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

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ABSTRACT

Optical measurement of mechanical parameters is gaining significant commercial interest in different industry sectors. Torsion, twist and rotation are among the very frequently measured mechanical parameters. Recently, twist/torsion/rotation sensors have become a topic of intense fiber-optic sensor research. Various sensing concepts have been reported. Many of those have different properties and performances, and many of them still need to be proven in out-of-the laboratory use. This paper provides an overview of basic approaches and a review of current state-of-the-art in fiber optic sensors for measurements of torsion, twist and/or rotation.

No MeSH data available.


E-field vector displacement rotation sensors using single lead fiber solutions with E-field rotation encoding employing (a) An FBG inscribed in the Hi-Bi fiber; and (b) An all-fiber wave-plate.
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sensors-17-00443-f017: E-field vector displacement rotation sensors using single lead fiber solutions with E-field rotation encoding employing (a) An FBG inscribed in the Hi-Bi fiber; and (b) An all-fiber wave-plate.

Mentions: All the solutions described above are two-port solutions, meaning that the SMF defining bend sensitive region must be accessed from both sides, i.e., using lead-in and lead-out fibers. This might be quite an important limitation in practical sensor design, as already discussed in previous sections. While the total elimination of the need for accessing the SMF on both sides is not viable, one side can be replaced by a compact and all-fiber polarization encoder. Two such designs were reported in the literature so far, shown in Figure 17. In [90] the authors used a polarized tunable laser source (low-cost design was archived by current tuning of VCSEL), which excited the sensing section of an SMF through an optical coupler. The other (far) side of the sensing SMF was spliced to a short section of HB fiber with inscribed FBG. Due to the intrinsic birefringence in the HB fiber, two resonance FBG wavelengths existed and reflectance from the FBGs deepened on the incident light wavelength and E-field orientation relative to the HB fiber principal axis. Thus, rotation of the E-field vector at the HB-fiber input causes variation in reflectance amplitudes at characteristics FBG wavelengths, while the ratio of those reflections encodes SMF twist/rotation (Figure 17a).The system is similar to the one described in Figure 16d and reference [86], except that it provides a more practical and cost efficient arrangement. Another single-lead-fiber version was described in [91]. Here, the setup described in [84] and Figure 16c is modified to allow access using a single fiber. To achieve this, linearly polarized light was again launched into the sensing section of the SMF, while using a quarter wave-plate and mirror at the end of the sensing SMF fiber. The quarter wave-plate used in reflection mode (with a mirror at the end) acts as half wave-plate, which flipped the polarization plane by 90° and, thus, allowed for E-field rotation encoding in a back-reflection mode (if a simple mirror would be used at the end of the SMF one could not detect rotation, as the E-field vector in the reference frame would remain unchanged). When using all-fiber wave-plates (produced out of HB fibers) there is a challenge to design a system that is not temperature sensitive. This was achieved in [91] by a combination of different HB fibers (Figure 17b).


Fiber-Optic Sensors for Measurements of Torsion, Twist and Rotation: A Review †
E-field vector displacement rotation sensors using single lead fiber solutions with E-field rotation encoding employing (a) An FBG inscribed in the Hi-Bi fiber; and (b) An all-fiber wave-plate.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5375729&req=5

sensors-17-00443-f017: E-field vector displacement rotation sensors using single lead fiber solutions with E-field rotation encoding employing (a) An FBG inscribed in the Hi-Bi fiber; and (b) An all-fiber wave-plate.
Mentions: All the solutions described above are two-port solutions, meaning that the SMF defining bend sensitive region must be accessed from both sides, i.e., using lead-in and lead-out fibers. This might be quite an important limitation in practical sensor design, as already discussed in previous sections. While the total elimination of the need for accessing the SMF on both sides is not viable, one side can be replaced by a compact and all-fiber polarization encoder. Two such designs were reported in the literature so far, shown in Figure 17. In [90] the authors used a polarized tunable laser source (low-cost design was archived by current tuning of VCSEL), which excited the sensing section of an SMF through an optical coupler. The other (far) side of the sensing SMF was spliced to a short section of HB fiber with inscribed FBG. Due to the intrinsic birefringence in the HB fiber, two resonance FBG wavelengths existed and reflectance from the FBGs deepened on the incident light wavelength and E-field orientation relative to the HB fiber principal axis. Thus, rotation of the E-field vector at the HB-fiber input causes variation in reflectance amplitudes at characteristics FBG wavelengths, while the ratio of those reflections encodes SMF twist/rotation (Figure 17a).The system is similar to the one described in Figure 16d and reference [86], except that it provides a more practical and cost efficient arrangement. Another single-lead-fiber version was described in [91]. Here, the setup described in [84] and Figure 16c is modified to allow access using a single fiber. To achieve this, linearly polarized light was again launched into the sensing section of the SMF, while using a quarter wave-plate and mirror at the end of the sensing SMF fiber. The quarter wave-plate used in reflection mode (with a mirror at the end) acts as half wave-plate, which flipped the polarization plane by 90° and, thus, allowed for E-field rotation encoding in a back-reflection mode (if a simple mirror would be used at the end of the SMF one could not detect rotation, as the E-field vector in the reference frame would remain unchanged). When using all-fiber wave-plates (produced out of HB fibers) there is a challenge to design a system that is not temperature sensitive. This was achieved in [91] by a combination of different HB fibers (Figure 17b).

View Article: PubMed Central - PubMed

ABSTRACT

Optical measurement of mechanical parameters is gaining significant commercial interest in different industry sectors. Torsion, twist and rotation are among the very frequently measured mechanical parameters. Recently, twist/torsion/rotation sensors have become a topic of intense fiber-optic sensor research. Various sensing concepts have been reported. Many of those have different properties and performances, and many of them still need to be proven in out-of-the laboratory use. This paper provides an overview of basic approaches and a review of current state-of-the-art in fiber optic sensors for measurements of torsion, twist and/or rotation.

No MeSH data available.