Fabrication Of Polymer Binary Grating Based On Digital Mask Technique

Polymer materials have the advantages of lightweight, simple chemical synthesis process and low cost, and by comparing with the inorganic materials such as silicon,silica etc., they have higher electro-optic coupling coefficient, higher thermal coupling coefficient and lower dielectric constant. Their facbrication technologies, as well as that of the silicon substrate, are compatible with those of the large-scale integrated circuits, and what more attractive is that lower processing temperature is needed.Therefore, more and more researches have been done in designing, fabricating and applying the polymer micro-optical elements.Firstly, the development trend of the application of the polymer micro optical elements is described, and fabrication technologies of fabricating polymer micro-optical elements are summarized. We find that the digital mask lithography technology has the advantage in fabricating polymer micro optical elements because the refractiv index of photosensitive polymer may change with exposure dose which is matching with the characteristic that digital gray mask has the flexibility of regulating the exposure dose.Secondly, the system structure, working principle, optical path, and mask generation methodare are introduced in detail. Photosensitive optical polymer materials whose refractive index may vary with the exposure dose can be employed to fabricate micro-optical elemenst. The commercial photosensitive polymer material SU-8 is employed as the fabricating material, and the relationship of its exposure dose and exposure depth are studied by using of digital gray mask.Finally, taking the fabrication of polymer phase grating as an example, the technology process wih digital lithography system is introduced in detail. By controlling the exposure dose with the designed gray scale distribution and the exposure time of the digital mask, expected refractive index or refractive index distribution can be written in the polymer film so that the micro-optical elements ofexpected functions such as phase grating are fabricated. The diffraction experiment of the fabricated grating sample is also carried out. The new method has the advantages that low cost, short production cycle, flexible fabrication for mask. In addition, the process flow of the new method is streamlined because it excludes some processes such as developing or etching and prevents the elements from physical, chemical or high temperature damages etc. Therefore, the method of adjusting the exposure dose based on digital mask lithography system for fabricating micro-optical elements proposed in this paper is feasible.