Patent ID: 7447139

Claim:
A light-receiving element for receiving a reflection of laser light irradiated through an objective lens to a rotating multi-layer recording medium having a plurality of information recording layers stacked one over another through a return path optical system and converting the reflected light into an electrical signal, the light-receiving element comprising: a first light-receiving section having a circular light-receiving region; and a second light-receiving section disposed adjacent to an outer circumference of the first light-receiving section, wherein a following relational expression is satisfied: π(0.5λ/( NA/β )) 2 ≦S 1 ≦π(0.24 d·β·NA/n ) 2 where λ represents the wavelength of the laser light; d represents the distance between recording layers of the multi-layer recording medium; n represents the refractive index of a light-transmitting layer between the recording layers; NA represents the numerical aperture of the objective lens; β represents the lateral magnification of the return path optical system; and S 1 represents the surface area of the light-receiving region of the first light-receiving section.