Optical Storage Systems Research Articles

Three-Dimentional Optical Storage Medium Using Arranged Nano-spheres

In this study, we have developed a multi-layered optical storage medium with nano-spheres as the recording medium. We made a three-layered medium of spheres and thereby realized a three-dimensional high-density optical storage system. Using a reflection confocal optical system, we read out clock signals from the medium. The system records data and reconstructs it jitter-free.

Improved Gap Control System Using a Disturbance Observer for Near-Field Recording

In a solid immersion lens (SIL) based near-field recoding (NFR) system which is one of the emerging technologies for next-generation optical data storage systems, it is essential that the air gap between the SIL and the rotating disk is maintained at less than 50 nm without collision in order to obtain the proper coupling efficiency of evanescent waves. To fabricate a reliable near-field air gap servo system, various disturbances such as disk vibration, external shock and overshoot have to be considered, and these possible disturbances have to be prevented effectively. We propose an improved gap servo system using a disturbance observer (DOB), which has a reduced overshoot and rejection performance for the previously mentioned disturbances. The effectiveness of the proposed controller is verified by experimentally. The experiment results, show that the overshoot was reduced using the proposed near-field air gap servo system with a DOB. In the case of the ramp approach mode with and without the hand-over mode in the mode-switching servo, the overshoots were decreased to 50.9% and collision was avoided, respectively. In addition, in the case of the modified approach mode with and without the hand-over mode in the mode-switching servo, the overshoot was decreased to 2.9 and 3.7%, respectively. Consequently, the access time was decreased in each approach case without the hand-over mode using the DOB-based controller. In addition, the disturbance rejection performance of the external shock was improved to 9.11%.

Markov Random Field Detection on Two-Dimensional Intersymbol Interference Channels

We present a novel iterative algorithm for detection of binary Markov random fields (MRFs) corrupted by 2-D intersymbol interference (ISI) and additive white Gaussian noise. We assume a first-order binary MRF as a simple model for correlated images. We assume a 2-D digital storage channel, where the MRF is interleaved before being written and then read by a 2-D transducer; such channels occur in recently proposed optical disk storage systems. The detection algorithm is a concatenation of two soft-input/soft-output (SISO) detectors: an iterative row-column soft-decision feedback (IRCSDF) ISI detector, and a MRF detector. The MRF detector is a SISO version of the stochastic relaxation algorithm by Geman and Geman. On the 2times2 averaging-mask ISI channel, at a bit error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> , the concatenated algorithm achieves SNR savings of between 0.2 and 2.0 dB over the IRCSDF detector alone; the savings increase as the MRFs become more correlated, or as the SNR decreases. The algorithm is also fairly robust to mismatches between the assumed and actual MRF parameters.

Recording Capacity Enhancement of Micro-Reflector Recording

Micro-reflector recording is a potential candidate for sub-terabyte optical storage systems. In this paper, the latest progress on increasing storage capacity and on improving recording transfer rate of micro-reflector recording is presented. With our dynamic tester, we successfully recorded ten signal layers dynamically in a monolithic recording material. For every signal layer, moderate bit error rate was obtained by employing readout signal processing. Our experimental results indicate the potential for increasing recording transfer rate and recording density.

High-End Silicon PDICs

Abstract. An overview on integrated silicon photodiodes and photodiode integrated circuits (PDICs) or optoelectronic integrated circuits (OEICs) for optical storage systems (OSS) and fiber receivers is given. It is demonstrated, that by using low-cost silicon technologies high-performance OEICs being true competitors for some III/V-semiconductor OEICs can be realized. OSS-OEICs with bandwidths of up to 380 MHz and fiber receivers with maximum data rates of up to 11 Gbps are described. Low-cost data comm receivers for plastic optical fibers (POF) as well as new circuit concepts for OEICs and highly parallel optical receivers are described also in the following.

Design of Super-resolution Filters with a Gaussian Beam in Optical Data Storage Systems

Super-resolution filters based on a Gaussian beam are proposed to reduce the focusing spot in optical data storage systems. Both of amplitude filters and pure-phase filters are designed respectively to gain the desired intensity distributions. Their performances are analysed and compared with those based on plane wave in detail. The energy utilizations are presented. The simulation results show that our designed super-resolution filters are favourable for use in optical data storage systems in terms of performance and energy utilization.

R&amp;D activity trend on optical storage technology

The research and development direction of optical storage systems are reviewed and discussed. Also, some of the prospective area to be explored for the new storage systems is shown in Consumer Electronics (CE) environment.

Innovative Three-Axial Actuator for High-Density Optical Drive

As the density in optical data storage systems increases, a drive capable of tilt control thus becomes necessary in order to improve the tilt margin as the coma aberration is accordingly increased. In this paper, we propose an innovative three-axial actuator based on a traditional four-wire scheme with an additional pair of tilting magnets. The proposed coil-driven servo can independently compensate plusmn1 tilt degree associated with a torque variation of less than 5%. The driving forces of the focusing and tracking are kept constant while the tilt servo is activated.

Servo Study of Radially Polarized Beam in High Numerical Aperture Optical Data Storage System

In this paper, we employed full vector diffraction treatment to study the dependence of the servo signals to the doughnut-shaped focus radiation of radial polarization, which provides a smaller spot size than linear polarization, and the resistance to the primary aberrations in a numerical aperture (NA)=1.0 optical data storage system. Compared with linear polarization, at strong focusing, a radially polarized beam leads to 14% asymmetry reduction in the linear range of the focus-error signal (FES) curve and to at least 56% variation reduction in crosstalk in a weakly aberrated system. These characteristics make radial polarization a potential candidate for next-generation high-density optical systems.

Spot size and depth of focus in optical data storage system

Different definitions of spot size and depth of focus in optical data storage systems are analyzed and compared numerically. It appears that the differences between the definitions become more significant as the numerical aperture of the optical system increases. The relationship between spherical aberration and axial intensity is studied, and a general definition of the depth of focus based on this analysis is proposed.

Hybrid Catadioptric System for Holographic and Disk Application

In this paper, we reveal a new device for use as an optical data storage system. The system is made up of Cassegrain-like structures. The volume (35×20×20 mm3) of the system is the size of a pickup head used in conventional optical storage. It has compatibility with several conventional optical disk technologies. Namely, the system provides a platform for integration with compact disc (CD), digital versatile disc (DVD), Blu-ray disc (BD) and holographic systems. The full width half maximums (FWHMs) of the spot size for a CD have been measured in this system and are 0.98 and 0.95 µm in the tangential and radial directions, respectively.

Dynamic laser feedback noise measurement for the optical information storage system

The conventional measuring system of laser feedback noise for an optical pickup was specifically implemented only for laser diodes by using a static optical system. With no closed-loop servo control, it is impossible to measure the genuine laser noise distribution of a pickup while operating in an optical drive. By modifying the optical system of a commercial pickup, this study built up a system that was integrated with precision mechanical design, optical design, servo control design, and opto-electronic signal inspection for providing dynamic real-time laser feedback noise measurement. Using this system, some experimental results have been observed. The laser feedback noise is responsible to the focusing point within the linear range of an optical pickup head. It has the maximum value while the lens is on the best focus. The higher the environmental temperature, the noisier the laser output will be. Besides, the central frequency of noise is dependent on the disk rotation speed, and the noise level is reducible by increasing the disk rotation speed.

Hybrid laser micro/nanofabrication of phase change materials with combination of chemical processing

Abstract Phase change materials have been widely applied in optical data storage technique to produce rewritable versions of compact disks and digital versatile disks random access memory and are still promising for higher capacity optical data storage. In optical data storage system, laser irradiation is used to write and read information in phase change film. The original phase state of phase change film without annealing is amorphous state. After laser irradiation, the laser energy transferred to phase change film increases temperature to create crystalline features. To study the effects of laser wavelength and fluence on feature fabrication, different kinds of laser systems are used to irradiate non-annealing phase change film to fabricate crystalline features in micro/nano-sizes. Electrical force microscopy and near-field scanning optical microscopy are used to characterize the electrical and optical properties of phase change film, respectively. Two kinds of phase change film, Ge 1 Sb 2 Te 4 and Sb 2 Te 3 , are used. Alkaline solution has the ability to etch the amorphous and crystalline states of phase change film selectively. The phase change film patterned by laser irradiation is etched by alkaline solution to fabricate two- and three-dimensional structures. The etching selectivity and rate of alkaline solution for the two phase change films are studied. It provides a novel approach to fabricate new functional micro/nano devices by combining further etching or deposition techniques.

Future Memory Storage Technology: Protein-Based Memory Devices May Facilitate Surpassing Moore's Law

Storage media based on biomolecules may provide a commercially viable alternative to current magnetic and optical storage systems. Our research is aimed at developing the storage media systems based on newly designed thermostable bacteriorhodopsin (bR) mutants and exploring limits of high-density optical recording using far-field and near-field approach

Adaptive Decomposition of Noise Sources in Digital Recording Systems With Media Noise

In digital recording systems, the total amount of data-dependent media noise increases considerably as recording densities increase. A proper noise characterization is crucial for the design of receivers for high-density storage systems. This characterization involves the selection of a proper noise model and subsequently the accurate estimation of the parameters of the selected model. The estimation algorithm proposed in this paper jointly estimates the parameters of both media and additive noise with a high accuracy. The proposed algorithm makes use of the data dependency of the media noise to distinguish between the different noise sources. The algorithm is simple and as a result can be implemented in recording systems, with only a limited amount of complexity, as an easy add-on to read-channel ICs. From the simulation results and the analytical derivation of the estimation algorithm, we can clearly indicate which data patterns yield near-optimal estimation performance. These patterns are the ideal test patterns in experimental systems. We propose and discuss test patterns for magnetic and optical storage systems

Holographic Information Storage System: Today and Future

Holographic information storage systems using Collinear Technologies is proposed by Optware Corporation, Yokohama, Kanagawa, Japan, and in which the information and reference beams are modulated coaxially by the same spatial light modulator (SLM). With this unique configuration, the optical pickup can be designed as small as the DVDs and can be placed on one side of the recording disk. In a Holographic Versatile Disc (HVD) structure, the preformatted metadata reflective layer is used for the focus/tracking servo and reading address information, and the dichroic mirror layer is used for detecting holographic recording information without interfering with the preformatted information. A two-dimensional (2-D) digital page data format is used, and the shift-multiplexing method is employed to increased recording density of HVD. Experimental and theoretical studies suggest that the holographic material is very effective to increased recording density of the system. As the servo technology is being introduced to control the objective lens to be maintained precisely to the disk in the recording and the reconstructing process, a vibration isolator is no longer necessary. HVD will be compatible with existing disk storage systems, like CD and DVD, and enable us to expand its applications into other optical information storage systems

Integrated Tracking and Focusing Systems of MEMS Optical Pickup Head

This paper presents a novel bidirectional-driven microelectromechanical systems (MEMS) light manipulation stage. The designed device consists of two actuators integrated with a lens to act as both tracking (in-plane) and focusing (out-of-plane) components for optical pickup head. The actuator is driven by thermal, as well as magnetic, means. According to a static-load deflection test, this device can achieve bidirection actuation with output displacement up to plusmn54.5 mum. In addition, this MEMS device has a very small form factor and provides an excellent response time and size reduction. It can be employed on the portable optical storage system

Minimum-Latency Tracking of Rapid Variations in Two-Dimensional Storage Systems

The trend of increasing storage densities results in growing sensitivity of system performance to variations of storage channel parameters. To counteract these variations, more adaptivity is needed in the data receiver. Accurate tracking of rapid variations is limited by latencies in the adaptation loops. These latencies are largely governed by delays of the bit detector. In two-dimensional storage systems, data are packaged in a group of adjacent tracks or rows, and for some of the rows the detection delays can increase dramatically with respect to one-dimensional systems. As a result, the effective latencies in the adaptation loops preclude the tracking of rapid variations and really limit the performance of the system. In this paper, a scheme is proposed that overcomes this problem and that can be used for timing recovery, automatic gain control, and other adaptive circuits. Rapid variations for all the rows are tracked using control information from rows for which detector latency is smallest. This works properly if rapid variations are common across the rows as is the case, for example, for the two-dimensional optical storage (TwoDOS) system. Experimental results for TwoDOS confirm that the scheme yields improved performance with respect to conventional adaptation schemes

Proposal of new Tera Byte Optical Storage System named as SVOD (Stacked Volumetric Optical discs)

Proposal of new Tera Byte Optical Storage System named as SVOD (Stacked Volumetric Optical discs)

Improved performance in coaxial holographic data recording

We describe a coaxial holographic recording system for achieving high recording density. We implement several techniques, such as an objective lens with high numerical aperture (NA), high capacity page data format, a random binary phase mask, and an optical noise reduction element. Our system successfully realizes a hologram recording/retrieving at a low diffraction efficiency less than 2.0 x 10(-3) and achieves a raw data density of 180 Gbit/in.(2), thus demonstrating the potential of a coaxial holographic system for high-density optical storage systems.