Laser diode active height control system for data storage applications

Abstract

We describe and characterize an active height control system for near-field data storage applications using a commercial laser diode as a direct position sensor. The self-mixing interference signal was experimentally characterized and the effective spot size of the laser sensor was also measured. A control system utilizing interference in the laser as feedback signal was constructed to drive a conventional DVD pickup with the laser sensor mounted. The residual position error is +/- 9nm when the rotation speed of a glass disk was 1500rpm and the vertical runout was 16 mu m. The approach limit was estimated to be 25nm when the laser size is reduced to 100 mu m.