About
52
Publications
5,276
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
496
Citations
Additional affiliations
July 1990 - present
Publications
Publications (52)
Confocal scanning combined with low-coherence interferometry is used to provide remote refractive index and thickness measurements of transparent materials. The influence of lens aberrations in the confocal measurement is assessed through ray-trace modeling of the axial point-spread functions generated using optical configurations comprised of pair...
A novel dual beam Optical Coherence Tomography (OCT) instrument has been developed for high velocity flow measurement, principally in microfluidics applications. The scanned dual beam approach creates a pair of image-frames separated by a small spatiotemporal offset. Metre-per-second flow measurement is achieved by rapid re-imaging by the second be...
A novel dual beam Optical Coherence Tomography (OCT) system is presented for microfluidics applications. The dual sensing-light-sheet approach presented here achieves high velocity flow measurement because the rapid re-imaging by the second sensing-light-sheet allows for particle tracking between each image-frame of the pair. We have demonstrated m...
This paper describes a technique for measuring refractive index and thickness of transparent plates using a fibre-optic low-coherence interferometer. The interferometer is used to independently measure quantities related to the phase and group refractive indices, np and ng, of the material under investigation. Additionally, the dispersion of the ph...
A dual-beam Optical Coherence Tomography system has been developed, using a bespoke dual optical fibre, to simultaneously image microfluidic channel structures and measure high velocity flows (presently 250μm/s) from a single optical access point.
Duct-profiling in test samples up to 25 mm in diameter has been demonstrated using a passive, low-coherence probe head with a depth resolution of 7.8 μm, incorporating an optical-fibre-linked conical mirror addressed by a custom-built array of single-mode fibres. Zemax modelling, and experimental assessment of instrument performance, show that degr...
A passive, endoscopic optical coherence tomography (OCT) probe has been demonstrated, incorporating an imaging fibre bundle and 45° conical mirror, and with no electromechanical components at the probe tip. Circular scanning, of the beam projected onto the proximal face of the imaging bundle, produces a corresponding circular scan at the distal end...
Imaging fibre bundles and a conical mirror have been used to construct a passive, endoscopic OCT probe with no
scanning components at the probe tip. Circular scanning of the beam projected onto the proximal face of the imaging
bundle results in a corresponding circular scan at the distal end of the probe. A 45° base-angle conical mirror turns the
o...
Imaging fibre bundles are widely used in image transmission systems in the visible spectral range1. Their image transmission capabilities and flexibility make them interesting for OCT endoscopy2. However, cross-talk occurring between individual fibres and multimode transmission cause deterioration of the images obtained with OCT systems. In this st...
Fiber imaging bundles have been investigated for use in endoscopic optical coherence tomography (OCT) systems, to obviate the requirement for scanning components within the endoscope probe section. Images have been acquired using several optical configurations, two of which are common path in design. Configurations have been selected as having pote...
OCT probes for endoscopy typically use a single optical fibre to deliver light to the measurement region. 2D imaging is achieved using mechanical scanning components at the probe tip. We are investigating an OCT system in which fibre imaging bundles replace the single probe fibre, allowing many thousand measurement points to be addressed without an...
Endoscopic OCT probes deliver light to the measurement region via a single optical fibre mounted in a probe head. The output beam is focused onto the sample, providing a single point measurement. The beam is translated, using mechanical scanning at the probe tip, to address a line or area of sampling points and produce an image. We are investigatin...
Three component planar flow-field measurements are made using imaging fibre bundles to port different views of the measurement plane, defined by a laser light sheet, to a single imaging head. The Doppler frequency shifts of light scattered by particles entrained in the flow are transduced to intensity variations using a Mach-Zehnder interferometric...
An OCT system incorporating a coherent fibre imaging bundle is described. Fibres are accessed sequentially by a beam focused onto the input face of the bundle, allowing 2D or 3D images to be acquired using point detection. A Fizeau interferometer configuration is used, in which light from the distal end of a fibre in the bundle (forming the referen...
A planar Doppler velocimetry system to measure flow velocity fields is described. The technique uses a Mach-Zehnder interferometric filter to convert Doppler frequency shifts into intensity variations. The free spectral range of the filter can be selected by adjusting the optical path difference of the interferometer. This allows the velocity measu...
This paper describes the development of a Mach-Zehnder interferometric filter based planar Doppler velocimetry (MZI-PDV) flow measurement technique. The technique uses an unbalanced Mach-Zehnder interferometer (MZI) to convert Doppler frequency shifts into intensity variations. The free spectral range of the interferometric filter can be selected b...
An imaging fibre bundle is incorporated into a full-field imaging OCT system, with the aim of eliminating the mechanical scanning currently required at the probe tip in endoscopic systems. Each fibre within the imaging bundle addresses a Fizeau interferometer formed between the bundle end and the sample, a configuration which ensures down lead inse...
An imaging fibre bundle is demonstrated for spatially-multiplexed probe beam delivery in OCT, eliminating the mechanical scanning currently required at the probe tip in endoscopic systems. Images acquired using the bundle-based system are presented.
Two frequency planar Doppler Velocimetry (2ν-PDV) is a modification of the Planar Doppler Velocimetry (PDV) method that allows velocity measurements to be made, quickly and non intrusively, across a plane defined by a laser light sheet. In 2ν-PDV the flow is illuminated sequentially with two optical frequencies, separated by about 700MHz. A single...
This paper describes the development of optical fibre low-coherence speckle interferometers capable of three-dimensional surface profiling with a resolution of 10–20 µm and a depth range of typically tens of centimetres. The technique is absolute, enabling the measurement of steps and through holes. The inclusion of optical fibres enables compact,...
Several optical coherence tomography (OCT) systems are proposed using optical-fibre components and based around Fizeau sensing interferometers. The theoretical signal-to-noise ratio (SNR) is calculated for each of the proposed configurations, using a constant set of assumed values for illumination and detection parameters. The SNR values obtained a...
To eliminate mechanical scanning in the probe head of an endoscopic OCT
system, we propose the use of an imaging fibre bundle for probe beam
delivery. Each fibre in the bundle addresses a Fizeau interferometer
formed between the bundle end and the sample, allowing acquisition of
information across a plane with a single measurement. Depth scanning
c...
We report the investigation of a Fizeau interferometer-based OCT system. A secondary processing interferometer is necessary in this configuration, to compensate the optical path difference formed in the Fizeau interferometer between the end of the fibre and the sample. The Fizeau configuration has the advantage of 'downlead insensitivity', which el...
A modified Planar Doppler Velocimetry (PDV) technique, two frequency PDV (2v-PDV), is described that allows measurements of the velocity field over a plane defined by a laser light sheet using sequential illumination of the flow with two closely separated (&IGHz) frequencies of laser light. This allows a common-path imaging head to be used containi...
A planar Doppler velocimetry (PDV) system has been designed which is able to generate two beams from a single source separated in frequency by 690 MHz. This allows a common-path imaging head to be constructed, using a single imaging camera instead of the usual camera pair. Both illumination beams can be derived from a single laser and a set of acou...
An optical fiber, Fizeau configuration Optical Coherence Tomography (OCT) system is presented in this paper. The interferometer is formed between the distal end of the sample-arm fiber and the sample itself. This ensures 'downlead insensitivity;' polarization variation is not a problem, as it is in the standard Michelson configuration. Path-length...
An optical fiber, Fizeau configuration Optical Coherence Tomography
(OCT) system is presented in this paper. The Interferometer is formed
between the distal end of the sample-arm fiber and the sample itself.
This ensures 'downlead insensitivity;' polarization variation is not a
problem, as it is in the standard Michelson configuration. Path-length...
This paper describes a planar Doppler velocimetry (PDV) technique that is capable of measuring the three, instantaneous and time average components of velocity over two spatial dimensions using a single pair of signal and reference cameras. The three views required to obtain three-component velocity information are guided from the collection optics...
The development of a planar Doppler velocimetry is described. The technique is capable of measuring the three, instantaneous components of velocity in two dimensions using a single pair of signal and reference cameras. PDV can be used to measure the instantaneous 3-D velocity of a fluid by using an absorption line filter (ALF) to determine the Dopp...
A Planar Doppler Velocimetry (PDV) illumination system has been designed which is able to generate two beams, separated in frequency by about 600 MHz. This allows a common-path imaging head to be constructed, using a single imaging camera instead of the usual camera pair. Both illumination beams can be derived from a single laser, using acousto-opt...
The development of a planar Doppler velocimetry is described. The technique is capable of measuring the three, instantaneous components of velocity in two dimensions using a single pair of signal and reference cameras. PDV can be used to measure the instantaneous 3-D velocity of a fluid by using an absorption line filter (ALF) to determine the Dopp...
The development of a planar Doppler velocimetry is described. The technique is capable of measuring the three, instantaneous components of velocity in two dimensions using a single pair of signal and reference cameras. PDV can be used to measure the instantaneous 3-D velocity of a fluid by using an absorption line filter (ALF) to determine the Dopp...
A single-camera Planar Doppler velocimetry system has been demonstrated, in which illumination beams at two closely-spaced optical frequencies are derived from a single Argon-ion laser. The frequency of one beam lies on an absorption line of iodine vapour, and the other just off the absorption line. The beams sequentially illuminate a plane within...
This paper describes a planar Doppler velocimetry (PDV) technique that is capable of measuring the three, instantaneous components of velocity in two dimensions using a single pair of signal and reference cameras. PDV can be used to measure the instantaneous 3-D velocity of a fluid by using an absorption line filter (ALF) to determine the Doppler s...
A simple in-fibre technique for the measurement of small frequency separations is described. A sinusoidal frequency modulation, applied to the source, is converted into phase modulation of an optical carrier, thereby enabling measurement of the frequency modulation amplitude. The source must be continuously tunable, which makes the technique partic...
Laser diode emission wavelength modulation is demonstrated as a technique for measuring the phase and gradient of displacement amplitude of a vibrating object using continuous wave illumination in a path length imbalanced speckle shearing interferometer. The unwanted mismatch in the magnification of the two images in the shearing interferometer and...
The development of a portable, single component Doppler global velocimetry (DGV) head, based around a wavelength-stabilised argonion laser and a fast digital image-processing system, is described. The normalised two-dimensional DGV image, in which intensities are linearly related to velocities, can be displayed and updated at the 25 Hz camera frame...
A technique is presented for the slope measurement of objects using an electronic shearography system. To detect the gradients of an object shape, a laser diode is modulated to produce two wavelengths on successive image frames. These two frames are then subtracted to generate correlation fringes which depict slope variations of the object surface....
A multiplexed sensor network incorporating wavelength-division demultiplexers (WDMs) constructed from birefringent fibre is presented. Experimental results from a hybrid fibre/bulk-optic version exhibit a worst case optical cross-talk, limited by the extinction ratio for the polarisation-splitting fibre component, of −10 dB. Consideration of typica...
Phase stepping by wavelength modulation of the optical source is demonstrated in a path-length unbalanced shearing interferometer. A magnification difference, which accompanies the path-length imbalance in the interferometer, introduces an unwanted radial shear, which is shown to be compensated by inclusion of a block of high-refractive-index mater...
Direct injection-current modulation of a diode laser source is demonstrated for phase-stepping, heterodyning and
stroboscopic illumination in a shearing interferometer. The techniques are proposed as an alternative to the use of mechanical
phase-shifters such as piezoelectric transducers, offering the advantages of ease of implementation, extended...
Doppler Global Velocimetry (DGV) is a full-field optical technique for the measurement of fluid flow velocities. The flow is illuminated using a light sheet, and the Doppler shift imposed on light scattered from moving particles within the sheet is imaged through a cell containing iodine vapor onto a solid-state array camera, thereby converting the...
Polarization-based in-line wavelength filters have been designed
and evaluated. These are compact devices fabricated from single-mode
optical fiber possessing high linear birefringence. A minimum passband
width of 10 nm has been demonstrated at a passband separation of 60 nm.
Both bandpass and bandstop devices can be produced. The filters are
const...
Material testing is an important task during product design,
manufacturing and inspection processes. Speckle techniques are
increasingly used as effective tools for this work. In this paper, we
discuss the use of speckle interferometric techniques such as electronic
speckle pattern interferometry (ESPI) and shearography for
non-destructive testing...
Birefringent filters, analogous to bulk-optic Solc filters, have been constructed from linearly birefringent optical fiber. Controlled twisting of portions of the fiber is used to rotate the polarization azimuth between retarder elements, and allows the devices to be made from continuous lengths of fiber. Filters having up to four elements have bee...
Wavelength fibers have applications in wavelength-division multiplexed optical communications and sensor systems. Bulk-optic birefringent filters offer sub-nanometer passband widths, but are not compatible with optical fiber systems. However, fiber analogues of the bulk-optic filters can be constructed using birefringent fiber. A cut-and-splice tec...
In-line wavelength-division demultiplexers (WDMs) based on a polarisation separation technique using birefringent optical fibre are presented. The theory of the devices is developed and the factors affecting their performance are discussed. Devices capable of demultiplexing wavelengths separated by ∼30 GHz and ∼200 GHz, respectively, are demonstrat...
