Andrew Gillooly

Bending and orientational characteristics of long period gratings written in D-shaped optical fiber [directional bend sensors]

Long period gratings (LPGs) were written into a D-shaped single-mode fiber. These LPGs were subjected to a range of curvatures, and it was found that as curvature increased, there was increasingly strong coupling to certain higher order cladding modes without the usual splitting of the LPGs stopbands. A bend-induced stopband yielded a spectral sensitivity of 12.55 nm/spl middot/m for curvature and 2.2/spl times/10/sup -2/ nm/spl deg/C/sup -1/ for temperature. It was also found that the wavelength separation between adjacent bend-induced stopbands varied linearly as a function of curvature. Blue and red wavelength shifts of the stopbands were observed as the sensor was rotated around a fixed axis for a given curvature; thus, in principle, this sensor could be used to obtain bending and orientational information. The behavior of the stopbands was successfully modeled using a finite element approach.

Highly sensitive transverse load sensing with reversible sampled fiber Bragg gratings

We present the implementation of optical load sensors utilizing mechanically induced reversible sampled fiber Bragg gratings (SFBGs). The load is measured by the reflectivity of the first-order Fourier component of the induced SFBGs. The theoretical and experimental characterization indicates that such SFBGs can be tailored to realize load sensors with high sensitivity of near-linear response and free of influence from environmental and system noises.

Chirped fibre Bragg grating optical wear sensor

A novel sensor is demonstrated to allow a real-time measurement of the physical wear applied to the surface of an object. Two different measurement methods are presented, both utilizing the reflected power from a sacrificial chirped fibre Bragg grating to give the wear measurement. The measurement systems are simple to implement with the possibility of low cost designs depending on the application. The sensor can measure wear with a resolution of 120 μm.

Distributed load sensor by use of a chirped moiré fiber Bragg grating.

A chirped moiré fiber Bragg grating has been demonstrated to be capable of measuring the magnitude, position, and footprint of a transverse load. The device provides an average spatial resolution of 164 microm and has a load accuracy of 0.15 N/mm, or 50 microepsilon.

High survivability fiber sensor network for smart structures

Linear fiber optic sensor arrays are prone to catastrophic failure if a breakage occurs along the length of the array. A coupler chain array is proposed and experimentally demonstrated to have a lower susceptibility to signal loss when damage is implemented on the array. Three different array designs are compared and discussed.

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.

Sensing applications of long-period gratings in various fibre types

In this paper we review the sensing features of long period Bragg gratings and report on studies aimed at optimizing the sensitivities to various measurands by using different fiber geometries.

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 LPGs 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, dλ/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.

Implementation of chirped fiber 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.

Ultra-narrow asymmetric filter for transmission with 0.8 bit/s/Hz spectral efficiency

A novel approach is proposed to ultra-narrow optical filtering in dense WDM transmission. The filter based on fiber Bragg grating is specially designed and fabricated to be slightly asymmetric. A feasibility of 8/spl times/40Gbit/s DWDM RZ transmission with 0.8 bit/s/Hz spectral efficiency (without PDM and FEC) over 1280 km of SMF/DCF link has been confirmed by numerical modelling.