The name Blu-ray Disc is derived from the blue-violet laser used to read and write this type of disc. Because of its shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red (650 nm) laser. A single layer Blu-ray Disc can store 25 gigabytes (GB), over five times the size of a single layer DVD at 4.7 GB. A dual layer Blu-ray Disc can store 50 GB, almost 6 times the size of a dual layer DVD at 8.5 GBThe name Blu-ray Disc is derived from the blue-violet laser used to read and write this type of disc. Because of its shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the DVD format. A single layer Blu-ray Disc can store 25 gigabytes (GB). A dual layer Blu-ray Disc can store 50 GB.
| Media type: | High-density optical disc |
| MPEG-2, MPEG-4 AVC (H.264), and VC-1 | |
| Capacity: | 25 GB (single layer), 50 GB (dual layer) |
| Read mechanism: | 1x@36 Mbit/s & 2x@72 Mbit/s |
| Developed by: | |
| Usage: | Data storage, High-definition video and PlayStation 3 Games |
Blu-ray Disc is a next-generation, optical disc format that enables the ultimate high-def entertainment experience. Blu-ray Disc provides these key features and advantages:
- Maximum picture resolution
- Largest capacity available anywhere (25 GB single layer/50 GB dual layer)
- Best audio possible
- Enhanced interactivity
- Disc robustness.
Disc structure
Like its rival format HD, DVD, Blu-ray uses a "blue" (technically violet) laser operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and near infrared lasers at 650 nm and 780 nm respectively.
The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD sized disc. The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85 and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot. This allows more information to be stored in the same area. In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding that further increase the capacity.
Since the Blu-ray data layer is closer to the surface of the disk, compared to the DVD standard, it was at first more vulnerable to scratches. The first discs were housed in cartridges for protection. Advances in polymer technology eventually made the cartridges unnecessary.
TDK was the first company to develop a working scratch protection coating for Blu-ray discs. It was named Durabis. In addition, both Sony and Panasonic's replication methods include proprietary hard-coat technologies. Sony's rewritable media are sprayed with a scratch-resistant and antistatic coating. Verbatim recordable and rewritable Blu-ray Disc discs use their own proprietary hard-coat technology called ScratchGuard.
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