PR5510 can detect the lateral position of a light spot on the sensor. It consists of triangular photodiodes with reciprocal orientation, together with a differential transimpedance amplifier. If illuminated uniformly, the output is Vcc/2; if the light is biased towards one of the triangles, the output is higher or lower than Vcc/2, proportional to the deviation from the centre position.
light beam alignment
optical position detectors