Design of an optical system in an ultra-short throw projector using the aspheric surfaces

The ultra-short throw projector with interactive function has been popular these days. To perform interactively, a pen is equipped, e.g., containing an infrared LED. To detect the movements of the pen, another optical system is needed. The optical systems used in these projectors need to achieve special performance qualities, especially a small distance between the projector and the screen while maintaining high optical performance and a large field of view (FOV). In this paper, an optical system to detect the movements of the pen is designed. We begin the design procedure with an existing optical system whose FOV is relatively small. To expand the FOV, an element is added to the existing system using the Wassermann-Wolf method for a pair of conjugate foci. Then a table of coordinates of points is gotten and fitted into two aspheric surfaces. CODE V is further used to optimize the performance of optical system. Manufacturing method of the optical system are taken into account as well.The f/number of the optical system is 1.1, the value of MTF (modulation transfer function) is more than 0.6 at 100 cycles/mm, FOV is 69°, object distance is 300 mm, and the maximum distortion is less than 4%.