Two-axis bend measurement with Bragg gratings in multicore optica fibre

We describe what is to our knowledge the first use of fiber Bragg gratings written into three separate cores of a multicore fiber for two-axis curvature measurement. The gratings act as independent, but isothermal, fiber strain gauges for which local curvature determines the difference in strain between cores, permitting temperature-independent bend measurement.

Microwave photonic filtering using Gaussian-profiled superstructured fibre Bragg grating and dispersive fibre

Microwave photonic filtering is realised using a superstructured fibre Bragg grating. The time delay of the optical taps is precisely controlled by the grating characteristics and fibre dispersion. A bandpass response with a rejection level of >45 dB is achieved.

Simultaneous measurement of strain and curvature using superstructure fibre Bragg gratings

We report the first demonstration of the simultaneous measurement of strain and curvature, with temperature compensation, using a single superstructure fibre Bragg grating (SFBG). The SFBG exhibits the properties of both the fibre Bragg grating (FBG) and the long period fibre grating (LPG) such that its spectral response facilitates strain measurement from the wavelength shift of the FBG-like characteristic, and independent measurement of curvature from the LPG-like mode-splitting characteristic. The dependence of the LPG mode-splitting on the mode order has also been investigated and utilised for the measurement of very small curvatures.

A simple method for the fabrication of intrinsically apodized chirped fibre Bragg gratings

A new and simple fabrication technique is reported for the UV inscription of intrinsically apodized chirped fibre gratings at an arbitrary Bragg wavelength employing a single chirped phase-mask in a scanning Talbot interferometer set-up. Chirped gratings have been successfully produced over a large wavelength range and with bandwidths up to 5 nm. These gratings exhibit the time-delay response of a small ripple effect. In the present paper a comparison with previously reported fabrication methods is given, showing the advantages and disadvantages of the different methods.

Quadratic behaviour of fibre Bragg grating temperature coefficients

We describe the characterization of the temperature and strain responses of fiber Bragg grating sensors by use of an interferometric interrogation technique to provide an absolute measurement of the grating wavelength. The fiber Bragg grating temperature response was found to be nonlinear over the temperature range -70 °C to 80 °C. The nonlinearity was observed to be a quadratic function of temperature, arising from the linear dependence on temperature of the thermo-optic coefficient of silica glass over this range, and is in good agreement with a theoretical model.

Analysis of single and multiple, non-permanent, tunable, birefringent spectral holes in a fibre-Bragg grating stop-band produced via uniaxial pressure

We present an experimental and numerical study of transversely loaded uniform fibre-Bragg gratings. A novel loading configuration is described, producing pressure-induced spectral holes in an initially strong uniform grating. The birefringence properties of these gratings are analysed. It is shown that the frequency splitting of the two spectral holes, corresponding to two orthogonal polarisation states, can be adjusted precisely using this loading configuration. We finally demonstrate a new and simple scheme to induce multiple spectral holes in the stop-band. © 2003 Elsevier Science B.V. All rights reserved.

High extinction ratio in-fibre polarisers based on 45° tilted fibre Bragg gratings

We report a near-ideal in-fiber polarizer implemented by use of 45° tilted fiber Bragg grating structures that are UV inscribed in hydrogenated Ge-doped fiber. We demonstrate a polarization-extinction ratio of 33 dB over a 100-nm operation range near 1550 nm. We further show an achievement of 99.5% degree of polarization for unpolarized light with these gratings. We also theoretically investigate tilted grating structures based on the Green's function calculation, therein revealing the unique polarization characteristics, which are in excellent agreement with experimental data.

Monitoring of deployment process of shape memory polymers for morphing structures with embedded fibre Bragg grating sensors

This article demonstrates the use of embedded fibre Bragg gratings as vector bending sensor to monitor two-dimensional shape deformation of a shape memory polymer plate. The shape memory polymer plate was made by using thermal-responsive epoxy-based shape memory polymer materials, and the two fibre Bragg grating sensors were orthogonally embedded, one on the top and the other on the bottom layer of the plate, in order to measure the strain distribution in both longitudinal and transverse directions separately and also with temperature reference. When the shape memory polymer plate was bent at different angles, the Bragg wavelengths of the embedded fibre Bragg gratings showed a red-shift of 50 pm/°caused by the bent-induced tensile strain on the plate surface. The finite element method was used to analyse the stress distribution for the whole shape recovery process. The strain transfer rate between the shape memory polymer and optical fibre was also calculated from the finite element method and determined by experimental results, which was around 0.25. During the experiment, the embedded fibre Bragg gratings showed very high temperature sensitivity due to the high thermal expansion coefficient of the shape memory polymer, which was around 108.24 pm/°C below the glass transition temperature (Tg) and 47.29 pm/°C above Tg. Therefore, the orthogonal arrangement of the two fibre Bragg grating sensors could provide a temperature compensation function, as one of the fibre Bragg gratings only measures the temperature while the other is subjected to the directional deformation. © The Author(s) 2013.

A technique for mitigating the effect of the writing-beam profile on fibre Bragg grating fabrication

We propose and demonstrate a pre-compensation mechanism to account for the writing-beam profile which when applied to the design of advanced fibre Bragg gratings helps to achieve a desired design spectral response. We use the example of a complex multi-channel grating as an example to demonstrate the improvement achievable using the pre- compensation and find good agreement between experimental results and numerical calculations.

Realisation of single polarisation state of fibre ring laser by utilising intracavity 45° tilted fibre Bragg grating

Single polarisation operation of fibre ring laser has been realised by employing an intracavity 45°tilted fibre Bragg gratings (45° TFBGs). The degree of polarisation of 99.94% of the laser was demonstrated with good stability.

Two-axis accelerometer based on multicore fibre Bragg gratings

We report an accelerometer based upon a simple fibre cantilever constructed from a short length of multicore fibre(MCF) containing fibre Bragg gratings (FBGs). Two-axis measurement is demonstrated up to 3 kHz.