The application of a long period grating array for respiratory function monitoring

In this paper, multiplexed sensor network capable of monitoring the shape changes of the torso for respiratory function monitoring is developed. As a demonstration, LPGs written into refractive index insensitive, progressive three layered fibre are embedded into supporting material is then placed on a resuscitation training manikin simulating respiration. A derivative spectroscopy interrogation technique is implemented and the bend sensitivity of the LPGs is used to reconstruct the shape of the manikin's torso. © 2003 IEEE.

Simple design of nonuniform fiber Bragg grating with sharp reflection

In this paper we consider the possibility of using intermediate solutions, in which ideal apodisation profile for a dispersion-free, sharp-reflection profile fibre Bragg grating approximated in different degrees. The ideal apodisation profile for a flat dispersion, 50 GHz bandwidth grating was obtained using the layer-peeling algorithm. To verify the modelled results a version of the 5-section grating has been manufactured with excellent agreement between the model and the experimental results. The performance penalty due to multiple reflections from the FBGs in different situations was studied. The results showed that in the approximated gratings some post-compensation must be included to account for the local deviations from zero dispersion. © 2003 IEEE.

An optical pump controlled tunable phase-shifted fiber grating transmission filter

Optical pump controlled, remotely tunable phase-shifted fiber grating transmission filters were analyzed. The transmission peak had a full width hail maximum (FWHM) bandwidth. With increasing control pump power, the resonant peak shifted towards the longer wavelength side. The efficiency of the system was largely affected by the greater number of sections of doped fiber as well as the absence of recirculation of unabsorbed pump beam. The configuration, besides its simplicity and cost-effectiveness, exhibited wavelength-independent pump-induced phase shifts and no anisotropic effects during operation.

High performance microwave photonic response of superstructured fibre Bragg grating with designed apodisation function

The microwave photonic responses based on the superstructure fibre Bragg gratings with designed apodisation profile are investigated. The rejection level of more than 60 dB for a bandpass filtering response is demonstrated.

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.

Near-constant time delay response of fibre grating Sagnac loop filters

A theoretical and experimental investigation of the time delay characteristics of fiber Bragg grating-based Sagnac loops (FBGSLs) is presented. Analytic expressions for the phase and time delay of the FBGSL have been derived and excellent agreement is found between their predictions and experimental results for configurations incorporating uniform-period and chirped-period gratings. For symmetrical grating structures, it is found that the FBGSL time delay response is similar to that of the incorporated grating; with asymmetrical gratings, the FBGSL response is quite different. It is shown that wavelength-division-multiplexing filters exhibiting near-zero dispersion characteristics can be implemented using FBGSLs.

A high sensitivity long period grating Mach-Zehnder refractometer

A refractive index sensing system has been demonstrated, which is based upon an in-line fibre long period grating Mach-Zehnder interferometer with a heterodyne interrogation technique. This sensing system has comparable accuracy to laboratory-based techniques used in industry such as high performance liquid chromatography and UV spectroscopy. The advantage of this system is that measurements can be made in-situ for applications in continuous process control. Compared to other refractive index sensing schemes using LPGs, this approach has two main advantages. Firstly, the system relies on a simple optical interrogation system and therefore has the real potential for being low cost, and secondly, so far as we are aware it provides the highest refractive index resolution reported for any fibre LPG device.

Sensing applications of arrayed waveguide grating devices

Progress in optical fibre sensor research has often been achieved by taking advantage of components developed for use in telecommunications, where the greater existing market is able to support the rapid commercialisation of novel devices. In the last few years there has been considerable interest in the telecommunications community in deploying arrayed waveguide gratings (AWGs) produced in a range of technologies in a variety of roles. We feel it is therefore surprising that there have been very few reports of research into using AWGs for sensing. In this paper we consider some possible roles for these devices in interrogation systems for interferometric and fibre Bragg grating (FBG) sensors.

Fiber grating type dependence of temperature and strain coefficients and application to simultaneous temperature and strain measurement

Although fiber Bragg gratings (FBGs) have been widely used as advanced optical sensors, the cross-sensitivity between temperature and strain has complicated independent measurement procedures for these two measurands. We report here, for the first time to our knowledge, the results of a systematic investigation of the dependence of both temperature and strain sensitivities on the grating type, including the well-known Type I, Type IIA, and a new type which we have designated Type IA, using both hydrogen-free and hydrogenated B/Ge codoped fibers. We have identified distinct sensitivity characteristics for each grating type, and we have utilised them to implement a novel dual-grating, dual-parameter sensor device with performance superior to that of previously reported grating-based structures.

Suppression of cladding-mode coupling loss in Bragg grating using standard single-mode fiber

We present a technique for suppressing cladding-mode coupling loss in fiber Bragg grating fabrication. Suppression of cladding-modes down to 0.2 dB in a Bragg grating of 18dB reflectivity has been achieved in hydrogen-loaded standard single-mode fiber.