JP2006078942A - Hologram recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep the area of irradiation of a hologram recording material with reference light to be always constant without inducing mechanical abrasion irrespectively of the variation in the incidence angle of the reference light at the time of recording a hologram by an angle multiplex recording system without degrading a high scanning speed and a small-size lightweight configuration. <P>SOLUTION: If a diffraction grating 111 and a hologram recording material 14 are disposed in an imaging relationship through a telecentric optical system comprising lenses 12, 13, this ensures that, even when the deflection angle of the reference light 200 is varied by the diffraction grating 111 to thereby vary the angle of incidence on the hologram recording material 14, the area of irradiation of the hologram recording material with the reference light 200 can be kept constant because of the imaging relationship of the diffraction grating 111 and the hologram recording material 14. This effect can be realized without inducing any mechanical abrasion and without degrading a high scanning speed and a small-size lightweight configuration. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hologram recording apparatus that multiplex-records a hologram on a hologram recording medium by an angle multiplexing method.

  In recent years, a hologram recording / reproducing apparatus that records and reproduces large-capacity data using hologram technology has been proposed (for example, see Non-Patent Document 1). In this hologram recording / reproducing apparatus, a technique called multiple recording is used to improve the recording density. This is different from conventional recording in that a large number of independent pages are recorded in one place. Typical examples of such multiplex recording methods are angle multiplex recording, shift multiplex recording, phase code multiplex recording, and other various methods such as speckle multiplex.

  FIG. 13 is a diagram for explaining a case where a hologram is recorded on a hologram recording material (hologram recording medium) by the angle multiplexing method. Signal light and reference light are branched from laser light emitted from a laser light source (not shown), and signal light 100 spatially modulated by a spatial modulator (not shown) passes through a signal light optical system (not shown). The light is focused on the hologram recording material 10. On the other hand, the reference light 200 enters the scan mirror 1 through a reference light optical system (not shown), is reflected by the scan mirror 1 and enters the lens 2 of the reference light optical system. The lenses 2 and 3 constitute a 4f optical system, the reference light 200 irradiates the hologram recording material 10 by the lens 3, and interference fringes generated by the interference between the signal light 100 and the reference light 200 are recorded on the hologram recording material 10. . Here, when the angle of the scan mirror 1 is changed, only the incident angle of the reference light 200 to the hologram recording material 10 is changed according to the angle change, and a different hologram for each incident angle is generated on the hologram recording material 10. Multiple recording is performed in the same recording area.

  FIG. 14 is a diagram for explaining that the area where the reference light 200 irradiates the hologram recording material 10 changes due to the change in the incident angle of the reference light 200 described above. Even if the incident angle of the reference beam 200 to the hologram recording material 10 (medium normal standard) is different, the thickness of the beam is constant, so that the incident angle A and the incident angle B are apparent from the figure. The irradiation area in the case of the incident angle B is larger.

FIG. 15 is a diagram showing how the irradiation area changes with respect to the change in the incident angle of the reference light 200 described above. If the beam diameter of the reference beam 200 is φ1, as shown in FIGS. 15A, 15B, and 15C, the angle of the scan mirror 1 changes and the incident angle of the reference beam 200 increases. The diameter of the irradiated part of the hologram recording material 10 of the reference light 200 increases in the order of φ1, φ2, and φ3.
IBM J.RES DEVELOP VOL 44 NO.3 MAY 2000 `` Holographic data storage ''

  As described above, when the incident angle of the reference beam 200 with respect to the hologram recording material 10 is changed in the angle multiplex recording method, the signal beam 100 has a constant incident angle regardless of the change in the incident angle of the reference beam 200. The same area portion of the hologram recording material 10 is irradiated. Therefore, it means that the range in which the reference light 200 irradiates the hologram recording material 10 including the irradiation range of the signal light 100 increases as the irradiation area of the reference light 200 increases. However, it is originally desirable that the reference light 200 is irradiated within the hologram recording material 10 in a range that covers the irradiation range of the signal light 100 to the minimum necessary. This is because the irradiation of the unnecessary portion of the reference beam 200 causes the hologram recording material 10 to be more exposed to light, which wastes the dynamic range and leads to a decrease in recording capacity.

  Therefore, it is conceivable that the range in which the reference light 200 irradiates the hologram recording material 10 is always constant regardless of the change in the incident angle of the reference light 200. A mechanism for changing the size mechanically or a method of inserting two 4f projection optical systems connected in series to the reference light optical system can be considered, but the former method is unrealistic when the scanning speed is increased. At the same time, such a mechanical mechanism has a disadvantage that its life is short due to wear or the like. In the latter method, the two 4f projection optical systems connected in series have a large number of optical components, which is disadvantageous in reducing the size and weight of the reference light optical system, and hence the pickup.

  The present invention has been devised in view of the above circumstances, and the object of the present invention is to reduce the incident angle of the reference light when recording a hologram by the angle multiplex recording method without impairing a fast scan speed and a compact and lightweight configuration. It is an object of the present invention to provide a hologram recording apparatus that can always keep the area where the reference light irradiates the hologram recording material without mechanical wear even when the reference beam changes.

  In order to achieve the above object, the present invention provides an angle-multiplexed hologram recording apparatus for recording interference fringes of signal light and reference light on a hologram recording medium, the diffractive optical element for changing the reference light angle, and the hologram recording And a telecentric optical system having an imaging relationship between the medium and the diffractive optical element.

  Thus, in the present invention, if a diffraction grating, for example, is used as the diffractive optical element, and the diffraction grating and the hologram recording medium are arranged so as to form an image relationship with each other via a telecentric optical system (for example, 4f optical system), Even if the angle of incidence on the hologram recording medium is changed by changing the deflection angle of the reference light by the grating, the irradiation area of the reference light on the hologram recording medium is as follows because the diffractive optical element and the hologram recording medium are in an imaging relationship. It can be kept unchanged. In addition, this effect can be realized by using only one set of telecentric optical system, and can be realized without mechanical wear, etc., so that it can cope with a high scanning speed and make the reference light optical system small and light. Can do.

According to the present invention, by disposing the diffractive optical element that changes the reference light angle and the hologram recording medium so as to form an imaging relationship with each other via the telecentric optical system, the high scanning speed and the small and lightweight configuration are impaired. In addition, when the hologram is recorded by the angle multiplex recording method, even if the incident angle of the reference light changes, the area on which the reference light irradiates the hologram recording material can be made constant without mechanical wear.
In addition, by changing the diffraction efficiency of the diffractive optical element for each deflection angle, the intensity ratio between the signal light and the reference light can always be kept constant.

  When recording holograms using the angle multiplex recording method, the area on which the reference light irradiates the hologram recording material, even if the incident angle of the reference light changes, is free from mechanical wear, supports high scanning speed, and is compact and lightweight. The purpose of making it always constant by the configuration is realized by arranging the diffractive optical element for changing the reference light angle and the hologram recording medium so as to form an imaging relationship with each other via the telecentric optical system.

  FIG. 1A to FIG. 1C are block diagrams showing the configuration of the reference light optical system of the hologram recording apparatus according to the first embodiment of the present invention. The reference light optical system of the angle multiplexing type hologram recording apparatus includes a diffractive optical element (hologram scanner) 11, a lens 12, a lens 13, and a hologram recording material 14. The diffractive optical element 11 functions as an angle deflection device, and is referred to. The incident angle of the light 200 on the hologram recording material 14 is changed. The lenses 12 and 13 are a 4f optical system that is a telecentric imaging optical system, and the diffraction grating 111 and the hologram recording material 14 are arranged so as to form an imaging relationship with each other.

  FIG. 2 is a diagram showing a detailed configuration example of the diffractive optical element shown in FIG. This figure is an example using a diffraction grating 111 which is the simplest example of the diffractive optical element 11. The incident light is diffracted by the diffraction grating 111 and the angle is deflected.

  In this diffraction grating 111, as shown in FIG. 3A, the diffraction grating interval changes continuously as the disk-shaped substrate 112 rotates, and as a result, the light deflection angle changes continuously. It has become. That is, the incident beam can be scanned by incorporating diffraction gratings with different pitches into the disk-shaped substrate 112 and rotating them as shown by arrows. FIG. 3B shows the relationship between the scanner angle (rotation angle of the substrate 112) of the diffraction grating 111 shown in FIG. 3A and the deflection angle. The deflection angle increases continuously as the scanner angle increases. It is increasing linearly.

  Next, the operation of the present embodiment will be described. In FIG. 1A, the reference beam 200 is incident on the diffraction grating 111, the reference beam 200 is deflected and incident on the lens 12 according to the scanner angle a of the diffraction grating 111 at that time, and further recorded on the hologram by the lens 13. The light is incident on the material 14 at an angle corresponding to the scanner angle a. Similarly, as shown in FIG. 1B, the reference light 200 is deflected according to the scanner angle b of the diffraction grating 111 and is incident on the lens 12, and is incident on the hologram recording material 14 by the lens 13. Incident light is incident at an angle corresponding to the scanner angle b. Similarly, as shown in FIG. 1C, the reference light 200 is deflected according to the scanner angle c of the diffraction grating 111 and is incident on the lens 12, and is incident on the hologram recording material 14 by the lens 13. Incident light is incident at an angle corresponding to the scanner angle c.

  Since the reference light 200 emitted from the diffraction grating 111 is imaged on the hologram recording material 14 by a telecentric imaging optical system as shown in FIG. 4, the incident area (spot size of the reference light) of the hologram recording material 14 is It becomes the same as the range of the reference light. Since the range of the reference light is constant regardless of the scanner angle of the diffraction grating 111, the irradiation range of the reference light 200 formed on the hologram recording material 14 is also the irradiation range of the reference light 200 on the hologram recording material 14. It is constant regardless of the scanner angle of the diffraction grating 111, that is, the incident angle of the reference light 200 to the hologram recording material 14.

  Here, when a continuous change type beam scan as shown in FIG. 2 is used as the diffraction grating 111, the time for which the beam is at a certain angle is extremely short. As a result, the time for reproducing one angle-multiplexed hologram page is extremely short. If the reproduction time of one page of the hologram is short, the power of the reproduction laser is weak or the diffraction efficiency of the recorded hologram data is low, the light intensity received by the image sensor becomes weak, and the S / N ratio deteriorates. In some cases, playback becomes impossible. Such a problem becomes more prominent when the beam scan speed is increased in order to improve the data transfer rate.

  FIG. 5 is a diagram for explaining the configuration of the diffraction grating 121 for avoiding problems caused when the diffraction grating 111 as described above is used. As shown in FIG. 5A, the diffraction grating 121 has a configuration in which the diffraction grating interval does not change continuously, but changes discontinuously and stepwise for each division angle α. That is, the diffraction grating interval is constant during the division angle α, but the diffraction grating interval changes at a predetermined ratio for each division angle. Therefore, when this diffraction grating 121 is used, as shown in FIG. 5B, the scanner angle is a constant deflection angle during a certain division angle range, and the deflection angle is stepped when the next division angle is entered. The operation that changes to is repeated. Eventually, as shown in FIG. 5B, it is possible to obtain a relationship in which the deflection angle changes discretely with respect to changes in the scanner angle. In this case, since the time for which the incident angle of the reference beam 200 is at a certain angle becomes long and the reproduction time of the hologram becomes long, a reproduction image with a good S / N can be obtained, and therefore the data transfer rate is increased. be able to.

  According to the present embodiment, the diffractive optical element 11 (the diffraction grating 121 in this example) is used in place of the galvanometer mirror that is often used as an angle multiplexing type beam scanning device, and the discontinuous as shown in FIG. A change in the incident angle of the reference light can be easily realized, and a reproduced image with a good S / N can be obtained even when the diffraction efficiency of hologram data is low, the light intensity received by the image sensor is low, or when the data transfer rate is further increased. Obtainable.

  Further, by using the 4f optical system including the lenses 12 and 13 and arranging the diffraction grating 121 and the hologram recording material 14 so as to form an imaging relationship with each other, a change in the incident angle of the reference light 200 to the hologram recording material 14 is achieved. Regardless of this, the irradiation area on the hologram recording material 14 can be made constant, and the exposure portion can be minimized to prevent the dynamic range of the hologram recording material 14 from being lowered. Moreover, since the irradiation area of the reference light 200 on the hologram recording material 14 is made constant by a set of 4f optical systems, the optical system can be reduced in size and weight, and has no mechanical wear portion. Excellent durability.

  In addition, as shown in FIG. 5, the step of changing the deflection angle stepwise can be realized using the diffraction grating 111 having the configuration shown in FIG. In this case, the substrate 112 of the diffraction grating may be rotated stepwise instead of continuously, but rotation control is difficult.

  Note that, in the type in which the deflection angle shown in FIG. 5 changes discontinuously, the diffraction grating interval assigned to each division angle is constant, so the reference light 200 corresponding to the diffraction grating interval is transferred to the hologram recording material 14. If there is a deviation in the incident angle, the reproduced image becomes darker by that amount. Therefore, if the diffraction grating interval assigned to the division angle is set so as to slightly change, the optimum incident angle of the reference beam 200 is slightly deviated due to a temperature change or the like even within this division angle range. However, it is possible to obtain a bright reproduced image. FIG. 6 is a diagram showing a change in the deflection angle with respect to a change in the scanner angle when this type of diffraction grating is used. The diffraction grating interval changes step by step for each division angle range. The diffraction grating interval is slightly changed.

  By the way, in the angle multiplexing method, it is important to keep the light intensity ratio between the signal light and the reference light constant. In this embodiment, although the change in the light intensity due to the change in the beam area of the reference light 200 is small, the light intensity ratio still changes due to the dependency of the surface reflection of the hologram recording material on the reference light incident angle, etc., so that the correction can be performed. It is desirable. For this purpose, the diffraction efficiency of the diffraction grating 111 (or 121) may be changed for each deflection angle. However, the diffraction efficiency is the ratio of the 0th-order light and the 1st-order light shown in FIG. 2, and the diffraction efficiency can be changed by changing this ratio. There are several already known ways to change this diffraction efficiency.

  For example, when the diffraction grating 111 is a phase type, there is a method of adjusting the phase change amount of the diffraction grating 111. For this, for example, the diffraction efficiency can be changed by changing the thickness of the concavo-convex portion forming the diffraction grating, and the thickness of the concavo-convex portion forming the diffraction grating for each division angle range of the diffraction grating 111 is changed to the signal light. What is necessary is just to change so that the light intensity ratio of reference light may become fixed.

  When the diffraction grating 111 is of the amplitude type, coding is performed with different light absorption rates for each split angle range of the diffraction grating 111, and the optical density is changed to change the diffraction efficiency for each deflection angle. The light intensity ratio of light can be made constant. Furthermore, the diffraction efficiency can also be changed by adjusting the width of the diffraction grating forming the diffraction grating 111 to change the light transmittance, and using this, the light intensity ratio between the signal light and the reference light is constant. It can also be made.

  Further, in the above embodiment, for example, in the case of 100 multiplexing by angle multiplexing, the diffraction grating interval of the diffraction grating 111 is cut so as to obtain the deflection angle of the reference light that realizes 100 multiplexing by one rotation. However, the diffraction grating interval may be cut so as to realize 100 multiplexing in half rotation.

  FIG. 7 is a block diagram showing the configuration of the reference light optical system of the hologram recording apparatus according to the second embodiment of the present invention. The reference light optical system according to the present embodiment includes a diffraction grating 111 and a telecentric optical system including a mask 16 and lenses 17 and 18 for converging a light beam, and the structure after the diffraction grating 111 is the same as that shown in FIG. The illustration is omitted.

  Next, the operation of the present embodiment will be described. The mask 16 and the diffraction grating 111 are disposed so as to form an imaging relationship with each other via a telecentric optical system. As a result, since the opening of the mask 16 is reflected on the diffraction grating 111, the reference light 200 irradiated onto the diffraction grating 111 becomes reference light in a range limited by the opening.

  For example, when the diffraction grating 111 is of the type shown in FIG. 5, (1) the reference beam 200 irradiates the diffraction grating 111 at least in FIG. 8 (for the sake of simplicity, a telecentric optical system comprising lenses 17 and 18). Is omitted and conforms to the configuration of FIG. 9). Further, (2) the irradiation range of the reference light 200 with respect to the size of the divided region N makes the time for scanning the boundary between the divided region N and the divided region N + 1 as short as possible so that the deflection angle of the reference light 200 becomes indefinite. Must be as short as possible. In addition, (3) the range in which the reference light 200 is applied to the hologram recording material 14 must cover the range in which the signal light is applied. Also, (4) the reference light 200 uses a relatively strong and flat part, and only the necessary part is irradiated onto the hologram recording material, so that the hologram recording material 14 is not unnecessarily exposed. In this way, the dynamic range of the hologram recording material 14 must be ensured. Therefore, the beam diameter of the reference beam 200 must be adjusted to an appropriate size that satisfies these four conditions. In the present embodiment, the adjustment is performed by changing the size of the opening of the mask 16. It can be done easily and accurately.

  As a simpler configuration than that of the above-described embodiment, the same effect can be obtained even if the telecentric optical system is omitted and the mask 16 is disposed close to the diffraction grating 111 as shown in FIG.

  FIG. 10 is a block diagram showing the configuration of the reference light optical system of the hologram recording apparatus according to the third embodiment of the present invention. The reference light optical system of the angle multiplexing type hologram recording apparatus includes a telecentric optical system including an angle fine adjustment mirror 20 and lenses 21 and 22, a telecentric optical system including a mask 16 and lenses 17 and 18, and a diffraction grating 121. The configuration after the diffraction grating 121 is the same as that of FIG.

Next, the operation of the present embodiment will be described. The angle fine adjustment mirror 20 and the mask 16 are disposed so as to form an image-forming relationship with each other via a telecentric optical system including lenses 21 and 22. The path of the reference beam 200 is changed by the angle fine adjustment mirror 20 and input to the lens 22. When the angle of the angle fine adjustment mirror 20 is changed, the path of the reference light 200 is changed by the change angle and is input to the telecentric optical system including the lenses 21 and 22 and is irradiated onto the mask 16. However, since the fine angle adjustment mirror 20 and the mask 16 are in an imaging relationship, the angle of the reference light 200 that is narrowed down and emitted by the mask 16 similarly changes due to the change in the angle of the fine angle adjustment mirror 20, and the lens 17. , 18 is incident on a telecentric optical system. Since the mask 16 and the diffraction grating 121 are in an imaging relationship, the reference light 200 is incident on the diffraction grating 121 and changed at an angle corresponding to the change in the angle of the light emitted from the mask 16. Thereby, by finely adjusting the angle fine adjustment mirror 20, the incident angle of the reference light 200 on the hologram recording material can be finely changed.

  According to the present embodiment, when the diffraction grating 121 that performs the stepwise deflection shown in FIG. 5 is used, the reference light 200 is caused by the shrinkage of the hologram recording material due to the displacement of components of the optical component, temperature change, or the like. When the optimum incident angle to the hologram recording material is deviated, the reproduced image becomes dark. However, the angle fine adjustment mirror 20 finely adjusts the incident angle of the reference light 200 to the hologram recording material to correct the angle. It is possible to reproduce images with high quality at all times.

  FIG. 11 is a block diagram showing the configuration of the reference light optical system of the hologram recording apparatus according to the fourth embodiment of the present invention. FIG. 11A has a configuration in which the mask 16 is arranged close to the diffraction grating 121 except for the telecentric optical system including the lenses 17 and 18 from the configuration shown in FIG. FIG. 11B has a configuration obtained by removing the telecentric optical system including the lenses 21 and 22 from the configuration of FIG. If the configuration is simplified in this manner, the number of optical components can be reduced and the pickup can be reduced in size and weight. However, when the angle fine adjustment mirror 20 is rotated, the optical axis is shifted from the center. However, if the angle adjustment angle of the angle fine adjustment mirror 20 is small, performance and effects that can be practically obtained even with the simplest configuration as shown in FIG.

  In the above embodiment, the optimum image reproduction is realized by finely adjusting the incident angle of the reference beam 200 to the hologram recording material. However, as shown in FIG. 12, the arrangement angle of the hologram recording material 14 is finely adjusted. Even if the incident angle of the reference beam 200 is relatively finely adjusted, the same effect can be obtained.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect. For example, in the above embodiment, the diffractive optical element is used as the hologram scanner, but the same effect can be obtained by using an acousto-optic element.

It is the block diagram which showed the structure of the reference beam optical system of the hologram recording device which concerns on the 1st Embodiment of this invention. It is a figure explaining operation | movement of a diffraction grating as a diffractive optical element shown in FIG. It is the figure which showed the structural example of the diffraction grating shown in FIG. 1, and the relationship between a scanner angle and a deflection angle. FIG. 2 is a block diagram illustrating an operation of the reference light optical system illustrated in FIG. 1. FIG. 6 is a diagram illustrating another structure example of the diffraction grating illustrated in FIG. 1 and a relationship between a scanner angle and a deflection angle. It is a figure explaining the structure of the diffraction grating for avoiding the malfunction which arises when the diffraction grating shown in FIG. 5 is used. It is the figure which showed the structure of the reference beam optical system of the hologram recording device which concerns on the 2nd Embodiment of this invention. It is a figure explaining a mode that the irradiation range of the reference light which irradiates a diffraction grating with the mask shown in FIG. 7 is limited. It is the figure which showed the other Example of the reference light optical system which concerns on 2nd Embodiment shown in FIG. It is the block diagram which showed the structure of the reference beam optical system of the hologram recording device which concerns on the 3rd Embodiment of this invention. It is the figure which showed the other Example of the reference light optical system which concerns on 3rd Embodiment shown in FIG. FIG. 10 is a diagram illustrating still another example of the reference light optical system according to the third embodiment illustrated in FIG. 9. It is a figure explaining the case where a hologram is recorded on a hologram recording material (hologram recording medium) by an angle multiplexing system. It is a figure explaining that the area which a reference light irradiates a hologram recording material by the change of the incident angle of a reference light changes. It is the figure which showed a mode that the irradiation area changed with respect to the change of the incident angle of reference light.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Diffractive optical element 12, 13, 17, 18, 21, 22 ... Lens, 14 ... Hologram recording material, 16 ... Mask, 20 ... Angle fine adjustment mirror, 111, 121 ... Diffraction grating, 112: Substrate.

Claims (14)

An angle multiplexing type hologram recording apparatus for recording interference fringes between signal light and reference light on a hologram recording medium,
A diffractive optical element that changes a reference light angle;
A telecentric optical system having an imaging relationship between the hologram recording medium and the diffractive optical element;
A holographic recording apparatus comprising:   2. The hologram recording apparatus according to claim 1, wherein the diffractive optical element is a diffraction grating, and the diffraction grating interval has a diffraction grating interval that continuously changes with respect to a deflection angle.   2. The hologram recording apparatus according to claim 1, wherein the diffractive optical element is a diffraction grating, and the diffraction grating interval has a diffraction grating interval that changes discretely with respect to a deflection angle.   The diffractive optical element is a diffraction grating, and the diffraction grating interval has a diffraction grating interval that varies discretely with respect to the division angle obtained by dividing the deflection angle, and the diffraction grating interval within the same division angle slightly changes. The hologram recording apparatus according to claim 1, wherein:   The hologram recording apparatus according to claim 1, wherein the diffractive optical element has different diffraction efficiency for each deflection angle.   The hologram recording apparatus according to claim 1, wherein the reference light optical system in which the reference light travels includes an optical system that limits a reference light beam diameter.   7. The hologram recording apparatus according to claim 6, wherein the optical system for limiting the beam diameter of the reference light has a slit for narrowing the reference light beam.   8. The hologram recording apparatus according to claim 7, wherein the slit is disposed close to the diffractive optical element via a telecentric optical system.   The hologram recording apparatus according to claim 7, wherein the slit is disposed in proximity to the diffractive optical element.   The hologram recording apparatus according to claim 1, wherein the reference light optical system includes an optical component that finely adjusts a reference light angle.   The optical component that performs fine adjustment of the reference light angle is a scan mirror that changes the path of the reference light, and the scan mirror is disposed in the reference light optical system on the light source side of the diffractive optical element. Item 2. A hologram recording apparatus according to Item 1.   The hologram recording apparatus according to claim 11, wherein a mask is disposed close to the diffractive optical element.   The hologram recording apparatus according to claim 11, wherein a mask is disposed close to the diffractive optical element via a telecentric optical system.   14. The hologram recording apparatus according to claim 11, wherein a scanning mirror is disposed on the diffractive optical element via a telecentric optical system.

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