Laser Radar for Precise Vehicle Velocity Measurement

In this dissertation, new exploration of a pulse laser radar system is presented with two splitted parallel laser beams for the measurement of precise velocity of moving vehicles along with their contours and ranging distances. The emission of optical pulses is eye-safe, and hence the radar can be classified as a class-1 laser system. The laser emission comprises powerful and ultrashort optical pulses using the modulation concept of highly dynamic carrier injection into the active zone of a single-heterostructure laser diode. The emitted laser pulses have a wavelength of 904 nm. Two splitted laser beams are produced from one laser. Transmitted parallel laser beams consist of a fast sequence of very short laser pulses with a rise time of 28 picoseconds and a pulse width (FWHM) of 32 picoseconds. Two broadband photodetectors with high sensitivity (50 A/W) are axially installed to their corresponding transmitted laser beams in order to avoid any beam detection interference between each other. Two synchronized optical reference signals are taken from the laser transmitter to the photodiodes via optical fibers having core diameters of 125 μm each. The range detection of targets is performed according to the time-of-flight principle. The velocity of vehicle is determined by the correlation of measured contours, detected by both photodetectors. The radar system can be used for the detection of bi-directional and multiple automotive targets in a highly congested traffic. The length and height are determined along with the velocity of the moving targets. Finally, the velocity for a car based on contour measurement is experimentally evaluated.