From Double Layers to Blue Lasers

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By: Rich D 9Ambrise R ecordable DVD has fol- lowed its read-only predecessor to become one of the recent success stories in data storage. Sales of DVD recorders of all for- mats are expected to surpass 11 million units over the next 18 months according to IDC. But just as the market for first-generation DVD recorders is taking off, new technology developments will boost optical technolo- gy to 100 gigabytes or more per disc in the next three years.

A Truce in the Format Wars: DVD-R/RW A key factor in the growth of recordable DVD technology is that the market confusion over multiple recordable for- mats 4DVD-R/-RW, DVD+R/+RW and DVD- RAM 4 has largely been resolved. New generations of multifunction DVD drives that support all of the popu- lar DVD media formats have made the competing formats almost irrelevant. Multi- function drives are grouped into three categories based on their functionality: DVD Multi drives can write to DVD-R, DVD-RW and DVD-RAM media; DVD Super Combo drives support DVD-R, -RW, +R and +RW media; and DVD Super Multi drives can handle all five media formats, -R, -RW, +R, +RW and RAM.

Additionally, these drives are typically downward-compa- tible with CD-R and CD-RW recording ... more. less.

capability. Double Layer DVD+R/+RW While much of the attention on the DVD market has focused on the major capaci- ty improvements enabled with the emerging blue laser technology, standard DVD technology will soon received a boost from dou- ble-layer media that increas- es per-disc capacity from 4.7 to 8.5 gigabytes. Double- layer media is widely used for DVD-ROM/DVD video applications as a convenient way to extend capacity with- out requiring the disk to be turned over, and this techno- logy is making its way into recordable DVD media and drives. The first double-layer recordable DVD product will be DVD+R media. Composition of a Double Layer DVD Disc As shown in Figure 1, dou- ble-layer media is composed of two dye-based recording layers. The semi-transparent metal reflector layer is www.wwpi.com Computer Technology Review ® AWestWorld Productions, Inc. Publication MAY2004 VOLUME XXIVNumber 5 THE STANDARD OF EXCELLENCE FOR STORAGE TECHNOLOGY INFORMATION DVD Update: From Double Layers to Blue Lasers DVD Update: required between the two recording layers to ensure that the laser can properly read back data from layer 0. However, the addition of this layer and the extra distance from the laser to layer 1 requires a higher-powered laser diode than those used in single-layer designs. Still, only half of the laser power is available to record on layer 1. To compensate for the lower available power, the media is designed with higher reflectance, above 50 percent. Since the DVD standard requires media of at least 18 percent reflectance, the dou- ble-layer design offers enough headroom to compensate for the extra distance the laser beam needs to travel. Double-layer recording also presents another issue not present in single-layer DVD: how to address two physical layers as one logical volume. The problem occurs when only part of the disc is recorded. When reading the disc, the laser can jump from layer 0 to layer 1 when seek- ing data. If nothing has been recorded on the second layer, the laser has no location ref- erence point and becomes lost. To eliminate this prob- lem the disc needs to be cde- iced, d a process similar in concept to hard disk format- ting. When a double-layer DVD disc is de-iced, null data is written on any unrecorded sections to com- pletely fill the disc, enabling the laser to jump layers and navigate the entire disc with- out getting lost. Kind of Blue: Blu-ray and HD-DVD Beyond double-layer media, the next milestone in DVD development is the new class of blue violet laser-based products. Blue laser technol- ogy combines a shorter wavelength laser diode with other media and drive improvements to boost capacity by a factor of four or five over standard DVD products. As with first-generation DVD products, the blue laser class is evolving with two main competing formats: Blu-ray Disc and HD-DVD. Two other high capacity for- mats 3 Enhanced Versatile Disc and Forward Versatile Disc 3 have been developed bygovernment-related research projects in China and Taiwan respectively for those domestic markets. Neither the EVD nor FVD is likely to have any market impact outside the home countries. At first glance the Blu- ray Disc (BD) and HD-DVD competition for marketshare is reminiscent of the recent DVD-R/-RW vs. DVD+R/ +RW contest in the standard recordable DVD market. As previously mentioned, that issue has been largely resolved with multi-function drives, allowing the formats to coexist peacefully. The -R and +R formats were also similar enough that once discs were recorded in either format, they could be played back on virtually any DVD drive. That is not the case with BD and HD-DVD. These two high-capacity for- mats have different capaci- ties and different media designs that will preclude post-recordingplayback compatibility. HD-DVD Overview The HD-DVD format can best be viewed as an exten- sion of the current 4.7 GB DVD recordable technology. It was developed by Toshiba and NEC and has been pro- posed as the high-definition standard to the DVD Forum. This format incorporates blue laser technology and tighter track density to pro- duce a capacity of 20 GB per side using single-layer media. An HD-DVD ROM version supports a capacity of 15 GB. HD-DVD uses the same media structure as DVD with the recording layer residing between two 0.6mm sub- strates that are bonded back- to-back. This will enable Number of Recording Layers BD BD HD-DVD HD-DVD SingleDoubleSingleDouble Hours of High Definition Video 2+4 - 524 Capacity 25GB 25GB 50GB 50GB 20GB 20GB 40GB 40GB Laser wavelength 405nm405nm405nm405nm Numerical aperture (NA) 0.85 0.85 0.85 0.85 0.65 0.65 0.65 0.65 Protecton layer 0.1mm0.1mm0.6mm0.6mm Data transfer rate 36Mbps 36Mbps 36Mbps 36Mbps 36Mbps 36Mbps 36Mbps 36Mbps Table 1: Comparison of rewritable Blu-ray and HD-DVD formats Figure 1 same laser beam by refocusing on second layer media manufacturers to use the same manufacturing processes and production lines with only minor modifi- cations to produce HD media, meaning that, at least initially, recordable HD-DVD media will be less expensive than Blu-ray Disc media, which is built around a completely different design. HD-DVD drives and media support the Universal Disc Format (UDF) enhancing compatibi- lity with existing systems and applications that support UDF on DVD platforms. By using a lens with the same numerical aperture as current DVD drives, the HD- DVD format ensures back- ward-read compatibility with current DVD and even CD media utilizing its simplified design. Blu-Ray Disc Overview Blu-ray Disc is the high- capacity DVD format devel- oped by a consortium of com- panies, the Blu-ray Founders Group, consisting of Hitachi- Maxell, LG Electronics, Matsushita Electric, Mitsu- bishi Electric, Pioneer, Philips Samsung, Sony, Sharp, TDK and Columbia Tri-Star.Additionally, Hewlett-Packard and Dell have endorsed BD as the standard for high-capacity DVD recordable computer drives. Unlike the HD-DVD for- mat, BD technology was cre- ated from scratch, and as such it provides certain capacity and technical advantages. The BD format specifies a single-sided, sin- gle-layer capacity of 23.3 to 27 gigabytes per disc and a data transfer rate of 36 Megabits per second. The Blu-ray technology is a departure from previous CD and DVD optical record- ing systems. In those cases the recordable versions of the technology were extensions of original ROM designs. Instead, BD was created first as a recordable format and the BD-ROM standard is a subset of the recordable stan- dard. The Blu-ray Disc spec- ification v1.0 provides four formats: BD-ROM: a read-only format developed for prerecorded content BD-R: a write-once for- mat developed for PC data storage BD-RW: a rewritable for- mat developed for PC data storage BD-RE: a rewritable for- mat developed for HDTV recording As with other blue laser for- mats, and like HD-DVD, BD technology utilizes a shorter wavelength, 405 nanometer blue violet laser that, when combined with a higher numerical aperture and tighter track pitch, enables greatly improved bit density on the 120mm disc (Figure 2). But this is where similari- ty ends between BD and HD- DVD formats. BD media is composed of a single 0.1mm substrate topped by a record- ing layer, which in turn is protected by a 0.1mm cover layer with a scratch-resistant hardcoat. This new media design minimizes or eliminates some issues related to the composition of DVD and HD media. With standard DVD media the laser can be split into two beams when it pass- es through a substrate layer. If this split becomes exces- sive, read errors are induced. Second, because the record- ing layer is now closer to the objective lens in the optical assembly of the drive, disc tilt sensitivity is reduced. If the disc is not perfectly flat and perpendicular to the laser axis, the beam can become distorted, a condition known as disc tilt. This con- dition increases or decreases based on the thickness of the cover layer. The blue laser DVD mar- ket is evolving, with high- definition video the corner- stone application driving the market, but data storage applications are likely to be the early winners while the debate over which format to support and copy protection issues are settled by the major studios. In fact, Sony is already shipping Blu-ray video recorders in Japan and is offering its Blu-ray-based Professional Disc for data applications in the U.S. In addition to distributing high-definition movies on ROM media, the BD and HD formats provide adequate data rates for real-time recording of content deliv- ered over broadband connec- tions for both consumer and business applications. Their capacity and low cost make blue laser data drives also well suited for records com- pliance solutions to meet the requirements under Sarbanes- Oxley and the other new gov- ernment regulations. While these new high- capacity formats will likely find broad acceptance in pure data storage applications, the winner of the Blu-ray vs. HD- DVD battle may be deter- mined by which one becomes the dominant ROM format. The read-only versions of the BD and HD formats are not compatible, and it is unlikely that the major studios will decide to distribute their movies on multiple high-defi- nition DVD formats. Among the studios, WarnerBrothers has endorsed the HD-DVD format, while Columbia- TriStar (which is owned by Sony) has committed to the Blu-ray Disc. Regardless of the studio decision, both HD-DVD and Blu-ray manufacturers will produce recordable drives for the data storage market. Expect to see the broad avail- ability of blue laser record- able drives early in 2005 fol- lowed by double-layer ver- sions of both HD-DVD and Blu-ray formats. Rich D 9Ambrise is director of technology at Maxell Corporation of America (Fair Lawn, NJ) www.maxell-data.com Reprinted by permission from the publisher of the May 2004 edition of Computer Technology Review ® . © 2004 WestWorld Productions, Inc. 1.2 mm substrate 0.6 mm substrate 0.1 mm substrate = 780 nm NA = 0.45 = 650 nm NA = 0.6 = 405 nm NA = 0.85 700 MB 4.7 GB 25 GB CDDVDBD Figure 2 Maxell Corporation 22-08 Route 208 Fair Lawn, NJ 07410 Tel: 800-533-2836 www.maxell-data.com Atechnology and marketing leader in premium recordable media products since 1969, Maxell Corporation of America is a full-line manufacturer of digital and analog media products for the data storage, consumer and broadcast markets. Maxell's Data Storage Group serves the needs of cus tomers from the desk- top to the data center with one of the industry's broadest lines of premium digital recording media. Offerings include DLTtape, Super DLTtape, LTO and DDS data cartridges. Maxell is a full line supplier of recordable DVD media, including DVD-R/RW, DVD+R/RW, DVD-RAM, as well as CD- R/RW media. All Maxell data storage products are backed by a limited lifetime warranty and 24 hour toll-free technical support. Additional information on Maxell can be found on the company's website: www.maxell-data.com. CP# 410

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