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Patent Issued for Holographic Memory Apparatus and Method for Adjusting Incident Angle of Reference Beam

August 5, 2014



By a News Reporter-Staff News Editor at Information Technology Newsweekly -- Hitachi-LG Data Storage, Inc. (Tokyo, JP) has been issued patent number 8787136, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventor is Shimada, Kenichi (Tucson, AZ).

This patent was filed on May 2, 2013 and was published online on July 22, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "The present invention relates to an apparatus for recording information on a recording medium by holography, an apparatus for reproducing the information from the recording medium, and a method for adjusting incident angle of reference beam.

"At the present time, capacities of optical disks exceeding 100 GB have been attained based on BDXL (trade mark) format. In the future, further improvement of capacity will be required for optical disks due to tremendous growth of the field of information technology. In many research institutes, study has been made on next-generation storage techniques. As one of the storage techniques, attention is focused on a holographic recording technique. The holographic recording technique is a technique for recording information by overlapping signal beam having two-dimensionally modulated page data by a spatial light modulator with reference beam in a recording medium, and by producing refractive index modulation within the recording medium due to an interference pattern generated in the medium at the time. Since a plurality of pieces of page data can be multiple-recorded at the same location of the recording medium, higher-speed recording and a larger capacity can be attained. Up until now, a plurality of multiple recording techniques have been proposed, and a typical one of such techniques is angle multiplex recording. In an apparatus based on the angle multiplex recording, precise adjustment of an incident angle of reference beam becomes important. In US2009/0207710, for example, there is disclosed a method of, upon reproduction of a series of angle multiplex holograms, estimating an incident angle optimum for reproduction of a next hologram by use of a reproduction result of one of the holograms just before thereto or before by several ones.

"JP-2009-54214, further, describes in Paragraph 0025 and so on that 'When a beam spot is moved along a direction crossing an array direction of light receiving elements, an angle detection signal of the reference beam varies within a range between a certain constant positive potential and a negative potential. That is, the level of the angle detection signal of the reference beam varies according to the incident angle of the reference beam during recording. With such an arrangement, when the reference beam is applied so that the center of the beam spot is located on boundaries of mutually-adjacent light receiving elements of an optical detector 32, the reference beam angle detection signal has a level of zero. And, for example, the zero-cross point can be associated with the positioning point of the reference beam angle. In this case, for example, when the angle of the reference beam is suitable, the level of the reference beam angle detection signal becomes zero. When the level of the reference beam angle detection signal is zero or in a predetermined range within the vicinity of zero, the main controller 300 determines that the angle of the reference beam to be adequate.'"

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "In the method shown in US2009/0207710, SNR (signal to noise ratio) is defined as a quality evaluation index of a hologram reproduced image, and a variation in the S is used to estimate an optimum incident angle of the reference beam.

"In US2009/0207710, in order to detect a variation in the SNR, an offset angle is intentionally added always by +.DELTA..PHI. or -.DELTA..PHI. and then reproduced. Although explanation of detailed technical contents is omitted because it is descried in US2009/0207710, since reproduction is made always with an angle shifted by about .DELTA..PHI. with respect to the optimum incident angle of the reference beam, reproduction quality will be always deteriorated in principle.

"Further, in order to calculate SNR, it becomes necessary to calculate it with use of an average value of brightness distribution of pixels to be originally turned ON and OFF and a standard deviation thereof in a hologram reproduced image. Thus, this requires more complicated signal processing than simple estimation of a light quantity.

"In addition, because of the adjustment method of using SNR, it is necessary for a hologram for SNR calculation to be previously recorded, and this method is unsuitable for adjustment of an incident angle when a hologram is not preset yet is recorded.

"JP-2009-54214 is directed to a technique for detecting the incident angle of reference beam but to the angle detection method not reflecting on a tilt of the disk. In a tilted state of the disk, a relative tilt between the disk and the reference beam cannot be strictly estimated.

"In view of the above problems, the object of the present invention is to accurately adjust the incident angle of reference beam upon hologram recording and reproduction.

"The above object is attained with the inventions disclosed, for example, in Claims.

"In accordance with the present invention, the incident angle of the reference beam can be accurately adjusted upon recording and reproduction."

For the URL and additional information on this patent, see: Shimada, Kenichi. Holographic Memory Apparatus and Method for Adjusting Incident Angle of Reference Beam. U.S. Patent Number 8787136, filed May 2, 2013, and published online on July 22, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8787136.PN.&OS=PN/8787136RS=PN/8787136

Keywords for this news article include: Information Technology, Hitachi-LG Data Storage Inc., Information and Data Storage.

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Source: Information Technology Newsweekly


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