Recent research on fibre optic long-period gratings (LPGs) is reviewed with emphasis placed upon the characteristics of LPGs that make them attractive for applications in sensing strain, temperature, bend radius and external index of refraction. The prospect of the development of multi-parameter sensors, capable of simultaneously monitoring a number of these measurands will be discussed.

https://iopscience.iop.org/article/10.1088/0957-0233/14/5/201/pdf

Optical fibre long-period grating sensors: characteristics and application

Sensing characteristics of an optical fibre long-period grating Michelson refractometer

Thermal characteristics of long-period gratings 266 nm UV-point-by-point induced

Optical fibre long period grating sensors with nanostructured coatings

The present invention provides an Erbium-Doped Fiber Amplifier (EDFA) and a source that employs the EDFA for generating light in an S-band of wavelengths. A fiber amplifier (10) in a depressed cladding or W-profile fiber has a core (12) doped with the active material (18) and defined by a core cross-section and a refractive index no. A depressed cladding (14) of index n1 surrounds the core (12) and a secondary cladding (16) of index n2 surrounding the depressed cladding (14). The fiber amplifier is pumped a level of high relative inversion D, such that the active material exhibits positive gains in a short wavelength band and high gains in a long wavelength band. In one embodiment, the core cross-section, the depressed cladding cross-section and the refractive indices no, n1, and n2 are selected to provide distributed ASE suppression at wavelengths longer than cutoff wavelength λc over the length of fiber amplifier (10). In another embodiment, such selection provides a roll-off loss curve about a cutoff wavelength λc. The roll-off loss curve yields losses at least comparable to the high gains in the long wavelength band and losses substantially smaller than the positive gains in the short wavelength band. To obtain the desired roll-off loss curve the refractive index no in the core is selected such that an effective index neff experienced by the confined mode maximizes a roll-off slope of the roll-off loss curve before the cutoff wavelength.

Amplifiers and light sources employing s-band erbium-doped fiber and l-band thulium-doped fiber with distributed suppression of amplified spontaneous emission (ase)

We analyzed the effects of hydrogen molecule diffusion on LP 0 m mode coupling of long-period gratings with two assumptions. The fibers were treated in a H 2 chamber at a temperature 90°C and pressure around 107 atm for five days. And then we fabricated long-period gratings with these fibers after holding them at room temperature and one atmosphere pressure for 15 min to 55 h and measured coupling of LP 0 m mode. We used diffusion coefficient of hydrogen molecule, which considered the fiber as a perfect cylinder, and assumed that the core and the cladding have the same diffusion coefficient. Corning ‘Flexcor1060’ was used as a photosensitive fiber which has cutoff wavelength, 920 ± 50 nm, and the cladding/coating diameter, 125 ± 2.0 μm/250 ± 15 μm. Core diameter is 5.0 μm and numerical aperture is 0.14. The hydrogen molecule concentration is averaged in the region of the core and the cladding with time and LP 0 m mode coupling was simulated with coupled mode theory and two assumptions. We were able to predict the coupling peak wavelengths that change with time. These results were useful for designing the transmission spectrum of long-period gratings.

S.B. Lee

Papers

Effects of hydrogen molecule diffusion on LP0m mode coupling of long-period gratings