The Polarization Properties Of Subwavelength Periodic Dielectric Gratings

The polarization properties of diffraction by rectangle phase gratings with periods from 1 to 1/10 times wavelength are investigated by FDTD algorithm.The Perfectly Matched Layer (PML) absorbing boundary condition was used Supposing the period of the phase grating is 240 nm,the fill factor b/d was set to be 0.5, and the thickness of thegrating was changed from 120 nm to 210 nm.The material index is1.35. The wavelengthof the incident wave was 1.55μm.The phase and amplitude modulation of a light wave passing through such grating depends on the polarization of the incident light wave. The relative phase retardation of parallel electric field is always larger than that of vertical electric field, so the grating can be considered to have larger effective index for parallel electric field than that for vertical electric field. and which is bigger is determined by the optical thickness of the grating. the polarization related about diffraction of a phase grating with period of 1 to 1/10 times of incident wavelength is discussed. A method combine reactive ion beam etching and electric beam exposure is consider to produce subwavelength grating. All the possible errors in process and experiment are analysed. A expierment is designed to research how the phase and amplitude modulation of a light wave passing through such grating depends on the polarization of the incident light wave.