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How Holographic Storage Works
Posted by
timothy
on Mon Jun 26, 2000 07:49 PM
from the nod-head-wisely dept.
from the nod-head-wisely dept.
The Chef writes: "Tweak3D.net has yet another excellent article for nerds -- err, I mean, guys looking to fill their brain with technical know-how. This time it's on holographic storage for PCs. Yeah, that's right -- storing files using holography! Go here for the story." This is something that gets mentioned in passing frequently but it's nice to have the technology explained nicely. Thanks for the overview!
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How Holographic Storage Works
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Re:I'm more jaded by the day, here's why (Score:3)
The external hologram surface may indeed be sensitive to damage. This is why Harddrives come packaged inside of metal cases. Sunlight would be blocked out as well. Additionally, magnetism, which damages non-optical drives, would not harm this drive. Generally speaking, optical storage devices have always been more reliable then magnetic media. You didn't learn much about holograms when you made one in 1977, because much of what you said here is wrong. As an explorer, you probably made a reflecting-light hologram, similar to what is on a VISA card. These are inaccurate as the picture changes depending upon the angle and colors of light reflecting upon the foil. Using a transmission-light hologram is much more accurate. When a monochromatic light source (expanded laser) shines upon the film, the original image is created in 3 dimensions. The image is very insensitive to precise alignment of the lasers. The laser can be angled within a range of more then 10 degrees. The film can hold more information then one 3-D image. This is what IBM is refering to. Additional monochromatic light sources can store multiple images in the film, each constructing a 3D image when transmitted through the film. After too many images are added to the film, it can't reconstruct images as well. Think of this as overexposing regular film, it's almost similar to this. The solution to this is not to have many images. One true 3D image (which holograms construct - not false ones like 3D glasses construct) already holds much more information then it's 2D counterpart. I'm a little unsure about the practicality of a holographic drive in the near future, but IBM is known for applying it's research to products. The copper technology and advanced layering of ceramic insulaters/semiconductors are examples of this. Holography has already met and surpassed traditional optical methods when it comes to nondestructive testing.
I recommend Optical Methods of Engineering Analysis by Gary Cloud for more reading in the area of holograms and how/why they work. This book is very applied and mentions many practical examples of holograms in industry.
Finally, my grammar nazi side is pointing out that you misspelled manufacturing. It's late and I probably misspelled more then just that, so I forgive you.
Bad Vibrations (Score:4)
One possible answer is because of the sensitivity of holographic equipment to vibrations. A hologram encodes phase differences between laser beams. Errors in the phase encoding mean errors in the data retrieval - you get a blurry or disjoint hologram, or you lose your data.
Light is in the hundreds of nanometers range of wavelength. This means a vibration in the equipment (a movement of one part relative to another) of only a tenth of a micron can completely throw the phase encoding out of alignment. Imagine a tape deck whose heads needed positioning to submicron precision.
Making holographic images is therefore rather difficult if, say, a large lorry rolls past your window. A hard-drive with the same problem would be absolutely useless.
So until a suitably hard substrate can be found on which to engineer this equipment, it's only a pipedream. Maybe nanotechnology will create such a material ... I doubt it'll happen before then.
oops, went over a bump (Score:3)
The author mentions, enticingly, that the potential of the technology is to store 10 gigs or more in an area roughly the size of a "single gambling die". This, clearly, is a fantastic dream.
Regrettably, the real problem that the article doesn't really touch is the space and more importantly, the precision and energy, required by the laser that is needed to read and write to the medium. Just glancing at the interior of my relatively rudimentary CD-ROM drive, I can see that its mechanism consumes considerably more area than a die. And it doesn't even rely upon the sophisticated network of lenses described in the PRISM research project.
You all know how inconvenient it was/is to transport a CD player through rough terrain and expect it to work continuously. Imagine trying to get any kind of ruggedness out of this badass!
However, 10 gigs smaller than the last joint in my thumb.... yum.
-konstant
Yes! We are all individuals! I'm not!
Why (Slash) God(s), why? (Score:3)
I'm more jaded by the day, here's why (Score:5)
However, the storage capacity cited is 10GB/cm^3 cubic centimeter) not cm^2 (square centimeter) as you stated. By comparison, given how thin the magnetic films are, I doubt the 75GB HDD even has 1 cc of active storage volume so holograms do not approach the volumetric density of magnetic media.
The key of course is that holograms offer the promise of true volumetric storage, where magnetic media is limited to the thin film [though who can forget the hedelberg group who used a thin film -- namely a roll of commercial adhesive tape [villa-bosch.de] to as an optical medium for up to 10GB a few minths ago?)
So, since it comes down to form factor, I'm not excited. The problem with the HDD is the overall associated mechanism, and with 1 GB matchbook 10G-resistant HDDs out there *today*, I'm not sure when I'll ever be excited. There is no reason to expect we'll be carrying 'naked' (or packaged) holographic media, any more than we carry naked (or packaged) *high density* platters today -- and holographic drives may well be larger, more expensive, more fragile, etc. than HDDs in 2003, as well. In 2003, you won't be able to *buy* a new HDD as puny as 10GB, if indeed they are still maanufacturing that size, today.
The external hologram surface may turn out to be sensitive to damage (though I can hope for the use of confocal optics, etc. to image the volume despite surface imperfections or contamination) and the volume may be vulnerable to sunlight.
The hologram technology used here showed promise because it can be multiplexed with different laser colors and at different angles, but the 'clarity' of the signal goes down with the square of the number of channels, until it is unintelligible. This does not bode well for rapid breakthroughs (though if we could predict them, they wouldn't be breakthroughs). Precise alignment is necessary to assure high density, reliable readings. it seems likely that the 2003 holographic drive will be larger, more expensive, and offer no appreciable advantage (aside from ?magnetic insensitivity?, if that counts)
Aside from the probability of actually seeing a production drive someday, I think that several other holographic technologies are more promising. and none of the holographic technologies show signs of exceeding the practical capacities of straight optical media in the predictable future -- i.e. the next three years. Standards, not technical capabilities, block DVD-R from coming out *this year*
Hey, I want my petabyte encrypted keychain as much as the next guy... but, you know, 'fire' still has many unparalleled uses, in the nuclear age. And I'd rather grill than irradiate my dead cow this weekend anyway
Sigh (Score:3)
Fawking Trolls! [slashdot.org]
the only problem... (Score:3)
FluX
After 16 years, MTV has finally completed its deevolution into the shiny things network
Captain, we must get to base!!! (Score:3)
inspired by this paragraph.
However, as you keep recording more data pages slightly away from previous pages, the holograms will begin to appear dimmer and fogged up because their patterns must share the material's finite dynamic range and the data page is physically etched into the crystal. Eventually you will run out of space to store because the crystal has depleted all of its physical storage capacity, sort of like write once, read many media such as CD-R.
This is how they get so much data, you can shift the angle ever so slightly and have a new canvas. Mix this with a billion nano-bots with flashlights and miniature crystal-zamboni's and you've got some serious disk space.
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The practical nature of holographic storage (Score:3)
The main problem with holographic storage is creating a usable and stable reader/writer. People have managed to create holographic storage devices from such fanciful things as spinning glass rods and tanks of supercooled gel
By the way
There have been some recent advances in fixed holographic storage, which would allow a 1-6 terabyte hard disk to be made, with no moving parts. However, the cost/gigabyte is still well over that achievable by magnetic media (but under that of copper memory).
Perhaps in the next five years we will see the advent of the non-spinning drive, and portable disk space approaching the petabyte. Enough storage to keep most of what we now consider to be human knowledge.
Reach out, extend to, and embrace the universe.
-Einstien
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Embrace, extend, and engulf the universe.