Helical Intermediate-Period Fiber Grating for Refractive Index Measurements With Low-Sensitive Temperature and Torsion Response

All Fiber-Optic Immunosensors Based on Elliptical Core Helical Intermediate-Period Fiber Grating with Low-Sensitivity to Environmental Disturbances

“…The fabrication process is detailed in the Supplementary Information . Previous research has demonstrated that the manufacturing technique is a high-efficiency and quick approach for producing HIPFG with strong chemical–physical stability, high RI sensitivity, and repeatability [ 30 , 31 , 33 ]. The fabricated E-HIPFG grating period was determined to be 17.5 μm using the formula Ʌ = 30 V 2 /Ω, where Ω is the rotation rate of left translation stages, and V 2 is the working velocity of another stage.…”

“…The fabricated E-HIPFG grating period was determined to be 17.5 μm using the formula Ʌ = 30 V 2 /Ω, where Ω is the rotation rate of left translation stages, and V 2 is the working velocity of another stage. The period of E-HIPFG was half of the period of HIPFG in single-mode fiber produced using the same system parameters [ 30 ]. The half grating period of the E-HIPFG is due to the two-fold axial symmetry of the elliptical core fiber, which possesses inherent major and minor axis structures.…”

“…Helix intermediate-period fiber gratings (HIPFGs) are a type of period fiber grating with a helical grating structure whose period is less than 100 μm, with a grating length of only a few centimeters [ 30 ]. According to the papers discussed above, HIPFGs have been widely used as all-fiber sensors because they offer low insertion loss, excellent stability, and insensitivity to environmental parameters such as temperature, strain, and torsion, in addition to the benefits of typical LPFGs [ 30 ].…”

“…Helix intermediate-period fiber gratings (HIPFGs) are a type of period fiber grating with a helical grating structure whose period is less than 100 μm, with a grating length of only a few centimeters [ 30 ]. According to the papers discussed above, HIPFGs have been widely used as all-fiber sensors because they offer low insertion loss, excellent stability, and insensitivity to environmental parameters such as temperature, strain, and torsion, in addition to the benefits of typical LPFGs [ 30 ]. The following is a sensing principle description of the HIPFG-based immunosensor: the helical grating structure of HIPFGs introduces periodic perturbations to the refractive index (RI) in optical fiber and consequently contributes to mode coupling of the fundamental core mode into the forward propagation cladding mode.…”

“…In the phase-match condition, the coupling strength becomes relatively strong and visible as resonance bands in the transmission spectrum. The i -th resonant wavelengths satisfy the following equation [ 30 , 31 , 32 , 33 , 34 ]: where and are the effective refractive index of the fundamental core mode and the i th order cladding mode, respectively. is the i th order resonance wavelength, and Λ is the grating period of the HIPFG.…”