Research On Design Theory And Parallel Manufacturing Technology Of Binary Optical Elements

Binary optics is a new and developing branch of optics based on the optical wave diffraction theory, and a leading science formed by coupling optics and microelectronics. Binary optical elements, also called diffractive optical elements, have many advantages, such as small size, light weight, replicating easily, low cost, high diffraction efficiency, many design variables, wide range of optional materials, peculiar chromatic dispersion performances, and so on. Therefore they can implement some new functions, for example microminiature, array, integration and arbitrary wave transformation, which are difficult for traditional optical elements to realize. And binary optical technology has been proved to be very useful in many practical applications, for instance spacial technique, ultra-precision manufacturing, micro-opto-electro-mechanical system, computer technique, information processing, optical fiber communication, biomedicine, national defense, military affairs and entertainment, etc.The theories, methods and techniques related to designing and fabricating binary optical elements are investigated in this dissertation, which mainly include fine design theory, analyzing chromatic dispersion performances, parallel manufacturing techniques and designing novel elements. The main works and contributions obtained in this dissertation include as follows:1. Based on the Kirchhoff s scalar diffraction theory, the sampling theorem in the input and output planes when finely designing binary optical elements is systematically established from the angle of spatial frequency spectrum for the first time. The existence and overlapping phenomena of spatial expanding components are discovered. The forming mechanism of spatial expanding components is studied deeply, and the corresponding conditions to eliminate their impacts are derived. The distortion mechanism of output pattern at non-sampling points is explored. The approximate sampling principles for different optimization algorithms are given, and the effectiveness of sampling theorem when finely designing diffractive optical elements is validated by simulated experiments.2. The expanded two-dimensional Yang-Gu algorithm and improved weighted Yang-Gu algorithm are proposed based on the elementary principle of Yang-Gu algorithm. Their theoretical models, iterative formulas and main operating procedures are studying thoroughly, and the convergence of weighted Yang-Gu algorithm is proved theoretically. The two-dimensional Yang-Gu algorithm can be used to design two-dimensionaldiffractive optical elements with arbitrary structures, including rotationally asymmetric structures and structures with non-separable-variables phase functions. Compared with the ordinary Yang-Gu algorithm, the weighted Yang-Gu algorithm can evidently decrease the sensitivity to initial phases, and avoid the iterative process getting into the local extremum, consequently improve qualities of diffractive optical elements.3. Utilizing the empirical formula of refractive index with the change of wavelength, the chromatic dispersion performances of diffractive optical lenses are studied completely. The relationships among the intensity distributions in focal plane and axial direction, diffraction efficiency, focal distance, wavelength, structural parameters, material factor are analyzed in detail. The preconditions, which the formulas for designing diffractive lenses and multiorder diffractive lenses with low numerical apertures come into existence, are educed, and then the more exact design formulas are given. By using the body-of-revolution finite-difference time-domain method, focusing performances and rules of chromatic dispersion for binary subwavelength diffractive micro-lenses are discussed for the first time. The pure-diffractive achromatic beam splitter composed of a phase-only splitter and a diffractive lens is designed, and this combined element can effectively eliminate the chromatic dispersion in the longitudinal direction.4. An innovative method for designing a subwavelength Dammann grating is proposed based on the rigorous couple-wave analysis theory and the genetic algorithm for the first time, and this novel binary-phase grating has higher diffraction efficiency. The influences of fabrication error on diffraction efficiency and intensity uniformity of gratings are analyzed. Several subwavelength Dammann gratings with more than 90% diffraction efficiency are designed, and their efficiency are higher than those of the conventional Dammann gratings.5. An innovative method for parallel manufacturing gray-scale masks based on an electro-addressable transmitted intensity-modulating spatial light modulator is proposed for the first time. The basic principle, total project and control flow of the manufacturing system are investigated in detail. Some crucial units such as optical source, spatial light modulator, projection objective, two-dimensional air-bearing stage and program of generating pattern are analyzed thoroughly, and then the prototype machine is integrated synthetically. The model for accurately controlling precision of gray level is established, and the corresponding control strategies are given to accurately control the exposure dose. Finally some binary and gray-scale masks are fabricated.The method for manufacturing gray-scale masks presented here adopts a stepperexposure mode, so it can highly improve the fabricating speed, shorten the fabricating cycle, and reduce the process cost. Furthermore, it can make the minimum feature size come to the order of micron, and the device for manufacturing gray-scale masks can be low-cost.6. An innovative method for parallel direct writing binary optical elements based on an electro-addressable transmitted intensity-modulating spatial light modulator is proposed for the first time. The basic principle, total project and control flow of the manufacturing system are investigated in detail. The two novel methods of clearing up the pixelilation effect caused by low fill factor of spatial light modulator are presented, which utilize diffractive micro-lens arrays and phase-only beam shaping element arrays respectively. The math-model about parallel optical subsystem in this system is established, and the simulating results are given. Based on the analysis of parallel direct writing technics, the model of profile-control in photoresist for multilevel relief or continuous relief elements is established, and the corresponding control strategies are given. Finally some diffractive optical elements are fabricated.The parallel direct writing method for fabricating binary optical elements presented here has intrinsic parallel characteristics owing to its stepper exposure mode, therefore it can improve the writing velocity at large, and overcome the disadvantages caused by the traditional laser direct writing system, fore example low throughput, long period, and high cost. By use of predominant performances of spatial light modulator and new-style optical subsystem, it can make the minimum feature size come to the order of submicron, and be propitious to decrease the depth error of binary optical elements. Furthermore, it offers many advantages to manufacture high quality binary optical elements with superfine structure and continuous profile, and the device for direct writing binary optical elements can be low-cost.