Characteristics of phase-compensation techniques in magnetooptical read-back systems

Magnetooptical storage systems are designed to obtain high signal-to-noise ratios (SNRs), so that reliable read-back signals are obtained. One characteristic of the optical components in such systems is that they typically introduce a phase shift between the two components of the polarized read-back light. This phase shift reduces the signal amplitude and can increase noise, resulting in reduced SNR. To compensate for the phase shift, and thus restore SNR to the maximum possible value, compensation optics are inserted into the read-back system. This paper discusses various techniques for phase compensation and the characteristics of each technique with respect to alignment and component quality. A Jones calculus model is used to calculate signal and sensitivity to noise currents.