27-06-2014, 10:25 AM
INTRODUCTION TO BLU RAY DISC
BLU RAY DISC.docx (Size: 1.44 MB / Downloads: 15)
1 What is a Blu-ray disc?
Blu-ray disc is a next-generation optical disc format jointly developed by a group of leading consumer electronics and PC companies called the Blu-ray Disc Association (BDA), which succeeds the Blu-ray Disc Founders (BDF). Because it uses blue lasers, which have shorter wavelengths than traditional red lasers, it can store substantially more data in the same amount of physical space as previous technologies such as DVD and CD.
A current, single-sided, standard DVD can hold 4.7 GB (gigabytes) of information. That's about the size of an average two-hour, standard-definition movie with a few extra features. But a high-definition movie, which has a much clearer image, takes up about five times more bandwidth and therefore requires a disc with about five times more storage. As TV sets and movie studios make the move to high definition, consumers are going to need playback systems with a lot more storage capacity.
The advantage to Blu-ray is the sheer amount of information it can hold :
• A single-layer Blu-ray disc, which is roughly the same size as a DVD, can hold up to 27 GB of data — that's more than two hours of high-definition video or about 13 hours of standard video.
• A double-layer Blu-ray disc can store up to 54 GB, enough to hold about 4.5 hours of high-definition video or more than 20 hours of standard video. And there are even plans in the works to develop a disc with twice that amount of storage.
1.2 Why the name Blu-ray?
The name Blu-ray is derived from the underlying technology, which utilizes a blue-violet laser to read and write data. The name is a combination of "Blue" and optical ray "Ray". According to the Blu-ray Disc Association, the spelling of "Blu-ray" is not a mistake. The character "e" is intentionally left out because a daily-used term can’t be registered as a trademark.
1.3 Who developed Blu-ray?
The Blu-ray Disc format was developed by the Blu-ray Disc Association 1BDA),
a group of leading consumer electronics and PC companies with more than 130 members from all over the world.
1 INTRODUCTION TO BLU-RAY TECHNOLOGY
The Objective of Blu-ray The standards for 12-cm optical discs, CDs, DVDs, and Blu-ray rewritable discs (BD-RE Standard) were established in 1982, 1996, and 2002, respectively. The recording capacity required by applications was the important issue when these standards were decided (See fig). The requirement for CDs was 74 minutes of recording 2- channel audio signals and a capacity of about 800 MB. For DVDs, the requirement as a video disc was the recording of a movie with a length of two hours and fifteen minutes using the SD (Standard Definition) with MPEG-2 compression. The capacity was determined to be 4.7 GB considering the balance with image quality.
In the case of the Blu-ray *1) Disc, abbreviated as BD hereafter, a recording of an HDTV digital broadcast greater than two hours is needed since the BS digital broadcast started in 2000 and terrestrial digital broadcast has begun in 2003. It was a big motivation for us to realize the recorder using the optical disc. In a DVD recorder, received and decoded video signals are compressed by an MPEG encoder and then recorded on the disc.
To record in the same fashion for an HDTV broadcast, an HDTV MPEG-2 encoder is required. However, such a device for home use has not yet been produced. In the case of BS digital broadcasts, signals are sent as a program stream at a fixed rate, which is 24 Mbps for one HDTV program. In the program stream of BS digital broadcast there is a case that the additional data stream is multiplexed, and it is desirable to record and read the data as is. Two hours of recording requires a recording capacity of 22 GB or more. This capacity is about 5 times that of DVDs, which cannot achieve this capacity by merely increasing their recording density.
2 OPTIMIZATION OF THE COVER LAYER THICKNESS
Roots of a 1.2 mm substrate existed in the video disc. One of advantages of laser discs has been that they are hardly affected by dirt or dust on the disc surface since information is recorded and read through a cover layer. The first commercial optical disc, which was the videodisc called VLP or Laser Disc, used a 1.2 mm thick transparent substrate, through which information was read. This thickness was determined from conditions such as: - Deterioration of the S/N ratio due to surface contamination was suppressed to a minimum since it used analog recording,
- A disc of 30 cm in diameter can be molded,
- The disc has sufficient mechanical strength,
- The disc is as thin as possible while satisfying the flatness and optical uniformity.
The last condition is because the thinner the cover layer, the more easily the performance of the objective lens to converge the laser beam can be improved. This convergence performance of the objective lens is expressed by what we call NA (Numerical Aperture), and the diameter of a converging light is inversely proportional to NA (Fig. 1.2.1). Thus NA is required to be as large as possible. However, when the optical axis of the objective lens shift from the perpendicular to the disc surface, a deterioration of the convergence performance (aberration) occurs and its amount grows proportionally to the cube of NA. Since we cannot avoid discs from tilting to some extent from the optical axis of the objective lens due to the bending of discs or inclination of the mounting and it has prevented the value of NA from increasing.
.3 LASER TECHNOLOGY
The technology utilizes a "blue" (actually blue-violet) laser diode operating at a
wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and infrared lasers at 650 nm and 780 nm respectively.
As a color comparison, the visible color of a powered fluorescent black light tube is dominated by mercury's bluish violet emissions at 435.8 nm. The blue-violet laser diodes used in Blu-ray Disc drives operate at 405 nm, which is noticeably more violet (closer to the violet end of the spectrum) than the visible light from a black light. A side effect of the very short wavelength is that it causes many materials to fluoresce, and the raw beam does appear as whitish-blue if shone on a white fluorescent surface (such as a piece of paper). While future disc technologies may use fluorescent media, Blu-ray Disc systems operate in the same manner as D and DVD systems and do not make use of fluorescence effects to read out their data.
The blue-violet laser has a shorter wavelength than CD or DVD systems, and this shrinking makes it possible to store more information on a 12 cm (CD/DVD size) disc. The minimum "spot size" that a laser can be focused is limited by diffraction, and depends on the wavelength of the 11 light and the numerical aperture (NA) of the lens used to focus it. By decreasing the wavelength (moving toward the violet end of the spectrum), using a higher NA (higher quality) dual-lens system, and making the disk thinner (to avoid unwanted optical effects), the laser beam can be focused much tighter at the disk surface. This produces a smaller spot on the disc, and therefore allows more information to be physically contained in the same area. In addition to optical movements, Blu-ray Discs feature improvements in data encoding, closer track and pit spacing, allowing for even more data to be packed in
DISC STRUCTURE
Configuration of SL and DL Discs
Figure shows the outline of a Single Layer BD Read-Only disc and Figure shows the outline of a Dual Layer BD Read-Only disc. To improve scratch resistance, the over layer can optionally be protected with an additional hard coat layer. One of the features that differentiate Blu-ray Disc from DVD recording systems is the position of the recording layer within the disc. For DVD, the recording layer is sandwiched between two 0.6-mm thick layers of plastic – typically polycarbonate.
The purpose of this is to shift surface scratches, fingerprints and dust particles to a position in the optical pathway where they have negligible effect - i.e. well away from the point of focus of the laser. However, burying the recording layer 0.6 mm below the surface of the disc also has disadvantages.
Due to the injection molding process used to produce them, disc substrates suffer from stress-induced birefringence, which means that they split the single incident laser light into two separate beams. If this splitting is excessive, the drive cannot read data reliably from the disc. Consequently, the injection molding process has always been a very critical part of CD and DVD production. Another critical manufacturing tolerance, particularly for DVDs, is the flatness of the disc, because the laser beam becomes distorted if the disc surface is not perpendicular to the beam axis - a condition referred to as disc tilt. This distortion increases as the thickness of the cover layer increases and also increases for higher numerical To overcome these disadvantages, the recording layer in a Blu-ray Disc sits on the surface of a 1.1-mm thick plastic
substrate, protected by a 0.1-mm thick cover layer.
With the substrate material no longer in the optical pathway, birefringence problems are eliminated. In addition, the closer proximity of the recording layer to the drive's objective lens reduces disc tilt sensitivity. This only leaves the problem of surface scratching and fingerprints, which can be prevented by applying a specifically
CONCLUSION
Anyone old enough to recall fond memories of Rubik's Cubes, Family Ties, and Duran Duran likely remembers another '80s phenomenon: the VHS vs. Betamax war.
The two competing video-recording technologies emerged together in the 1970s, when Sony's (NYSE: SNE) Betamax VCR, a pioneer in the industry, fought for market share against a rival VHS version developed by Matsushita (NYSE: MC).
VHS technology quickly gained widespread acceptance, while Betamax followed a divergent path into obscurity. In 1988, with less than 5% of the market, Sony finally threw in the towel by announcing plans to market a VHS-based recorder. While the end came slowly, the decision would prove to be a death knell for the Betamax name.
Fast-forward to today. The growing popularity of high-definition television
(HDTV) has fostered a new wave of recording technology, soon to supplant the VCR, and possibly even DVD. Again, two competing technologies are vying for acceptance, but this time Sony appears to be on the winning side.
The Blu-ray Disc Founders (not to be confused with the effusively painted
Blue Man Group) is a consortium of 13 leading electronics firms. It has developed a
superior optical disc known as the Blu-ray Disc (BD). As opposed to the red lasers currently used to produce DVDs, blue beams have a shorter wavelength, allowing for enhanced precision and more tightly compressed data. While a typical DVD holds 4.7 GB of information, a BD contains 25 GB - enough storage for two hours of HDTV or 13 hours of standard television. Dual-layer discs under development will hold an astounding 54 GB. Aside from greater storage capacity, Blu-ray discs will also contain more interactive features.
The world's two foremost computer manufacturers, Hewlett-Packard (NYSE: HPQ) and Motley Fool Stock Advisor holding Dell Computer (NASDAQ: DELL), were formally added to the Blu-ray alliance, virtually ensuring the future adoption of BD technology for PC data storage.
The competing format, known as HD-DVD, is simultaneously under joint development by Toshiba and NEC. Though HD-DVD technology appears to be an underdog at this point, it has recently gained notoriety by winning the support of the DVD forum, a confederation of DVD-related companies.
Blu-ray, has already earned an early endorsement from Columbia TriStar Pictures (Hollywood), which has committed to using the Blu-ray technology.