Study of the Vernier Effect Based on the Fabry–Perot Interferometer: Methodology and Application

Microsphere Coupled Off-Core Fiber Sensor for Ultrasound Sensing

A compact fiber ultrasound-sensing device comprising a commercially available Barium Titanate (BaTiO₃) glass microsphere coupled to an open cavity off-core Fabry-Perot interferometer (FPI) fiber sensor is proposed and demonstrated. The open cavity is fabricated through splicing two segments of a single mode fiber (SMF-28) at lateral offsets. The lateral offset is matched to the radius of the microsphere to maximize their coupling and allow for an increased sensing response. Furthermore, the microsphere can be moved along the open-air cavity to allow for tuning of the reflection spectrum. The multiple passes of the FPI enabled by the high refractive index microsphere results in a 40 dB enhancement of finesse and achieves broadband ultrasound sensing from 0.1-45.6 MHz driven via a piezoelectric transducer (PZT) centered at 3.7 MHz. The goal is to achieve frequency detection in the MHz range using a repeatable, cost effective, and easy to fabricate FPI sensor design.

Fiber-tip polymer filled probe for high-sensitivity temperature sensing and polymer refractometers

A compact and robust Fabry-Perot interferometer (FPI) based on polymer core is proposed and experimentally demonstrated. The fabrication is low-cost and has simple processes, including fusion splicing and polymer injection. Its characteristic is that the polymer fills the entire capillary core, which is easy to demodulate, and provides a good platform for the refractive index measurement of the polymer after curing. The experimental result shows a linear temperature sensitivity of 1226.64 pm/°C between 39°C and 54°C. Furthermore, we also used the Vernier effect to improve the temperature sensitivity as high as -15.617 nm/°C. The proposed FPI structure provides potential application in the research of sensors and polymer optical fibers.

A High Precision Fiber Optic Fabry–Perot Pressure Sensor Based on AB Epoxy Adhesive Film

This paper proposes a Fabry–Perot pressure sensor based on AB epoxy adhesive with ultra-high sensitivity under low pressure. Fabry–Perot interference, located between single-mode fiber (SMF) and hollow-core fiber (HCF), is an ultra-thin AB epoxy film formed by capillary action. Then the thick HCF was used to fix the HCF and SMF at both ends with AB epoxy adhesive. Experimental results show that when the thickness of AB epoxy film is 8.74 μm, and the cavity length is 30 μm, the sensor has the highest sensitivity. The sensitivity is 257.79 nm/MPa within the pressure range of 0–70 kPa. It also investigated the influence of the curing time of AB epoxy on the interference spectrum. Experiments showed that the interference spectrum peak is blue-shifted with the increase of curing time. Our study also demonstrated the humidity stability of this pressure sensor. These characteristics mean that our sensor has potential applications in the biomedical field and ocean exploration.