Optimization of the pulse detection structure of the active ranging optical system

An active range detection system with high power laser source requires a high precision of pulse timing. Although the trigger time stamp can be obtained electrically on the circuit board level, it is crucial to detect the actual transmitting laser pulse signal to monitor the malfunction of the laser. To detect the signal, inserting a reflector in the optical path is suggested so that the photodiode can detect the signal directly. To insert the reflector and pulse detection photodiode in the optical path of the transmitting laser, it is required to confirm the obscuration ratio of the laser module by the shadow of the reflector. The shape of the reflector was set to be rectangular due to the manufacturability although the elliptical reflector shows a better performance in the aspect of the vignette. As a result, it is confirmed that the obscuration is tolerable enough to cover the requirement of 0.8 of the nominal irradiances of the signal of each pixel when the reflector angle is set to be 47 ° and insertion depth is between 0.9 mm and 2 mm.