This PDF file contains the front matter associated with SPIE Proceedings Volume 9959, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

We report the experimental verification of cavity enhanced recording of image bearing holograms in Fe:LiNbO3 with a 532 nm wavelength, CW, single mode, DPSS, Nd:YAG, laser with a cavity on the reference arm. Diffraction efficiency evolution was monitored via pseudo-phase-conjugate readout during recording. Additionally, optimization of grating strengths in standing wave cavity writing is explored, and a means of eliminating unwanted gratings via quarter wave plates with isotropic recording media is proposed.

We successfully completed the development of a GaN based Tunable laser for Tapestry holographic data storage through collaborative research with InPhase Technologies in 2010. After the collaborative research, with the aim to achieve further advance development for commercial storage use, we have continued to improve the laser characteristics, especially coherence property and high optical output power are significant issues for holographic data storage. Longitudinal single mode lasing is one of most important property in hologram recording; therefore we addressed to optimize laser diode structure for external cavity laser. In parallel to that, we have reviewed not only a Laser diode structure but also laser drive processing, and have successfully developed a function. In the case of performing high visibility hologram recording, prior to exposing to medium, both the laser driving current and the wavelength are slightly adjusted to achieve single mode lasing. We call this function “Mode Stabilizer”. Mode Stabilizer can automatically execute the adjustments in combination with an internal mode sensor for visibility sensing. This function is advantageous in that erroneous page-recording can be avoided. Moreover, we achieved high optical output power of 100 mW increased from conventional 45 mW, by optimizing the device structure of GaN Laser diode. With this high optical output power, acceleration of recording bit rate becomes possible.

Shift multiplexing method using a spherical wave is proposed for a holographic memory system based on a computer-generated hologram (CGH). In the proposed method, a propagated signal beam along an optical axis is generated by a CGH. The zero order beam of the CGH is obtained as a point source in the Fourier plane. This point source becomes a spherical reference beam on a recording medium by displacing a Fourier transform lens. The use of the spherical reference beam allows us to implement shift multiplexing in the holographic memory based on a CGH. Shift selectivity of the proposed method is numerically evaluated. In addition, shift multiplexing with the proposed method is numerically demonstrated.

The exact solutions of the set of nonlinear coupled differential equations pertaining to Bragg and non-Bragg orders for the case of interacting angular spectra in a photorefractive medium are obtained numerically. An iron doped lithium niobate is used as a photorefractive material, and the incident wavelength is taken to be 514 nm. During traditional two-beam coupling within a photorefractive material, many non-Bragg orders may also be generated. For solving the set of coupled equations numerically, interactions between the spectra of two Bragg and two non-Bragg orders are considered. The spatial evolution of the spectra of these diffracted orders hence their spatial profiles are studied numerically for different incident profiles.

In microholographic recording, expensive laser diodes having no spectrum broadening (single mode) and no wavelength variation are used. On the other hand, in conventional optical disk systems, cheap laser diodes having spectrum broadening (multimode) and wavelength variation are used. It is a great advantage if the laser diodes for conventional optical disk systems can be used for microholographic recording. Therefore, the effect of wavelength change in microholographic recording was investigated through a numerical simulation. The laser diodes were modeled so that the full width at 1/e2 maximum of the spectrum was 0.8 nm and the center wavelength was 405 nm. The numerical aperture of the objective lenses was 0.85 and the thickness of the recording medium was 300 μm. The diffraction efficiency of the diffracted beam from a microhologram was calculated using the coupled wave theory and the following results were obtained. The diffraction efficiency decreased by three orders of magnitude by replacing single-mode laser diodes with multimode laser diodes, which makes it necessary to enhance the readout signal. The tolerance of the optical path length difference between the signal and reference beams was -50 ~ 110 μm, which makes it necessary to adjust the optical path length difference. The tolerance of the wavelength variation was 405 ± 0.5 nm, which makes it necessary to select the laser diodes. The conclusion was that it is not practical to use the laser diodes for conventional optical disk systems for microholographic recording.