Patent number 3,931,459 : Video Disc
Inventor: Adrianus Korpel
Assignee: Zenith Radio Corporation
Filed: Feb. 4, 1974
Summary of the Invention [Excerpt]: "Optical image reproducing systems have been proposed as adjuncts to home color television receivers to increase their use by arranging for the play back of recorded program material through such receivers. As heretofore proposed, the program material is stored in a carrier, such as a disc quite similar to well known audio discs, to be read by a beam of energy, usually a laser beam, to develop an electrical signal representation of the stored information."
In other words, stick the round, flat shiny thing into the right kind of player, and you can watch "Xanadu" whenever you like. Oh, wait, 1974... make that "The Exorcist" or maybe "American Graffiti." Actually, video disc movies and players wouldn't be available to the public until the early 80s, several years after the application for this patent was filed by Zenith. It was one of many disc-related patents filed by many companies even though, two other companies, Sony and Philips, were the primary developers of the technology. Not that it mattered much back then since, in the US, most people wanted their movies on VHS videotape. At least they did until the DVD -- with it's commentary tracks, extra scenes and additional cinematic goodies -- became the format of choice in the late 1990s. Which brings us to Blu-ray (capital "B", lowercase "r", don't forget the hyphen and, for God's sake, don't stick an "e" in there and write "Blue").
You have to wonder: Is the entertainment industry going to keep doing this to us every few years? Getting us hooked on their product like drug dealers and then making us come back, again and again, to re-buy the same stuff in a new form? How many media players and versions of "Blade Runner" do I really need to buy? And what's the difference between a DVD and a Blu-ray disc anyway?
Entertainment industry executives -- entrepreneurial champions of the capitalist ethos or money-grubbing scumbags, take your pick -- love to find new reasons for the media-mad public to hand over some cash. But just as poly cotton blends have replaced bison pelts in our wardrobes, embracing the new video technology is about more than just money or fashion: It's about good science and genuine progress. Progress that helps you experience, with hitherto unimagined clarity and nuance, the campfire fart scene from "Blazing Saddles."
Video discs, CDs, DVDs and Blu-ray discs are all variations on a theme, that theme being optical storage media. There are three things needed for optical data retrieval to work: a disc, a disc reader and a little light.
Visible light is part of the electromagnetic spectrum just like radio waves and microwaves. And, like radio waves and microwaves, visible light has wave-like characteristics. Wavelengths of light are usually measured in nanometers, one nanometer (abbreviated "nm") being equal to 0.00000003937 inches. A typical sheet of typing paper is around 0.004 inches thick or roughly 101,600 nm. The visible portion of the electromagnetic spectrum, has wavelengths between 400 and 700 nm, give or take. Light whose wavelength is just over 700 nm is (invisible) infrared light, and light that is a bit less than 400 nm is (equally invisible) ultraviolet light. Other kinds of (invisible) electromagnetic radiation, like microwaves and x-rays, lie beyond the range of infrared and ultraviolet.
Different wavelengths of visible light correspond to the different colors of the rainbow. The white light from an average light bulb is a mix of every wavelength of visible light, so it's not just one color, it's every color all at once. But lasers are made to emit light of some particular wavelength which is why the light from a laser has a specific color. The ability to set the wavelength of light emitted by a laser is essential for reading optical data discs.
Optical storage media, like Blu-ray discs, are made out of several layers -- but only one (or, sometimes, two) of those layers keep them from being nothing more than undersized Frisbees. Sandwiched between clear protective outer layers is a shiny, reflective layer containing microscopic indentations of various lengths called pits. The pits follow a path, only a few hundred nanometers wide, that spirals outward from the center of the disc. The arrangement of the pits -- alternating with non-indented areas called lands -- kind of looks like a long Morse code message when the pitted layer is seen through a powerful microscope.
|Digital data is burned onto a CD, DVD or Blu-ray disc in a path that spirals outward from the center of the disc. If the spiral path of a Blu-ray disc were stretched into a straight line, it would be over 37 miles long.|
It's tempting to think of the pits and lands as directly representing the zeros and ones of the digital data that's been burned or stamped onto the disc, but that's not quite right. It's still binary information, but the pits and lands are both read by the computer as zeros. It's where the transition from pit to land (or vice versa) takes place that the computer sees a one. If the laser shines its beam on a flat reflective area (a land) the beam will just be reflected back to the reader and the computer will see a zero. However, if the beam hits an indentation (a pit) the laser beam suddenly stops getting reflected, the computer registers the change as a one. The computer also registers a one when the beam goes from a light-scattering pit to a shiny land.
After that, it's all about timing. The laser beam scans every part of the disc for a specific unit of time. Whenever the laser beam encounters a lengthy pit or a long stretch of land while reading the disc, it notes how many units of time it took to scan that region and records that number as the number of zeroes in a row it saw. If several short pits are close together, the computer will see a bunch of transitions in that tiny time interval and register each of them as a one. Keep in mind: the time it takes to do all of this is usually measured in microseconds (1 microsecond = one-millionth of a second).
According to the Blu-ray Disc Association (www.blu-rayAssociation.com), here's what's different about a Blu-ray disc...
The smallest pits on a CD can be no smaller than 600 nanometers because the laser reading them has a wavelength of about 780 nanometers. On a DVD, the pits can be as small as 400 nm because the laser reading them emits light with a wavelength of about 650 nm, more focused than the CD reader's laser. But on a Blue-ray disc, the pits can be as tiny as 150 nm because the laser reading them only has a wavelength of roughly 405 nm, a wavelength of light that corresponds to the blue region of the visible spectrum. Using a laser light with a smaller wavelength allows the player to read smaller pits. Smaller pits means more pits fit on a disc. Fitting more pits on a disc means fitting more data on a disc... meaning two different commentary tracks, two Spanish language versions and a "Finding Your Inner Stripper" featurette will all fit quite easily on your Blu-ray disc of "Showgirls."
Knowing what we know about light waves and wavelengths, and knowing that we've known it for over a century, you might wonder why the developers of this technology didn't start with blue lasers. As it turns out, a number of technical issues stood in the way of doing that. When companies were first trying to get CDs and video discs to market, blue lasers were very expensive and would have put the disc players beyond the budget of the typical home user. Also, data transfer rates using the available hardware were too slow to handle such a huge amount of information. There are some excellent books with charts listing the percent differences in data transfer rates for various computer setups, but reading them kept putting me to sleep, so I can't go into that here.
I should mention that this whole business of wavelengths and pit sizes also explains why a Blu-ray player can read a CD, but a CD player can't read a Blue-ray disc. With software, you can have the kind of compatibility that allows documents created in an older version of the software to be opened by a newer version. But when software developers are being sweet, consumer-friendly non-assholes, their programs will also let you save a document created in the newer version in a way that allows someone to open it in an older version. With hardware, that kind of compatibility is a lot trickier, but again, it all goes back to wavelengths.
A 405 nm laser in a Blu-ray player can scan the larger pits and lands of a CD, but the laser in a CD player isn't compatible with the Blu-ray format. The pits and lands on a Blu-ray disc are too small and close together to be read by a 780 nm laser beam. The CD reader's laser would take in too much information and the computer would have no idea of how to pick out what it needed from everything it was seeing. It would be as if you were doing maintenance on a car engine and someone was behind you giving you step-by-step instructions, then, suddenly, another 15 people showed up and they all started giving you instructions at the same time. Even if they were all giving you correct instructions, it would just sound like useless noise. Naturally, the same thing happens when a DVD player tries to read a Blu-ray disc.
The science behind Blu-ray is, y'know, there... but really it's all about your favorite movies and TV shows being available for you to watch in the privacy and comfort of your own home. It's about letting your friends think you only watch moody, deep art house films while copies of "Porky's" and "Eyeborgs" are secretly stashed away in your condo. But be warned, when "Eyeborgs II" comes out, you might be watching it on a new player. That's right, they're planning on doing it to us again.
As I mentioned before, wavelengths corresponding to blue light aren't nearly as small as you can get when it comes to the electromagnetic spectrum. Beyond the blue there are even smaller wavelengths in the ultraviolet range. This raises the question: Is an ultraviolet disc reader on the horizon? Soon, perhaps, but not right away. The new frontier being investigated for optical data storage is three-dimensional holographic storage. Here, we're into the realm of nanotechnology where data is written using both the surface area and the thickness of the disc's data layer. When fully developed, this new technology will have the potential to store 100+ GB of data on a single CD-sized disc. Imagine the whole Harry Potter series or an entire season of "Seinfeld" on one disc. Imagine having to shell out even more money for another fuckin' player!
- Blu-ray Disc Association, http://us.blu-raydisc.com
- Compact Disc Technology by Heitaro Nakajima and Hiroshi Ogawa (with translation by Charles Aschmann), 1992, published by Ohmsha, Ltd. and IOS Press.
- DVD Demystified, 2nd Ed., by Jim Taylor, 2001, published by McGraw-Hill.
- How Computers Work, 2nd Ed., by Ron White, 1995, published by Ziff-Davis Press.