| 摘要 |
PURPOSE:To obtain an optical signal reader of good SN ratio and high precision by irradiating light to an information recording medium and controlling the intensity of a light source so that the quantity of incident light of a photodetector which receives the light from this medium is constant. CONSTITUTION:The light incident on an information recording medium D from a light source L is polarized and has the frequency, the phase, etc. changed in the reflection or transmission stage and is outputted from the medium D. This output light is received by the second photodetector and is fed back to the other input terminal of a comparing amplifier, and thereby, the quantity of received light of the second photodetector, namely, the photoelectric output is constant. Thus, the light which is outputted from the information recording medium D and is divided by an optical beam splitter or the like is converted to the variance of a physical quantity such as the variance of the polarization angle, the variance of the frequency, the variance of the phase, or the like other than the quantity of light and is converted photoelectrically by the first photodetector to read information. |
