Design And Fabrication Of The Guided-Mode Resonance Tunable Filters

Guided-mode resonance(GMR)effect occurs in periodic waveguide structures where an incident wave is coupled to a leaky waveguide mode and yields a resonant peak.Optical filters based on the GMR effect have narrow bandwidth and high diffraction efficiency in resonant wavelength.The transmittance or reflection efficiency can reaches about 100%.Compared with traditional thin film filters,these filters have simpler structure and adjustable spectral response.In this dissertation,based on the GMR effect,theoretical design,experimental fabrication,and application were discussed.It focuses on the design and fabrication of tunable GMR filters,as well as the potential application of optical elements bases on theses filters.Numerical analysis theory is presented firstly,which includes two types of commonly used numerical analysis method: the equivalent medium theory and the rigorous coupled wave theory.In the analysis of subwavelength structures,the equivalent medium theory,as an auxiliary method,can help us to know the diffraction of grating quickly and to estimate appropriate structure parameters.Then the rigorous diffraction theory of grating vector can be used to perform precise calculation,which greatly saves the time of analysis.Secondly,principle of the GMR effect is explained.The influence of different structural parameters on the spectral response of GMR filter is analyzed.GMR structure with ideal spectral response can be designed by adjusting the structure parameters.According to the analysis of localized electric field on the surface of a GMR structure,we expounds the principle of GMR structure applied within the biological sensing,and points out that when the height of the grating thickness increase to a certain extent,spectral response remains the same.For the design of antireflection of GMR structure with a single layer,the thickness of the film after the equivalent is set to integer times of half a wavelength(resonance wavelength).For double guided mode resonance structure,in order to obtain good antireflective effect,the grating layer and the thickness of the waveguide layer are designed to a quarter of a wavelength optical thickness.In the preparation of GMR structure,this paper compares two kinds of typical guided mode resonance structure,and elaborates production process and key point for the GMR structure with a uniform thin film waveguide layer.In the design of GMR filter,bandwidth-tunable notch filter is firstly proposed.In this thesis,two kinds of structure that can adjust the bandwidth of GMR filter are designed.Firstly,taking advantage of the polarization-selective characteristics of ID GMR filter,two GMR filters are combined with each other.The resonance peak of TM mode of the first filter is in the same place with that of TE mode of the second filter.Combining with the twisted nematic phase liquid crystal cell,the bandwidth of the filter can be changed through adjusting the voltage of the liquid crystal cell that changes the polarization of transmission light.The second kind of GMR filter based on non-polarizing filtering effect makes full use of unmoved resonance wavelength and continuous change of bandwidth with the change of polarization of incident light.In addition,lO^im and 70^im spacer are put in the liquid crystal cell to change the thickness,which show the sensitivity of bandwidth to the driving voltage in the liquid crystal cell.Based on the sensitivity of spectral response of the GMR filter to change of waveguide thickness,a new type of GMR filter to achieve the resonance wavelength tuning is designed.Using ion beam etching technology,wedge film with gradient of thickness is fabricated,which is designed as the waveguide layer.When the incident point moves,the thickness of the waveguide layer is different;this can realize continuous adjustment of the resonance peak.In the experiment,wedge-shaped thin film waveguides with a thickness difference of about 50 nm is fabricated in the size of 35 mm * 35 mm of substrate,which realize the largest 41 nm movement of resonance peak.The relationship between the size of isosceles triangle flap as well as the thickness difference of wedge film,and the movement range of resonance peak are discussed.In addition,a tunable color filter is fabricated taking advantage of tunable resonance peak with the change of incident angle.The resonance peak in the range of visible light is stimulated by the negative first order diffraction wave.When the incident angle is 25°,35° and 47°,the corresponding peak is 627 nm? 552 nm and 480 nm5 respectively.When the incident angle changes,another peak located in the range of infrared,which is stimulated by the positive first order diffraction,cannot be feel by peopled eyes.Thus,only the resonance peak within the scope of visible light can be observed.