OPTICAL HEAD

PURPOSE:To miniaturize an optical head by specifying the refractive index difference between the ordinary light and extraordinary light of a double refractive prism and the difference between the refractive index of a glass prism and the refractive index of either thereof to prescribed values or above. CONSTITUTION:The first and second luminous fluxes separated by the double refractive prism P4 vary in the refractive index within the prism P4 and, therefore, the imaging positions of the first and second luminous fluxes from the composite prism 2 vary. Therefore, a photodetector 10 deviates from the imaging point of the second luminous flux and a spot 11 is made smaller than 12 in a focusing state, if the first luminous flux is imaged on a photodetector 9 in the focusing state by paralleling the exit surface of the two luminous fluxes of P4 and a semiconductor substrate 13. The shape of the spot 11 on the detector 9 changes, if an objective lens 7 changes from the focusing position to a magneto-optical recording medium 8. When the optical head is so constituted that the refractive index difference between the ordinary light and extraordinary light of the P4 is >=0.03 and the difference between the refractive index of the glass prism and the refractive index of either of the ordinary light and the extraordinary light of the P4 is >=0.15, the relearning light is separated and the aberration is sufficiently given and, therefore, the small-sized optical head is obtd.