The blue period of lasers
Author: Mr. Belvedere -
Date: 27-7-2002
As we all know, CD players and recorders read and write the CD's with the aid of a laser. Laser is short for: Light Amplification by Stimulated Emission of Radiation. See http://www.howstuffworks.com/laser1.htm for a complete explanation of what a laser actually is.
In a nutshell this means that high emitted energy gives radiation in the form of light, sort of like a lightbulb does. However laser light is very different than your average lightbulb. Laser comes in a straight direct beam and in only one wavelength (only red, only green, only blue etc). This wavelength is measured in nanometers and science uses the Greek letter Lamda (
) for this.
See http://www.howstuffworks.com/light2.htm for more information about wavelengths and light.
Because a laser is a very tiny and direct beam it is perfect to reflect the data written on a cd, because the data is long (over 3 miles!) but it is very small (about 5 microns).
(Picture courtesy of http://www.howstuffworks.com/cd2.htm)
The laser sends a beam towards the cd data and the beam gets reflected or not, thus resulting in high or low digital signal. To put it simple: If the reflected beam gets picked up by the receptor, it's a 1 ,if not.. it's a 0.
If you write data on a cd, the real laser power kicks in. It actually heats up a certain part of the cdrom surface, thus creating a physical 0 or 1 on the cdrom, which can later be read by your cd player. This will be explained more thoroughly later on (Pages 9 and 10).
The smaller the wavelength of a laser is, the smaller the beam can be. If the beam is smaller .. it can also read/write the same data using a smaller width (less than 1 micron!). So, on the same amount of surface, a laser with a smaller wavelength can read/write far more data on that surface than a laser with a bigger wavelength! And that's what Blu-Ray is! A laser with a smaller wavelength. Blue.
Blu-Ray uses a blue laser. Because it uses a blue laser it can store enormous more amounts of data on it than was ever possible using red laser on the same amount of surface (being a 120 mm disc).
To have an even greater precision and make sure every part of the laserlight actually gets hit on the part that is needed for writing/reading the disc, a special lens is used in every cd player.
(Picture courtesy of http://www.howstuffworks.com/cd2.htm)
As perfect as your cd may be the surface is never 100% flat. So it constantly needs to focus to get the information out (Example: You will need binoculars if you want to read the license plate of a car, if that car is at a 10 mile distance of yourself). And even IF the surface was 100% flat, the disc spins. And it spins quite fast! So it can even move up and down a little bit (vibrations) (To follow our example: You will need to refocus your binoculars for that license plate if the car moves away from you or gets closer to you constantly, while you are experiencing an earthquake).
The light gathering capacity of the lens is measured in 'Numerical Apertures" or NA for short. The bigger NA (which means the lens can gather more light), the better.
It also tells about power and refraction, but we won't go into that. If you want more information about the NA formulas and methods see:
http://www.gonda.ucla.edu/bri_core/na.htm or http://www.microscopyu.com/articles/formulas/formulasna.html
1st Generation
The Compact Disc (CD for short) is been here for over 20 years now. With the help of a 780 nanometer (red) laser the data on the single layer gets read. The first CD's were meant for audio, and later on the CD-ROM came into place giving us 650/700 megs of space per disc.
2nd Generation
The development of DVD (Digital Versatile Disc) introduced an enormous upgrade of capacity, giving enough room (4,7 GigaBytes) for high quality sound and multimedia on a single disc. The throughput is much higher and a 650 nanometer laser is used. Now there are also 2 layers for even more capacity. This gives plenty of room to put an entire movie on a single DVD.
3rd Generation
Blu-ray owes its name from the color of the 405 nanometer used laser (Blue/Violet) to read and write data on the Blu-ray Discs (BD).
Blu-ray can contain 27GB, which can be read at 36MB/s on single speed.
Shuji Nakamura of Nichia Chemical Industries Ltd., Tokushima, Japan.
Blue lasers aren't new. The first blue laser diode was developed in 1996 by Shuji Nakamura, researcher at Nichia Corp. More information about him can be found here :
http://www.sciencewatch.com/jan-feb2000/sw_jan-feb2000_page3.htm.
Already in 2001 Matsushita and Sony developed their own blue lasers and a consortium was quickly formed in February 2002 to get to some decent standard (See press release here: http://www.matsushita.co.jp/corp/news/official.data/data.dir/en020219-4/en020219-4.html).
Nowadays the Blu-ray standard is supported by 9 leading companies who call themselves 'The Blu-ray Disc Founders". They are:
| Hitachi | http://www.hitachi.com/ |
| LG Electronics Inc. | http://www.lge.com |
| Matsushita Electrical Industrial | http://www.matsushita.co.jp |
| Pioneer Corporation | http://www.pioneerelectronics.com/ |
| Royal Philips Electronics | http://www.philips.com |
| Samsung Electronics | http://www.samsung.com |
| Sharp Corporation | http://sharp-world.com/index.html |
| Sony Corporation | http://www.sony.com |
| Thomson Multimedia | http://www.thomson-multimedia.com |
Toshiba (www.toshiba.com) decided not to participate in the Blu-ray Disc Founders. Various newssources describe that Toshiba believes the DVD Forum (www.dvdforum.org) is more suitable for making uniform standards and they proposed their own 30Gb standard.
Customers are hardly used to the various DVD standards and now it seems the war about disc standards is far from over
AOL Time Warner (www.aoltimewarner.com) and Mitsubishi Electric (global.mitsubishielectric.com) also haven't joined the Blu-Ray Disc Founders yet.
On top of that has NEC (www.nec.com) announced a 35Gb optical disc method, with the possibilities to record 14 hours in DVD quality using a different type of blue laser. NEC proposed this as another standard.
Who needs such enormous amounts of data and throughput? What is the purpose behind this?
The answer: The big companies want to sell you HDTV.
HDTV is High-resolution Digital Television combined with Dolby Digital surround sound (AC-3). For a complete explanation about HDTV see: http://www.howstuffworks.com/hdtv.htm
HDTV drives on 3 cornerstones; Bigger, sharper and better than your old tv set. Mind you that HDTV is not cheap and it isn't available worldwide for a long time.
With the help of Blu-Ray recording devices it is possible to record up to 2.5 hours of very high quality audio and video on a single BD.
The recording and playback of 2.5 hours HDTV Video on a single Blu-ray disc. (C) Philips Research
It also possible put more than 13 (!) hours of VHS quality video on a single BD , making it an nice replacement for your old VCR.
Apart from that you can store 27 Gigabytes of data on a single disc. This is of course excellent for archiving purposes. Unfortunately there's not much known about the durability of a BD, so it remains to be seen if the Blu-Ray Discs have enough quality for archiving purposes that need to be 100% secure (medical data, military documents etcetera).
It also seems that Blu-Ray comes right on time. The current harddisks you can buy are already well over 100 Gigabytes each. With the aid of a Blu-Ray writer you would need about 4 BD's to backup that amount of data, but with DVD you would need 22 DVD's!
Further, think of the possibillities for games. Using multimedia in games costs enormous amounts of data. There are already games that require 7 CD's. Of course you can put this on a single DVD, but if this trend follows over the years and the software companies decide that bigger is better, the Blu-Ray technology may come in handy.
36 Megabits per second throughput is also more than enough for almost any personal little webserver. It could be pretty cool that you could run your website by using a pc with a Blu-Ray recorder in it, and that's it. You have 27 Gigabytes of rewritable webspace at your fingertips. Only needing a little harddisk for the operating system, drivers and you're up and running. The only problem could be that if you keep filling the disc at full speed, it's full in about 2,5 hours
The nine companies involved will all develop products that take full advantage of Blu-ray Disc's large capacity and high-speed data transfer rate.
They are also thinking about improving Blu-Ray already. For instance by developing a larger capacity, such as over 30GB on a single sided single layer disc and over 50GB on a single sided double layer disc and finding ways to enhance the throughput , making 2x Blu-Ray recorders (giving a throughput of 72 mbits per second).
Some companies jump right on the storage-wagon and promise even 120 Gigabytes per disc in the year 2007 (http://www.plasmon.com/udo)
Blu-Ray also promises some added security , making ways for copyright protections. Then again it may be already a well known kind of 'protection"
Blu-Ray Discs can have a uniqe ID written on them to have copyright protection inside the recorded streams. So they say.. BUT a unique ID does not make a copyprotection and there are already websites that claim it is '.. just another RID code ..".
The Recorder Unique Identifier (RID) is a 97-bit code recorded every 100 sectors. It is composed of a brand name identifier, a type number, and a drive serial number. Some recorders such as the Philips CDR870/880 write this RID on their discs to discourage copying.
The philips CDR880 recorder
Basically you have two version of recording:
- One time recording : making permanent changes to a disc
- Record many times : the ability to change a disc many times
If you use a CD-R (one time recording) the material on the disc itself is changed for ever. There is no way to get the material back into it's old state.
If you use a CD-RW (record many times) the material on the disc itself changes, but can be changed back again. You can do this as long as the material doesn't get worn out. After about a 1000 times the material does not change back to another state anymore. The materials used to make such a rewritable method possible are special crystals that can go back to their original state.
By heating up the crystals, they change form. Now when you quickly cool them. they stay in that form (which is different from its original form). This is called the amorphous state of the crystals. They have changed form and it stays that way. Your cd player can read it
(although it has a little less reflection than cd-r's, it has no problems with it).
Now, if we want to erase the CD-RW , we have to make sure that we lose all the data. So we want to get rid of the amorphous state. By heating up the material again, but this time using more time and less heat, the material gradually wants to take back its old form again , and thus the info is erased. This state is called the (poly)crystalline state.
So, by very quickly heating it and very quickly cool it, we can give the crystals another state (the amorhphous state) which thus contains data and by quite slowly heating it and quite slowly cool it, we can give the crystals their old form back (the crystalline state) which contains no more data. It's a constant change of phases. And so they called it phase change recording.
(Picuture courtesy of Pioneer)
The Blu-Ray Discs (BD) use the same recording method as DVD-RW and DVD+RW discs. This means you can rewrite them.
But there's another fun thing to the recording method. The discs are of a special format. The crystals that can change back and forth are not scattered over the disc or everywhere. There's a pattern of lines where this material exists. These patterns are called grooves.
Remember those old LP's? They have grooves as well! A given line which the needle of the pickup had to follow in order to play the music.
Of course on a Compact Ddisc, DVD and especially a BD, you cannot see those grooves with the naked eye anymore. We are talking about microns here!
