Collinear holographic data storage system is a promising candidate for next-generation storage technique. Numerical simulation plays a vital role in the process of revealing physical insight into the effectiveness of proposed methods and providing guidance for further system optimization. In this work, we demonstrated a GPU accelerated numerical model for image formation in collinear holographic data storage system. An average 125 times speedup with 99.8% accuracy was achieved with our accelerated model compared to conventional CPU based simulation. Applications of our model for collinear holographic data storage system such as wavelength drift compensation and noise study were demonstrated.
Collinear holography has been good candidate for a volumetric recording technology of holographic data storage system (HDSS), because of there are not only large storage capacities, high transfer rates, but also the unique configuration, in which the information and reference beams are modulated co-axially by the same spatial light modulator, as a new read/write method for HDSS are very promising. The optical pickup can be designed as small as DVDs, and can be placed on one side of the recording media (disc). In the disc structure, the preformatted reflective layer is used for the focus/tracking servo and reading address information, and a dichroic mirror layer is used for detecting holographic recording information without interfering with the preformatted information. A 2-dimensional digital page data format is used and the shift-multiplexing method is employed to increase recording density. As servo technologies are being introduced to control the objective lens to be maintained precisely to the disc in the recording and reconstructing process, a vibration isolator is no longer necessary. In this paper, we introduced the principle of the collinear holography and its media structure of disc. Some results of experimental and theoretical studies suggest that it is a very effective method. We also discussed some methods to increase the recording density and data transfer rates of collinear holography using phase modulated page data format.
Collinear holographic storage system is one of the advantages of the promising candidate as its unique system design. The wavelength margin is a very important characteristic which can make a laser diode to be used possible as a light source in a holographic storage system, because of the bit-error-rate (BER) of a reconstructed page data pattern will be so high that we cannot decode it correctively, even though the wavelength drift of the diode was small enough. To solve the problem, we studied a method of decreasing BER by adjusting the focal length of the lens to compensate the wavelength drift in the collinear holographic storage system. Once we changed the focal length of the lens, the angles can also be changed to satisfy the Bragg condition. So we find that decreasing the focal length of the lenses can compensate the wavelength drift up effectively and vice versa.
Almost all current collinear holographic storage systems record and reproduce the amplitude information but ignore the phase information. To utilize phase information as the useful data is a significant study. Instead of amplitude modulation, using phase encoding and decoding to get phase information is one way to raise storage density. By adding phase encoding to the amplitude encoding, we realized the phase modulation. To reduce the computation load we simplified multilayer phase-scale model to binary 0 and π phase model. By controlling the proportion of 0 and π phase, different phase modulation models can be represented. In the simulation, we use the angular spectrum theory to build the system mathematical model. We got an effective range of the phase modulation called degree of freedom curve of phase encoding, which can promise both low bit-error-rate (BER) and high code rate. Using this curve, we can make phase encoding more efficiently. Once the dynamic response range of the materiel, the gray levels of phase encoding, and the demanded BER determined, we can calculate the degree of freedom curve to prepare for the followed phase encoding.
Holographic data storage system is a promising candidate of the next-generation of storage equipment. However,
conventional technologies (called 2-axis holography) still have essential issues for commercialization of products. In
this paper, we introduce the collinear holography that can produce a small, practical data storage system more easily than
conventional 2-axis holography. In this technology the information and reference beams are displayed co-axially by the
same SLM. With this unique configuration the optical pickup can be placed on one side of the recording media. The
special media structure uses a pre-formatted reflective layer for the focus/tracking servo and for reading address
information. It also uses a dichroic mirror interlayer for detecting holographic recording information without
interfering with the preformatted information. A 2-dimensional digital page data format is used and the
shift-multiplexing method is employed to increase recording density.