Theoretical And Experimental Study On Diffractive Optical Elements For Array Illumination

The phenomenon of self-imaging of periodic objects, also known as Talbot effect, was first observed by H. F. Talbot in 1836. When a periodic object is illuminated with a coherent light, exact Talbot images will be found at the Talbot distance from the object, and fractional Talbot images will be found at the fractional Talbot distance from the object. The array illuminator basing on the Talbot effect can transforms a plane wave into an array of focus spots. The design of the Talbot illuminator basing on the fractional Talbot effect is very simple. It has no use for complex iterative algorithm, through choosing different fractional Talbot distance and designing different phase-only distribution obtain array illumination effect with different high compression ratios. Since Lohmann and Thomas first observed the array illuminator based on fractional Talbot effect, more and more investigator made same theoretical and experimental investigation in this aspect. The diffractive optical elements for array illumination have been applied in light power distribution, multicenter interlinkage, optical communication and optical calculation. In this dissertation we analyse fractional Talbot effect of some simple period array objects based on reciprocal vector theory of Talbot effect and design some Talbot illuminators. Finally, some computer-simulated results and experimental results are also given. On this condition, we propose a simple method for generating an array of spots with an inhomogeneous intensity distribution by use of an improved phase-only TAI, so the existing TAIs have disadvantage of transforming a plane wave into an array of specific spots with a uniform intensity distribution is overcome. The design of this improved TAI is based on an interesting"phase contrast"effect in the diffraction of a TAI we observed in experiments: if we add a specific phase structure onto each unit cell of a TAI, a similar structure of intensity distribution could be obtained in the output spots near the fractional Talbot plane. Finally we use the method of designing Talbot array illuminator based on reciprocal vector theory design same microlens array based on LCD, and compare with the traditional method of designing microlens array. Through the theoretical and computer-simulated study of focus characteristic of microlens array based on LCD, find a new way of reducing diffraction noise of focus spots, Which can reduce diffraction noise and improve quality of focus spots through making the focus of microlens array and the lattice parameter of LCD satisfy certain condition. The main innovative researches are as follows:1. A new Talbot array illuminator called phase contrast Talbot array illuminator (PCTAI)is derived with combination of the fractional Talbot effect and phase contrast of diffraction, and some examples and experiments are also given. As examples, we design some types of PCTAIs for generating an array of different spots. Respectively, and study their output characteristic by computer-simulated and experimental results. Some experimental results revealing the phase contrast effect and demonstrating the feasibility of the PCTAIs are also given.2. Through the theoretical and computer-simulated study of focus characteristic of microlens array based on LCD, find a new way of reducing diffraction noise of focus spots, and give a formula and design method of microlens array with low noise. When the LCSLM is illuminated with the microlens array pattern, taking into account the pixel structure of the LCSLM, there may be exist an optimal focus of a microlens array. We design some microlens with different parameters, through some theoretic analysis and computer- simulated results study, we finally give the optimal focus of a microlens array based on LCD.