New Equalizer to Improve Signal-to-Noise Ratio

Abstract

Signal-to-noise ratio (SNR) of an optical memory disc deteriorates as the recording density increases. The authors have coped with this problem and developed a new equalizer which can improve the SNR by boosting higher frequency components on the readout signal without increasing the inter-symbol interference (ISI). The authors measured the jitter values on a prototype disc applying the new equalizer. The disc had a capacity of 15 Gbytes, a track pitch of 0.37 µm and a minimum pit length of 0.25 µm. An optical head with a second harmonic generation (SHG) blue laser with a wavelength of 430 nm and an objective lens with a NA of 0.6 was used. As a result, it was confirmed that the new equalizer could improve not only the SNR but also the tilt margins. Furthermore, the correlation between the jitter and the bit error rate observed on a conventional equalizer was found unchanged even with the new equalizer.