Journal of the Korean Physical Society, Vol. 47, August 2005, pp. S18∼S23 Optical Parameters of Light Beam in Multilayer Nano-Structures S. A. Shylo, * A. S. Lapchuk, J. S. Song and K. S. Kim Samsung Electro-mechanics, Suwon, Gyunggi 443-743 (Received 5 September 2004) In this paper, we propose a multilayer optical data storage method in which ultra thin metallic or Ge2Sb2Te5 layers are used for recording information. The thin layers with large losses have small dependence of reflection coefficient on direction of beam propagation and for this reason are promising as recording layers. The properties of multilayer memory based on metallic and Ge2Sb2Te5 layers 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 ultra-thin recording layers. The numerical simulation of optical properties of a multilayer optical data storage system on the basis of ultra-thin film has shown that it is possible to obtain more than 10 recording layers for a ROM type disk with pits made from ultra-thin silver or aluminum film. It was also shown by numerical simulation that it is possible to obtain 8 recording layers for aRW-type disk with recording layers as ultra-thin strips of Ge2Sb2Te5. PACS numbers: 42.79.Vb, 42.70.Ln, 42.62.Cf, 41.85.Ew Keywords: Nano-structures, High density data storage, Optics I. INTRODUCTION The objective lens with a large numerical aperture and the blue laser diode have gained widespread acceptance for increasing data capacity in optical data storage sys- tems [1,2]. The application of scalar theory for calcula- tions of laser beam intensity that is focused with an ob- jective lens having such aperture can lead to significant errors. The implementation of vector theory is also nec- essary for simulation of focused-beam propagation in a multilayer medium, since reflection and transmission co- efficients of an oblique ray from a boundary with different medium considerably depend on ray field polarization [3]. This article develops algorithms for calculation of beam intensity in a focused spot and simulation of focused- beam propagation in a multilayer medium. Then, we applied these algorithms to carry out an investigation of properties of multilayer optical data storage systems. Multilayer optical data storage in which information is stored in many recording layers of a single information carrier is promising for a significant increase of informa- tion capacity of optical data storage systems. Unfortu- nately, the fast degradation of a focused-beam spheri- cal wave front and the decreasing beam intensity when it propagates through recording layers make it difficult for real applications. The wave-front degradation is due to different transmission coefficients (different amplitude and phase of transmission coefficient) for rays propagat- ing in different directions. We propose a multilayer op- * E-mail: sergiy.shylo@samsung.com; Fax: +82-31-210-5219 tical data storage method in which ultra thin metallic or Ge 2 Sb 2 Te 5 layers are used for recording information. The thin layers with large losses have small dependence of reflection coefficient on direction of beam propagation and for this reason are promising as recording media. The properties of multilayer memory based on metallic and Ge 2 Sb 2 Te 5 layers are investigated on the basis of vector diffraction theory. The algorithm for calculation of field intensity in a focused laser spot is developed in the second section of the paper. The algorithm for sim- ulation of focused beam propagation through multilayer structure is formulated in third section of the paper. The developed approaches are applied to investigation of pro- preties of a multilayer recording system based on ultra- thin recording layers in the fourth section of the paper. II. FIELD CALCULATION NEAR FOCAL PLANE ON THE BASIS OF VECTOR DIFFRACTION THEORY An objective lens treats an incident beam as shown schematically in Figure 1. It is assumed that the im- pinging light beam at the entrance pupil of the objective lens is a plane wave with Gaussian field distribution. In our algorithm, the objective lens is expected to be an object which transfers a plane wave to a spherical wave with appropriate polarization rotation and with specified aberration. In such a situation, the focused-beam field -S18-