Fiber-Optic Interferometric Torsion Sensor Based on a Two-LP-Mode Operation in Birefringent Fiber

Abstract

A fiber-optic sensor for torsion measurement, based on a two-linearly polarized (LP)-mode operation in ultrahigh birefringent photonic crystal fiber is described. The structure of the photonic crystal fiber presents two large asymmetric holes adjacent to the core fiber. When linearly polarized light is injected inand -directions, respectively, two separate interferometers can be obtained. In one of these cases, as torsion is applied to the sensing head a beat between the two interferometers is formed due to the simultaneous excitation of the two polarization states. The detection technique to read the torsion sensor is based on the analysis of the fast Fourier transform, which proved to be an effective and simple solution. The sensor exhibited reduced sensitivity to temperature.Index Terms-Optical fiber sensor, two-mode operation interferometer.

Photonic liquid crystal fiber intermodal interferometer

“…When LP light is launched at 45º relatively to the eigenaxes of the high birefringent PCF, both polarization states of the two spatial modes LP01(xy) and LP11(xy) are simultaneously excited, generating a multibeam interference [12].…”

Design of a high-birefringence photonic crystal fiber using an asymmetric defect in the fiber core

“…These highly birefringent fibers have been widely employed in optical devices and communication systems to control the polarization state of the propagating light and eliminate the polarization mode dispersion. In addition, high birefringent fibers can also be adopted to form interferometers to function as sensitive sensors for temperature [13], pressure [14], strain [15], and torsion [16].…”

Ultrahigh birefringence index-guiding photonic crystal fiber and its application for pressure and temperature discrimination

“…PCF technology is far more superior in producing PMFs. Hi-Bi can be achieved simply by introducing two large air holes close to the core of conventional, single-mode PCF [6,7].…”

“…For commonly used PM-1550-01 fiber, (probably the only commercially PM-PCF available from NKT Photonics), the birefringence is ∼3.9 × 10 −4 [8]. Recently, Frazão reported a fiber optic interferometric torsion sensor using a PM-PCF with two large air holes fabricated in an XLIM laboratory, demonstrating a group birefringence of ∼8.1 × 10 −3 [7]. Different asymmetrical PCF structures also were tailored to enhance its birefringence for conduct strain [9] and temperature-independent measurement [10].…”

“…Different asymmetrical PCF structures also were tailored to enhance its birefringence for conduct strain [9] and temperature-independent measurement [10]. The highest experimental birefringences reported for index-guiding PCFs were on the order of 10 −3 [3,7,[11][12][13]. It should be noted that the highest group birefringence reported were found in a photonic bandgap fiber (0.025 at the wavelength of 1550 nm), achieved via elliptical air core [14,15].…”