Method and apparatus for phase-encoded homogenized Fourier transform holographic data storage and recovery
View Patent ↗An apparatus for writing and reading holograms, comprising a spatial light modulator (SLM) operable in phase mode, having a plurality of pixels for generating an object beam that overlaps with a reference beam; a holographic recording medium (HRM) in the path of the object beam; and a first lens element disposed in the path of the object beam between the SLM and the HRM; wherein the HRM is disposed at or near the Fourier transform plane of the first lens element.
1. A method of recording multiplexed holograms, comprising:
recording a first phase-encoded Fourier transform hologram or a fractional Fourier transform hologram with a first reference beam; and
recording a second phase-encoded Fourier transform hologram or a fractional Fourier transform hologram with a second reference beam at the same location or at a substantially overlapped location on a holographic recording medium,
wherein the angle between the first and the second reference beams is less than the angular separation between the primary diffraction peak and the first minimum of the Bragg angle selectivity curve of the first or the second holograms.
2. The method of claim 1 , wherein the angular separation of the first and the second reference beam is less than about 1/10 of the angular separation between the primary diffraction peak and the first minimum of the Bragg angle selectivity curve of the first or the second holograms.
3. A method of recording multiplexed holograms, comprising:
recording a first phase-encoded Fourier transform hologram or a fractional Fourier transform hologram with a first wavelength; and
recording a second phase-encoded Fourier transform hologram or a fractional Fourier transform hologram with a second wavelength at the same location or at a substantially overlapped location on a holographic recording medium
wherein the difference between the first and the second wavelengths is less than the wavelength separation between the primary diffraction peak and the first minimum of the Bragg wavelength selectivity curve of the first or the second holograms.
4. The method of claim 3 , wherein the wavelength separation of the first and the second holograms is less than about 1/10 of the wavelength separation between the primary diffraction peak and the first null of the Bragg wavelength selectivity curve of the first or the second holograms.
5. A method of recording multiplexed holograms, comprising:
recording a first Fourier transform hologram or a fractional Fourier transform hologram with a first reference beam; and
recording a second Fourier transform hologram or a fractional Fourier transform hologram with a second reference beam at the same location or at a substantially overlapped location on a holographic recording medium,
wherein either the difference in angle or the difference in wavelengths between the first and second reference beams is less than either the angular separation or wavelength separation, respectively, between the primary diffraction peak and the first minimum of a Bragg selectivity curve of the first or the second holograms.
6. The method of claim 5 , wherein the angle between the first and second reference beams is less than the angular separation between the primary diffraction peak and the first minimum of the Bragg angle selectivity curve of the first or the second hologram.
7. The method of claim 6 , wherein the angular separation of the first and second reference beam is less than about ¼th of the angular separation between the primary diffraction peak and the first minimum of the Bragg angle selectivity curve of the first or the second hologram.
8. The method of claim 6 wherein the recorded multiplexed holograms are phase encoded data pages.
9. The method of claim 6 , wherein the angular separation of the first and second reference beam is less than about 1/10th of the angular separation between the primary diffraction peak and the first minimum of the Bragg angle selectivity curve of the first or the second hologram.
10. The method of claim 5 , wherein the first and second reference beams are at first and second wavelengths, respectively, and wherein the wavelength difference between the first and second wavelengths is less than the wavelength separation between the primary diffraction peak and the first minimum of the Bragg wavelength selectivity curve of the first or the second hologram.
11. The method of claim 10 wherein the recorded multiplexed holograms are phase encoded data pages.
12. The method of claim 10 , wherein the wavelength separation of the first and second hologram is less than about ¼th of the wavelength difference between the primary diffraction peak and the first minimum of the Bragg wavelength selectivity curve of the first or the second hologram.
13. The method of claim 10 , wherein the wavelength separation of the first and second hologram is less than about 1/10th of the wavelength difference between the primary diffraction peak and the first minimum of the Bragg wavelength selectivity curve of the first or the second hologram.