Ultra-Wideband Mid-Infrared Chalcogenide Suspended Nanorib Waveguide Gas Sensors with Exceptionally High External Confinement Factor beyond Free-Space

• Published in: ACS nano Vol. 17; no. 18; pp. 17761 - 17770
• Main Authors: Pi, Mingquan, Zheng, Chuantao, Zhao, Huan, Peng, Zihang, Guan, Gangyun, Ji, Jialin, Huang, Yijun, Min, Yuting, Liang, Lei, Song, Fang, Bai, Xue, Zhang, Yu, Wang, Yiding, Tittel, Frank K.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 26-09-2023
• Subjects: wideband gas sensor; waveguide sensor; on-chip gas detection; lift-off method; chalcogenide waveguide; suspended waveguide
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.3c02699

On-chip waveguide sensors are potential candidates for deep-space exploration because of their high integration and low power consumption. Since the fundamental absorption of most gas molecules exists in the mid-infrared (e.g., 3–12 μm), it is of great significance to fabricate wideband mid-infrared sensors with high external confinement factor (ECF). To overcome the limited transparency window and strong waveguide dispersion, a chalcogenide suspended nanorib waveguide sensor was proposed for ultra-wideband mid-infrared gas sensing, and three waveguide sensors (WG1–WG3) with optimized dimensions exhibit a wide waveband of 3.2–5.6 μm, 5.4–8.2 μm, and 8.1–11.5 μm with exceptionally high ECFs of 107–116%, 107–116%, and 116–128%, respectively. The waveguide sensors were fabricated by a two-step lift-off method without dry etching to reduce the process complexity. Experimental ECFs of 112%, 110%, and 110% were obtained at 3.291 μm, 4.319 μm, and 7.625 μm, respectively, through methane (CH4) and carbon dioxide (CO2) measurements. A limit of detection of 5.9 ppm was achieved for an averaging time of 64.2 s through the Allan deviation analysis of CH4 at 3.291 μm, leading to a comparable noise equivalent absorption sensitivity of 2.3 × 10–5 cm–1 Hz–1/2 as compared to the hollow-core fiber and on-chip gas sensors.