Patent Application
20050231775
The present invention relates to a recording medium made of a photosensitive material, so-called a holographic memory, and especially the present invention relates to a method for holographic recording and reproducing and an optical information recording and reproducing apparatus using the holographic memory.
A volume holographic recording system is known as a digital data recording system using a principle of holography. This system is characterized in that information is recorded on a recording medium made of a photosensitive material such as a photorefractive material as a variation of a refractive index of the medium.
One of conventional methods for holographic recording and reproducing uses the Fourier transform for recording and reproducing.
Referring to
As described above, the coherent parallel pencil is diffracted by the dot pattern data, and forms an optical image with the Fourier transform lens. The distribution of the image on the focal plane of the Fourier transform lens, namely on a Fourier plane, interferes with the coherent reference beam. Then, interference fringes are recorded on the recording medium in the vicinity of a focal point. After finishing the record of a first page, the turnable mirror is turned by predetermined degrees and moved in parallel, in order to vary the incident angle of the reference beam 12b into the recording medium 10. Then, a second page is recorded following the same procedure as above. Multiple angle recording is carried out in this way.
On the other hand, the inverse Fourier transform is used in reproducing a dot pattern image. In reproducing the recorded information, as shown in
Referring to
The conventional holographic recording and reproducing apparatus requires high spec two lenses, which are the Fourier transform lens and the inverse Fourier transform lens. The apparatus also needs to be provided with a high accuracy paging control mechanism for controlling the reference beam in recording and reproducing the information. Therefore, there is a disadvantage that the apparatus becomes large in size.
An object of the present invention is to provide a method for holographic recording and reproducing and an apparatus therefor which can decrease in size and record a hologram on a holographic recording medium.
According to the present invention, there is provided a method for holographic recording and reproducing comprising a recording process and a reproducing process,
The signal beam is a light beam resulted from such operation that a coherent reference beam spatially modulated in accordance with information to be recorded, which comprises a 0th-order beam having a wavefront having the same shape wherever regardless spatial modulation; and a diffraction beam subjected to the spatial modulation. Thus, the present invention uses the 0th-order beam of the signal beam as reference light for a holographic recording.
In recording, the recording medium is illuminated with the signal beam to generate optical interference fringe patterns caused by the 0th-order beam and the diffraction beam at the path of the signal beam to record the refractive index grating in the recording medium correspondingly to the interference fringe patterns.
In reproducing, the recording medium particularly the refractive index grating therein is illuminated with a signal beam which is not spatially modulated i.e., non-modulated reference beam with the same positional and angular condition of the signal beam used in the recording. Since the non-modulated reference beam includes the 0th-order beam as a major components, the illumination of the non-modulated reference beam to the refractive index grating of the recording medium generates a reproduced wave having a wavefront as the same as that of the signal beam used in the recording.
In a detection of the reproduced wave, the reproduced waves emitted from the refractive index grating in the recording medium overlap with the non-modulated reference beam used for the reproducing. Removing or reducing the non-modulated reference beam used for the reproducing facilitates to detect the reproduced wave easily and reproduce the recorded information electrically.
According to the present invention, there is also provided a recording medium made of a photosensitive material capable of being recorded by illumination with a coherent light beam, the recording medium comprising an incident-light-processing area provided in said recording medium on an opposite side of an entrance surface of the recording medium on which the light beam is incident, the incident-light-processing area separating a 0th-order beam and a diffraction beam of the light beam from each other to return a part of the incident beam to the inside of said recording medium.
To removing or reduce the non-modulated reference beam used for the reproducing, as shown in
There are considered the use of a phase conjugate wave as one of methods for a holographic recording and reproducing system in the recording and reproducing method. The reproducing method with the phase conjugate beam generally requires the identical reference beam in both the recording and reproducing similarly to the other methods. For example, there is a method for recording and reproducing information in which the refractive index grating is generated and recorded by interference in the recording medium in such a manner that the signal beam is irradiate to the recording medium and reflected by a mirror to generate a phase conjugate wave back to the recording medium so that the phase conjugate wave and the signal beam interfere each other. In such recording and reproducing method, there are drawbacks such as a necessity to insert and detach the reflecting mirror, a degradation of light source with a return of the signal beam particularly the 0th-order beam, and a large-sized device including an optical systems to prevent the return light. In contrast, according to the present invention, the incident-light-processing area dissolves the problems because the 0th-order beam and the diffraction beam in the incident light are processed individually with different processed such as a separation to return a part of the incident beam to the inside of the recording medium.
In addition, there is no necessity to provide respective two optical systems for the reference beam and signal beam differently than the conventional holographic recording and reproducing method in the present invention. Furthermore, the method of the present invention does not require a condenser lens with a high performance which is used as an objective lens and the like. Adopting this recording and reproducing method is highly effective to simplify and miniaturize a recording and reproducing apparatus, because of using the 0th-order beam and the diffraction beam (spatially modulated in accordance with information to be recorded) included in the signal beam.
According to the present invention, there is further provided a method for holographic recording comprising the steps of:
According to the present invention, there is still further provided a method for holographic reproducing comprising the steps of:
According to the present invention, moreover there is provided a holographic recording and reproducing apparatus for recording information as a diffraction grating area in a recording medium, and for reproducing said recorded information from said diffraction grating area, said holographic recording and reproducing apparatus comprising:
According to the present invention, there is also provided a holographic recording apparatus for recording information as a diffraction grating area in a recording medium, comprising:
According to the present invention, there is furthermore provided a holographic reproducing apparatus for reproducing information recorded as a diffraction grating area in a recording medium, the reproducing apparatus comprising:
According to the present invention, there is furthermore provided another holographic recording and reproducing apparatus for recording information as a diffraction grating area in a recording medium, and for reproducing said recorded information from said diffraction grating area, said holographic recording and reproducing apparatus comprising:
According to the present invention, there is also provided another holographic recording apparatus for recording information as a diffraction grating area in a recording medium, comprising:
According to the present invention, there is further provided another holographic reproducing apparatus for reproducing information recorded as a diffraction grating area in a recording medium, the reproducing apparatus comprising:
FIGS. 15 to 17 are schematic sectional views for explaining the recording process carried out by the holographic recording and reproducing apparatus according to modified examples of the embodiment of the present invention.
FIGS. 24 to 26 are schematic sectional views for explaining the recording process carried out by the holographic recording and reproducing apparatus according to modified examples of the other embodiments of the present invention.
Embodiments of the present invention will be hereinafter described with reference to the accompanying drawings.
The present embodiment does not use the reference beam provided by another optical path in recording. Instead, only the signal beam is incident on the recording medium, and a refractive index grating generated by interference between the 0th-order beam and the diffraction beam of the signal beam is recorded. After that, the reproduced wave is reproduced from the refractive index grating by illuminating the refractive index grating only with the reference beam. An incident-light-processing area is integrally provided in the recording medium on an opposite side of an entrance surface thereof on which the light beam is incident. The incident-light-processing area separates a 0th-order beam and a diffraction beam of the light beam from each other to return a part of the incident beam to the inside of the recording medium.
The beam expander BX expands the diameter of the light beam 12 passing through the shutter SHs. The light beam 12 becoming a parallel pencil is incident on the spatial light modulator SLM. The spatial light modulator SLM displays light and dark dot matrix signals, in accordance with electronic data received from an encoder 25. The electronic data is represented as a series of a page unit corresponding to a two-dimensional page. Upon passing through the spatial light modulator SLM on which the data is displayed, the reference beam is optically modulated into a signal beam 12a including the data as a dot matrix component. The condenser lens 160 performs the Fourier transform on the dot matrix component of the signal beam 12a passing through the beam splitter 15, and converges it so that the signal beam 12a comes into a focus behind a mounted recording medium 10. When the shutter SHs is opened, the signal beam 12a or the reference beam 12 is incident on the principal surface of the recording medium 10 at a predetermined incident angle, a zero-degree for example, due to the condenser lens 160. The beam splitter 15 is a splitting unit to separate a reproduced wave (described later) from the optical path of the reference beam to supply it the photo detector 20 of a photoelectric transfer device like a CCD. The spatial light modulator SLM and the CCD 20 are disposed at the focal point of the condenser lens 160.
In addition, the beam splitter 15 is disposed in such a position as to be able to send the reproduced wave to the CCD 20. The CCD 20 is connected to a decoder 26. The decoder 26 is connected to the controller 32. Taking a case where information corresponding to the type of a photorefractive crystal is attached to the recording medium 10 in advance, when the recording medium 10 is mounted on a movable stage 60, which is a holding section to move the recording medium 10, the controller 32 automatically reads the information with a proper sensor to perform controllings of the movement of the recording medium 10 and the recording and reprocusing adapted to the recording medium 10.
Referring to
The operation in a recording process will be hereinafter described.
The controller 32 shown in
Then, the recording signals are sent from the encoder 25 to the spatial light modulator SLM, and the spatial light modulator SLM displays a specific pattern corresponding to data to be recorded.
Then, the shutter SHs is opened, and the spatial light modulator SLM is illuminated with a reference beam 12. A signal beam 12a is generated in the reference beam 12 spatially modulated by the spatial light modulator SLM on which the pattern is displayed in accordance with information to be recorded. The recording medium 10 is irradiated with the generated signal beam 12a to the to start the recording process.
The recording process of the refractive index grating using the signal beam 12a (i.e., 0th-order beam and diffract ion beam therein) in the recording medium will be hereinafter described in detail.
As shown in
Since the recording medium 10 is illuminated with the signal beam 12a, the hologram-reference beam and the hologram-signal beam are optically interfered with each other to create an optical interference fringe pattern P1, so that a refractive index grating P1 is recorded in the recording medium 10 due to the photorefractive effect.
The 0th-order beam (i.e., hologram-reference beam) of the signal beam 12a passes through the 0th-order-beam-processing area R1 of the incident-light-processing area R and goes out from the opposite side of the recording medium 10, on which the signal beam 12a is incident. The diffraction beam (i.e., hologram-signal beam) of the signal beam 12a is reflected by the diffraction-beam-processing area R2 of the incident-light-processing area R back to the recording medium 10. Therefore such diffraction beam of the signal beam 12a reflected by the diffraction-beam-processing area R2 is referred to as “reflected-hologram-signal beam”.
The reflected-hologram-signal beam and the hologram-reference beam are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P2, so that a refractive index grating P2 is recorded corresponding to the optical interference fringe pattern P2 in the recording medium 10 due to the photorefractive effect.
In this way, the 0th-order beam and the diffraction beam (i.e., the signal beam 12a) from the spatial light modulator SLM together with the reflected diffraction beam from the diffraction-beam-processing area R2 create the set of the three-dimensional interference patterns inside the recording medium 10 in the recording. As shown in
After recording of the recording medium 10, the shutter SHs is closed by control of the controller 32.
When the recording is finished at the predetermined recording position of the recording medium 10, the recording medium 10 is forced to move (in a “y” direction of
The recording medium 10 and the spatial light modulator SLM are relatively disposed with respect to the optical axis in such a manner that the extending direction DTR of the track TR makes a predetermined angle of θ (θ≠0) with the extending direction DSLM of a row in the pixel matrix of the spatial light modulator SLM. Otherwise the extending direction of a column of the spatial light modulator SLM pixel matrix may be used for the angle setting between the recording medium 10 and the spatial light modulator SLM. The reason for this configuration of the angle setting between the recording medium 10 and the spatial light modulator SLM is as follows.
Generally, the spatial light modulator SLM displays a two-dimensional dot pattern whether or not to allow light to pass through each pixel based on information to be recorded during recording. The spatial light modulator SLM spatially modulates the reference beam 12 passing therethrough to generate the signal beam 12a. Then, the Fourier transform lens or condenser lens 160 performs the Fourier transform on the signal beam 12a to illuminate the recording medium 10 and to form on a Fourier plane FF a dot image caused by the 0th order beam and diffraction beam.
As shown in
When using the spatial frequency (1/a) based on the pixel pitch of the spatial light modulator SLM, the wavelength (λ) of the signal beam 12a and the focal length (f) of the Fourier transfer lens (condenser lens 160), then the distance (d1) between the 0th-order beam and the 1st-order diffraction beam on the Fourier plane FF can be expressed as follows: d1=(1/a)·(λ)·(f). Taking a case where, for example, the spatial light modulator having the pixel dot pitch of 10 μm, the wavelength of the signal beam 12a is 530 nm and the focal length is 14 mm, the distance (d1) between the 0th-order beam and the 1st-order diffraction beam is approximately 750 μm, according to the above equation. Since the highest frequency component in the signal beam 12a modulated by the spatial light modulator SLM that corresponds to the pixel matrix pitch, dot images corresponding to such pixel matrix pitch appear at positions farthest from the dot image caused by the 0th order beam of the signal beam 12a on a Fourier plane FF. Therefore, on the Fourier plane FF, the most part of the spectrum distribution of spatial frequency caused by the spatial light modulator resides within the area which centers on the 0th-order beam of the signal beam 12a and is delineated by the 1st-order diffraction beams that correspond to the pixel pitches along the row and column directions in the the spatial light modulator SLM.
The dot image caused by the diffraction beam corresponding to the extending direction Ds of a row of the spatial light modulator SLM pixel matrix is included in the incident-light-processing area R in the Fourier plane FF. When the extending direction DTR of the track TR makes an angle θ=0 with the extending direction DSLM of a row in the pixel matrix of the spatial light modulator SLM with respect to the optical axis of the signal beam intersecting them, the dot image corresponding to a spatial frequency component in the row extending direction DSLM of the spatial light modulator SLM falls on the track TR.
Therefore the diffraction beam corresponding to the row extending direction DSLM of the spatial light modulator SLM is not reflected by the diffraction-beam-processing area R2. Accordingly, there is no reflected-hologram-signal beam (corresponding to the row extending direction DSLM of the spatial light modulator SLM) originated from the signal beam 12a in the generation of the optical interference fringe pattern P2 above-mentioned, so that no optical interference occurs with the hologram-reference beam of the signal beam 12a. In other words, when the extending direction DTR of the track TR makes an angle θ=0 with the extending direction DSLM of a row in the pixel matrix of the spatial light modulator SLM with respect to the optical axis of the signal beam intersecting them, any information based on the diffraction beam corresponding to the row extending direction of the spatial light modulator SLM is not recorded in the refractive index grating P2 of the recording medium 10.
The low frequency component of information to be recorded concentrates in the vicinity of the 0th-order beam, but the 0th-order beam is passed through on purpose. This embodiment uses the remaining diffraction beam which appears at points around the 0th-order beam.
In order to effectively use the diffraction beam, namely to optically interfere the reflected-hologram-signal beam of the signal beam 12a (corresponding to the row extending direction of the spatial light modulator SLM) with the 0th-order beam of the signal beam 12a (i.e., hologram-reference beam), the recording medium 10 and the spatial light modulator SLM are relatively disposed with respect to the optical axis in such a manner that the extending direction DTR of the track TR makes a predetermined angle θ (θ≠0) with the extending direction DSLM of a row (or a column) of the spatial light modulator SLM pixel matrix.
The operation in a reproducing process will be hereinafter described.
The controller 32 controls the position of the movable stage 60 holding the recording medium 10, as shown in
Then, in order not to modulate a reference beam 12 spatially modulated by the spatial light modulator SLM, the information which changes all pixels into a transparent state is sent from the encoder 25 to the spatial light modulator SLM, and the spatial light modulator SLM displays a transparent pattern.
Then, the shutter SHs is opened, and the spatial light modulator SLM is illuminated with reference beam 12 to generate a signal beam 12a. Then the recording medium 10 is illuminated with the signal beam 12a. In this way, the reproducing is started. It is noted that the signal beam 12a is not spatially modulated during the reproducing process because the spatial light modulator SLM displays the transparent pattern. Therefore no diffraction beam due to the spatial modulation occurs and thus the signal beam 12a includes only the 0th-order beam (i.e., hologram-reference beam).
The reproducing process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam) in the recording medium 10 will be hereinafter described.
As shown in
The first reproduced wave is reflected back by the diffraction-beam-processing area R2 of the incident-light-processing area R to the recording medium 10 and goes out from the entrance surface of the recording medium 10 and passes through the condenser lens 160. The second reproduced wave, being originated from the diffraction grating recorded with the light reflected by the diffraction-beam-processing area R2 in the recording process, goes out from the entrance surface of the recording medium 10 and passes through the condenser lens 160. In this way, at least the first and second reproduced waves go out from the entrance surface of the recording medium 10 and pass through the condenser lens 160.
After passing through the condenser lens 160, the first and second reproduced waves are reflected by the beam splitter 15 and form an image dot pattern corresponding to the recorded information on the photo detector 20. Then the photoreceptor of the CCD 20 receives it to re-convert its dot pattern signals into the electrical digital data signals. Then, the digital data signals are sent to the decoder 26 to reproduce the original data.
Next the shutter SHs is closed by control of the controller 32, after reproducing of the recording information at the predetermined recording position.
Next the recording medium 10 is forced to move (in a “y” direction of
In other words, the incident-light-processing area R of the recording medium 10 comprises a 0th-order-beam-scattering area SC scattering the 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) and a diffraction-beam-processing area R2 reflecting the diffraction beam (i.e., hologram-signal beam). The 0th-order-beam-scattering area SC continuously extends to a “y” direction of
The recording process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam and hologram-signal beam) in the recording medium will be hereinafter described.
Since the recording medium 10 is illuminated with the signal beam 12a, the hologram-reference beam and the hologram-signal beam are optically interfered with each other to create an optical interference fringe pattern P1, so that a refractive index grating P1 is recorded in the recording medium 10 due to the photorefractive effect.
The 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) is scattered by the 0th-order-beam-scattering area SC of the incident-light-processing area R back to the recording medium 10. Therefore such scattered 0th-order beam of the signal beam 12a is referred to as “scattered-hologram-reference beam”. The diffraction beam (i.e., hologram-signal beam) of the signal beam 12a is reflected by the diffraction-beam-processing area R2 of the incident-light-processing area R back to enter the recording medium 10 as the reflected-hologram-signal beam.
The reflected-hologram-signal beam and the hologram-reference beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P2, so that a refractive index grating P2 is recorded corresponding to the optical interference fringe pattern P2 in the recording medium 10 due to the photorefractive effect.
The scattered-hologram-reference beam and hologram-signal beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P3, so that a refractive index grating P3 is recorded in the recording medium 10 due to the photorefractive effect.
The scattered-hologram-reference beam and reflected-hologram-signal beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P4, so that a refractive index grating P4 is recorded in the recording medium 10 due to the photorefractive effect.
Therefore, in the embodiment shown in
The reproducing process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam) in the recording medium 10 will be hereinafter described.
The signal beam 12a is not spatially modulated during the reproducing process because the spatial light modulator SLM displays the transparent pattern. Therefore no diffraction beam due to the spatial modulation occurs and thus the signal beam 12a includes only the 0th-order beam.
The recording medium 10 is illuminated with a signal beam 12a (which is not spatially modulated i.e., hologram-reference beam) with the same positional and angular condition of the signal beam used in the recording. Just then, the refractive index gratings P1 and P2 are illuminated with the signal beam in the recording medium 10, so that there emanate a first reproduced wave from the refractive index grating P1 corresponding to the recorded information and a second reproduced wave from the refractive index grating P2 respectively. Next the signal beam 12a (i.e., hologram-reference beam) is scattered by the 0th-order-beam-scattering area SC of the incident-light-processing area R back to the recording medium 10 and becomes a scattered-hologram-reference beam. Since the refractive index grating P3 and the refractive index grating P4 in the recording medium 10 are illuminated with the scattered-hologram-reference beam, there emanate a third reproduced wave from the refractive index grating P3 corresponding to the recorded information and a fourth reproduced wave from the refractive index grating P4.
The scattered-hologram-reference beam goes out from the entrance surface of the recording medium 10, a part of which passes through the condenser lens 160. However, the scattered-hologram-reference beam is hardly received by the photo detector 20 because of being scattered. This phenomenon contributes to simplification of the reproducing of the recorded information.
The first and third reproduced waves originated from the diffraction beam component are reflected by the diffraction-beam-processing area R2 of the incident-light-processing area R back to the recording medium 10 and go out from the entrance surface of the recording medium 10 and passes through the condenser lens 160. The second and fourth reproduced waves originated from the diffraction beam component reflected by the diffraction-beam-processing area R2 in the recording process go out from the entrance surface of the recording medium 10 and passes through the condenser lens 160. In this way, at least the first, second third and fourth reproduced waves go out from the entrance surface of the recording medium 10 and pass through the condenser lens 160. The later processes are performed in the same manner of the embodiment shown in
In other words, the incident-light-processing area R of the recording medium 10 comprises a 0th-order-beam-deflecting area RL deflecting the 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) and a diffraction-beam-processing area R2 reflecting the diffraction beam (i.e., hologram-signal beam). The 0th-order-beam-deflecting area RL continuously extends to a “y” direction of
The recording process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam and hologram-signal beam) in the recording medium will be hereinafter described.
Since the recording medium 10 is illuminated with the signal beam 12a, the hologram-reference beam and the hologram-signal beam are optically interfered with each other to create an optical interference fringe pattern P1, so that a refractive index grating P1 is recorded in the recording medium 10 due to the photorefractive effect.
The 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) is deflected and reflected by the 0th-order-beam-deflecting area RL of the incident-light-processing area R back to the recording medium 10. Therefore such deflected and reflected 0th-order beam of the signal beam 12a is referred to as “deflected-hologram-reference beam”. The diffraction beam (i.e., hologram-signal beam) of the signal beam 12a is reflected by the diffraction-beam-processing area R2 of the incident-light-processing area R back to enter.
The reflected-hologram-signal beam and the hologram-reference beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P2, so that a refractive index grating P2 is recorded corresponding to the optical interference fringe pattern P2 in the recording medium 10 due to the photorefractive effect.
The deflected-hologram-reference beam and hologram-signal beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P3, so that a refractive index grating P3 is recorded in the recording medium 10 due to the photorefractive effect.
The deflected-hologram-reference beam and reflected-hologram-signal beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P4, so that a refractive index grating P4 is recorded in the recording medium 10 due to the photorefractive effect.
Therefore, in the embodiment shown in
The reproducing process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam) in the recording medium 10 will be hereinafter described.
The signal beam 12a is not spatially modulated during the reproducing process because the spatial light modulator SLM displays the transparent pattern. Therefore no diffraction beam due to the spatial modulation occurs and thus the signal beam 12a includes only the 0th-order beam.
The recording medium 10 is illuminated with a signal beam 12a (which is not spatially modulated i.e., hologram-reference beam) with the same positional and angular condition of the signal beam used in the recording. Just then, the refractive index gratings P1 and P2 are illuminated with the signal beam in the recording medium 10, so that there emanate a first reproduced wave from the refractive index grating P1 and a second reproduced wave from the refractive index grating P2 respectively. Next the signal beam 12a (i.e., hologram-reference beam) is deflected and reflected by the 0th-order-beam-deflecting area RL of the incident-light-processing area R back to the recording medium 10 and becomes a deflected-hologram-reference beam. Since the refractive index grating P3 and the refractive index grating P4 in the recording medium 10 are illuminated with the deflected-hologram-reference beam, there emanate a third reproduced wave from the refractive index grating P3 corresponding to the recorded information and a fourth reproduced wave from the refractive index grating P4.
The deflected-hologram-reference beam goes out from the entrance surface of the recording medium 10, a part of which passes through the condenser lens 160. Alternatively, a configuration preventing the beam from returning to the condenser lens 160 may be provided by a modified slanting angular shape of 0th-order-beam-deflecting area RL. Even if a part of the beam returns to the condenser lens 160, it is hardly received by the photo detector 20 because of being deflected. This phenomenon contributes to simplification of the reproducing of the recorded information.
The first and third reproduced waves originated from the diffraction beam component are reflected by the diffraction-beam-processing area R2 of the incident-light-processing area R back to the recording medium 10 and go out from the entrance surface of the recording medium 10 and passes through the condenser lens 160. The second and fourth reproduced waves originated from the diffraction beam component reflected by the diffraction-beam-processing area R2 in the recording process go out from the entrance surface of the recording medium 10 and passes through the condenser lens 160. In this way, at least the first, second third and fourth reproduced waves go out from the entrance surface of the recording medium 10 and pass through the condenser lens 160. The later processes are performed in the same manner of the embodiment shown in
According to both the adjacent modified examples described above, since the 0th-order beam of the signal beam 12a is returned to the inside of the recording medium 10 via the incident-light-processing area R, it is possible to efficiently use an amount of illuminated light and further these configurations contribute to simplification of the reproducing of the recorded information.
In the above embodiments, the holographic recording and producing in the reflective form in which the diffraction-beam-processing area R2 of the incident-light-processing area R reflects the light beam are described, but a transparent diffraction-beam-processing area R2 can also be used with the same effect in the present invention.
In recording, as shown in
Since the recording medium 10 is illuminated with the signal beam 12a, the hologram-reference beam and the hologram-signal beam are optically interfered with each other to create an optical interference fringe pattern P1, so that a refractive index grating P1 is recorded in the recording medium 10 due to the photorefractive effect as shown in
The 0th-order beam (i.e., hologram-reference beam) of the signal beam 12a passes through the 0th-order-beam-processing area R1 of the incident-light-processing area R and also the diffraction beam (i.e., hologram-signal beam) of the signal beam 12a passes through the diffraction-beam-processing area R2 of the incident-light-processing area R.
In reproducing, as shown in
In the embodiment shown in
In other words, the incident-light-processing area R of the recording medium 10 comprises a 0th-order-beam-scattering area SC scattering the 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) and a diffraction-beam-processing area R2 allowing the diffraction beam (i.e., hologram-signal beam) to pass therethrough. The 0th-order-beam-scattering area SC continuously extends to a “y” direction of
The recording process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam and hologram-signal beam) in the recording medium will be hereinafter described.
Since the recording medium 10 is illuminated with the signal beam 12a, the hologram-reference beam and the hologram-signal beam are optically interfered with each other to create an optical interference fringe pattern P1, so that a refractive index grating P1 is recorded in the recording medium 10 due to the photorefractive effect.
The 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) is scattered by the 0th-order-beam-scattering area SC of the incident-light-processing area R back to the recording medium 10 and becomes a scattered-hologram-reference beam. The diffraction beam (i.e., hologram-signal beam) of the signal beam 12a passes through the diffraction-beam-processing area R2 of the incident-light-processing area R and goes out from the opposite side of the entrance surface of the recording medium 10 on which the beam is incident.
The scattered-hologram-signal beam and the hologram-reference beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P2, so that a refractive index grating P2 is recorded corresponding to the optical interference fringe pattern P2 in the recording medium 10 due to the photorefractive effect.
Therefore, in the embodiment shown in
The reproducing process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam) in the recording medium 10 will be hereinafter described.
The signal beam 12a is not spatially modulated during the reproducing process because the spatial light modulator SLM displays the transparent pattern. Therefore the signal beam 12a includes only the 0th-order beam.
With the signal beam 12a (i.e., hologram-reference beam) the recording medium 10 is illuminated under the same positional and angular condition of the signal beam used in the recording. Just then, the refractive index grating P1 is illuminated with the signal beam in the recording medium 10, so that there emanates a first reproduced wave from the refractive index grating P1 corresponding to the recorded information.
The 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) is scattered by the 0th-order-beam-scattering area SC of the incident-light-processing area R back to the recording medium 10 and becomes a scattered-hologram-reference beam. The refractive index grating P2 of the recording medium 10 is illuminated with the scattered-hologram-reference beam, so that there emanates a second reproduced wave from the refractive index grating P2 corresponding to the recorded information.
The first and second reproduced waves pass through the diffraction-beam-processing area R2 of the incident-light-processing area R, and go out from the opposite side of the entrance surface of the recording medium 10 on which the beam is incident and passes through the condenser lens 16a. The later processes are performed in the same manner of the embodiment shown in
Since the scattered-hologram-reference beam goes out from the entrance surface of the recording medium 10, the scattered-hologram-reference beam is hardly received by the photo detector 20 because of being scattered. This phenomenon contributes to simplification of the reproducing of the recorded information.
In other words, the incident-light-processing area R of the recording medium 10 comprises a 0th-order-beam-reflecting area RR reflecting the 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) and a diffraction-beam-processing area R2 allowing the diffraction beam (i.e., hologram-signal beam) to pass therethrough. The 0th-order-beam-reflecting area RR continuously extends to a “y” direction of
The recording process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam and hologram-signal beam) in the recording medium will be hereinafter described.
Since the recording medium 10 is illuminated with the signal beam 12a, the hologram-reference beam and the hologram-signal beam are optically interfered with each other to create an optical interference fringe pattern P1, so that a refractive index grating P1 is recorded in the recording medium 10 due to the photorefractive effect.
The 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) is reflected by the 0th-order-beam-reflecting area RR of the incident-light-processing area R back to the recording medium 10. Therefore such 0th-order beam of the signal beam 12a reflected by the 0th-order-beam-reflecting area RR is referred to as “reflected-hologram-reference beam”. The diffraction beam (i.e., hologram-signal beam) of the signal beam 12a passes through the diffraction-beam-processing area R2 of the incident-light-processing area R and goes out from the opposite side of the entrance surface of the recording medium 10 on which the beam is incident.
The reflected-hologram-reference beam and the hologram-signal beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P2, so that a refractive index grating P2 is recorded corresponding to the optical interference fringe pattern P2 in the recording medium 10 due to the photorefractive effect.
Therefore, in the embodiment shown in
The reproducing process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam) in the recording medium 10 will be hereinafter described.
The signal beam 12a is not spatially modulated during the reproducing process. Therefore no diffraction beam due to the spatial modulation occurs and thus the signal beam 12a includes only the 0th-order beam.
With the signal beam 12a (i.e., hologram-reference beam) the recording medium 10 is illuminated under the same positional and angular condition of the signal beam used in the recording. Just then, the refractive index grating P1 is illuminated with the signal beam in the recording medium 10, so that there emanates a first reproduced wave from the refractive index grating P1 corresponding to the recorded information.
Next the signal beam 12a (i.e., hologram-reference beam) is reflected by the 0th-order-beam-reflecting area RR of the incident-light-processing area R back to the recording medium 10 and becomes a reflected-hologram-reference beam. The refractive index grating P2 of recording medium 10 is illuminated with the reflected-hologram-reference beam, so that there emanates a second reproduced wave from the refractive index grating P2 corresponding to the recorded information.
The first and second reproduced waves pass through the diffraction-beam-processing area R2 of the incident-light-processing area R, and go out from the opposite side of the entrance surface of the recording medium 10 on which the beam is incident and passes through the condenser lens 16a. The later processes are performed in the same manner of the embodiment shown in
The reflected-hologram-reference beam goes out from the entrance surface of the recording medium 10, and can not reach the condenser lens 16a. This phenomenon contributes to simplification of the reproducing of the recorded information.
In other words, the incident-light-processing area R of the recording medium 10 comprises a 0th-order-beam-deflecting area RL deflecting the 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) and a diffraction-beam-processing area R2 allowing the diffraction beam (i.e., hologram-signal beam) to pass therethrough. The 0th-order-beam-deflecting area RL continuously extends to a “y” direction of
The recording process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam and hologram-signal beam) in the recording medium will be hereinafter described.
Since the recording medium 10 is illuminated with the signal beam 12a, the hologram-reference beam and the hologram-signal beam are optically interfered with each other to create an optical interference fringe pattern P1, so that a refractive index grating P1 is recorded in the recording medium 10 due to the photorefractive effect.
The 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) is deflected and reflected by the 0th-order-beam-deflecting area RL of the incident-light-processing area R back to the recording medium 10 and becomes a deflected-hologram-reference beam. The diffraction beam (i.e., hologram-signal beam) of the signal beam 12a passes through the diffraction-beam-processing area R2 of the incident-light-processing area R and goes out from the opposite side of the entrance surface of the recording medium 10 on which the beam is incident.
The deflected-hologram-reference beam and the hologram-reference beam of the signal beam 12a are optically interfered with each other in the recording medium 10 to create an optical interference fringe pattern P2, so that a refractive index grating P2 is recorded corresponding to the optical interference fringe pattern P2 in the recording medium 10 due to the photorefractive effect.
Therefore, in the embodiment shown in
The reproducing process of the refractive index grating using the signal beam 12a (i.e., hologram-reference beam) in the recording medium 10 will be hereinafter described.
The signal beam 12a is not spatially modulated during the reproducing process. Therefore no diffraction beam due to the spatial modulation occurs and thus the signal beam 12a includes only the 0th-order beam.
With the signal beam 12a (i.e., hologram-reference beam) the recording medium 10 is illuminated under the same positional and angular condition of the signal beam used in the recording. Just then, the refractive index grating P1 is illuminated with the signal beam in the recording medium 10, so that there emanates a first reproduced wave from the refractive index grating P1 corresponding to the recorded information.
Next the 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) is deflected by the 0th-order-beam-deflecting area RL of the incident-light-processing area R back to the recording medium 10 and becomes a deflected-hologram-reference beam. The refractive index grating P2 of recording medium 10 is illuminated with the deflected-hologram-reference beam, so that there emanates a second reproduced wave from the refractive index grating P2 corresponding to the recorded information.
The first and second reproduced waves pass through the diffraction-beam-processing area R2 of the incident-light-processing area R, and go out from the opposite side of the entrance surface of the recording medium 10 on which the beam is incident and pass through the condenser lens 16a. The later processes are performed in the same manner of the embodiment shown in
The deflected-hologram-reference beam goes out from the entrance surface of the recording medium 10, and can not reach the condenser lens 16a. This phenomenon contributes to simplification of the reproducing of the recorded information.
According to these modified examples described above, since only the 0th-order beam of the signal beam 12a is returned to the inside of the recording medium 10 via the incident-light-processing area R, it is possible to efficiently use an amount of illuminated light and further these configurations contribute to simplification of the reproducing of the recorded information.
In the above embodiments, the holographic recording and producing in the form in which the incident-light-processing area R is integrally provided in the recording medium 10 are described, but the incident-light-processing area R may be provided to the apparatus with the same advantageous effect in the present invention.
As shown in
As shown in
The process of recording and reproducing of hologram of this embodiment is identical to the apparatus case shown in
Furthermore
As shown in
In other words, the incident-light-processing area R adjacent to the recording medium 10 comprises a 0th-order-beam-reflecting area RR reflecting the 0th-order beam of the signal beam 12a (i.e., hologram-reference beam) and a diffraction-beam-processing area R2 allowing the diffraction beam (i.e., hologram-signal beam) to pass therethrough.
These modified examples have configurations to return only the 0th order beam of the signal beam to the inside of the recording medium 10, so that it is possible to efficiently use an amount of illuminated light. The incident-light-processing area has a function to separate the incident beam to return a part thereof to the inside of the recording medium in order to individually process the 0th-order beam and the diffraction beam in the incident light with different processes. Therefore the incident-light-processing area may have a 0th-order-beam-processing area allowing the 0th-order beam to pass through or absorbing the 0th-order beam; and a diffraction-beam-reflecting area reflecting or deflecting or scattering the diffraction-beam. Alternatively the incident-light-processing area may have a 0th-order-beam-processing area reflecting or scattering or deflecting or absorbing the 0th-order beam; and a diffraction-beam-reflecting area reflecting or deflecting the diffraction-beam.
Furthermore, according to another embodiment of the present invention, the recording medium 10 may be provided in a disk or card form. For example, a cartridge CR shown in
In addition to the above embodiments of the holographic recording and reproducing method and the apparatus therefor, the present invention apparently includes a recording method, a reproducing method, a recording apparatus, and a reproducing apparatus of the hologram. In the above embodiments, the laser beam is spatially modulated in accordance with the two-dimensional data, in other words, two-dimensional modulation is used. The present invention, however, is applicable to a holographic recording and reproducing method and apparatus which spatially modulate the laser beam in accordance with one-dimensional data. In the above embodiments, the photorefractive material is used for the photosensitive material of the recording medium, but other photosensitive materials such as hole burning material, photochromic material and the like may be used for the photosensitive material of the recording medium.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-225052 | Aug 2002 | JP | national |
| 2002-225053 | Aug 2002 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP03/09649 | 7/30/2003 | WO | 5/6/2005 |
