| 摘要 |
PURPOSE:To widen the discrimination range of a frequency discriminator and to make an automatic offset locking adjustment by feeding discrimination outputs of the 1st and the 2nd frequency discriminators back to an oscillation frequency control part, and controlling the intermediate frequency of an intermediate frequency electric signal to a specific value. CONSTITUTION:The intermediate frequency of an electric signal 10 is discriminated by the 1st frequency discriminator 11 (electric circuit), but when the intermediate frequency deviates from a set value, the 1st control signal 12 proportional to the amount of the deviation is outputted from the 1st frequency discriminating circuit 11 and sent to the impressed current control circuit 32 of a local oscillation light source 6. The 2nd multiplexed light 9, on the other hand, is made incident to the 2nd wide-band frequency discriminator 13. When the wavelength (frequency) of the signal light component 17 is equal to that of a local oscillation light component 18, both incidence positions 19 and 20 are coincident with each other, but when their wavelengths are different, both incidence positions 19 and 20 shift from each other. An electric output proportional to the amount of the deviation is outputted from a detecting circuit 16 as the 2nd control signal 21 and sent to the temperature control circuit 22 of the local oscillation light source 16. |
