Measurement of optical phase and polarization in the media and systems of optical data storage

Abstract

This dissertation presents the measurement of optical phase in the media and systems of optical data storage, polarization dependence of signals from periodic one-dimensional arrays of magnetic domains in magneto-optical media and crystalline domains in amorphous phase-change media, and optical characterization of multilayer stacks used as optical data storage media. Digital signals in optical data storage systems can be encoded in the intensity, polarization or phase of the carrier beam. Both surface structure and material property variations can create a phase modulation at the exit pupil. Current optical data storage systems do not make use of this phase modulation and its recovery could increase the strength of the generated signal. We experimentally describe a variant of Zernike's phase-contrast microscope to measure the small phase object, an interferometer to measure the relative optical phase on reflection between amorphous and crystalline regions of the phase-change media of optical data storage, and a method to measure optical phase information in disk system. In order to increase the data density in optical data storage, the wavelength becomes shorter and the numerical aperture of the objective lens becomes higher. In the interaction of the focused beam with a grooved, multilayer disk, the different response to s- and p-polarized light upon reflection from the disk results in different complex-amplitudes and has strong impact on readout and servo signals for the two fundamental components of polarization. Polarization dependence of signals from periodic one-dimensional arrays of magnetic domains in magneto-optical (MO) media and crystalline domains in amorphous phase change (PC) media are studied by theoretical calculation and experiment. Currently, many different multilayer stacks are designed to enhance the contrast of readout signal, reduce noise, increase the storage density and speed, or improve media reliability. A good understanding of the range of values of the optical constants should help to improve the accuracy of optical and thermal design of the storage media. The refractive index n and the absorption coefficient k of these materials vary to some extent with the film thickness and with the film deposition environment. We report the observed variations of optical constants among samples of differing structure and among samples fabricated in different laboratories.