Holographic recording medium and holographic recording/reproducing apparatus using the same

• US 6,856,433 B2
• Filed: 09/08/2003
• Issued: 02/15/2005
• Est. Priority Date: 09/10/2002
• Status: Expired due to Fees

• Current Assignee: Enhanced Energy Systems, Inc., National Institute for Materials Science
• Original Assignee: National Institute for Materials Science, Pioneer Corporation
• Inventors: Hatano, Hideki, Yamaji, Takashi, Kitamura, Kenji, Nakamura, Masaru, Takekawa, Shunji
• Primary Examiner(s): BOUTSIKARIS, LEONIDAS
• Application Number:
  US10/656,879
• Publication Number:
  US 20040120020A1
• Time in Patent Office: 526 Days
• Field of Search: 359/3, 359/7, 430/1, 430/2, 365/125, 365/216
• US Class Current: 359/7
• CPC Class Codes: G03H 1/02 Details of features involved during the holographic process; Replication of holograms without interference recording
• CPC Class Codes: G03H 2001/0491 by monitoring the hologram formation, e.g. via a feed-back loop
• CPC Class Codes: G03H 2260/54 Photorefractive reactivity wherein light induces photo-generation, redistribution and trapping of charges then a modification of refractive index, e.g. photorefractive polymer
• CPC Class Codes: G11B 7/0065 Recording, reproducing or erasing by using optical interference patterns, e.g. holograms

Abstract

A holographic recording medium exhibiting a high recording sensitivity without execution of reduction treatment. A system records information on the holographic recording medium by using a gating light within a wavelength band causing less optical damage to the holographic recording medium. The holographic recording medium includes a single crystal of lithium niobate (LiNbO₃) or lithium tantalate (LiTaO₃) containing Mn as a dopant.

Claims

1. A two-color holographic recording medium comprising:

a crystal body including a lithium niobate single crystal or a lithium tantalate single crystal which has substantially stoichiometric composition and is doped with only Mn in the range from 1 wt ppm to 100 wt ppm.

2. The two-color holographic recording medium according to claim 1,

said crystal body includes a first energy level, a second energy level, and a third energy level,

wherein said first energy level exists at a deeper energy position than said second energy level measured from the bottom of a conduction band,

wherein said third energy level exists at a deeper energy position than said second energy level measured from the bottom of the conduction band,

wherein carriers are excited from said first energy level to said second energy level by the irradiation of a gating light at a wavelength of 410 nm or shorter,

wherein said carriers excited to said second energy level are trapped to said third energy level by the irradiation of a signal light and a reference light at a wavelength longer than said gating light.

3. The two-color holographic recording medium according to claim 1,

wherein a product α

_g·

L of an optical absorption coefficient (α

_g) of said lithium niobate single crystal or lithium tantalate single crystal with respect to a gating light having a wavelength of 410 nm or shorter and a length (L) of said single crystal along said gating light incident direction is within a range of 0.5 to 2.0.

4. A holographic recording/reproducing apparatus for recording information in a two-color holographic recording medium and for reproducing information from said two-color holographic recording medium comprising:

a first irradiation means for irradiating said two-color holographic recording medium with a gating light having a wavelength of 410 nm or shorter; and

a second irradiation means for irradiating said two-color holographic recording medium with a signal light containing information to be recorded and a reference light,

wherein said gating light has a shorter wavelength than those of said signal light and said reference light,

wherein said two-color holographic recording medium comprises a crystal body including a lithium niobate single crystal or a lithium tantalate single crystal which has substantially stoichiometric composition and is doped with only Mn in the range from 1 wt ppm to 100 wt ppm.

5. A method for recording information on a two-color holographic recording medium comprising:

providing the two-color holographic recording medium comprises a crystal body including a lithium niobate single crystal or a lithium tantalate single crystal which has substantially stoichiometric composition and is doped with only Mn in the range from 1 wt ppm to 100 wt ppm;

irradiating the crystal body with a gating light having a wavelength of 410 nm or less;

irradiating the crystal body with a recording light with a wavelength greater than 410 nm during the irradiation of the gating light.

6. The method according to claim 5, wherein said crystal body includes a first energy level, a second energy level, and a third energy level,

wherein said first energy level exists at a deeper energy position than said second energy level measured from the bottom of a conduction band,

wherein said third energy level exists at a deeper energy position than said second energy level measured from the bottom of the conduction band,

wherein carriers are existed from said first energy level to said second energy level by the irradiation of the gating light,

wherein said carriers existed to said second energy level are trapped to said third energy level by the irradiation of the recording light.

7. The method according to claim 5, wherein the recording light comprises a reference light and a signal light, both with the same wavelength.

8. The method according to claim 5, wherein a product α

_g·

L of an optical absorption coefficient (α

_g) of said lithium niobate single crystal or lithium tantalate single crystal with respect to said gating light and a length (L) of said single crystal along said gating light incident direction is within a range of 0.5 to 2.0.