| 摘要 |
PURPOSE:To easily and stably perform the control by leading divided light beams and a recording light beam to an information recording medium through approximately equal optical paths and throwing respective light beams as light spots having prescribed diameters. CONSTITUTION:The divergent luminous flux of a semiconductor laser 2 is colli mated by a collimator lens 4 and is limited by an aperture 5 and is divided to three luminous fluxes by a diffraction grating 6. The diffraction grating 6 divides the luminous flux to 0th-order diffracted light and + or -1st-order diffracted light, and the 0th-order diffracted light is used for information repro ducing and AF control, and + or -1st-order diffracted light are used for AT control. The film thickness of the grating part of the diffraction grating 6 is so set that I0<=I1 is true where I0 and I1 are the intensity of 0th-order diffracted light and that of + or -1st-order diffracted light respectively. These three luminous fluxes are reflected by a dichroic prism 7 and are thrown to an optical card 11 through the optical path approximately equal to that of the luminous flux of a semicon ductor laser 1, namely, through a polarizing beam splitter 8, a quater wave plate 9, and an objective lens 10. Thus, the control is easily and stably performed. |
