A Model of SuperRens Effect to Describe Future Generation Optical Data Storage

Gidon, S., Hyot, B., Poupinet, L.
CEA Grenoble Leti

In the quest for a higher data storage capacity, different solutions for the future generations of optical discs (after the Blu-ray format, BD) are under investigations.

An increase of the NA beyond 0.85 (NA of the BD format) requires the use of near field optics with all the difficulties inherent to those techniques (fine control of the distance between the optical head and the media). Today a novel emergent technique, allows writing and/or reading information bits which are smaller than the resolution limit of the optical head without increasing the complexity of the detection system. This new solution implies the use of a “superresolving” structure made of a specific thin film stack.

The complexity of the involved mechanisms and the coupled interaction of many physical phenomena (electromagnetic, thermal, electronic…) have, up to now, often restricted the pertinence of the simulation results presented in the articles. Most of the simulation programs use FDTD methods for the calculation of the electromagnetic field in the multilayer stack [9]. Occasionally, some papers step forward to estimate the temperature distribution [2]. But they don’t take into account the coupled effects and give access to only partial results.

In the case of our study, we propose a model based on the Drude formalism whose physical principle is the photogeneration of free carriers. We take into account the non-linear aspect of the problem using the COMSOL Multiphysics software by solving the two coupled equations on optic (calculation of the electromagnetic field) and electronic contribution (generation and transport of the free carriers). Moreover, another specificity of our simulation is the calculation of a representative value of the readout signal in a far field plane.