Blu-ray disks--an overhaul in progress

High-capacity data storage took a leap forward in 2004, when the first Blu-ray disc devices entered the Japanese market. Due to their high storage capacity and cost-effective manufacture, Blu-rays are predicted to make DVDs obsolete. But how do they work, and do they make good on their promise?

Blu-ray disks exceed the capabilities of CDs and DVDs in several ways. They store more data, making them the current standard for high-definition media storage. High-definition signals have a greater bandwidth and require more storage to preserve quality; high-definition video takes up far more space than a single CD or DVD can allow. A single-layered Blu-ray disk, on the other hand, can store more than four hours of HD video, and a double-layered disk can store twice as much without compromising quality.

In optical media, the recording layer is manufactured to have bumps and lands. When the laser shines on the bumps, the light bounces back earlier than if it hits a land, and it hits the reader. In Blu-ray disks, the bumps are smaller and closer together, and the tracks are spaced at a smaller distance. The smaller the distances and sizes, the more data that can be stored. In comparison, DVDs have a track pitch (or track separation distance) of 740 nm and a bump size of 400 nm, while Blu-rays have a track pitch of 320 nm and a bump size of 150 nm. To read this data, a blue (actually violet) laser shines at a wavelength of 405 nm. Red lasers, in comparison, shine at either 780 nm for CDs or 650 nm for DVDs. The smaller aperture (opening that lets the light through) and wavelength of Blu-ray optical readers focus precisely enough to read the data on the disk.

The construction of Blu-rays solves reading problems that CDs and DVDs still face. Blu-ray disks are placed closer to the optical reader, which reduces the chance of disk tilt and consequently the chance that light won't be reflected back at a 90˚ angle. They're also constructed so that the laser doesn't have to shine through two layers of plastic to get to the recording layer. DVDs store the data beneath the plastic, which can lead to birefringence, or the splitting of laser light into two differently-refracted beams which can't read the disk. Blu-rays store the data on top of the layer instead, preventing this phenomenon.

In addition, Blu-ray disks transfer data faster than DVDs, allowing large files to be written in less time. The disks also offer greater copyright protection; they're encoded with encryption that keeps them from being duplicated illegally. Also, the disks are built with practicality in mind; they are designed with a layer that reduces the likelihood and effects of scratches and fingerprints.

Do Blu-ray disks hold good on their promise to revolutionize video and data storage? Their specifications and design agree completely. Today, Blu-ray hasn't overhauled our current standards of optical media, but with movie titles being sold in the format and software such as Final Cut Studio offering (limited) Blu-ray usability, the technology's getting closer. With our country now using HD television as its standard, the overhaul is in sight. With companies like Pioneer announcing an optical storage medium that uses a UV laser to read a 500-GB disk, that overhaul is just a matter of time.

To learn more about Blu-ray, HD television and video, and the standards that continue to vie for attention, check out the links and learn more about the history that establishes where the technology stands today.