David E. Call

Design tradeoffs for beyond 20 Gb/in.2: Using a merged notched head on advanced low noise media (invited)

Design considerations for areal densities beyond 20 Gb/in.2 are discussed, and in particular a demonstration at 24.8 Gb/in.2 is shown. The demonstrations used a single combined write and read head (Merge, Notched head). In this article we will discuss the tradeoffs in kilobytes per inch (KBPI) and tracks-per-inch in obtaining areal densities at 25 Gb/in.2 densities. The KBPI is limited by both the total signal-to-noise ratio and the nonlinear-transition shift. Simple estimates of the increase in channel performance from class IV partial response (PR4), extended partial response 4 (EPR4), and modified EEPR4, as well as the addition of codes which eliminate bit shift and tribit errors are discussed as large contributors to the increase in the areal density.

Dependence Of Laser-Feedback Noise On Optical-Path Length

Laser-feedback noise in a GaAIAs laser was investigated as a function of optical-path length and modulation frequency.

Light intensity modulation direct overwrite on 130-mm 2X MO media

Direct overwrite (DOW) at 2X operating densities has been demonstrated utilizing an IBM 2X drive and exchange coupled multilayered media. To generate the writing waveforms required for DOW, modifications of the laser driver electronics were implemented. The drive was integrated into a test bed to study the light intensity modulation direct overwrite media writing and overwriting characteristics. In this paper, we show that utilizing simple write waveforms consisting of PHi superimposed on a pedestal power, does not permit the attainment of satisfactory figure of merits (FOMs). We show that by modifying the write waveform we increase the temperature gradients that precisely define the written marks. Consequently, it is possible to achieve good FOMs even at OD conditions, and this is done by implementing straightforward modifications to the laser drive electronics of an IBM 2X drive.