The name Blu-ray Disc derives from the blue-violet laser used to read the disc. While a standard DVD uses a 650 nanometre red laser, Blu-ray uses a shorter wavelength, a 405 nm blue-violet laser, and allows for almost six times more data storage than a DVD.
Making permanent changes to a disc. If we use BD‐R the material on the disc itself is changed forever.
here is no way to get the material back into its old state. The recording material is crystalline in nature. As scan spot falls on the surface it changes to amorphous. We cannot change it back to crystal state.
Record Many Times
If we use a BD‐RW the material on the disc itself changes, but can be changed back again .We can do this as long as the material doesn’t get worn out. By heating up the crystals, they change form. Now when we quickly cool them, they stay in that form itself. That is the material is changed from crystal state to amorphous state.
Now, if we want to erase the BD‐RW, we have to make sure that we lose all the data. So we want to get rid of that amorphous state. By heating up the material again, but this time taking more time and less heat, the material gradually wants to take its old form again, and thus the information is erased. This state is called the crystalline state.
So, by very quickly heating it and very quickly cooling it, give the crystal another state (Amorphous state) which thus contains the data and by very quite slowly heating it and cooling it, we can give the crystals their old form back (crystalline state) which contains no more data. It’s a constant change of phases. And so it is called as phase change recording.
Data is stored in the form of grooves, on an optical disc. Next to the grooves, there are lands. Lands are the borders between the grooves. Grooves and lands have a sinus form. This is called a wobbled groove. In the groove, pits are formed to store data.
