Research On Diffraction Characteristics Of Phase Grating Based On Rigorous Coupled Wave Analysis (RCWA) Method

As an important beam splitter,optical diffraction grating plays an important role in most optical systems.Its diffraction efficiency and dispersion ability usually have a decisive influence on the performance of the optical system.Compared with other types of diffraction gratings,transmission phase diffraction have many advantages,such as low insertion loss,high diffraction efficiency,compatibility between fabrication process and conventional micro/nano technology,more flexible design,and high dispersion.Therefore,they have been widely used in practical optical systems,and have important research significance and practical application value.In this paper,according to the design and development requirements of 966 1/mm and 1200 1/mm transmission phase diffraction gratings in the research process of high-end port number wavelength selective switch,the theoretical analysis model and numerical analysis program of periodic structure optical elements are established with rigorous coupled wave theory(RCWA),and the diffraction characteristics of phase gratings in quartz and silicon-based material systems are studied.The analysis and research provide a necessary and efficient theoretical analysis and design method for further experimental development of high diffraction efficiency and high dispersion phase diffraction grating.The main work of this paper is as follows:1.Based on the theory of rigorous coupled wave analysis(RCWA),a rigorous vector theoretical analysis model of periodic structure optical elements is established for TE and TM input polarized light fields.Compared with the scalar diffraction theory,the model has no limitations such as far-field approximation and paraxial approximation.On this basis,the corresponding matlab numerical calculation and analysis program is compiled,and the reliability of the calculation results is verified.2.The optical diffraction characteristics of 966 1/mm phase diffraction gratings on quartz and silicon are studied by the numerical calculation and analysis program.In the case of TE and TM incident polarization,when the transmission positive first-order diffraction efficiency reaches the highest,the corresponding grating duty ratio and modulation depth are analyzed,and the reasonable grating structure is determined.The results show that when the material is quartz,the best diffraction efficiency can be achieved when the duty cycle is 52%and the modulation depth is 2.31 ?m under TE polarization;Under TM polarization,when the duty cycle is 72%and the modulation depth is 5.44?m,the best diffraction efficiency can be achieved;When silicon is used as the material,under TM polarization,the transmission positive order can achieve the best diffraction efficiency when the duty cycle of grating is 91%,the modulation depth is 2.41 ?m.Meanwhile,the results show that 966 1/mm silicon-based rectangular phase grating is not suitable for TE polarization.In view of the reasonable grating structure,the diffraction performance within the applicable wavelength range is studied.For the case that the required modulation depth of grating is too deep,a grating stacking structure is proposed and analyzed,which can effectively reduce the modulation depth of grating modulation half under the premise of ensuring the diffraction efficiency.This structure is of great significance for the actual grating production.At the same time,combined with the grating deformation caused by the possible etching deviation in the actual production process,the modeling analysis and diffraction performance calculation of the deformed phase grating are carried out by using the program.3.By using the numerical calculation and analysis program,the optical diffraction characteristics of 1200 l/mm phase diffraction gratings on quartz and silicon are studied.The results show that when quartz is used as the material,the optimum grating structure parameters are:duty cycle=19%,modulation depth=3.8?m;The optimal structure parameters of the grating under TE polarization are:duty cycle=52%,modulation depth=1.88 ?m;when silicon is used as the material,the optimal structure parameters of TM polarization grating are:duty cycle=92%,modulation depth=1.89 ?m,while 1200 1/mm silicon-based rectangular phase grating is not suitable for TE polarization.The parameters of grating duty cycle and modulation depth are optimized when the first-order diffraction efficiency reaches the highest.Meanwhile,the diffraction performance of the reasonable grating structure in the applicable wavelength range is studied,and the possible etching deviation in the actual production is modeled and analyzed.