One-dimensional Photonic Crystal Surface Waves And Their Sensing Applications

As photonic crystals are truncated at the surface, surface states will be introduced into the forbidden band due to the broken translational symmetry. Electromagnetic waves corresponding to surface states propagate along the interface of photonic crystals and external medium, known as Bloch surface waves (BSWs). Surface states can change the spatial distribution of the electromagnetic field, leading to the enhancement of the local electromagnetic field on the surface, which can be used to enhance relevant optical effects, such as surface fluorescence effect, surface Raman effect etc. BSWs of one-dimensional photonic crystals (1D-PC) are quite similar to the widely studied surface plasmon resonance:when they are excited, a narrow resonance dip will appear on the corresponding reflection spectrum; the location and intensity of this resonance dip vary with the external refractive index. Therefore, we can employ the properties of BSWs to develop new optical sensors based on detecting the refractive index.This thesis systematically studies properties (such as dispersion relation, field distribution etc) of surface states of ID-PCs with the plane wave expansion method, discusses the origin of surface states of1D-PCs and rules of surface states’existing, and also offers the theoretical approach to designing1D-PC BSW devices. The transmission properties of BSWs are studied with the transfer matrix method. We are the first to study the reflection phase properties and its sensing applications of1D-PC BSWs in both theory and experiment, and also the first to propose a BSW sensing technique based on phase detection, which promises applications in the label-free biological and chemical sensing.This thesis consists of six chapters.In Chapter1, we briefly introduce the concept of photonic crystals and their general properties, and review some important progress in photonic crystal fields in recent years, the research history and research status of1D-PC BSWs.In Chapter2, we introduce the theoretical research methods used in this thesis. The plane wave expansion method commonly used in the calculation of photonic crystal band is introduced briefly, the transfer matrix method and angular spectrum decomposition for a Gaussian beam are deduced in detail. Besides, calculation program written by the author based on the transfer matrix method is also introduced, which can calculate reflectivity and transmittance, reflection phase, ellipsometric parameters and field distribution of multilayer films, and, with the aid of angular spectrum decomposition for a Gaussian input beam, also can visualize transmission of Gauss beam in multilayer films and calculate reflectivity of Gauss beam.In Chapter3, the basic properties of ID-PC surface states are studied systematically with the plane wave expansion method. Our studies show that for TM and TE polarization, surface states can both exist, but their dispersion curves do not coincide and so they will not be excited at the same time; the field of surface states is localized at the surface, and the larger the parallel wave vector is, the higher the locality is.We discuss the origin of surface states, and furthermore confirm that the surface states of photonic crystals originate from band-edge states of finite photonic crystals. The surface termination result in difference in environment between the last layer and the internal of1D-PCs. In suitable conditions, band-edge states separate from the allowed band and enter the forbidden band, forming surface bound mode.Effects of the last layer on ID-PC surface states are also studied, for the sake of which we introduce truncation parameter t. For ID-PC composed of alternatively layer of high refractive index with a thickness dH and the layer of low refractive index with a thickness dL, lattice constant is a. with different ta value representing different truncation on the surface of photonic crystals. When ta<1/2dH and ta>1/2dH+dL, the corresponding last layer is the layer of high refractive index; when1/2dH<ta<1/2dH+dL, it is the layer of low refractive index. It is shown that surface states do not exist for all the range of ta values. For the first forbidden band, we conclude rules as follows:1When parallel wave vector is large. In addition to the light cone of the dielectric layer with low refractive index, the band structure, dispersion curves for TE and TM polarizations are very similar. In this area, when1/2dH<ta<1/2dH+dL, there is no surface state. When ta<1/2dH, for TE and TM polarizations surface states can exist. And the thiner the last layer is.the higher frequency of the surface states is. When ta>1/2dH+dL,for TM polarizations surface states can not exist, but for TE polarizations surface states can exist at ta≈1a and are located close to at the bottom of the second allowed band. When ta gradually gets close to dH/2, surface states gets close to the band edge on the top of the first allowed band.2. When parallel wave vector is small. The law is similar to the case in which wave vector is large, but the case follows the rules less strictly. When ta≈0or1a, surface state for TE polarization is located close to the center of the forbidden band, but surface state for TM polarization is located close to at the bottom of the second allowed band. When ta>1/2dH+dL, TM polarization still has no surface states while TE polarization does for the wide range of ta values; the closer ta gets to dH/2, the closer surface states gets to the band edge on the top of the first allowed band. However, when1/2dH<ta<1/2dH+dL, for TE andTM polarization no surface states can exist.Ror TE polarization surface state can exist the when ta>dH/2+dL+dH/4, and the surface state is quite close to the top of the first band.In Chapter4, we propose the theoretical design method of1D-PC BSW devices and study theoretically transmission properties of1D-PC BSWs. When BSW is excited, a resonance dip will appear in the reflection spectrum. As the photonic crystals are composed of all-dielectric with little loss, resonance dips of BSWs are very sharp, their full width at half maximum (FWHM) is less than0.1. Our calculations show that periodicity of photonic crystals and loss of dielectric layer composed of photonic crystals both have a great impact on FWHM and depth of resonance dip. In order to get good devices, periodicity of photonic crystals is optimized according to the loss of dielectric layers.We also study the reflection phase properties of BSWs on1D-PCs. It is shown that when the BSW resonance occurs, the corresponding reflection phase changes rapidly. Gradient of reflection phase curve near resonance location depend on the periodicity and loss of1D-PC composed of the BSW device. In contrast to the reflectivity behavior, when there is little or no loss of dielectric, the depth of resonance dip will dwindle or even disappear, but the phase keep a large steepness. In this case, reflectivity phase has been more sensitive compared to the reflectivity intensity, so detecting phase is more alternative for BSW sensing applications.Combining the transfer matrix method with angular spectrum decomposition for a Gaussian input beam, We analyze the influence of Gauss beam divergence angle on the BSW reflectivity and offer quantitative results of this influence. Our studies shows that. Gauss beam divergence angle will widen and shallow resonance dip of BSWs, and the width of the widened dip approximates the Gauss beam angle, thus affecting the sensitivity and detection limit of BSW devices. The laser beam with better collimation can be used to improve the detection liimt and sensitivity of BSW device. With angular spectrum decomposition method for a Gaussian input beam, we also realize the visualization of1D-PC BSWs. This method can simulate the actual situation in which the beam excites the BSW, can help study more intuitively the transmission characteristics, such as propagation distance of BSWs and the giant Goos-Hanchen Effect caused by BSWs. For our device, propagation distance of BSWs is about300u m. Despite a large amount of calculation, it is a good research method.In Chapter5, we alternatively grow TiO2and SiO2multilayer films using the electron beam evaporation method assisted by ion-beam on a semi-cylindrical prism, and successfully fabricate1D-PC BSW devices. The ellipsometric parameters of the fabricated devices are computed with the transfer matrix method, and reflection properties of the designed device are characterized by spectroscopic ellipsometry. Our experimental results show that the ID-PC device we design can sustain the BSWs and spectroscopic ellipsometry can effectively characterize BSW device. By measuring ellipsometric parameters and, we can obtain both the reflection amplitude and phase information of BSWs simultaneously. Spectroscopic ellipsometry can characterize reflection phase properties of BSW devices. The experimental results also verify expected abrupt phase change induced by the BSW resonance in the1D PC.We study sensing applications of BSW devices and propose a BSW sensor based on phase detection. With respectively the angular interrogation and wavelength interrogation methods, we prove experimentally that the reflection phase of BSWs is very sensitive to minor changes in the external refractive index of ID-PC; The angular sensitivity of our BSW devices based on angular interrogation is42.94o/RIU, and the phase sensitivity is as high as6.57X103o/RIU. The sensitivity of our BSW devices based on wavelength interrogation is631nm/RIU. We also evaluate their phase sensitivity by figure of merit (FOM). It is demonstrated that the phase sensitivity of the BSW device is higher by nearly1order of magnitude than its amplitude sensitivity.In this these, we study systematically properties of1D-PC surface states, summerize the existing laws of surface states and supply theoretical foundation for the design of1D-PC BSW devices. We also summarize the effect of finite ID-PC periodicity and dielectric loss on reflectivity and reflection-phase of BSWs and successfully characterize transmission properties of BSW devices using the spectroscopic ellipsometry. We are the first to study the reflection phase properties and their sensing applications of1D-PC Bloch surface waves in both theory and experiment, also the first to present the BSW sensing technique based on phase detection, which promises the application in label-free biological and chemical sensing field.