OTO218_p16_19_Tech_Bluray 15/1/09 15:55 Page 16 technology The Blu-ray Disc was announced in February 2002. In 2005 the Blu-ray Disc Association (BDA) was formed and is now a voluntary membership group open to any organisation “with an interest in creating, upholding and/or promoting the BD formats”.The aim of the BDA is to develop Blu-ray Disc specifications; ensure BD products are manufactured by licensees; promote the wide adoption of BD formats and provide useful information to those interested in supporting BD formats. Blu-ray Disc formats Recordable versions of Blu-ray Discs also exist for use as a backup medium for computer data, as well as other applications. There is therefore a range of different formats based on Blu-ray, just as there are with DVD. G BD-ROM: a read-only disc format that would normally contain movies in HD content. G BD-R: a recordable format for archiving large amounts of data or video. G BD-RE: a rewritable disc format for recording video or data. All BD formats can be made in single-layer (25GB) and dual-layer (50GB) versions. Blu-ray Disc characteristics The developers of the Blu-ray Disc claim that it has the following characteristics: G Broadest industry support from manufacturers and So do you want to content providers. G Lifespan of at least 10 to 15 years due to its high storage capacity. G The strongest, renewable content protection, which includes strict licensing procedures. make Blu-ray Discs? G Cost of manufacture should be within 10% of the cost of DVD manufacture. G Highest capacity, for full-length movies in the There are a number of areas of expertise required to make highest quality HD video on a single disc. G Use of a hard coating, which offers stronger Blu-ray Discs, as Graham Sharpless explains resistance to scratches and fingerprints. IT HAS BEEN 12 YEARS since DVD was What is Blu-ray? Blu-ray versus DVD launched in Japan and 26 years since CD The Blu-ray Disc was developed to succeed DVD, Some of the key differences between Blu-ray and DVD appeared. The much more recent Blu-ray which was seen to be threatened by the launch of are listed in the table below: Disc (BD) represents the latest – possibly the last high-definition television (HDTV) services, – generation of optical disc format. All three which would make standard-definition PARAMETER DVD-ROM BD-ROM discs share a common form factor: they are 12cm (SD) video appear inferior in comparison. Layers 1 2 1 2 in diameter and 1.2mm thick, and are read by a HDTV offers increased picture resolution Number of sides 1 2 1 1 laser diode. But the similarities end there. DVD and a native widescreen format, with Capacity (GB) 4.7 9.4 9 25 50 discs can hold up to 13 times more data than image sizes up to 1080 lines of 1920 Substrate thickness (mm) 0.6 1.1 a CD, and BD can hold the equivalent of pixels. The BD developers, including Cover layer thickness (mm) 0.6 0.1 about 80 CDs. consumer electronic companies such as Laser wavelength (nm) 650 (red) 405 (blue) Disc replicators and their equipment suppliers Sony, Philips and Panasonic, believed that Numerical aperture 0.6 0.85 have faced significant engineering challenges in a disc capacity of over 20GB was needed Track pitch (microns) 0.74 0.32 manufacturing discs of all formats; with each to store a full-length movie in HD video Minimum pit size 400nm 150nm generation these challenges become greater, using MPEG-2. Blu-ray Discs can store Hard coat needed No Yes while at the same time the pressure to reduce 25GB per layer and dual-layer versions are Modulation 8 to 16 8 to 12 the cost of manufacture also increases. also now available. 16 | one to one | January/February 2009 www.oto-online.com OTO218_p16_19_Tech_Bluray 13/1/09 17:27 Page 17 technology Figure 1: Pit geometry compression sided or dual-layer disc software. SPDC does much the same so that Blu-ray (although this is a Discs are not left with an out-of-date technology that beneficial consequence) cannot be updated. but to make it easier to BDs also include a ROM-Mark, which is added read the data on the disc during mastering and prevents physical copying of the when it is not totally flat. disc by remastering from the raw data. (A similar Even with this change, the technique is used for SACD discs.) tolerance to disc tilt has to be tighter than for CDs. In BD manufacturing process the early years, DVD BD requires both mastering and replication processes, replicators often had but these are very different from the processes problems maintaining the involved in DVD replication. The smaller pits, reduced tight tolerances, cover layer and tighter tolerances present significant particularly during the challenges for the disc replicator starting out lifetime of the discs. manufacturing these discs. Blu-ray Discs, as the name suggests, use a BD mastering 405nm blue-violet laser to As with DVD mastering, BD mastering can be divided read the data and an into data formatting, laser beam recording and increased numerical stamper production. But the similarities end there as aperture of 0.85. But these an almost totally new approach is needed to meet the changes were regarded as critical requirements of BD – especially for the first two BDAV insufficient to achieve the required capacity without of these processes. BDAV is a read-only disc format for HD movies and is manufacturing tolerances being too tight.Therefore the The BD formatter/encoder is responsible for the the BD equivalent of DVD-Video. Unlike DVD-Video, cover layer thickness was reduced further. Following AACS content protection (including key handling), error BDAV supports HD video using a choice of three video extensive research by several companies, a cover layer of protection, 8 to 12 modulation and the ROM-Mark. compression codecs (MPEG-2, MPEG-4 AVC/H.264 and 0.1mm was chosen. A single layer BD then comprises a Its output is used to modulate the laser in the laser VC1), and provides advanced graphical and interactive 1.1mm substrate, which does not need to be transparent, beam recorder. features that are far superior to DVD-Video. Like with a 0.1mm cover layer. Figure 2 shows the difference Suppliers of BD-ROM mastering formatters include DVD-Video, BDAV includes region coding, but there between CD, DVD and BD cover layers and laser beams. DCA, whose Titan can format all formats including are only three regions. For dual-layer BDs the cover layer consists of a space BD-ROM, and Eclipse Data’s ESP 7000 Encoder, which There are two HD video formats, 1920 x 1080 and 1280 layer of 0.03mm and a cover layer of 0.07mm with a can also format all discs. x 720. Both of these are in 16:9 widescreen format and semi-reflective layer between. Manufacturing BDs with The very small pit sizes needed for Blu-ray Discs use progressive scan video, at 50 or 60Hz, instead of the cover layers that meet the tight tolerances has proved to require very short wavelength lasers – if conventional interlaced video at 25 or 30Hz used in DVD and broadcast be a major challenge for the developers of the format, as laser beam recording is used – and increased PAL and NTSC TV. well as the equipment suppliers and replicators. numerical aperture. Possible solutions include the use Even 720 lines of video is a significant improvement One particular challenge has been the problem of of a Deep UV (DUV), typically 266nm laser, electron on 480 lines of interlaced video, which is one reason why fingerprints, which can make Blu-ray Discs unplayable, beam recording and dye polymer technologies. HDTV has taken off in the US. However, there is not such because of the thin cover layer.The use of a caddy was But perhaps the most successful technology is Phase an improvement compared with the 576 lines used in regarded as unacceptable so a special hard coat has been Transition Mastering (PTM), developed by Sony and also Europe. At average viewing distances of 2.7m, a developed to prevent fingerprints remaining on the disc. used by Singulus Mastering. PTM uses a 405nm laser (as large-screen display is needed to benefit fully from HD currently used for CD and DVD glass mastering) video and 1080 lines is probably overkill in most homes, Hybrid BDs together with an inorganic substrate that responds to without very large screen sizes. It is possible to combine BD and DVD data on a single the narrower peak of the laser beam to achieve the Even where the full benefit of 1080 lines cannot be dual-layer disc, comprising a semi-reflective BD layer, small pit size of 150nm. Heat is used to record the fully appreciated, the other features of HD video, under the 1.1mm cover layer, and a DVD layer 0.5mm information and changes the phase of the sensitive layer widescreen and progressive scan, plus enhanced graphics below the BD layer. Such discs would play on both DVD from amorphous to crystalline. After developing, a and advanced interactivity, make BDAV more desirable and BD players and so could have the same content as SD mother can be produced directly from the master, so than plain DVD-Video. video on the DVD layer and HD video on the BD layer. reducing the number of stages in creating stampers.