Blair I. Finkelstein

Rewritable optical disk drive technology

Optical disk drives provide an effective solution to the growing need for removable high-capacity storage. In this paper, we review the technology behind the optical disk drives used in IBMs optical storage systems. The basic physics of data recording and readout and the engineering of the primary building blocks of an optical drive (the optical head, the servo system, and the data channel) are discussed. We also outline the technological directions of future optical drives as they must continue to improve in performance and capacity.

Noise sources in magnetooptic recording

This paper investigates nonwhite noise sources important in magnetooptic recording. These noise sources are experimentally characterized, and their contribution is quantified across a 20-MHz bandwidth.

Design and characterization of a quadrilayer magneto-optic disk

The use of quadrilayer film structures can maximize the magnetooptic (MO) effect in reflected light used for readout in optical data storage. A computer program and a multifilm optical model have been utilized to search for optimized quadrilayer structures based on various figures of merit (FOMs), including differential MO signal, shot-noise-limited SNR, and SNR expressions arising from other noise sources. Selection among various FOMs allows tradeoffs relative to the magnitude of the reflectance or thermal efficiency in writing. Disks were fabricated on the basis of the simulation design rules, and experiments were conducted to assess the recording performance. The authors report on the optimization search used in the design program and the formation of the associated FOMs, and they present data on signal and noise to illustrate the value of the model. >

Superdense optical storage

The CD-ROM has made optical storage a common computing resource. Soon, though, other optical technologies will be cramming even more data into still less space. Four technologies (high-density rewritable disks, optical tape, volume holographic storage and electron trapping) could far exceed todays storage capabilities. Nor are these technologies just research efforts in university or corporate laboratories; the focus is now on developing actual products, and small companies have already formed to do so. Here, the authors examine: what is the technologys current status; what are the challenges to its realization; and what are its chances for commercial success?. >

Spot and mark-size characterization in magneto-optic recording

The attainable performance of a magnetooptic (MO) recording system is determined by the laser intensity profile and the size and shape of the written magnetic domain. The authors present a computer model that provides MO readout waveforms based on an overlap integral of the scanning laser spot and the written domains. This model and regression analysis are applied to experimental magnetooptic readout waveforms, and the laser profile and mark size are determined. A nonlinear least-squares fit of readout data yields a unique determination of the laser-spot profile and written-domain size. The effects of groove width and thermal blooming on domain shape can be included in the modeling. The results are compared to those of other spot and domain measurements, and close agreement is obtained. >

Optimum design of optical storage media for drive compatibility

Interchangeability standards for writable optical data storage media allow considerable range in the design of media and optical devices. Naturally, the most reliable system performance occurs when the media design is made fully compatible with the particular characteristics of the drive. This paper treats design of the thin film structure of magneto-optical media for optimum readout compatibility with the drive. The methodology centers on maximization of system signal-to-noise ratio (SNR) under general conditions of system noise composition. We present simple models for the behavior of the various noise components in optical disk drives-medium, laser, shot, electronic. The total system noise model is supplied with relative component weights derived from experimental noise decomposition measurements on the physical system (drive or tester). By changing the relative weights of system noise components, one can readily identity optimum medium designs under different conditions of noise dominance. >

Optimum laser power and pulse length for recording of magneto‐optical media

This paper discusses the relationship between optimum laser power and pulse length to obtain the maximum signal amplitude in pulse position modulation magneto‐optical (MO) recording. The American National Standards Institute standard (X3B11) for 89‐mm disks contains an expression for the maximum allowable optical‐pulse power incident at the surface of the recording disk as a function of laser‐pulse length: Pw=C[(1/tw)+(1/(tw)1/2], where C=75, Pw is the power in mW, and tw is the laser‐pulse duration in nanoseconds. This expression was derived empirically, with C a media characteristic (set to 75 in the standard). To evaluate the adequacy of this empirical equation, disks from five different MO disk suppliers were evaluated for write performance. Having examined different metrics to determine optimum write power for a given laser‐pulse length, the power producing the maximum signal amplitude for 1.56‐μm mark spacings was selected as the performance criterion. Signal amplitude maximizes because of the compe...

Effects of focus misregistration on optical disk performance

The effects of focus misregistration (FMR) on signal amplitude, jitter, write performance, peak shift, and the figure-of-merit parameter were investigated as a function of track position, pattern, write power, and crosstalk. Experimental results for FMR offsets were compared to theoretical predictions. A Monte Carlo model of FMR distribution was generated from experimental results. These results were then compared to results from noise injection into the focus servo. In the test system, the tracking servo failed under focus noise injection before system performance degraded appreciably.

Peak shift analysis for magneto‐optical storage

This paper explores the thermal induced peak shift in magneto‐optical (MO) recording. A complete model is presented that includes the writing and reading on magneto‐optical media. Data is shown for the readback signal amplitude and peak shift versus write power and pulse length that corroborate the model. The mark shapes are calculated from a purely thermal Green’s function model.

Adjacent track crosstalk in magneto‐optical recording (abstract)

As the areal density of future magneto‐optical (MO) disk drives is increased, adjacent track interference on readout will become a more significant engineering problem. Many issues are involved in the analysis of this problem, including tracking servo misregistration, the transverse dimension of written domains, the reading laser beam intensity profile (especially aberrations), the nature of the optical‐transfer function for reading information to each side of the track center, and diffraction effects involving disk grooves and the linearly polarized read beam. The change from pulse‐position to pulse‐width modulation significantly increases the recording system sensitivity to adjacent track crosstalk (ATC). We conducted a variety of experimental tests of ATC to separate and understand the above effects. Two numerical scalar diffraction models of MO readout have been used to make quantitative predictions of signal amplitude as a function of off‐track displacement and written frequency. Sensitive measures o...