الفهرس 
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Abstract
The position-sensitive detector (PSD) is the heart of many applications such as optical communication, object detection, and laser tracking systems. It is a simple photodiode configuration capable of detecting the centroid position of a light spot projected on its surface, and this can be Laser Quadrant Detector (QD) or Lateral Effect Photodiode (LEP). The position information is calculated from the relative magnitudes of a few photocurrent signals provided by the PSD. In a QD, the output photocurrents are derived by projecting a light spot on four photodiodes forming a 2x2 structure on a common substrate, while LEP is a single photodiode in which embedded resistive layers are used to generate the position-sensitive signal currents.In this thesis we are interested in measurement, modeling and performance evaluation of the laser four-quadrant detector. Each photodiode is modeled using differential equation then implemented and solving using ORCAD – Pspise. The simulation results showed that a reverse bias voltage should be applied to the photodiode to decrease the junction capacitance and increase the photocurrent; this will increase the photodiode sensitivity with a small increase in the dark current. Also the model is used to investigate the effect of donor concentrations, acceptor concentrations and intrinsic region concentrations. The simulation results showed that the donor concentration should be kept as small as possible in order to improve the photodiode performance, the acceptor concentrations have a small effect on the performance, as the intrinsic region concentration increase , improves the photodiode performance by decreasing the junction capacitance with a small increase in the dark current . The model validation was done by comparing the model results with the experimental measurements. The design of an optical system is performed by using Zemax optical design program, to collect, focus and optimize the laser spot size incident on the Quadrant detector surface. Finally, a Laser Spot Position Determination System is implemented and experimentally tested and verified.