JP4779694B2 - Hologram recording medium evaluation apparatus and hologram recording medium evaluation method - Google Patents

Description

  The present invention relates to a hologram recording medium evaluation apparatus and a hologram recording medium evaluation method for evaluating the characteristics of a hologram recording medium.

  Conventionally, the M number (M / #) is used as one of the evaluation characteristics of a hologram recording medium. This M number (M / #) is, for example, as described in Patent Document 1, when n-page holograms are multiplexed and reproduced until recording is not possible in the same area in the recording layer of the hologram recording medium. It is a characteristic calculated | required by the diffraction efficiency from this hologram.

The M number (M / #) can be obtained by multiplex-recording n-page holograms, irradiating the hologram recording medium with a reference laser beam, and measuring the diffraction efficiency in each recording. The diffraction efficiency can be detected by measuring the intensity of light transmitted through the reference laser light and the intensity of diffracted light.
JP-A-2005-208426

  However, some hologram recording media have a low diffraction efficiency for each recording even if the number of multiple recordings is large. Such a hologram recording medium has a large M number (M / #), but in order to accurately reproduce information recorded on the hologram recording medium, it is necessary that the diffraction efficiency of the reference laser beam is at least about 1%. If the diffraction efficiency of each recording is smaller than this, the amount of light received by the photosensor is small in data reproduction, and accurate data reproduction cannot be performed. That is, the M number (M / #), which is a characteristic for evaluation of a conventional hologram recording medium, has a large number of recordings that cannot be reproduced accurately even if the diffraction efficiency of each recording is small. In other words, it may not necessarily represent the multiple recording performance.

  The present invention has been made in view of such circumstances, and provides a hologram recording medium evaluation apparatus and a hologram recording medium evaluation method capable of correctly grasping the multiplex recording performance of the hologram recording medium. .

  The apparatus for evaluating a hologram recording medium according to claim 1, when recording data on the hologram recording medium, a table for holding the hologram recording medium, and irradiating the hologram recording medium with information laser light including a signal corresponding to the recording data Information laser light irradiating means, recording reference laser light irradiating means for irradiating the hologram recording medium with a recording reference laser light at an angle different from the information laser light when recording data on the hologram recording medium, and hologram recording When recording data on the medium, diffraction efficiency measuring means for measuring the diffraction efficiency of the recording area of the hologram recording medium, and the maximum number of times that multiple recording can be performed on the hologram recording medium until the predetermined diffraction efficiency is achieved. Multiple recording limit measurement means for measuring as an evaluation characteristic is provided.

  3. The hologram recording medium evaluation apparatus according to claim 2, wherein the diffraction efficiency measuring means irradiates the recording region of the hologram recording medium with a diffraction efficiency measuring laser beam having a wavelength different from that of the information laser beam and the recording reference laser beam. Laser beam irradiation means for measuring efficiency, laser beam intensity measuring means for measuring the intensity of the laser beam diffracted by the laser beam for measuring the diffraction efficiency in the recording area of the hologram recording medium and the intensity of the transmitted laser beam, and the laser beam intensity And a diffraction efficiency calculating means for calculating the diffraction efficiency in the recording area of the hologram recording medium based on the intensity of the diffracted laser light measured by the measuring means and the intensity of the transmitted laser light.

  The method for evaluating a hologram recording medium according to claim 3 is characterized in that when data is recorded on the hologram recording medium, the diffraction efficiency of the recording area of the hologram recording medium is measured, and multiple recording is performed on the hologram recording medium until a predetermined diffraction efficiency is achieved. And the limit number of times that multiple recording can be performed is measured as an evaluation characteristic.

  The method for evaluating a hologram recording medium according to claim 4 is different from the two laser beams of the information laser beam including a signal corresponding to the recording data and the recording reference laser beam irradiated at a different angle from the information laser beam. The laser beam for measuring the diffraction efficiency of the wavelength is irradiated to the recording area of the hologram recording medium, and the intensity of the laser beam diffracted by the laser beam for measuring the diffraction efficiency in the recording area of the hologram recording medium and the intensity of the transmitted laser beam are measured. The diffraction efficiency in the recording area of the hologram recording medium is calculated from the measured intensity of the diffracted laser beam and the intensity of the transmitted laser beam.

  According to the first and third aspects of the present invention, multiple recording is performed on the hologram recording medium until a predetermined diffraction efficiency is obtained, and the limit number of times that multiple recording can be performed is measured as an evaluation characteristic. Therefore, it is possible to obtain a numerical value indicating how many times recording can be performed with good reproduction, and to correctly grasp the substantial multiplex recording performance of the hologram recording medium.

  According to the second and fourth aspects of the invention, the diffraction efficiency measurement laser beam measures the intensity of the laser beam diffracted in the recording area of the hologram recording medium and the intensity of the transmitted laser beam, respectively, and measures the diffracted laser. Since the diffraction efficiency in the recording area of the hologram recording medium is calculated based on the intensity of the light and the intensity of the transmitted laser beam, it is possible to perform recording until a predetermined diffraction efficiency is achieved in each recording, and the limit for performing multiple recording It is possible to correctly grasp the actual multiplex recording performance of the hologram recording medium based on the number of times.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. FIG. 1 is a configuration diagram showing an example of a hologram recording medium evaluation apparatus according to the present invention. FIG. 2 is a graph showing a change in the diffraction efficiency η of the hologram recording medium with respect to the irradiation time of the laser beam. FIG. 3 is a flowchart showing the operation of the hologram recording medium evaluation apparatus in the η% multiplex number measurement program.

  In the figure, a hologram recording medium evaluation apparatus 1 for evaluating characteristics of a hologram recording medium 5 includes laser light sources 100 and 110, various optical system elements 102 to 112, photosensors 114 and 116, laser drive circuits 52 and 54, and an angle control circuit. 62, a position control circuit 64, a controller 20, an input device 22, a display device 24, and the like.

  The controller 20 controls the entire hologram recording medium evaluation apparatus 1, and is connected to an input device 22 for inputting data and a display device 24 for displaying data and various settings. Laser drive circuits 52 and 54, an angle control circuit 62, a position control circuit 64, and the like, which will be described later, are connected, and overall control is performed by performing these controls.

  In the following description, the limit number of times that multiple recording can be performed when recording is performed until a predetermined diffraction efficiency is achieved in each recording in the multiplex recording on the hologram recording medium 5 is referred to as “η% multiplex number”. Changes in laser irradiation time and diffraction efficiency in each recording are shown in FIG. As multiple recording is performed, the rate of increase in diffraction efficiency decreases, and no matter how many times the laser beam is irradiated, it does not reach the specified diffraction efficiency (the diffraction efficiency set by the saturated diffraction efficiency). Lower). The number of times of multiplex recording performed until this state is reached is “η% multiplex number”.

  Next, the detailed configuration and operation of the hologram recording medium evaluation apparatus 1 of the present embodiment will be described. First, the laser light emitted from the recording laser light source 100 is collimated by the collimator lens 102 and then split by the beam splitter 104 into information laser light and recording reference laser light. Since the information laser beam in this case does not pass through the SLM (spatial light modulation element), the information laser beam and the recording reference laser beam are substantially the same. The laser beam divided into two is reflected by the mirrors 106 and 108 and irradiated onto the hologram recording medium 5 at different angles for recording (in this case, recording without information).

  Apart from the recording laser beam, there is a diffraction efficiency measuring laser beam. The laser light emitted from the laser light source 110 of the diffraction efficiency measurement laser light is converted into parallel light by the collimator lens 112, and then the information laser light and the recording reference laser light are at different angles at the hologram recording medium 5. Is irradiated. The laser beam diffracted by the hologram recording medium 5 is received by the photosensor 114, and the transmitted laser beam is received by the photosensor 116, and a signal corresponding to the received light amount is output. In the hologram recording medium evaluation apparatus 1 configured as described above, after the operator sets the hologram recording medium 5 on the stage, the operator instructs the controller 20 to execute the program of the flow shown in FIG. As a result, the η% multiplexing number is automatically measured and displayed on the display device 24.

  Hereinafter, description will be given according to the flowchart shown in FIG. In the following description, the reference numerals in parentheses correspond to the reference numerals in the flowchart of FIG. First, an appropriate value (for example, 1.5%) is input from the input device 22 as a value X% set as the diffraction efficiency in each recording (S102). Next, the laser beam for measuring the diffraction efficiency is irradiated (S106), and the irradiation angle (mirror position and angle) of the recording reference laser beam is set (S108).

  Next, the information laser beam and the recording reference laser beam are irradiated to start recording (S110). Since the laser beam for measuring the diffraction efficiency has already been irradiated and the amount of light detected by the photosensors 114 and 116 has been input to the controller 20, the diffraction efficiency η is calculated (S116). It is confirmed whether the diffraction efficiency η is equal to or greater than X% (S118). If not, it is confirmed whether the diffraction efficiency is not saturated (S128 to S136), and if not saturated, the calculated value is cleared (S130). ), And returns to the calculation of the diffraction efficiency (S116).

  When the diffraction efficiency η becomes X% or more (S118), the laser beam is stopped (S120), the number of n is increased by 1 (S122), the irradiation time measurement is stopped, and the measurement value is reset. (S124) The laser beam irradiation angle (mirror position and angle) is changed (S126), and the process returns to the above-described laser beam irradiation (S110). Then, the next multiple recording is performed. The number n is the number of times of multiple recording.

  Next, confirmation of whether the diffraction efficiency is not saturated (S128 to S136) will be described below. First, it is confirmed whether the irradiation time T when the measurement is started (S112) together with the laser beam irradiation (S110) is time m · Y (time Y is set in advance. M is incremented by 1 for each time Y). If not (S128), the calculated value is cleared (S130), and the process returns to the calculation of diffraction efficiency (S116). If so, the difference from the previous diffraction efficiency η is compared (S132). At this time, if the difference is larger than Z (a value that is not substantially different, predetermined within the range of measurement accuracy), the current diffraction efficiency η is stored as the diffraction efficiency η is still increasing (S134). ), The calculated value is cleared (S130), and the process returns to the calculation of diffraction efficiency (S116). If the difference from the previous diffraction efficiency η is smaller than Z (S132), it is determined that the diffraction efficiency η has not changed during time Y. That is, it is determined that the diffraction efficiency is saturated, the laser beam is stopped (S138, S140), the measurement of the irradiation time T is stopped (S142), and the value of n is displayed as the “η% multiplex number” on the display device 24. (S144) and the program is stopped.

  The above is a method of determining the limit of multiplex recording when the diffraction efficiency is saturated without exceeding the initially set X% with the laser beam intensity constant, but by changing the laser beam intensity, The limit may be determined. For example, when the speed of change of the diffraction efficiency at the start of irradiation of the recording laser beam decreases, the intensity of the laser beam is increased accordingly, and is set to a predetermined magnification (for example, twice) from the intensity of the first laser beam. If the laser beam intensity increases, the intensity of the laser beam is not increased any more, and if the saturation does not exceed the initially set X%, it may be determined that the limit of multiplex recording is reached.

  Further, the intensity of the laser beam may be increased in accordance with the saturated diffraction efficiency. Furthermore, the same laser beam intensity is used until the diffraction efficiency is expected to saturate without exceeding the initially set X%, and when expected, the laser intensity is increased to a predetermined magnification (for example, twice) at a time. It is also possible to perform recording and raise it, and when it is saturated without exceeding the initially set X%, it may be determined that there is a limit of multiple recording.

  As described above, according to the hologram recording medium evaluation apparatus 1 of the present embodiment, multiplex recording is performed on the hologram recording medium 5 until a predetermined diffraction efficiency is achieved, and the η% multiplex number that is the limit number of times that multiplex recording can be performed is evaluated. Since it is measured as a characteristic for use, it is possible to correctly grasp the substantial multiplex recording performance of the hologram recording medium 5. In other words, the η% multiplex number is a characteristic that means how many times a record that can be reproduced with high accuracy can be multiplex-recorded. If it is evaluated by the η% multiplex number, it is evaluated by the M number (M / #). Rather, the multiplex recording performance of the hologram recording medium 5 can be evaluated with a value that matches the actual utility.

  Further, the intensity of the laser beam diffracted by the diffraction efficiency measurement laser beam in the recording region of the hologram recording medium 5 and the intensity of the transmitted laser beam are measured, respectively, and the measured intensity of the diffracted laser beam and the intensity of the transmitted laser beam are measured. Thus, by calculating the diffraction efficiency in the recording region of the hologram recording medium 5, it is possible to perform recording until a predetermined diffraction efficiency is obtained in each recording, and the multiplex magnification of η% is a substantial multiplexing of the hologram recording medium 5. It is possible to correctly grasp the recording performance.

  As described above, according to the present invention, it is possible to provide a hologram recording medium evaluation apparatus and a hologram recording medium evaluation method that can correctly grasp the multiplex recording performance of the hologram recording medium.

It is a block diagram which shows an example of the hologram recording-medium evaluation apparatus which concerns on this invention. It is the figure which showed the change of the diffraction efficiency (eta) of the hologram recording medium with respect to the irradiation time of a laser beam. 10 is a flowchart showing the operation of the hologram recording medium evaluation apparatus in the η% multiplexing number measurement program.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hologram recording medium evaluation apparatus 5 ... Hologram recording medium 20 ... Controller 22 ... Input device 24 ... Display device 52 ... Laser drive circuit 54- ... Laser drive circuit 62 ... Angle control circuit 64 ... Position control circuit 100 ... Laser light source 102 ... Collimator lens 104 ... Beam splitter 106 ... Mirror 108 ... Mirror 110 ... Laser light source 112 ... Collimating lens 114 ... Photo sensor 116 ... Photo sensor

Claims (4)

In the hologram recording medium evaluation apparatus,
A table for holding the hologram recording medium;
An information laser beam irradiation means for irradiating the hologram recording medium with an information laser beam including a signal corresponding to the recording data when recording data on the hologram recording medium;
A recording reference laser beam irradiation means for irradiating the hologram recording medium with a recording reference laser beam at an angle different from that of the information laser beam when recording data on the hologram recording medium;
Diffraction efficiency measuring means for measuring the diffraction efficiency of the recording area of the hologram recording medium when recording data on the hologram recording medium;
An evaluation of a hologram recording medium, comprising: multiple recording limit measurement means for performing multiple recording on the hologram recording medium until a predetermined diffraction efficiency is obtained, and measuring a limit number of times the multiple recording can be performed as an evaluation characteristic apparatus. The diffraction efficiency measuring means is
Diffraction efficiency measurement laser light irradiation means for irradiating a recording area of the hologram recording medium with a diffraction efficiency measurement laser light having a wavelength different from that of the information laser light and the recording reference laser light;
Laser beam intensity measuring means for measuring the intensity of the laser beam diffracted by the diffraction efficiency measuring laser beam in the recording region of the hologram recording medium and the intensity of the transmitted laser beam, respectively;
And a diffraction efficiency calculating means for calculating the diffraction efficiency in the recording area of the hologram recording medium based on the intensity of the diffracted laser light measured by the laser light intensity measuring means and the intensity of the transmitted laser light. Item 2. The apparatus for evaluating a hologram recording medium according to Item 1. In the evaluation method of the hologram recording medium,
When recording data on the hologram recording medium, measure the diffraction efficiency of the recording area of the hologram recording medium,
A method for evaluating a hologram recording medium, comprising: performing multiplex recording on the hologram recording medium until a predetermined diffraction efficiency is obtained, and measuring a limit number of times the multiplex recording can be performed as an evaluation characteristic. Recording hologram light with a diffraction efficiency measurement laser beam having a wavelength different from the two laser beams of an information laser beam including a signal corresponding to recording data and a recording reference laser beam irradiated at an angle different from the information laser beam Irradiate the recording area of the medium,
The diffraction efficiency measurement laser beam measures the intensity of the laser beam diffracted in the recording area of the hologram recording medium and the intensity of the transmitted laser beam, respectively.
4. The method for evaluating a hologram recording medium according to claim 3, wherein the diffraction efficiency in the recording area of the hologram recording medium is calculated from the measured intensity of the diffracted laser beam and the intensity of the transmitted laser beam.

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