| 摘要 |
<p>An optical scanning device for scanning a record carrier (22), the record carrier having an outer face (24), wherein the optical scanning device comprises a radiation source system (2) arranged to generate radiation (3); an objective system (20) having an exit face (24), the objective system being arranged between the radiation source system and the record carrier; a radiation detector arrangement for generating detector signals representing information detected in the radiation after interaction with the record carrier; and a position control system (42) for controlling a gap size of a gap between the exit face of the objective system and the outer face of the record carrier, the position control system providing for evanescent coupling of the radiation across the gap. The optical scanning device is arranged to process the detector signals to generate error signals suitable for controlling characteristics of the device during scanning of a record carrier, the error signals including a first error signal (E1) for use by the position control system for controlling the gap size. The optical scanning device is characterised in that the optical scanning device is arranged to generate a second error signal (E2), different to the first error signal, for use by the position control system for controlling the gap size.</p> |
