新型衬底开槽结构的LiNbO_3波导强度调制器设计分析

Research on the Design of LiNbO_3 Waveguide Intensity Modulator with a New Back Slot Structure

提出了一种在LiNbO3衬底背面沿垂直光传播方向的开槽结构的波导调制器,不仅可以通过开槽的方式替代通常LiNbO3基片和电极之间的SiO2缓冲层,起到减小驱动电压和抑制直流(DC)漂移的作用,而且由于其开槽部分和未开槽部分的截面图都比较规则,开槽部分又符合部分电容法的应用条件,在设计中可以避开有限元法(FEM)而采用施瓦兹-克里斯托弗耳(SC)变换进行计算。数值计算结果表明,在电极长度为40 mm的LiNbO3衬底上,开槽时选取开槽处的厚度为15μm,开槽宽度为38.5 mm,调制器调制带宽可以达到40.00 GHz,阻抗为63.10Ω。说明这种结构在没有SiO2缓冲层的情况下同样能够实现光波和微波的速度匹配,对于调制器的制作设计更加便利和精确。

A LiNbO3 waveguide intensity modulator with a new back slot structure is proposed. The direction of the back slot is vertical to the beam propagation. The back slot structure can achieve low drive power and suppress the direct current （DC）-drift voltage. In addition, because both the cross section of the back slot part and the other are relatively regular, and the structure of back slot part satisfies the condition of the partial capacitances method, the Schwartz-Christoffel （SC） conform mapping can be used to design the modulator instead of the finite element method （FEM）. The calculation shows that when the thickness of the back slot part is 15 μm and the width is 38.5 mm in the LiNbO3 with 40 mm electrode, 40.00 GHz modulation bandwidth can be achieved and the impedance is 63. 10 Ω. It is clear that this structure can also satisfy the velocity-matching condition without the buffer layer of silicon dioxide （SiO2）. So this type of back slot structure is proved to be more convenient and feasible for the design of waveguide modulator.