Caucheteur Christophe, Voisin Valérie, Albert Jacques
Opt Express. 2015 Feb 9;23(3):2918-32. doi: 10.1364/OE.23.002918.
Plasmonic optical fiber sensors are continuously developed for (bio)chemical sensing purposes. Recently, surface plasmon resonance (SPR) generation was achieved in gold-coated tilted fiber Bragg gratings (TFBGs). These sensors probe the surrounding medium with near-infrared narrowband resonances, which enhances both the penetration depth of the evanescent field in the external medium and the wavelength resolution of the interrogation. They constitute a unique configuration to probe all the fiber cladding modes individually. We use them to analyze the modal distribution of gold-coated telecommunication-grade optical fibers immersed in aqueous solutions. Theoretical investigations with a finite-difference complex mode solver are confirmed by experimental data obtained on TFBGs. We show that the refractometric sensitivity varies with the mode order and that the global SPR envelope shift in response to surrounding refractive index (SRI) changes higher than 1e-2 RIU (refractive index unit) can be ~25% bigger than the local SPR mode shift arising from SRI changes limited to 1e-4 RIU. We bring clear evidence that the optimum gold thickness for SPR generation lies in the range between 50 and 70 nm while a cladding diameter decrease from 125 µm to 80 µm enhances the refractometric sensitivity by ~20%. Finally, we demonstrate that the ultimate refractometric sensitivity of cladding modes is ~550 nm/RIU when they are probed by gold-coated TFBGs.
等离子体光纤传感器不断地被开发用于（生物）化学传感目的。最近，在镀有金的倾斜光纤布拉格光栅（TFBG）中实现了表面等离子体共振（SPR）的产生。这些传感器利用近红外窄带共振探测周围介质，这既增加了倏逝场在外部介质中的穿透深度，又提高了询问的波长分辨率。它们构成了一种独特的配置，可单独探测所有光纤包层模式。我们使用它们来分析浸入水溶液中的镀有金的电信级光纤的模式分布。用有限差分复模求解器进行的理论研究得到了在TFBG上获得的实验数据的证实。我们表明，折射灵敏度随模式阶数而变化，并且响应于周围折射率（SRI）变化高于1e - 2 RIU（折射率单位）时的全局SPR包络位移可能比由限于1e - 4 RIU的SRI变化引起的局部SPR模式位移大~25%。我们明确证明，用于产生SPR的最佳金厚度在50至70纳米之间，而包层直径从125微米减小到80微米可使折射灵敏度提高约20%。最后，我们证明，当用镀有金的TFBG探测时，包层模式的最终折射灵敏度约为550纳米/RIU。
