Low Detection-limit Refractive Index Sensor Based On Asymmetric Coupled Structure

In the field of biochemistry, Optical sensors have been widely used in clinical screening, medical diagnostics, environment monitoring and food safety, due to its great properties such as anti-electromagnetic interference, multiplexed detection, small size, high sensitivity, and fast response. Theoretical and simulational investigations on microfiber-based and silicon slot waveguides-based asymmetric coupler are carried out. The main contents of this thesis includes the following aspects.The research background and significance of optical sensors are introduced, and the current research of optical microfiber-based and silicon waveguides-based sensors are highlighted. Meanwhile, the propagation characteristics and applications of microfiber and silicon slot waveguides for sensing are summarized. The theoretical study are performed to investigate the asymmetric directly coupler. The performance index of the coupler for sensing are summarized.An asymmetric microfiber coupler based optical sensor is proposed. A finite-difference time-domain(FDTD) method is used to simulate the structure of the asymmetric coupler. The effect of coupling distance and microfiber diameter to sensing performance is analyzed. This asymmetric coupler based optical sensor achieves a maximum sensitivity of 4549nm/RIU. With a optimization of the sensitivity and the detection limit, a sensitivity of 3212nm/RIU with a bandwidth of 12 nm is achieved.An optical sensor based on the coupling of silicon waveguides and slot waveguides is proposed. FDTD Solutions is used to obtain the light propagation in the couper. The single-peak and narrowband characteristics of this coupler is verified. The effect of waveguides parameters and the device parameter to sensing performance is discussed and analyzed. This sensor achieves a sensitivity of 445nm/RIU with a bandwidth of 6nm. The design and fabricating procedure of this sensor on 220 nm silicon-on-insulator(SOI) structures are discussed, and preliminary fabrication of this devices is carried out.