Moving object detector for vehicles - has modulated laser rays for reflection which are amplified and demodulated and the doppler offset extracted

摘要

Modulated laser radiation (S1) is emitted from a laser diode (1) modulated by an integral photodiode (3). Reflected signals (E1) from the target (2) pass through a collimation lens (4) and are amplified in the laser cavity. The beat frequency from the moving target is extracted by the photodiode (3) producing the doppler return (homodyne system) (6). The return passes through a high pass filter (7), smoothing circuit (8) and then to a processor (9) which outputs the distance (D) and speed (V) of the vehicle. ADVANTAGE- Allows weak signals to be received without interference from car lights or sunlight thus making the system more secure.