What is a Blu Ray Disk?
A blu ray disk is a digital video disk that can record, store and play back high definition video, digital audio and computer data.
Consider the single-sided, standard DVD. It is capable of storing 4.7 GB of data (or about the size of the average two-hour, standard-definition movie). However, high-definition films have much greater clarity and need five times more bandwidth. Obviously standard DVD disks are inadequate and Blu Ray disks are the solution.
Today’s television sets and movie studios have made the leap toward high definition technology and playback options with greater storage capacity are becoming essential for capture and storage.
So, how does Blu Ray Work? Before we tell you, let’s cover some of the advantages to a Blu Ray.
Increased Storage Capacity with a Blu Ray Disk
* A single-layer Blu ray disk is about the same size as a standard DVD but it is able to store up to 27 GB of data – in excess of two hours of high-definition video or about 13 hours of standard video!
* A Double-layer Blu ray disk has a storage capacity of up to 54 GB and can hold 4.5 hours of high-definition video or more than 20 hours of standard video. Developments suggest that Blu ray disks will soon be able to hold double this amount.
Blu ray Discs Offer Increased Interactivity
* With the advent of the Blu Ray disk, computer users will have the added advantage of being able to download subtitles and other interactive movie features direct from the Internet. Tasks they will be able to perform include:
* Recording High Definition Television (HDTV) with perfect quality
* Skipping to any place on the blu ray disk instantly
* Recording a program while at the same time watching a second program on the disk
* Create a play list
* Editing and re-ordering data stored on the disk.
* Search automatically for an empty space on the disk (to avoid mishaps)
* Access the Web and download features like subtitles.
The Blu ray Disc has an Increased Transfer Rate
Data transfer rates on Blue Ray are 36 Mbps (megabits per second). Much higher than DVDat 10 Mbps. A Blu-ray disc can record 25 GB of material in a little over an hour and a half!
A Blu ray Disc Offers Increased Security
Blu ray discs are better protected than DVDs. A secure encryption system is fitted with each disk, This is a unique ID that protects against video piracy and copyright infringement.
How Blu Ray Works
Disks store digitally encoded video and audio information in spiral grooves called pits. These grooves run from the center of the disk to the edges. The data is accessed when a laser reads the other side of these pits i.e. the ‘bumps’ enabling us to watch a movie or listen to a CD.
If a disk contains a large amount of information the pits are packed closely together and are much smaller. As the pits become smaller the laser needs to become more and more accurate in its ability to read the data.
DVDs use a red laser to read and write data but the Blu Ray disk uses a blue laser to access the information. Blue lasers have a shorter wavelength (405 nanometers) than red lasers (650 nanometers) and the smaller beam has the ability to focus on the pits more accurately.
Blue Ray disks can read information recorded in pits as small as 0.15 microns (µm) (1 micron = 10-6 meters) long i.e. twice as small as the pits on a DVD. In addition Blu Ray has reduced the track pitch from 0.74 microns to 0.32 microns.
The combination of the smaller pits, smaller beam and shorter track pitch mean that a single-layer Blu Ray disk can hold in excess of 25 GB of information, that’s about five times the amount of information that can be stored on a DVD disk.
A Blu-ray disk is about 1.2 millimeters thick (the same as a DVD), but the disks store data in different ways. DVD disks store data between two polycarbonate layers, each 0.6-mm thick. This polycarbonate layer can cause a problem called birefringence i.e. the substrate layer refracts the laser light into two separate beams.
If the beam is split too wide apart, the disk cannot be read and if the DVD surface is not perfectly and perpendicular to the beam, it may lead to ‘disk tilt’, in which the laser beam is distorted. For these reasons the manufacturing of DVDs is a very involved process.
How do Blu Ray Disks Avoid These Problems?
Blu Ray disks alleviate reading problems by placing data on top of a 1.1. mm thick polycarbonate layer. Since the data is on top birefringence is avoided. In addition the recording layer is in very close proximity to the objective lens of the reader so disk tilt is eliminated. The disk is protected by placing a hard coating over the disks surface.
The injection-molding process on a single 1.1-mm disc reduces the manufacturing costs and is balanced by the cost of adding the protective layer.
In the end the price is virtually the same as that of a DVD.
What about Formats for Blu Ray Disks?
Blu Ray has been designed in several formats:
* BD-ROM (read-only) – for pre-recorded content * BD-R (recordable) – for PC data storage * BD-RW (rewritable) – for PC data storage * BD-RE (rewritable) – for HDTV recording