LiDAR is not just a sensor. From a pure photonics lens it is a closed-loop light system — emission, interaction, return, detection, timing, reconstruction.
From a pure photonics viewpoint, LiDAR is a light-based measurement system. A laser source emits controlled photons; light propagates through the atmosphere where it may scatter or attenuate; it interacts with a material (reflection, partial absorption, surface-dependent response); reflected photons return to the sensor; a photodetector converts photons into an electrical signal; and finally, time delay + intensity are interpreted as distance and structure.
A photonic LiDAR sensor is essentially a closed-loop light system: Photon emission → interaction → return → detection → timing → reconstruction.