Fabrication Of Micro Optical Elements With Coding Gray-tone Mask Designed By Error-Diffusion Method

In recent years, micro-system have been dramatically advance in micro-optics, micro mechanical and microelectronic device, that will be applied in extensive field and will effect the technology, the model of production and the living quality of people deeply. In 1995, micro-system that had been looked as a high and new technology directly contacted to the defense and the development of economy has been priority researched and exploited in American finance plan. The micro, array and integration optical elements have prospective applications in many fields and prodigious amounts of work have been presented.A great progress has been made in the field of design and fabrication of micro-optics. Now, micro-optics is applied in many scopes, such as aviation, optical communication, optical calculation, optical information processing and laser fabrication, etc. In order to further extend the field of micro-optics application, such more effective micro-optics fabrication methods are required. Therefore, the study on novel fabrication method of micro optical elements is one of the most important directions and advancing edges nowadays.At the present time, micro optical elements with continuous relief structure are usually fabricated by the multi-mask photolithography. But this method needs multilevel masks that will introduce alignment error, adding complexity in the fabrication process. This limits the development of the micro-optics and micro-systemIn this paper, aiming at developing fabrication methods of micro-optics, based on the current technology which code gray-tone mask by Lohmann's method, we propose to code gray-tone mask by error-diffusion method to fabrication of micro optical elements. Comparedto the other encoding methods, error-diffusion method has shared a major advantage of fast computation and much goodness, such as good quantization quality, high diffraction efficiency, small fabrication size and so on. Suggested by this, a new error-diffusion coding method is presented to design the coding gray-tone mask in order to avoid the disadvantage that designed by Lohmann's encoding method. Based on the theory of error-diffusion method, comparison of error-diffusion methods for computer-generated holograms, a correct weight for error-diffusion method is given. In the processing of correcting the mask design, distorted compensation and edge-enhanced ED algorithm are proposed. Nonlinear effects in aerial image formation have been taking into account to correct the mask design. And a satisfying simulation result is obtained with the designed coding gray-tone mask.