Research On Splitting Characteristics Of The Subwavelength Polarization Grating

When the subwavelength structure has a comparative or smaller periodic and aperiodic structure than the working wavelength,the grating reflectivity,transmissivity,polarization characteristics,spectrum and phase delay is very different from the conventional diffraction optical element features and has greater potential applications.This thesis mainly researches subwavelength polarization grating,for which the diffraction characteristics,phase delay and application in laser beam combining system were studied.This paper proposes a novel subwavelength polarization diffraction grating structure.The garting can achieve high efficiency and high uniformity for the beam splitting by optimizing its structural parameters.The main research contents is as follows:(1)The diffraction properties of the subwavelength polarization grating was analyzed.The application of subwavelength grating in laser beam combining system during recent years was illustrated.(2)The theory researches methods of grating were analyzed.We elaborated on the solving principles of rigorous coupled wave theory and equivalent medium theory.Using the rigorous coupled wave theory calculated the diffraction efficiency of incident light for TE mode,TM mode and cone light pattern.(3)Combined with the rigorous coupled wave theory,the simulation model of grating was established.The influence of grating layer thickness,transmission layer thickness,pattern size,shape pattern,grating layer,duty ratio on the diffraction efficiency and phase delay of the grating were discussed.When the grating pattern is rectangular,incident light wavelength is 1550 nm,the number of spatial harmonics is 21 by 21,the duty ratio is0.1818,the transmission rate of the grating is 0.9846 and the phase delay is 1.01 ?.(4)Subwavelength structure parameters were optimized and designed to meet the requirements of the polarization diffraction grating.The main technology and process flow of grating were introduced.(5)Vector optical system was built to validate the splitting characteristics of subwavelength grating.The splitting function of duplicator,triplicator and a 1-by-4splitter was accomplished.The experimental efficiency of a duplicator,a triplicator and a1-by-4 splitter are 97.5%,84.3% and 82.6%.The experimental uniformity of a duplicator,a triplicator and a 1-by-4 splitter are 0.95,0.91 and 0.91.