringes with different phase shift amounts for each pixel on the imaging surface of the image sensor is recorded, and in the reconstructive apparatus, a reconstructed image can be obtained using multiple interference fringes with different phase shift amounts by a parallel phase shift method. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2015-1726 (pages 13-14, Figures 9-11) [Overview of the project] [Problems that the invention aims to solve]
[0006] In the digital holography apparatus described in Patent Document 1, multiple types of interference fringes with different phase shift amounts can be spatially divided and multiplexed recorded in a single image taken by an image sensor using a single optical path, making it possible to capture a hologram containing three-dimensional object information as a video using an image sensor. However, there is a problem in that each polarization region of the polarizer array must be matched to each pixel on the imaging surface, which requires extremely high precision in the design of the optical system. In addition, in the digital holography apparatus described in Patent Document 1, a reconstructed image is reconstructed from a hologram recorded with multiple types of interference fringes with different phase shift amounts superimposed, so there is a problem in that the computation time becomes enormous when processing a large number of interference fringes.
[0007] This invention was made in view of these problems, and aims to provide a hologram recording method, a hologram playback method, and a holography apparatus that enable multiplex recording and playback of holograms in a simple manner using incoherent light. [Means for solving the problem]
[0008] To solve the aforementioned problems, the hologram recording method of the present invention is A method for recording holograms using incoherent light, This system is characterized by recording multiple interference fringes with different orientations on a single hologram by changing the angle of the mirror relative to the central optical axis in the optical system during a single image capture by the image sensor. This feature allows for the spatial frequency of interference fringes to be changed while maintaining correlation by altering the angle of the mirror relative to the central optical axis in a single image capture by the image sensor. This enables the recording of multiple interference fringes with different orientations and spacings on a single hologram. As a result, high-speed imaging of holograms using incoherent light at speeds exceeding the performance of the image sensor becomes possible.
[0009] The optical system has an optical path that enables self-interference by incoherent light, The present invention is characterized by changing the angle of one of the two mirrors that constitute the optical path. This characteristic makes it easy to control the optical path difference by changing the angle of one of the two mirrors that make up the optical path.
[0010] The optical system has an optical path that enables self-interference by incoherent light, This method is characterized by changing the angles of both of the two mirrors that constitute the optical path. This feature allows for a high degree of freedom in changing the angle by altering the angles of both mirrors that make up the optical path.
[0011] The optical system has an optical path that enables self-interference by incoherent light, The device is characterized by having two light waves, split by a polarizing beam splitter, pass through the same optical path in opposite directions using two of the aforementioned mirrors, and then causing them to self-interfere. This characteristic allows for actively angling the two light waves, and because the two light waves travel through approximately the same optical path, the path difference is reduced, making it easy to cause the two lights to self-interfere. As a result, by changing the angle of the mirror, multiple interference fringes with different orientations and spacings can be easily recorded on a single hologram.
[0012] The hologram reproduction method of the present invention is This hologram reproduction method uses incoherent light for hologram recording, and by changing the angle of the mirror with respect to the central optical axis in the optical system during a single image capture by the image sensor, it reproduces a reconstructed image from multiple interference fringes recorded in different orientations on a single hologram. This method is characterized by subtracting the average of all pixel values from the pixel values of the hologram, and by cropping and reconstructing the portion of the hologram that contains interference fringes. This feature allows for the reduction of direct light components in holograms, thereby enhancing the contrast of interference fringes, while also efficiently removing noise components from holograms.
[0013] The holographic apparatus of the present invention, A holography apparatus comprising an optical system that enables self-interference by incoherent light, and an image sensor that records interference fringes formed by the self-interference, The optical system is characterized by having an angle-changing means for changing the angle of the mirrors constituting the optical system with respect to the central optical axis of the optical system. According to this feature, in one shooting by the image sensor, by changing the angle of the mirror with respect to the central optical axis in the optical system by the angle changing means, the spatial frequency of the interference fringes can be changed in a state with correlation, and a plurality of interference fringes with different directions and intervals can be easily recorded on one hologram. Therefore, high-speed shooting of a hologram by incoherent light at a speed exceeding the performance of the image sensor becomes possible.
Brief Description of Drawings
[0014] [Figure 1] It is a schematic diagram showing a holography apparatus using an optical system with IFTH in an embodiment of the present invention. [Figure 2] It is a schematic diagram showing the positional relationship of each element constituting an optical system using IFTH in an embodiment. [Figure 3] It is a diagram showing the principle of generation of interference fringes by self-interference of incoherent light. [Figure 4] It is a schematic diagram of a reproduction optical system in incoherent digital holography. [Figure 5] It is a pinhole used in the verification experiment in the example. [Figure 6] (a) is a hologram obtained by shooting a pinhole, (b) is an enlarged view of a frame portion where interference fringes appear in the hologram of (a), and (c) is a reproduced image reproduced by performing a Fourier transform on the hologram of (a). [Figure 7] (a) is a hologram obtained by changing the angle of the mirror from the time of shooting the pinhole in FIG. 6(a), (b) is an enlarged view of a frame portion where interference fringes appear in the hologram of (a), and (c) is a reproduced image reproduced by performing a Fourier transform on the hologram of (a). [Figure 8](a) is a hologram obtained by changing the mirror angle once during a single pinhole exposure, (b) is a magnified view of the frame area in the hologram (a) where interference fringes appear, and (c) is a reconstructed image obtained by performing a Fourier transform on the hologram (a). [Modes for carrying out the invention]
[0015] After much trial and error, the inventors discovered that by changing the angle of a mirror relative to the central optical axis in an optical system that enables self-interference using incoherent light, the spatial frequency of interference fringes can be changed while maintaining correlation. Based on this discovery, by changing the angle of a mirror relative to the central optical axis in an optical system that enables self-interference using incoherent light during a single image capture with an image sensor, multiple interference fringes with different orientations and spacings can be recorded on a single hologram. This makes it possible to create interference fringes on a single hologram in a single capture that would have previously required multiple captures, and furthermore, enables high-speed imaging of holograms using incoherent light at speeds exceeding the performance of the image sensor. In addition, insights into an optical system suitable for recording these multiple interference fringes have been obtained, which are described below.
[0016] Embodiments of the present invention will be described below. However, the present invention can be implemented in many different forms and is not limited to the embodiments and examples shown below.
[0017] In this embodiment, an optical system using incoherent off-axis Fourier triangular holography (IFTH) (see Figure 1) is used, which allows for the separation and imaging of object light, direct light, and conjugate light in a single image taken with an image sensor using incoherent light emitted from a light source such as an incandescent light bulb, LED, halogen lamp, or fluorescent lamp, by utilizing the self-interference of incoherent light. The optical system using IFTH is a self-interference type optical system based on a Sagnac interferometer, and is configured to cause self-interference after two light waves, which have been split by a polarizing beam splitter, pass through the same optical path in opposite directions using two mirrors M1 and M2. "Self-interference" refers to causing interference of light waves by taking advantage of the characteristic that the optical path difference between light waves emitted from the same light source is short.
[0018] Furthermore, in this embodiment, the optical system used for recording the hologram (interference fringes) is not limited to an optical system using IFTH, but may also be an optical system using other techniques such as Fourier incoherent single-channel holography (FISCH), Fresnel incoherent autocorrelation holography (FINCH), or coded aperture correlation holography (COACH), as long as it enables self-interference by incoherent light.
[0019] Here, the principle of interference fringe generation due to self-interference of incoherent light will be explained using Figure 3. As shown in Figure 3, when the object to be photographed (subject) is considered as a collection of point light sources, first, the spherical wave emitted from the point light sources passes through the first polarizer, aligning its polarization direction, and then enters the birefringent element. The leading and lagging axes of the birefringent element are arranged to be parallel to the s-polarization component (see solid arrow) and the p-polarization component (see dotted arrow), respectively. When the light waves 1 and 2, whose polarization directions have been aligned by passing through the first polarizer, pass through the birefringent element, a phase difference is created between the s-polarization component and the p-polarization component, and they are separated into two light waves 1 and 2 with orthogonal polarization directions. At this time, since the two separated light waves 1 and 2 have orthogonal polarization directions, no interference occurs between them. However, as a result of their polarization directions being aligned by passing through the second polarizer, self-interference occurs and interference fringes are formed on the image sensor. Note that in Figure 3, the transmission axes of the first and second polarizers are tilted at 45 degrees with respect to the leading and lagging axes of the birefringent element, respectively.
[0020] In the case of incoherent light, interference fringes are not formed between light waves emitted from different point light sources; only light waves emitted from the same point light source self-interfere, forming interference fringes. In other words, on the image sensor, interference fringes are formed by the light waves emitted from each point light source, and the sum of these fringes is recorded as a hologram.
[0021] The holography apparatus in this embodiment will be explained with reference to Figure 1. As shown in Figure 1, the holography apparatus utilizes an optical system using IFTH and mainly consists of a white light source emitting incoherent light, a transmissive object to be photographed, a bandpass filter that transmits only specific wavelengths, a lens L0, a first polarizer, a polarizing beam splitter, two lenses L1 and L2, two mirrors M1 and M2, a second polarizer, a mirror M3, a lens L3, and an image sensor that records a hologram (interference fringes). In this embodiment, the polarizing beam splitter performs the same function as the birefringent element in Figure 3. Also, in Figure 1, the light wave incident on the polarizing beam splitter is reflected and split into light wave 1 (s-polarized) that passes through the optical path in the order of lens L1, mirror M1, mirror M2, and lens L2, and light wave 2 (p-polarized) that passes through the optical path in the order of lens L2, mirror M2, mirror M1, and lens L1. In other words, the two light waves 1 and 2, which are split by the polarizing beam splitter, will travel along the same optical path in opposite directions through the two mirrors M1 and M2.
[0022] In this embodiment, at least one of the two mirrors M1 and M2 is configured to be angle-changeable relative to the central optical axis of the optical system by an angle-changing means. A dynamic mirror device such as a two-dimensional scanning galvanometer mirror or a spatial phase modulator (SLM) is used as the angle-changing means, allowing the angle of the mirror relative to the central optical axis of the optical system to be changed by external control.
[0023] In this embodiment, for example, by changing the angle of one of the two mirrors M1 and M2, M2, with respect to the central optical axis in an optical system using IFTH, the spatial frequency of the interference fringes recorded by the image sensor while maintaining correlation, i.e., the direction and spacing of the interference fringes, can be changed.
[0024] Furthermore, the inventors have confirmed that the reconstructed image, which is reconstructed from interference fringes recorded on the image sensor after the angle of mirror M2 is changed, appears at a position rotated from the reconstructed image, which is reconstructed from interference fringes recorded on the image sensor before the angle of mirror M2 was changed. Specifically, the reconstructed image, which is reconstructed from interference fringes, appears at a position that revolves around (hereinafter simply referred to as "rotated") the direct light component that appears at the center of the image, depending on the angle of mirror M2.
[0025] Preferably, the angle of mirror M2 is controlled by the angle changing means such that the position of the reconstructed image, reconstructed from interference fringes recorded on the image sensor after the angle change of mirror M2 is rotated by an angle of less than 180 degrees, based on the position of the reconstructed image, reconstructed from interference fringes recorded on the image sensor before the angle change of mirror M2. For example, when the angle of mirror M2 is changed once during a single image capture by the image sensor, the angle of mirror M2 is controlled such that the position of the reconstructed image, reconstructed from interference fringes recorded on the image sensor after the angle change of mirror M2 is rotated by an angle of 90 degrees, based on the position of the reconstructed image, reconstructed from interference fringes recorded on the image sensor before the angle change of mirror M2. This allows for efficient recording of the target information in a hologram.
[0026] Furthermore, during a single image capture by the image sensor, the angle of the mirror M2 may be changed multiple times, provided that noise does not cause a degradation in the image quality of the reconstructed image. In this case, it is preferable that the amount of angle change of the mirror M2 is controlled so that the reconstructed image, reconstructed from the interference fringes recorded by the image sensor, appears at equally spaced positions each time the angle of the mirror M2 is changed.
[0027] Furthermore, when utilizing self-interference using incoherent light, it is difficult to form interference fringes on the image sensor, so it is preferable to align the central optical axis of the optical system as much as possible. One example of the procedure for aligning the central optical axis of the optical system is as follows: First, arrange only the polarizing beam splitter and mirrors M1, M2, and M3, and with the optical path to the image sensor secured, a laser light source adjusted horizontally is incident on the polarizing beam splitter, and the angle between the polarizing beam splitter and mirrors M1, M2, and M3 is adjusted, and the irradiated laser is set as the central optical axis of the optical system. Next, arrange each lens according to its focal length and adjust its position so that the laser set as the central optical axis of the optical system passes through the center of the lens. Finally, arrange the first polarizer, second polarizer, bandpass filter, transmission-type imaging target, and white light source.
[0028] Furthermore, as shown in Figure 2, the positional relationship of each element constituting the optical system, specifically the distance z between the transmission-type imaging target and the lens L0, is also shown. s The focal lengths f0 of lens L0, f1 of lens L1, f2 of lens L2, f3 of lens L3, and d2 of lens L3 are arranged to be in a predetermined positional relationship. Note that in Figure 2, the transmission-type imaging target is z s The lenses are arranged so that the positional relationship is f0. Also, the distance between lenses L1 and L2 via mirrors M1 and M2 is f1 + f2. Furthermore, the distance between lenses L1 and L3 via the polarizing beam splitter and mirror M3 is f1 + f3, and similarly, the distance between lenses L2 and L3 is f2 + f3.
[0029] Next, the propagation of light waves in a holography apparatus will be explained using Figure 1. As shown in Figure 1, in a holography apparatus, light waves emitted from a white light source pass through a transmission-type imaging target, then pass through a bandpass filter, where only specific wavelengths are transmitted, increasing the monochromaticity of the light waves, and further change in phase when passing through lens L0. Lens L0 is a convex lens, and its phase conversion effect focuses the incident plane wave light to a predetermined focal length before it enters the polarizing beam splitter. The phase-changed light waves then pass through the first polarizer, aligning their polarization direction at a 45-degree angle. The light waves incident on the polarizing beam splitter are separated into two light waves 1 and 2 depending on their polarization direction. Specifically, the polarizing beam splitter reflects the s-polarized light wave 1 at a 90-degree angle and transmits the p-polarized light wave 2. As light wave 1, which is s-polarized, and light wave 2, which is p-polarized, pass through lenses L1 and L2, their phases change. They are then reflected by mirrors M1 and M2, which are positioned at appropriate angles, and travel along the same optical path in opposite directions before being incident on the polarization beam splitter again. The two light waves 1 and 2 then pass through the second polarizer and lens L3 in that order in the optical path to the image sensor, which is secured by the polarization beam splitter and mirror M3, before reaching the image sensor. On the image sensor, they form interference fringes due to self-interference.
[0030] Here, regarding a 0.3 mm diameter pinhole as the object to be photographed (see Figure 5), as described in the embodiment later, when interference fringes are recorded on the image sensor using coherent light, the interference fringes appear across the entire hologram. In contrast, when interference fringes are recorded on the image sensor using self-interference with incoherent light, as in this embodiment, the interference fringes appear only in a portion of the hologram (see Figures 6 to 8, etc.). In other words, when interference fringes are recorded on the image sensor using self-interference with incoherent light, as in this embodiment, the interference fringes are recorded on the hologram at a smaller size compared to when interference fringes are recorded on the image sensor using coherent light. Furthermore, since the information of the object to be photographed is recorded as interference fringes, the parts of the hologram other than the interference fringes become a source of noise in the reconstructed image.
[0031] From these facts, by recording a plurality of interference fringes on a single hologram while changing the angle of the mirror by using self-interference of incoherent light, more interference fringes can be recorded in different directions on a single hologram while protecting the interference fringes necessary for forming a reproduced image. Thus, in the present embodiment, by utilizing the characteristics of interference fringes when using self-interference of incoherent light, it is possible to angularly multiplex-record a plurality of interference fringes on a single hologram.
[0032] Next, a method for reproducing the hologram obtained by the hologram recording method in the present embodiment will be described.
[0033] A hologram recorded by an optical system using IFTH is considered to be simply the sum of contributions from all point light sources, and since the object light is included in the form of an inverse Fourier transform, it is necessary to perform a Fourier transform for reproducing the hologram. In order to perform a Fourier transform, in addition to the object image, a conjugate image identical to the object image appears at a point-symmetric position in the reproduced image, and the direct light component appears at the center of the image, so it is separable from the component of the object light, and degradation of image quality due to direct light can be suppressed. Note that, as in the present embodiment, when the distance z between the transmissive imaging object in the holography apparatus and the lens L0 s and the focal length f0 of the lens L0 are in the same plane (z s = f ), a reproduced image can be obtained simply by performing a Fourier transform, but when z s ≠ f0, a reproduced image can be obtained by using a diffraction integral at the distance z between the transmissive imaging object and the lens L0. s
[0034] As shown in FIG. 4, in the reproduction optical system in incoherent digital holography, a reproduced image is obtained by utilizing the Fourier transform action of the lens L. r The Fourier transform action of the lens L means that the distribution of light waves on the front focal plane appears as the distribution of light waves on the rear focal plane after being Fourier-transformed. Further, FIG. 4 shows the distance z from the focal plane. r rThis indicates that the object image and its conjugate image appear point-symmetrically at the specified position. Therefore, if you want to adjust the reconstruction plane, you can obtain a reconstructed image at any position by appropriately calculating the propagation of the reconstructed light from the hologram using the angular spectral method.
[0035] Furthermore, in this embodiment, as a hologram reproduction method, a hologram recording method utilizing self-interference by incoherent light is used to improve the image quality of the reproduced image reproduced from multiple interference fringes of different orientations recorded on a single hologram. This is achieved by subtracting the average of all pixel values from the pixel values of the hologram, and by cropping and reproducing only the portion of the hologram that contains interference fringes. This reduces the direct light component in the hologram, strengthens the contrast of the interference fringes, and efficiently removes noise components from the hologram. [Examples]
[0036] Herein, the holography apparatus according to the embodiment described above will be specifically explained below.
[0037] Table 1 shows the positional relationships of the elements that constitute the optical system using IFTH in this embodiment (see Figures 1 and 2).
[0038] [Table 1]
[0039] The polarizing beam splitter (Edmund Optics 65-603) used in the optical system of this embodiment is a cube-shaped device measuring 50 × 50 × 50 mm. The image sensor (Baumer TXG50) used in the optical system of this embodiment has a pixel count of 2448 × 2050 and a pixel spacing of 3.45 μm. The bandpass filter (Edmund Optics BPF86365 for fluorescence) used in the optical system of this embodiment has a central transmission wavelength of 525 nm and a bandwidth of 15 nm. Of the two mirrors M1 and M2 used in the optical system of this embodiment, one of the mirrors, M2, is a mirror whose angle can be manually changed on two axes. A LUXYR-LED PICO manufactured by K-Able was used as the white light source.
[0040] [Verification experiment] First, using the optical system in this embodiment, we will photograph a pinhole (pinhole diameter 0.3 mm) shown in Figure 5 as the target object to verify whether it is possible to take images using an optical system with IFTH. Specifically, by photographing the pinhole, we will verify whether it is possible to record a hologram when the target object is a single, most basic point light source.
[0041] In this embodiment, the object to be photographed was positioned at the focal length f0 of lens L0.
[0042] As shown in the hologram in Figure 6(a) and its enlarged view in Figure 6(b), interference fringes can be seen in small size in a portion of the hologram obtained by pinhole photography. Furthermore, as shown in the reconstructed image in Figure 6(c), two bright spots can be seen in the reconstructed image. In this embodiment, after the Fourier transform to obtain the reconstructed image from the hologram, the pixel values due to direct light in the center were sometimes too large to see the object image. Therefore, a threshold was set so that the object image would be visible, and all pixel values above the threshold were adjusted to the threshold before the reconstructed image was reproduced.
[0043] Here, we will explain the propagation of light waves from a point source in an optical system using IFTH. Light waves emitted from a point source placed at the focal plane of lens L0 are first converted into parallel light by lens L0, and then separated into two light waves based on their polarization direction when incident on a polarizing beam splitter. Subsequently, the two light waves reflected by the mirror are again incident on the polarizing beam splitter, modulated to become parallel light, and then pass through lens L3, which is placed in the optical path from the polarizing beam splitter to the image sensor. As a result, they are ultimately incident on the image sensor as parallel light at different angles, forming interference fringes. Furthermore, it is presumed that the two light waves are incident on the sensor surface of the image sensor at angles other than 0 degrees, creating a state similar to an off-axis hologram, thereby separating and reconstructing object light from direct light and conjugate light. In addition, the range in which interference fringes are formed on the image sensor is limited to the region on the image sensor where the two light waves overlap. Furthermore, given the condition that interference occurs within a range where the difference in optical path lengths of the two light waves does not exceed the coherence length of the light source used, it is presumed that small-sized interference fringes from the point source appeared in a portion of the image, as shown in Figures 6(a) and (b), centered around the location where the difference in optical path lengths is smallest.
[0044] [Image quality enhancement processing for replayed images] In the verification experiment described above, interference fringes appeared only in a portion of the recorded hologram. Since the information of the subject being photographed is recorded as interference fringes, the parts other than the interference fringes cause noise in the reconstructed image. Furthermore, when using the self-interference of incoherent light, the light intensity on the image sensor decreases, weakening the contrast of the interference fringes. To solve these problems and improve the image quality of the reconstructed image, the hologram obtained in the verification experiment described above was subjected to a process in which the average value of all pixel values was subtracted from the pixel values of the hologram recorded on the image sensor (hereinafter referred to as "image quality improvement process A"), and a process in which only the parts with interference fringes were cropped (hereinafter referred to as "image quality improvement process B").
[0045] By performing both image quality enhancement processes A and B, the direct light component in the hologram is reduced, and areas other than interference fringes that were causing noise are removed. This allows for a clearer reproduction of the object light component, resulting in improved image quality of the reproduced image.
[0046] [Angle-multiplex recording of holograms using IFTH] In the optical system using IFTH in this embodiment, the two light waves split by the polarizing beam splitter are passed through the same optical path in opposite directions by two mirrors M1 and M2, and then self-interfered with. By changing the angle of one of the two mirrors M1 and M2, mirror M2, the direction and spacing of multiple interference fringes are changed, thereby performing angle-multiplexed recording of a hologram using incoherent light.
[0047] Furthermore, the extent to which the direction and spacing of interference fringes change in response to changes in the angle of mirror M2 also varies depending on the relative positions of each element constituting the optical system and the position of the object being photographed.
[0048] To verify that the spatial frequency of interference fringes, i.e., the direction and spacing of interference fringes, can be changed on a hologram by changing the angle of mirror M2 with respect to the central optical axis of the optical system, a holographic device using the same IFTH optical system as in the verification experiment described above was used to photograph the pinhole shown in Figure 5.
[0049] Comparing Figure 6(b) and Figure 7(b), it can be seen that changing the angle of mirror M2 alters the direction and spacing of the interference fringes. More specifically, by tilting mirror M2 at a predetermined angle relative to the central optical axis of the optical system, it can be seen that the interference fringes change direction, rotating approximately 50 degrees clockwise. It can also be seen that the spacing of the interference fringes has slightly increased.
[0050] As shown in Figures 6(c) and 7(c), it can be confirmed that there is virtually no difference in image quality between the reconstructed images. Both image quality enhancement processes A and B described above were applied during the reconstruction of the reconstructed images.
[0051] From these findings, it was confirmed that by changing the angle of mirror M2 with respect to the central optical axis of the optical system, the direction and spacing of interference fringes on the hologram can be changed with virtually no effect on the image quality of the reconstructed image.
[0052] Next, we verify the angular multiplexing recording of holograms using incoherent light. In this embodiment, the angle of mirror M2 is controlled by a computer connected to mirror M2 of a holography device using an optical system with IFTH (see Figure 1). Specifically, the angle of mirror M2 is controlled to change n times with respect to the central optical axis of the optical system during the exposure time T of the image sensor (camera). This allows n+1 types of interference fringes to be captured on a single hologram in different orientations during the exposure time T. Furthermore, by cutting out and reconstructing these interference fringes from a single hologram on which n+1 types of interference fringes have been angular multiplexed, n+1 reconstructed images can be obtained from a single hologram.
[0053] Here, with the image sensor exposure time set to 1 second, the angle of mirror M2 was controlled to change once relative to the central optical axis of the optical system, and the result of angle multiplex recording of a stationary object (the pinhole mentioned above) is shown in Figure 8. The angle of mirror M2 is tilted at a predetermined angle relative to the central optical axis of the optical system, as in the verification described above. In addition, both image quality improvement processes A and B described above were performed during the reconstruction of the reconstructed image.
[0054] As shown in Figures 8(a) and 8(b), it can be confirmed that two types of interference fringes with different orientations and spacings are recorded on a single hologram in an overlapping, intersecting state. Furthermore, as shown in Figure 8(c), it can be confirmed that the reconstructed image reconstructed from these two types of interference fringes exhibits the same characteristics as the reconstructed images shown in Figures 6(c) and 7(c), respectively. In addition, it can be confirmed that the reconstructed image from a hologram recorded with two types of interference fringes intersecting and overlapping does not generate new noise and is reproduced without a significant loss of image quality.
[0055] As explained above, in a holography device using an optical system with IFTH, angle-multiplexing of holograms can be easily performed by controlling the angle of the mirror. Furthermore, by utilizing the multiple reconstructed images reconstructed from the multiple interference fringes angle-multiplexed on the hologram, it is possible to improve the image quality of the reconstructed image (still image) and expand the field of view.
[0056] Furthermore, the angular multiplexing of holograms demonstrated in this embodiment shows that high-speed shooting of holograms using incoherent light is possible at a speed exceeding the performance (frame rate) of the image sensor, indicating that this can be applied to shooting moving objects, i.e., video recording.
[0057] Furthermore, the angle-multiplexing recording of holograms demonstrated in this embodiment can be achieved simply by changing the angle of the mirrors constituting the optical system, and since high-speed control is possible using the angle-changing means, high-speed shooting can be easily performed.
[0058] Furthermore, since the holography apparatus in this embodiment changes the angle of one of the two mirrors that make up the optical path, it is easy to control the optical path difference between the two light waves.
[0059] Furthermore, in the holography apparatus of this embodiment, using an optical system with IFTH, two light waves split by a polarizing beam splitter are passed through the same optical path in opposite directions by two mirrors, and then self-interfered with. This allows for actively setting an angle between the two light waves, and because the two light waves pass through approximately the same optical path, the optical path difference is small, making it easy to cause the two lights to self-interfere. As a result, by changing the angle of the mirrors, multiple interference fringes with different orientations and spacings can be easily recorded on a single hologram.
[0060] In this embodiment, angular multiplex recording of a hologram using incoherent light with a transmissive target was described. However, the method is not limited to this; angular multiplex recording of a hologram using incoherent light with a reflective target (reflective object) is also possible. Furthermore, the target is not limited to a two-dimensional object; a three-dimensional object is also possible.
[0061] Although embodiments of the present invention have been described above with reference to the drawings, the specific configurations are not limited to these embodiments, and any changes or additions that do not depart from the spirit of the present invention are also included.
[0062] For example, incoherent light is not limited to light emitted from light sources such as incandescent bulbs, halogen lamps, fluorescent lamps, and LEDs, but may also be natural light such as sunlight.
[0063] Furthermore, in the above embodiment, a configuration was described in which a mirror whose angle can be manually changed on two axes is used as an angle-changing means for changing the angle of the mirror constituting the optical system. However, the invention is not limited to this, and a galvanometer mirror or SLM may also be used as an angle-changing means.
[0064] Furthermore, in the above embodiment, both of the two light waves split by the polarizing beam splitter are affected by the angle change of mirror M2. However, the configuration is not limited to this, and only one of the two light waves split by the polarizing beam splitter may be affected by the angle change of the mirror. For example, if an SLM is used as the angle change means, only the light wave that becomes p-polarized among the two light waves split by the polarizing beam splitter will be affected by the angle change of the mirror, thus creating a configuration in which only one of the two light waves split by the polarizing beam splitter is affected by the angle change of the mirror.
[0065] Furthermore, although the above embodiment described a method in which only the angle of one of the two mirrors M1 and M2 in the optical system is changed with respect to the central optical axis, the invention is not limited to this, and the angle of only mirror M1 may be changed, or the angles of both mirrors M1 and M2 may be changed. Note that by changing the angles of both mirrors that constitute the optical path, the degree of freedom in changing the angles can be increased.
[0066] Furthermore, although the above embodiment was described as recording multiple interference fringes with different orientations and spacings overlapping and intersecting on a single hologram, the invention is not limited to this, and the multiple interference fringes may be recorded partially overlapping, or they may be recorded at completely separate positions without overlapping. [Industrial applicability]
[0067] This invention enables self-interference using incoherent light by changing the angle of a mirror with respect to the central optical axis. This allows for the recording of multiple interference fringes with different orientations and spacings on a single hologram in a single image capture by an image sensor. By utilizing multiple reconstructed images reconstructed from these interference fringes, still images can be obtained with high precision. Furthermore, it enables high-speed shooting of holograms using incoherent light at speeds exceeding the performance of the image sensor. This makes it applicable to the shooting of moving objects, i.e., video recording, and has industrial potential. In addition, it becomes possible to record and reconstruct many shooting targets at high speed using incoherent light emitted from an inexpensive light source, thereby reducing the cost of holography equipment.
Claims
1. A method for recording holograms using incoherent light, A hologram recording method characterized by recording multiple interference fringes of different orientations on a single hologram by changing the angle of a mirror with respect to the central optical axis in the optical system during a single image capture by an image sensor.
2. The optical system has an optical path that enables self-interference by incoherent light, The hologram recording method according to claim 1, characterized in that the angle of one of the two mirrors constituting the optical path is changed.
3. The optical system has an optical path that enables self-interference by incoherent light, The hologram recording method according to claim 1, characterized in that the angles of both of the two mirrors constituting the optical path are changed.
4. The optical system has an optical path that enables self-interference by incoherent light, The hologram recording method according to claim 1, characterized in that two light waves, split by a polarizing beam splitter, are passed through the same optical path in opposite directions by two of the aforementioned mirrors, and then subjected to self-interference.
5. This hologram reproduction method uses incoherent light to record holograms, and by changing the angle of the mirror with respect to the central optical axis in the optical system during a single image capture by the image sensor, a reconstructed image is reconstructed from multiple interference fringes recorded in different orientations on a single hologram. A hologram reproduction method characterized by subtracting the average of all pixel values from the pixel values of the hologram, and cutting out and reproducing the portion of the hologram that has interference fringes.
6. A holography apparatus comprising an optical system that enables self-interference by incoherent light, and an image sensor that records interference fringes formed by the self-interference, A holography apparatus characterized by having an angle-changing means for changing the angle of a mirror constituting the optical system with respect to the central optical axis of the optical system.