Direct detection LiDAR system and method with step frequency modulation (FM) pulse-burst envelope modulation transmission and quadrature demodulation

A direct detection LiDAR system, comprising:

• a signal generator for generating an output signal having a variable frequency;
• a modulation circuit for receiving the output signal from the signal generator and modulating the output signal to generate a pulsed modulation envelope signal configured to comprise a plurality of pulses, two or more of the plurality of pulses having two or more respective different frequencies, the modulation circuit further applying the pulsed modulation envelope signal to an optical signal to generate a pulse-envelope-modulated optical signal comprising a plurality of pulses modulated by the pulsed modulation envelope signal;
• optical transmission elements for transmitting the pulse-envelope-modulated optical signal into a region;
• optical receiving elements for receiving reflected optical signals from the region;
• and
• receive signal processing circuitry for receiving the reflected optical signals and using quadrature detection to process the reflected optical signals, the receive signal processing circuitry comprising at least one light detection element which demodulates the reflected optical signals to recover a portion of a reflected version of the output signal from a reflected version of the pulse-envelope-modulated optical signal.