Theoretical And Experimental Research On Planar Photonic Crystals

Photonic crystals (PCs) possess wide application prospects in the fields of micro optics and photonic integrated circuits, because of the fascinating physical properties and good abilities of controlling photons. In this thesis, we investigated one dimensional (1D) and two dimensional (2D) planar PCs, both theoretically and experimentally. On the one hand, we studied the basic physical characteristics of planar PCs, and proposed some kinds of novel functional devices based on planar PC structures; on the other hand, we explored and improved the fabrication technologies, and developed the test set-up for the passive planar PCs independently.The main works and conclusions of this thesis are as follows:1. Developed time-domain and frequency-domain simulation platforms for the planar PCs. In order to investigate the physical characteristics of planar PCs and conduct numerical simulations for the design and performance analysis of functional devices based on planar PCs, we developed the simulation platforms based on finite-difference time-domain (FDTD) method and scattering matrix method.2. Explored and improved the fabrication technologies, and developed the test set-up for planar PCs. We developed stable fabrication technologies for silicon based planar PCs, which can be utilized to fabricate planar PCs with feature size as small as 200nm. The patterns of fabricated samples are uniform, and the surface and sidewall of the patterns are smooth, and the tilted angle of the sidewall is less than 4°. We also developed a test set-up to measure the reflection spectra of passive planar PCs. With this set-up, the smallest area which can be measured is around 20μm×20μm when using an objective lens with magnification of 20×. And the absolute error of the measured reflectivity is around 0.01 for this set-up.3. Studied the reflection characteristics of 1D planar PCs systemically by using the developed simulation and experiment platforms. We theoretically calculated the band structures and eigen modes of 1D planar PCs, and analyzed the relationships between the leaky modes and refection spectra of 1D planar PCs. We also discussed the effects of the structural parameters on the reflection spectra of the 1D planar PCs in detail. In the experiments, we fabricated and measured some SOI (silicon on insulator) 1D planar PC samples. The experiment agreed well with the simulation. This part of researches provided guidance for the design of functional devices based on 1D planar PCs.4. Proposed and designed some kinds of novel frequency-selection devices based on 1D planar PCs. 1) Proposed bandwidth tunable filters based on single-layer 1D planar silicon PCs, whose bandwidths can be tuned continuously and dynamically. 2) Proposed directional mirrors based on single-layer 1D planar silicon PCs, which have broad bandwidths and big angular tolerances. For example, the relative bandwidth of a designed mirror which works around the incident angle of 45°is about 23.6% with reflectivity higher than 99%, and the angular tolerance of the same mirror is about 21o at the central working frequency. 3) Designed a mirror with big angular tolerance by using double-layer 1D planar silicon PCs. Within the incident angle range of±15o, the relative bandwidth of the proposed mirror is about 19.3% with reflectivity higher than 99.5%.5. Proposed and designed ultra compact polarization-controlling devices based on 1D planar PCs. 1) Designed a polarizer based on a single-layer planar silicon PC. The relative bandwidth of the polarizer is about 20.4% with transmittance over 98% and extinction ratio higher than 20dB. 2) Proposed a polarizing beam splitter based on a single-layer planar silicon PC. The relative bandwidth of the polarizing beam splitter is about 14.1% with reflection and transmission extinction ratios higher than 20dB when the incident angle equals 45o.6. Proposed and designed a novel optical one-way transmission device by cascading a silicon/silica 1D planar PC and a silica/air diffraction grating. The relative bandwidth of the proposed one-way transmission device is about 12.3% with forward transmittance higher than 69% and backward transmittance lower than 1%.7. Proposed and designed a silicon based laser structure by combining an active nanowire and a 2D planar PC silicon waveguide. A laser cavity with high Q factor and small mode volume can be formed by putting an active nanowire on the top of a 2D planar PC silicon waveguide. The energy of the laser can be exported directly from the planar PC waveguide after modifying the PC waveguide slightly. The in-plane exporting efficiency of the laser can be higher than 70% while the Q factor of the working mode is over 3×105.