Shift Multiplexing Research Articles

Shift multiplexing by planar waveguide referencing

We present a new method with which to implement shift multiplexing by planar waveguide referencing. In this method, a planar waveguide is used to steer the reference beam, and we implement shift multiplexing by shifting the recording medium. A spatial selectivity as high as 1.1 microm is obtained. By using waveguide referencing we can make a compact and simple holographic system.

Holographic digital data storage using phase-modulated pixels

We propose and demonstrate the use of phase images for holographic data storage. Use of phase images as input leads to uniform diffraction efficiency of multiplexed data pages. Use of binary phase-based data pages with 0 and π phase changes produces uniform spectral distribution at the Fourier plane. This in turn facilitates better recording of higher spatial frequencies. We experimentally demonstrate a phase-based holographic data storage system using shift multiplexing in a Fe:LiNbO 3 crystal, and use it for associative retrieval. Preliminary studies indicate high discrimination capabilities of phase-based holographic data storage system over the amplitude-based system in a content-addressable memory.

High-transfer-rate high-capacity holographic disk data-storage system.

We describe the design and implementation of a high-data-rate high-capacity digital holographic storage disk system. Various system design trade-offs that affect density and data-rate performance are described and analyzed. In the demonstration system that we describe, high-density holographic recording is achieved by use of high-resolution short-focal-length optics and correlation shift multiplexing in photopolymer disk media. Holographic channel decoding at a 1-Gbit/s data rate is performed by custom-built electronic hardware. A benchmark sustained optical data-transfer rate of 10 Gbits/s has been successfully demonstrated.

Remote multiplexing of holograms with random patterns from multimode fiber bundles.

We propose the remote multiplexing of holograms with random patterns from a multimode fiber bundle used as the reference beams. The random pattern reference beam is characterized by the superposition and concatenation of propagation modes of multimode fiber and free space. For angle, shift, and wavelength remote multiplexing we compare two methods of laser coupling to the fiber bundle, i.e., direct coupling and lens coupling. A theoretical discussion that uses mode orthogonality is provided to describe multiplexing characteristics, and the theory is verified by experimental results. These remote-multiplexing methods can be applied to general multimode waveguide arrays for construction of compact and integrated optical systems in which multiplexing can be controlled remotely.

Holographic shift multiplexing in thin volumetric media

We describe a three-dimensional theoretical model of holographic shift multiplexing in thin volumetric media in paraxial approximation. In the case of shift multiplexing with three-dimensional beams, additional cross talk is found and its origin is attributed to Bragg-matching synchronism which occurs when shift in both transverse dimensions (x and y) is considered. The origin of this cross talk is attributed to three-dimensional Bragg degeneracy. The experimental results obtained for the case of two spherical wave front beams are in excellent agreement with the theoretical predictions. We propose theoretically that the cross talk in spherical multiplexing can be minimized if reference and signal waves have the same radius of curvature.

Folded shift multiplexing.

Shift multiplexing is a holographic recording method that uses a spherical reference wave. We extend the principle to a thin slab of holographic material that acts as a waveguide. Total internal reflection folds the reference spherical beam in one dimension. We demonstrate that the shift selectivity with the folded spherical beam is independent of the slab thickness but depends instead on the numerical aperture of the coupled spherical wave. A shift selectivity of 0.5 microm has been achieved with a 1-mm-thick LiNbO3 crystal and 50 high-definition data pages are recorded with this method.

Compact Holographic Storage by Using a Fiber Bundle to Guide the Reference Beam

We propose a compact volume holographic storage system, in which a fiber bundle is used to guide the reference beam. For demonstrating the system, phase-coded multiplexing is implemented by changing the incident direction of the reference beam upon the fiber bundle. Shift multiplexing is also performed by moving the medium. Because no lens or complicated phase modulation system is necessary in the reference arm, the holographic storage system can become more compact. Multiple images are stored in a crystal using the phase coded and shift multiplexing techniques.

Diffraction selectivity of holograms with random phase encoding

We have analyzed the lateral sensitivity of volume holograms based on random phase encoding. The diffraction characteristics are associated with induced two-dimensional destructive interference when the random phase plate, e.g. a ground glass, is laterally shifted. The random phase plate generates the first dimension of destructive interference, and the finite size of the hologram generates the second dimension of destructive interference. The former and the latter are responsible for the random phase multiplexing and the shift multiplexing of holographic storage, respectively. The developed analysis can be used to describe the shifting sensitivity of the hologram based on both random phase multiplexing and shift multiplexing.

Shift multiplexing with spherical reference waves

Shift multiplexing is a holographic storage method particularly suitable for the implementation of holographic disks. We characterize the performance of shift-multiplexed memories by using a spherical wave as the reference beam. We derive the shift selectivity, the cross talk, the exposure schedule, and the storage density of the method. We give experimental results to verify the theoretical predictions.