Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Long-Period Fiber Gratings <s> We present a new class of long-period fiber gratings that can be used as in-fiber, low-loss, band-rejection filters. Photoinduced periodic structures written in the core of standard communication-grade fibers couple light from the fundamental guided mode to forward propagating cladding modes and act as spectrally selective loss elements with insertion losses act as backreflections <-80 dB, polarization-mode-dispersions <0.01 ps and polarization-dependent-losses <0.02 dB. <s> BIB001 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Long-Period Fiber Gratings <s> The authors examine the changes in wavelength and attenuation of long period fibre gratings subjected to bends with curvatures from 0 to 4.4 m/sup -1/. The wavelength change with curvature is nonlinear, with a projected minimum detectable curvature change of 2/spl times/10/sup -3/ m/sup -1/. The magnitude of the bend-induced wavelength shift depends on the rotation of the cylindrical fibre relative to the bending plane. <s> BIB002 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Long-Period Fiber Gratings <s> Abstract We report the development and demonstration of a long-period grating refractometer. The principle of operation is based on the using of a long-period grating that is structurally induced by a CO 2 laser, and where the resonance wavelengths are shifted as the refractive index of medium surrounding the cladding of the long-period grating. The different concentrations for three types of solutions (ethylene glycol, salt, and sugar) were experimentally measured, and results show that, as a refractometer, this fiber-based device not only can differentiate chemicals based on their refractive index, but it can also become a concentration indicator of a particular chemical solution, and applied in the oil and petroleum industry. <s> BIB003 </s> Plasmonic Optical Fiber-Grating Immunosensing: A Review <s> Long-Period Fiber Gratings <s> The influence of grating length and bend radius of long-period gratings (LPGs) on refractive index sensing was examined. Sensitivity to refractive indexes smaller than that of silica could be enhanced by bending LPGs. Bent LPGs lost sensitivity to refractive indexes higher than that of silica, whereas a 20-mm-long LPG arranged in a straight line had considerable sensitivity. These experimental results demonstrated that the sensitivity characteristics of LPGs to refractive index could be controlled by grating length and bend radius. <s> BIB004
Long-period fiber gratings (LPFGs) correspond to a periodic refractive index modulation of the fiber core with a uniform period of a few hundreds of µm. In single-mode optical fibers, they couple the forward-going core mode into forward-going cladding modes BIB001  , as illustrated in Figure 6 . Their transmitted amplitude spectrum is composed of a few wide resonances (FWHM~20 nm) spread over a wavelength range of several hundreds of nm. These resonances appear at wavelengths given by the following phase matching condition: λ i clad = (n eff,core − n i eff,clad )Λ. As they propagate close to the cladding-surrounding medium interface, these modes are inherently sensitive to SRI changes, which yield important wavelength shift  BIB003 BIB004 . They are also sensitive to bending so that care must be taken to avoid unwanted spectral fluctuations when LPFGs are used for SRI sensing BIB002 . LPFGs are usually produced through amplitude masks. They can also be easily manufactured point-by-point or using electric arc discharges. Long-period fiber gratings (LPFGs) correspond to a periodic refractive index modulation of the fiber core with a uniform period of a few hundreds of µ m. In single-mode optical fibers, they couple the forward-going core mode into forward-going cladding modes BIB001  , as illustrated in Figure 6 . Their transmitted amplitude spectrum is composed of a few wide resonances (FWHM ~ 20 nm) spread over a wavelength range of several hundreds of nm. These resonances appear at wavelengths given by the following phase matching condition: λ i clad = (neff,core − n i eff,clad)Λ. As they propagate close to the cladding-surrounding medium interface, these modes are inherently sensitive to SRI changes, which yield important wavelength shift  BIB003 BIB004 . They are also sensitive to bending so that care must be taken to avoid unwanted spectral fluctuations when LPFGs are used for SRI sensing BIB002 . LPFGs are usually produced through amplitude masks. They can also be easily manufactured point-by-point or using electric arc discharges. 