Study On Multi-layer Optic Disk Readout Technology With Confocal Microscopy

One reason that computers have become increasingly important in daily life is because they offer unprecedented access to massive amounts of information.The decreasing cost of storing data and the increasing storage capacities of ever smaller devices have been key enablers of this revolution.Current storage needs are being met because improvements in conventional technologies,such as magnetic hard disk drives,optical disks,and semiconductor Memories,have been able to keep pace with the demand for greater and faster storage.However,there is strong evidence that these surface-storage technologies are approaching fundamental limits that may be difficult to overcome,as ever-smaller bits become less thermally stable and harder to access.Exactly when this limit will be reached remains an open question:some experts predict these barriers will be encountered in a few years,while others believe that conventional technologies can continue to improve for at least five more years.In either case,one or more successors to current data storage technologies will be needed in the near future.An intriguing approach for next generation data-storage is to use light to store information throughout the three-dimensional volume of a material.By distributing data within the volume of the recording medium,it should be possible to achieve far greater storage densities than current technologies can offer.For instance,the surface storage density accessible with focused beams of light (without near-field techniques) is roughlyl/λ~2.With green light of roughly 0.5 micron wavelength,this should lead to 4 bits/sq,micron or more than 4 Gigabytes (GB) on each side of a 120mm diameter,1mm thick disk.But by storing data throughout the volume at a density of1/λ~3,the capacity of the same disk could be increased 2000-fold,to 8 Terabytes(TB).It is interesting to note that the DVD disk standard exceeds this rough estimate of the areal density limit despite using light of slightly longer wavelength.However,no laboratory demonstration of volumetric storage to date has gotten closer than approximately 1%of the 1/λvolumetric density limit.The vast unrealized potential of volumetric storage,coupled with the hard limitations encroaching upon surface optical(and magnetic) storage,has fuelled a large number of research efforts.In this paper,a multilayer optical data storage method in which confocal microscopy is used for its optical sectioning is proposed.A confocal microscopy has the ability to collect optical sections from thick specimens,the key to the confocal approach is the use of spatial filtering(pinhole) to eliminate out-of-focus light or flare in specimens that are thicker than the plane of focus.For this reason the confocal multi-layer technology is promising as a new multi-layer optic storage method,in which when a layer has been chosen by being focused with the laser beam,the light from other layers in a certain distance-always tens of microns-will not be propagated through the pinhole and detected by a sensitive sensor.This means the information recorded in different layers can be read separately,the interference between layers is greatly suppressed.The properties of multilayer memory based on confocal microscopy are investigated on the basis of vector theory.The algorithms for calculation of field intensity in a focused laser spot and focused beam propagation through multilayer structure have been elaborated.The developed algorithms are applied for investigation of properties for multilayer recording based on confocal microscopy.The numerical simulation of optical properties of a multilayer optical data storage system with three layers has been shown in the paper.We used pits and bumps to record information.The results of the experiment and the conclusion are obtained finally.Multi-layer optical disk readout technology and its theory analysis basing on confocal microscopy in this paper,can effectively eliminate the interference problems between different layers in three-dimension optical storage.It is a key technology in the development of multi-layer optical storage technology,and will be of great significance.