DVD Burning Bits.com - Doubling the data storage capacity of recordable DVD to 8.5 Gbyte

Abstract
Philips and MKM have developed a technology for single-sided double layer DVD+R recordable discs, which will nearly double the data storage capacity of DVD+R discs. Both layers of the disc are accessed from the same side, meaning there is no need to turn the disc over to take advantage of the additional capacity. Consumers will be able to record up to 8.5 Gbyte of data, up to 16 hours of video on a single double layer disc. The technology was demonstrated at CEATEC Japan in October of this year, the technical specifications and format book are expected before the end of the year and double layer DVD+R products are expect to reach the consumer market in 2004.

Introduction
The DVD+R/+RW format is becoming increasingly popular for digital video recording and PC data-storage applications. From the beginning, the DVD+R/+RW format was designed with backward compatibility in mind so as to allow playback in existing DVD players and DVD read only drives.
Currently, DVD+R/+RW discs allow users to store up to 4.7 Gbyte of information on a single-sided 12-cm disc. Efforts to increase storage capacity on a single-sided disc were undertaken with the same eye toward compatibility with existing players and read only drives. Because the DVD read-only standard already features double layer media, the natural way to increase DVD+R storage capacity is to add an extra storage layer that can be accessed from the same side of the disc. Philips and MKM have developed the technology for double layer DVD+R discs compatible with the double layer DVD-ROM standard.

Consumer Benefits
The primary benefits for consumers are nearly a doubling of recording time on a single disc while remaining compatible with DVD video players and DVD-ROM drives. Consumers will be able to record up to 8.5 Gbyte of data, up to 16 hours of video without having to turn over the disc. Table 1 summarizes the main features of existing DVD media and the newly developed double layer DVD+R disc.

Table 1: Overview of storage capacity and recording time for different DVD media. The newly developed double layer DVD+R features almost doubled recording capacity and recording time compared to the single layer DVD+R and DVD+RW media.

Overcoming Technological Challenges
Philips and MKM focused their research on the development of double layer organic dye media, recording technology, and logical format development. The objective was to stay as close as possible to existing DVD-ROM double layer and DVD+R formats and technologies.
One challenge to overcome was to minimize the interference between data recorded in the first recording layer (Figure 1: L0) while recording on the second layer (L1). In addition, the first layer requires the use of a transparent thin metal layer that should still have enough cooling power allowing controlled recording of data in the first layer.

Philips in cooperation with MKM were able to reach major innovations in the materials used for the spacer layer, the transparent metal reflector, and recording layers while remaining within the boundaries set by the requirements for backwards compatibility with double layer DVD-ROM.

How it Works
Dye-based optical recording
Double layer DVD+R discs uses a thin organic dye film to store data. The recording principle is based on irreversibly modifying the dye�s physical and chemical structure, induced by heating with a focused laser beam. The recorded marks have different optical properties than their unmodified surroundings, giving the same read-out signals as read-only discs, based on the length of the recorded marks and unmodified spaces between them.

The double layer DVD+R disc
Adding an additional storage layer to DVD+R that can be accessed from the same side of the disc provided challenging issues in organic dye based optical recording. A cross-section of a double layer DVD+R disc is depicted in figure 1.
The transmission of the first recording layer (L0) should be larger than 50% to allow for read-out and recording of the second recording layer (L1). In the first layer, we use a thin silver-alloy layer as reflector material. The reflection of the first layer should be at least 18% to ensure compatibility with the double layer DVD-ROM standard. To realize such high transmission and reflection values, the dye material and deposition, groove shapes, and silver deposition are optimised.
The second recording layer should have a high reflection (>50%) and high power sensitivity, because the first recording layer absorbs and reflects part of the incoming light. We have optimised the groove shape and recording layer to achieve this. Effectively, at least 18% reflection of the second layer is required.
The transparent spacer layer is about 55 �m thick and serves to physically separate the two recording layers. The laser beam can easily be focused on either of the two layers by adjusting the position of the objective lens.
Video recording on double layer DVD+R
Video recording on both layers of a double layer DVD+R has been demonstrated. The disc has been recorded on a Philips� prototype double layer drive. The recorded disc can be played back on existing DVD video players and DVD-ROM drives. The layer-jump in the video stream is handled smoothly by the existing drives.

The double layer DVD+R format
Table 2 summarizes the main physical parameters achieved in the DVD+R double layer system. The physical format of double layer DVD+R is developed to achieve the highest possible compatibility with the existing DVD9 and DVD+R formats. The wobble-addressing scheme is the same as in DVD+R and DVD+RW and allows the same loss less linking accuracy as is achieved in both these formats. The wobble period reflects the 10% longer bit length of double layer DVD media compared to single layer media. The channel bit length of 146 nm is the same as in double layer DVD-ROM (DVD9), which was then chosen to improve system margins. The electrical signals derived from a recorded double layer DVD+R disc meet the same requirements as those for double layer DVD-ROM discs. This ensures maximum compatibility with existing legacy drives.

Conclusions
We have demonstrated the feasibility of double layer DVD+R. Recording on both layers is successful and are accessed from the same side. This will give the consumer the benefit of recording up to 8.5 Gbyte of data, up to 16 hours of recording without the need to turn over the disc.

The technology was demonstrated at CEATEC Japan in October of this year, the technical specifications and format book are expected before the end of the year and double layer DVD+R products are expect to reach the consumer market in 2004.

>a href="http://www.research.philips.com/Assets/Downloadablefile/double-layer_dvdr-2617.pdf">Download the white paper