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Method and system for maintaining and controlling the signal-to-noise ratio of hologams recorded in ferroelectric photorefractive materials
| Details |
Inventors: Wilde, Jeffrey P.; Hesselink, Lambertus;
Assignee: Board of Trustees of the Leland Stanford Junior University (Palo Alto, CA)
Primary Examiner: Dzierzynski; Paul M.
Assistant Examiner: Schuberg; Darren E.
Attorney, Agent or Firm:
A hologram with a dynamically controlled diffraction efficiency and enhanced signal-to-noise ratio is recorded in ferroelectric photorefractive materials, such as strontium barium niobate (Sr.sub.x Ba.sub.1-x Nb.sub.2 O.sub.6) (SBN), BSTN, SCNN, PBN, BSKNN, BaTiO.sub.3, LiNbO.sub.3, KNbO.sub.3, KTN, PLZT and the tungsten bronze family. The diffraction efficiency of the hologram is dynamically controlled by applying an electric field along the polar axis of the ferroelectric photorefractive recording medium. Electrically controlled diffraction is used in conjunction with hologram fixing and operation of the material at a temperature in the vicinity of or above its Curie temperature to additionally provide prolonged, low-noise readout. The general methods for recording and reconstructing a hologram (or a set of multiplexed holograms) using these techniques is disclosed. A plurality of configurations employing the improved hologram are disclosed, including an optical crossbar switch in guided-wave and free-space formats that can function as a component in a variety of parallel optical processing systems, a reconfigurable dynamic wavelength filter, and a page-based holographic data storage system. |
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DETAILED DESCRIPTION What is claimed is: 1.
A hologram with improved diffraction efficiency and readout characteristics, comprising: a ferroelectric photorefractive recording medium having an optical interference pattern recorded therein which modulates the index of refraction of said recording medium, said refractive index modulation being fixed in said recording medium to substantially maintain the space-charge field during readout, said recording medium being maintained at a temperature in the vicinity of or above the ferroelectric phase transition temperature during readout; and an electric field selectively applied to said recording medium during readout for selectively altering said index of refraction of said medium, and thereby increasing the diffraction efficiency of said hologram.
2.
The hologram of claim 1, wherein said recording medium is a ferroelectric crystal, and said electric field is applied along the polar axis of said crystal.
3.
The hologram of claim 1, wherein said refractive index modulation is fixed by elevating the temperature of said medium.
4.
The hologram of claim 3, wherein said temperature lies in the range of 50.
degree.
250.
degree.
C.
5.
The hologram of claim 3, wherein said medium is doped with an ion to promote said fixing.
6.
The hologram of claim 5, wherein said ion is a proton, and said fixing is achieved by elevating said temperature of said medium to the range of 50.
degree.
-250.
degree.
C.
7.
The hologram of claim 1, wherein said refractive index modulation is fixed by cooling said medium through a solid-solid phase transition to deactivate one or more photorefractive impurity center.
8.
The hologram of claim 1, wherein said refractive index modulation is fixed by utilizing a two-photon charge transfer excitation.
9.
The hologram of claim 1, wherein said refractive index modulation is fixed by using a readout beam that has a wavelength in a spectral region for which said recording medium is not photosensitive.
10.
The hologram of claim 10, wherein said recording medium is at least one doped ferroelectric, said ferroelectric selected from the group consisting of SBN (Sr
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Optical Systems 
