Brian Lee Lawrence

Micro-Holographic Storage and Threshold Holographic Recording Materials

This paper presents a new injection-molded holographic recording media with a threshold optical response that is specifically designed for single-bit holographic data storage. The concept of a threshold response in a holographic recording material is discussed and the benefits of such a material relative to standard linear materials are evaluated. Micro-holograms are recorded in the new material and the performance is compared to similar measurements in a linear material. The results show that the material has a threshold recording energy of approximately 1 µJ/pulse in a low-numerical-aperture (NA) test system, corresponding to 50 nJ/pulse in a high-NA system. In addition, the threshold material shows a 1000-fold improvement in continuous-wave (CW) read-out stability and a 25% reduction in hologram size as compared to the linear material.

Microholograms Recorded in a Thermoplastic Medium for Three-Dimensional Data Storage

This paper presents a three-dimensional optical data storage system that combines a new recording material with a micro-holographic data format. The micro-holographic approach stores data as single-bit micro-holograms arranged in multiple layers throughout the volume of the disk, similar in format to standard physical layer formats. This approach offers much less sensitivity to environmental conditions than the page-based holographic approach in addition to an increased compatibility with current technologies. The new recording medium is based on an injection-moldable, dye-doped thermoplastic material that makes mass distribution of the new format economically viable. The recording of the micro-holograms in the new material indicates that the dimensions of the micro-holograms are larger than those calculated using simple laser beam waist approximations and that multiple layers of micro-holograms significantly impact signal levels. Ultimately, the results show that calculations of data densities achievable by the micro-holographic approach must take these effects into account.

Characterization of microholograms recorded in a thermoplastic medium for three-dimensional optical data storage

A three-dimensional optical data storage system that combines a new recording material with a microholographic data format in which data are stored as single-bit microholograms is presented. This format offers less sensitivity to environmental conditions than the page-based holographic approach in addition to an increased compatibility with current storage technologies. The new recording material is based on a thermoplastic material. The results presented indicate that the dimensions of the microholograms are larger than those calculated by use of simple laser beam waist approximations and that multiple layers of microholograms would significantly affect signal levels. Data densities achievable with the microholographic format will likely be limited by those effects.

Improved sensitivity of dye-doped thermoplastic disks for holographic data storage

Holographic data storage materials based on dye-doped thermoplastics are currently under development. The materials are injection moldable into the standard disk format and have much lower shrinkage than photopolymer materials. Injection-molded disks with dyes from the class of o-nitrostilbenes presented acceptable capacities but a very low sensitivity. In this paper, theoretical analysis and experimental results on the sensitivity and sensitivity improvement for dye-doped thermoplastic disks are presented. Theoretical analysis shows that the quantum efficiency of the dye transformation is the key parameter for sensitivity improvement. An experimental method for measuring the quantum efficiency was developed. Dyes based on the diarylethene functionality with orders of magnitude higher quantum efficiency were identified. Sensitivities measured from the blended diarylethene/polycarbonate, injection-molded, 1.2mm thick disks showed sensitivities of ∼10–100cm∕J at both 532 and 405nm wavelengths.

Characterization of a preliminary narrow-band absorption material for holographic data storage

A new holographic data storage material is currently being developed at General Electric. This material is based on a thermoplastic host doped with dyes with narrowband absorption resonances. The dye is photosensitive and irreversibly bleaches under exposure to light. The reduction in concentration of the dye in the host after exposure induces refractive index variations at wavelengths away from the dye absorption peak according to the well-known Kramers-Kronig relationship. The approach proposed here requires different recording and readout wavelengths to prevent data erasure during readout. Samples were produced using different dyes and various concentrations in a polycarbonate host. The extensive experience developed in the past with polycarbonate for optical media promises to make the proposed material very inexpensive. These samples were characterized using holographic techniques as well as using spectroscopic transmission and ellipsometry. The results of the characterizations indicate that this material approach can offer very large dynamic range, but have thus far shown very low sensitivity. Further work is required to demonstrate materials having both sufficient dynamic range and sensitivity for holographic storage applications. We believe that if this condition can be satisfied, this new material approach will be an excellent candidate for high-density holographic media for content distribution.

Dye-doped thermoplastics for holographic data storage

Holographic data storage materials based on a dye-doped thermoplastic that could find application in professional archival and consumer applications are described. The dye is selected from the class of o-nitrostilbenes, which irreversibly bleaches under exposure to light and shows high thermal stability before and after exposure. The reduction in concentration of the dye in the host after exposure induces refractive index variations over a wide range of wavelengths and extends well away from the dye absorption peak conforming to the Kramers-Kronig relationship. The materials are injection moldable into the standard disc format and have negligible shrinkage during data storage. Samples were produced using different dyes and various concentrations in a polycarbonate host and processed on professional CD/DVD equipment. The refractive index change is as high as 0.04, with a measured instantaneous sensitivity of 0.5 cm/J and M/# = 0.3.

Micro-Holograms Recorded in a Thermoplastic Medium for Three-Dimensional Data Storage

A micro-holographic approach using a dye-doped thermoplastic material as a recording medium is in development at General Electric. Preliminary characterization results indicate that micro-holograms present larger dimensions than those expected from the recording beam properties.

Thermoplastic media for holographic data storage

The growing prevalence of digital technologies has led to increased data generation so that new storage technologies must be developed to handle expanding capacity demand. Holographic data storage is a very promising candidate with the potential to provide ultra-high density data storage. Currently, many teams are developing holographic storage technology, with much of the emphasis on professional archival applications. However, consumer-oriented applications are also growing rapidly and the requirements for these applications are different from those for professional archival storage. In particular, a holographic medium for consumer applications must be simple, cheap, and easy to process. In addition, where content distribution is the intended application, the medium must also be compatible with mastering and replication processes. We present a new holographic medium designed to meet the requirements of consumer oriented applications. The media is based on thermoplastic materials that are modified by the inclusion of photo-chemically active dyes. A series of 0.6 and 1.2 mm thick discs were injection molded and characterized for holographic storage capacity and sensitivity. The first series of samples showed large refractive index modulations of 0.03 but a poor sensitivity of 0.1 cm/J. Analysis of the data showed that the low sensitivity limited the usable capacity of the media to M/# values of ~1. A new series of dyes were synthesized with optimized efficiency and injection molded in 1.2 mm substrates. These substrates demonstrated comparable usable capacity but with significantly increased sensitivities. The results of the measurements of the injection-molded thermoplastic media are presented.

Micro-Holograms Recorded in a New Thermoplastic Medium for Holographic Data Storage

This paper updates the recent progress in the micro-holographic format data recorded on a new dye-doped thermoplastic medium. The new medium is 400 times more sensitive than our first generation material. Characterization shows that micro-holograms can he written at a much faster rate

Improved Sensitivity of Dye-Doped Thermoplastic Discs for Holographic Data Storage

Significant sensitivity improvement was achieved in dye-doped thermoplastic materials for holographic data storage at 405nm. The sensitivity characterization method and measurement results are reported.