Holographic Storage

I first read about holographic storage around 1990. The idea is that you can store information in three-dimensions in a crystalline material which you can both write to and read from by crossing two laser beams and writing with their interference pattern. The two beams are a reference beam and a data beam, patterned by a 2-D mask, and storing that image in a light sensitive material. The reference beam can then read the data by projecting the data image on a photosensitive array. By changing the frequency or angle of incidence of the reference beam, you can store multiple 2-D data masks in the same block of material, multiplexing the images together and reading them out individually, vastly increasing the amount you can store.

Back in 1990, I was looking forward to when holographic storage was available on every desktop. Of course, that day's still not here, and I was wondering what had happened to it. Well, it hasn't gone away entirely, and there are companies still working on it. Via MIT's Technology Review (not available without a subscription, I'm afraid):

You could store a whole lot of stuff on a one-terabyte computer disc--say a million novels, 250,000 MP3 song files, or hundreds of full-length movies. A Lucent Technologies spin-off is hoping to bring you that kind of capacity using a long-talked-about technology: holographic storage, in which a laser records data in three dimensions on a polymer medium. The technology can store up to 300 times as much data as traditional optical drives of the same physical size, and the startup, Longmont, CO-based InPhase Technologies, says it will start selling the holographic drives next year.

Unfortunately, it's not yet rewritable, although InPhase hopes it will be in a couple of years. And even then commercial availability looks to be four years away, and these estimates tend to be optimistic. InPhase Technology has a website, and the explanation of how holographic storage works is here.