PURPOSE:To implement the processing of a signal with a high accuracy and a high sensitivity, by restricting passage time of a beat signal determined from a transmitted light and the reflected light thereof to switch the center frequency of a band filter in a circuit from a scanning mode to a stationary mode and vice versa. CONSTITUTION:Light beam of a laser beam source 10 is light modulated 12 by the frequency of an oscillation source 11 and a transmission light Lt is transmitted to a target. A received light Lr reflected on the target is mixed with a local light with a splitter 14, an electrical signal containing a beat is detected with a detector 15 and amplified 16 to be inputted X into an analog multiplier 17 as signal Ris. A gate signal Gs from a gate signal generation circuit 18 is inputted into a Y terminal of the multiplier to restrict the passage time of the signal Ris and the signal Ris is applied to a BPF 22. The center frequency of the BPF 22 is switched over to a scanning mode and a stationary mode with a mode control circuit 23 restricted by a signal processing circuit 26. In the scanning mode, a distance to the target is determined and in the stationary mode, a beat signal along is fetched as based on the reflected light from the target. Thus, the signal is processed with a high accuracy and a high sensitivity.
展开▼
