JP2006119332A - Hologram recording medium and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase data readout rate and to suppress crosstalk, in an optical waveguide type hologram recording medium. <P>SOLUTION: A two-layer structure is provided to, for example, one cladding layer 4 of two cladding layers 3, 4 so stacked that a core layer 2 as an optical waveguide on which reference light B1 is made incident is held between these, and a hologram pattern is formed between the two layers of the cladding layer 4. At this time, the first cladding layer 4a kept in contact with the core layer 2 is made of a photorefractive material whose refractive index rises upon irradiation with access light B2 different from the reference light B1, so that diffracted light according to the hologram pattern 5 can be emitted to the outside only in the irradiated region. As a result, light utilization efficiency increases to increase data readout rate, and stray light is controlled to suppress crosstalk. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention particularly relates to an optical waveguide type hologram recording medium. The present invention also relates to a reproducing apparatus for reproducing such a hologram recording medium.

FIG. 14 is a diagram for explaining the structure of a conventional optical waveguide type hologram recording medium and the data reading method thereof.
In FIG. 14, the structure of the conventional hologram recording medium 110 is shown in a sectional view.
In FIG. 14, a conventional hologram recording medium 110 is formed, for example, by laminating a clad layer 114, a core layer 112, and a clad 113 layer in this order on a substrate 111 as shown. The core layer 112 is an optical waveguide in this case, and is formed of a member having a higher refractive index than the two cladding layers 113 and 114 sandwiching the core layer 112.
The optical waveguide utilizes the property that light propagates to a region having a high refractive index. That is, when the core layer 112 having a high refractive index is inserted between the clad layers 113 and 114 having a low refractive index in this way, the reference light B1 incident from the end face side of the recording medium as shown in FIG. 112 to propagate through.
In this case, the shape of the surface where the core layer 112 and the clad layer 113 are in contact with each other is made uneven as shown in the figure. In other words, this forms concavo-convex shapes (hologram pattern 115 in the figure) having different refractive indexes, and desired information can be recorded by the pattern.

In order to read data from such a hologram recording medium 110, first, the illustrated reference beam B1 is incident. As described above, the reference light B1 propagates through the core layer 112 that is an optical waveguide.
As the reference light B1 propagates through the core layer 112 in this way, the reference light B1 is diffracted at the portion where the hologram pattern 115 is formed, and becomes a diffracted light as shown in the drawing. Radiated out of the waveguide.

  On the playback device side, for example, only the diffracted light corresponding to the desired data portion of the diffracted light emitted in this way is narrowed down by the aperture 121 shown in the figure. In this way, the diffracted light that has passed through the aperture 121 is imaged on the two-dimensional photodetector 120 and the image is obtained as a data signal, whereby the data recorded on the hologram recording medium 110 is read out.

In addition, the following patent documents can be cited as prior documents on such an optical waveguide type hologram recording medium.
JP 2003-228848 A

Here, according to the above description, in the configuration of the conventional hologram recording medium 110 and its reproducing apparatus, the reference light B1 incident on the core layer 112 is radiated on all surfaces on which the hologram pattern 115 is formed, It can be seen that only the necessary portion of the diffracted light is incident on the photodetector 120 and data is read out.
According to this, in reading the desired data portion, only a part of the incident reference light B1 is used. That is, most of the reference light B1 is invalid for information reading.
Therefore, in the configuration of the conventional hologram recording medium 110 and its reproducing apparatus, the light utilization efficiency for reading information is extremely low.

Here, the amount of light incident on the photodetector 120 greatly affects the data reading rate from the recording medium.
That is, if the amount of light incident on the photodetector 120 is small, the imaging efficiency of the diffracted light corresponding to the hologram pattern 115 is low correspondingly, so that it takes a long time to detect data, and as a result, data is read out. The rate tends to get worse. Conversely, if the amount of incident light is large, the imaging efficiency is improved and the readout rate is improved.

In view of this, the fact that the light use efficiency for reading information is low as described above is disadvantageous for improving the reading rate.
In other words, the fact that the light use efficiency is low as described above means that the light amount of the reference light B1 must be increased by that amount in order to obtain a predetermined reading rate. That is, this leads to an increase in power consumption of the apparatus.

Further, in the conventional configuration, the reference light B1 incident as described above is radiated on all surfaces on which the hologram pattern 115 is formed, so that stray light is likely to be generated, which is also disadvantageous in terms of crosstalk. .
Since this is disadvantageous in terms of crosstalk, the information recording density of the recording medium cannot be effectively improved.

Therefore, in the present invention, in view of the above problems, the hologram recording medium is configured as follows.
That is, the hologram recording medium of the present invention includes two clad layers and a core layer sandwiched between the clad layers to form an optical waveguide, and the core layer or the clad layer has a required An optical waveguide type hologram recording medium in which an information signal is stored by forming a hologram pattern, wherein at least a part of at least one of the core layer or one of the cladding layers is a photo It is composed of a refractive material or a photochromic material.

In the present invention, a reproducing apparatus for reproducing such a hologram recording medium is configured as follows.
That is, two clad layers and a core layer sandwiched between these clad layers are provided to form an optical waveguide, and a required hologram pattern is formed on the core layer or the clad layer. A reproducing apparatus for reproducing an optical waveguide type hologram recording medium in which an information signal is stored. First, a first light for propagating reference light to the optical waveguide formed on the hologram recording medium is provided. First light irradiation means for irradiation is provided.
Further, a second light irradiating means for irradiating the hologram recording medium with a second light different from the first light is provided.
In addition, information signal detection means for obtaining an information signal by detecting diffracted light corresponding to the hologram pattern emitted from the hologram recording medium by irradiation with the reference light and the second light is provided. .

If, for example, a photorefractive material is used for a required portion of the recording medium as in the present invention, the refractive index of only that portion is changed according to the required light irradiation.
Here, in the optical waveguide type hologram recording medium as in the present invention, the reference light (first light) is incident on part of the core layer and the cladding layer. At this time, the reference light is different from the reference light. Irradiation with other light (second light) changes the refractive index of only a portion of the core layer or cladding layer irradiated with this light, that is, this refractive index has changed. The relationship of the refractive index between each layer can be changed in a part.
As described above, the relationship between the refractive indexes of the respective layers can be changed only in the portion irradiated with other light different from the reference light, so that only the portion irradiated with this light corresponds to the reference light according to the hologram pattern. Can be diffracted. That is, diffracted light can be emitted outside the optical waveguide.
When a photochromic material is used, the light absorption rate of only that portion is changed in accordance with the irradiation of the other light. If such a photochromic material is used at least in a portion where the hologram pattern is formed, the hologram pattern can be optically revealed only in the portion irradiated with the other light.
Accordingly, even in this case, diffracted light corresponding to the hologram pattern can be emitted only from a desired portion irradiated with light other than the reference light.

In this way, according to the present invention, it is possible to emit diffracted light only from a desired portion irradiated with another light (second light) different from the reference light (first light). When reading out a desired data portion, the utilization efficiency of the reference light can be significantly improved as compared with the conventional case.
If the use efficiency of the reference light is improved in this way, the image formation efficiency of the diffracted light to the photodetector can be improved correspondingly, thereby improving the data reading rate.
In addition, the imaging efficiency of the diffracted light on the photodetector is improved. In other words, the amount of reference light for obtaining a predetermined readout rate can be reduced, and accordingly, the power consumption on the reproducing apparatus side is correspondingly reduced. It will be possible to reduce this.

Further, as described above, diffracted light is obtained only at a desired portion irradiated with light other than the reference light, so that stray light can be effectively suppressed, and thus crosstalk can be effectively suppressed.
In addition, by suppressing the crosstalk in this way, it is possible to improve the information recording density of the recording medium.

Hereinafter, the best mode for carrying out the invention will be described.
The best mode for carrying out the invention is hereinafter referred to as an embodiment.

<First Embodiment>
First, FIG. 1 and FIG. 2 are sectional views showing the structures of hologram recording media as a first example and a second example, respectively, in the first embodiment of the present invention.
First, as shown in these drawings, an optical waveguide hologram recording medium as in the present invention includes two clad layers and a core layer laminated so as to be sandwiched between the clad layers. The provided optical waveguide is formed. This optical waveguide is formed for propagating the reference light B1 irradiated from the end face side of the recording medium in the hologram recording medium as shown in the figure for reading information stored in the hologram recording medium.
The optical waveguide utilizes the property that light propagates through a region having a high refractive index. That is, generally, the optical waveguide is configured such that the reference light B1 propagates through a core layer having a relatively high refractive index sandwiched between two cladding layers having a relatively low refractive index (relative to the reference light B1). Has been.

Also in the first embodiment, the basic structure as an optical waveguide type for propagating the reference light B1 in a region having a relatively high refractive index, sandwiched between the two cladding layers having a relatively low refractive index. Take.
As a specific structure, in the first embodiment, as shown in FIGS. 1 and 2, first, one clad layer is composed of two layers.
That is, of the clad layer 3 and the clad layer 4 formed so as to sandwich the core layer 2, in this case, the clad layer 4 is constituted by two layers of the first clad layer 4a and the second clad layer 4b. In this case, the layer in contact with the core layer 2 is the first cladding layer 4a.
Further, a hologram pattern 5 is formed on the surface of the first cladding layer 4a and the second cladding layer 4b that are in contact with each other.
That is, as shown in the drawing, the cross-sectional shape of the contact surface of each layer is an uneven shape, and necessary information is stored by this uneven shape forming pattern.

Here, in the structure as described above, also in the first embodiment, the refractive index relationship between the core layer 2, the cladding layer 3, and the cladding layer 4 is that of the core layer 2 with respect to the cladding layers 3 and 4. A relationship in which the refractive index is higher is obtained.
According to this, the reference light B1 irradiated from the end face side of the recording medium is normally propagated only through the core layer 2, and thus formed between the first cladding layer 4a and the second cladding layer 4b. The diffracted light corresponding to the hologram pattern 5 is not emitted to the outside. That is, according to the configuration described so far, the diffracted light is not radiated over the entire surface as in the prior art.
In the drawing, for easy understanding, the layer having a higher refractive index with respect to the reference light B1 is shown in darker color.

  And as 1st Embodiment, after taking the structure until now, the photorefractive material from which a refractive index changes at least any one of the core layer 2 and the 1st cladding layer 4a according to light irradiation is used. It is comprised by.

First, as a specific example, in the hologram recording medium 1 as the first example shown in FIG. 1, the first cladding layer 4a side is made of a photorefractive material. That is, a material whose refractive index changes according to irradiation with another laser beam (referred to as access beam) B2 different from the reference beam B1 as shown in the drawing is selected.
As the photorefractive material selected for the first cladding layer 4a in this way, a material having a property that the refractive index increases only while the access light B2 is irradiated as described above is selected. Yes.
As the photorefractive material used in the first example, for example, a photorefractive polymer such as benzylbutyl phthalate to which 4-amino-4nitroazobenzene or the like is added may be used. Alternatively, an inorganic material such as silver oxide (AgO) may be used.
For the other cladding layer 3, core layer 2, and second cladding layer 4b, a material whose refractive index does not change even when irradiated with the access light B2 is used. For example, the clad layer 3 and the second clad layer 4b may be made of a material such as a photopolymer or UV resin that does not change its refractive index as used in the related art.

As for the refractive index of the photorefractive material as the first cladding layer 4a, the refractive index is nCL and the access light B2 is irradiated at a portion where the access light B2 is not irradiated and the photorefractive effect is not obtained. When the refractive index in the portion where the photorefractive effect is obtained is nCL + ΔnCL, and the refractive index of the core layer 2 is nC, at least the following relationship is established.
“NCL <nc ≦ nCL + ΔnCL”
That is, the first cladding layer 4a has a refractive index lower than that of the core layer 2 in the portion not irradiated with the access light B2, and a refractive index higher than that of the core layer 2 is obtained in the portion irradiated with the access light B2. It is what.

According to the hologram recording medium 1 as the first example of the first embodiment having the above structure, in the non-irradiation region where the access light B2 is not irradiated, the light wave field distribution KB of the illustrated reference light B1 As indicated by KB1 and KB3, the reference light B1 irradiated from the end face side propagates only through the core layer 2.
In this case, since the hologram pattern 5 is formed between the first cladding layer 4a and the second cladding layer 4b as can be seen from the figure, the reference beam B1 propagates only through the core layer 2 in this way. No diffracted light is emitted to the outside.

In the irradiation region irradiated with the access light B2, the first cladding layer 4a in this portion has a refractive index higher than that of the core layer 2 due to the photorefractive effect, as indicated by A in the figure. The That is, in this irradiation region, an optical waveguide is formed by the first cladding layer 4a and the core layer 2 having a high refractive index, sandwiched between the cladding layer 3 and the second cladding layer 4b having a low refractive index on both sides. Will be.
Therefore, the reference light B1 in this irradiation region is propagated through the first cladding layer 4a together with the core layer 2, as indicated by the field distribution KB2 in the figure. Thus, the reference light B1 is also propagated through the first cladding layer 4a, so that the reference light B1 is diffracted by the hologram pattern 5 formed between the first cladding layer 4a and the second cladding layer 4b. As a result, the diffracted light shown in the figure is emitted outside the optical waveguide.
The diffracted light should be incident on a two-dimensional photodetector provided on the reproducing apparatus side that reproduces the hologram recording medium 1, and the diffracted light is incident on the two-dimensional photodetector. Information is read according to the hologram pattern 5 by forming an image and detecting this as an electrical signal.

In this way, according to the hologram recording medium 1 shown in FIG. 1, the diffracted light diffracted by the hologram pattern 5 can be emitted to the outside only in the portion irradiated with the access light B2.
According to this, when reading out the desired data portion, the reference light is compared with the configuration in which the diffracted light based on the irradiation of the reference light B1 is radiated on all the surfaces where the hologram pattern is formed as in the prior art. The utilization efficiency of the laser beam irradiated as B1 can be remarkably improved.

If the utilization efficiency of the light of the reference light B1 can be improved in this way, the imaging efficiency of the diffracted light on the photodetector on the reproducing apparatus side of the hologram recording medium 1 can be improved accordingly. The data read rate on the side can be improved.
Further, the improvement of the imaging efficiency of the diffracted light on the photodetector in this way can reduce the amount of the reference light B1 to be irradiated when obtaining a predetermined readout rate. The power consumption on the playback device side can also be reduced.

In addition, since the diffracted light is obtained only in the desired portion irradiated with the access light B2 as described above, stray light that has been a problem in the conventional configuration can be effectively suppressed, and thus the crosstalk can be effectively suppressed. Figured.
If the crosstalk is suppressed in this way, the information recording density of the hologram recording medium 1 can be improved.

Subsequently, as the hologram recording medium 12 of the second example shown in FIG. 2, the core layer 2 side is constituted by a photorefractive material.
As the photorefractive material used on the core layer 2 side as described above, a material whose refractive index decreases in response to the irradiation with the access light B2 is selected. For the photorefractive material used in the second example, for example, lithium niobate, lithium tantalate, or barium titanate may be selected.
For the other cladding layer 3 and the first cladding layer 4 (the first cladding layer 4a and the second cladding layer 4b), a material whose refractive index does not change even when irradiated with the access light B2 is used. For example, in this case as well, a material such as a photopolymer or UV resin that does not change the refractive index as used in the related art may be used.

Further, in the second example, regarding the refractive index of the core layer 2 made of the photorefractive material as described above, the refractive index in the part where the access light B2 is not irradiated and the photorefractive effect is not obtained is nC, and the access light B2 is When the refractive index in the portion where the photorefractive effect is obtained by irradiation is nC−ΔnC, and the refractive index of the first cladding 4a in contact with the core layer 2 is nCL, at least,
“NC−ΔnC ≦ nCL <nc”
The relationship is established.
That is, in the second example, the core layer 2 has a refractive index higher than that of the first cladding layer 4a in a portion where the access light B2 is not irradiated, and has a refractive index equal to or lower than that of the first cladding layer 4a in a portion irradiated with the access light B2. It is intended to be obtained.

According to the hologram recording medium 12 as such a second example, in the non-irradiated region where the access light B2 is not irradiated, the reference light B1 is only the core layer 2 in this case as shown by the field distributions KB1 and KB3. To be propagated.
As described above, in the first embodiment, the hologram pattern 5 is formed between the first clad layer 4a and the second clad layer 4b. In this case as well, diffracted light is emitted to the outside in the non-irradiated region. There is no.
In the irradiation region irradiated with the access light B2, the core layer 2 in this portion has a refractive index lower than that of the first cladding layer 4a due to the photorefractive effect, as indicated by A in the figure. (A in the figure). That is, when the refractive index of the core layer 2 is set to be equal to or lower than the refractive index of the first cladding layer 4a in this way, the reference light B1 in this portion propagates through at least the first cladding layer 4a. . At this time, depending on how the refractive index of the core layer 2 decreases, the reference light B1 propagates through the core layer 2 as shown by the field distribution KB2 in the figure.

Accordingly, even in this case, as a result, the reference beam B1 is diffracted by the hologram pattern 5 formed between the first cladding layer 4a and the second cladding layer 4b only in the irradiation region, and is diffracted as the diffracted light outside the optical waveguide. Will be emitted.
In this way, since the diffracted light by the hologram pattern 5 can be emitted only in the irradiation region irradiated with the access light B2, the same effect as in the first example shown in FIG. 1 can be obtained even in this case.

Here, in realizing such a hologram recording medium 12 as the second example, as described above, the refractive index of the core layer 2 and the first cladding layer 4a is “nC−ΔnC ≦ nCL <nc”. A relationship needs to be established.
According to this relationship, in this case, the refractive index (nCL) of the first cladding layer 4a is determined by the refractive index (nC−ΔnC) in the irradiation region of the core layer 2 and the refractive index (nc) in the non-irradiation region. Therefore, it is necessary to fit in between them accurately.
This adjustment can be performed, for example, by adjusting the film forming conditions if the first cladding layer 4a is formed by forming a niobium oxide film or a tantalum oxide film by sputtering.
For example, in normal sputtering, argon gas is used as a process gas, and oxygen gas can be used as a process gas together with the argon gas, and the partial pressure of these gases can be adjusted. That is, when the oxygen gas partial pressure is increased, the refractive index can be adjusted low, and conversely, when the oxygen gas partial pressure is decreased, the refractive index can be adjusted high.

In the first embodiment described so far, in the hologram recording medium 1 shown in FIG. 1, the refractive index of the core layer 2 is not a photorefractive material, and the refractive index is also in accordance with the irradiation of the access light B2. However, in the first embodiment, the refractive index of the first cladding layer 4a is relatively lower between the core layer 2 and the first cladding layer 4a in the irradiation region. What is necessary is just to make it become more than a refractive index.
Therefore, in the configuration of FIG. 1, as described above, the first cladding layer 4a is made of a photorefractive material whose refractive index increases in the irradiation region, and the refractive index of the core layer 2 decreases in the irradiation region. The same effect can be obtained by using a photorefractive material.
In FIG. 2, only the core layer 2 is made of a photorefractive material whose refractive index is lowered. In this case as well, for the same reason, the core layer 2 is made of a photorefractive material, and then the first cladding layer 4a. Even if the side is made of a photorefractive material whose refractive index increases, the same effect can be obtained.

<Second Embodiment>
3 and 4 show cross-sectional views of the configurations of the hologram recording media of the first example and the second example, respectively, in the second embodiment of the present invention. In these drawings, portions already described in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.
In the hologram recording medium of the second embodiment, unlike the first embodiment, the clad layer 3 and the clad layer 4 that are stacked with the core layer 2 interposed therebetween are both in one layer. In this case, the core layer 2 is constituted by two layers of the first core layer 2a and the second core layer 2b as shown in the figure. In this case, the first cladding layer 2 a is in contact with the cladding layer 3.
In addition, the hologram pattern 5 is formed between the first core layer 2a and the second core layer 2b.

In such a structure, also in the second embodiment, the refractive index of the core layer 2 is increased with respect to the refractive indexes of the cladding layer 3 and the cladding layer 4 so that an optical waveguide for the reference light B1 is formed. Has been.
Also in the second embodiment, in order to obtain the same effect as in the first embodiment, it is necessary to prevent the diffracted light from being emitted outside only by irradiation with the reference light B1. As this mechanism, in the case of the second embodiment, the refractive index and the absorptance of the first core layer 2a and the second core layer 2b are set to be equal. As a result, there is no difference in refractive index and absorptance between the first core layer 2a and the second core layer 2b, and the hologram pattern 5 formed between these layers is not optically manifested. It will be a thing. That is, the diffraction of the reference light B1 by the hologram pattern 5 does not occur, and as a result, it is possible to prevent the diffracted light from being emitted outside in the non-irradiated region.

  In the second embodiment, one of the first core layer 2a and the second core layer 2b is made of a photorefractive material in the above structure.

First, in the hologram recording medium 13 as the first example shown in FIG. 3, a photorefractive material is used for the first core layer 2a.
As the photorefractive material in this case, a material whose refractive index increases in response to the irradiation with the access light B2 is selected as in the configuration shown in FIG.

According to the hologram recording medium 13 as the first example having the above configuration, the refractive index of the first core layer 2a is increased by the photorefractive material having the above properties in the irradiation region irradiated with the access light B2. (A in the figure).
According to this, as described above, the refractive index between the first core layer 2a and the second core layer 2b, which has been set to the same refractive index (and absorptivity) in the state where the access light B2 is not irradiated, is provided. A difference arises, and the hologram pattern 5 formed between the first core layer 2a and the second core layer 2b can be optically manifested only in this irradiation region.
Further, as described above, the refractive index of the first core layer 2a increases, so that the reference light B1 propagates through both the first core layer 2a and the second core layer 2b in the non-irradiated region. Will propagate only through the first core layer 2a having a high refractive index in the irradiated region (see field distributions KB1 to KB3 in the figure).

In this way, the hologram pattern 5 is manifested in the irradiation region, and the reference light B1 is propagated through the first core layer 2a on which the hologram pattern 5 is formed, so that the access light B2 is also irradiated in this case. Diffracted light can be emitted to the outside only in the portion.
That is, the same effect as that of the hologram recording medium 1 shown in FIG. 1 can be obtained by the hologram recording medium 13 as the first example shown in FIG.

  Next, as the hologram recording medium 14 as the second example shown in FIG. 4, a photorefractive material is used for the first core layer 2a as in FIG. 3, but in this case, the configuration shown in FIG. In the same manner as above, a photorefractive material whose refractive index decreases in response to the irradiation with the access light B2 is selected.

According to the hologram recording medium 14 of the second example, as in the case of the first example, the refractive index (and the absorptance) in the non-irradiated region where the access light B2 is not irradiated is the first core layer 2a. In this case, the hologram pattern 5 formed between the first core layer 2a and the second core layer 2b is optically apparent even in this case. Do not turn. At the same time, the reference light B1 propagates through the first core layer 2a and the second core layer 2b (see KB1 and KB2 in the figure).
Then, in the irradiation region irradiated with the access light B2, the refractive index of the first core layer 2a is lowered due to the photorefractive effect of the above property (A in the figure), and the hologram pattern 5 is optically manifested and is referred to In this case, the light B1 propagates only through the second core layer 2b side whose refractive index is relatively high (field distribution KB2 in the figure).

  In this way, the hologram pattern 5 is manifested only in the irradiation region, and the reference beam B1 is propagated through the second core layer 2b on which the hologram pattern 5 is formed. Diffracted light can be emitted to the outside only at the portion irradiated with the light B2. That is, the same effect as that of the hologram recording medium 1 shown in FIG. 1 can be obtained by the hologram recording medium 14 of the second example.

  In the second embodiment, in both the first and second examples, the photorefractive material is used only for the first core layer 2a. However, the photorefractive material is used for the second core layer 2b. Even if it exists, the effect similar to these 1st examples and 2nd examples is acquired. In addition, since the effect | action when using a photorefractive material for the 2nd core layer 2b in this way is the same as that of a 1st example and a 2nd example, description by illustration here is abbreviate | omitted.

<Third Embodiment>
FIG. 5 and FIG. 6 show the configurations of the hologram recording media of the first example and the second example, respectively, according to the third embodiment of the present invention by cross-sectional views. In these drawings, portions already described in FIG. 1 are denoted by the same reference numerals and description thereof is omitted.
Also in the hologram recording medium of the third embodiment, as in the second embodiment, the clad layer 3 and the clad layer 4 which are stacked so as to sandwich the core layer 2 are made into one layer. Also in this case, the core layer 2 is a two-layered structure including a first core layer 2a and a second core layer 2b. Here, the first cladding layer 2a is also in contact with the cladding layer 3.
Also in this case, the hologram pattern 5 is formed between the first core layer 2a and the second core layer 2b.

In such a structure, also in the third embodiment, the refractive index of the core layer 2 is made higher than that of the cladding layers 3 and 4 so that an optical waveguide for the reference light B1 is formed. is doing.
And also as 3rd Embodiment, by setting the refractive index and absorption rate of the said 1st core layer 2a and the 2nd core layer 2b equally similarly to previous 2nd Embodiment, The diffracted light is not radiated to the outside only by irradiation with the reference light B1.

  In the third embodiment, in the above structure, at least a part of the core layer 2 is configured by a photochromic material whose light absorption rate is changed in accordance with the irradiation of the access light B2. is there.

As an example, in the hologram recording medium 15 as the first example shown in FIG. 5, the entire second core layer 2b is made of a photochromic material.
As the photochromic material in this case, a material whose absorption rate is increased in response to the irradiation with the access light B2 is selected. An example of a photochromic material having such properties is diarylethene.

According to the hologram recording medium 15 as the first example of the third embodiment having the above configuration, in the non-irradiation region where the access light B2 is not irradiated, the refractive indexes of the first core layer 2a and the second core layer 2b, and Since the absorptance is equivalent (for example, both are colorless), the hologram pattern 5 formed between the first core layer 2a and the second core layer 2b is not optically manifested, and thus the reference light B1 Is not radiated to the outside.
Then, in the irradiation region irradiated with the access light B2, the absorption rate of the second core layer 2b by the photochromic material having the above-described properties with respect to the reference light B1 is increased (A in the figure). The second core layer 2b is colored by such an increase in the absorptance, and the hologram pattern 5 formed between the second core layer 2b and the first core layer 2a is optically manifested. Become.
Further, in this case, since the refractive indexes of the first core layer 2a and the second core layer 2b are also equal in the irradiation region, the reference light B1 propagates through the first core layer 2a and the second core layer 2b. (Refer to KB2).

In this way, in the irradiation region, the hologram pattern 5 becomes obvious and the reference light B1 propagates through the first core layer 2a and the second core layer 2b, and in this case also, the access light B2 is irradiated. Diffracted light can be emitted to the outside only in the portion.
Thus, the same effect as that of the hologram recording medium 1 shown in FIG. 1 can be obtained by the hologram recording medium 15 as the first example of the third embodiment.

  Even when the same photochromic material is used for the first core layer 2a, the same action as described above can be obtained, and as a result, the same effect can be obtained. However, in this case, since the diffracted light KS is emitted in the direction opposite to the direction shown in FIG. 5, the two-dimensional photodetector is assumed to be disposed on the side corresponding to the reproducing apparatus side. That's fine.

Subsequently, in the hologram recording medium 16 as the second example of the third embodiment shown in FIG. 6, the hologram pattern 5 between the first core layer 2 a and the second core layer 2 b in the core layer 2 is formed. A photochromic material is used for the portion to be formed.
As the photochromic material in this case, a material having a property of increasing the absorption rate is selected.
The photochromic material has a refractive index / absorption rate equivalent to that of the core layer 2 (the first core layer 2a and the second core layer 2b) when only the reference light B1 is irradiated.

According to the hologram recording medium 14 of the second example as described above, in the non-irradiated region where the access light B2 is not irradiated, the photochromic material as the hologram pattern 5 has the same refractive index / absorption rate as the core layer 2. The hologram pattern 5 does not appear optically. Therefore, diffracted light is not emitted to the outside. In this case, since there is no portion having a different refractive index in the core layer 2, the reference light B1 propagates through the core layer 2 as indicated by the field distributions KB1 to KB3.
Then, in the irradiation region irradiated with the access light B2, the absorptance of the photochromic material as the hologram pattern 5 increases (A in the figure), and the hologram pattern 5 becomes optically apparent.
That is, also in the second example shown in FIG. 6, the diffracted light can be radiated to the outside only at the portion irradiated with the access light B2, and the same effect as the hologram recording medium 1 shown in FIG. Can be obtained.

  In the configuration of the second example, a photorefractive material is used for the portion where the hologram pattern 5 is formed, and the refractive index of the portion of the hologram pattern 5 is the other portion of the core layer 2 only in the irradiation region of the access light B2. It is possible to obtain the same effect by making it different from the refractive index.

Here, the hologram recording medium as an embodiment of the present invention has been described so far, but in these, at least a part of the core layer 2 or the cladding layers 3 and 4 is constituted by a photorefractive material or a photochromic material. Thus, the diffracted light can be obtained only in the region irradiated with the access light B2 different from the reference light B1 propagating through the optical waveguide. As a result, diffracted light corresponding to the hologram pattern 5 is obtained only from the required region, and the use efficiency of the light as the reference light B1 can be improved and the effect of suppressing stray light can be obtained.
However, at this time, if the state in which the refractive index or the absorptance changes is continued after the irradiation of the access light B2, the diffracted light is emitted even after the access light B2 is irradiated. Diffracted light is also emitted from the outside of the region where the light is applied, and the spectral utilization efficiency cannot be improved and stray light cannot be suppressed.
For this reason, as a photorefractive material / photochromic material used in each embodiment, it is preferable to select a material having a time constant as low as possible for a property change corresponding to the irradiation of the access light B2.

  In each of the embodiments, for convenience of explanation, a case where the hologram recording layer (layer on which the hologram pattern 5 is formed) is a single layer in the hologram recording medium has been described. A hologram recording medium in which hologram recording layers are multilayered can be realized by laminating a set of “core layer 2 and cladding layer 4”.

Next, the configuration of a reproducing apparatus that reproduces the hologram recording medium of the embodiment described so far will be described with reference to FIGS.
7 to 13 show only the case where reproduction is performed with respect to the hologram recording medium 1 of the first example of the first embodiment shown in FIG. 1, but each of the cases shown in FIGS. Even when the hologram recording medium is reproduced, the reproduction can be performed by adopting the same configuration.
7 to 13, only the configuration of the optical system according to the gist of the present invention in the reproducing apparatus of the embodiment is shown, and the other parts are omitted.
7 to 13, since the hologram recording medium 1 has already been described in FIG.

First, as a common matter of the reproducing apparatus as the embodiment shown in FIGS. 7 to 13, a first laser LD1 for irradiating the reference light B1 and a second laser for irradiating the access light B2 are provided. It is equipped with LD2.
Then, the reference light B1 from the first laser LD1 and the access light B2 from the second laser LD2 are simultaneously irradiated onto the hologram recording medium, so that only the irradiation area irradiated with the access light B2 corresponds to the hologram pattern 5. The diffracted light is obtained, the diffracted light is detected by the two-dimensional photodetector 52, and data is read out.

FIG. 7 shows a configuration of a playback apparatus 50 as a first example in the playback apparatus as such an embodiment.
The reproducing apparatus 50 as the first example is provided with a pickup 51 including a second laser LD2 for irradiating the access light B2 as shown in the figure, and the pickup 51 is moved to move a desired portion on the hologram recording medium 1 Is configured to read out the data.

  In FIG. 7, the first laser LD1 is a laser light source for irradiating the reference light B1 as described above, and the laser light emitted from the first laser LD1 is condensed by the condenser lens L1 shown in the figure. Then, the light is incident on the optical waveguide formed inside from the end face side of the hologram recording medium 1.

Further, the laser light emitted from the second laser LD2 for irradiating the access light B2 passes through the collimator lens L2, and is converted into desired parallel light, divergent light, or convergent light, and is irradiated onto the dichroic mirror 53. . The dichroic mirror 53 reflects light having a wavelength from the second laser LD2, and transmits light having the wavelength from the first laser LD1. Therefore, the laser beam from the second laser LD 2 irradiated as described above is reflected by the dichroic mirror 53.
The laser beam from the second laser LD2 reflected by the dichroic mirror 53 is condensed through the objective lens L3 shown in the figure, and is irradiated onto the hologram recording medium 1 as access light B2.
In this case, the access light B2 irradiated through the objective lens L3 is irradiated from the direction orthogonal to the irradiation direction of the reference light B1 as shown in the figure.

As described above, in the hologram recording medium of the embodiment, diffracted light corresponding to the hologram pattern 5 is emitted from the portion irradiated with the access light B2 as described above in the state where the reference light B1 is irradiated. The
The diffracted light thus radiated is transmitted through the dichroic mirror 53 via the objective lens L3, and is imaged on the two-dimensional photodetector 52 shown in the figure. That is, the hologram pattern 5 formed in the irradiation region of the access light B2 is imaged on the two-dimensional photodetector 52 by this.
In the two-dimensional photodetector 52, the hologram pattern 5 thus formed is detected as an electric signal, and information stored in the irradiation area of the access light B2 is thereby read out as a data signal.

  The second laser LD2, the collimator lens L2, the objective lens L3, and the two-dimensional photodetector 52 are formed in a pickup 51 surrounded by a broken line in the drawing. The pickup 51 is held so as to be movable in the X direction in the figure by a slide mechanism (not shown), for example, so that data of a desired portion on the hologram recording medium 1 can be read.

  With the configuration as described above, the reproducing device 50 shown in FIG. 7 can reproduce the hologram recording medium of the embodiment.

Here, with respect to the photorefractive material used in the hologram recording medium according to the first and second embodiments described above, the photorefractive effect is particularly remarkable for light having a short wavelength.
For this reason, it is preferable that the access light B2 irradiated by the second laser LD2 is set to a short wavelength such as ultraviolet light because the action as the embodiment described above can be obtained with certainty.
Also, according to this, it is preferable to make the photorefractive effect with respect to the irradiation of the reference light B1 smaller. Therefore, it is preferable that the reference light B1 from the first laser LD1 has a long wavelength such as red light or infrared light.
Further, also in the photochromic material used in the hologram recording medium as the third embodiment, the change in the absorptance becomes remarkable with respect to light having a short wavelength. Accordingly, when reproducing the hologram recording medium of the third embodiment, the same can be said for the wavelengths of the reference light B1 and the access light B2.
For the photochromic material, the wavelength of the access light B2 is more preferably blue light to infrared light.

Further, the access light B2 here is so-called “coherent” light from the laser light source, but instead, it may be “incoherent” light using, for example, an LED (Light Emitting Diode) as a light source. it can.
In particular, when the hologram recording layer is a multilayer as a hologram recording medium, the first laser and the condenser lens L1 are the same as the stacking direction of the layers in the hologram recording medium so that reading can be performed in each layer. What is necessary is just to comprise so that it can move to a direction.

Next, FIG. 8 shows a configuration of a playback device 60 as a second example.
In this figure, the parts already described in FIG.
As the reproducing apparatus 60 of the second example, the second laser LD2 for irradiating the access light B2 and the two-dimensional photodetector 52 are provided at positions facing each other via the hologram recording medium 1 as shown in the figure. Thus, the dichroic mirror 53 required in the configuration of FIG. 7 can be omitted.

  In this case, the laser light emitted from the second laser LD2 is condensed via the collimator lens L2 and the objective lens L3 shown in the figure, and is irradiated onto the hologram recording medium 1 as the access light B2. Also in this case, the diffracted light corresponding to the hologram pattern 5 is emitted from the irradiation region of the access light B2 in the hologram recording medium 1 by the incidence of the reference light B1 from the first laser LD1 side and the irradiation with the access light B2. Is emitted.

  In the case of the second example, in order to guide the diffracted light to the two-dimensional photodetector 52, an objective lens L4 is provided on the opposite side through the hologram recording medium 1 as viewed from the second laser LD2. By passing through the objective lens L4, the emitted diffracted light forms an image on the two-dimensional photodetector 52. As a result, the two-dimensional photodetector 52 can read out the hologram pattern 5 formed in the irradiation region of the access light B2 in the hologram recording medium 1 as a data signal, as in the first example.

  In this case, the second laser LD2, the collimator lens L2, the objective lens L3, the objective lens L4, and the two-dimensional photodetector 52 provided at positions facing each other through the hologram recording medium 1 are illustrated. Since the pickup 61 integrated with the pickup 61 can be slid in at least the X direction, data of a desired portion can be read out.

FIG. 9 shows the configuration of a playback device 70 as a third example. Also in this figure, the parts already described in FIG.
The reproduction apparatus 70 of the third example is obtained by omitting the objective lens L4 from the configuration of the second example shown in FIG. That is, in such a third example, for example, a hologram lens is incorporated in the hologram pattern 5 in the hologram recording medium 1 so that the diffracted light forms an image on the two-dimensional photodetector 52 even without the objective lens L4. It is suitable when it is made to tie.
In this case, as shown in the drawing, the pickup 71 by the second laser LD2, the collimator lens L2, and the objective lens L3 can be slid in at least the X direction, so that data of a desired portion can be read out.
That is, in this case, the movable part on the detection side of the diffracted light can be omitted.

FIG. 10 shows a configuration of a playback device 80 as a fourth example. In this figure as well, the parts already described in FIG.
In the fourth example, a plurality of second lasers LD2 for irradiating the access light B2 are provided at positions facing through the hologram recording medium 1 when viewed from the two-dimensional photodetector 52 side. Thus, for example, a movable part for reading data of a desired part such as a pickup can be omitted.

In this case, as the plurality of second lasers LD2 provided as described above, for example, four lasers LD2a to LD2d are provided. A microlens array 81 is provided for condensing the laser light emitted from each of the plurality of second lasers LD2 onto the hologram recording medium 1 as access light B2.
The microlens array 81 is formed with a plurality of lens portions by lens portions 81a to 81d, each of which can collect the respective laser beams emitted from the second laser LD2a to the second laser 2d. It is provided so that it may become a position.

In this fourth example, as shown in the following FIGS. 11A to 11D, by selectively lighting one desired laser among the second laser LD2a to the second laser LD2d, Data reading of a desired portion on the hologram recording medium 1 is performed.
The example of FIG. 11 shows an example in which data reading is performed by sequentially turning on the second laser LD2a to the second laser LD2d one by one.
First, as shown in FIG. 11A, when only the second laser LD2a is turned on, the emitted light from the second laser LD2a passes through the lens portion 81a in the microlens array 81, thereby forming the access light B2. Irradiated onto the hologram recording medium 1. In response to this, diffracted light corresponding to the hologram pattern 5 formed in the area irradiated with the access light B2 is emitted, and in the two-dimensional photodetector 52, the hologram in the area irradiated with the second laser LD2a is thereby emitted. Pattern 5 is read out as a data signal.
Then, as shown in the transitions of FIGS. 11B to 11D, when the second laser LD2b, the second laser LD2c, and the second laser LD2d are turned on, the lenses 81b, 81c, and 81d, respectively. The access light B2 via the beam is irradiated onto the hologram recording medium 1, whereby the hologram pattern 5 formed in each irradiation region is sequentially read out.

Thus, according to the reproduction apparatus 80 of the fourth example, the data of a desired portion on the hologram recording medium 1 can be read by turning on one desired second laser LD2 among a plurality of provided reproduction apparatuses. it can.
And according to the structure of such a 4th example, movable parts like the pick-up 51, 61, 71 demonstrated previously can be abbreviate | omitted. If such a movable part can be omitted, it is advantageous for reducing the size of the apparatus and power consumption.

FIG. 12 shows the configuration of a playback device 90 as a fifth example. In this figure as well, the parts already described in FIG.
In the fifth example, by using the galvano mirror 91 shown in the figure, it is possible to irradiate the desired position on the hologram recording medium 1 with the access light B2.

In the fifth example, a second laser LD 2, a collimator lens L 2, and a galvano mirror 91 are provided on the opposite side through the hologram recording medium 1 when viewed from the side where the two-dimensional photodetector 52 is provided. In this case, the laser light emitted from the second laser LD2 passes through the collimator lens L2 and is reflected by the galvanometer mirror 91, and this reflected light is irradiated onto the hologram recording medium 1 as the access light B2.
The diffracted light radiated in response to the incidence of the access light B2 and the reference light B1 from the first laser LD1 side passes through the objective lens L4 provided on the opposite side through the hologram recording medium 1 when viewed from the galvanomirror 91 side. The image is formed on the two-dimensional photodetector 52.
At this time, the irradiation position of the access light B2 to the hologram recording medium 1 can be controlled by the rotation angle of the mirror surface of the galvano mirror 91, and thus the access light B2 can be irradiated to a desired portion on the hologram recording medium 1. It is said.
In this case, the two-dimensional photodetector 52 and the objective lens L4 are formed in the pickup 92 shown in the figure, and the pickup 92 is slid according to the radiation position of the diffracted light corresponding to the irradiation of the access light B2. By driving, data can be read.
With such a configuration, it is possible to perform data reading of a desired portion on the hologram recording medium 1 also by the reproducing device 90 of the fifth example.

FIG. 13 shows the configuration of the playback apparatus 100 as a sixth example. In this figure, the parts described in FIG. 7 and FIG.
Similar to the reproducing device 90 shown in FIG. 12, the reproducing device 100 allows the desired light to be irradiated with the access light B2 by the galvano mirror 91, and omits the objective lens L4.
That is, such a configuration is similar to the third example described above, in which, for example, a hologram lens is incorporated in the hologram pattern 5 in the hologram recording medium 1 so that the diffracted light is two-dimensional light even without the objective lens L4. This is suitable when an image is formed on the detector 52.
Then, according to the configuration of the sixth example as described above, it is possible to omit the pickup 91 that is required in the reproducing apparatus 90 of FIG.

Note that the hologram recording medium and the reproducing apparatus of the present invention are not limited to the configurations of the embodiments described above.
For example, as a reproducing apparatus, a necessary configuration can be added as appropriate, for example, by adding a lens that is necessary in designing an actual optical system.

It is sectional drawing which showed the structure as a 1st example of the hologram recording medium as 1st Embodiment in this invention. It is sectional drawing which showed the structure as a 2nd example of the hologram recording medium as 1st Embodiment. It is sectional drawing which showed the structure as a 1st example of the hologram recording medium as 2nd Embodiment in this invention. It is sectional drawing which showed the structure as a 2nd example of the hologram recording medium as 2nd Embodiment. It is sectional drawing which showed the structure as a 1st example of the hologram recording medium as 3rd Embodiment in this invention. It is sectional drawing which showed the structure as a 2nd example of the hologram recording medium as 3rd Embodiment. It is the figure which mainly showed the structure of the optical system about the structure of the 1st example of the reproducing | regenerating apparatus as embodiment in this invention. It is the figure which mainly showed the structure of the optical system about the structure of the 2nd example of the reproducing | regenerating apparatus as embodiment in this invention. It is the figure which mainly showed the structure of the optical system about the structure of the 3rd example of the reproducing | regenerating apparatus as embodiment in this invention. It is the figure which mainly showed the structure of the optical system about the structure of the 4th example of the reproducing | regenerating apparatus as embodiment in this invention. It is the figure illustrated about the data read-out method of the reproducing | regenerating apparatus of the 4th example. It is the figure which mainly showed the structure of the optical system about the structure of the 5th example of the reproducing | regenerating apparatus as embodiment in this invention. It is the figure which mainly showed the structure of the optical system about the structure of the 6th example of the reproducing | regenerating apparatus as embodiment in this invention. It is a figure for demonstrating the conventional hologram recording medium and its reading method.

Explanation of symbols

  1, 12, 13, 14, 15, 16 Hologram recording medium, 2 core layer, 2a first core layer, 2b second core layer, 3, 4 cladding layer, 4a first cladding layer, 4b second cladding layer, 5 Hologram pattern, 50, 60, 70, 80, 90, 100 Playback device, 51, 61, 71, 92 Pickup, 52 Two-dimensional photodetector, 81 Micro lens array, 81a-81d Lens part, 91 Galvano mirror, LD1 1 laser, LD2 (LD2a to LD2d) second laser, L1 condenser lens, L2 collimator lens, L3 objective lens, L4 objective lens

Claims (15)

Two clad layers and a core layer sandwiched between the clad layers are provided to form an optical waveguide, and a required hologram pattern is formed on the core layer or the clad layer, thereby forming an information signal. Is an optical waveguide type hologram recording medium in which is stored,
A hologram recording medium, wherein at least a part of at least one of the core layer or one of the cladding layers is made of a photorefractive material or a photochromic material. One of the clad layers is composed of two layers of a first clad layer and a second clad layer, and the hologram pattern is formed between the first clad layer and the second clad layer. And at least one of the core layer and the first cladding layer in contact with the core layer is made of the photorefractive material.
The hologram recording medium according to claim 1.   The hologram recording medium according to claim 2, wherein the first cladding layer is made of the photorefractive material whose refractive index is increased by a photorefractive effect.   3. The hologram recording medium according to claim 2, wherein the core layer is made of the photorefractive material whose refractive index is lowered by a photorefractive effect. The core layer is composed of two layers of a first core layer and a second core layer having the same refractive index, and includes the first core layer and the second core layer. The hologram pattern is formed between them, and at least one of the first core layer and the second core layer is made of the photorefractive material.
The hologram recording medium according to claim 1.   6. The hologram recording medium according to claim 5, wherein any one of the first core layer and the second core layer is made of the photorefractive material whose refractive index is increased by a photorefractive effect. .   6. The hologram recording medium according to claim 5, wherein either one of the first core layer and the second core layer is made of the photorefractive material whose refractive index is lowered by a photorefractive effect. . The core layer is composed of two layers of a first core layer and a second core layer having the same refractive index, and includes the first core layer and the second core layer. The hologram pattern is formed therebetween, and at least a part of the core layer is made of the photochromic material.
The hologram recording medium according to claim 1.   9. The hologram recording medium according to claim 8, wherein any one of the first core layer and the second core layer is made of the photochromic material.   9. The hologram recording medium according to claim 8, wherein a portion of the core layer where the hologram pattern is formed is made of the photochromic material. Two clad layers and a core layer sandwiched between the clad layers are provided to form an optical waveguide, and a required hologram pattern is formed on the core layer or the clad layer, thereby forming an information signal. A reproducing apparatus for reproducing an optical waveguide type hologram recording medium in which is stored,
First light irradiating means for irradiating first light for propagating reference light to the optical waveguide formed on the hologram recording medium;
Second light irradiation means for irradiating the hologram recording medium with second light different from the reference light;
An information signal detection means for obtaining an information signal by detecting diffracted light corresponding to the hologram pattern emitted from the hologram recording medium by irradiation of the reference light and the second light;
A playback apparatus comprising: The second light irradiation means is configured to irradiate the hologram recording medium with the second light reflected by the dichroic mirror,
The information signal detecting means is configured to detect the diffracted light that is emitted from the hologram recording medium and obtained through the dichroic mirror.
The playback apparatus according to claim 11. The second light irradiation unit is configured to irradiate the second light to the hologram recording medium from a position facing the information signal detection unit via the hologram recording medium.
The playback apparatus according to claim 11. The second laser irradiation means includes
The information signal detecting means is provided on the opposite side through the hologram recording medium, and is configured to selectively irradiate the second light from a plurality of positions.
The playback apparatus according to claim 11.   12. The reproducing apparatus according to claim 11, wherein the second light irradiation unit is configured to irradiate the hologram recording medium with the second light reflected by a galvano mirror.

Images