The next generation of optical storage

The next generation of optical storage

Jan 01, 2019 / By : / Category : 老域名购买

As long ago as 1920 it was recognized that optical storage would potentially give the highest possible storage density. However, the realization of reliable optical storage systems had to wait for the development of the laser. Even then, it was not until the development of the compact disc that optical storage really penetrated the consumer market. Now technology has moved on and we are currently awaiting news of the split points decision in the fight between Blu-ray and HD DVD. Even as that fight rages on, researchers have been looking ahead and we are right there looking over their shoulders. 老域名出售

First, let's look at some of the basic, underlying information. For a single layer disc, the information capacity is limited by diffraction. This law governs how small a spot light can be focused to. Diffraction is governed by three factors; wavelength, numerical aperture, and the refractive index of the medium the lens is in. Blue light focuses tighter than red, thus, Blu-ray and HD DVD have benefited from the transition from red to blue lasers. However, going to shorter wavelengths means ultraviolet light and good bye to cheap optics. The numerical aperture can be thought of as a measure of the light-gathering power of a lens. Unfortunately, technology has run headlong into physics, making further improvements in the numerical aperture difficult. and this is also at the maximum physically possible in current systems.

Thus the question is "What next?" Part of the answer may lie in the medium between the lens and the disc. When lithography needed higher resolution, researchers effectively increased the numerical aperture of their lenses by putting them in liquid. However, placing a liquid between the disc and the lens is problematic, since no one wants their removable storage coming out of the player damp. The answer may lay in putting a solid between between the lens and the disc, as long as the solid can be placed to within a small fraction of a wavelength of the disc. This presents some mechanical engineering problems but nothing fundamental and could boost the single layer storage density up to 125GB.

At this point, resolution can take you no further, but encoding more than a single bit per location can. This has been tried with limited success before, but, technology has finally caught up with ideas and this may now be feasible. Instead of simply putting islands on the disc track, the information is encoded in a spiral staircase, which has the strange effect of adding angular momentum to the light, which can be detected by looking at the polarization. Thus the direction and step size of the staircase can change the information encoded, which means that somewhere between two and eight bits can be encoded per location. The initial demonstrations showed that the techniques for encoding multiple bits in the angular momentum of light are promising, though understandably noisy given the low numerical aperture used to collect the signal.

The paper presents a fascinating review of the past and an intriguing insight into the very next steps in optical data storage. Although they briefly mention more far-off possibilities, such as holographic storage, they have deliberately limited themselves to those techniques for which current mass production techniques will provide high volume content distribution.

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