Micro-force measurement with pre-curvature long-period fiber grating-based sensor

Walter S J Ferreira,Paulo S S Dos Santos,João M S Sakamoto,Pedro A S Jorge,Paulo Caldas,H Michinel,M.F Costa,O Frazao

doi:10.1051/epjconf/202023812009

Abstract

In this work, a long-period fiber grating (LPG) based sensor was evaluated as a sensing device for micro-force measurement, in the order of micro Newtons. It was used an LPG fabricated by arc-inducted technique in a SMF-28 standard optical fiber. The optical fiber was fixed between two clamps with a separation of 150 mm with the middle of the LPG located at the center. Characterizations were performed in terms of temperature, curvature and strain. The grating was then used as a micro-force sensor by means of both curvature and strain, induced by a hung mass in a stretched fiber. Furthermore, the evaluation of a precurvature LPG was performed to assess if an increase of sensitivity is achieved. Micro-force sensitivity achieved with the stretched LPG was 1.41 nm/mN and it was demonstrated that its sensitivity can be enhanced to 5.14 nm/mN with a pre-curvature of 2.2 m–1 applied to the LPG, achieving a spectral resolution of at least 15.6 μN.

Highlights

The research field in optical fiber sensors (OFS) has been steadily growing, mainly because OFS presents interesting characteristics, such as resistance to most common chemicals, lightweight, inherently small form factors, and capability to withstand high temperatures, as well as their immunity to electromagnetic interference
A body of calibrated mass induces the curvature and strain, and the response of a stretched long-period fiber grating (LPG) and a precurvature LPG written in SMF-28 optical fiber to measure microforce is studied, in order to assess if an increase of sensitivity is achieved for the pre-curvature LPG
The electric-arc LPGs fabrication setup consists of a broadband light source (BBLS) connected at one end of the Corning SMF-28 optical fiber, and the other end connected to an Optical Spectrum Analyzer (OSA) to monitor the evolution of the LPG modes while in production

Summary

. Introduction

The research field in optical fiber sensors (OFS) has been steadily growing, mainly because OFS presents interesting characteristics, such as resistance to most common chemicals, lightweight, inherently small form factors, and capability to withstand high temperatures, as well as their immunity to electromagnetic interference. Bhatia [1] showed that lower temperature sensitivities are achieved for longer grating periods, contrasting with higher sensitivities for curvature, RI and strain for shorter grating periods, so there should be suitable parameters for producing a LPG tuned for having higher sensitivities for curvature and strain sensing while diminishing the effects of temperature fluctuations [8] At present, both strain and curvature sensors have been developed and vastly reported with sensitivities around 5.285 nm/m1 and 49.3 pm/m-1 for curvature and up to 2 pm/με and 1.2 pm/με for strain, for LPGs and FBGs, respectively [9]–[13]. A body of calibrated mass induces the curvature and strain, and the response of a stretched LPG and a precurvature LPG written in SMF-28 optical fiber to measure microforce is studied, in order to assess if an increase of sensitivity is achieved for the pre-curvature LPG

Materials and methods

Results and discussion

Conclusions