Blue Laser CD-ROMS

[Creedyou]

I heard something about this from a friend. He said you will be able to fit more data on a CD because blue lasers have shorter wavelengths than the current red ones. How does shorter wavelengths equal more data? Anyone know the size capacity of a blue laser CD?

 

[stev0]

i remember reading something about this a while ago. i believe it went something like: because of the narrower wavelengths of the blue lazers (a thinner lazer 'beam' i guess you could say) it would be able to read data that was burned into a narrower area...

 

[imgod2u]

The technology is actually supposed to be an upcomming generation of DVD's, named BluRay. It supposedly is able to store somewhere around 20 GB per side or something.

 

[Jeff7]

Originally posted by: imgod2u
The technology is actually supposed to be an upcomming generation of DVD's, named BluRay. It supposedly is able to store somewhere around 20 GB per side or something.

27GB I think it is.
DVD's and CD's use small pits in the medium to signify binary data, though I don't remember which signifies a 1 or 0 - pit or flat. Shorter wavelength=smaller pits=higher pit/data density.

 

[Mingon]

the pits deflect the laser giving a 0 iirc the reflection gives the 1

 

[Cogman]

The dvds are going to have to be expencive though. They while have to use a scratch resistant material on the Dvds as a small scratch will do more damage then it would normally would on a red cd. (more bits in small aria = more bits that can be damaged in a small aria)

 

[Eteq]

You're right that the DVDs would be more expensive - even if the laser allows for a narrower wavelength, the DVD manufacturing process would have to make pits and valleys that are much smaller - while blue lasers may make DVD drives cheaper than red lasers, the DVDs themselves wouldn't really be made cheaper in any way...

 

[Creedyou]

Originally posted by: Eteq
You're right that the DVDs would be more expensive - even if the laser allows for a narrower wavelength, the DVD manufacturing process would have to make pits and valleys that are much smaller - while blue lasers may make DVD drives cheaper than red lasers, the DVDs themselves wouldn't really be made cheaper in any way...

I don't think there would have to be much change to the disk as it is the laser that makes the valleys in the disk.

 

[Jeff7]

Originally posted by: Creedyou

Originally posted by: Eteq
You're right that the DVDs would be more expensive - even if the laser allows for a narrower wavelength, the DVD manufacturing process would have to make pits and valleys that are much smaller - while blue lasers may make DVD drives cheaper than red lasers, the DVDs themselves wouldn't really be made cheaper in any way...

I don't think there would have to be much change to the disk as it is the laser that makes the valleys in the disk.

But the media needs to be of high enough quality to reliably accept very tiny pits. And as has been mentioned, there would need to be some improved scratch resistance. A scratch in a CD may obscure a small enough amount of data that the error correction can handle it; that might not be the case with a blue-laser drive.

 

[devicenull]

it is true, blue light lasers will give you better density, but i recall a move to use UV light and multilayer discs resulting in 100gb+ discs. that was almost 5 or 6 years ago too

 

[MrDudeMan]

Originally posted by: devicenull
it is true, blue light lasers will give you better density, but i recall a move to use UV light and multilayer discs resulting in 100gb+ discs. that was almost 5 or 6 years ago too

so basically like a little hard drive....

that would be so sweet...100gb per disc on a CD-ROM

 

[everman]

Originally posted by: MrDudeMan

Originally posted by: devicenull
it is true, blue light lasers will give you better density, but i recall a move to use UV light and multilayer discs resulting in 100gb+ discs. that was almost 5 or 6 years ago too

so basically like a little hard drive....

that would be so sweet...100gb per disc on a CD-ROM

No, a hard drive is magnetic, dvd = optical.
I would think that if you really wanted to use blue laser discs reliably they would need be in protective cartriges that is insterted into the machine where it is then extracted. Too much risk of damage otherwise. I don't see why it would really catch on with DVD movie players either, as currently we fit an entire movie on a disc+ more easily, but maybe for HDTV quality DVDs?

 

[AbsolutDealage]

Originally posted by: Creedyou

Originally posted by: Eteq
You're right that the DVDs would be more expensive - even if the laser allows for a narrower wavelength, the DVD manufacturing process would have to make pits and valleys that are much smaller - while blue lasers may make DVD drives cheaper than red lasers, the DVDs themselves wouldn't really be made cheaper in any way...

I don't think there would have to be much change to the disk as it is the laser that makes the valleys in the disk.

actually, when DVDs/CDs are pressed professionally, they are not laser burned. They are stamped from a mask. Just FYI

 

[ViRGE]

Originally posted by: Jeff7

But the media needs to be of high enough quality to reliably accept very tiny pits. And as has been mentioned, there would need to be some improved scratch resistance. A scratch in a CD may obscure a small enough amount of data that the error correction can handle it; that might not be the case with a blue-laser drive.

Can't you just allocate more space to error correction then?

 

[zephyrprime]

The wavelength of light is THE limiting factor for optical disk capacity. On the subatomic scale, the location of objects is blurry because of quantum mechanics. The uncertainty of the location of a wavelength of light is related to it's wavelength.

In optical disks, the separation distance of pits and lands is only a little bigger than the wavelegth of light used to read from the disk. If the separation distance were made shorter so that it were equal to the wavelength of light, then the photons would mistakenly read adjacent bits rather than the target bit a high percentage of the time.

It's pretty easy to calculate the size of a bit on a optical disk compared to the wavelength of light used.

Area of dvd: (0.18meters/2)^2*pi - (0.043meters/2)^2*pi = 0.024 meters squared
Data on DVD = 4.7*1 billion bytes * 8bits/byte = 37.6 billion bits (this may be inaccurate due to error correcting codes and stuff)

0.024 m^2/37.6 billion = 640,000 square nanometers

Wavelength of light used by DVDs = 650nm.

650^2 = 422500 square nanometers.

So you can see that the physical size of a bit on a DVD is not much bigger than the "size" of a red photon! It's actually pretty incredible technology when you think about it. (my estimate of the size of a bit on a DVD is a little on the big size because I assumed DVDs use a simple data encoding scheme but I know it must actually use some sort MFM or RLL or some other sort of thing like that.)

 

[Jeff7]

Originally posted by: ViRGE

Originally posted by: Jeff7

But the media needs to be of high enough quality to reliably accept very tiny pits. And as has been mentioned, there would need to be some improved scratch resistance. A scratch in a CD may obscure a small enough amount of data that the error correction can handle it; that might not be the case with a blue-laser drive.

Can't you just allocate more space to error correction then?

I suppose that could be possible; of course, that will reduce the size of the media, and would add overhead. I don't know if manufacturers would rather do that, or else go ahead with a cartridge system. I imagine that it would be feasible to maybe take 1GB of the media or more depending on its final size, use that for error correction data, and use a beefier processor in the drive to deal with the increased demands of CRC's.

 

[ViRGE]

It would seem to me that even at larger chips, and reduced data size, it's the right thing to do. Plain ole' data CD's seem to survive scrathes easily(even at the cost of the ECC sectors compared to an audio CD), so a similar data-ECC ratio should give similar reliability in terms of scrathes to BluRay discs, shouldn't it?

 

[Smilin]

I think the fix to scratching is to fall back to some old school technology of sleeves for the disk.
Make the optical disk sit inside a shell the same way a magnetic disk does in 3.5" floppies.

 

[jasonpetras]

I was doing a bit of reading about the lasers they are going to use in the Blu-ray disks. The current leaders in the technology are Sony and Nichia. For all of you out there who like to memorize numbers, the wavelength to be used is 405nm (it is actually violet in color) with an expected capacity of 23 to 27 GB per side. The article goes on further to say that these lasers will enter mass production by the end of this year '03. So we will probably see these uber-DVDs some time at the mid to end of '04 (guessing). For me personally, I would love to see these disks. HDTV encoded movies!

For a nice, fairly technical explaination of the whole wavelength to aperture (pit size) question, read [L = this]http://www.chipchapin.com/CDMedia/cdda3.php3[/L]

 

[unclebabar]

In a quasi-related question, does anyone know what the difference between DVD- and DVD+ is? I'm not talking about the superficial differences, e.g.-> What's the difference between the various DVD recordable formats, and what should I buy?. Do they use different wavelengths of laser or something? I know DVD-R general and DVD-R professional do. What's the big hurdle in intergrating the formats (other than killing the royalty payments for one camp or the other)? I've heard one is CLV (-?) and the other is CAV (+?). Any other physical technical differences? (not really interested in hearing about Mt. Rainier support). Are the dyes formulations incompatible? What would you get if you put a DVD- wavelength laser in a DVD+ drive? (or vis versa)