Optimization And Design Of Optical Devices In 2D-3D Hetero-structure

In recent years,the 2D-3D hetero-structure has received the widespread attention as a good platform for dense integrated circuit.In this structure,the characteristics of the 2D structure,such as the simple device design,well transmission,can be used.At the same time,the integrated devices along the stacking direction in the woodpile structure is also be realized.By the finite-difference time-domain method(FDTD),some optical devices,such as the directional couplers,the waveguides,the spatial integrated waveguides,and the wavelength division demultiplexers in 2D-3D hetero-structures working in the terahertz wave,are designed,simulated and analyzed in detail.The main research contents are as follows:Firstly,a planar directional coupler is designed in the 2D layer of the 2D-3D hetero-structure.The coupling length is studied in detail by modulating the woodpile structure parameters on both sides of the directional coupler and the width of the rods between the two waveguides in the 2D plane.The results show that the coupling length is shortened to less than 3.0a when a in woodpile structure locating of the nearest stacked layer is changed.The coupling length is shortened because the average refractive index in the coupling region is decreased.In order to further reduce the average refractive index,the width of the rods between the input waveguide and the coupling waveguide is also considered.It is found that the coupling length is shortened further when the width is reduced.And an ultra-short coupling length less than 2a is obtained when the width of rods reaches 0.18a.Secondly,a straight waveguide is introduced in the 2D layer of the 2D-3D hetero-structure.The influence of parameters in the woodpile structure on the both sides of waveguide is studied.Firstly,we consider the translation optimization method.It is means that the 2D structure is shifted along a direction perpendicular to the waveguide.In this case,the symmetry between the woodpile and the waveguide is changed.The results show that the band wide of the waveguide is modulated significantly when the shifting distance is increased continuously.The band wide is increased to 0.54 THz when the moving distance is 0.5a.Then the stacking order of the woodpile structure on both sides of the waveguide is also considered.The wide guide band from 0.345[c/a]to 0.444[c/a]is obtained.The ratio ?f/_fc reaches 25.12%.In this case,the guide band wide is increased by 1.89THz.Next,a 2D-3D hetero-structure including of two 2D layers is designed.The waveguides are introduced in 2D layers.The spatial integration is studied.The results show that the guide band of the output waveguide is significantly widened and the guide band wide is increased to 1.38THz when the stacking order of the woodpile structures on both sides of the input and output waveguides is adjusted.In order to further improve the transmission characteristics of the output port,the vertical coupling waveguide is also optimized.It is means that the x=0.5L,where L and x represent the length of the cavity and the position of the cavity,is selected.The results show that the output waveguide has well output characteristics in x and y directions When x=0.5a.And two guide bands have been obtained.The range in x direction is 0.362[c/a]?0.385[c/a]and 0.402[c/a]?0.441[c/a].The range in y direction is 0.365[c/a]?0.394[c/a]and 0.401[c/a]?0.419[c/a].Finally,a wavelength division demultiplexer including of two output waveguides is designed in the 2D layer of the 2D-3D hetero-structure.And the transmission characteristics are studied when the cavities are introduced in the woodpile structure on both sides of the output waveguides.The research results show that the frequency selection characteristics in the wavelength division multiplexer can also be achieved through the adjustment of the cavities.