钛扩散铌酸锂脊形波导理论分析与初步制备

Theoretical Analysis and Preliminary Fabrication of Ti-Diffused LiNbO_3 Ridge Waveguides

铌酸锂脊形波导最近引起了广泛研究兴趣,它通常采用刻蚀钛扩散或质子交换铌酸锂条形波导或平板波导的方法制作而成。对由这两种方法制备的钛扩散铌酸锂脊形波导在1550nm波长处的横电基模光场分布进行了仿真分析。结果指出,当钛扩散条件相同时,通过刻蚀钛扩散铌酸锂平板波导得到的脊形结构在横向和纵向上对导模均具有更好的束缚能力。这种脊形波导的制作工艺相对简单,它对导模的强束缚有利于减小铌酸锂电光调制器尺寸和提高光电重叠积分因子。实验制备了钛扩散铌酸锂平板波导,并基于微机电系统(MEMS)工艺在其表面制作出Cr膜马赫-曾德尔干涉计(MZI)阵列图案,然后在SF6气氛中对平板波导进行反应离子刻蚀,初步得到了铌酸锂脊形波导MZI阵列。扫描电镜分析结果显示制得的脊形波导横截面呈梯形状,两侧面较粗糙,脊高约670nm。

Lithium niobate （LN） ridge waveguides have recently attracted considerable attention, and they are usually fabricated by etching LN channel or slab waveguides prepared by Ti indiffusion or proton exchange. The field profile of the fundamental transverse electric （TE） mode guided in each of the two LN ridge waveguides converted from the Ti-indiffused channel and slab waveguides is simulated at 1550 nm wavelength. The simulation results indicate that the LN slab waveguide can offer the resulting ridge structure a stronger confinement of the TE mode as compared with the channel waveguide made under the same Ti-indiffusing conditions. The strong confinement of the guided mode allows for miniaturizing the LN-based photonic devices and for enhancing the electro-optical overlapping factor. It is also simple to fabricate the ridge structure from LN slab waveguides. On the other hand, Ti-indiffused LN slab waveguides are prepared, on which a chromium layer with a pattern of Mach-Zehnder interferometer （MZI） array is fabricated by the micro electro mechanical systems （MEMS） process. The ridge waveguide MZI array is realized by reactive ion etching of the slab LN waveguide in the SFG atmosphere. Investigations by scanning electron microscopy reveal that the prepared LN ridge waveguides have a ridge height of 670 nm and an isosceles trapezoid cross section and their sidefaces are rather coarse.