JP5162733B2 - Holographic image recording apparatus and image recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image recording device and an image recording method by holography where the simplification of a system constitution and the high speed recording of an image by the high speed acquisition of phase shift hologram data are attained, and further, the simplification and speeding-up of color image recording are attained. <P>SOLUTION: The image recording device 1 comprises: a coherent light generating means 2 for generating coherent light 21; a beam splitter 3 for splitting the coherent light 21 into reference light 22 and illuminating light 23 and emitting the same; an irradiating means 4 for irradiating an object 10 with the illuminating light 23; an image recording means 5 having a light receiving face 5a in which light sensor parts composing pixels are two-dimensionally arranged, and recording the information of light made incident on the light receiving face 5a; and a reference light incidence means 6 for making the reference light 22 incident on the light receiving face of the image recording means 5. The reference light incidence means 6 tilts the propagation direction of reference light LR made incident on the respective pixels of the light receiving face 5a in such a manner that the main phase values of the reference light LR are controlled to the mutually different values in the adjacent pixels, and makes the reference light LR incident on the light receiving face 5a. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an image recording apparatus and an image recording method for electronically recording an image of an object by a phase shift digital holography method.

  Holography divides laser light into coherent illumination light and reference light, receives the object light generated by illuminating the model object with the illumination light and the reference light propagated through another path on the photographic plate surface, This is a technique for recording an interference pattern on the light receiving surface on a photographic dry plate, and a hologram developed by developing this dry plate. By applying reproduction illumination light to the hologram, a stereoscopic image (virtual image) of the object can be reproduced and viewed at the position where the object was.

  Computer holography is a technology that expresses an object as data inside the computer, performs physical simulations of light reflection, diffraction, and interference on the computer, and calculates the data of the interference pattern on any surface defined as the hologram surface. is there. Based on the calculation result, a hologram is produced using some display device. Since an object is defined by data on a computer, a model object is unnecessary and optical correction is possible. Further, the interference patterns recorded in the memory can be displayed one after another on a reflective liquid crystal display or the like to materialize the hologram, and the object image can be continuously reproduced by irradiating the reference light.

  In digital holography, an interference pattern is detected and recorded electronically by a CCD image sensor, a CMOS image sensor or the like instead of a photographic plate. The recorded light intensity distribution is numerically processed by a computer to calculate an object light wave to create a hologram. By using digital holography, wavefront information of object light can be acquired in the form of a two-dimensional complex amplitude distribution on the image sensor surface. Based on this wavefront information, object images at various viewpoints and positions can be obtained as in the above-described computer holography. Also, in digital holography, it is possible to record a high-quality three-dimensional image by removing interference fringes created by object lights.

  Phase shift digital holography is a technique for acquiring the above-described complex amplitude distribution. A conventional hologram using a photographic plate or the like is real type data because the phase information of the object beam is fixed and recorded by a method called interference instead of recording the instantaneous phase of the light wave. The complex amplitude is composed of a plurality of data such as amplitude and phase, or real part and imaginary part. Accordingly, in order to obtain the complex amplitude, a plurality of hologram data are required. In the phase shift digital holography, a plurality of hologram data having different phase states of the reference light with respect to the object beam are used.

  As a method of shifting the phase of the reference light, there is a method of inserting a thin glass plate into the propagation path of the reference light or moving the position of a mirror that reflects the reference light using a piezo element. For example, using a piezo element, three types of hologram data are acquired in a state where the phase of the reference light is shifted by π / 2, and the complex amplitude of the object light is calculated from simultaneous equations between the pixel data of the three holograms. The example to obtain | require is known (for example, refer patent document 1).

In addition, there is a method of acquiring a plurality of hologram data collectively by changing the phase state of the reference light for each pixel on the light receiving surface. For example, by inserting phase shift array elements arranged in an array so that adjacent elements have a phase difference of π / 2 from each other in the propagation path of the reference light, the cross-section of the reference light has a phase distribution. The information of the interference pattern in which the phase of the reference light is changed in four stages of 0, π / 2, π, and 3π / 2 is recorded in the hologram. In this case, each 1/4 of the pixel data in one hologram forms four types of holograms (see, for example, Patent Document 2).
Japanese Patent No. 3471556 JP 2005-283683 A

  However, in the image recording by the phase shift digital holography as shown in Patent Document 1 described above, in order to record a plurality of holograms having different phase states, it is necessary to record a plurality of times while changing the phase state of the reference light. There is a limit to speeding up image recording. In general, since the shift amount with respect to the control parameter for phase shift has wavelength dependence, when recording a color image, a reference light system for each color is necessary. However, for each color and for each phase state of the reference light In addition, it becomes difficult to record holograms at high speed.

  Further, in the image recording by the phase shift digital holography as shown in the above-mentioned Patent Document 2, it is necessary to strictly match the pixel positions of the phase shift array element and the CCD image sensor, and high alignment accuracy is required. Therefore, there is a problem of ensuring reliability against pixel position shift due to disturbance. In addition, it seems difficult to reduce the cost of such a phase shift array element with high accuracy.

  The present invention solves the above-described problems, and realizes simplification of the system configuration and high-speed acquisition of phase shift hologram data to enable high-speed image recording, and simplification and speed-up of color image recording. An object of the present invention is to provide a holographic image recording apparatus and an image recording method capable of easily realizing the above.

In order to achieve the above object, the invention of claim 1 is directed to an image recording apparatus for electronically recording an image of an object by a phase shift digital holography method, coherent light generating means for generating coherent light, and generation of the coherent light. A beam splitter that emits the coherent light generated by the means into reference light and illumination light, an irradiation means for irradiating the object with the illumination light emitted by the beam splitter, and an optical sensor unit that constitutes a pixel. An image recording means for recording information of light incident on the light receiving surface, and a reference light incident for causing the reference light emitted by the beam splitter to enter the light receiving surface of the image recording means and means, wherein the reference light incident means, you the center of each pixel of the reference light incident on each pixel of the light receiving surface That the phase value becomes a different value in adjacent pixels, and to periodically change an integer multiple of the pixel pitch, tilt the propagation direction of the reference light from the normal direction of the light receiving surface, the image The recording means electronically uses an interference pattern formed on the light receiving surface by the reference light incident by the reference light incident means and object light from the object generated by irradiation of illumination light by the irradiation means as image information of the object. To record.

According to a second aspect of the present invention, in the image recording apparatus according to the first aspect, the reference light incident means is configured such that the phase value of the reference light incident on the pixels has a phase value at the center of the pixels between adjacent pixels. The reference light is incident so that a phase difference of / 2 or π is obtained.

  According to a third aspect of the present invention, in the image recording apparatus according to the first aspect, the image recording means includes a CCD image sensor.

  According to a fourth aspect of the present invention, in the image recording apparatus according to the first aspect, the image recording means is configured using a CMOS image sensor.

  According to a fifth aspect of the present invention, in the image recording apparatus according to the first aspect, the coherent light generating means includes three coherent light generators for generating three colors of red, green, and blue, The irradiating means and the reference light incident means are provided corresponding to the coherent light generating means, respectively.

According to a sixth aspect of the present invention, a light beam generating step for generating mutually coherent reference light and illumination light and a light receiving surface formed by two-dimensionally arranging photosensor portions constituting pixels are incident on each pixel of the light receiving surface. phase value in the center of each pixel of the light wave becomes a different value in adjacent pixels, and, tilting the propagation direction to periodically change an integer multiple of the pixel pitch from the normal direction of the light receiving surface A reference light incident step of causing the reference light to enter, an irradiation step of irradiating the object with the illumination light in parallel with the reference light incident step, a reference light incident on a light receiving surface in the reference light incident step, and the reference light An image recording step of electronically recording an interference pattern formed on the light receiving surface by object light generated by irradiation of illumination light in the irradiation step as image information of the object.

  A seventh aspect of the invention is the image recording method according to the sixth aspect, further comprising an amplitude calculation step of obtaining a complex amplitude of the object light based on the image information recorded by the image recording step.

According to the first aspect of the present invention, the propagation of the reference light is such that the phase value ( main phase value ) at the center of each pixel of the reference light incident on each pixel on the light receiving surface is different from each other in adjacent pixels. Since the direction is inclined from the normal direction of the light-receiving surface, image information necessary for determining the complex amplitude of the object light, that is, a plurality of hologram data (hereinafter referred to as the phase data of the reference light in the phase shift digital holography) (Also referred to as phase shift hologram data) can be acquired by one recording. Therefore, high-speed recording of images by high-speed acquisition of phase shift hologram data can be realized. The present invention is based on the phenomenon that the reference light phase is periodically distributed on the light receiving surface when the light receiving surface is obliquely irradiated with the reference light composed of plane waves, and a plurality of reference light phases differing using the periodic distribution of the phases. The interference pattern is simultaneously recorded.

  Therefore, in order to make the phase values different from each other in adjacent pixels, it is only necessary to incline the propagation direction of the reference wave from the normal direction of the light receiving surface, so that a spatial light modulation element or phase shift array element for changing the phase Alternatively, a phase modulation plate such as glass to be inserted into the optical path is unnecessary, and the system configuration of the reference light incident means is simplified. As described above, since the condition adjustment by the reference light incident means is only adjustment of the propagation direction, it is easy to ensure the stability of the image recording apparatus, and a highly reliable and easy-to-use apparatus can be realized.

  In addition, according to the present invention, it is possible to easily realize the simplification and speeding up of color image recording. That is, phase shift hologram data necessary for colorization can be acquired by recording three times corresponding to the three colors only by setting the incident angles of the three parallel reference lights of red, green, and blue. Further, the phase sharing of the pixels on the light receiving surface can be made common to different colors by simply adjusting the incident angle for each light of different colors. That is, since the wavelength dependency in the phase shift can be absorbed by the incident angle, it is possible to easily realize the color image correspondence without complicating the system configuration.

  The acquisition of the three phase shift hologram data corresponding to the three colors described above can be performed at high speed by switching the laser light sources at high speed by configuring the coherent light generating means using pulse laser light sources of the respective colors. Therefore, according to the present invention, a compact and inexpensive three-dimensional moving image recording apparatus can be realized by using a pulse laser and a light receiving element, and a color image of a moving subject or a changing subject can be recorded at a high speed. Dimensional color moving images can be recorded in real time. The image recording apparatus of the present invention is capable of image recording for clear three-dimensional color moving image display with little noise, and is used in fields such as video technology, information, medical, design support, and virtual reality. be able to.

  According to the invention of claim 2, the light receiving surface formed by arranging pixels in a square lattice is covered with a set of four pixels combined in a square shape in which the phase difference between adjacent pixels is π. Thus, two hologram data having different phase states can be acquired by one recording. The pixel arrangement is simple and data processing is easy. In order to obtain the complex amplitude of the object light from the hologram data, it is necessary to obtain three unknowns: the amplitude of the object light, the amplitude of the reference light, and the phase difference between the object light and the reference light. Therefore, the unknown can be reduced by one by adding a measurement that blocks either the object light or the reference light and measures the intensity of the other light.

  In addition, the light receiving surface formed by arranging the pixels in a square lattice is covered with a set of four pixels that are linearly combined so that the phase difference between adjacent pixels is π / 2, and the phase state Four different hologram data can be acquired by one recording. Of the four hologram data, the complex amplitude of the object light can be obtained using three or four pieces of data.

  In addition, the light receiving surface formed by arranging the pixels in a square lattice pattern is set to 2 × 4 so that the phase difference between adjacent pixels in one direction is π and the phase difference between pixels in the other direction is π / 2. It is possible to acquire four pieces of hologram data having different phase states by one recording by covering the eight sets. In this case, two pixels of the same phase value are arranged in eight pixels by arrangement of shogi and chess. In addition, the phase difference between two arranged pixels is π, and the phase difference between four arranged pixels is π / 2. According to such an arrangement of in-phase pixels, the distribution of pixels having the same phase can be made uniform, the deviation of the distribution of data points can be suppressed, and four hologram data with different phase states can be recorded at one time. You can get it.

  According to the third aspect of the present invention, the image recording means is configured by using the CCD image sensor that can reduce the pixel size with less noise, so that it is possible to record a fine and less noise image.

  According to the invention of claim 4, since the image recording means is configured using the CMOS image sensor which has a degree of freedom of selection of pixels to be read, operates at a low voltage and can reduce power consumption, an easy-to-use image recording apparatus is provided. realizable.

  According to the invention of claim 5, since the system for acquiring hologram data using three colors of coherent light is provided, it is possible to easily record a color image. The acquisition of three phase shift hologram data corresponding to the three colors can be executed by switching the laser light source using the laser light source for each color as the coherent light generating means. Further, when a pulse laser light source is used as the laser light source, color image recording can be executed at a higher speed. Moving light and time-varying phenomena can be imaged by speed of light recording.

  According to the invention of claim 6, the propagation direction is inclined so that the main phase value of the reference light incident on each pixel on the light receiving surface becomes a different value in adjacent pixels, and the reference light is made incident on the light receiving surface. Since the interference pattern between the reference light and the object light on the light receiving surface is recorded, image information necessary for determining the complex amplitude of the object light, that is, hologram data having different phase states in the phase shift digital holography is recorded once. It can be easily obtained by recording.

  According to the seventh aspect of the present invention, since the complex amplitude is obtained based on the recorded image information, an image with less noise from which the conjugate image or the like is removed can be easily reproduced using the complex amplitude.

  Hereinafter, an image recording apparatus and an image recording method based on a phase shift digital holography method according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows an image recording apparatus 1 according to the first embodiment. The image recording apparatus 1 includes a coherent light generation unit 2 that generates coherent light, a beam splitter 3 that emits the coherent light 21 from the coherent light generation unit 2 into reference light 22 and illumination light 23, and a beam splitter 3. The irradiation means 4 for irradiating the object 10 with the illumination light 23 emitted from the light source and the light receiving surface 5a formed by two-dimensionally arranging the light sensor portions constituting the pixels and recording information of light incident on the light receiving surface 5a. Image recording means 5 and reference light incident means 6 for making reference light 22 emitted by the beam splitter 3 incident on the light receiving surface of the image recording means 5 are provided.

  The coherent light generating means 2 is composed of a laser. Therefore, the coherent light 21 is a laser light. The beam splitter 3 is composed of, for example, a half mirror. The reference light 22 is coherent light 21 that has passed through the beam splitter 3, and the illumination light 23 is coherent light 21 that has been reflected by the beam splitter 3.

  The irradiating means 4 includes lenses 41 and 42, and irradiates the object 10 with illumination light Li that is expanded into a parallel beam by expanding the beam diameter of the illumination light 23 by the collimator function of these lenses 41 and 42. Since the illumination light Li is parallel light, it is a plane wave. The illumination light Li does not have to be parallel light and does not have to be a plane wave.

  The image recording means 5 includes, for example, an image sensor 51 composed of a CCD image sensor, and an image recording unit 52 that records image data output from the image sensor 51 and processes the data. The optical sensor part of the CCD image sensor constitutes a pixel, and the two-dimensional array surface of the optical sensor part constitutes the light receiving surface 5a.

  The reference light incident means 6 includes a mirror M and lenses 61 and 62. The direction of the reference light 22 is changed by the mirror M, and the beam diameter of the reference light 22 is enlarged by the collimator function of the lenses 61 and 62 to be parallel light. The reference light LR is incident on the light receiving surface 5a. Since the reference light LR is a parallel light like the illumination light Li, it is a plane wave.

  The reference light incident means 6 changes the propagation direction of the reference light LR of the light receiving surface 5a so that the main phase value of the reference light LR incident on each pixel of the light receiving surface 5a becomes a predetermined different value in adjacent pixels. The reference light LR is incident on the light receiving surface 5a at a predetermined angle from the normal direction. The incidence of the reference light LR on the light receiving surface 5a is a feature of the phase shift digital holography in the present invention, and will be described in detail after the description of the second embodiment described later.

  Under the above-described configuration, the reference light LR incident by the reference light incident unit 6 and the object light Lo from the object 10 generated by the irradiation of the illumination light Li by the irradiation unit 4 form an interference pattern on the light receiving surface 5a. Form. As a matter of course, the optical system in the image recording apparatus 1 has a difference in path length between the reference light LR and the object light Lo from the laser light source of the coherent light generation means 2 to the light receiving surface 5a within the coherence length of the laser light. It is set to fit. The image recording means 5 detects an interference pattern on the light receiving surface 5 a by the image sensor 51 and electronically records the output as image information of the object 10 in the image recording unit 52. The recorded image data can be moved using a communication means or a portable recording medium separately provided in the image recording apparatus, and can be used in other places and apparatuses.

  The incidence of the reference light LR on the light receiving surface 5a by the reference light incident means 6 is adjusted by the incident angle with respect to the light receiving surface 5a so that a specific phase state appears for each specific pixel. The image information recorded by 5 is obtained by collectively recording a plurality of pieces of hologram data (a plurality of pieces of phase shift hologram data) having different phase states in the phase shift digital holography. In other words, the image information received all at once by the two-dimensionally arranged pixels corresponds to a plurality of pieces of phase shift hologram data.

  The image recording means 5 may use a CMOS image sensor as the image sensor 51 instead of the CCD image sensor. Also in this case, like the CCD image sensor, the photosensor portion of the CMOS image sensor constitutes a pixel, and its two-dimensional array surface constitutes the light receiving surface 5a.

  When a CCD image sensor is used for the image recording means 5, it is possible to form the light receiving surface 5a with less noise and smaller pixel dimensions, and it is possible to record a fine and less noise image. Further, when a CMOS image sensor is used for the image recording means 5, it is possible to realize an easy-to-use image recording apparatus 1 by taking advantage of characteristics such as a high degree of freedom in selecting pixels to be read, low voltage operation, and low power consumption.

(Second Embodiment)
FIG. 2 shows a flowchart of an image recording method according to the second embodiment. The image recording method of the present embodiment is a method of recording an image by phase shift holography using, for example, the image recording apparatus 1 of the first embodiment described above. Therefore, description will be made with reference to FIG. 1 again. Therefore, the description here is a part of the content described above. That is, in this image recording method, the light receiving surface 5a includes a light beam generating step S1 that generates the coherent reference light LR and the illumination light Li, and the light receiving surface 5a formed by two-dimensionally arranging the optical sensor units constituting the pixels. A reference light incident step S2 for injecting the reference light LR by inclining the propagation direction from the normal direction of the light receiving surface 5a so that the main phase values of the light waves incident on the respective pixels are different from each other in adjacent pixels. I have.

  Further, in the present image recording method, the irradiation step S3 for irradiating the object 10 with the illumination light Li in parallel with the above-described reference light incident step S2, and the reference light LR incident on the light receiving surface 5a in the reference light incident step S2 An image recording step S4 for electronically recording an interference pattern formed on the light receiving surface 5a by the object light Lo from the object 10 generated by the irradiation of the illumination light Li in step S3 as image information of the object 10. .

  According to this image recording method, the propagation direction is inclined so that the main phase value of the reference light LR incident on each pixel of the light receiving surface 5a is different from each other in adjacent pixels, and the reference light LR is applied to the light receiving surface 5a. Since the interference pattern between the reference light LR and the object light Lo on the light receiving surface 5a is recorded, the image information necessary to determine the complex amplitude of the object light Lo, that is, the phase state in the phase shift digital holography is recorded. A plurality of different hologram data can be easily acquired by one recording.

  The image recording method described above can further include an amplitude calculation step S5 for obtaining a complex amplitude of the object light Lo based on the image information recorded in the image recording step S4. Since the complex amplitude is obtained based on the recorded image information in the amplitude calculation step S5, when the image is reproduced in the next step, the complex amplitude is used to reproduce an image with less noise from which a conjugate image or the like is removed. It becomes easy and the utilization efficiency of image information improves.

(Detailed description of reference light incidence in the first and second embodiments)
With reference to FIGS. 3A and 3B and FIGS. 4A and 4B, the phase shift due to the oblique incidence of the reference light LR will be described. In the image recording apparatus 1 and the image recording method of the present invention, the parallel reference light LR is obliquely irradiated onto the light receiving surface 5a of a light receiving device such as a CCD image sensor, and the phase of the reference light LR on the light receiving surface 5a is periodically changed. An interference pattern formed by the object light Lo and the reference light LR is recorded by being distributed.

  Each pixel on the light receiving surface 5a uses the light reception intensity integrated over the entire sensor section of each pixel as the normal image sensor, so the light reception intensity recorded for each pixel. Is proportional to the received light intensity at the center of each pixel. Therefore, when the received light intensity is recorded using a CCD image sensor or the like, an interference pattern sampled at intervals equal to the pixel pitch on the light receiving surface 5a can be recorded.

  When the incident angle of the reference light LR is set so that the main phase (that is, the phase at the center of the pixel) of the reference light LR is distributed on the light receiving surface 5a with a period that is an integral multiple of the pixel pitch, the phase shift element is Without use, a set of a plurality of interference patterns having different phase states of the reference light LR, that is, a plurality of hologram data having different phase states in the phase shift digital holography method can be acquired by one imaging.

(Diagonal irradiation of parallel reference light and pixel phase)
3A and 3B show a state in which the reference light LR having the wavelength λ is obliquely incident on the light receiving surface 5a in the image recording apparatus 1 and the image recording method. Here, an xyz orthogonal coordinate system is defined in which the light receiving surface 5a is an xy plane, and the direction perpendicular to the light receiving surface 5a is the z axis. It is assumed that the pixels are arranged in a grid pattern on the light receiving surface 5a, and the x axis and the y axis are the pixel arrangement directions.

As shown in FIGS. 3A and 3B, the reference light LR obliquely incident on the light receiving surface 5a has an incident angle θx in the zx plane and an incident angle θy in the zy plane. Then, the phase distribution φ _R (x, y) of the reference light LR on the light receiving surface 5a with the point x = y = 0 as a reference is expressed by the following equation (1).

The above equation (1) indicates that the phase distribution φ _R (x, y) changes in the x-axis direction and the y-axis direction with the periods λ / sin θ _x and λ / sin θ _y , that is, linear on the light receiving surface 5a. It shows that the distributed equiphase points (intersection lines formed between the wavefront having a constant phase value and the light receiving surface 5a) are periodically distributed. Therefore, if the interference pattern formed by the object light Lo and the reference light LR is recorded by sampling the equiphase value pixels on the surface of the light receiving element, a plurality of interference patterns having different optical phases can be recorded by one shooting. .

The above is the effect of obliquely entering the reference light LR. If the reference light LR is perpendicularly incident on the light receiving surface 5a, θx = θy = 0, and thus φ _R (x, y) = 0, and a phase distribution on the light receiving surface 5a cannot be obtained.

  Here, a specific example of the phase distribution for each pixel on the light receiving surface 5a will be described. FIG. 4A shows that the phase with respect to the origin of the xy coordinate is π by appropriately selecting the incident angles θx and θy described above according to the wavelength λ of the reference light LR and the pitch of the pixel array. Shown is a state where the light receiving surface 5a is completely covered by a set of four pixels combined in a square shape such as / 2, 3π / 2, π / 2, 3π / 2 (each section indicates a pixel region, the same in the following) ). The state of the light receiving surface 5a indicates a state in which the main phase value of the reference light LR incident on each pixel is different from each other in adjacent pixels, that is, a phase difference between adjacent pixels is π.

  On the light receiving surface 5a in FIG. 4A, one phase-shifted digital hologram is obtained by a set of pixels having a phase value of 3π / 2, and another one by a set of pixels having a phase value of π / 2. One sheet of phase shift digital hologram is obtained. That is, two pieces of phase shift hologram data in which the phase of the reference light LR is shifted by π can be acquired by one recording.

  The pixel arrangement described above is simple and data processing is easy. In order to obtain the complex amplitude of the object light Lo from the hologram data, it is necessary to obtain three unknowns: the amplitude of the object light Lo, the amplitude of the reference light LR, and the phase difference between the object light Lo and the reference light LR. Therefore, the complex amplitude of the object light Lo is obtained by adding one measurement to block either the object light Lo or the reference light LR and measuring the intensity of the other light, thereby reducing the unknown by one. Can do.

  FIG. 4B shows the x and y directions so that the phase with respect to the origin of the xy coordinates is π / 4, 3π / 4, -3π / 4, and −π / 4. A state in which the light receiving surface 5a is completely covered by a set of four pixels combined side by side is shown. Main phase values differ by π / 2 between adjacent pixels. According to the phase value distribution in this state, four hologram data having different phase states can be obtained by one recording. However, since the distribution of the in-phase value pixels is staggered, the example of FIG. 4B is not very preferable.

(Preferred pixel distribution for phase shift)
FIG. 5 shows a more preferable phase and pixel arrangement in which four hologram data with different phase states can be acquired by one recording. Such an arrangement will be described again by appropriately selecting the incident angles θx and θy shown in FIGS. 3A and 3B in accordance with the wavelength λ of the reference light LR and the pitch of the pixel array. The That is, the phase shift attribute is determined for each pixel by setting the incident condition of the reference light LR. As a result of setting the incident condition of the reference light LR, the light receiving surface 5a formed by arranging pixels in a square lattice pattern is changed to pixels having a phase of −3π / 4, −π / 4, π / 2, and 3π / 4. It can be covered with 8 sets of 2 × 4, and four hologram data with different phase states can be acquired by one recording.

  In FIG. 5, when attention is paid to 8 pixels arranged in the x-axis direction and 4 pixels in the y-axis direction (pixels in the thick solid line frame in the figure), Pixels corresponding to + 3π / 4 pixels are arranged one position to the right and two positions above. All the pixels are arranged with pixels having the same phase as each other and arranged in a Keima manner. Further, the phase difference is set to π between two pixels arranged in the x-axis direction, and the phase difference is set to π / 2 between four pixels arranged in the y direction. According to such a phase and pixel arrangement, the distribution of pixels having the same phase on the light receiving surface 5a can be made more uniform (uniform), so that a high-quality phase shift that suppresses the deviation of the distribution of data points. Digital hologram data can be acquired.

  The state of uniformity described above can be confirmed by the shading diagram shown in FIG. This shading diagram is obtained by recording an interference pattern between the reference light LR set under the above-described incident conditions and the parallel object light Lo perpendicularly incident on the light receiving surface 5a.

  Such a shading diagram can be used as an adjusting means for setting the incident angles θx and θy of the reference light LR to predetermined angles. That is, it is only necessary to adjust the incident angles θx and θy of the reference light LR so that the image output from the image sensor 51 is enlarged and displayed on the monitor, and the grayscale display for each pixel is clearly obtained. In addition, such adjustment includes means for operating the incident angles θx and θy, for example, control means for controlling the control current of the actuator means for tilting the mirror M, with the electric signal value corresponding to the gray value as the target value. It can be automated by this control means.

(Interference pattern sampling)
The reference light LR whose incident conditions are set so as to have the phase value distribution shown in FIG. 5 and the scattered light (object light Lo) emitted from the object 10 illuminated by the illumination light Li are the light receiving surface 5a. Is incident, the interference pattern formed by the reference light LR and the object light Lo is recorded as a hologram. The contents of this recording will be described using mathematical expressions. When the object light Lo of the angular frequency ω on the light receiving surface 5a is O (x, y, t) and the reference light LR is R (x, y, t), it can be expressed by the following equation (2) ) (3). Further, the light intensity I (x, y) measured by averaging over the light receiving surface 5a is expressed by the following equation (4). Equation (4) is a mathematical representation of the hologram.

The first term and the second term on the right side of the above equation (4) correspond to the light intensities of the object light Lo and the reference light LR, respectively, which are low frequency components I generated by the interference between the direct current component Id and the object light Lo. _L (x, y) is constructed. The first and second terms do not include the phases of the object light Lo and the reference light LR. The third term is a high frequency component I _H (x, y) that represents an AC component of an interference pattern created by the object light Lo and the reference light LR. This third term includes the amplitude O _O and the phase φ _O which are wavefront information of the object light Lo. That is, the wavefront information (complex amplitude) of the object light Lo is recorded by the third term on the right side. When the amplitude O _O and the phase φ _O are obtained, the complex amplitude of the object light Lo is obtained, and the wave front of the object light Lo, that is, the image reproduction can be performed by the complex amplitude.

By measuring a plurality of data corresponding to the above equation (4) under conditions where the phase of the reference light LR is different, that is, by recording a plurality of phase shift hologram data, based on simultaneous equations between the data, The amplitude O _O and the phase φ _O can be obtained.

  The above-described interference pattern I (x, y) will be described in the case of recording on a finite light-receiving surface with a pixel pitch d and the number of pixels N × N.

In this case, the interference pattern on the light receiving surface 5a can be represented by a Fourier series having a basic period Nd determined from the pixel pitch d and the size N of the light receiving surface. Therefore, the high frequency component I _H (x, y) for the object light Lo at the viewing angle θ _O is represented by a Fourier series in which the integers m and n are in the ranges m _MIN <m <m _MAX and n _MIN <n <n _MAX . It is expressed as the following equation (5). Note that the tilde above the capital letter I in the formula that appears below is ignored.

By the way, in each pixel such as a CCD image sensor, the value integrated over the entire surface of the optical sensor unit is recorded as the intensity of the incident light, so that the high frequency component recorded by the pixel having the center coordinates (x _S , y _S ) is recorded. The value is expressed by the following formula (6).

The function (πm / N) sin (πm / N) (πn / N) sin (πn / N) on the right side of the above equation (6) changes gently with respect to the integers m and n. Therefore, the integral value of I _H (x, y) is expressed by the following equation (7) for an object (subject) having a viewing angle θ _O that satisfies the inequality, θ _O << (λ / d). Can be approximated.

Here, the integers m _R and n _R are determined from the incident angle of the reference light, and m _R = N (d / λ) sin (θ _x ) and n _R = N (d / λ) sin (θ _{y, respectively.} ). That is, the value of the high frequency component I _H recorded in each pixel is set to a constant d ² (πm _R / N) sin (I _H (x _S , y _S ) sampled at the center (x _S , y _S ) of the pixel. It is equal to a value obtained by multiplying πm _R / N) (πn _R / N) sin (πn _R / N). Therefore, when an object satisfying the viewing angle θ _O satisfying θ _O << (λ / d) is recorded on the light receiving surface, an interference pattern I _H generated by the object light Lo and the reference light LR is obtained from the interference pattern sampled at the center of each pixel. It will be recorded as (x _S , y _S ).

(Derivation of complex amplitude hologram)
When the incident angle of the reference light LR is set to a specific value so that the phase period of the reference light LR on the light receiving surface 5a is an integral multiple of the pixel pitch d, a plurality of interference patterns for different reference light phases are simultaneously recorded. it can. At this time, the interference pattern with respect to the same reference light phase is recorded by skipping pixels, and the interval between the recording pixels is an integral multiple of the pixel pitch. For a subject whose viewing angle θ _O satisfies θ _O << λ / d, the amplitude O _O and the phase φ _O of the object light Lo gradually change between the pixels of the light receiving surface 5a. Therefore, as described above, in the recording data for the same reference light phase, the pixel values that are not recorded can be obtained with sufficient accuracy by interpolation.

  Under the incidence conditions of the reference light LR that can take four types of phase values shown in FIG. 5 described above, four types of independent recording data (phase shift hologram data) can be obtained. Interpolation processing is performed on each data, and the complex amplitude of the object light Lo on the light receiving surface 5a can be obtained using three or four pieces of interference pattern data.

FIG. 7 shows the phases φ ₁ , φ ₂ , φ ₃ , and φ ₄ of the reference light LR at the centers of the four pixels around the focused lattice point (pixel boundary intersection) on the light receiving surface 5a. The phase Δφ ₁ , Δφ ₂ , Δφ ₃ , Δφ ₄ at the _four pixel centers around the lattice point when the reference light phase φ _G of the focused lattice point is used as a reference can be obtained by referring to the above equation (1). The following equations (8) and (9) are obtained.

From the interference patterns (hologram data) collectively recorded for the _four phases φ ₁ , φ ₂ , φ ₃ , φ ₄ , four interference patterns (phase shift hologram data) are obtained by the above-described interpolation for each phase. Ask for. The values of the four interference patterns in the pixel at the upper right of the lattice point are I ₁ , I ₂ , I ₃ , and I ₄ , respectively, and the cosine components that are the real part and imaginary part of the complex amplitude with reference to the phase φ _{G of the} lattice point I _C and sine component I _S are represented by the following equations (10) and (11), respectively.

Then, using a cosine theorem and a sine theorem of trigonometric functions, I ₁ , I ₂ , I ₃ , and I ₄ can be represented by a DC component Id and low-frequency components I _L and I _C , _IS , respectively. Conversely, the cosine component I _C and the sine component I _S of the complex amplitude hologram can be obtained from four equations representing I ₁ , I ₂ , I ₃ , and I _{4, and} are expressed by the following equations (12) and (13). .

By the addition / subtraction operation shown in the above formulas (12) and (13), the DC component I _d in I ₁ , I ₂ , I ₃ , and I ₄ and the low frequency component I _L caused by the interference between the object lights Lo disappear. Only the target AC component generated by the interference between the object light Lo and the reference light LR remains. In this way it is possible to obtain all the pixels complex amplitude excluding the DC component I _d and the low-frequency components I _L, consisting of complex amplitude obtained can be reproduced image of high quality.

(Derivation of complex amplitude inline hologram)
The complex amplitude hologram obtained by the equations (12) and (13) is a spatial carrier type hologram based on an off-axis method for obliquely irradiated parallel reference light. If the off-axis hologram for the oblique irradiation reference light is converted into an in-line hologram for the vertical irradiation reference light (incident angle θ _x = θ _y = 0), the spatial frequency of the interference pattern can be lowered, so the amount of hologram data for the same recorded image Can be reduced. However, in order to perform such hologram conversion, calculation processing for conversion is required.

  However, if the incident angle of the reference light LR is set to a specific value so that the phase period of the parallel reference light LR on the light receiving surface 5a is twice or four times the pixel pitch, without performing complicated calculation, An in-line hologram can be obtained directly from the interference pattern recorded only by the addition / subtraction operation, and the calculation process for hologram conversion can be omitted. This is shown below.

As shown in FIG. 5, the case where the incident angles θ _x and θ _y are set so that the phase periods in the x direction and the y direction are respectively twice and four times the pixel pitch d will be described. In this case, d, λ, θ _x , and θ _y satisfy the relationship of the following expression (14).

Further, when the incident angles θ _x and θ _y of the reference light LR are set so as to satisfy the above equation (14), the phase of the lattice point at the coordinates (id, jd) on the xy plane is expressed by the above equation. From (1), φ _R (id, jd) = (2i + j) π / 2. The phase of the reference light LR at the center of each pixel with the lattice point shown in FIG. 7 as a reference is expressed by Δφ ₁ = 3π / 4, Δφ ₂ = −π / 4, Δφ ₃ = −3π according to the equations (8) and (9). / 4, Δφ ₄ = π / 4. In this case, the cosine component I _InC and the sine component I _InS of the complex amplitude of the inline hologram are _{expressed by the} following equations (15) and (16) when (2i + j) is an even number, and the following equation (17) when (2i + j) is an odd number: (18) That is, a complex amplitude inline hologram (inline hologram having complex amplitude information) can be obtained only by adding and subtracting the recorded interference pattern data.

(Third embodiment)
Next, with reference to FIG. 8, a color-compatible image recording apparatus according to the third embodiment will be described, and with reference to FIGS. 9 to 12, an example of recording data including image examples will be described. The image recording apparatus 1 according to the present embodiment is different from the image recording apparatus 1 according to the first embodiment shown in FIG. 1 that includes one coherent light generation unit 2 (laser light source). Three coherent light generating means 2 are provided so as to generate three colors of red R, green G, and blue B coherent light.

  Further, the image recording apparatus 1 includes a beam splitter 3, an irradiation unit 4, and a reference light incident unit 6 corresponding to each coherent light generation unit 2. Except for these points, the image recording apparatus 1 of the present embodiment is the same as that of the first embodiment described above, and a duplicate description is omitted. The image recording means 5 is used in common for the three colors.

  According to this image recording apparatus 1, the color image recording can be easily simplified and speeded up. That is, the phase shift hologram data necessary for colorization can be acquired by recording three times corresponding to the three colors only by setting the incident angles to the light receiving surface 5a of the parallel reference lights LR of the three colors of red, green, and blue. .

  Further, by adjusting the incident angle for each light of a different color, the phase sharing of the pixels on the light receiving surface 5a can be made common to different colors. That is, since the wavelength dependency in the phase shift can be absorbed by the incident angle, it is possible to easily realize the color image correspondence without complicating the system configuration. The reason that the image recording means 5 is common to the three colors is due to this wavelength-dependent absorption ability.

  The acquisition of the phase shift hologram data three times corresponding to the three colors described above can be performed at a higher speed by switching the light speed of the laser light source by configuring the coherent light generation means 2 using three pulse laser light sources corresponding to each color. Can be executed.

  Therefore, according to the present invention, a compact and inexpensive three-dimensional moving image recording apparatus can be realized by using a pulse laser and a light receiving element, and a color image of a moving subject or a changing subject can be recorded at a high speed. Dimensional color moving images can be recorded in real time. The image recording apparatus 1 is capable of image recording for displaying a clear three-dimensional color moving image with little noise, and is used in fields such as video technology, information, medical, design support, and virtual reality. Can do.

(Reference light incident angle adjustment method)
In order to obtain three-color phase-shift digital holograms from the three-color interference patterns of red, green, and blue, it is necessary to set the incident angles θx and θy of each reference light LR to predetermined values. The setting of the incident angle can be performed based on the shading diagram shown in FIG. 6 as in the first embodiment.

  That is, also in the case of a color image, the phase shift method using the 2 × 4 pixel group shown in FIG. 5 which is the basis of FIG. 6 can be applied for each color. Therefore, for each color, the shading diagram of FIG. 6 can be used as a means for adjusting the incident angles θx and θy of the reference light LR. The automation of the adjustment is the same as described above, and the description is omitted.

(Recording of 3D color images)
The optical system of each color is set so that the path length difference between the reference light LR and the object light Lo from the laser light source to the light receiving surface 5a is within the coherence length of the laser light. Further, as described above, the interference patterns on the light receiving surfaces 5 a of red, green, and blue, which are formed by the reference light LR and the object light Lo, are recorded by the image sensor 51 and the image recording unit 52.

  As a method for recording a three-dimensional color image by substantially one shooting, the three color pulse laser light sources are time-divided so that their oscillation times do not overlap, and a single color image sensor 51 is used to interfere with three colors. A method of recording a pattern in an extremely short time and a method of simultaneously recording three colors using a color-compatible image sensor 51 can be used. The former method requires accurate adjustment of the oscillation time of the three-color pulse laser and high-speed reading of the recording data from the image sensor 51. In contrast, the latter method may have a problem of sensitivity, but can avoid a problem of recording speed.

(Example of recorded image)
A dice having a side length of 2 cm was placed as a subject object 10 at a position 75 cm away from the image sensor 51, and a phase shift hologram was recorded using the three-dimensional color image recording apparatus 1. FIG. 9 shows an interference pattern recorded with green laser light, and FIGS. 10A and 10B show enlarged images of the cosine component and sine component of the complex amplitude in-line hologram obtained from the hologram data, respectively. Hologram data was recorded in one image using the image recording method of the second embodiment described above using a continuous wave laser instead of a pulse laser. The cosine component and the sine component of the complex amplitude in-line hologram are normalized using the effective value of the amplitude and then displayed with 256 gradations.

  The interference pattern shown in FIG. 9 includes not only the interference pattern created by the object light Lo and the reference light LR but also the interference pattern (noise) created by the object light Lo, so that the original object light Lo and the reference light LR are The interference pattern to be created is displayed as a high-frequency interference pattern image with low contrast as a result of the disturbance due to this noise. On the other hand, in the in-line hologram shown in FIGS. 10A and 10B, the component generated by the interference between the object lights Lo is removed, and the interference pattern formed by the object light Lo and the reference light LR is purely contrast. Is displayed as a high-definition, low-frequency interference pattern image.

  FIGS. 11A, 11B, and 11C show the complex amplitude in-line holograms acquired for the three colors red, green, and blue as described above, and reproduced by numerical calculation from the complex amplitude data. A blue image is shown. These images have high image quality without noise and are reproduced at the same position as the subject on which the images are recorded.

  FIG. 12 shows a color image reproduced from the above-described red, green, and blue complex amplitude data. The color image shown in FIG. 12 that has been recorded in this manner, calculated, and reproduced is a high-quality color image without color misregistration.

  The present invention is not limited to the above-described configuration, and various modifications can be made. For example, the relationship between the pixels and the phase on the light receiving surface 5a is not limited to those shown in FIGS. 4A and 4B and FIG. 5, and the entire relationship is rotated by 90 °, and the x axis and the y axis are interchanged. The relationship is also included. Further, the arrangement of the optical system shown in FIGS. 1 and 8 and the types of optical elements such as lenses and mirrors are not limited to those shown in these drawings. The phase difference between the pixels is not limited to π / 2 or π, and may be π / 3. In addition, the pixel arrangement row of the image sensor is not limited to a lattice shape, and may be an arbitrary two-dimensional array. Therefore, a light receiving surface that covers a two-dimensional plane by a staggered arrangement of hexagonal pixels or a pixel arrangement having a plurality of sizes may be used. Note that the terms such as phase, phase value, and phase state described above originally represent matters that are relative to each other, but are used in a simplified manner within a range that does not cause misunderstanding.

1 is a conceptual configuration diagram of an image recording apparatus according to a first embodiment of the present invention. 6 is a flowchart of an image recording method according to a second embodiment of the present invention. (A) and (b) are diagrams for explaining incidence of reference light on a light receiving surface in the image recording apparatus and the image recording method. (A) and (b) are diagrams for explaining an example of phase shift for each pixel in the image recording apparatus and the image recording method. The figure explaining the other example of the phase shift with respect to each pixel of the light-receiving surface in an image recording device and an image recording method same as the above. FIG. 6 is a shading display diagram of an interference pattern by reference light and normal incidence parallel object light on the light receiving surface of the pixel configuration shown in FIG. 5. Explanatory drawing of the complex amplitude calculation in the lattice point of the pixel arrangement | sequence shown in FIG. FIG. 9 is a conceptual configuration diagram of a color-compatible image recording apparatus according to a third embodiment of the present invention. The figure which shows the example of the red interference pattern recorded by the image recording apparatus same as the above. 9A is a diagram of a hologram corresponding to the real part of the complex amplitude of the interference pattern of FIG. 9, and FIG. 10B is a diagram of a hologram corresponding to the imaginary part of the complex amplitude. 9A is a red image reproduced from the interference pattern of FIG. 9, FIG. 9B is a green image reproduced from the interference pattern recorded together with the interference pattern of FIG. 9, and FIG. The figure of the blue image reproduced from the interference pattern recorded with the pattern. The figure of the color image reproduced based on the interference pattern which reproduced the image of Drawing 11 (a) (b) (c).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image recording device 2 Coherent light generation means 3 Beam splitter 4 Irradiation means 5 Image recording means 6 Reference light incident means 51 Image sensor 5a Light-receiving surface Li Illumination light Lo Object light LR Reference light

Claims (7)

In an image recording apparatus that electronically records an image of an object by a phase shift digital holography method,
Coherent light generating means for generating coherent light;
A beam splitter that divides the coherent light generated by the coherent light generation means into reference light and illumination light, and
Irradiating means for irradiating an object with illumination light emitted by the beam splitter;
An image recording unit having a light receiving surface formed by two-dimensionally arranging photosensor portions constituting pixels and recording information of light incident on the light receiving surface;
A reference light incident means for making the reference light emitted by the beam splitter incident on a light receiving surface of the image recording means,
The reference light incident means has a phase value at the center of each pixel of the reference light that is incident on each pixel on the light receiving surface, which is different from each other in adjacent pixels , and periodically at an integral multiple of the pixel pitch. In order to change, the propagation direction of the reference light is tilted from the normal direction of the light receiving surface,
The image recording means uses, as image information of an object, an interference pattern formed on the light receiving surface by the reference light incident by the reference light incident means and object light from the object generated by irradiation of illumination light by the irradiation means. An image recording apparatus for electronic recording.
The reference light incident means causes the reference light to be incident so that the phase value of the reference light incident on each pixel has a phase difference of π / 2 or π between adjacent pixels. The image recording apparatus according to claim 1.
  The image recording apparatus according to claim 1, wherein the image recording unit is configured using a CCD image sensor.   The image recording apparatus according to claim 1, wherein the image recording unit is configured using a CMOS image sensor.   Three coherent light generating means are provided to generate three colors of red, green, and blue coherent light, and the beam splitter, the irradiating means, and the reference light incident means are respectively connected to the coherent light. The image recording apparatus according to claim 1, wherein the image recording apparatus is provided corresponding to the light generation means. A light flux generating step for generating mutually coherent reference light and illumination light;
The phase value at the center of each pixel of the light wave incident on each pixel on the light receiving surface on the light receiving surface formed by two-dimensionally arranging the photosensor portions constituting the pixels is different from each other in adjacent pixels , and A reference light incident step in which the reference light is incident by tilting the propagation direction from the normal direction of the light receiving surface so as to periodically change at an integer multiple of the pixel pitch ;
An irradiation step of irradiating the object with the illumination light in parallel with the reference light incident step;
An interference pattern formed on the light receiving surface by the reference light incident on the light receiving surface in the reference light incident step and the object light from the object generated by the illumination light irradiation in the irradiation step is electronically recorded as image information of the object. An image recording method comprising: an image recording step.
  The image recording method according to claim 6, further comprising an amplitude calculation step of obtaining a complex amplitude of the object light based on the image information recorded by the image recording step.