Study Of Grating Light Valves In Laser Scanning System

Grating light valve (GLV) is a kind of device based on MOEMS, which is suitable in laser scanning system for its high modulation accuracy, high response speed and high light intensity endurance. Nowadays abroad, GLV has been widely used in laser phototypesetter and CTP system, but in China it is still at the beginning stage and no products available.In this dissertation, a conception is firstly proposed in China that GLV can be applied in laser scanning system as a modulator. The inaugurated structure is designed, the processing technologies are thoroughly studied, and the GLV sample is fabricated. It has significance of promoting the competitive value of domestic production in this field. Also in this dissertation, a close packing technique of micro optical fibers array is introduced using in multi-channel laser scanning system. This technique has very high practical value because it can solve the problem of output spots isolating in standard fiber close packing, increase the depth of focus effectively, and decrease the demand of the position accuracy to exposure film. The details of the researches are as follows:1. Introduced the principle and different structure of GLV at different development stages, analysed the influencing factor of GLV working efficiency, and proposed a GLV device with independent designed structure. Different from the one available abroad, in this GLV structure, movable and fixed ribbons are not in the same plane at initial state, fabricating by difference materials. This kind of structure not only simplified the technologies and lowered the difficulty of fabrication, but also enhanced the diffraction efficiency by reduced the region of "black area". The new structure GLV is fast in response, large of dynamic range and low of driving voltage.2. Studied of the fabrication technologies of GLV device including photolithography and etching techniques, and solved the critical problems in fabrication. In our study, high accuracy is demanded because the size of grating in working area of GLV is as small as several micrometers. AZ4620 positive photosensitive resist is used in photolithography and reasonable parameters of fabrication are obtained through lots of experiments, which ensure excellent uniform of photosensitive resist surface and adherence between photosensitive resist with substrate. Reactive Ion Beam Etching (RIBE) is used, and the proper ratio of solution is achieved in chemical etching. Besides, phenomenon of stiction during fabrication processes of GLV is analyzed, and solutions were pointed out as immersed in acetone or ethanol, to decrease surface tension. 3. Based on the study of micro fabrication techniques, GLV device samples were fabricated successfully, and the optical characters and dynamic performance were measured. The measurement results of diffraction coincide well with theoretical analysis, with some deviations in data. The measurement results of zero order and first order diffractive light intensity ranges from 28%-80% and 32%-78% of theoretical values, and both of the voltages to get the maximum or minimum light intensity are less than theoretical voltages. The reason is mainly because of the size deviation of the GLV sample brought during fabrication. The corresponding time are got, including rise and fall time of 620μs and 500μs, which are within microsecond, and coincide well with theoretical analysis.4. Proposed a close packing technique of micro optical fiber in laser scanning system. A method is introduced to obtain diameter of 5-10μm micro optical fiber through drawing under high temperature. Comparing to standard optical fiber, the micro optical fiber has some good transmission characters such as low loss, high constraint, large dispersion, high tensile strength, etc. During scanning, "Black area" occurred in standard optical fibers close packing caused by the separation of output spots, and defect of short focus depth is generated. Micro optical fibers close packing can not only solve this problem, also can decrease the film position demand during exposure by increasing the focus depth, and bring convenience in practical alignment operation. Through experiments, V shaped silicon substrate is fabricated, micro fibers are drawn, and close packing is operated successfully. Comparing to standard fiber close packing, the qualities of output light spots are much better, but still not as good as ideal state. Better drawing technique of micro fiber and V shaped silicon substrate fabrication technology are deserved for further research.At last, a summary of the works in this dissertation was given, and the further research prospect was pointed out.