FBGs written in specialty fiber for high pressure/high temperature measurement

Abstract

In this paper, we evaluate different thermal treatments in order to stabilize fiber Bragg gratings written by a femtosecond pulsed laser in specialty highly birefringent micro-structured optical fiber, targeting pressure monitoring at high pressure and high temperature environments. We have obtained a pressure sensitivity of 3.30 pm/bar up to 1400 bar and 290 °C. An effective thermal treatment has been experimentally implemented, yielding a nearly unchanged reflectivity at high temperature in combination with stable temperature and pressure readings: a standard deviation of 0.42 bar in the pressure reading was observed over 7 days at 280°C.

Extreme Environment Sensing Using Femtosecond Laser-Inscribed Fiber Bragg Gratings

“…This approach relies on the waveguide-induced birefringence of the grating response rather than the structural birefringence associated with the nanograting structures of the Type II index change. Recently, a complex ‘butterfly’ microstructured photonic crystal fiber which possessed a roughly 3-fold increase in birefringence as compared to side hole fibers, was used to create a fs-UV Type I FBG combined pressure/temperature sensor for extreme pressure monitoring (up to 140 MPa and 290 °C) [ 108 ]. The increased birefringence of the novel photonic crystal fiber created a more sensitive pressure induced wavelength spread of the states of polarization of the Bragg resonance.…”

Novel Fiber Grating for Sensing Applications

“…Additionally, the PCF sensors based on FBGs also have other applications, such as the measurement of pressure, high temperature, magnetic field, and even for the detection of the gene. Huang et al inscribed an FBG by a femtosecond laser in a highly birefringent Butterfly PCF for the measurement of pressure in the ultra‐high pressure or the ultra high‐temperature environment. The peak separation between the fast‐axis mode and the slow‐axis mode was selected to detect the pressure.…”

Large dynamic range pressure sensor based on two semicircle-holes microstructured fiber

“…However, The typical pressure sensitivity of FBG written in SMF is only 3–4 pm/MPa 9 , too small for the discrimination of low pressure variation. Specially-designed optical fiber with air-hole structure along the fiber was fabricated to improve pressure sensitivity up to 20–30 pm/MPa 10 – 12 . This was a significant improvement but is still too small for many applications.…”

“…Pressure measurement was conducted up to 50 MPa, which was limited by the equipment available in our laboratory. However, optical fiber sensors based on fused silica have been demonstrated to withstand very high pressure and measured pressure up to 200 MPa was reported 12 , 24 . Such optical fiber sensor would need to be able to measure pressure as small as 1 kPa, if it was to achieve better than 106-dB dynamic range.…”