| 摘要 |
PROBLEM TO BE SOLVED: To monitor a recored/erased state while instantaneously reproducing information from a just recorded/erased information track by reproducing the information from a information track recorded/erased with a main beam with a subbeam. SOLUTION: The liminous flux emitted from a semiconductor laser 1 is separated into three luminous fluxes of a 0-order diffracted light 4, a plus 1-st order diffracted light 5 and a minus 1-st order diffracted light 6 by a luminous flux separating means consisting of a the diffraction grating 3 provided in a hologram unit 2. The luminous fluxes 4-6 are respectively transmitted through a grating plane 7 to be exited from the unit 2 and are transmitted through a quater-wave plate 8 to become circular polarized lights from linearly polarized lights and from optical spots (SPs) 11-13 through an objective lens 9. The SP11 performs the recording/erasing/reproducing of information and the SPs12, 13 detect tracking error signals. Moreover, the SP13 is made to be an ellipse long in a radial direction and reproduces information which are recorded/erased by the SP11. Thus, the recorded/erased state is instantaneously monitored without providing a light source for monitoring. |
