Research On The Photonic Devices Made Of Multi-dimensional Structured Thin Films

Dielectric wave-structured thin films(DWTFs) is one kind of two-dimensional peoriodic structures. There are two polarization modes inside this structure, which are TE mode and TM mode. Since the different band structures between the two modes, DWTFs can work as a polarization splitter within several wavelength ranges at normal incident angle or within a single wavelength range possessing a wide incident angle range. DWTFs have frequency range with characteristic of strong dispersion which possesses many special optical properties such as collimation, negative refraction and super-prism. The dispersion in super-prism can be 0.89°/nm. The positive refraction of TE mode and negative refraction ofTM mode make the two transmitted modes to be separated by an angle of 46°inside DWTFs. Thanks to the negative refraction, DWTFs can realize lensing in its near field. The imaging quality can be improved by collimation effect. The best resolution is of subwavelength scale 0.28λ₀. DWTFs with gradient filling factor can bend the propagating path of TM mode. The sensitivities of the position of the emergent light to the incident angle and wavelength are 0.29μm/deg and 0.38μm/10nm, respectively. DWTFs can be fabricated by the E-beam evaporation and ICP reactive ion etching on the photosensitive resist grating.Because of the different phase retardation between the TE and TM mode, the new kind thin film phase grating composed by DWTFs and one-dimensinal periodic thin films possesses polarization dependent far field diffraction pattern and near field Talbot effect. In the far field, TE mode and TM mode can be separated by the 0 order and±1 order. In the near field, the self-imaging of the thin film phase grating is shifted by a half of the grating period between the two modes.The propagation of surface plasmon wave(SPW) in the slit in metallic thin films is analysed. At oblique incident angle, light propagates from one side to the other side in the slit to form the zigzag path. So, there can be single side radiation with high intensity at the exit of the slit in the silver thin films with the full width at the half maximum(FWHM) of the intensity distribution of 43nm at the near field. The mode expansion method and numerical simulation method reveal that the narrow absorbing or transmission band in the shorter wavelength range for the metallic grating with large duty cycle is due to the exciting of surface plasmons(SPs), and the broad absorbing or transmission band in the longer wavelength range is due to the cavity mode resonance. The numerical simulation work alse indicates that the metallic grating on the front interface help the slit to achive enhanced transmission, and the metallic grating on the rear interface help to form the light beaming phenomenon which is also verified by the diffraction theory of SPs and the rigorous coupled-wave analysis(RCWA). The silver grating with large duty cycle is fabricated by the physical vapour deposition method and the photosensitive resist stripping process.The PS-PMMA diblock copolymer can be made to phase-separate, creating nanoporous polymer film useful for antireflection. The remaining reflection of such a nano-structured polymer film on glass is 2.5%. The polymer molecular weight and solution concentration influence the morphology and antireflection performance of the nanoporous film greatly. The ion bombardment can be applied on the surface of PMMA substrate to get stochastic cylindrical nano-structure call 'moth-eye', which can help to reduce the Fresnel reflection to be less than 1%.