Aberration correcting element in the optical head of a recording and reproduction system using independent control of phase distribution and defocus pattern variables

42Even in the case where there is used technique such as "high NA", "multi-layer recording", etc., in order to carry out optimum correction of wave front aberration produced thereby with a simple technique, such an aberration correcting element to vary variable A and variable B (A≠B) of phase distribution formula A(−r)−B(−r) as phase correction pattern by aberration correcting element is realized by using a liquid crystal element. The liquid crystal element forms such an electrode pattern to generate phase distribution corresponding to spherical aberration at one transparent electrode (A), and forms such an electrode pattern to generate defocus pattern at the other transparent electrode (B). In addition, by controlling applied voltages with respect to these electrodes, it becomes possible to independently carry out variable control of the above-described variables A and B.