کنفرانس مهندسی برق ایران

صفحه اصلی / سی و چهارمین کنفرانس بین المللی مهندسی برق

Fabrication of a planar optical waveguide with Ti:LiNbO3 diffusion technique

نویسندگان :

Reza Khoddami Ashkezari¹ Arian Mousavi Madani² Mohammad Mohsen Ebrahimi Seyghalan³ Soheil Moradi⁴ Mehdi Fardmanesh⁵

1- دانشگاه صنعتی شریف 2- دانشگاه صنعتی شریف 3- دانشگاه صنعتی شریف 4- دانشگاه صنعتی شریف 5- دانشگاه صنعتی شریف

کلمات کلیدی :

Lithium niobate،Titanium-diffused substrate،Optical waveguide

چکیده :

Lithium niobate LiNbO3 is a widely used platform for integrated photonics, especially optical waveguides. This work presents a practical and optimized fabrication process for planar LiNbO3 waveguides on X-cut substrates. Key steps include improved organic cleaning to remove micron-scale particles, controlled DC magnetron sputtering of the titanium layer, optimized photolithography for small feature sizes, and a refined titanium-diffusion process using wet oxygen and argon. A central challenge addressed in this work is the realization of micron-scale waveguide designs incorporating a splitter angle of approximately one degree. Such a small branching angle imposes stringent requirements on lithography accuracy and demands precise control of the titanium diffusion process, as excessive lateral diffusion would distort the splitter geometry and prevent achieving the desired angle. Careful optimization of pattern definition and diffusion parameters was therefore essential to preserve the intended waveguide geometry. In addition, the limited substrate size and the requirement for the waveguide input and output facets to be located at the substrate edges introduced further lithographic challenges, as photoresist thickness nonuniformity near the edges can degrade pattern fidelity. These edge-related issues were addressed through process adjustments to ensure reliable pattern transfer and uniform waveguide definition across the entire substrate. Successful titanium diffusion was verified through optical microscopy by adjusting the focal plane to distinguish the diffused waveguide region from the substrate surface. Electrode patterning was performed through Ti/Au sputtering and HF-based wet etching. The proposed process provides a reliable and repeatable method for fabricating high-quality LiNbO3 photonic devices. The UV-Vis and FTIR (Fourier Transform Infra Red) spectra of LiNbO3 before and after Titan diffusion show minimal and controlled changes in light absorbance and transmission in the visible and near-infrared regions. These results indicate that the Titan diffusion process was effective without causing significant structural damage to the substrate.