applications

FMCW LiDAR

Presently, all commercially mature solutions of LiDAR are based on the time-of-flight detection method. In time-of-flight LiDAR, a laser pulse is modulated and send out to an object via a scanning mirror. From the time, which the signal takes to return, the distance is inferred (time-of-flight, TOF). A key advantage of time-of-flight is the cost of the lasers, which can be very cheap as the temporal coherence of the laser source is not required to be high. A different approach is based on coherent LiDAR (also known as frequency modulated continuous wave, FMCW, LiDAR) that is an optical analog to the coherent acoustic echolocation strategies used by bats or dolphins. It uses chirped signals to instantaneously determine both distance and velocity of an object. The method is based on homodyne detection, i.e. beating the back-reflected signal with a local oscillator derived from the same laser source and maps time-to-frequency. Critically, if the object moves the return signal frequency will experience also a Doppler shift. Hence, it can also directly measure the relative object speed by virtue of the Doppler effect.