Increasing Optical Disc Data Density by Using Nano-scale Metallic Wire Polarisers
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
CD and DVD became the major portable and backup data storage devices because their reliability and economical cost when mass produced. As the computer technology grew, higher data storage density on CD/DVD disc was demanded. Using a shorter wavelength light source was the common technique to achieve this goal from both research and industry. However, the limit of wavelength had almost reached for applying it to optical storage. The nano-scale metallic wire polariser that was designed in this thesis provided a possible solution. This thesis introduces the method of using the nano-scale metallic wires to form a grating polariser as the data pit on CD/DVD disc. The polariser is a type of scattering polariser and could transmit one linear polarisation of the light and reject its orthogonal counter part. The designed pattern was tested by using XFDTD, an electromagnetic simulation program based on the finite difference time domain method. As the wave source was a red laser with a wavelength of 650nm, the simulation cell size was set to be 10nm. The dispersive materials were simulated by the Debye model. The electric field results were measured on X, Y, and Z components. The results were analysed by a pre-written Matlab program to find the transmission and crosstalk coefficients. The single polariser simulations showed that there are great potentials in this design. However, inter-cell crosstalk became the major problem in the polariser array simulations. The groove pattern and titanium material were used to optimise the polarisation effect. The simulation showed that a standard-sized disc with a titanium polariser array could have 5.5GB storage capacity and a 15 to 20dB inter-cell extinction ratio for an optical pickup with a red laser (650nm) and a numerical aperture (NA) of 0.6. Although the improvement is only marginal over existing optical data storage technology, there are many further researches possible to carry on such as the fabrication of the polariser arrays.