| 摘要 |
PURPOSE:To realize high senitivity and low noise by using a semiconductor laser to a local oscillator, and providing a feedback circuit so as to keep intermediate frequency constant at all times, thereby controlling the temp. of the semiconductor laser. CONSTITUTION:The light signal applied to an input terminal 1 and the light from a local oscillator 2 using a semiconductor laser are applied by a square detector 4, by which an intermediate frequency signal 6 is obtained. One of the signal 6 is conducted to a base band reproducing and detecting circuit, and the other is conducted to a feedback circuit consisting of a mixer 8, a frequency discriminator 10, etc. The circuit 10 which controls the oscillation frequency of the local oscillator 2 so as to obtain always the same intermediate frequency controls the frequency deviated from the intermediate frequency by the signal from the feedback circuit and controls the temp. of the semiconductor laser of the local oscillator 2 thereby correcting the intermediate frequency in such a manner that it is fixed at a desired set value at all times despite the fluctuations in the input signal obtained at the input terminal 1. |
