We describe the first application of multiplexed fibre Bragg grating strain sensors in a multicore fibre. Sets of gratings, acting as strain gauges, are co-located in the multicore fibre such that they enable the curvature to be measured. Multiple sets of these gratings allow the curvature to be measured at several points along the fibre. This sensor is configured to monitor displacement of concrete tunnel sections, and was demonstrated capable of displacement measurement with a resolution of ±0.1 mm over a range of several millimeters.
We report experimental measurements of the strain and temperature sensitivity of the optical phase in a singlemode polymer optical fibre. These values were obtained by measuring optical path length change using a Mach-Zender interferometer.
Point-probe optical fiber chem-sensors have been implemented using cladding etched fiber Bragg gratings. The sensors possess refractive index sensing capability that can be utilized to measure chemical concentrations. The Bragg wavelength shift reaches 8 nm when the index of surrounding medium changes from 1.33 to 1.44, giving maximum sensitivity more than 10 times higher than that of previously reported devices. More importantly, the dual-grating configuration of the point-probe sensors offers a temperature reference function, permitting accurate measurement of refractive index encoded chemical concentrations.
The curvature- or bend-sensing response of long-period gratings (LPG) UV-inscribed in D-shaped fiber has been investigated experimentally. Strong fiber orientation dependence of the spectral response when such LPGs are subjected to dynamic bending has been observed and is shown to form the basis for new vector sensors.
We report experimental measurements of the reflection spectra of Bragg gratings inscribed in 4-core fibers under transverse loading. Broadening and splitting of the Bragg peaks from each core are observed as a function of load and fiber orientation.
Fiber Bragg gratings (FBGs) have attracted a lot of attention in recent years due to their wide applications in optical telecommunications and smart sensing. They have been used as DWDM filters, dispersion compensators, gain flattening filters, optical switch and connection devices, and temperature/strain sensors. FBGs have been found to exhibit four different type structures according to their different growth mechanisms. Each type of FBG exhibits unique thermal and strain properties. Generally, the Type I gratings in hydrogenated and hydrogen-free fibers are used most for applications. However, some novel devices may be achieved by combinational structure of different types of gratings in the future. In this paper, we propose a novel concept of fabrication and application of FBGs with hybrid grating types. We have observed a complex growth behavior of a hybrid-type grating in the UV exposure to a B/Ge codoped fiber through a phase mask. A new model has been developed to simulate the complex growth behavior of the hybrid-type gratings, giving results in excellent agreement with experiment.
We propose a simple Er-doped fiber laser configuration for achieving stable dual-wavelength oscillation at room temperature, in which a high birefringence fiber Bragg grating was used as the wavelength-selective component. Stable dual-wavelength oscillation at room temperature with a wavelength spacing of 0.23nm and mutually orthogonal polarisation states was achieved by utilising the polarisation hole burning effect. An amplitude variation of less than 0.7dB over 80s period was obtained for both wavelengths.
A simple method for achieving fast wavelength switching in a fiber laser was demonstrated using a Fabry-Perot semiconductor filter and a set of fiber Bragg gratings. A build-up time as short as 1.6microsecond(s) was obtained.
We propose a novel structure of Er-doped fiber ring laser, in which a fiber Bragg grating and an all-fiber M-Z interferometer are used to select wavelength. Output laser with line-width narrower than 0.1 nm at 1.53 micrometers waveband is obtained.
We design a kind of all-fiber high-sensitivity temperature sensor based on intensity measurement, by using long period fiber grating (LPG) as sensor element and using tunable erbium-doped fiber ring laser as optical source. In the temperature range of 74 degrees Celsius, the logarithm of the transmissive intensity of LPG is linear with the measured temperature and the linearity of sensing measurement can be repeated well. The resolution of temperature measurement is 0.1 degrees Celsius.
We demonstrate the higher pressure and temperature sensitivity of a fiber Bragg grating (FBG) sensor when it is packaged with a polymer jacket. The Bragg wavelength shift due to pressure and temperature can be enhanced by the polymer packaged by about 31.5 times for pressure and 7.7 times for temperature. The experiment results are consistent with the theoretical analysis. The sensitivity enhancement is due to the driving effect of the polymer substance. The 'structured' grating exhibits no significant chirp.
A novel structure for multiple wavelength operation and narrow line-width ring Er-doped fiber laser, in which the multiple fiber gratings are in series connection, is proposed. The feasibility of this new structure is confirmed in experiment and the stable operation of dual wavelength is obtained.