QPD is a PD or APD with a photosensitive surface divided into four quadrants with very small spacing between adjacent areas and a common substrate. The signal spot of regular shape is irradiated to the four quadrants at the same time, so that the quadrants can generate different photocurrent signals, and the two-dimensional coordinates of the spot can be accurately obtained by calculation. The position resolution of the detector can be up to 0.1μm or less, and it is less affected by the signal-to-noise ratio and very suitable for applications that require high alignment accuracy.
Application: Spot centering, precision displacement measurement, vibration detection, angle measurement, eye tracking, guidance, etc.
