張榮森

The purpose of this thesis is to investigate the thickness effects on sub-wavelength (period <λ) Lamellar grating waveguide sensors with TE polarization incidence and the effects of waveguide thickness on the sensitivity of the sub-wavelength Lamellar grating waveguide sensor with TE polarization incidence. In addition, two simple and low cost prototypes of real-time non-contact pulse measurement devices have been successfully developed; they could be useful, efficient and objective reference for Traditional Chinese Medicine (TCM) pulse diagnosis. According to the simulation result of Lamellar grating thickness versus sensor sensitivity, it reveals that as the thickness of Lamellar grating is increased, the more resonance modes will be induced as well. This proves that the Lamellar grating possesses the characteristics of the effective refractive index waveguide layer in physics. However, it is difficult to recognize the peak shift of the fundamental mode while the thickness of grating is different and the thickness of waveguide is the same. On the other hand, referring to the simulation of the effects of waveguide thickness on the sensitivity of the sub-wavelength Lamellar grating, the calculation shows that the thicker waveguide layer will induce more guided modes. Also, the variation of guided modes and the sensitivity of fundamental mode are investigated. Comparing the spectrum sensitivity of fundamental mode of different waveguide thickness, the peak shift of the thinner waveguide layer is larger than the thicker one’s. In other words, thinner waveguide layer is a better selection for the use of sensor. The first chapter discusses the overview of present techniques of label-free biosensor, optical label-free biosensor structures including: surface plasmon resonance, interference sensor, optical waveguide, optical fiber, photonic crystal and the detection limits of optical biosensors. The second chapter mentions the basic theory of the grating-coupled waveguide and makes a brief introduction of simulation method. The purpose is to systematize various theories of relevant grating-coupled waveguide and to do a brief introduction of how to estimate the wavelength spectrum peak. The third chapter talks about thickness effects on the Lamellar grating waveguide sensors with TE-polarization incidence. The relationship between the Lamellar grating coupled sensor and efficiency is discussed. Rigorous coupled wave analysis (RCWA) method and finite difference time domain (FDTD) are used to calculate the relationship between the thickness of one-dimension low refractive Lamellar grating and the wavelength. Simulation results reveal that as the thickness of Lamellar grating is increased, the more high order modes will be induced. Nevertheless, the position of peak wavelength of the fundamental mode is mainly determined by the thickness of the waveguide layer. Concerning about the simulation of sensor sensitivity, we set a thin film of the effective refractive index close to water (defined as nf = 1.334) to replace the bio donor and acceptor layer. Simulation result reveals that for the thinner grating (dg = 100nm), the thickness of the bio donor and acceptor layer is increased to 1000nm, the maxima peak wavelength shift (PWS), δλmax=λP. Longest -λP. shortest = 742.48-737.38, is 5.1 nm, still unable to be treated as sensitivity measurement standard. However, if we refer to the Q-value (quality value) of peak wavelength of the guided modes, as the thin film thickness is less than 100nm, Q-value difference is easy to be recognized. Therefore, while waveguide thickness is the same and the grating thickness is different, Q-value could be a valid index for the sensitivity. The fourth chapter focuses on waveguide thickness effects on the sensitivity of the sub-wavelength Lamellar grating waveguide sensor. Referring to Chapter 3, the thinner grating defined as dg=100nm and the energy band of thinner structure are studied. Also, we study the characteristics of guided modes while the grating thickness dg=100nm and dg=1000nm are under different waveguide thickness (dWG). The calculation results show that the thicker waveguide layer will induce more guided modes. Comparing the spectrum sensitivity of fundamental mode of different waveguide thickness, the peak shift of the thinner waveguide layer is larger than the thicker one’s. Therefore, no matter we take the grating thickness or the waveguide thickness as grating waveguide sensors, less thickness has higher sensitivity. Chapter five and Chapter six respectively present that simple and low cost prototypes of single-channel and two-channel sound detectors are fabricated as pulse measurement devices; they are useful tool and objective reference for Traditional Chinese Medicine pulse diagnosis. A simple high sensitivity condenser microphone is used as receiver. With commercial LabVIEW software program, we have designed highly sensitive pulse diagnosis detector. By the vibration signals of pulse and performing Fourier Transform, we cannot only obtain the signals of health conditions of individuals, but also provide a real-time and reliable data for TCM pulse diagnosis. Most importantly, these are non-contact, harmless, and reusable measurement devices; the patients do not need to waste time for waiting and the doctors can do immediate and efficient diagnosis for the patients who are not able to move or to be moved physically. This study designs and fabricates a simple and low cost pulse measurement based on a commercial laptop. The measurement results demonstrate that pulse signals are acquired correctly and two-channel sound detectors can successfully acquire vibration signals of pulse. As a result, these non-contact pulse measurement devices can promote the development of Traditional Chinese Medicine and reduce the cost for disease diagnosis.