基于光刻的长周期及高阶Bragg波导光栅的研究

发布时间：2018-05-16 05:17

本文选题：长周期波导光栅 + 高阶Bragg波导光栅　；参考：《天津理工大学》2017年硕士论文

【摘要】：随着以波导光栅为代表的集成光器件的应用,人们对于波导光栅的研究愈发广泛。波导光栅可以在LiNbO_3晶体,聚合物,玻璃等多种材料上制备出来,其结构设计多样。目前常见的制作工艺包括:紫外光刻(UV),电子束刻蚀(EBL),聚焦离子束刻蚀(FIB),双光束干涉等。LiNbO_3晶体自身具有电光效应,因而选用LiNbO_3晶体作为衬底制备而成的波导光栅可实现电控调谐。本文以x切LiNbO_3晶体作为衬底,通过光刻及钛扩散工艺制作出二次钛扩散长周期波导光栅。提出利用LiNbO_3波导制备工艺一次性制备的长周期波导光栅及高阶Bragg波导光栅结构,并运用光刻及退火质子交换工艺一次性制作出长周期及高阶Bragg波导光栅。具体工作内容如下:第一,对二次钛扩散长周期波导光栅的结构及特性进行研究。理论上分析了光栅栅长及光栅周期的变化对透射谱特性的影响。耦合系数一定时,栅长增加,零值带宽减小,光栅透射率先减小后增大。完全耦合时,透射率最小,且周期越大,中心波长越大。实验上利用光刻及钛扩散工艺在LiNbO_3单模波导上制作了周期为420微米的二次钛扩散长周期波导光栅,并对光栅透射谱的测量进行了探究。第二,提出利用LiNbO_3波导制备工艺一次性制备的长周期波导光栅结构。理论上分析了波导宽度差、光栅栅区倾角的变化对透射谱特性的影响。随着波导宽度差增大,零值带宽减小,透射率呈现周期性变化。随着栅区倾角减小,零值带宽减小幅度变缓,透射率变化的周期变大。实验上利用光刻及退火质子交换工艺在LiNbO_3晶片上一次性制作出周期为百微米量级的长周期波导光栅,并对光栅透射谱的测量进行了探究。第三,提出利用LiNbO_3波导制备工艺一次性制备的高阶可调谐Bragg波导光栅结构。理论上分析了占空比,波导宽度差,栅区倾角,外加电压等参数的变化对光栅反射谱的影响。随着占空比增大,折射率调制度呈现周期性变化。在最佳占空比下,波导宽度差增大,最大反射率及零值带宽均增大,中心波长向长波方向偏移。随着栅区倾角的减小,最大反射率及零值带宽增量幅度减小,中心波长偏移量减小。随着外加电压增大,光栅反射谱形状不变,中心波长向长波方向偏移。实验上利用光刻及退火质子交换工艺在LiNbO_3晶片上一次性制作出周期为微米量级的高阶Bragg波导光栅,并对光栅光谱进行了测量及分析。
[Abstract]:With the application of integrated optical devices, such as waveguide gratings, the research of waveguide gratings is becoming more and more extensive. Waveguide gratings can be fabricated on LiNbO_3 crystals, polymers, glass and other materials. At present, the common fabrication techniques include: UV lithography, electron beam etching, focused ion beam etching, double beam interference and so on. Linbo _ 3 crystal has its own electro-optic effect. Therefore, the waveguide grating fabricated by LiNbO_3 crystal as substrate can be electrically tuned. In this paper, the secondary titanium diffusion long-period waveguide grating is fabricated by photolithography and titanium diffusion on x cut LiNbO_3 crystal substrate. Long period waveguide gratings and high order Bragg waveguide gratings fabricated by LiNbO_3 waveguide fabrication process are proposed. Long period and high order Bragg waveguide gratings are fabricated by photolithography and annealing proton exchange technology. The main contents are as follows: first, the structure and characteristics of the second-order titanium diffusion long-period waveguide grating are studied. The influence of grating gate length and grating period on transmission spectrum is analyzed theoretically. When the coupling coefficient is constant, the grating length increases, the zero bandwidth decreases, and the grating transmission decreases first and then increases. When fully coupled, the transmissivity is the smallest, and the longer the period is, the greater the central wavelength is. Using photolithography and titanium diffusion technique, a 420-micron second-order titanium diffusion long-period waveguide grating was fabricated on LiNbO_3 single-mode waveguide. The measurement of the transmission spectrum of the grating was investigated. Secondly, the long period waveguide gratings fabricated by LiNbO_3 waveguide fabrication process are proposed. The influence of waveguide width difference and grating dip angle on the transmission spectrum is analyzed theoretically. With the increase of waveguide width difference, the zero bandwidth decreases and the transmittance changes periodically. With the decrease of the inclination angle of the gate region, the amplitude of the zero bandwidth decreases and the period of the transmissivity increases. Using photolithography and annealing proton exchange process, the long period waveguide grating with a period of 100 micron order was fabricated on LiNbO_3 wafer at one time, and the measurement of the transmission spectrum of the grating was investigated. Thirdly, a high order tunable Bragg waveguide grating structure fabricated by LiNbO_3 waveguide fabrication process is proposed. The effects of the parameters such as duty cycle, waveguide width difference, grating dip angle and applied voltage on the grating reflectance spectrum are analyzed theoretically. With the increase of duty cycle, the refractive index modulation changes periodically. Under the optimal duty cycle, the waveguide width difference increases, the maximum reflectivity and zero bandwidth increase, and the center wavelength shifts to the long wave direction. The maximum reflectivity and the increment amplitude of zero bandwidth decrease with the decrease of the inclination angle of the gate, and the center wavelength offset decreases. With the increase of applied voltage, the shape of the grating reflectance spectrum is invariant, and the center wavelength shifts to the direction of long wave. High-order Bragg waveguide gratings with a period of micron order are fabricated on LiNbO_3 wafer by photolithography and annealing proton exchange process. The spectrum of the grating is measured and analyzed.
【学位授予单位】：天津理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN25

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