Blu-ray and AOD (Advanced Optical Disc)
HD DVD (High-Density DVD) specs
Optical drives are ready for a massive upgrade . . . out with old, 650 nm wavelength red lasers . . . and in with the new, 405 nm wavelength blue lasers. The blue laser's shorter wavelengths produce more rapid bursts of light, which means the burn marks are smaller and closer together, which means you can cram more data onto a disc !!
It's all about capacity, and with a blue laser, you can pack up to 27 GB on a single side of a disc !!!. With a blue laser, you can fit a 2-hour HDTV movie on a single disc - this is something that red lasers can't even come close to.
Current DVD drives use red lasers (630 to 650 nm), and the "easiest" way to increase areal density is to switch to shorter-wavelength lasers, i.e. blue or violet lasers with wavelengths as low as 400 nm. This will make possible about 15 GB of data per layer per side. To achieve, say, 45 GB of data per side per layer, even shorter, UV range lasers will be needed. Still, compact, reliable, and inexpensive short-wavelength lasers are hard to make.
Three primary blue-laser technologies are available now:
ZnSe lasers brought the first success to the field, but these lasers have problems with relatively short life-time at the required power levels, and also are at the green end of the blue range (460 to 520 nm).
GaN In-doped lasers have already demonstrated high reliability at wavelengths as short as 370 nm and are considered to be a very promising future technology.
SHG (Second-Harmonic Generation) lasers offer the best durability at the moment. This technology either doubles the frequency of a given infrared laser or directly generates a second harmonic in the blue portion of the spectrum. For example, for a given infrared laser with a wavelength of 850 nm, this technology will double the laser light frequency (using a so-called distributed Bragg reflector or DBR), and produce blue light at 425 nm.
Can DVD-RW Discs be keep up with the Advances in Laser Technology ?? this is a major issue. The manufacturing tolerances for 120 mm DVD disks, which are already very high for red lasers, have to be improved dramatically for blue lasers. Blue lasers with smaller bits will make this issue even more complex. Also, servo-control with smaller spot size and higher (potentially) spin rates is another issue.
Blu-ray vs AOD
These two competing formats use a blue laser, instead of the red laser used with traditional DVD's. Both formats make use of blue laser diodes, which is how they are able to have capacities well beyond the 8.5GB of a dual-layer DVD. As the name suggests, the lasers used in the system emit a blue light, which has a shorter wavelength than the red light used in CD and DVD players. This means the size of the laser spot on the disc is smaller and so more data can be fitted in the same space. At around $1,000 per component, blue laser diodes are prohibitively expensive, but several companies are about to enter mass production of the devices which should drive prices under $100.
The Toshiba/NEC format is capable of storing 15GB of data on a single-layer prerecorded disc, or 30GB on a two-layer disc. A rewritable version of the format will store 20GB on single-layer discs and 40GB on two-layer discs, making use of the space between data tracks using a technology called land and groove recording.
The Blu-ray format has a capacity of around 27GB, and seems to have the edge. It is supported by the following nine corporations:
High Definition: The Future of DVD
High Definition DVD Tutorial: Blu-Ray Disc and Advanced Optical Disc
As wonderful a technology that DVD-Video is, what can possibly be better? Well, how about High Definition DVD (HD DVD)? Take everything thatís great about DVD-Video but increase the picture resolution from a standard definition 480i (or enhanced definition 480p if you have a progressive scan DVD player) to a high definition resolution of 720p or 1080i. Yes, high definition as in High Definition Television (HDTV)!
Before we go into the HD DVD format, you should know that a format already exists today that allows playback and recording of HDTV: Digital VHS (D-VHS). For more information on this video tape-based format, read our Digital-VHS Overview. In this article, we focus on the next generation HD DVD format, as an optical disc format. We will discuss the challenges of recording HDTV, the formats under consideration, and backwards compatibility issues with the existing DVD-Video format.
Here we go again. We finally have a great way to record TV and Movies on one DVD disc. Now comes HDTV, and it won't fit !!! Enter HD DVD.
The ability to record to an optical disc format is a wonderful thing. Anyone who has ďburnedĒ a CD-R for data or music knows: random, direct, and quick navigation to the track you want. There is no need to fast forward or rewind a tape.
The ability to record video and audio to an optical disc format like one of the three recordable DVD formats (e.g., DVD-R/RW, DVD+R/RW, and DVD-RAM) is also a wonderful thing. But can you use DVD-R/RW, DVD+R/RW, or DVD-RAM media to record high definition TV? No, these recordable DVD formats cannot do the job because:
Video resolution: The resolution of DVD is 480 horizontal lines of resolution (480i or 480p for progressive scan) compared to high definitionís 720 lines of progressive scan (720p) or 1080 lines of interlaced scan (1080i).
Data rate: The maximum data transfer for DVD is about 10 Mbps, while HDTV requires up to 25 Mbps. There is simply not enough bandwidth to put an HDTV program on a recordable DVD format.
Data capacity: With the higher data rate demanded by HDTV, comes higher data capacity that is required to store all this high definition picture.
A new optical disc format has to be invented to record HDTV. And in this realm, there are two extremes of possible solutions:
Reduce the data rate: One way of recording HDTV is to compress the MPEG-2 digital video information to a lower data rate (i.e., use less digital data). Since the type of compression weíre talking about is lossy, picture quality will degrade somewhat as the compression increases to lower the bit rate. The idea is to compress enough to decrease the bit rate to data capacity levels supported by current technology, while trying to preserve the high definition picture quality to a reasonable standard.
Support the higher data rate and data capacity: Another way of recording HDTV is to record it at the higher data rate required by HDTV, but use brand new technology that would support the higher data rate and higher data capacity. This allows the high definition signal to pass without excessive compression, preserving the detail of the original high definition picture.
Unfortunately, the development of HD DVD has split into two camps. Each with its own proposed format for the next generation HD DVD format. Each camp follows a different approach in terms of the two extremes we discussed above. We will take each of these formats in turn.
Editorís Note: On this web site, we use the term ďHigh Definition DVDĒ or ďHD DVDĒ (with a space in between) to generically refer to the new high definition capable DVD format, without references to any one particular format. In some literature, ďHD-DVDĒ is used. Others use ďHD-DVDĒ (with the dash) refers to the Advanced Optical Disc (AOD) format discussed below.
Blu-Ray Disc Format
The first HD DVD format announced was the Blu-Ray Disc. This format was developed outside of the DVD Forum, a body that supports the successful DVD-Video format. It was formulated by a consortium of nine manufacturers called the ďBlu-Ray Disc FoundersĒ. These companies include Hitachi, LG Electronics, Matsushita Electric Industrial, Pioneer, Royal Philips Electronics, Samsung Electronics, Sharp, Sony, and Thomson.
The idea behind this format is to use a new blue-violet laser technology (hence its name), with a shorter wavelength of 405 nanometers (nm). This translates to a smaller laser beam width, so that the spot that represent a single bit of data can be made smaller, taking up less real estate on the disc surface. This means that more bits (or data) can be crammed onto the standard diameter 12-cm optical disc. The data capacity increases to a maximum of 27 GB for a single-layered Blu-Ray Disc. There are actually three data capacities with a single-layered disc: 23.3 GB, 25 GB, and 27 GB. A dual-layered double-sided Blu-Ray Disc can hold up 46.6 GB, 50 GB, or 54 GB, without ďflippingĒ sides.
Recording is made using phase-change technology, similar to that used in rewriteable recordable DVD formats (DVD-RW, DVD+RW, and DVD-RAM) and CD-RW. MPEG-2 video compression is used. To record the high bandwidth signal of HDTV, Blu-Ray Disc format supports a data transfer rate of up to 36 Mbps. With HDTV broadcast consuming about 25 Mbps, this is plenty fast to record HDTV. Blu-Ray Disc can hold up to 2 hours of HDTV content, or 4 hours of Standard Definition TV (SDTV, 480i). If analog TV broadcast is recorded, up to 16 hours can be held at an average data rate of 3.8 Mbps. For audio, Blu-Ray Disc offers Dolby Digital at a data rate of 32 Kbps - 384 Kbps, or pulse code modulation (PCM) at up to 2.3 Mbps using 16-bit, 20-bit, or 24-bit word lengths. For copy protection, Blu-Ray Disc uses a unique identifier to realize high quality copyright protection functions.
The Blu-Ray Disc uses a cartridge to protect the optical discís surface from dust, scratches, and fingerprints. The cartridge should also make this format more durable. A 23.3-GB capacity Blu-Ray Disc, capable of holding a two-hour high-definition program, sells for about $30 (currently available only in the Japanese market).
Blu-Ray Disc with protective cartridge
Applications for the Blu-Ray Disc format includes pre-recorded high definition movies, home HDTV recording, and computer data storage. The Blu-Ray Disc Founders began licensing this technology in February 2003. Two months later, Sony introduced the worldís first Blu-Ray Disc Recorder, the Sony BDZ-S77 Blu-Ray Disc Recorder, to its Japanese market for the equivalent price of $3,800 U.S.
Sony BDZ-S77 Blu-Ray Disc Recorder ($3,800)
The Blu-ray Disc using blue-violet laser achieves over 2-hour digital high definition video recording on a 12cm diameter CD/DVD size phase change optical disc.
The following Nine leading companies have jointly established the basic specifications for a next generation large capacity optical disc video recording format called ďBlu-ray DiscĒ. Hitachi, Ltd.,LG Electronics Inc., Matsushita Electric Industrial Co., Ltd., Pioneer Corporation, Royal Philips Electronics, Samsung Electronics Co., Ltd.,Sharp Corporation, Sony Corporation, Thomson Multimedia
The Blu-ray Disc enables the recording, rewriting and play back of up to 27 gigabytes (GB) of data on a single sided single layer 12cm CD/DVD size disc using a 405nm blue-violet laser.
By employing a short wavelength blue violet laser, the Blu-ray Disc successfully minimizes its beam spot size by making the numerical aperture (NA) on a field lens that converges the laser 0.85. In addition, by using a disc structure with a 0.1mm optical transmittance protection layer, the Blu-ray Disc diminishes aberration caused by disc tilt. This also allows for disc better readout and an increased recording density. The Blu-ray Discís tracking pitch is reduced to 0.32um, almost half of that of a regular DVD, achieving up to 27 GB high-density recording on a single sided disc.
Because the Blu-ray Disc utilizes global standard ďMPEG-2 Transport StreamĒ compression technology highly compatible with digital broadcasting for video recording, a wide range of content can be recorded. It is possible for the Blu-ray Disc to record digital high definition broadcasting while maintaining high quality and other data simultaneously with video data if they are received together. In addition, the adoption of a unique ID written on a Blu-ray Disc realizes high quality copyright protection functions.
The Blu-ray Disc is a technology platform that can store sound and video while maintaining high quality and also access the stored content in an easy-to-use way. This will be important in the coming broadband era as content distribution becomes increasingly diversified. The nine companies involved in the announcement will respectively develop products that take full advantage of Blu-ray Discís large capacity and high-speed data transfer rate. They are also aiming to further enhance the appeal of the new format through developing a larger capacity, such as over 30GB on a single sided single layer disc and over 50GB on a single sided double layer disc. Adoption of the Blu-ray Disc in a variety of applications including PC data storage and high definition video software is being considered.
Advanced Optical Disc (AOD) Format
Created by Toshiba in conjunction with NEC, the Advanced Optical Disc (AOD) format is relatively new in comparison with the Blu-Ray Disc format. But interestingly enough, the AOD format is already being supported by the DVD Forum, a consortium that includes all nine members of the ďBlu-Ray Disc FoundersĒ. Note that the DVD Forum does not specify standards. It does not design formats, rather it provides support in terms of format compliance verification. Designing formats is under the realm of manufacturers or teams of manufacturers. The AOD format standardization is nearing its completion. The Toshiba-NEC team expects to complete the version 1.0 specifications by second quarter of 2004.
Details are still sketchy for the AOD format. But here is the information that we do have. The AOD format also uses blue laser technology with a 405 nm wavelength and uses a 12-cm optical disc. In terms of data capacity, a single-layered read-only (pre-recorded) disc would hold 15 GB, while a dual-layered disc doubles the capacity to 30 GB. A rewritable (recordable) version holds 20 GB.
So how can the OADís 15 GB data capacity compared with Blu-Ray Discís 23.3 GB still hold the same 2-hour movie in high definition? The answer is higher compression of the video bitstream. Does this mean a loss of resolution of the high definition signal? We donít know yet, but there is talk of OAD using MPEG-4 video encoding. Optimized for handheld and wireless devices, MPEG-4 also offers some additional optimizations over the current widespread MPEG-2 video encoding, to allow for more efficient compression. In other words, MPEG-4 may be able to encode the same video footage at the same quality as MPEG-2, but use slightly less data.
The fundamental advantage of the AOD format over the competing Blu-Ray Disc format, according to Toshiba and NEC is principally lower cost. They claim lower costs in replicating pre-recorded movies, since existing fabrication plants can be retrofitted to produce software on the AOD format. The Toshiba-NEC team said that the AOD players and recorders would be smaller than Blu-Ray Disc players and recorders. Again, details are sketchy.
Basically, the AOD format is an evolution of the DVD-Video format to provide HDTV pre-recorded content and recording capabilities. Even Toshiba has admitted that AOD as an interim and transitional format, with the Blu-Ray Disc format as the long-term solution. We canít help but wonder why we need a transition format, when Sony has already introduced a production Blu-Ray Disc recorder, the Sony BDZ-S77. This point is further reinforced when you realize that AOD-based hardware products will not show up for market until late 2003 or early 2004. Additionally, we do not believe that everyday consumers will buy into the idea of transitioning from DVD-Video to AOD, only to transition again to the Blu-Ray Disc format a few more years beyond that. We do not buy into Toshiba and NECís ďtransitionalĒ AOD format. We would prefer to see one HD DVD format, even if it takes years for Blu-Ray Disc hardware to come down to mass-market prices. We believe most everyday consumers would agree with this viewpoint.
The table below summaries the key parameters of the Blu-Ray Disc and Advanced Optical Disc formats.
Key parameters of the Blu-Ray Disc and
Advanced Optical Disc formats
|Blu-Ray Disc||Advanced Optical Disc (AOD)|
|Single-Layer||23.3, 25, 27||15
|Dual-Layer||46.6, 50, 54||
|Maximum Recording Time, HDTV||Single-Layer||2 hours||2 hours|
|Dual-Layer||4 hours||4 hours|
|Maximum Data Rate [Mbps]||36.0||?|
|Disc Diameter [cm]||12.0||12.0|
|Laser Wavelength [nm]||405||405|
Backwards Compatibility with DVD-Video
With a HD DVD format looming around the near horizon, you may wonder: is it still a good idea to invest in a DVD-Video collection? Absolutely. There are no technical or financial reasons that would preclude the new generation of HD DVD players and recorders from playing back existing DVD-Video software. We believe that manufacturers will make HD DVD hardware with backward compatibility for the current DVD-Video format. Your library of DVD-Video titles should play in the new HD DVD hardware, just like your library of audio CDs can play in your DVD-Video player. So continue to add to your wonderful DVD-Video collection without concern.
We should note, however, that you will need a new HD DVD player or recorder to play the new HD DVD discs, whether Blu-Ray Disc or AOD turns out to be the winner of the HD DVD format war. Your existing DVD-Video player will not be able to playback any of the future HD DVD software. This is analogous to the fact that you need to buy a DVD-Video player to play DVD-Video discs, and that your 10-year old audio CD player cannot play back DVD-Video. (Donít even bother to try.)