Design Of Subwavelength Structure Binary Optical Element

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 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 technology, ultra-precision machining, micro-opto-electro-mechanical system, computer technique, information processing, optical fiber communication, biomedicine and national defense and military affairs, etc. Subwavelength binary optical elements, because of the special property traditional optical elements do not possess, expands the applied field of binary optical elements.Optimal design method of subwavelength binary optical element is investigated in this paper. Phase delay elements, polarizing beam splitters and Dammann gratings are designed based on this method. The main contributions of this paper are as follows:1. The achromatic quarter wave plates of subwavelength gratings is investigated by the effective medium theory, and dispersion of the material is considered based on the empirical formula in design. A method of widening achromatic wavelength scope based on the material dispersion itself is proposed. The result shows that achromatic wavelength scope of the quarter wave plates of subwavelength grating are raised by considering the material dispersion. The achromatic quarter wave plates are designed applied to near infrared wavelength and visible light wavelength respectively. Phase retardation maintained at±2°are both achieved in the designed wavelength interval.2. The design method of asymmetrical polarizing beam splitters is proposed based on rigorous couple wave theory, where TE and TM polarized waves are mainly diffracted in the 1^st and 0^th orders, respectively. Aiming at 1.55μm incident wave which is often used in fibre-optic communication, there is a high extinction ratio in the design parameter and the extinction ratio of TE and TM polarized waves in the 1^st and 0^th transmissive orders are better than 100 when the incident wavelength is varied in the range from 1.5μm to 1.6μm and the incident angle is in the range from 53.8°to 58.9°.3. High-efficiency Dammann gratings are designed based on the genetic algorithm and rigorous coupled-wave analysis theory. The difficult problem of eliminating the zero-order diffraction light is solved during designing the Dammann gratings with even diffractive beams. Three subwavelength-structure Dammann gratings, whose beam splitting ratios are two, four, and six respectively, are designed by using the self-programming emulating package. The efficiencies of the Dammann gratings we designed are more than 93%, and the Dammann gratings have the high uniformity and the low zero-order diffraction efficiency.