Classic Computer Magazine Archive CREATIVE COMPUTING VOL. 11, NO. 9 / SEPTEMBER 1985 / PAGE 43

Let there be light. (Optical storage devices) Timothy Onosko.

Thomas Edison invented the phonograph in 1877. Using tin foil as a recording medium, it was the first mechanical device developed to store sound information. In Germany, during World War II, the Magnetophon company introduced magnetic tape recording, a vast improvement over the previous magnetic storage method, wire recording. Also during the 1930s, the first optical recording system--soundtracks for motion pictures--appeared.

These recording techniques are still in use today, and each has evolved in its own way. Ironically, the oldest--the mechanical phonograph record--has changed the least. Even though new manufacturing methods and materials have increased frequency response and diminished surface noise, the phonograph record is still limited to storing only audio signals, subject to wear, and easily damaged. Magnetic recording, on the other hand, has flourished and, because it can record and reproduce information other than sound, has become a vital part of most modern technologies, including video recording and computing.

Optical recording, until relatively recently (the late 1970s and early 1980s) has existed as the stepchild of these other storage techniques. Having left behind the limitations of their origin--movie soundtracks--the future of optical media is best represented by two consumer products, laser videodiscs and compact audio discs.

Recording technologies are defined by their ability to store large amounts of information (capacity and density, which is measured as the capacity per square inch or centimeter of the surface of the medium) and to capture and play back information at a high rate of speed (resolution). Video requires greater capacity and resolution than audio, for instance.

In a mechanical device like the phonograph, there are two primary limitations: The width of an individual groove in a spiral track (capacity) and the ability of recording and playback devices to make and detect the variations on the wall of the groove (resolution). With magnetic devices--tape recorders and disk storage machines for computers--the limitations are similar. Each particle of the magnetic material that coats the surface of a tape or disk contributes to the ultimate capacity of the medium. And, record/playback heads must be able to focus magnetic energy on an ever-smaller spot to take advantage of this capacity.

Magnetic techniques continue to improve, however, in terms of both capacity and resolution. One promising development in magnetic storage is the use of new recording media. While tapes and disks have traditionally been coated with a very fine powder of metal oxide or metal particles, new materials have instead a thin film surface layer of metal molecules only a few atoms thick. This is accomplished by breaking down metals with a bombardment of high-energy electrons, and then depositing the material on a surface inside a vacuum. These so-called metal evaporation processes (known as "sputtering" and vacuum deposition) have already been demonstrated by Japanese tape companies, and promise to be the basis for new video recorders, digital audio tape recorders, very high density computer floppy disks, and video floppy disk still cameras.

The optical media, however, point the way for the most significant advances in recording for the remainder of this century and beyond. Simply put, optical technologies offer enormous capacities and extremely high resolution, making them ideal for every purpose, from audio recording to information storage on machines not yet invented.

A look at optical recording offers an excellent opportunity to trace the way technologies contribute to one another's development. For optical recording to become practical, other new technologies first had to be invented. The most important of these was the laser. Its ability to generate an extremely fine beam of light makes optical recording possible. Because the physical dimensions involved in optical recording are extremely small (measurements of a micron--a millionth of a meter--and less are common), a means of visually inspecting the recordings was necessary. Without the scanning electron microscope, this would be impossible.

To make copies of optical recordings, the microscopic manufacturing techniques learned from large-scale integrated circuits were required. Finally, to assure that the information coming from an optical recording--particularly digital information--was free of errors, the software technology of error correction was needed. Optical recording relies on all of these, and one exciting new development works partially in conjunction with certain magnetic principles, as well.

Currently, optical recording research centers on three different kinds of media: Prerecorded (read-only), recordable (write once but read only afterwards) and erasable (repeatable full cycles of write, read and erase). The laser videodisc (LV) and audio compact disk (CD) are both examples of read-only discs. They work in almost exactly the same manner, with one major difference. The laser videodisc reproduces an analog signal, and the CD stores and plays back digital information.

The laser videodisc was developed during the early 1970s, at first separately by MCA, the giant entertainment conglomerate, and Philips of the Netherlands, a large electrical and electronics corporation. The two eventually traded patents and jointly finished developmental work on the videodisc. Later, when the manufacturing of prerecorded discs ran into severe technical problems, IBM, which had been conducting its own optical research, joined the other two companies in a new corporation, known as DiscoVision Associates. In the end, though, all three companies pulled out of the U.S. venture and left the videodisc, all but dead, to Pioneer of Japan, which has since done a remarkable job in correcting many of the technical and manufacturing mistakes of the past.

How the Laser Videodisc Works

Here is how the laser videodisc works. The shiny surface of the 12" (30-centimeter) videodisc is encoded with tiny--a little more than a micron wide--pits or surface deformities arranged in a spiral track. The length of each pit and the distance between one pit and another determines the information. In this case, it is a single signal that contains the video, color data and audio. (Color and audio are buried in the signal as subcarriers.)

This encoded video signal also includes other information such as frame numbers and running time. The data are part of the vertical interval, the unused lines of a video picture you can see when a television set is not adjusted properly and the image "rolls." Some of these lines are used for "closed captioning" (numbers and words that can be superimposed on the screen for the benefit of the hearing impaired) and for VITS, a reference signal used by certain TV receivers to automatically adjust color, hue, and tint.

The surface on which the pits are etched is sealed with a thick coating of optically clear plastic, called a scuff coat, which then becomes the first surface of the disc, the only one you can actually touch.

To read the disc, a beam of light originates from a very low-powered laser (typically less than 5 milliwatts and about as bright as a common flashlight) and travels to the inside surface of the disc by a system of lenses, mirrors, and prisms. When the beam is reflected by one of the pits, its polarity changes. It travels back along the original path to a special prism (called a Wollaston prism) that can differentiate between the light going to the disc and the light--now carrying information--reflected by the surface. The laser beam then strikes a photosensitive electronic element that converts it to a video signal.

While this process seems simple, it is actually quite complex and, in practice, demands extreme precision. In a videodisc player, for instance, the beam is actually split into several parts, some of which are used to keep the main reading beam centered on the proper track. It is also necessary to mount the objective, or focusing lens, inside an electrical servo mechanism so that it can precisely follow-focus the inside surface. This lens moves up and down to adjust for errors in flatness and accommodate disc warpage. And, of course, the disc must be perfectly centered--the spindle hole placed exactly in the center of the disc--so that the optical system can follow the spiral track while it rotates.

If a mechanical phonograph record is either warped or not properly centered, the sound comes out with an annoying "wowing." (It is distorted by time errors.) Nonetheless, the record does play; it makes sounds. Videodisc players contain mechanical devices (moving mirrors and lenses) and electronic circuitry to correct for such time distortion. Too much warpage or a grossly off-center track, however, will cause an optical record not to play at all.

Other common problems in optical records are caused by dust and dirt trapped between the surface and the scuff coat (a piece of common house dust can be several times wider than a track on the disc) and malformed pits. A videodisc player sometimes cannot properly follow the narrow spiral track, leading to visual distortion known as crosstalk, in which the laser beam reads part of the tracks adjacent to the one it is trying to play.

As originally designed, laser videodiscs can be recorded in one of two formats. The first, called standard play or CAV (for constant angular velocity) can contain up to 30 minutes of NTSC (U.S. standard) video in motion or up to 54,000 still frames per side. The CAV discs rotate at a constant speed of 1800 RPM, which corresponds to 30 times per second, the exact frame rate of NTSC standard television. So, for each rotation of the videodisc, one single TV frame is reproduced.

The second videodisc format is called extended play or CLV (for constant linear velocity). CLV discs rotate at variable rates of speed, depending on which part of the disc is being read. At the beginning of a disc (the inside tracks, nearest to the center hole), it spins at 1800 RPM and gradually slows until, at the end (the tracks nearest the edge) it is rotating at a third of that rate, or 600 RPM. The reason? each video frame on a CLV disc occupies the same length of spiral track. The disc begins with approximately one frame per rotation, but as the diameter increases, one rotation equals three frames. This effectively doubles the playing time (60 minutes per side) while sacrificing some of the unique features of the CAV disc, such as still frame, slow motion, and reverse play.

The videodisc is an important model for all present and most future optical technologies. Most current optical methods are improvements on or refinements of this technology.

Compact Discs and CD-ROM

Compact discs, for example, are really miniature videodiscs, 4.7" (120 mm) in diameter, that reproduce digital audio instead of analog video. All CDs are CLV format discs, since there would be no benefit to an audio "still frame" or slow motion playback. They rotate at between 500 RPM (at the inside) and 200 RPM (outside). The maximum playing time is about 70 minutes per side.

The digital information contained on the discs is read out in serial fashion, one bit after the other, at a rate of about two million bits per second. Inside the CD player, electronic digital-to-analog circuitry turns the data into sound. Because CDs are subject to the same kinds of problems as videodiscs -- including warpage, surface defects, and crosstalk -- the integrity of the information is protected by redundant recording and a software error correction technique known as the Reed Solomon Cross Interleave Code (CIRC).

As of this writing, no double-sided compact discs have been pressed for consumer consumption. A common manufacturing practice is press the CD with the same information on both sales. After both sides are checked for errors, the side with the highest rate is chosen for imprinting with the label, rendering it useless.

The advantage of both LV and CD discs is that they are suitable media for storing virtually any kind of information. Laser videodiscs can contain digital audio, and, in fact, a new formal devised by Pioneer Laserdisc Corporation puts two digital audio tracks in the unused space between video tracks. Likewise, compact disks with full video and computer graphics have been demonstrated by Sony. The design specifications of the compact disc designate several megabytes as user bits, currently allocated for text (on-screen video "liner notes," etc.) and video graphics. Forthcoming new CD players will have video outputs for connection to a monitor or TV set, in addition to standard audio outputs.

Since compact discs and laser videodiscs have such enormous capacity and can transfer information at very high speeds, it seemed obvious that someone would suggest their use as a computer medium. In 1984, Sony and Philips proposed the cD-ROM (For Compact Disc--Read Only Memory), and standardized on a formal that organizes the 540 million bytes (or characters) contained on the disc into 2000-byte blocks. not long afterwards, Pioneer suggested the laser videodisc for a similar purpose, naming it the LV-ROM (for LaserVision ROM). The LV-ROM, claims Pioneer, has a capacity of over 1 gigabyte (1 billion bytes of information), when played on a specially modified videodisc player.

It is widely believed that the CD-ROM will have enormous impact on all types of computing. Several startup companies, including Cytation, Inc., a San Francisco group with ties to the consumer electronics industry, are involved in developing collections of data appropriate to the gigantic capacity of the CD-ROM. Any large database in existence seems to be a likely candidate for pressing on a CD. Most often mentioned are newspaper and magazine files (an entire year of the Wall Street Journal or the New York Times on a single side?), goverment records including patent and copyright files, catalogs (the Library of Congress card catalog), volumes of legal proceedings, and, of course, encyclopedias (the all-time favorite "blue-sky" prediction of optical media proponents).

It is obvious that the ideal information for CD-ROM is already available via online database services. Information services like Nexis and Lexis--the literature and legal search systems of Mead Data--could conceivably be threatened by the CD-ROM publishers. Or, the online services might themselves become suppliers of CD-ROMs. In any case, most online services will retain a slight edge in their ability to update their records instantl.

Still, the vast majority of information sold by these services are old files which require few changes. A CD-ROM issued each month could easily serve the needs of many present users. Compact discs are inexpensive; mastering one costs less than $5000, and each copy costs less than $5. These prices are very low when compared to paper publishing.

Unfortunately, the business of applying compact disc technology to computers is not as simple as plugging a CD player into a PC. One of the greatest hurdles is standardization. Even though the information on CD-ROMs is organized in a standard way, a standard hardware interface between the players and personal computers has yet to emerge. A hardware interface standard is essential, because audio CD players are designed to transfer information serially, while most personal computers use a parallel scheme for communicating with disk drives. Settling on a standard hardware interface will also allow the creation of optical disk operating system software for CD-ROMs.

The SCSI (for Small Computer Systems Interface, pronounced, oddly enough, "scuzzy") is one, though not the only, proposal for such standardization. It is based on the SASI (the first two initials of which stand for Shuggart Associates) interface already in use in PCs for hard disks. Other proposals include the IEEE-488 bus and high speed RS-232 serial transfer.

Manufacturers of CD-ROM players are quoting transfer rates from disk of about 153,000 bytes per second--not quite as fast as an audio CD, but fast enough for even the most demanding information applications. Access between the 2000-byte blocks of information is claimed to be 50 milliseconds, with the longest time required to go between widely spaced blocks being 1.5 seconds.

Most Japanese manufacturers, including Hitachi, have expressed interest in the CD-ROM system. In the United States, 3M Corporation and Digital Equipment Corporation also have plans for the disk, and IBM is rumored to have a similar interest. Sony was the first to demonstrate a CD-ROM system in operation with an IBM PC in fall, 1984. A sample CD-ROM containing several hundred graphic screens and a database of Olympic sports records hs been circulating among hardware and software developers throughout 1985.

The expected manufacturer's price for a CD-ROM player (minus the interface and software) should eventually be $250 to $300. A complete subsystem for a personal computer should retail for about $1000 to $1500. Considering Sony's recent breakthroughs in price and miniaturization of players (notably its Walkman-style D-5 CD player), this goal seems reasonable. All indications are that CD-ROM players should begin showing up in the United States in the last quarter of 1985 or the beginning of 1986.

DRAW and WORM Research

While compact discs cannot (yet) be recorded on the same machines on which they are played, recordable optical discs have existed for several years either as laboratory projects or in limited commercial production. This type of disc is known as DRAW (For Direct Read After Write) and WORM (Write Once, Read Mainly). Like other optical devices, it can be designed to record audio, video, or data.

These write-once systems are basically adaptations of the original laser videodisc scheme, with an important addition. They use a higher-powered laser to write the information on a material. Pits are formed by either vaporizing or physically deforming the surface of the disc. Another method involves changing the structure of certain unique chemicals.

Originally, DRAW research centered around the first kind of process, in which the pits were burned into the reflective surface. The videodiscs themselves were constructed from something often referred to as a "tellurium-air sandwich." Tellurium is a metal used as a component of blasting caps, produced mainly by the United States, Canada, Peru, and, not surprisingly, Japan. When hit by laser light, the tellurium destroys a tiny portion of the surface around it, forming a pit. Discs produced in this manner can be played on a standard LV disc player.

Phase change DRAW materials work very differently. The disc surface is coated with a compound of rare earth metal materials that can go from a crystalline to an amorphous chemical state and, in doing so, alter its reflective properties. When the material is crystalline, it is highly reflective. In its amorphous state, it is absorptive, or non-reflective. DRAW discs are written and read with high and low-powered laser beams. High-powered beams cause the phase change, low-powered beams read the information already recorded. Most phase change systems are irreversible, so they cannot be accidentally erased. While manufacturers claim long shelf life, the longevity of a phase change is still questioned by some scientists.

Some erasable optical media also use phase-change principles. Energy Conversion Devices, of Troy, MI, is an innovative company which has devised a reversible (or erasable) phase change material and has licensed its use to Hitachi and Matshushita in Japan. Hitachi has also announced another erasable material which is a chemical compound of tin, tellurium, and selenium.

If there is a bet to be made on the future of optical storage media, though, most industry analysts would place it on an exotic and, until recently, little known process known as magneto-optical recording. As its name implies, magneto-optical techniques rely on both magnetic and optical sciences. The major keys to this recording process are two well-known physical phenomena, the Curie effect and the Faraday effect.

The Curie effect involves raising a magnetic material to a specific temperature called the Curie point. At this temperature, and while exposed to a magnetic field, the material becomes magnetized. The area raised to the Curie point can be smaller than the magnetic field, however. In other words, the magnetic field being created by a recording head can be several times larger than the spot on the material being recorded.

The density of magnetic records is determined not only by the size of magnetic particles, but also by the ability of the recording head--essentially a coil--to focus the energy. The Curie effect allows this concentration of energy to be determined by te diameter of a laser beam used to heat the surface, not the recording head. In practice, making a magneto-optical recording involves focusing the laser to a spot a micron or so in diameter, then magnetizing the surface with a relatively large magnetic head that does not even need to contact the disc. Because only this small spot is heated to its Curie point, it alone is magnetized. The remainder of the particles on the surface are left unaffected.

Usually, the same magnetic head is used for both playback and recording. But if the magnetized spot is much smaller than the recording head, how can it be read? This is where the second important phenomenon comes in.

British scientist Sir Michael Faraday found that when light is reflected from a magnetic surface it is changed. Light waves are either random or polarized in a particular direction. To better understand this, experiment by crossing the lenses of a pair of broken Polaroid sunglasses or, better still, an old pair of 3-D movie glasses. (Simple explanations of polarity can also be found in most high school physics textbooks.) When light is reflected back from a magnetized surface, its polarity changes--it is rotated--ever so slightly.

This rotation is nearly undetectable, from about 0.05 (five hundredths) to 0.3 (three tenths) of a single degree. It is enough, however, to be read by an optical and electronic device.

Again a product of continued technological advancement, magneto-optical recording is attractive because capacities meet or exceed those of the LV or CD disc. Magnetic materials are familiar to researchers, and a magneto-optical disc can be recorded, played back, erased, and recorded again without practical limit. This is truly a recording technique for the next century, although it is almost certain to begin its impact before the end of this decade.

In the United States, 3M Corporation and IBM are developing magneto-optical discs, with AT&T believed to be hovering in the wings. In Japan, the research is almost feverish and is centered at KDD, a well-known developer of telecommunications equipment. T D K Corporation, however, with its deep understanding of magnetic materials is actively pursuing inexpensive magneto-optical optical materials and recently showed its first samples of 12" discs to the press. A Sony project, lead by Dr. Senri Miyaoka, the inventor of the Trinitron picture tube, might yield a magneto-optical audio or videodisc player by the end of 1985.

While there is definitely a laser in the future of almost every consumer of electronic and technical goods, one more issue looms.

Where Do We Go Next?

Recording has gone from the mechanical cylinder, to mechanical disc, to magnetic tape, to magnetic disk, to optical disk, and finally, to the magneto-optical disc. Does it stop there? If not, where do we go next?

Drexler Technology of Mountainview, CA, says the next move is a credit card-sized piece of plastic striped with its propriety optical recording medium called Drexon. This material, which begins as silver-based and photosensitive, is specially processed to take on a shiny appearance. Information can be printed on the card in the form of microscopic spots read with a low-power laser. A slightly higher-powered beam, however, can also write information by burning through the reflective surface to reveal a black, absorptive layer underneath.

The Drexon LaserCard, which costs about $1.50 in production quantities, can currently store up to 2 million bytes of information, the equivalent of about three printed books. Recently, the card made headlines when it was adopted for use by blue cross of Maryland, whose members will carry their medical information on "LifeCards" as they have been dubbed. While a Drexon card can't yet compete with the capacities of the laser videodisc or CD, the company says it will increase the capacity to perhaps 20 million bytes by decreasing the size of the spots. (Drexler seems to fit to the task. Its products, other than the Drexon card, serve the micro-electronics manufacturing industry.)

Already, Drexler has issued 20 technology licenses to companies around the world who are interested in building readers and recorders for the cards and exploiting their potential. Of there, there are four licensees in the United States: Blue Cross of Maryland, Wang Laboratories, NCR Corporation, and Honeywell, most of whom are tight-lipped about their intentions.

Drexler has granted 11 licenses to Japanese companies, almost all of whom make computer, electronic, or consumer products: Toshiba, Matsushita (Panasonic and Technics brands in the U.S.), Canon, Fujitsu, Omron, Computer Services Corporation (Japan's largest vendor of computer software), Gakken (a book, magazine, and educational publisher), Logitec (which has demonstrated a Drexon card-based video game), Nippon Coin Company (vending machines), Olympus, and Sharp. Japan's Dempa Shimbun, the electronics industry trade newspaper, says Matsushita plans to introduce a Drexon card reader late in 1985 or early in 1986, priced between $150 and $200.

The optical card may be propelled by Japan's current fascination with credit cards, which have only recently become of interest to the masses. The credit card has given rise to credit card-sized calculators and microprocessor-based "debit cards" (both from Casino). In 1984, green public telephones that accept magnetic cards (sold in various denominations at candy counters and cigarette stands) made their appearance on the streets of Tokyo. The new Washington Shinjuku Hotel uses magnetic-striped cards as room keys. Their size? Credit card, of course.

One of the most potent new industrial alliances with intentions for developing an optical card is TMP, Tokyo Magetic Printing. It was formed last year as a joint venture of Toppan Printing (Japan's largest) and TDK Corporation. Although its name says magnetic, the company's future is probably optical. TDK is rapidly becoming more familiar with optical, high-density magnetic and magneto-optical storage techniques, while Toppan is already well-advanced in its own optical research project, mass replication of holograms. The potential of holography for mass information storage has barely been explored, but it could eventually lead to recording densities and resolutions far, far beyond those of today's media.

The idea of using a card, instead of a tape or disc isn't just a gimmick. An optical card is a far more elegant device for storing information. It does not move, so it does not need a problematic center hole, like a disc. Instead of spinning, a scanning laser bean illuminates the surface. And, since it is usually pressed against a window when read or played back, warpage is not a problem. Instead of a pile of floppy discs, videocassettes, videodiscs, or compact discs, the entire library, filing cabinet, video, and record collection of a home or office might one day be contained in a small envelope, of--for those with the hording instinct--a shoebox.

In any case, the gods of modern technology have spoken. They have said: "Let there be light . . ."