| Integration and miniaturization of sensors are the trends of the integrated optical devices in the future. Photonic crystal (PhC) is a periodic arrangement of different kinds of materials, with the properties of photonic band gap (PBG), photonic localization and photonic guidance etc. The structures of PhC sensors sized about micrometer with micro-cavities consist of two periodical kinds of materials, in which the parts of materials are removed. The photons are localized in the micro-cavities to obtain the resonances of high quality factor (Q) and small mode volume (V), and the resonances will be shifted when the refractive index (RI) is changed around the micro-cavities. Therefore,the relationship between the shift of resonant wavelength and the change of RI in the sensing solutions can be calculated by this phenomenon, and PhC sensors can meet the need of the integrated optical devices with integration and miniaturization. Being supported by the research projects of China, this thesis is devoted to optimizing the performances of PhC sensors for bio-chemical sensing based on integrated optical technology and the need of PhC sensors with micro-cavities for the detection and sensing.Based on silicon-on-insulator (SOI) one dimensional PhC (1D-PhC)or two dimensional PhC (2D-PhC), through the theoretical analysis of PhC structures: plane wave method (PWM) and finite-difference time-domain (FDTD) method, this thesis mainly studies the basic properties of PhC, including PBG and localization, and also studies the guidance and localization properties between PhC waveguides and micro-cavites. Based on the analysis of these properties, 1D-PhC or 2D-PhC structures with different micro-cavities are designed, and the electric field distributions and transmission spectra are analyzed in detail,so that the 1D-PhC or 2D-PhC structures for bio-chemical detection and sensing can be achieved. Then, through electron beam lithography(EBL), reactive-ion etching (RIE) and scanning electronic microscopy(SEM) etc, one dimensional subwavelength grating (SWG) racetrack resonators are fabricated based on the theoretical results. The testing results show that the fabricated SWG racetrack resonators is a potential candidate for the optical bio-chemical detection and sensing, and the designs can provide excellent schemes. The detailed study results in this dissertation are as follows:(1) The design of high-performance PhC bio-chemical (array)sensor based on ring (ring-slot) defect PhC structures.A high Q ring-slot PhC structure which consists of ring-slot in the center of the structure and two lines defect waveguides is designed. The photons are localized in the region of ring-slot by adjusting the width of ring-slot and the size of central air holes within the ring-slot. The simulation results show that the performances are enhanced by improving the photon localization and light-matter interaction, and the Q up to 104 and sensitivity (S) of 160nm/RIU are achieved.A high figure of merit (FOM) ring-defect PhC structure is designed,in which a ring-defect is etched in the center of PhC structure. In order to achieve the optimal Q, the air hole inner the ring-defect and the waveguide are varied from 0.2a to 0.65a and from 0.9W1 to 1.02W1,respectively when there is one air hole inner the ring-defect. The optimal Q is achieved when the air hole and wa,veguide width are 0.40a and 0.985W1. In order to confine the light within the defect and enhance light-matter interaction, the number of air holes is increased by one circle, and the maximum product of Q and S are obtained when the number of air holes equals 7, and thus the FOM, in theory, is about 8000 larger than the best value reported in other PhC sensors.An array sensor structure with 3 ring-slots is designed based on the high Q ring-slot PhC structure, in which the input light is split into three waveguides with the theory of the splitter, and the detectors are placed at the output of three waveguides and monitored the transmission efficiencies and spectra. The simulation results show that the Qs in water environment are 11029, 10153 and 10669, and the Ss are 145.5 nm/RIU(refractive index unit), 140nm/RIU, 134nm/RIU, respectively. As a result, the minimum crosstalk among three ring-slot structures is less than -25.8dB.Based on the designs above, the theoretical high Q, high FOM and array sensor PhC structures are achieved and will provide the excellent ideas for the design of PhC bio-chemical sensors.(2) The design of high-integration 1D PhC low-index mode nanobeam cavities bio-chemical sensors.1D PhC low-index mode nanobeam cavities are designed by tapering the width of the host PhC waveguide away from the center of the cavity while keeping other parameters constant. The low-index mode band of cell in the center of cavity is localized in the PBG of the cells away from the center of cavity by quadratically tapering waveguide widths. Therefore, the photon localization is enhanced and the Q is increased. Simultaneously, the photon is localized in the region of the elliptical holes and the large interaction will be expected between light and analytes. The simulation results show that the 0 of ?104 and S of 390nm/RIU in water are achieved.Compared with the first scheme of low-index mode nanobeam cavities, 1D PhC low-index mode nanobeam cavities are designed by tapering the major axis of elliptical holes from the center to two sides of cavities. The effective refractive index of cells is decreased and the frequency is pushed to higher frequencies gradually away from the center of cavities. The low-index mode in the center of cavities is limited in the cavities, thus high Q and high S can be obtained. The simulation results indicate that the Q about 104 and S of 244.7nm/RIU are achieved.The size of nanobeam cavities is about 6.4?m×0.85?m with only 8 periods.Compared with the other structures of 1D PhC and 2D PhC structures, the designs of 1D PhC low-index mode nanobeam cavities sensors possess some merits due to the high sensitivity, small size and easy integration. The designs will provide better ideas for on-chip optical bio-chemical sensing.(3) The design of enhanced detection limit of 1D PhC subwavelength grating resonator bio-chemical sensors.Based on the great overlap of light-matter and high sensitivity, a transverse magnetic (TM) SWG racetrack resonator is studied and demonstrated in order to improve the detection limit (DL) in SWG structure. In theory, the overlap of TM and TE mode of SWG structure,and the coupling efficiency between SWG bus and racetrack waveguide are analyzed. The simulation results show that the overlap increases as the decrease of Si duty cycle and the width of pillars. Then, the silicon duty cycle of 0.7 and width of 600nm for pillars are chosen, and a group of SWG racetrack resonators with different coupling length are fabricated. The experimental results show the optimal Q of 9800 is achieved when the gap and the coupling length are 140 nm and 6.5 ?m,respectively, and the S is 429.7nm/RIU. Thus a minimum DL of 3.71×10-4 RIU is achieved, which marks a reduction of 32.5% compared to the best value reported for SWG micro-ring sensors and provides an excellent scheme in optical sensor realm. |
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