Patent Application
20090262404
The present invention relates to a holographic recording medium and, more particularly, to a holographic recording medium in which a fixing process is performed by applying bleaching light in order to fix holographic recorded data in the medium.
As a medium in which large-capacity information can be recorded at high density, there is a holographic recording medium. In the holographic recording medium, page data having capacity of several hundreds of megabytes can multiplex-recorded in the same region. The holographic recording is such that a light beam from a single light source is separated to reference light and information light and the same position on the recording medium is irradiated with the reference light and the information light and an irradiation angle or a wavelength of the reference light is varied to generate different interferences, so that different information is recorded in the same position on the recording medium in piles.
The region in which information is recorded by the holographic recording is a region having a three-dimensional thickness and its optical characteristics are varied even when weak light such as a fluorescent lamp in a room is applied, depending on its material. When the optical characteristics are varied, a reproduction error could be generated. Thus, a medium in which a holographic recording medium is housed in a cartridge or a medium in which a light shielding layer is provided on a holographic recording layer have been proposed (refer to Patent Document 1).
In addition, according to a holographic recording medium in which data can be written only one time such as a CD-R, in order to stabilize the optical characteristics, after data is recorded with hologram, data fixing process called bleaching is performed. The bleaching is a process such that a region in which holographic recording has been performed is irradiated with white light (referred to as bleaching light) having relatively high intensity which does not destroy its recorded data.
In the recording region irradiated with the bleaching light, reactivity of the recording material is fixed and its optical characteristics are not varied by weak light such as a fluorescent lamp, so that the recorded data can be stably reproduced.
As shown in
When the reference light and the information light are applied at the same time from an upper part of the glass substrate 10-2 of the medium, data is recorded in a region of the holographic material layer 13. After the data is recorded, the bleaching light is applied to fix the recorded data. Thus, the data is fixed in the region of the holographic material layer 13 irradiated with the bleaching light.
As shown in
Patent Document 1: Japanese Unexamined Patent Publication No. 2004-279942
However, when the data is fixed by the bleaching light in the conventional holographic medium, there are following problems.
As shown in
According to the unrecorded region 19, it is assumed that data has not been recorded yet.
As shown in
As a result, as shown in
Alternatively, in the fixed region in the unrecorded region 19, its diffraction efficiency is extremely lowered and even if the recording and reproducing can be performed thereafter, SNR at the time of recording and reproducing deteriorates.
As described above, when the bleaching process is performed in the conventional holographic recording medium, recording and reproducing characteristics deteriorate and recording capacity is reduced in the boundary region of the recording completed region.
In addition, data is managed by logical and physical addresses in a conventional storage. Since the logical address and the physical address are related at an initial stage, when the unrecorded region becomes a region in which data cannot be recorded, performance is considerably lowered because of its recording error or frequent occurrence of alternating processes. Thus, in the case of the medium in which recording capacity is varied, it is necessary to develop a data management method which is different from the conventional method.
Accordingly, the present invention was made in view of the circumstances as described above, and the present invention is a holographic recording medium in which bleaching light can be prevented from proceeding to an unintended holographic recording region.
The present invention provides a holographic recording medium including a holographic material layer in which information is to be recorded by irradiating the same region with information light corresponding to the information to be recorded and reference light to read the recorded information, wherein the holographic material layer is divided into a plurality of recording zones by a plurality of light shielding walls, and the light shielding wall is formed of a material which does not transmit bleaching light irradiated for fixing the recorded information to the recording zone in which a recording process has been performed.
Preferably, the light shielding wall reflects or absorbs the bleaching light so that the bleaching light proceeds only to a recording zone in which the recorded information is to be fixed, and the bleaching light does not proceed to a recording zone adjacent to the recording zone in which the recorded information is to be fixed.
Herein, the light shielding wall may include either acrylic or polycarbonate material.
Preferably, the holographic material layer is formed on a disk-shaped or polygonal substrate, the light shielding wall is formed on the substrate and in the holographic material layer in a latticed pattern, and the recording zone is a region surrounded by the lattice-shaped light shielding walls. Herein, examples of the substrate may include a glass substrate, a resin substrate and the like.
The substrate may be a laminated substrate formed by laminating various types of substrates. In the later-described embodiment, a structure including a glass substrate and a resin substrate provided with a reflection film is described as one example of the substrate (refer to
Preferably, the holographic material layer is formed on a disk-shaped or polygonal substrate, the light shielding wall is formed on the substrate and in the holographic material layer, a waveguide layer to introduce the bleaching light is provided between the substrate and the holographic material layer, and the waveguide layer is formed so that the applied bleaching light is led to each recording zone of the holographic material layer.
Preferably, the holographic recording medium includes a light shielding member provided on the holographic material layer and the light shielding wall, and the light shielding member is any one of a thin film which can be removed from/attached to each recording zone, a movable member which can control permission and prohibition of light proceeding to the holographic material layer in each recording zone, and a liquid crystal element which can vary light transmission to the holographic material layer in each recording zone.
Preferably, each of recording zones, divided by the light shielding walls, may have the same area.
Preferably, each of recording zones, divided by said light shielding walls, may have a different area.
Preferably, the shape of the light shielding wall may be any of a linear shape, a wobble shape having changed linearly corresponding to recording spots of the bleaching light, and a wobble shape having changed in a curve corresponding to recording spots of the bleaching light.
According to the present invention, since the holographic material layer is divided into the plurality of recording zones by the light shielding walls which do not transmit the bleaching light, the bleaching light applied to a certain recording zone can be prevented from being diffused or proceeding to its adjacent recording zone.
In addition, when the adjacent recording zone is an unrecorded region, the bleaching light is not diffused in that unrecorded region. Thus, when data is recorded in the unrecorded region in the future, the SNR at the time of recording and reproducing is improved and substantial recording and reproducing characteristics can be improved. Furthermore, the substantially intended recording capacity can be assured and the same data management method as in the conventional storage can be employed.
An embodiment of the present invention will be described with reference to the drawings hereinafter. In addition, the present invention is not limited to the embodiment.
Referring to
The above medium is different from the conventional medium shown in
The holographic recording is volume recording and the holographic material layer 33 has a thickness of about several millimeters in general, in which information is multiplex-recorded. However, its thickness depends on its specification.
The multiplex recording is performed with information light and reference light outputted from a single light source and split by a beam splitter. The information light is light corresponding to information to be recorded and it is modulated by a special light modulator (SLM) having two-dimensional special information corresponding to the information to be recorded.
Although the reference light is used for reading recorded information, at the time of recording, it is also used for recording the information in the holographic material layer 33 by interference with the information light applied to the same region.
In a recording process, the information to be recorded is recorded as two-dimensional page data when the information light and the reference light are applied to the same region of the holographic material layer.
In addition, when the reference light whose angle is varied is applied to the same region in which the data has been recorded, multiplex recording of plural pieces of two-dimensional page data can be performed, for example.
In addition, this medium according to the present invention is a so-called write-once medium which is fixed by bleaching (fixing process) so that recorded data is not erased and not varied due to a chemical reaction.
a) shows a state in which the holographic material layer 33 is divided into three recording zones (A, B and C) by the light shielding walls 34.
For example, when information is recorded in the zone B, reference light and information light outputted from a single light source are applied to the zone B and plural pieces of information are multiplex-recorded in the holographic material layer 33 of the zone B by varying an irradiation angle of the reference light.
The light shielding wall 34 does not transmit bleaching light 15 and it is formed of a material which does not transmit the bleaching light 15, so that the bleaching light 15 does not proceed to the adjacent recording zone. The bleaching light 15 is to fix the already recorded information in the recording zone.
For example, when the zone B shown in
In the case of
Thus, the light shielding wall 34 which does not transmit the bleaching light 15 is made of a colored acrylic resin, for example.
In addition, the light shielding wall may be made by mixing a material such as carbon graphite to the above resin and coloring the mixture, thereby transmitting no bleaching light. In general, when it absorbs the bleaching light, the color is preferably black.
In addition, the holographic material layer 33 is formed of a material mainly containing (meta)acrylate, styrene, vinyl ether, epoxy and the like. Depending on its material, a chemical reaction generated when the bleaching light is applied could be spread in the region to which the bleaching light does not directly proceed.
That is, diffusion could occur in the fixed region due to the chemical reaction of the holographic material layer 33 other than the diffusion in the fixed region due to scattering or diffraction of the bleaching light as shown in
Thus, it is preferable that the light shielding wall 34 has a property (which is inactive to the chemical reaction) to prevent the fixed region from being diffused by the chemical reaction. For example, the acrylic resin or polycarbonate is inactive to the chemical reaction.
In
In addition, although it is not shown in
When it is assumed that the zone B is a recording completed region and the zone A is an unrecorded region in
Therefore, the unrecorded region (zone A) is prevented from being fixed by mistake. Then, when data is recorded in the unrecorded region (zone A), the data can be recorded in good SNR. That is, good recording and reproducing characteristics of the unrecorded region can be assured and recording capacity in which stable recording and reproducing can be performed as designed can be assured.
Meanwhile, the medium shown in
In addition, in the recording process with the reference light and the information light, it is also necessary to control the position of the optical component so that only one recording zone is irradiated with a recording spot as will be described below (refer to
The medium shown in
A medium shown in
The medium in
In the case of
A construction formed by making an area of each divided zone equal as thus described is called an equally divided construction. The construction examples of
The equally divided construction has advantages of facilitating format and control and having high compatibility with a current operating system (OS). It further has an advantage of being able to obtain the same user-friendliness as at an initial stage even after expansion of a used region of a disk.
It is to be noted that a construction formed by making an area of each divided zone different, as in
The medium in
Further, in
In a case where a volume of data to be recorded is already known, in the media having the unequally divided construction, the data can be recorded in a recording zone almost consistent with the data volume, if there is such a recording zone, so as to effectively use a recording volume. That is, an empty region in which data is substantially not recorded can be reduced.
A relatively large volume of data can be recorded in each region on the left half. Each region on the right half is a region suitable for recording of a relatively small volume of data.
Although
For example, as shown in
Generally, a medium may be divided into regions with N kinds of different areas.
Further, regions formed so as to have larger areas toward the right side as in
One recording zone is surrounded by linear-shaped light shielding walls.
Here, one circle corresponds to a recording spot of bleaching light. In the shift multiplex method, the recording spot is shifted in any of up and down, right and left directions within one recording zone.
In the example of
In the case of
Although the unused regions are very small regions as compared with the recording zones where recording spots are applied, the larger the number of divided recording zones, the larger the area of the unused regions.
It is therefore preferable to reduce as large an area of the unused regions as possible in view of effective use of the recording volume.
The shape of the light shielding wall 34 is the linear shape in the configurations of
In
In
Any of the light shielding walls 34 in the wobble shape is preferably changed at the same intervals as the intervals of the recording spots.
Making the light shielding walls have the wobble shape in such a manner can lead to reduction in unused regions and can thus lead to the effective use of the recording volume, so as to increase the recording volume that substantially contributes to recording, as compared with
Next, an example of a medium provided with a waveguide layer will be explained.
A medium shown in
The inputted bleaching light 15-C proceeds into the waveguide layer 35 and also proceeds to the upper holographic material layer 33 by scattering and reflection. The holographic recorded data in the zone is fixed by this upward bleaching light 15.
b) shows that the bleaching light 15-B proceeds upward in the zone B. Here, although the bleaching light 15-B is diffused in the zone B, it does not proceed to the adjacent zone A because the light shielding wall 34 exists in the right side.
Therefore, when it is assumed that the zone B is a recording completed region and the zone A is an unrecorded region in
A medium shown in
A medium shown in
A medium shown in
For example, the inlet Z5 is connected to the zone 5 through a waveguide layer 35 and data in the zone 5 is fixed by the bleaching light inputted from the inlet Z5. The position of the inlets 25 is not limited to a position in the vicinity of the inner periphery as shown in
In this case, the recording and reproducing device has a position adjustment mechanism to irradiate the inlet of the zone to be fixed with the bleaching light 15.
Several embodiments for the medium including the waveguide layer have been described. When the waveguide layer is provided, the mechanism to adjust the irradiation position with the bleaching light can be simplified.
According to a medium shown in
Alternatively, it is preferable that a thin film which can be removed from/attached to each recording zone is used so that a recording process and a fixing process can be performed in each recording zone.
a) shows a state when the medium is shipped. For example, the thin film (light shielding member) 41 which covers the holographic material layer 33 is attached to each recording zone. Thus, the holographic material layer 33 can be protected while it is stored.
b) shows a state at the time of recording process and at the time of fixing process by the bleaching light. In this case, after the light shielding thin film 41 is removed from the zone B in which the data is to be recorded or fixed, for example, the zone B is irradiated with information light and reference light. Alternatively, the fixing process is performed in the zone B by irradiation of the bleaching light. After the fixing process by the bleaching light, since the data is fixed and not erased, it is not necessary to attach the light shielding thin film 41 again. In this case, a tool or a mechanism to remove the light shielding thin film 41 is needed.
The light shielding members (41A, 41B and 41C) can be slid in the right and left direction of the drawing. When the light shielding member 41B of the zone B to be irradiated with the light is slid, for example, the light can be transmitted to the holographic material layer 33 of the zone B. In this case, it is necessary to provide a mechanism to slide the light shielding member 41 in each zone.
a) shows a state in which the medium is shipped and
a) shows a state in which the medium is shipped and the liquid crystal element 42 stably shields the light.
b) shows a state in which the liquid crystal element 42 in a zone B is driven to transmit the light to the zone B.
The embodiments in which the light shielding member 41 is provided on the holographic material layer 33 have been described. In this case, since the light shielding member 41 is provided, in addition to the effect that the bleaching light is prevented from being diffused to the unrecorded region by the light shielding wall 34, a chemical reaction of the holographic material layer due to external light can be prevented at the time of storage.
In a case the holographic recording medium according to the present invention is a transportable medium like a conventional CD-ROM or DVD-R, when the medium according to the present invention is inserted into the recording and reproducing device and a recording command is transferred to the recording and reproducing device from a higher-order device such as a personal computer connected to the recording and reproducing device, a recording process is started.
The flowchart shown in
This recording process is executed by a microcomputer having a CPU and the like mounted on the recording and reproducing device.
It is determined whether the recording command is provided from the higher-order device or not in step S1 in
Although the recording to the holographic recording medium has a feature in that multiplex recording is performed to a two-dimensional region in general, a method of performing multiplex recording to the same physical region includes an angle multiplex method or a shift multiplex method. For example, according to the shift multiplex method, while a part of a prior recording spot and a part of the next recording spot are overlapped, the recording is performed, shifting the recording spot sequentially.
According to the present invention, when the recording spot is shifted, the position of the recording spot is controlled so that it may be shifted within one recording zone and it may not be shifted beyond the recording zone.
In other words, the position of the optical component for recording is controlled so that the reference light or the information light may not proceed to the adjacent zone beyond the light shielding wall 34 according to the present invention.
Here, one circle corresponds to the recording spot and the recording spot can be moved around in one zone only.
When the recording spot is controlled as shown in
The recording process in step S2 may be almost the same as the recording process in the conventional holographic material layer.
For example, the following processes are sequentially performed:
(1) a process for physically moving a component for recording, in which a position of the recording component is controlled so that a physical position of the medium indicated by the recording command may be irradiated with the recording spot,
(2) a process for preparing a recording process, in which an encoding process and the like is performed to the data to be recorded so that the data is converted to a form to be recorded in the medium actually,
(3) a holographic recording process in which the reference light and the information light are applied to a predetermined position of the medium,
(4) a verifying process or a rewriting process to confirm whether the recording is performed normally or not, and
(5) a process such as a completion noticing process to inform the higher-order device of the completion of the commanded recording.
However, according to the present invention, in the media shown in
It is determined whether the bleaching is to be performed or not in step S3 in
When it is not, the operation is returned to the step S1. When the bleaching is to be performed, the operation proceeds to step S4.
The case it is determined that the bleaching is to be performed is as follows:
(a) a case the holographic recording medium is changed according to a specific operation of a user,
(b) a case a bleaching command for a specific recording zone is received from the higher-order device by an input of the user, and
(c) a case a zone runs out of free space as a result of confirming the present recorded capacity in each zone, or a case remaining capacity is less than a predetermined value (remaining capacity<recorded capacity×1%, for example).
Although the present invention is not limited to the above three cases, when any case among the three cases is generated, the bleaching process s performed in step S4.
In step S4 shown in
Here, as described in
Since the holographic recording medium according to the present invention includes the light shielding wall 34 shown in
The same manufacturing method as the conventional method may be used for the holographic recording medium according to the present invention except for a step of providing the light shielding wall 34.
For example, the resin substrate 32 provided with the reflection film 31 is manufactured by spattering the reflection film 31 formed of a material such as aluminum or aluminum chrome or silver to the entire of the resin substrate 32 formed of acrylic material.
Then, as shown in
Then, as shown in
Then, as shown in
Then, as shown in
In addition, as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-272445 | Sep 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/316875 | 8/28/2006 | WO | 00 | 3/12/2008 |
