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Optics Give Hard Drives a New Lease on Life

Photonics Spectra
Apr 1998
Charles T. Troy

The Winchester-style disk drive, nearing the limits for magnetic storage, has been given a new lease on life, thanks to optics. Computer hard-drive maker Seagate Technology and its Quinta Corp. subsidiary have combined optical switching, fiber optics, microlenses, micromachined mirrors and a new medium with proven Winchester technology to produce a unit capable of packing 40 Gb of data into 1 square inch. Such densities would break the so-called superparamagnetic barrier -- the point at which traditional magnetic hard-disk media can no longer maintain a stable domain.

Quinta engineers combined optical and traditional components in their new drive including an optical switching unit, 1; optical fiber, 2; a head, 3; with a servo-driven mirror, 4; and a novel recording medium, 5.

The technology, officially called Optically Assisted Winchester, was developed by Quinta in an effort to exploit the delivery advantages offered by fiber and optics, and Winchester's mechanical superiority, while avoiding the penalties of one and the limits of the other.

Essentially the system employs an optical switch module that controls laser pulses and sends them down optical fibers deployed along an actuator arm to the read/write head. There, lenses of less than 350 µm focus the beam while servo-driven micromirrors direct the beam to locations on the disk.

Lighter substrate

The combination permits adjustments between tracks without moving the actuator arm, providing the potential for densities in excess of 100,000 tracks per inch. According to Quinta, the medium, while similar in construction to conventional Winchester types, can use a lighter plastic substrate and employs an amorphous rare-earth transitional material as the magnetic structure. The material and its amorphous character make it less likely to be affected by the superparamagnetic limit.

Phil Montero, Quinta's manager of corporate marketing and communications, told Photonics Spectra that most of the technical details would have to remain proprietary for legal and patent reasons.

Photonics Spectra was, however, able to discover some details about the lenses, which are supplied by Geltech of Orlando, Fla. Michael S. Toro, Geltech's vice president of sales and marketing, indicated that the lenses are diffraction-limited aspheres molded from a special glass made by Corning. The lenses are pressed from diamond-turned molds and require no postpolishing. Because of nondisclosure agreements with Quinta, Toro was unable to supply more detailed information.

Montero described the switch as a "fixed optics module" that controls delivery of a diode laser down either single or multiple fibers to a microlens, which focuses the beam to a very narrow spot size. Position of the beam-produced spot on the disk is controlled by micromachined mirrors designed by an in-house team and farmed out for fabrication.

The trick, Montero said, was combining miniature optics and fiber to produce a low head weight with Winchester mechanics to match magnetics speed. The far-field optical scheme also provides a 15-µm depth of field, twice the head's flying height, which allows a large margin of error. In addition, the medium supports vertical, rather than horizontal recording, while overlapping of spots offers even greater densities through so-called crescent recording.

Montero said that the product is targeted at the large data storage user, a market with an appetite for capacity and a thirst for lower costs. James Porter, president of Disk/ Trend -- the Mountain View, Calif., firm that tracks the industry -- told Photonics Spectra that the price per megabyte of data storage has dropped from $11.54 in 1988 to 10 cents in 1997 and could be reduced by 10 times that by 2000.

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