Discussion of Several Problems in Four-Quadrant Photoelectric Tracking Technology,

A four-quadrant detector is frequently used as a photoelectric sensor to detect the azimuth of a target in photoelectric tracking devices including the laser seeker, laser theodolite, etc. In the process of tracking, the optical signal coming from a target is focused and projected, through an optical system, onto the photosensitive surface of the four-quadrant detector to form a target image spot. It is through the distribution of the target image spot on the four quadrants that the four-quadrant detection system calculates the azimuth deviation angle of the target relative to the optical axis of the tracking system. An ideal detection system should produce deviation data which are in a linear relationship with the actual deviation of the target relative to the center of the four-quadrant detector. Nonetheless, the ideal conditions can hardly be realized owing to various constraints. To find proper means, a detailed calculation was made of some vigorous constraints, such as the data extraction method, image spot dimensions and the like. In spite of the foregoing efforts, some of the problems are still expected to be studied further. For instance the four-quadrant diagonal algorithm may produce entirely different signal transfer characteristics of the system because of different normalization methods employed, and the enlargement of the target imaging spot on the four-quadrant detector may impose an effect on the curve slope of the signal transfer function, etc. From this, however, a good deal of useful information has been gained.