Optical Sensing

Novel uses for surface measurement

In astronomy atmospheric turbulence severely degrades image resolution for large telescopes. 

Modern telescopes use Adaptive Optics (AO) to improve image quality by measuring and correcting the wavefront errors due to this turbulence.

We are using wavefront measurement techniques in industrial and bio-medical metrology.

Novel fibres & characterisation

A new type of fibre - photonic crystal fibre - offers the exciting possibility of new sensor designs and configurations thus extending the potential applications for fibre sensors.

Photonic crystal fibres exhibit optical and physical properties that are different to conventional fibre, allowing novel sensor schemes.

Current work aims to exploit these differences for:

• Temperature measurement
• Strain measurement
• Spectroscopy
• Pressure sensing

Multiple core fibres have been demonstrated for fringe projection in velocimetry.

Long duration sensing applications - for example environmental monitoring - and high accuracy measurements require an accurate knowledge of fibre and grating properties over a wide range of conditions.

Temperature dependence of grating stress coefficient are measured over a range of temperatures and applied strain to fully characterise the sensing element.

Fibre gratings

Gratings are short sections of fibre containing a periodic modulation of the core refractive index. They act as wavelength-specific internal mirrors. This reflected wavelength depends on both strain and temperature of the grating fibre - hence the use in sensing, as optical strain gauges or optical thermometers.

Fibre Grating Sensors for Environmental Monitoring

In collaboration with AWE we are investigating the uses of fibre gratings for long term environmental monitoring applications.

Atmospheric pressure sensor using ‘T-shape’ dual fibre Bragg gratings for strain amplification (schematic below)

Using temperature-compensated Bragg grating strain gauges to measure diameter of a test cylinder to <3mm resolution

Gratings in Multicore Fibre and Hi-Bi Fibre

In collaboration with Aston University we are investigating potential applications of Bragg gratings in 4-core fibre for pitch and roll attitude sensing and shape measurement, and gratings in Hi-Bi fibre for multi-axis strain measurement.

Pitch and roll measurement has potential applications ranging from structural monitoring to array shape measurement systems. In most cases miniaturised remote operation sensors are essential.

Prototype pitch and roll sensor, further developments include suitable packaging for use in practical applications.