| 摘要 |
PURPOSE:To reduce effect of a return light noise with an improved change in wavelength by using a distributed feedback laser as a light source for recording and reproduction to oscillate a laser only by a time obtained by dividing a reciprocating optical length by a light velocity to a recording medium from the light source in reproduction. CONSTITUTION:Light from a distributed feedback laser 17 is focused onto a recording surface of an optical disc 2 passing through a beam splitter(BS) 21, a collimator lens 18, a lambda/4 plate 22 and an objective lens 19. The reflected light thereof is reversed and reflected on the BS21 to be focused onto a photodetector 23 through a cylindrical lens 20. A control section 15 performs a fast switching at an oscillation frequency of an oscillator 24 (ON or OFF at a time as obtained by dividing a reciprocating optical path length by light velocity) to turn ON or OFF a laser diode 25 containing the laser 17 through a switch 26. In other words, a comparator 28 compares a signal from a monitor diode 27 with a reference voltage in reproduction and a differential signal is amplified to be inputted into an adder 31. The switch 26 is operated at the above frequency to drive an LD25. |
