Enhancing the smoothness of silicon nitride waveguides with femtosecond laser annealing

CHIEN-HUNG CHEN^1*, NIEN-LIN HOU², PEI-HSUN WANG², HUNG-WEN CHEN^1,3

¹International Intercollegiate Ph.D. Program, National Tsing Hua University, Hsinchu, Taiwan
²Department of Optics and Photonics, National Central University, Taoyuan, Taiwan
³Institute of Photonics Technologies, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:CHIEN-HUNG CHEN, email:ch.ch.hung@gmail.com

We introduce a technique to enhance silicon nitride waveguide resonators using femtosecond laser annealing at 1035 nm wavelength. After annealing, the quality (Q) factor of these waveguides improves by about 1.3 times. Atomic force microscopy (AFM) analysis reveals a marked reduction in surface roughness post-annealing, from 7.1 nm to 1.8 nm. Waveguides with initially high Q values retain their quality, while those with lower Q values see significant improvement. The primary reason for the Q-factor boost is attributed to the reduction in surface roughness. Additionally, Raman spectroscopy verified the Si₃N₄ film's composition remains consistent post-annealing within the power range of 0.6 W to 1.6 W. Our findings highlight femtosecond laser annealing's promise for crafting efficient low-loss integrated photonics.

Keywords: Laser annealing, Surface roughness, Atomic force microscopy, quality (Q) factor