In order to achieve a uniform illumination distribution confined to a given rectangular region, a feedback modification
strategy is introduced in the design of free-form optical surface. The whole process of this strategy includes two steps:
solving the initial structure and feedback process.
To solve the initial surface, we first divide the source space along its longitude and latitude direction with uniform angel.
Because the energy of each longitude and latitude micro-belt of free-form surface and each corresponding micro-belt on
the target plane is equal, the target plane can be divided into grids, and then the mapping relationship of source space and
target space is constructed. By using Snell’s Law and tangent plane iterative method, we obtain the coordinates of all grid
nodes and an initial free-form surface can be constructed. Afterwards we use specific feedback algorithm to improve the
illuminating performance. This method is proved to be efficient, the shape of illumination spot is dramatically improved
and the design result is satisfactory.