Improved Roman encoding based on DMD

Holographic lithography can be realized by loading computergenerated hologram(CGH) on digital micromirror device ( DMD) to form the digital mask. Roman encoding is a commonly used method to generate CGH, which uses the height and position of transparent rectangular hole to encode the amplitude and phase of sample unit of hologram respectively. Usually, as reconstructing the binary hologram,the multiple micromirrors of DMD are combined to represent a single rectangular hole, and the utilization and resolution of its pixels can reduce. To solve the problem, an improved Roman encoding is introduced, which can make full use of the binary pulse width modulation of DMD and use the grayscale value to encode the amplitude of the sample unit, convert the transmittance of hologram from binary to grayscale and reduce the number of micro mirrors occupied by a single sample unit effectively. MATLAB is used to build the simulation model to reconstruct and analyze the CGHs produced by improved Roman encoding and Burch encoding. The results indicate that the diffraction efficiency of the improved Roman encoding is 3 times as much as that of the Burch encoding. The reconstruction experiment based on DMD is conducted, which demonstrates that the diffraction efficiency of the improved Roman encoding is 2 times as much as that of the Burch encoding. Therefore, using the improved Roman encoding can achieve higher diffraction efficiency.