A Polarization Readout Method Applied to a Groove Baseband Recording Optical Read-Only Memory Discs

In our pervious papers, we proposed a method named groove baseband recording (GBR), to record a multilevel signal onto optical read-only memory discs. We use signal processing to generate a multilevel recording signal, which satisfies the DC-free and zero-intersymbol interference condition. The resultant multilevel signal is emboss-recorded as position displacement of groove walls. In this study, we use the polarization effect to detect the position displacement of the groove walls. By our experiments, we confirmed sufficient signal-to-noise ratio and full bandwidth given by the optical transfer function. We also encountered a strong signal distortion, for which we introduced a feedback to reduce nonlinear characteristics existing in the recording and playback systems. An experimental disc of 0.7 micron track pitch and 0.194 micron/bit density is fabricated. When a magneto optical equivalent optical pickup is used to playback this disc, we confirm a 2-dimensional eye pattern of 16 levels is clearly observed.