High range precision laser radar system using a Pockels cell and a quadrant photodiode

Abstract

for various applications. The system measures the range of scenes of interest and generates three-dimensional data. With such data, LADAR systems can be used for topographic mapping, automatic target recognition, autonomous safe landing and so on [1][2][3]. To complete these kinds of missions, range precision is the most important parameter of LADAR systems.Various techniques are employed to obtain optical distance measurements including interferometry, time of flight (TOF) and triangulation [4]. For long-range measurements and working outdoors, TOF methods are employed in many LADAR systems [5]. The conventional TOF LADAR system transmits a laser pulse (start signal), triggering the time to digital converter (TDC). The transmitted laser pulse reflects off a target. The laser-return pulse (stop signal) is detected by an avalanche photodiode (APD). The APD generates an electrical signal to stop the TDC. The time interval between the start signal and the stop signal is converted into distance. Range precision is determined by the closeness of such measurements to independent range results acquired under identical environmental circumstances [6].The range precision of the LADAR system depends on a number of factors including the laser pulse width, the timing resolution of the APD, the timing resolution of the TDC, shot noise and the timing jitters generated by electronics [7,8]. Because of these factors, range precision has a limit. Generally, the range precision of the conventional LADAR system is several centimeters [9, 10]. A commercial LADAR system has several millimeters in range precision [11]. To obtain better range precision, a shorter laser pulse width is needed. However, short laser pulses require a high-bandwidth APD and a high timing resolution TDC [12]. This limitation can be overcome by averaging with the improvement proportional to 1/√(the number of results averaged), as compared to a single measurement result Abstract We have proposed and demonstrated a novel technique to measure distance with high range precision. To meet the stringent requirements of a variety of applications, range precision is an important specification for laser radar systems. Range precision in conventional laser radar systems is limited by several factors, namely laser pulse width, the bandwidth of a detector, the timing resolution of the time to digital converter, shot noise and timing jitters generated by electronics. The proposed laser radar system adopts a Pockels cell and a quadrant photodiode and only measures the energy of a laser pulse to obtain range so that the effect of those factors is reduced in comparison to conventional systems. In the proposed system, the measured range precision was 5.7 mm with 100 laser pulses. The proposed method is expected to be an alternative method for laser radar system requiring high range precision in many applications.

Development of a miniature electron-optical device for nanosatellite based on the «Synergy» platform for researching the North-West region of Russia

“…In [25] published in the journal Applied Physics B, the authors showed the developed flash lidar using Pockels cells (PCs) and a photodiode. Pockels cells change the polarization state of the radiation passing through it as a function of time, thus allowing the photodiode, coupled with micropolarizers, to measure the polarization state, obtaining information about the distance to the object of reflection.…”

High resolution three-dimensional flash LIDAR system using a polarization modulating Pockels cell and a micro-polarizer CCD camera

“…A high range precision 3D imaging LIDAR system using a Pockels cell and a quadrant photodiode (QPD) was also previously developed and demonstrated [14]. The Pockels cell changes the polarization state as a function of time and the QPD, which is aligned with micropolarizers, measures the polarization state to acquire range information.…”