Han Jinli, Zhang Yunfang, Liao Changrui, Jiang Yuying, Wang Ying, Lin Chupao, Liu Shen, Wang Jiachen, Zhang Zhe, Zhou Jiangtao, Wang Yiping
Opt Express. 2020 May 11;28(10):14263-14270. doi: 10.1364/OE.390674.
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.
一种新型的光纤界面定向波导耦合器通过飞秒激光刻写在无芯光纤表面，并成功应用于高灵敏度折射率测量。首先刻写主臂，将来自输入单模光纤的光耦合到光纤界面，然后再回到输出单模光纤。在主臂附近平行刻写一个侧臂。当满足相位匹配条件时，在主臂中传播的光可以有效地耦合到侧臂中，这在耦合波长处产生一个明显的光谱凹陷。由于在光纤界面波导中激发了强倏逝场，所提出的器件在1.44 - 1.45的折射率范围内实现了高达约8249 nm/RIU的灵敏度。所提出的光纤定向耦合器具有高机械强度、紧凑的结构和优异的折射率灵敏度。因此，它在生化传感的实际应用中具有巨大的潜力。
