Sources of noise in erasable optical disk data storage

Noise sources in the readback signal for phase-change and magneto-optical disks at red, green, and blue wavelengths are examined, and a simple model is presented to explain the observed noise spectra. For phase-change disks the media noise, which corresponds to ~0.4% fluctuation in the disk's amplitude reflection coefficient, is the limiting performance factor for the conventional detection scheme. In magneto-optical media the depolarization noise, whose fluctuations are ~0.05% of the disk's reflection coefficient, is the major contributor to the media noise in the differential detection scheme. In phase-change optical disks the main sources of noise are the roughness of the groove profiles and the graininess of the polycrystalline recording layer. In nongrooved regions of the disk the media noise measured with green light is found to be nearly the same as that obtained with the red light. In magneto-optical disks the scattering of light from the rough groove profiles, as well as media inhomogeneities, gives rise to depolarization. Measurements on nongrooved regions of a magneto-optical disk indicate that the media noise obtained with the green light is somewhat higher than that obtained with the red light.     

Erase profiles of floppy disk heads

An experimental method is described to measure the amplitude profiles across written tracks used in rigid and floppy disk drives. This method allows determination not only of read, write, and side-erasure widths associated with the heads, but also of the detailed shape of the written profiles. These profiles may be obtained for tracks in the as-written condition, or after modification by the write or erase functions of the head. This method was applied to floppy disk heads in order to determine the trim erase characteristics of straddle erase, tunnel erase, and the implicit side erase characteristic of the read/write core itself. A number of typical track profiles are shown, demonstrating the usefulness of this technique. It was found that the straddle erase elements exhibit erasure both under the air gap and under the poles straddling the read/write core; the tunnel erase elements exhibit uniform erasure across their erase gaps but are subject to azimuthal misalignment effects; and the read/write cores themselves exhibit an implicit erase function during normal writing which, in the case studied, extended about 360 μm (9 μm) to each side of the core. Applications of this method to evaluate heads for use at high track densities are also outlined.     

Photonic content-addressable memory system that uses a parallel-readout optical disk

We describe a high-performance associative-memory system that can be implemented by means of an optical disk modified for parallel readout and a custom-designed silicon integrated circuit with parallel optical input. The system can achieve associative recall on 128 × 128 bit images and also on variable-size subimages. The system's behavior and performance are evaluated on the basis of experimental results on a motionless-head parallel-readout optical-disk system, logic simulations of the very-large-scale integrated chip, and a software emulation of the overall system.     

Single-crystal ferrite technology for monolithic disk heads

Manufacturing processes and improved designs for rigid disk drive heads have been developed to take advantage of the properties of single-crystal ferrite. The processes allow photolithographic patterning of air-bearing surface features, creation of features with controlled depth, and laser track trimming without thermal damage or redeposition     

Design issues for practical rigid disk magnetoresistive heads

Some of the issues of magnetoresistive (MR) head design are discussed from the point of view of practical, high-reliability, low-cost, manufacturable heads for rigid disk files. The major advantages of MR heads over single element inductive thin-film heads are that the MR head gives an ideal, easy to equalize output waveshape, can be used on disks with high coercivities for high linear densities, and is less subject to stability problems at narrow trackwidths. The major advantages of MR heads over metal-in-gap ferrite heads are in narrow trackwidth and high-frequency potential. Disadvantages of MR heads in the rigid disk environment include concerns about reliability and, more specifically, possible environmental fragility, loss of performance due to imperfect alignment between the read and write elements and/or due to signal asymmetry, and the possibility of higher cost/price     

Magneto-optical disk drive technology using multiple fiber-coupled flying optical heads. Part II. Laser noise considerations

A magneto-optical data storage system utilizing single-mode fiber is capable of providing high signal-to-noise ratio (SNR) recording if laser noise sources are properly managed. In particular, mode partition noise (MPN) associated with use of a Fabry-Perot laser diode can be a significant problem in a fiber-based system. The various mechanisms leading to MPN as well as to laser phase noise are discussed in the context of a system constructed with polarization-maintaining fiber. The primary noise mechanisms include spurious fiber-endface reflections and errors in the quarter-wave plate on the recording head. An understanding of these effects is essential for fabrication of a fiber-based recording system with suitable SNR performance.     

一种电可擦写可读出的有机薄膜存储器件

报道一种具有可逆电双稳特性的有机薄膜存储器件.器件采用三明治夹层结构Ag/DBCN/Al,DBCN为有机分子材料的简称.这种薄膜器件可以通过改变外加电场的大小来控制所处的状态,表现出高电压区(＞6V)为高阻态(＞106Ω),低电压区(1～2V)为低阻态(～103Ω)的特性,外电场消失时其状态能够长时间保持稳定(超过3个月),还可以用小电压脉冲信号(＜0.5V)来读取其状态信息.此外还发现该器件具有良好的耐热稳定性.     

Magneto-optical disk drive technology using multiple fiber-coupled flying optical heads. Part I. System design and performance

A novel flying-optical-head data storage technology is described. It is based on a micro-optical recording head that contains a silicon micromachined torsional mirror for high-bandwidth track following. Multiple heads and disks are contained in a Winchester-style rotating disk drive. Single-mode optical fibers provide light delivery to and from the heads. Both polarization-maintaining and low-birefringence fiber systems have been implemented for magneto-optical (MO) recording. A fixed optics module containing a laser diode, MO detection optics, and a 1 x N fiber bundle switch has been developed as an integral part of this new recording architecture. A 5.25-in. (13.33-cm), half-height prototype drive design and its performance are presented.     

Design of combined pick-up optical heads

A pseudoray method is suggested for the initial design for the composition of combined optical CD-DVD read-write heads. The effectiveness of the method is shown in the design of the optical system for the CD-DVD read-write heads.     

An eddy‐current and micromagnetism model with applicationsto disk write heads

As data rates increase and the size of the disk write head decreases it is likely that a standard non‐linear eddy‐current simulation of a disk write head will not fully capture dynamic effects. In this paper we propose a coupled eddy‐current and micromagnetics model for the disk write head. We present a simple finite difference formulation derived from a mass‐lumped finite element method. This derivation allows us to verify that, before time discretization, the semi‐discrete scheme obeys the same energy decay equality as the partial differential equation model. We show some numerical results for an ‘academic’ disk writer model. Copyright © 2004 John Wiley & Sons, Ltd.     

Measurement of the thermal conductivity of erasable phase-change optical recording media

We describe a method to estimate the thermal conductivity of the substrate, the dielectric layer, the phase-change (PC) layer, and the reflective layer of PC optical recording media. The method relies on the amorphous-to-crystalline phase transition that occurs in the PC layer and takes advantage of the difference in the thermal diffusion behavior under different-sized focused spots. All the results obtained here are reliable with better than ?5% accuracy, which is within the margin of our experimental error.     

Semiconfocal optical disk readout with one linear-spread beam

A novel, to our knowledge, optics pickup for semiconfocal optical disk is proposed. Five tracks are imaged simultaneously by use of one linear-shaped beam that extends over the tracks in the radial direction with the focusing and the tracking position controlled. We also show how the cross talk between tracks is eliminated automatically. The approximately diffraction-limited width of the beam and the small-signal detector elements make semiconfocal detection possible in the tangential direction.     

Correlation optical velocimetry with a compact disk pickup

The compact disk pickup is a consumer electronics component that can be purchased for a low price owing to the great number of units produced every year. A typical three-beam head contains, enclosed in a tiny case, a quite complete sample of what can be found in an optoelectronics laboratory: a coherent source, a grating, a polarizing beam splitter, a fourth-wave plate, solid-state detectors, and much more. Exploiting the unique features of such a device for scientific aims is intriguing from many points of view. We present a straightforward application of a compact disk pickup to optical correlation velocimetry and show how a rather complicated discrete setup can be replaced successfully by this highly integrated component.     

Reflection-type holographic disk memory with random phase shift multiplexing

A reflection-type holographic disk memory system with random phase shift multiplexing is proposed. The experimental results show that a binary data page of 18x17 bits is recorded successfully at intervals of 4 mum in a Fe:LiNbO3 crystal with a thickness of 0.5 mm when six data pages are superimposed. Numerical results show that random phase modulation can improve the shift selectivity in shift multiplexing recording as well as in data security. Experimental and numerical results show that reflection-type holographic disk memory has a high potential for terabyte storage capacity as in transmission-type memory.     

Optical tunneling effect calculation of a solid immersion lens for use in optical disk memory

A solid immersion lens (SIL) has the advantage of easily decreasing the spot size for high data density in optical recording. To accurately obtain the optical tunneling effect for a high-N.A. SIL, we calculated the optical tunneling beam characteristics, using electromagnetic theory. Tunneling beam spot-size dependence on polarization direction and energy-transfer efficiency are also clearly shown.