Highly sensitive torsion sensor based on directional coupling in twisted photonic crystal fiber

Abstract

We demonstrate a novel torsion sensor based on a twisted photonic crystal fiber with an embedded liquid rod waveguide. Only one resonant dip appears in the transmission spectrum in the range of 1,350-1,650 nm, which is associated with the directional coupling between the core and rod modes. The relative position of the fiber core with respect to the liquid rod waveguide is altered owing to the torsion stress, which changes the phase-matching condition and leads to a resonant-wavelength shift. The helical structure of the liquid rod waveguide can improve the torsion sensitivity of the device and provide an ability to distinguish the rotation direction. The measured torsion sensitivities were as high as >203 and >208 nm&mm&rad %1 in the clockwise and counterclockwise rotations, respectively.

Helicity Enhanced Torsion Sensor Based on Liquid Filled Twisted Photonic Crystal Fibers

“…Then, one of the air holes located in the second ring of the air hole cladding of the twisted PCF is filled with standard RI liquid (as shown in Figure 5) via a femtosecond-laser-assisted method [22]. Detailed fabrication process of the LFTPCFs has been demonstrated elsewhere [17]. In order to ensure repeatability of this heating process, the flow rate of hydrogen and oxygen and the translation stages were controlled precisely by computer.…”

“…The value of nl is the RI of infiltrated liquid material, and can be changed in the second preparation step. The resonant dip shift is sensitive to torsion, and the shift directions for clockwise and counterclockwise can be distinguished because of the helical structure of the liquid rod waveguide [17]. By changing α, the transmission spectra of sample with α0 = 3.925 rad/mm, for example, are recorded as shown in Figure 8.…”

“…As such, with combining Sensors 2020, 20, 1490 2 of 10 the helical structure and the liquid-filled waveguide in PCF cladding, sensors with superior sensing performances can be developed readily. Recently, we have proposed and demonstrated a torsion sensor based on a liquid-filled helical PCF (LFTPCF), which presents very high sensitivity and definite direction discrimination simultaneously for torsion measurement [17]. However, the response mechanism of the torsion sensitivity to initial twisting rate and the refractive index of the filled liquid has yet to be investigated.…”

Sensing Characteristics of Tilted Long Period Fiber Gratings Inscribed by Infrared Femtosecond Laser

“…Optical fiber torsion sensors have been widely used in the automotive industry and for anthropomorphic robotics applications, due to their advantages of being lightweight and immune to electronic interference [ 33 ]. Several optical-fiber-based torsion sensors have been reported in the past few years, including corrugated LPFGs, UV radiation-induced tilted fiber gratings, and Sagnac interferometers [ 34 ]. However, many of these devices cannot effectively determine the direction (clockwise or counter-clockwise) of the applied torsion, which limits their practical application.…”

Directional Torsion Sensor Based on a Two-Core Fiber with a Helical Structure

“…To solve this problem, interferometers with helical or antisymmetric structures have been proposed. Plenty of the work emerging is based on helical twisted photonic crystal fiber (PCF) with quality sensitivity and identifiable direction [ 15 , 16 , 17 ]. The process of PCF production is complex.…”