Readout signals calculated for near-field optical pickups with land and groove recording

Optical disk readout signals with a solid immersion lens (SIL) and the land-groove recording technique are calculated by use of a simplified vector-diffraction theory. In this method the full vector-diffraction theory is applied to calculate the diffracted light from the initial state of the disk, and the light scattered from the recorded marks is regarded as a perturbation. Using this method, we confirmed that the land-groove recording technique is effective as a means of cross-talk reduction even when the numerical aperture is more than 1. However, the top surface of the disk under the SIL must be flat, or the readout signal from marks recorded on a groove decays when the optical depth of the groove is greater than lambda/8.     

Pulse-read on erasable thermal phase-change superresolution disks

New erasable thermal phase-change superresolution (EPSR) disks composed of mask and recording layers can increase recording density by the detection of the below-diffraction-limited marks within the readout spot. The formation of the aperture and the readout signal on the EPSR disk were analyzed. The feasibility of optically designed EPSR disks was evaluated by thermal simulation. A carrier-to-noise ratio of 32 dB at a mark size of 0.4 mum, 8 dB higher than that of a conventional disk, was obtained by application of a pulse-read method to the EPSR disks at a wavelength of 780 nm and a numerical aperture of 0.55.     

Superresolution Near-field Readout in Phase-Change Optical Disk Data Storage

Readout of a phase-change optical disk with a superresolution (SR) near-field structure (Super-RENS) is theoretically examined on the basis of three-dimensional, full-wave vector diffraction theory. Calculations have demonstrated that Super-RENS has a high spatial resolution beyond the diffraction limit in readout. The read signal is dependent on the nature of SR, the layer structure of the disk, and the state of polarization of the incident laser beam. For the Super-RENS in which antimony is used for SR readout, the readout signal is quite small, and the estimated carrier-to-noise ratio (CNR) is only ~30 dB for marks of 300 nm. For the Super-RENS in which a metallic region is formed during readout, the read signal is large, and the CNR can be as high as 50 dB in reading 300-nm marks.     

Vector diffraction analysis of optical disk readout

The optical disk readout signals from ROM disks are presented by use of a rigorous three-dimensional vector diffraction method. The optical disk is modeled as a crossed metal grating without restriction on the form of the information marks, and the permittivity of the metal is taken into account. The diffracted field from the disk is obtained by means of decomposing the focused incident beam into a spectrum of plane waves and then calculating the diffracted plane waves for each respective incident component. The readout signal is obtained by integration of the energy-flux density of the diffracted field according to the detection scheme of the optical disk system. A typical digital versatile disk (DVD) system is applied with this theory, and the result is far from that of scalar diffraction theory.     

Scalar diffraction modeling in optical disk recording using wave function assembling

A new scalar diffraction modeling method for simulating the readout signal of optical disks is described. The information layer is discretized into pixels that are grouped in specific ways to form written and unwritten areas. A set of 2D wave functions resulting from these pixels at the detection aperture is established. A readout signal is obtained via the assembly of wave functions from this set according to the content under the scanning spot. The method allows efficient simulation of jitter noise due to edge deformation of recorded marks, which is important at high densities. It is also capable of simulating a physically irregular mark, thereby helping to understand and optimize the recording process.     

Evanescent coupling in magneto-optical and phase-change disk systems based on the solid immersion lens

Results of numerical computations pertaining to evanescent wave coupling for near-field magneto-optical and phase-change disks based on the concept of the solid immersion lens are presented. We investigated the relation between the coupling efficiency and the width of the air gap in terms of the throughput of the recording process and the resolution of the readout signal. The simulations show a drastic decrease with a widening air gap of the coupling efficiency by means of evanescent waves into the recording medium. In magneto-optical readout, loss of the signal may be attributed to the reduction of magneto-optical interaction, the rise of reflectance, and the variation of the relative phase between the two components of polarization. In the phase-change readout the reduced reflectivity contrast between crystalline and amorphous marks is the cause of signal reduction.     

Laser-induced local heating of moving multilayer media

Earlier work on the local heating of stationary multilayer structures by focused laser light has been extended to deal with nonstationary situations. The numerical procedures described here are therefore applicable to many important technologies including optical recording, thermal marking, and laser annealing. We demonstrate this in two examples, namely, the effects of readout intensity on the readout signal from a quadrilayer magnetooptic disk and the writing threshold for ablative materials in single-layer and three-layer structures.     

Partial-response signaling for phase-change optical data storage without electronic equalization

We describe the application of partial-response (PR) signaling in rewritable phase-change optical data storage. No electronic filter is necessary to shape the readout signal to a certain PR target. A PR-like waveform at the output of the read channel is directly achieved by optical recording. A genetic algorithm is used to optimize the parameters for writing and therefore to minimize the difference between the actual readout signal and the ideal PR waveform. With a laser wavelength of 0.66 microm and an objective lens with a numerical aperture of 0.6, four linear densities were examined: 0.4, 0.3, 0.25, and 0.2 microm/bit (without modulation). Results showed that the linear density of 0.25 microm/bit can be realized on a rewritable digital-versatile disk.     

Optical readout for optical storage with phase jump

A novel, to our knowledge, optical readout for optical storage with phase jump is presented. In the readout scheme two coherent laser beams are focused on an optical disk with one beam scanning along pits and the other along land. When the probe beam scans across a pit, two phase jumps will take place in the interference resultant of the two beams if the phase difference between two beams is prefixed at pi, resulting in a phase pulse of 180 deg. The slopes of rising and falling edges of the phase pulse are infinite, and they are not affected by the intensity variation of the light source, stray light, and the vibration of the disk. Therefore this phase pulse can be used to read out the information on an optical disk. The use of phase jump will improve the signal-to-noise ratio of the readout signal and enhance the density of optical storage. An optical readout with phase jump was constructed. Both the theoretical design and the experimental verification are conducted. Experimental results show that the proposed optical readout is feasible.     

High density magneto-optical recording using 0.67 μm band highpower laser diode

High-density optical recording on a magnetooptical disk has been achieved by a compact optical head that uses a 0.67-μm-band high-power visible-light laser diode. The recording density has been improved to 1.5 times that for conventional optical recording, using a 0.83-μm laser diode, as a result of the increase in linear density and track density. The C/N ratio for the readout signal is greater than 50 dB     

Performance of a write-once multilayer optical disk that uses transparent recording material with an optical switching layer

A volumetric optical disk that has multiple transparent films with optical switching layers is used as a recording medium to increase the number of recording layers. In the disk the optical switching layer is adapted to reduce decay of laser energy and increase reading and recording sensitivity. Well-defined marks of approximately 100-nm depth can be placed precisely on the transparent films by a focused laser beam. Writing and reading of a four-layer recordable disk, fabricated by molding and spin bonding, have been demonstrated experimentally. The volumetric disk can achieve a high recording capacity with conventional optical pickups.     

Digitized molecular diagnostics: reading disk-based bioassays with standard computer drives

We report herein a digital signal readout protocol for screening disk-based bioassays with standard optical drives of ordinary desktop/notebook computers. Three different types of biochemical recognition reactions (biotin-streptavidin binding, DNA hybridization, and protein-protein interaction) were performed directly on a compact disk in a line array format with the help of microfluidic channel plates. Being well-correlated with the optical darkness of the binding sites (after signal enhancement by gold nanoparticle-promoted autometallography), the reading error levels of prerecorded audio files can serve as a quantitative measure of biochemical interaction. This novel readout protocol is about 1 order of magnitude more sensitive than fluorescence labeling/scanning and has the capability of examining multiplex microassays on the same disk. Because no modification to either hardware or software is needed, it promises a platform technology for rapid, low-cost, and high-throughput point-of-care biomedical diagnostics.     

Multi-level decision feedback equalization for saturation recording

An impediment to the practical use of fixed-delay tree search with decision feedback (FDTS/DF) for retrieving data from hard disk drives is that four additions and one multiplications must be evaluated in one clock cycle. It is shown here that on recording channels using 2/3(1,7) run-length-limited (RLL) coding, a detector achieving the performance of FDTS/DG can be implemented with a two-tap transversal filter. The feedback loop can be rearranged so that this transversal filter no longer resides in the forward path of the feedback loop. Instead, its transfer function is incorporated into the specification of the forward and backward equalizers. This modification leads to a simpler equalizer architecture in which the slicer performs binary decisions on a multilevel signal. Implementation issues pertaining to phase detection, gain detection, DC detection and adaptive equalization using a least-mean-squared (LMS) technique are addressed. Simulation results are given     

Rewritable optical-disk fabrication with an optical recording material made of naphthalocyanine and polythiophene

A novel rewritable optical disk that uses an optical recording material made of naphthalocyanine and polythiophene as the recording layer is described. In this system the complex refractive index of the recording material changes reversibly, depending on the aggregation states of naphthalocyanine induced by a conformation change of the polythiophene matrix. After recording, the imaginary part of the refractive index of the recording material increases to three times that of the unrecorded part, at a wavelength of 790 nm at which a semiconductor laser emits light. The fabricated polythiophene naphthalocyanine optical disk shows a high reflectivity of 58% and a large readout modulation amplitude (I(11)/I(top)) of 0.63. It is confirmed that the polythiophene/naphthalocyanine optical disk can be played back on conventional compact-disc players even after ten cycles of rewriting.     

An intelligent pressure sensor using neural networks

In this paper, we propose a scheme of an intelligent capacitive pressure sensor (CPS) using an artificial neural network (ANN). A switched-capacitor circuit (SCC) converts the change in capacitance of the pressure-sensor into an equivalent voltage. The effect of change in environmental conditions on the CPS and subsequently upon the output of the SCC is nonlinear in nature. Especially, change in ambient temperature causes response characteristics of the CPS to become highly nonlinear, and complex signal processing may be required to obtain correct readout. The proposed ANN-based scheme incorporates intelligence into the sensor. It is revealed from the simulation studies that this CPS model can provide correct pressure readout within ±1% error (full scale) over a range of temperature variations from -20°C to 70°C. Two ANN schemes, direct modeling and inverse modeling of a CPS, are reported. The former modeling technique enables an estimate of the nonlinear sensor characteristics, whereas the latter technique estimates the applied pressure which is used for direct digital readout. When there is a change in ambient temperature, the ANN automatically compensates for this change based on the distributive information stored in its weights     

Nonlinear model for an optical read-only-memory disk readout channel based on an edge-spread function

A point-spread function (PSF) is commonly used as a model of an optical disk readout channel. However, the model given by the PSF does not contain the quadratic distortion generated by the photo-detection process. We introduce a model for calculating an approximation of the quadratic component of a signal. We show that this model can be further simplified when a read-only-memory (ROM) disk is assumed. We introduce an edge-spread function by which a simple nonlinear model of an optical ROM disk readout channel is created.     

Evaluation of partial-response maximum-likelihood detection for phase-change optical data storage

We describe the application of partial-response (PR) maximum-likelihood (ML) detection in rewritable phase-change optical data storage. The input to this detector, which is simulated in software, is the actual signal (without any equalization), reproduced from reading of the recorded sequence on an optical disk. The detection algorithm involves the extraction of the impulse response from the readout signal, PR equalization, the adjustment of gain and recovery of clock, ML sequence estimation with the Viterbi algorithm, and analysis of PRML performance. With a laser wavelength of 0.69 mum and an objective lens with a numerical aperture of 0.6, three linear densities are examined: 0.35 and 0.31 mum/bit without modulation code and 0.2 mum/bit with the (1, 7) modulation code. The equalized signal exhibits good eye patterns, especially at the densities of 0.35 and 0.31 mum/bit. Analyses of noise and bit-error rate indicate that jitter, rather than noise, is the main obstacle to realizing ultrahigh density in phase-change media with PRML detection. We also briefly discuss the problem of the inherent nonlinear effect in phase-change readout.     

Effects of magnetic fields on flexible disk drive performance

The read/write heads in flexible disk drives operate in the presence of AC and DC magnetic fields generated by solenoids, motors, recording head erase structures, circuit board components, and external sources such as CRT flyback transformers present in "smart terminals and word processors. Time varying magnetic fields induce signal on the read/write coil and introduce interference. This interfering signal increases the error rate and can cause "extra bits". Steady state fields cause shifts in the location of transitions, which also translates into higher error rates. The benefits derived from various shield configurations in and external to the flexible disk drive are presented.     

Efficient computation of optical disk readout by use of the chirp z transform

Computation of the readout signal of an optical disk involves Fourier transforms from the objective lens pupil to the disk and, after interaction with the disk, from the disk to the objective pupil. Traditionally, the complex two-dimensional Fourier transform is numerically evaluated as a two-dimensional fast Fourier transform. To obtain sufficient resolution in the involved planes, one must choose sampling grid sizes of typically 1,024 x 1,024 or higher, resulting in a substantial computation time if the calculation is to be repeated many times. Discussed is an alternative method for evaluating the Fourier transform, based on the chirp z transform, by which a considerable improvement in efficiency can be obtained without loss of accuracy.