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Fiber-interface directional coupler inscribed by femtosecond laser for refractive index measurements

2020; Optica Publishing Group; Volume: 28; Issue: 10 Linguagem: Inglês

10.1364/oe.390674

1094-4087

Jinli Han, Yunfang Zhang, Changrui Liao, Yuying Jiang, Ying Wang, Chupao Lin, Shen Liu, Jiachen Wang, Zhe Zhang, Jiangtao Zhou, Yiping Wang,

Advanced Fiber Laser Technologies

A novel fiber-interface directional waveguide coupler was inscribed on the surface of a coreless fiber by femtosecond laser, and was successfully applied to highly sensitive refractive index (RI) measurements. The primary arm was first inscribed to couple light from a lead-in single mode fiber to the fiber interface, then back to a lead-out single mode fiber. A side arm was inscribed parallel and in close proximity to the primary arm. Light propagating in the primary arm could then be efficiently coupled into the side arm when a phase-matching condition was met, which produced a dramatic spectral dip at the coupling wavelength. The proposed device achieved a sensitivity as high as ∼8249 nm/RIU over an RI range of 1.44-1.45, due to strong evanescent fields excited in fiber-interface waveguides. The proposed in-fiber directional coupler exhibits high mechanical strength, a compact configuration, and excellent RI sensitivity. As such, it has significant potential for practical applications in biochemical sensing.