| 摘要 |
PURPOSE:To obtain frequency modulated signal light of fixed frequency shift by obtaining a beat signal of frequency corresponding to frequency shift by delay self-heterodyne detection using a part of signal light, and controlling modulation degree of light source to make the frequency of the beat signal to a fixed value. CONSTITUTION:A beat output 15 of the first and second reference light, that is, the beat output 15 (electric output) having peaks near zero frequency and shifted frequency is obtained in a light detector 14. The beat output 15 is amplified by an amplifier 16, wand then only a beat component 18 near shifted frequency is taken out by a band pass filter 17 and inputted to a frequency discriminator 19. The center frequency of the beat component 18 is compared with the set frequency in the frequency discriminator 19, and an error signal 21 obtained is fed back to a pulse driving circuit 3 through a low-pass filter 20. The pulse driving circuit 3 changes the amplitude of pulse current 5 based on the error signal 21 and controls to make the center frequency of the beat component 16 coincide with the set frequency. |
