OPTICAL HEAD AND DEVICE AND SYSTEM PROVIDED WITH THIS

摘要

The present invention is provided with a detection region for detecting light that is reflected from a first or a second information recording medium and that passes through an optical element. The first information recording medium and the second information recording media are multi-layer disks that have at least two layers, and the detection region includes a detection region (41) for detecting first order and above diffracted light that has a first wavelength, and a detection region (42) for detecting first order and above diffracted light that has a second wavelength. The detection region (41) is arranged such that it does not straddle across a region that is divided by a maximum range (38) of the dilation of zero order light coming from the first information recording medium that comes from a recording layer that differs from the recording layer that is to be recorded or reproduced, and the detection region (42) is arranged such that it does not straddle across a region that is divided by a maximum range (39) of the dilation of zero order light coming from the second information recording medium that comes from a recording layer that differs from the recording layer that is to be recorded or reproduced.