Photonics Sensors Group
The Photonics Sensors Group (PSG) was originally established as the Optical Fibre Sensing Group (OFSG) in 1993 and has trained a multitude of Honours, Masters and PhD graduates. With the restructuring of the Physics Department into the Division of Physics and Electronics in 2002, it was renamed the Photonics Sensors Group. The PSG has two photonics research laboratories, equipped with equipment such as visible, near and thermal infrared lasers, diode array spectrometers, a multitude of oscilloscopes and electro-optical transducers, precision optical benches, precision optical components for optical fibre and bulk optical experiments, and a plethora of gaseous electronics apparatus. We investigate photonics sensors in a whole range of applications in both gaseous and liquid media.
Current Research Projects
Observation of axial acoustic waves in multimode PMMA optical fibres; a new class of optical fibre sensor
Staff of the PSG have, for the first time observed axial acoustic waves in multimode polymethylmethacrylate (PMMA) optical fibres. Rapid electrostriction was induced in a 1.25 m length of PMMA optical fibre using a pulsed transverse electric field of ~106 V m-1. By observing the effects of birefringence on a polarised laser beam, acoustic waves travelling with a speed of 1050 m s-1 were observed to travel between the fibre ends. Simple calculations indicate that these acoustic waves comprised shear waves, although propagation of surface waves could not be ruled out. These observations suggest a whole new class of optical fibre sensors based on the propagation of axial acoustic waves.
Contact Professor David Lamb
Optical fibre anemometers
A novel laser-optical fiber Bragg grating anemometer (FBGA) has been devised for measuring the speed of a moving gas in the range of 0 – 1.5 m s-1. The instrument is more stable and yields an order of magnitude improvement in sensitivity (∆v ≈ 4 x 10-3 m s-1) over other optical fiber-based anemometers. Two optical fibre anemometers, one based on a Mach-Zehnder interferometer (OFIA) and another a novel laser-optical fibre Bragg grating sensor (FBGA) have been constructed to measure the speed of the convective air flow generated in the the particularly harsh, high-voltage environment of a dc, negative-polarity, partial (corona) discharge in atmospheric air. In both configurations the sensing section of the optical fibre anemometers are subjected to controlled, repetitive bursts of infrared radiation from a CO2 laser and the combination of localised heating and convective cooling by the corona wind results in an optical signal that is directly calibrated to the speed of the wind. Both the OFIA and FBGA successfully measured the speed of the corona wind in the discharge gap, with wind speeds ranging from zero to 0.7 m s-1 observed at different locations in the discharge gap. However, the FBGA, due primarily to the ability to average sensor response over many measurements, exhibited an order of magnitude higher sensitivity and the OFIA (∆v ≈ 4 x 10-3 m s-1 compared to 3 x 10-2 m s-1). Both sensors yielded measurements of wind speed that were an order of magnitude lower than similar measurements using laser Doppler anemometry (LDA), indicating that the seed particles introduced as part of the LDA system are providing false reading of wind speed due to acceleration by the gap electric field.
Contact Professor David Lamb
Investigating the sensitivity of PMMA optical fibres for use as an evanescent field absorption sensor in aqueous solutions
Polymethylmethacrylate (PMMA) optical fibres are low-cost polymer fibres that are generally more physically robust than silica fibres, are more flexible, yet like silica fibres have the potential to be used for practical evanescent field absorption sensors in aqueous solutions. However, evanescent field absorption in aqueous solutions is influenced by more than just the specific absorptivity of the solution in question. The physical configuration of the optical fibre itself, as well as surface charge interactions between the fibre and the chromophore in the solution also significantly affects the sensitivity of the fibre to evanescent field absorption. This research investigates numerous physical phenomena that influence evanescent field absorption for PMMA fibres using an aqueous solution of water and amido-black dye. Parameters investigated included fibre coiling configuration and bend radius, fibre interaction length, and effect of solution pH. Coiled fibres were found to be more sensitive to evanescent field absorption than straight (uncoiled) lengths, as was that obtained using fibres of progressively smaller bend radii. At high solution pH, the absorption versus solution concentration proved to be linear whereas at low pH the absorption versus concentration relationship exhibited a clear deviation from linearity. The nature of this latter deviation points to the importance accounting for electrostatic interactions between chromophore and fibre surface when designing a PMMA sensor for evanescent field absorption measurements in aqueous solutions.
Contact Dr Peter Lye
An optical fibre technique for measuring optical absorption by chromophores in the presence of scattering particles
The evanescent radiation field associated with a suitably-prepared silica optical fibre, whereby the outer cladding has been removed and the core immersed in a liquid, has been investigated for its applicability as a device for measuring the spectral absorption of a liquid containing both chromophore and suspended scattering material. It is found that the evanescent radiation field adjacent to the core-liquid boundary interacts with chromophores in a liquid in much the same way as radiation does when directed, unbound, through a cuvette containing the same liquid in an optical spectrophotometer. However, the small penetration depth of the evanescent field, of the order of one micron, results in a sensor which is found to be insensitive to light-scattering particulate matter than was present in the liquid.
Optical sensors for Monolayer Detection
The presence and thickness of monolayers on the surface of water will alter the physical characteristics of the surface and that such a physical alteration may be detected using an optical technique. The proposed project will investigate a number of optical techniques for the potential of detecting and quantifying the presence of monolayer compounds (effectively hexa- or octadecanol-related compounds) on the surface of water. A range of techniques will undergo an initial evaluation, including the following.
Emissivity: The direction of polarisation of radiation emitted from the water surface is possibly affected by the presence of monolayers. An entry-level evaluation will involve comparing the direction of polarization of emitted radiation at large angles (> 60o) from water with and without monolayers present.
Chemical absorption bands: The presence of C-H bonds in monolayer compounds to be investigated means C-H stretching bands will be present in the absorption spectra associated with the water surface. As C-H absorbs at a wavelength of 3.4 mm, an optical sensor tuned to this wavelength may provide some discrimination of water surfaces with and without monolayers compounds present. It may be further possible to correlate the absorption feature with monolayer thickness and condition.
Capillary/Faraday Waves: As the presence of monolayers affects the surface tension of water, it is possible that a sensor based on the artificial generation of Capillary/Faraday Waves on the surface of the water body and subsequent detection using optical reflectance, may allow for the detection and measurement of monolayers.
Quantitative surface scale detection using an intrinsic exposed core optical fibre sensor
Surface, or heterogeneous crystallization processes have been monitored directly using an intrinsic, exposed core optical fibre sensor (IECOFS). Optical power output was found to be linearly correlated with crystal size (R2 = 0.97, n = 9) and mass (R2 = 0.62, n = 13) and the optical signal was found to be restored following chemical removal of deposited crystals (without physical intervention). The IECOFS was found to be insensitive to bulk-solution (or homogenous) crystallization processes, compared to the conventional methods of optical turbidity or electrical conductivity measurements, making it a potentially powerful tool for the study of surface-only crystallization processes.
1. Boerkamp, M., Lamb, D.W. & Lye, P. (2008) "Progress in the application of exposed core, optical fibre sensors for detecting and monitoring surface crystallization processes" in Optical Design and Engineering III, Laurent Mazuray, Rolf Wartmann, Andrew Wood, Jean-Luc Tissot, Jeffery M. Raynor (Eds), Proc. SPIE 7110, 71002G-1, 0277-786X/08/$18 doi: 10.1117/12.797583.
2. Lamb, D.W., Boerkamp, M. & Lye, P.G. (2008) "Monitoring surface crystal growth using an intrinsic exposed-core optical fiber sensor (IECOFS)" in Proc 19th International Conference on Optical Fibre Sensors, David Sampson, Stephen Collins, Kyunghwan Oh, Ryozo Yamauchi (Eds), Proc. SPIE 7004, 700440, 0277-786X/08/$18 doi: 10.1117/12.785932.
3. Boerkamp, M., Lamb, D.W. & Lye, P.G. (2008) "PMMA optical fibers as intrinsic sensors of surface crystal growth" in Proc 19th International Conference on Optical Fibre Sensors, David Sampson, Stephen Collins, Kyunghwan Oh, Ryozo Yamauchi (Eds), Proc. SPIE 7004, 700440, 0277-786X/08/$18 doi: 10.1117/12.786072.
4. Boerkamp, M., Lamb, D.W. & Lye, P.G. (2007) "Using an intrinsic, exposed core, optical fibre sensor to quantify chemical scale formation", Journal of Physics: Conference Series. 76 (doi:10.1088/1742-6596/76/1/012016).
5. Lamb D. W., & Hooper A. (2006) “A comparative assessment of two optical fibre anemometers for measuring the speed of the electric wind in a negative polarity, atmospheric corona discharge”, Measurement Science & Technology, 17: 1343-1349.
6. Lamb D. W., & Hooper A. (2006) “A novel laser-optical fiber Bragg grating anemometer for measuring gas flows: Application to measuring the electric wind”, Applied Optics Letters, 31: 1035-1037.
7. Bunganaen, Y. & Lamb, D.W. (2005) “An optical fibre technique for measuring optical absorption by chromophores in the presence of scattering particles”, Journal of Physics: Conference Series 15: 67-73.
8. Hooper, A., & Lamb, D.W. (2005) “Using an optical fibre anemometer to measure the speed of the electric wind in a negative polarity, atmospheric corona discharge”, Journal of Physics: Conference Series 15: 219-225.
9. Lye, P.G., Boerkamp, M., Ernest A. E., & Lamb, D.W. (2005) “Investigating the sensitivity of PMMA optical fibres for use as an evanescent field absorption sensor in aqueous solutions”, Journal of Physics: Conference Series 15: 262-269.
10. Ernest A. E., & Lamb, D.W. (2005) “Observations of axial acoustic waves in multimode PMMA optical fibres and implications for a new class of optical fibre sensor”, Journal of Physics: Conference Series 15: 270-275.
11. Lamb, D.W., Bunganaen, Y., Louis, J., Woolsey, G.A., Oliver, R. & White, G. (2004) “FEFA- an optical fibre technique for measuring water colour in turbid samples” Freshwater & Marine Research 55: 533-543.
12. Lamb, D. W. and Woolsey, G. A. (1995)."Characterisation and use of an optical fiber interferometer for measurement of the electric wind", J.Appl.Opt., 34: 1608-1616.
13. Lamb, D. W. and Woolsey, G. A. (1995). "Laser interferometry of SF6 coronas", J.Phys.D:Appl.Phys., 28: 2077-2082.
14. Woolsey, G. A., O'Byrne, S. & Lamb, D. W. (1993). "Temperature profiles for axially symmetrical distributions using integrated optical fiber sensing", in Fiber Optics & Laser Sensors XI, Ramon P. de Paula (ed), Proc. SPIE, 2070: 486-492.
15. Woolsey, G. A., & Lamb, D. W. (1992). "Absorption of polarised 10.6 mm CO2 laser radiation by fused silica optical fibers", in Fiber Optics & Laser Sensors X, Ramon P. de Paula (ed), Proc. SPIE, 1795: 247-255.
16. Woolsey, G. A., Lamb, D. W., & Woerner, M. C. H. (1991). "Optical fiber sensing of corona discharges", in Fiber Optics & Laser Sensors IX, Ramon P. de Paula (ed), Proc. SPIE, 1584: 243-253.