OPTICAL DISC TRACK PITCH VARIATION MEASUREMENT USING 2 READOUT BEAMS

At present high-density optical discs have narrow track pitch values, and hence it is necessary not only to verify the precision of the trac k pitch, but also to determine the degree of track pitch variation. Tr ack pitch variation (TPV) is commonly measured using scanning electron ; laser scanning and scanning tunneling microscopies. However, these m ethods are time consuming and it is difficult to take TPV readings fro m large areas of the disc. We developed a TPV measurement system based on an optical disc player with two readout beams, and using this syst em we can rapidly measure the TPV over the whole disc surface. In this paper, we describe our TPV measurement system and present the results of TPV measurements taken from a disc containing continuous grooves w ith a track pitch of 0.84 mu m. We found that the TPV of these grooved discs ranged from 30 nm to 100 nm peak-to-peak (pk-pk) with a typical value of 40 nm pk-pk. The measurement resolution of our instrument is about 10 nm pk-pk.