Femtosecond-Laser Direct Writing of Double-Line and Tubular Depressed-Cladding Waveguides in Ultra-Low-Expansion Glass

• Published in: Photonics Vol. 12; no. 8; p. 797
• Main Authors: Wu, Yuhao, Guo, Sixuan, Cheng, Guanghua, Wang, Feiran, Wang, Xu, Zhang, Yunjie
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 08.08.2025
• Subjects: Aperture; Ceramics; Cladding; Crystals; Direct laser writing; Fabrication; Finite element method; Glass ceramics; High temperature; Integrated circuits; Lasers; Optics; Phase transitions; Process parameters; Propagation; Temperature requirements; Waveguides; Writing; Germany
• ISSN: 2304-6732; 2304-6732
• DOI: 10.3390/photonics12080797

Addressing the stability requirements of photonic integrated devices operating over wide temperature ranges, this work achieves controlled fabrication of femtosecond-laser direct-written Type II double-line waveguides and Type III depressed-cladding tubular waveguides within ultra-low-expansion LAS glass-ceramics. The light-guiding mechanisms were elucidated through finite element modeling. The influences of laser writing parameters and waveguide geometric structures on guiding performance were systematically investigated. Experimental results demonstrate that the double-line waveguides exhibit optimal single-mode guiding performance at 30 μm spacing and 120 mW writing power. For the tubular depressed-cladding waveguides, both single-mode and multi-mode fields are attainable across a broad processing parameter window. Large-mode-area characteristics manifested in the 50 μm core waveguide, exhibiting an edge-shifted intensity profile for higher-order modes that generated a hollow beam, enabling applications in atom guidance and particle trapping.