Multi-phase-shifted helical long period fiber grating based temperature-insensitive optical twist sensor

Abstract

A compact temperature-insensitive optical fiber twist sensor based on multi-phase-shifted helical long period fiber grating has been proposed and experimentally demonstrated in this paper. A multi-phase-shifted helical long period fiber grating is fabricated with a multi-period rotation technology. A π/2 and a 3π/2 phase shift is introduced in the helical long period fiber grating by changing the period. The helical pitch can be effectively changed with a different twist rate, which is measured by calculating the wavelength difference between two phase shift peaks. Although the wavelength of the phase shift peak also shifts with a change of the temperature, the wavelength difference between two phase shift peaks is constant due to two fixed phase shifts in the helical long period fiber grating, which is extremely insensitive to temperature change for the multi-phase-shifted helical long period fiber grating. The experimental results show that a sensitivity of up to 1.959 nm/(rad/m) is achieved.

Fiber-Optic Sensors for Measurements of Torsion, Twist and Rotation: A Review

“…To design and manufacture an LPFBG torsion sensor, in principle, any known LPFBG inscription method can be used. These include methods of LPFBG fabrication with ultraviolet (UV)-light [33,34], electric arc induced perturbations [35], mechanical corrugation [36], mechanical load (microbending) [37,38,39,40] and application of CO 2 laser induced perturbation [41,42,43,44,45,46,47,48,49,50,51,52,53]. …”

“…LPFBGs fabricated with high-frequency CO 2 pulses [41,42,43,44,45,46,47,48,49,50,51,52] induced a fair amount of linear birefringence due to asymmetrical distribution of the refractive index change on the cross-section of the LPFBG (Figure 10) which, in combination with the appearance of circular birefringence, gave rise to the manifestation of elliptical birefringence.…”

“…Further work in this area led to Multi-Phase Shifted Helical LPFBG (MPSH-LPFBG) sensors [49] that employ a multi-period rotation technique with π/2 and 3π/2 phase shifts in the MPSH-LPFBG period, thus creating three loss-dips in a selected loss band. The increase of the rotation angle shifts these peaks simultaneously towards longer wavelengths, however, with different rates.…”

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

“…Thus, it is necessary to break the symmetry of fiber devices to construct sensitivity-improved torsion sensors while maintaining their direction discrimination. In recent years, helical structures have been implemented in optical fibers to demonstrate novel strain sensors [5], twist sensors [6][7][8], and tunable filters [9]. Some of these devices have been realized by employing photonic crystal fibers (PCFs) [10][11][12][13] and exhibited good torsion-sensing characteristics as well.…”

Automatic Arc Discharge-Induced Helical Long Period Fiber Gratings and Its Sensing Applications

“…Furthermore, the effect of twisting on the propagation of light in the abovementioned optical fibers has been explored for controlling the dispersion, excitation of orbital angular momentum, and elimination of higher-order modes from fiber lasers. For instance, twist characteristics of H-LPFGs have been recently reported [8][9][10]. The co-directional or contra-directional twist applied to the helix will effectively change the grating period, thus make the resonance wavelength shift towards different directions.…”