Dual-wavelength method for high-density optical data storage

Abstract

Optical date storage systems use diffraction-limited optics. The recording density will be greatly increased by using a short wavelength. Currently, a second-harmonic generation semi-conductor laser with stable high power output is not available. Moreover, a system requiring less power is usually much more reliable and stable. Therefore, it is critical to reduce the power requirement of a short wavelength source in optical data storage systems. One possible way is to apply the antireflection coating technique to the magnetooptic (MO) medium. The key point is to achieve low reflectivity when writing and a large figure of merit when reading. We consider two different but close wavelengths for reading and writing. In the multilayer antireflection coating design, the loss in the MO medium was taken into account. After carefully selecting the number of thin film layers and their indices as well as thicknesses, a good result for a Co/Pt MO medium was obtained. The reflectivity at the writing wavelength is almost zero, showing that the incident light at this wavelength can be efficiently absorbed by the MO medium. At the reading wavelength, we obtained the enhanced Kerr rotation and relatively large reflectivity. The figure of merit Rθk2 can be as large as 0.25.