The matrices used to reduce speckle in laser projector system

It has been suggested to use Hadamard matrices H(M) of order M for speckle reduction in laser based projection displays by creating a set of M two-dimensional phase masks from rows or columns of the H(M) and introducing them sequentially into the intermediate image plane of the laser projector. The speckle contrast reduction can reach M-1/2. In this paper, we have analyzed the contrast reduction. The result presents that any matrices can be used to form phase mask as long as its columns are orthogonal to each other, such as the parts of columns of Hadamard matrix. The speckle contrast reduction is determined by the number of projection resolution elements lying in single camera resolution element. To get high quality image with low speckle contrast reduction by Hadamard matrix, its order should be as high as possible. However, it is impossible to implement by vibrating diffuser with high order due to the large vibration amplitude. The motionless time-vary diffuser with Hadamard matrix phase pattern based on MEMS technology and Electro-optical effect can be a good choice.