An optical disc device includes: an optical pickup including a first laser light source that emits laser light, an objective lens that focuses the laser light emitted from the first laser light source onto an optical disc, and a light receiving element that receives reflected light from the optical disc, and performs photoelectric conversion on the reflected light received to output a received-light signal; an FS signal generator that generates an FS signal indicating the light amount of the reflected light from the optical disc, based on the received-light signal from the light receiving element; and a dirt determiner that determines that dirt is present in the optical pickup, when the peak level of the FS signal is less than a dirt determination threshold, and controls the light receiving element to increase the peak level of the received-light signal from the light receiving element.

An information recording and playback device includes a recording and playback unit, and a controller. The controller divides a recording area of an optical disk into a first recording area which is at an inner circumference side, and a second recording area which is at an outer circumference side. The controller controls the recording and playback unit such that the unit records or plays back data in the first recording area at a first speed, and records or plays back data in the second recording area at a second speed slower than the first speed. The predetermined radius is set to a boundary between an area in which a control residual exceeds a predetermined reference value when servo control related to focusing and tracking is performed on the recording area of the optical disk, and an area in which the control residual does not exceed the predetermined reference value.

An optical disk drive and a digital servo method for the optical disk drive includes controlling functions of the optical disk drive with a microprocessor. Low-pass filtered and gain adjusted versions of individual photodetector output signals resulting from an illumination of an optical disk are received. Versions of the individual photodetector output signals are digitized to produce digital signals. A focus control signal and/or a tracking control signal is determined through at least one servo algorithm executed by a digital signal processor based on a focus error and/or tracking error, respectively, determined from the digital signals. The digital signal processor is an integrated circuit structured and arranged for manipulation of digital signals in accordance with programmed commands, and in a manner that operates faster than the microprocessor.