Intersymbol interference characterization and equalization for high density optical data storage

Abstract

In optical data storage, intersymbol interference (ISI) is one of the limiting factors for high storage density. To reduce ISI, we need to understand its characteristics and use appropriate signal processing techniques. In this thesis, we characterize ISI for various data patterns and compare Signal to Noise Ratio (SNR) with and without ISI equalization. To characterize ISI, we sample the readback waveforms and use a computer program for data processing. To compare SNR with and without equalization, we record a pseudo random sequence and compare the detected marks with original marks. We also compute SNR using the additive interleaving detection (AID) technique without ISI equalization. From our studies, ISI is found to be more significant as mark widths become smaller. We also found that SNR can be increased by 3-9 db with equalization. More interestingly, we found that AID gives good SNR even without ISI equalization. This indicates the simplicity of using AID for higher storage density.