The Study, Based On Photonic Crystal Thin Film Technology And Devices

Photonic crystals are the periodical arrays of materials with the different refractive indices which can control the light propagation. In this dissertation, my work is focused on the photonic crystal which is fabricated by the thin-film technology, including the numerical computational methods, the fabrication of the photonic crystal devices, such as, one-dimensional omnidirectional photonic crystal reflector, two-dimensional photonic crystal polarization splitter and the submicron imaging with a planar metallic lens as well as the measurement of the superprism effect in the photonic crystal.According to the incident angle domain, the design of an ultraviolet omnidirectional reflector deposited on substrate of quartz glass is briefly presented. The spectral wavelength region of the design is from 328.95nm to 352.11nm and the relative bandwidth is 6.80% in theory. An experiment has been done to verify the design by using HfO₂ and SiO₂. The experimental result shows that the band gap corresponds to wavelength band from 331.2nm to 350.4nm and the relative bandwidth is 5.63%.Study on the superprism effect in the thin-film photonic crystal. A wavelength dependent spatial lateral beam shift of a reflective Gaussian beam on the surface of a multilayer thin-film filter is demonstrated, which is designed so that the different wavelengths propagate at the different effective group propagation angles. The incident beam takes a Gaussian form and the numerical wave fields inside and outside the multilayer thin-film coatings are directly obtained from Maxwell's equations on matching the boundary conditions at the interfaces. The spatial lateral beam dispersion can be determined rigorously from the numerical wave fields in the region of the incident medium.A dramatic wavelength dependent negative lateral shift of the reflective beam is observed for the first time when the reflection group delay is negative and this spatial dispersion effect is much bigger than the previous reports. A thin-film Fabry-Perot filter is fabricated and the measurement setup is built to detect the lateral shift of the reflective beam. The splitting of the reflective beam and the enlargement of the transmitted beam are explained by a discrete Fourier decomposition technique.A method of designing two-dimensional photonic crystal polarization splitters is put forward. Optimal structure of a two-dimensional photonic crystal with a triangular lattice of Ge rectangular rods in BaF₂ is presented. It is shown how a maximum photonic band-gap for E polarization is obtained by optimally choosing the proper width of the rectangle rods. Thetwo-dimensional bandgap for E polarization of this design is 0.083(2pc/a, here a is the period of grating). The polarization frequency band corresponds to a wavelength band from 1.72/im to 2.4/mi with the theoretical relative bandwidth being 33.1%. The fabrication of such a photonic crystal polarization splitter is an easy process based on coating films on the grating and is suitable for industrial making. The transmitted spectrum of the two-dimensional photonic crystal polarization splitters used in infrared region is calculated by finite difference time domain (FDTD) method so that the band structure calculated by plane wave method (PWM) is proved. The polarization of the photonic crystal is verified by an experiment for the normal incidence.Study on the negative refraction phenomenon, the near-field subwavelength lensing and submicron imaging with a planar silver lens. Analyze the negative refraction and self-collimation phenomena in the two-dimensional photonic crystal from the equal frequency surface. The metallic thin film structure is modeled by a Drude media in the FDTD method. Using the transfer matrix method, the transmissivity of this structure for the evanescent wave is given, which illustrates the influence of the subwavelength imaging quality. In practice a Cr grating mask with 1/im period is imaged onto a photosensitive material through a silver thin film structure by utilizing the optical near-field lithography techniques.