Multimode Fabry⁻Perot Interferometer Probe Based on Vernier Effect for Enhanced Temperature Sensing.

André D Gomes,Hartmut Bartelt,Jan Dellith,Orlando Frazão,Hamid Latifi,Mohammad I Zibaii,Martin Becker,Manfred Rothhardt

doi:10.3390/s19030453

Abstract

New miniaturized sensors for biological and medical applications must be adapted to the measuring environments and they should provide a high measurement resolution to sense small changes. The Vernier effect is an effective way of magnifying the sensitivity of a device, allowing for higher resolution sensing. We applied this concept to the development of a small-size optical fiber Fabry–Perot interferometer probe that presents more than 60-fold higher sensitivity to temperature than the normal Fabry–Perot interferometer without the Vernier effect. This enables the sensor to reach higher temperature resolutions. The silica Fabry–Perot interferometer is created by focused ion beam milling of the end of a tapered multimode fiber. Multiple Fabry–Perot interferometers with shifted frequencies are generated in the cavity due to the presence of multiple modes. The reflection spectrum shows two main components in the Fast Fourier transform that give rise to the Vernier effect. The superposition of these components presents an enhancement of sensitivity to temperature. The same effect is also obtained by monitoring the reflection spectrum node without any filtering. A temperature sensitivity of −654 pm/°C was obtained between 30 °C and 120 °C, with an experimental resolution of 0.14 °C. Stability measurements are also reported.

Highlights

Biological and medical applications require minimally invasive sensors, especially for in-vivo operation
The free λ1λλ12λ2 spectral range (FSR) corresponding to the normal Fabry–Perot interferometer given by the silica λ1 and the positions of the the presence minima, of neff is the effective refractive index, and L is cavity is due multiple modes, silica produces are cavitywhere is around around
We developed a small-size fiber probe to generate the Vernier effect by structuring a Fabry–Perot interferometer with focused ion beam milling at the end of a tapered multimode tip

Summary

Introduction

Biological and medical applications require minimally invasive sensors, especially for in-vivo operation. The current tendency is towards developing miniaturized sensors that are capable of measuring physical, chemical, and biochemical parameters For this purpose, Fabry–Perot interferometers (FPIs) are a type of sensing structure that has been explored due to the ability of producing sensing probes that can be optically interrogated in a reflection configuration. Polymer FPIs can attain temperature sensitivities that are one order of magnitude higher due to their high thermal expansion coefficient [10,11]. The Vernier effect has increasingly been used in optical fiber sensing due to its ability to enhance the measurement sensitivity [13,14,15,16,17]. Fabry–Perot interferometer probe that is capable of achieving an enhanced spectral shift to temperature compared to the conventional silica cavity in a fiber tip. The envelope presents a node that shows a magnified wavelength shift to temperature due to the Vernier effect

Fabrication Process

Working

Conclusions