Ultrasensitive refractive index fiber sensor based on high-order harmonic Vernier effect and a cascaded FPI

Abstract

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.

High sensitivity fiber optic current sensor based on Fabry–Perot interferometer manufactured by femtosecond laser

“…In the HVE sensor, FPI 1 is reference interferometer and FPI 2 is sensing interferometer. Based on the principle of HVE [39], the FSR of the j-order HVE sensor spectrum outer-envelope is as follows:…”

“…We select the inner envelopes intersection of the HVE sensor to study the sensor changing with axial strain, thus the amplification factor for the strain sensitivity of the sensor S 1 can be derived as follows [39]:…”

Simultaneous Measurement of Microdisplacement and Temperature Based on Balloon-Shaped Structure

“…However, the mechanical properties of the sensor are insufficient due to the large offset of the offset core. Qiu et al [18] manufactured refractive index (RI) sensors by clamping the hollow fiber (HCF) section between the tail fiber introduced into the single-mode fiber (SMF) and the reflected SMF section to enhance the device's mechanical properties. Similar structures were used by Huang et al [19] to simultaneously measure strain and temperature.…”