Opt Express. 2023 Apr 10;31(8):13053-13064. doi: 10.1364/OE.484430.
This paper proposes and demonstrates an ultrasensitive refractive index (RI) sensor based on harmonic Vernier effect (HEV) and a cascaded Fabry-Perot interferometer (FPI). The sensor is fabricated by sandwiching a hollow-core fiber (HCF) segment between a lead-in single-mode fiber (SMF) pigtail and a reflection SMF segment with an offset of 37 µm between two fiber centers to form a cascaded FPI structure, where the HCF is the sensing FPI, and the reflection SMF is the reference FPI. To excite the HEV, the optical path of the reference FPI must be multiple times (>1) that of the sensing FPI. Several sensors have been made to conduct RI measurements of gas and liquid. The sensor's ultrahigh RI sensitivity of up to ∼378000 nm/RIU can be achieved by reducing the detuning ratio of the optical path and increasing the harmonic order. This paper also proved that the proposed sensor with a harmonic order of up to 12 can increase the fabricated tolerances while achieving high sensitivity. The large fabrication tolerances greatly increase the manufacturing repeatability, reduce production costs, and make it easier to achieve high sensitivity. In addition, the proposed RI sensor has advantages of ultrahigh sensitivity, compactness, low production cost (large fabrication tolerances), and capability to detect gas and liquid samples. This sensor has promising potentials for biochemical sensing, gas or liquid concentration sensing, and environmental monitoring.
本文提出并演示了一种基于谐波 Vernier 效应（HEV）和级联 Fabry-Perot 干涉仪（FPI）的超灵敏折射率（RI）传感器。该传感器通过将一段空心光纤（HCF）夹在引入单模光纤（SMF）尾纤和反射 SMF 段之间来制造，两个光纤中心之间的偏移量为 37 µm，形成级联 FPI 结构，其中 HCF 是传感 FPI，反射 SMF 是参考 FPI。为了激发 HEV，参考 FPI 的光程必须是传感 FPI 的多次（>1）。已经制造了几个传感器来进行气体和液体的 RI 测量。通过减小光程的失谐比并增加谐波阶数，该传感器可以实现高达 ∼378000 nm/RIU 的超高 RI 灵敏度。本文还证明，具有高达 12 阶谐波的所提出的传感器可以在实现高灵敏度的同时增加制造容差。较大的制造容差大大提高了制造重复性，降低了生产成本，并且更容易实现高灵敏度。此外，所提出的 RI 传感器具有超高灵敏度、紧凑性、低成本（大制造容差）和检测气体和液体样品的能力。该传感器在生化传感、气体或液体浓度传感以及环境监测方面具有广阔的应用前景。
