JPH06118306A - Reading method of optical storage device - Google Patents

Abstract

PURPOSE:To read three-dimensionally recorded data by a simple optical system without any interference between data by providing a two-dimensional photoelectric detectors which detects an image observed through a transmission type microscope optical system. CONSTITUTION:The light from a surface light source 1 is converged by a condenser lens 2 to light a medium 3 where data are recorded. A data image in a photopolymer is formed on the two-dimensional photoelectric detector 5 such as an objective 5 and a CCD. The detector reads all data in the visual field on a focal plane at a time by a two-dimensional detector such as a photoelectric detector. When an optical system is so adjusted that one data correspond to one pixel of the photoelectric detector, data of 250 Kbits can be read out at a time by using a two-dimensional photoelectric detector which has 512X512 pixels. The recording medium is scanned in an X-Y direction to read data in other areas on the same plane. Data recorded in respective depth-directional layers can be read out by moving a movable stage in a Z direction for scanning.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reading device for recording data in a recording device for three-dimensionally recording data by changing a refractive index in a recording medium.

[0002]

2. Description of the Related Art As computers have become more sophisticated and information has become more multidimensional in recent years, large-capacity data recording devices have become necessary. Being developed. But,
In these optical storage devices, the recording density per unit area is limited by the size of the focused spot diameter determined by the laser light used and the aperture of the lens, so it is difficult to dramatically improve the recording capacity. It was

In order to realize a larger recording capacity in the optical storage device, the optical storage device has a three-dimensional structure in which data is recorded not only in the two-dimensional plane but also in the depth direction (optical axis direction). Should be realized.

Several three-dimensional optical memories for writing data one by one on a recording medium have been proposed (DA Parth
enopoulos and PM Rentzepis: Science Vol. 245, 8
43-844, 1989; S. Hunteer, F. Kiamilev, S. Esener,
DA Parthenopoulos, and P. M. Rentzepis: Appl. Op
t. Vol. 29, 2058-2066, 1990; JH Strickler and
WW Webb: Opt. Lett. Vol. 16, 1780-1782, 1991).
This storage method writes data in a photopolymer by utilizing the fact that two-photon absorption occurs in proportion to the square of the light intensity. First, laser light is focused on a photopolymer that is a storage medium. Since the two-photon absorption occurs in proportion to the square of the light intensity, the two-photon absorption occurs only near the focal point where the laser light intensity is large, and the bonding state of the photopolymer changes. Due to the structural change of this photopolymer,
The refractive index changes only near the laser focus. The polymer is scanned in three dimensions and the data is recorded point by point in three dimensions. In this way, by recording the data three-dimensionally point by point, a large capacity optical memory can be realized.

A method using a confocal optical system has been proposed as a method for reading out three-dimensionally recorded data in a recording medium (Hashimoto, Kawata, Kawada: Proceedings of Kyoto Symposium on Optical Union Symposium p. 39-40, 1992). However, the confocal optical system has a problem in that the adjustment of the optical system is difficult and the device becomes expensive.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to realize a method for reading out three-dimensionally recorded data in a recording medium with a simple optical system without interference between data.

[0007]

According to the present invention, data recorded three-dimensionally in a recording medium is read using a transmission microscope optical system having an incoherent illumination system or a phase contrast microscope optical system. Is characterized by.

[0008]

According to the present invention, as a method for optically reading data recorded by a change in the refractive index of the recording medium in a recording apparatus for recording data three-dimensionally in the recording medium,
Transmission microscope optical system with incoherent illumination system,
Alternatively, a phase contrast microscope optical system is used. The former readout optical system constitutes a transmission microscope optical system having an incoherent illumination system and at least one objective lens.
The latter reading optical system constitutes a phase contrast microscope optical system having a partially coherent light source.

A principle of reading data recorded as a change in refractive index in a recording medium in a transmission microscope optical system having an incoherent illumination system will be described. First, the reading principle when the change in the refractive index formed in the recording medium is small, as in the case where a photorefractive crystal or the like is used in the recording medium, will be described.

The change in the refractive index formed as recording data in the recording medium is considered to be the superposition of sinusoidal phase gratings having various periods. When the illumination light enters one of the phase gratings, it is diffracted by this phase grating to generate 0th order light (transmitted light) and diffracted light. When the change in the refractive index of the phase grating is small, the high-order diffracted light can be ignored, and the image of the phase object is detected by the two interference fringes formed by the 0th-order diffracted light and the + 1st-order diffracted light and the −1st-order diffracted light, respectively. It is formed at the position of the image plane. The interference fringe formed by the + 1st-order diffracted light and the -1st-order diffracted light has a small amplitude and can be ignored. The two interference fringes due to the interference between the 0th-order diffracted light and the ± 1st-order diffracted lights are exactly 180 degrees out of phase with each other in the focal plane of the objective lens, so that the light intensity distribution is uniform. Therefore, the image of the phase grating is not observed. On the other hand, when observing the "blurred image" of the phase grating at a position shifted from the focal plane, the phase shift of the above two interference fringes is
It is not 180 degrees and the image of the phase grating can be observed. Even if there are many phase gratings, the image of each phase grating can be observed by shifting the focus position in the same manner. Therefore, the image of the data recorded as the change in the refractive index can be observed by defocusing and the data can be read. When the defocus amount increases, the blur of the data image increases, and the data image loses contrast. Therefore, the three-dimensionally recorded data can be read out.

Next, the principle of reading data in the case where the change in refractive index caused by photopolymer is large will be described. When the refractive index change of the phase grating becomes large, ±
The second or higher order diffracted light cannot be ignored. These diffracted lights interfere at the image plane to form an image of the phase object. for that reason,
High-order diffracted light also forms an interference fringe on the image plane to form an image. Even in this case, if all high-order diffracted light is collected and an image is formed, the image becomes uniform as in the case where the change in the refractive index is small,
No image of the phase grating is observed. However, in an actual optical system, all higher-order diffracted light cannot pass through the pupil of the objective lens and cannot be involved in image formation. Therefore, a bright and dark image is formed on the focal plane. Therefore,
When the change in the refractive index in the area where the data is recorded is large, the structure of the phase grating can be observed by the transmission microscope optical system without defocusing. Therefore, even if the change in the refractive index of the area where the data is recorded is large, the data can be read using the transmission microscope optical system.

In the present invention, incoherent illumination is used. Even with coherent illumination, you can read the image of the recorded data. However, with coherent illumination, the depth of focus becomes large, and the resolution of the three-dimensionally recorded data in the depth direction (optical axis direction) cannot be obtained. In incoherent illumination, the depth of focus of the optical system is shallow, and the data image of the other layer does not overlap the image of the data existing on the focal plane, and only one layer of data can be read out without interference.

The fact that a phase object can be observed with a phase contrast microscope optical system has been proposed and analyzed by Zernik (F.
Zernike: Z. Tech. Phys. Vol. 16, 454-457, 1935).
The imaging characteristics of the microscope when observing a phase object using the phase contrast microscope optical system are similar to those when observing an absorbing object using a normal transmission microscope optical system. When the three-dimensional data is observed using the phase contrast microscope optical system, the data image other than the focal plane is blurred. That is, the phase contrast microscope optical system has a depth resolution and can read out three-dimensionally recorded data.

[0014]

FIG. 1 shows an example of data reading using the transmission microscope optical system according to the present invention. This optical system includes an incoherent surface light source (1), a condenser lens (2), a recording medium (3) on which data is recorded as a change in refractive index, a three-dimensional movable stage (4), an objective lens (5), a CCD, etc. It is composed of a two-dimensional detector (6) such as a photoelectric detector. A surface light source such as a tungsten lamp, a halogen lamp, or a xenon lamp is used as a light source. The light from the surface light source (1) is condensed by the condenser lens (2) to illuminate the medium (3) on which data is recorded. In this embodiment, a photopolymer is used as a data recording medium. A two-dimensional photoelectric detector (6) such as a CCD for the data image in the photopolymer with the objective lens (5)
Image on top.

Since a two-dimensional detector such as a photoelectric detector is used as the detector, all data in the field of view of the focal plane can be read at once. If the optical system is adjusted so that one pixel corresponds to one pixel of the photoelectric detector, when a two-dimensional photoelectric detector having 512 × 512 pixels is used, 250 kilobits of data can be read at one time. The recording medium is scanned in the xy directions (in-plane directions) to read the data in other areas existing in the same plane. The data recorded on each layer in the depth direction is read by scanning the movable stage in the z direction (optical axis direction).

FIG. 2 shows an experimental example in which data is read according to the above embodiment. In each of (a) and (b), the left side is a pattern of data recorded in the photopolymer, and the right side is a result obtained by reading it with the transmission microscope optical system according to the present invention. (a) and (b) are the results of reading the sixth and eleventh layers of the data recorded in the eleventh layer in the depth direction. The white and round spots on each layer of the read data are the recorded 1-bit data. The in-plane data spacing is 3 micrometers, and the spacing between layers in the depth direction is 20 micrometers. It can be seen that the data of each layer can be read with good contrast without being affected by the data of the other layers. FIG. 3 shows another embodiment using a transmission microscope optical system. This optical system consists of a laser light source (7),
It is composed of an objective lens (5), a data recording medium (3), a three-dimensional movable stage (4), a condenser lens (2), and a surface detection (8).

The light from the laser light source (7) is focused on one point in the data recording medium by the objective lens (5).
The transmitted light and diffracted light from the recording medium are condensed by the condenser lens (2), and the intensity is detected by the surface detection (8) having no spatial resolution.

To read the three-dimensionally recorded data, the recording medium is three-dimensionally scanned. In this example,
The recording medium is scanned by the three-dimensional movable stage (4). In the optical system of the present embodiment, even though the laser which is the coherent light source is used, it is equivalent to the imaging characteristic of the transmission microscope optical system having the incoherent illumination system (Satoshi Kawada, Shigeo Minami: Optics Vol. 18). , 380-391, 199
2). Therefore, the laser scanning microscope optical system can read out the three-dimensionally recorded data.

In this embodiment, a surface detector having no spatial decomposition can be used as the detector. Therefore, a high sensitivity detector such as a photomultiplier tube can be used as the detector.
Therefore, even when the change in the refractive index of the data image is very small, the data can be read out with high sensitivity. Further, in the laser scanning microscope, since the illumination light is focused and irradiated on one point of the sample, there is no scattered light from other places, and the data can be read with good contrast.

In this embodiment, a scanning microscope is realized by using a stage that can move in three dimensions.
The beam may be scanned in the focal plane using a polygon mirror, a photoacoustic element, or the like. High-speed data reading is possible by scanning the beam.

FIG. 4 shows an embodiment of data reading using a phase contrast microscope optical system. This optical system includes a surface light source (1), a collector lens (9), and a ring slit (1).
0), a condenser lens (2), a data recording medium (3), a three-dimensional movable stage (4), an objective lens (5), a phase plate (11), and a two-dimensional detector (6).

Light from the incoherent surface light source (1) is passed through the collector lens (9) to the ring slit (1
0) Collected on. The light transmitted through the ring slit (10) illuminates the data recording medium (3) by the condenser lens (2). The light incident on the data recording medium is diffracted by the change in the refractive index in the recording medium, and is divided into transmitted light and diffracted light. The transmitted light and the diffracted light enter the phase plate (11) after passing through the objective lens (5). On this phase plate, a phase film made of a thin film and an absorption film are vapor-deposited at a position where an image of a ring slit is just formed, and a relative phase difference of 90 degrees is given between transmitted light and diffracted light. The transmitted light and the diffracted light that have passed through the phase plate interfere with each other on the image plane to form a certain data image in the recording medium. This data image is 2
The dimension detector 6 detects and reads the data. The data recorded in the depth direction is read by scanning the recording medium in the optical axis direction. Even with this reading method, all the data in the field of view can be read at once. 3D movable stage xy
The data is read by changing the field of view by scanning in the direction (in-plane).

FIG. 5 shows another embodiment using a phase contrast microscope optical system. This optical system includes a laser (7), a phase difference objective lens (12), a data recording medium (3), a three-dimensional movable stage (4), and a point detector (13). The light from the laser (7) is transmitted through the phase difference objective lens (1
The light is focused through 2) and one point on the data recording medium (3) is illuminated. The light transmitted and scattered through the recording medium (3) is coherently detected by the point detector (13). The recording medium is three-dimensionally scanned, and the three-dimensionally recorded data is read out. The point detector (13) may be a combination of a pinhole and a surface detector.

With this optical system, a detector having no spatial resolution can be used as in the embodiment of FIG. 3, so that a high-sensitivity detector such as a photomultiplier can be used. Therefore, highly sensitive data can be read. Further, since only one point of the recording medium is illuminated, there is no scattered light from other places, and a read image with high contrast can be obtained.

For scanning in the focal plane (xy), a beam may be scanned using a galvano mirror, a polygon mirror, a photoacoustic element, or the like. By scanning the beam, the three-dimensional data in the recording medium can be read at high speed.

[0026]

As described above, a large-capacity optical memory can be realized by realizing an optical storage device capable of reading data from a medium in which data is three-dimensionally recorded as a change in refractive index.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a transmission type microscope optical system for reading data according to the present invention.

FIG. 2 is an example of a result of reading three-dimensionally recorded data using the above-described embodiment.

FIG. 3 is an explanatory diagram of another embodiment of a transmission microscope optical system for reading data according to the present invention.

FIG. 4 is an explanatory diagram of an embodiment of a data reading device using a phase contrast microscope optical system.

FIG. 5 is an explanatory diagram of another embodiment of a data reading device using a phase contrast microscope optical system.

[Explanation of symbols]

 1 surface light source 2 condenser lens 3 recording medium on which data is recorded 4 three-dimensional scanning stage 5 objective lens 6 two-dimensional detector 7 laser light source 8 surface detector 9 collector lens 10 ring slit 11 phase plate 12 phase difference objective lens 13 inspection Ejector

Claims (3)

[Claims] 1. A recording apparatus for three-dimensionally recording data in a recording medium by locally changing the refractive index of the recording medium, comprising: an incoherent light source; and a transmission microscope optical system using the incoherent light source as illumination light. And a stage that scans the sample in the depth direction of the recording medium in which the data is three-dimensionally recorded, and a two-dimensional photoelectric detector that detects an image observed by the transmission microscope optical system. Characteristic three-dimensional data reading method. 2. The three-dimensional data reading method according to claim 1, wherein the transmission microscope optical system is a phase contrast microscope optical system having at least a phase difference objective lens. 3. A recording apparatus for recording the data three-dimensionally, comprising: a laser light source; a laser scanning microscope type 1 optical system using the laser light source as an illumination light source; and the laser scanning microscope type 1 in the storage medium. A three-dimensional data reading method, comprising: a scanning mechanism for three-dimensionally scanning a focal spot of an optical system; and a surface photoelectric detector for detecting scattered light from the storage medium.