| 摘要 |
PURPOSE:To easily eliminate the influence of drift without reference to variation of light from a light source by providing a light splitter on the incidence and emission sides of an optical modulator, and performing bias control on the basis of comparisons by the two splitters. CONSTITUTION:When light from a laser light source 5 is modulated by an optical modulator 6, part of the light is extracted through light splitters 10 and 12 before and after it and converted into electric signals by photodetectors 13 and 14, and they are compared mutually at a part 16 after passing through a 1/2 attenuator 15 and an LPF 18. Although a signal with a 50% duty ratio is applied from an oscillator 7 to the optical modulator 6, but the output of the comparator 16 is superposed as a bias, so even if temperature fluctuates, the optical modulator is controlled to an optinum operation point to draw a pattern corresponding to an electric modulated signal on a recording disk 4. Consequently, the influence of drift is removed easily from the device without reference to variation of light emitted from the light source. |
