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

Environmental monitoring has become essential in order to deal with environmental resources efficiently and safely in the realm of green technology. Environmental monitoring sensors are required for detection of environmental changes in industrial facilities under harsh conditions, (e.g. underground or subsea pipelines) in both the temporal and spatial domains. The utilization of optical fiber sensors is a promising scheme for environmental monitoring of this kind, owing to advantages including resistance to electromagnetic interference, durability under extreme temperatures and pressures, high transmission rate, light weight, small size, and flexibility. In this paper, the optical fiber sensors employed in environmental monitoring are summarized for understanding of their sensing principles and fabrication processes. Numerous specific applications in petroleum engineering, civil engineering, and agricultural engineering are explored, followed by discussion on the potentials of OFS in manufacturing.

A review on optical fiber sensors for environmental monitoring

We present a method for dispersion-tailoring of OmniGuide and other photonic band-gap guided fibers based on weak interactions (“anticrossings”) between the core-guided mode and a mode localized in an intentionally introduced defect of the crystal. Because the core mode can be guided in air and the defect mode in a much higher-index material, we are able to obtain dispersion parameters in excess of 500,000 ps/nm-km. Furthermore, because the dispersion is controlled entirely by geometric parameters and not by material dispersion, it is easily tunable by structural choices and fiber-drawing speed. So, for example, we demonstrate how the large dispersion can be made to coincide with a dispersion slope that matches commercial silica fibers to better than 1%, promising efficient compensation. Other parameters are shown to yield dispersion-free transmission in a hollow OmniGuide fiber that also maintains low losses and negligible nonlinearities, with a nondegenerate TE01 mode immune to polarization-mode dispersion (PMD). We present theoretical calculations for a chalcogenide-based material system that has recently been experimentally drawn.

/pdf/dispersion-tailoring-and-compensation-by-modal-interactions-sygiravmtm.pdf

Dispersion tailoring and compensation by modal interactions in OmniGuide fibers.

We investigate dual concentric core and microstructure fiber geometries for dispersion compensation. Dispersion values as large as -59 000 ps/(nm km) are achieved, over a broad wavelength range with full width at half maximum exceeding 100 nm. The trade-off between large dispersion and mode area is studied. Geometries with an effective mode area of 30µm2 and dispersion -19 000 ps/(nm km) and 80µm2 with -1600 ps/(nm km) are proposed.

Optimization of dual-core and microstructure fiber geometries for dispersion compensation and large mode area.

We present a systematic process of theoretical design and experimental fabrication of the large mode area and large negative dispersion photonic crystal fiber. An easily fabricated fiber structure is proposed. The influence of structure parameters deviations from the design on the chromatic dispersion are evaluated and a design rule is given. Finally our fabricated fiber and test results are demonstrated. The measured effective area of inner core mode is 40.7 μm2 which is the largest effective area of high negative dispersion photonic crystal fibers that have been experimentally fabricated. The measured peak dispersion is -666.2ps/(nm.km) and the bandwidth is 40nm.

Theoretical study and experimental fabrication of high negative dispersion photonic crystal fiber with large area mode field

We propose a novel dispersion compensating fiber design consisting of two highly asymmetric concentric cores. We show that the fundamental mode of the proposed fiber can have very large negative dispersion values [/spl sim/-5100 ps/(nm.km)] with larger mode field diameter (/spl sim/8-9 /spl mu/m) relative to the existing dispersion compensating fibers.

A novel design of a dispersion compensating fiber

Characterization and simulation of long period gratings fabricated using electric discharge

An efficient dispersion compensating fiber (DCF) design is proposed based on a coaxial fiber structure, which provides dispersion compensation over a broad wavelength region matching that of an erbium-doped fiber amplifier gain spectrum. The design can provide dispersion coefficient that is nearly twice those of existing DCF designs. Due to the basic nature of the dispersion curve of this design, the total link dispersion cannot only be compensated but also can be flattened.

P. Palai

Papers

A novel design of a dispersion compensating fiber

Characterization and simulation of long period gratings fabricated using electric discharge

A Dispersion Flattening Dispersion Compensating Fiber Design for Broadband Dispersion Compensation

Erbium-Doped Dispersion-Compensating Fiber for Simultaneous Compensation of Loss and Dispersion