Research On Femtosecond Laser Three-dimensional Disc Storage System And Related Technologies

The need for data storage is explosive, triggered by the development of multimedia and electronic communication networks. Mass storage devices are necessary to fulfill the increasing demands.A femtosecond laser three-dimensional disc storage system has been designed based on servo technology used in current optical disc storage devices and two-photon three-dimensional confocal fluorescent data storage. We built the system and researched on related theoretical and experimental issues. This project was supported by National Nature Science Foundation of China (No. 50275140 & No. 50335050) and "863" project (MEMS2003AA404-050).Firstly, we analyzed several servo methods of multi-layer disc storage system. Consulted the two-element lens technology used in compensation for spherical aberration, a varifocal layer-selection technology in three-dimensional storage system was proposed, and the movement of voice coil motor in following and layer-selection process was investigated. Considering the complexity of control and optical system in varifocal layer-selection method, we brought forward a two-pick-up both-side method as implementation scheme of the femtosecond laser three-dimensional disc storage system and studied the axial and radial synchronous errors between two pick-ups because of manufacture and assemblage. We proposed the fluorescence intensity servo technology used in confocal module and simulated it in Matlab with calibration data obtained from photobleaching material storage experiment.Secondly, according to the principle of confocal fluorescent microscope and its three-dimensional optical transfer function, we analyzed the connection between parameters in confocal module and the resolution of sigle-photon and two-photon confocal fluorescent system. The depth-discriminating ability of single-photon confocal fluorescent system with 10.4μm pinhole diameter is 3.6 times higher than that with 208.4μm pinhole diameter. The depth-discriminating ability of two-photon confocal fluorescent system with 7.8μm pinhole diameter is 1.56 times higher than that with 156.7μm pinhole diameter. Also, the two-photon confocal fluorescent system has better axial response than single-photon confocal fluorescent system when defocusing amount is large. We carried out two-photon confocal fluorescent imaging experiment with given-size fluorescent object, which verified the inverse relation between detector size and system resolution.Thirdly, we designed and fabricated the servo module in femtosecond laser three-dimensional disc storage system, and realized its servo function. The recording optical system and two-pick-up synchronous control circuit in confocal module were also completed. The synchronous control circuit was simulated by using its focusing input and output signal. The simulation result and measured data fitted well (fit=78.0259%). We built two-pick-up synchronous focusing error detection device and measured synchronous focusing errors under different excited frequencies. The storage experiment with photobleaching material (diphenylethylene) spin coating on DVD disc was executed, and preliminary result has been achieved.Finally, rebuilding original storage systems based on platform, we carried out three-dimensional optical storage experiments with femtosecond laser. Two-layer optical data storage in PMMA film doped with photochromic material (diarylethene derivative) was achieved. The distance between two bits in each layer and the two adjacent layers interval were 4μm and 8μm respectively. Three-layer optical data storage in PMMA film doped with photobleaching material (diphenylethylene BPSBP) was achieved. The distance between two bits in each layer and the two adjacent layers interval were 4μm and 15μm respectively. Nine-layer microexplosion data storage in Sm(DBM)3Phen/PMMA was achieved. The distance between two bits in each layer was 4μm and the two adjacent layers interval was 8μm. According to storage research on photochemical and photophysical properties of three kinds of materiels, photobleaching material and two-photon confocal fluorescent storage method were chosen in our femtosecond laser three-dimensional disc storage system.In conclusion, we implemented theoretical and experimental research on femtosecond laser three dimensional disc storage system. Meanwhile we discuss and look forward to the related projects in practical process. The work in this thesis is helpful for three-dimensional optical storage devices coming into mass storage market.