Application of long period gratings sensors to respiratory function monitoring

A series of in-line curvature sensors on a garment are used to monitor the thoracic and abdominal movements of a human during respiration. These results are used to obtain volumetric tidal changes of the human torso showing reasonable agreement with a spirometer used simultaneously to record the volume at the mouth during breathing. The curvature sensors are based upon long period gratings written in a progressive three layered fibre that are insensitive to refractive index changes. The sensor platform consists of the long period grating laid upon a carbon fibre ribbon, which is encapsulated in a low temperature curing silicone rubber. An array of sensors is also used to reconstruct the shape changes of a resuscitation manikin during simulated respiration. The data for reconstruction is obtained by two methods of multiplexing and interrogation: firstly using the transmission spectral profile of the LPG's attenuation bands measured using an optical spectrum analyser; secondly using a derivative spectroscopy technique.

The spectral sensitivity of long period gratings fabricated in elliptical core D-shaped optical fiber

Long period gratings (LPGs) were written into a D-shaped optical fibre, which has an elliptical core with a W-shaped refractive index profile. The LPG's attenuation bands were found to be sensitive to the polarisation of the interrogating light with a spectral separation of about 15nm between the two orthogonal polarisation states. In addition, two spectrally overlapping attenuation bands corresponding to orthogonal polarisation states were observed; modelling successfully reproduced this spectral feature. The spectral sensitivity of both orthogonal states was experimentally measured with respect to temperature, surrounding refractive index, and directional bending. These LPG devices produced blue and red wavelength shifts of the stop-bands due to bending in different directions. The measured spectral sensitivities to curvatures, d?/dR , ranged from -3.56nm m to +6.51nm m. The results obtained with these LPGs suggest that this type of fibre may be useful as a shape/bend sensor. It was also demonstrated that the neighbouring bands could be used to discriminate between temperature and bending and that overlapping orthogonal polarisation attenuation bands can be used to minimise error associated with polarisation.

Transverse loading of multicore fibre gratings

We report experimental measurements of the reflection spectra of Bragg gratings inscribed in 4-core fibres under transverse loading. Broadening and splitting of the Bragg peaks from each core are observed as a function of load and fibre orientation.

Impact of design of sharp non-uniform fibre Bragg gratings on system performance

The impact of design of sharp non-uniform fiber Bragg gratings on system performance was presented. The evolution of the Q-value of the worst channel against the propagation distance was shown. The results suggested that to apply approximated flat-dispersion gratings as inline filters in a periodic system, some post-compensation was included to account for the extra dispersion introduced by the gratings.

The sensing characteristics of long period gratings in three different types of fibre

In this paper, sensing characteristics of long period gratings in three different types of single mode optical fibre: a step-index fibre, a progressive three layered fibre and a suppressed-cladding fibre were investigated. It was found that variation in the refractive index profile and material constants of the fibre can produce a dramatic change in the spectral sensitivity for a particular measurand for a given long period grating attenuation band. © 2003 IEEE.

Implementation of chirped fibre Bragg gratings (CFBG) as optical wear sensors

This study discusses the fabrication and implementation of chirped fiber Bragg grating (CFBG) as optical wear sensors. Such a sensor has potential applications in monitoring grinding and milling machines through a safety device to check the wear on a car brake. The CFBG wear sensor has advantages over existing wear sensing techniques as it does not require electrical current to be passed through the sensor itself. This makes it eligible for application in combustible environments such as in the oil and gas industry.

A flexible approach for the apodization of planar waveguide Bragg gratings

A novel single-step technique for the apodization of planar waveguide Bragg gratings based on the polarization control method is proposed. First results are presented, showing successful side-lobe suppression in the reflection spectrum of the gratings.