The idea of using holograms to store data on computers has tantalized engineers since the 1960s, and now it finally looks like it’s going to market. Last month, InPhase Technologies, in Longmont, Colo., planned to release a holographic storage drive with 5.31-inch write-once, read-many disks that each hold 300 gigabytes. InPhase, a Bell Labs spin-off, says that by 2010, disks of that size will store 1.6 terabytes of data, while others as small as a credit card will hold at least 20 GB. Shortly thereafter, the company predicts, rewritable holographic media will allow the technology to compete with flash memory.
Today’s media record data in a single layer or, at most, two—giving CDs a 700-megabyte capacity, for instance. By contrast, InPhase’s holographic drive writes in layers all the way through its 1.5-millimeter-thick polymer disks. Instead of registering the data as pits on metal, the drive places them in optical checkerboard arrays that each contain just over a million light and dark pixels.
The patterns are created in two steps. First, a laser beam is split into two beams—one to carry data, the other to serve as a reference. Then the beams are made to interfere at a layer in the disk, producing bright spots wherever the wave peaks coincide. Those spots pack enough energy to induce a chemical change that fixes the holographic array in place, as a hologram. Each disk contains 3200 such holograms, and they can be multiplexed by varying the reference beam angle, the wavelength, or the position relative to the disk.
Skeptics point out that holographic storage has failed time and again because of problems with the medium (which have made it hard to record in many layers) and the hardware components (which must write and later read data with great speed and accuracy). But the Bell Labs scientists who founded the company are confident that those problems are solved.
They argue that their research has produced a superior photopolymer recording medium, one they have been selling for years to optical companies that produce CDs and DVDs. They also point out that years of volume production for other applications has ironed the kinks out of such critical hardware elements as solid-state lasers, CMOS active pixel detector arrays, and MEMS-based spatial light modulators.
More information is at http://www.inphase-technologies.com.