| 摘要 |
PURPOSE:To obtain a differential signal detecting system which receives no effect of a difference of power levels between read and write modes, the variation of the laser power, etc., by combining two or two sets of photodetectors and two diodes having characteristics coincident with each other. CONSTITUTION:Two or two sets of photodetectors 10 and 20 generate optical currents proportional to the optical power which is made incident to each photodetector. While the voltage obtained by flowing the optical current to diodes 11 and 21 having characteristics coincident with each other from photodetectors 10 and 20 respectively is extracted by signal lines 12 and 22. A differential amplifier 3 obtains the difference voltage between both lines 12 and 22. This difference voltage is decided by the optical current ratio between both detectors 10 and 20 and therefore receives no effect of variation of the laser power, etc. as well as no effect of a difference of power levels between read and write modes owing to the diode characteristics. Thus it is possible to obtain a differential signal detecting system which receives no effect of a difference of power levels between read and write mode, the variation of the laser power, etc. |
