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Compact Optical Fiber 3D Shape Sensor Based on a Pair of Orthogonal Tilted Fiber Bragg Gratings.

Feng D, Zhou W, Qiao X, Albert J - Sci Rep (2015)

Bottom Line: In this work, a compact fiber-optic 3D shape sensor consisting of two serially connected 2° tilted fiber Bragg gratings (TFBGs) is proposed, where the orientations of the grating planes of the two TFBGs are orthogonal.The measurement of the reflective transmission spectrum from the pair of TFBGs was implemented by Fresnel reflection of the cleaved fiber end.In the third (axial) direction, the strain is obtained directly by the shift of the TFBG Bragg wavelengths with a sensitivity of 1.06 pm/με.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Northwest University, Xi'an, 710069, China.

ABSTRACT
In this work, a compact fiber-optic 3D shape sensor consisting of two serially connected 2° tilted fiber Bragg gratings (TFBGs) is proposed, where the orientations of the grating planes of the two TFBGs are orthogonal. The measurement of the reflective transmission spectrum from the pair of TFBGs was implemented by Fresnel reflection of the cleaved fiber end. The two groups of cladding mode resonances in the reflection spectrum respond differentially to bending, which allows for the unique determination of the magnitude and orientation of the bend plane (i.e. with a ± 180 degree uncertainty). Bending responses ranging from -0.33 to + 0.21 dB/m(-1) (depending on orientation) are experimentally demonstrated with bending from 0 to 3.03 m(-1). In the third (axial) direction, the strain is obtained directly by the shift of the TFBG Bragg wavelengths with a sensitivity of 1.06 pm/με.

No MeSH data available.


Related in: MedlinePlus

(a) Sensitivities of the two selected cladding modes versus bending orientation from 0° to 360°; (b) Intensity differences of two TFBGs under the curvatures of 1.29 m−1 and 2.16 m−1 versus bending orientation.
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f4: (a) Sensitivities of the two selected cladding modes versus bending orientation from 0° to 360°; (b) Intensity differences of two TFBGs under the curvatures of 1.29 m−1 and 2.16 m−1 versus bending orientation.

Mentions: Figure 4a indicates how the responses from the two TFBGs vary with bend orientation for a given bend magnitude. It is clear that for each TFBG the response is approximately periodical with bend orientation with a period of 180 degrees (consistent with prior findings that the bend sensitivity maximizes in one particular orientation), but also that the two approximate sine-curves have a phase difference of 78 degrees, corresponding to the actual angular difference between the orientations of the tilt planes of the two gratings. The maximum sensitivities are −0.26 dB/m−1 and + 0.21 dB/m−1 at a measurement wavelength of 1565.75 nm, and −0.33 dB/m−1 and + 0.16 dB/m−1 at 1585.18 nm, respectively. Also, it can be seen from the curve that the first half plane (0–180 degree) exhibits higher amplitude compared with the second half plane (180–360 degree). This last finding was unexpected and will be discussed below. In order to further emphasize that measurements at these two wavelengths are sufficient to determine the magnitude and orientation of bending, Fig. 4(b) plots the results of Fig. 4(a) in parametric form, i.e. with the change in resonance amplitude of the two gratings relative to their initial value as horizontal and vertical coordinates respectively, and the bend orientation as a parameter labeled on each point (for two values of the bend magnitude). Clearly, each point in the plane of Fig. 4(b) corresponds to a different curvature, orientation and magnitude, as required. The distorted oval shapes of these curves reflects the fact that: a) the two TFBGs were not exactly at 90 degrees to each other; and b) the coupling strengths of the two TFBGs were not exactly equal. While it would be possible to improve on these two factors, it is clearly not necessary, as long as the ellipses observed in Fig. 4b are sufficiently open, meaning that the responses at two orientations differing by 90 degrees do not overlap. This is best understood from as follows: if the responses from TFBG1 and TFBG2 become more in phase as a function of bend orientation in Fig. 4a, the ellipses in Fig. 4b will become narrower along their short axis and converge to a single line for two TFBGs with tilt planes oriented in the same direction. Therefore the requirement for orienting the tilt planes of TFBG1 and TFBG2 at right angles to each other is quite relaxed and does not impose a fabrication complexity and cost beyond the range that is acceptable for the kind of applications where such devices might be used.


Compact Optical Fiber 3D Shape Sensor Based on a Pair of Orthogonal Tilted Fiber Bragg Gratings.

Feng D, Zhou W, Qiao X, Albert J - Sci Rep (2015)

(a) Sensitivities of the two selected cladding modes versus bending orientation from 0° to 360°; (b) Intensity differences of two TFBGs under the curvatures of 1.29 m−1 and 2.16 m−1 versus bending orientation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663507&req=5

f4: (a) Sensitivities of the two selected cladding modes versus bending orientation from 0° to 360°; (b) Intensity differences of two TFBGs under the curvatures of 1.29 m−1 and 2.16 m−1 versus bending orientation.
Mentions: Figure 4a indicates how the responses from the two TFBGs vary with bend orientation for a given bend magnitude. It is clear that for each TFBG the response is approximately periodical with bend orientation with a period of 180 degrees (consistent with prior findings that the bend sensitivity maximizes in one particular orientation), but also that the two approximate sine-curves have a phase difference of 78 degrees, corresponding to the actual angular difference between the orientations of the tilt planes of the two gratings. The maximum sensitivities are −0.26 dB/m−1 and + 0.21 dB/m−1 at a measurement wavelength of 1565.75 nm, and −0.33 dB/m−1 and + 0.16 dB/m−1 at 1585.18 nm, respectively. Also, it can be seen from the curve that the first half plane (0–180 degree) exhibits higher amplitude compared with the second half plane (180–360 degree). This last finding was unexpected and will be discussed below. In order to further emphasize that measurements at these two wavelengths are sufficient to determine the magnitude and orientation of bending, Fig. 4(b) plots the results of Fig. 4(a) in parametric form, i.e. with the change in resonance amplitude of the two gratings relative to their initial value as horizontal and vertical coordinates respectively, and the bend orientation as a parameter labeled on each point (for two values of the bend magnitude). Clearly, each point in the plane of Fig. 4(b) corresponds to a different curvature, orientation and magnitude, as required. The distorted oval shapes of these curves reflects the fact that: a) the two TFBGs were not exactly at 90 degrees to each other; and b) the coupling strengths of the two TFBGs were not exactly equal. While it would be possible to improve on these two factors, it is clearly not necessary, as long as the ellipses observed in Fig. 4b are sufficiently open, meaning that the responses at two orientations differing by 90 degrees do not overlap. This is best understood from as follows: if the responses from TFBG1 and TFBG2 become more in phase as a function of bend orientation in Fig. 4a, the ellipses in Fig. 4b will become narrower along their short axis and converge to a single line for two TFBGs with tilt planes oriented in the same direction. Therefore the requirement for orienting the tilt planes of TFBG1 and TFBG2 at right angles to each other is quite relaxed and does not impose a fabrication complexity and cost beyond the range that is acceptable for the kind of applications where such devices might be used.

Bottom Line: In this work, a compact fiber-optic 3D shape sensor consisting of two serially connected 2° tilted fiber Bragg gratings (TFBGs) is proposed, where the orientations of the grating planes of the two TFBGs are orthogonal.The measurement of the reflective transmission spectrum from the pair of TFBGs was implemented by Fresnel reflection of the cleaved fiber end.In the third (axial) direction, the strain is obtained directly by the shift of the TFBG Bragg wavelengths with a sensitivity of 1.06 pm/με.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Northwest University, Xi'an, 710069, China.

ABSTRACT
In this work, a compact fiber-optic 3D shape sensor consisting of two serially connected 2° tilted fiber Bragg gratings (TFBGs) is proposed, where the orientations of the grating planes of the two TFBGs are orthogonal. The measurement of the reflective transmission spectrum from the pair of TFBGs was implemented by Fresnel reflection of the cleaved fiber end. The two groups of cladding mode resonances in the reflection spectrum respond differentially to bending, which allows for the unique determination of the magnitude and orientation of the bend plane (i.e. with a ± 180 degree uncertainty). Bending responses ranging from -0.33 to + 0.21 dB/m(-1) (depending on orientation) are experimentally demonstrated with bending from 0 to 3.03 m(-1). In the third (axial) direction, the strain is obtained directly by the shift of the TFBG Bragg wavelengths with a sensitivity of 1.06 pm/με.

No MeSH data available.


Related in: MedlinePlus