A calibration system is described for the scanning and staring time-of-flight lidars under development for 3D imaging for autonomous driving and similar applications. These lidars must provide distances to objects in the scene with accuracies of a few centimeters while the received light energies span five orders of magnitude. They must operate reliably when exposed to temperature extremes. They must monitor at several dozen frames per second a wide field of view. To fulfill these requirements many lidar designs must incorporate non-linear electronic and optical systems that introduce systematic range-to-target errors that must be compensated by calibration. The calibration system’s alignment stages couple the transmitted laser pulses into a fiber loop which simulates laser propagation in free space for up to one kilometer while retaining a compact, practical device. Optical switches and a variable optical attenuator vary the simulated distance to target and the received pulse amplitude. High stability and repeatability are achieved. Tests of the calibration system will be described that measure the distortion of the laser pulse produced by propagating the laser beam through its fiber optic cables. The ability of the system to calibrate over temperature variations will be discussed.
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