Optical Disc Track Pitch Variation Measurement Using Two 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 track pitch, but also to determine the degree of track pitch variation. Track pitch variation (T P V) is commonly measured using scanning electron, laser scanning and scanning tunneling microscopies. However, these methods are time consuming and it is difficult to take T P V readings from large areas of the disc. We developed a T P V measurement system based on an optical disc player with two readout beams, and using this system we can rapidly measure the T P V over the whole disc surface. In this paper, we describe our T P V measurement system and present the results of T P V measurements taken from a disc containing continuous grooves with a track pitch of 0.84 µm. We found that the T P V 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.