In this paper, we report a simple fibre laser torsion sensor system using an intracavity tilted fibre grating as a torsion
encoded loss filter. When the grating is subjected to twist, it induces loss to the cavity, thus affecting the laser oscillation
build-up time. By measuring the build-up time, both twist direction and angle on the grating can be monitored. Using a
low-cost photodiode and a two-channel digital oscilloscope, we have characterised the torsion sensing capability of this
fibre laser system and obtained a torsion sensitivity of ~412μs/(rad/m) in the dynamic range from -150° to +150°.
Strain and thermal sensitivities of germanate and tellurite glass fibres were measured using a fibre Fabry-Perot (FFP)
interferometer and fibre Bragg gratings (FBG). The strain phase sensitivity for germanate and tellurite fibre were
5900×103 rad/m and 5600×103 rad/m respectively at a central wavelength of 1540nm using FFP interferometer, which is
consistent with the value of 1.22pm/με obtained for a germanate fibre FBG. The Young's modulus for germanate and
tellurite fibre were also measured to be 58GPa and 37GPa. The thermal responses of germanate fibre were examined as
24.71 and 16.80 pm/°C at 1540nm and 1033nm wavelength using the FBG.
We present an optical bend sensor based on a Bragg grating written in an eccentric core polymer optical fibre. The
grating wavelength shifts are studied as a function of bend curvature and fibre orientation and the device exhibits strong
fibre orientation dependence, wide bend curvature range of ± 22.7 m-1 and high bend sensitivity of 63 pm/m-1, which is
80 times higher than the reported sensor based on an offset-FBG in standard single mode silica fibre.
We report a distinctive polarisation mode coupling behaviour of tilted fibre Bragg gratings (TFBGs) with tilted angle
exceeding 45°. The ex-45° TFBGs exhibit pronounced polarisation mode splitting resulted from grating structure
asymmetry induced birefringence. We have studied and analysed the property of ex-45° TFBGs under transverse load
applied to their equivalent fast- and slow-axis. The results show that the coupling between the orthogonally polarised
modes takes place only when the load is applied to its fast-axis, giving a prominent directional loading response. This
transverse load related polarisation property may be exploitable for implementation of optical fibre vector sensors
capable of measuring the magnitude and orientation of the applied transverse load.
A multicore fibre (MCF) sensor to measure the radial deformation of a compliant cylinder under compression is
presented. The sensor is connectorised and need not be permanently bonded to the test object. A differential
measurement technique using FBGs written into the MCF makes the sensor temperature insensitive. FBG measurement
of axial strain of a cylinder under compression is also reported.
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.
We report the implementation of a low-cost high-resolution WDM interrogation system operating around 800nm region
with bandwidth up to 60 nm and resolution of 13 pm by utilising a tilted fibre Bragg grating as an out-coupling device
and a CCD-array detector. The system has been evaluated for interrogating fibre Bragg grating based strain, temperature
sensors, giving sensitivities of 0.6 pm/&mgr;&Vegr; and 5.6 pm/°C which are in good agreement with previously reported values.
Furthermore, the system has been utilised to detect refractive index change of sample liquids, demonstrating a capability
of measuring index change as small as 10-5.
An 800nm band fiber Bragg grating sensing interrogation system using TFBG as the core wavelength division
component is presented. A charge coupled device (CCD) linear array is put on the focal plane of the lens to
detect the light. TFBG is used to tap light out of the fiber core to fiber cladding. The sensing wavelength is
795 to 830nm, with accuracy of 20pm and scan speed 100Hz. Using FBG sensor, we achieve the temperature
sensitivity as 1.8°C and strain sensitivity as 18με.
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