Patent ID: 7522507

Claim:
An optical scanning device for scanning a multi-layer optical record carrier when positioned in a scanning location in the device, the device being configured for scanning a first information layer at a first information layer depth within the record carrier and a second information layer at a second information layer depth within the record carrier, the device comprising: a radiation source for generating a radiation beam; an objective lens, located in an optical path between the radiation source and the scanning location, for converging a radiation beam to a spot on an information layer; and an optical switching arrangement switchable between a first state, in which the device is arranged to scan said first information layer, and a second state, in which the device is arranged to scan said second information layer, wherein the optical switching arrangement comprises a non-mechanical compensator arranged to generate, without need of a mechanical system, a different amount of spherical aberration in a radiation beam when in said first state and when in said second state, wherein the non-mechanical compensator is further arranged to generate a different amount of vergence in a radiation beam when in said first state and when in said second state, the different amounts of spherical aberration and vergence being selected such that a free working distance between said objective lens and said optical record carrier remains substantially constant when switching between said first and second states.