CERES :: Browsing by Author "Tatam, Ralph P."

Browsing by Author "Tatam, Ralph P."

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Open Access
2D spatially-resolved depth-section microfluidic flow velocimetry using dual beam OCT
(MDPI, 2020-03-27) Hallam, Jonathan M.; Rigas, Evangelos; Charrett, Thomas O. H.; Tatam, Ralph P.
A dual beam optical coherence tomography (OCT) instrument has been developed for flow measurement that offers advantages over microscope derived imaging techniques. It requires only a single optical access port, allows simultaneous imaging of the microfluidic channel, does not require fluorescent seed particles, and can provide a millimetre-deep depth-section velocity profile (as opposed to horizontal-section). The dual beam instrument performs rapid re-sampling of particle positions, allowing measurement of faster flows. In this paper, we develop the methods and processes necessary to make 2D quantitative measurements of the flow-velocity using dual beam OCT and present exemplar results in a microfluidic chip. A 2D reference measurement of the Poiseuille flow in a microfluidic channel is presented over a spanwise depth range of 700 μm and streamwise length of 1600 μm with a spatial resolution of 10 μm, at velocities up to 50 mm/s. A measurement of a more complex flow field is also demonstrated in a sloped microfluidic section.
Open Access
3D planar velocity measurements, using Mach-Zehnder interferometric-filter-based planar Doppler velocimetry (MZI-PDV) and imaging fibre bundles
(2008-12-31T00:00:00Z) Lu, Z. H.; Charrett, Thomas O. H.; Ford, Helen D.; Tatam, Ralph P.; David, Sampson; Stephen, Collins; Kyunghwan, Oh; Ryozo, Yamauchi
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 filter. The free spectral range of the filter can be selected by adjusting the optical path difference of the interferometer. This allows the velocity measurement range, sensitivity and resolution to be varied. Any laser wavelength may be used. A phase locking system has been designed to stabilise the interferometric filter.
Open Access
Absolute angle measurement using dual-wavelength laser speckle: theory and method
(Elsevier, 2023-11-30) Gibson, Sam J.; Charrett, Thomas O. H.; Tatam, Ralph P.
This paper presents a method utilising the speckle pattern formed by dual-wavelength illumination for the measurement of the two out-of-plane surface angles with respect to the sensor frame. Theoretical expressions are derived relating the observed speckle shift between patterns formed by two wavelengths for tilted surfaces with both on-axis and off-axis detector positions. These expressions are verified experimentally, showing RMS errors of between 0.5–1.0 . Finally, an on-axis implementation of the concept is presented using dual-wavelength illumination generated from two modes of a standard FP diode laser. Simplified expressions for the calculation of surface angles from measured speckle shift using this arrangement are presented, given in terms of three sensor constants; the responsivity or sensitivity of the sensor, C, and the zero surface tilt speckle shifts, Ax0 and Ay0. Experimental results using this sensor for a range of surface tilts between 0.0° and 7.5° showed an RMS error of 0.10° in θx and 0.19° in θy.
Open Access
Acousto-optic frequency switching for single-camera planar Doppler velocimetry
(International Society for Optical Engineering; 1999, 2001-12-31T00:00:00Z) Ford, Helen D.; Nobes, David S.; Tatam, Ralph P.; Mercer, Carolyn R.; Cha, Soyoung S.; Shen, Gongxin X.
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 a seeded flow and the Doppler-shifted scattered light passes through an iodine cell onto a single solid-state camera. Light scattered from the measurement plane from the beam with its wavelength set to be off the absorption line is not affected by its passage through the cell, and provides a reference image, while that from the beam on the absorption line encodes the velocity information as a variation in transmission dependent upon the Doppler shift. The complex imaging system required for conventional PDV is eliminated, since superposition of the reference and signal images is automatic. The two beams are generated by an optical arrangement incorporating an acoustio- optic modulator, and are transmitted to the region of interest by a single mode optical fibre, which ensures both a smooth Gaussian illumination profile and co- linearity of the beams. The system is demonstrated using a spinning disc and a velocity resolution of +/-1 ms-1 is achieved.
Open Access
Advanced fibre optic long period grating sensors; design, fabrication and sensing
(Cranfield University, 2014-05) Wong, Rebecca; James, Stephen W.; Tatam, Ralph P.
This thesis describes the process and technique used to fabricate reproducible optical fibre long period gratings (LPG) of various types. It explores how they can be exploited for use as highly selective and sensitive sensors. A versatile method for fabricating LPG sensors has been demonstrated. The single system has the capability of fabricating LPGs of different configurations, such as uniform period, those operating at the phase matching turning point (PMTP), as well as phase shifted and chirped. LPGs were characterised for their sensitivities to temperature, axial strain and surrounding refractive index. The gratings at the PMTP were found to show higher sensitivities to external influences. Novel sensing configurations that exploit the properties of LPGs were also constructed. An LPG coated with a molecularly imprinted ceramic coating was demonstrated to offer a selective method for porphyrin detection. A composite nanoscale of a titanium oxide (TiO2) matrix and 5, 10, 15, 20 Tetrakis-(N-methyl-piridinium4- yl)-21H, 23H-porphine tertakis (p-toluenesulfonate) [TMPyP] porphyrin template film was deposited on the LPG via liquid phase deposition. Attempts to rebind porphyrins to the matrix were carried out. The LPGs transmission spectrum exhibited a higher sensitivity to the target TMPyP template than it did to other, structurally similar porphyrins, showing high selectivity. A continuously chirped long period grating (CCLPG) sensor for monitoring directional flow and cure of an epoxy resin is also presented. The asymmetric properties of the CCLPG were exploited to facilitate the measurement of the direction of the flow. The CCLPG was also used to monitor changes in the refractive index of the resin during its cure, showing close agreement with a fibre optic Fresnel refractometer.
Open Access
AFM observation of surface topography of fibre Bragg gratings fabricated in germanium-boron codoped fibres and hydrogen-loaded fibres.
(Elsevier Science B.V., Amsterdam., 2002-11-01T00:00:00Z) Wei, C. Y.; Ye, Chen-Chun; James, Stephen W.; Irving, Phil E.; Tatam, Ralph P.
This paper reports the measurement of the surface topology of optical fibres containing a fibre Bragg grating (FBG) using an atomic force microscope (AFM). The AFM observation was made on FBGs fabricated via the phase mask technique in germanium–boron codoped optical fibres, in hydrogen-loaded germanium–boron codoped fibres and in standard telecommunications optical fibres. The surface images reveal that a spatial corrugation pattern was induced by the UV- irradiation, with a period that is half of the period of the phase mask. This UV-induced surface structure was found only on the side of the fibre facing towards the incident UV-irradiation and did not appear on the rear surface. The AFM probe scanned a 10×10 μm2 surface area at seven sites along the 6.0 mm length of fibre that was exposed to the UV-irradiation. The amplitude of the spatial corrugation pattern observed on the AFM image was quantified for each site. It was found that the amplitude in a range of 0.7–3.2 nm was a function of UV-laser intensity distribution and the type of fibre. Hydrogen loaded optical fibres exhibited a corrugation with an amplitude twice as large as that observed in the Ge–B doped fibres that were not hydrogen-loaded. This correlates with the increase in photosensitivity produced by the hydrogen loading. A similar UV- induced spatial corrugation was also observed on standard telecom fibres, but without inducing the refractive index change in the fibre core. The observation of surface topology provides an insight into the structural changes induced during FBG fabrication. UV-induced densification and laser ablation could account for the formation of the surfac
Open Access
All-electronic frequency stabilization of a DFB laser diode
(Optical Society of America, 2017-05-10) Asmari, A.; Hodgkinson, Jane; Chehura, Edmon; Staines, Stephen E.; Tatam, Ralph P.
A laser diode’s junction voltage is a sensitive measure of its temperature and can be used in a thermal control feedback loop. To compensate for the temperature dependence of the laser’s internal resistance, we have measured the dynamic resistance, ∂V/∂I, by modulating the injection current and measuring the demodulated voltage. The junction voltage was thus controlled while operating at fixed DC injection current. Over an external temperature range of 15°C to 35°C, this stabilised the centre frequency (wavelength) of a 1651 nm DFB laser diode with a residual mean frequency shift of 60 MHz (0.5pm), less than the uncertainty on the centre frequency of 80 MHz (0.7 pm). Under the same conditions, conventional thermistor control gave a systematic wavelength shift of −8.4 GHz (−76 pm), and control of the uncompensated forward voltage gave a shift of 9.9 GHz (90 pm).
Open Access
All-optical switching based on optical fibre long period gratings modified bacteriorhodopsin
(Elsevier, 2017-11-24) Korposh, Sergiy; James, Stephen; Partridge, Matthew; Sichka, M; Tatam, Ralph P.
All-optical switching using an optical fibre long-period gating (LPG) modified with bacteriorhodopsin (bR) is demonstrated. The switching process is based on the photo-induced RI change of bR, which in turn changes the phase matching conditions of the mode coupling by the LPG, leading to modulation of the propagating light. The effect was studied with an LPG immersed into a bR solution and with LPGs coated with the bR films, deposited onto the LPGs using the layer-by-layer electrostatic self-assembly (LbL) method. The dependence of the all-optical switching efficiency upon the concentration of the bR solution and on the grating period of the LPG was also studied. In addition, an in-fibre Mach-Zehnder interferometer (MZI) composed of a cascaded LPG pair separated by 30 mm and modified with bR was used to enhance the wavelength range of all-optical switching. The switching wavelength is determined by the grating period of the LPG. Switching efficiencies of 16% and 35% were observed when an LPG and an MZI were immersed into bR solutions, respectively. The switching time for devices coated with bR-films was within 1 s, 10 times faster than that observed for devices immersed into bR solution.
Open Access
Ammonia sensing using lossy mode resonances in a tapered optical fibre coated with porphyrin-incorporated titanium dioxide
(Society of Photo-optical Instrumentation Engineers (SPIE), 2016-05-30) Tiwari, Divya; Mullaney, Kevin; Korposh, Sergiy; James, Stephen W.; Lee, Seung-Woo; Tatam, Ralph P.
The development of an ammonia sensor, formed by the deposition of a functionalised titanium dioxide film onto a tapered optical fibre is presented. The titanium dioxide coating allows the coupling of light from the fundamental core mode to a lossy mode supported by the coating, thus creating lossy mode resonance (LMR) in the transmission spectrum. The porphyrin compound that was used to functionalise the coating was removed from the titanium dioxide coating upon exposure to ammonia, causing a change in the refractive index of the coating and a concomitant shift in the central wavelength of the lossy mode resonance. Concentrations of ammonia as small as 1ppm was detected with a response time of less than 1min. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Open Access
An ammonia sensor based on Lossy Mode Resonances on a tapered optical fibre coated with porphyrin-incorporated titanium dioxide
(Elsevier, 2017-04) Tiwari, Divya; Mullaney, Kevin; Korposh, Sergiy; James, Stephen W.; Lee, Seung-Woo; Tatam, Ralph P.
The development of a highly sensitive ammonia sensor is described. The sensor is formed by deposition of a nanoscale coating of titanium dioxide, containing a porphyrin as a functional material, onto a tapered optical fibre. The titanium dioxide coating allows coupling of light from the fundamental core mode to a lossy mode supported by the coating, thus creating a Lossy Mode Resonance (LMR) in the transmission spectrum. A change in the refractive index of the coating caused by the interaction of the porphyrin with ammonia causes a change in the centre wavelength of the LMR, allowing concentrations of ammonia in water as low as 0.1 ppm to be detected, with a response time of less than 30 s.
Open Access
An analysis of fibre optic interferometer configurations for optical coherence tomography applications
(2003-10) Beddows, Ruth; Tatam, Ralph P.
The Michelson Interferometer has been the principal interferometer configuration for Optical Coherence Tomography (OCT) imaging. For OCT applications, in particular endoscopy, there may be polarisation induced signal fading due to environmental changes within the sample arm. The most significant cause of polarisation induced fading within OCT systems is suggested to be due to changes within the optical fibres. The Fizeau interferometer has been shown to eliminate this polarisation induced fading as the sample and reference arm experience the same environmental effects. However the Signal to Noise Ratio (SNR) o f the Fizeau configuration is lower than that o f the Michelson because a second processing interferometer is required. An investigation into suitable interferometer configurations for OCT was carried out in order to increase the performance o f the Fizeau interferometer compared with Michelson configuration. It was shown theoretically that by using a circulator and balanced detection, a standard Fizeau interferometer could achieve a signal to noise ratio (SNR) up to I8dB greater than the conventional Michelson interferometer and a comparable SNR to the Michelson interferometer optimised for power conservation. An analysis into the optical components used in OCT systems was carried out and the optimal Fizeau interferometer design was constructed. The Optimal design was shown to give an increase o f 26dB compared to the standard Fizeau interferometer relative to theoretical results using the same optical components. It was experimentally shown that the use o f an optical circulator within the Fizeau interferometer improves the SNR compared to the standard configuration.
Open Access
Application and performance of laser speckle odometry applied to a mobile industrial robot
(SPIE, 2023-08-15) Charrett, Thomas O. H.; Gibson, Sam; Tatam, Ralph P.
In this paper we report the application of a laser speckle odometer to a mobile industrial robot in a typical factory floor environment. The suitability of typical floor surfaces and features is assessed in terms of the ability to form speckle patterns with sufficient signal to noise for correlation-based processing. All tested surfaces including concrete, rubber tile, dried paint and oil stains, and hazard tapes were found to be suitable. A comparison of the velocimetry sensor output to the industrial robot’s internal SLAM and wheel encoder data is presented with good agreement of < 0.3mm/s at tested speeds of up to 250mm/s. Finally, a comparison of speckle odometry to the robot’s internal SLAM based navigation will be presented using a laser tracker to provide ground-truth measurement data. Both techniques were found to perform similarly, with errors of up to 80mm when traversing a 16m square path of 4m sides. The laser speckle odometry was however found to perform significantly better over the initial sides of the path with a maximum error of < 10mm in comparison to < 47mm for the robot’s internal odometry.
Open Access
Application of fibre optic sensing systems to measure rotor blade structural dynamics
(Elsevier, 2021-03-09) Weber, Simone; Kissinger, Thomas; Chehura, Edmond; Staines, Stephen; Barrington, James; Mullaney, Kevin; Fragonara, Luca Zanotti; Petrunin, Ivan; James, Stephen; Lone, Mudassir; Tatam, Ralph P.
This paper compares two fibre optic sensing techniques for vibration characterisation: (a) optical fibre Bragg grating (FBG) strain gauges and (b) a novel direct fibre optic shape sensing (DFOSS) approach based on differential interferometric strain measurements between multiple fibres within the same fibre arrangement. Operational mode shapes and frequency measurements of an Airbus Helicopters H135 bearingless main rotor blade (5.1 m radius) were acquired during a series of ground vibration tests undertaken in a controlled laboratory environment. Data recorded by the fibre optic instrumentation systems were validated using commercially available accelerometers and compared against a baseline finite element model. Both fibre optic sensing systems proved capable of identifying the natural frequencies of the blade in the frequency range of interest (0–100 Hz). The data from the FBG sensors exhibited a dependency on their position relative to the neutral axes of the blade, which meant that full characterisation of the flapping and lagging modes required careful consideration of sensor location in the chordwise direction. The DFOSS system was able to identify all structural dynamics, despite being located on the neutral axis in the lagging direction, due to its sensitivity to angle changes, rather than strain, and its biaxial measurement capability. The DFOSS system also allowed the operational mode shapes of the blade to be determined directly, without the requirement for strain transfer from the blade to the sensor and without the requirement for a model of the underlying structure. The accuracy of obtained natural frequencies and operational mode shapes is assessed, demonstrating the potential of the use of both fibre optic sensing systems for determining blade structural dynamics.
Open Access
Automated interlayer wall height compensation for wire based directed energy deposition additive manufacturing
(MDPI, 2023-10-16) Qin, Jian; Vives, Javier; Raja, Parthiban; Lasisi, Shakirudeen; Wang, Chong; Charrett, Thomas O. H.; Ding, Jialuo; Williams, Stewart; Hallam, Jonathan Mark; Tatam, Ralph P.
Part quality monitoring and control in wire-based directed energy deposition additive manufacturing (w-DEDAM) processes has been garnering continuous interest from both the academic and industrial sectors. However, maintaining a consistent layer height and ensuring that the wall height aligns closely with the design, as depicted in computer-aided design (CAD) models, pose significant challenges. These challenges arise due to the uncertainties associated with the manufacturing process and the working environment, particularly with extended processing times. To achieve these goals in an industrial scenario, the deposition geometry must be measured with precision and efficiency throughout the part-building process. Moreover, it is essential to comprehend the changes in the interlayer deposition height based on various process parameters. This paper first examines the behaviour of interlayer deposition height when process parameters change within different wall regions, with a particular focus on the transition areas. In addition, this paper explores the potential of geometry monitoring information in implementing interlayer wall height compensation during w-DEDAM part-building. The in-process layer height was monitored using a coherent range-resolved interferometry (RRI) sensor, and the accuracy and efficiency of this measurement were carefully studied. Leveraging this information and understanding of deposition geometry, the control points of the process parameters were identified. Subsequently, appropriate and varied process parameters were applied to each wall region to gradually compensate for wall height. The wall height discrepancies were generally compensated for in two to three layers.
Open Access
Automated manufacture of 3D reinforced aerospace composite structures
(2012-03-05T00:00:00Z) Dell'Anno, Giuseppe; Partridge, Ivana K.; Cartié, Denis D. R.; Hamlyn, A.; Chehura, Edmon; James, Stephen W.; Tatam, Ralph P.
Purpose- This study is part of the FP7 project ADVITAC and focuses on exploring an innovative combination of cutting edge technologies to be implemented within automated processes for composite parts manufacturing. The objective is the design of a production route for components with tailored fibre orientation and ply lay-up, with improved damage tolerance thanks to through-the-thickness reinforcement and integrated health monitoring systems based on optical fibres technology. Design/Methodology/Approach- The proposed technologies are described in detail and their compatibility and potential for integration are discussed. A set up for on-line monitoring of infusion and curing processes of carbon/epoxy laminates preformed by dry fibre placement technology is proposed, and a preliminary study of their mechanical performance is presented. The possibility of reinforcing through-the-thickness preforms manufactured with dry slit tapes automatically laid-up and consolidated by laser heating is investigated. Findings- Improved knowledge of interaction/compatibility between the discussed technologies and scope for application. Research limitations/implications- The paper reports the technical potential and practical feasibility of the proposed integrated production process. Limited quantitative evaluations on the materials performance are provided. The analysis of the technologies involved represents the early outcome of the ongoing ADVITAC project. Practical implications- This study contributes to the identification of a new generation of composite architecture which allows production cost and weight savings while retaining the level of quality suitable for demanding structural applications, with particular relevance to the aerospace field. Originality/value- This paper investigates for the first time the practical possibility of designing a single automated process involving dry fibre placement, tufting and optical fibre sensor monitoring for the production of complex composite components.
Open Access
Bladesense – a novel approach for measuring dynamic helicopter rotor blade deformation
(European Rotorcraft Forum, 2018-12-31) Weber, Simone; Southgate, Dominic; Mullaney, Kevin; James, Stephen; Rutherford, Robert; Sharma, Anuj; Lone, Mudassir; Kissinger, Thomas; Chehura, Edmond; Staines, Stephen; Pekmezci, Huseyin; Fragonara, Luca Zanotti; Petrunin, Ivan; Williams, Dan; Moulitsas, Irene; Cooke, Alastair; Rosales, Waldo; Tatam, Ralph P.; Morrish, Peter; Fairhurst, Mark; Atack, Richard; Bailey, Gordon; Morley, Stuart
Technologies that allow accurate measurement of rotorblade dynamics can impact almost all areas of the rotorcraft sector; ranging from maintenance all the way to blade design. The BladeSense project initiated in 2016 aims to take a step in developing and demonstrating such a capability using novel fibre optic sensors that allow direct shape measurement. In this article the authors summarise key project activities in modelling and simulation, instrumentation development and ground testing. The engineering approach and associated challenges and achievements in each of these disciplines are discussed albeit briefly. This ranges from the use of computational aerodynamics and structural modelling to predict blade dynamics to the development of direct fibre optic shape sensing that allows measurements above 1kHz over numerous positions on the blade. Moreover, the development of the prototype onboard system that overcomes the challenge of transferring data between the rotating main rotor to the fixed fuselage frames is also discussed.
Open Access
Characterisation of a cryostat using simultaneous, single-beam multiple-surface laser vibrometry
(American Institute of Physics Publishing, 2016-06-28) Kissinger, Thomas; Charrett, Thomas O. H.; James, Stephen W.; Adams, Alvin; Twin, Andrew; Tatam, Ralph P.
A novel range-resolved interferometric signal processing technique that uses sinusoidal optical frequency modulation is applied to multi-surface vibrometry, demonstrating simultaneous optical measurements of vibrations on two surfaces using a single, collimated laser beam, with a minimum permissible distance of 3.5 cm between surfaces. The current system, using a cost-effective laser diode and a fibre-coupled, downlead insensitive setup, allows an interferometric fringe rate of up to 180 kHz to be resolved with typical displacement noise levels of 8 pm · Hz−0 5. In this paper, the system is applied to vibrometry measurements of a table-top cryostat, with concurrent measurements of the optical widow and the sample holder target inside. This allows the separation of common-mode vibrations of the whole cryostat from differential vibrations between the window and the target, allowing any resonances to be identified.
Open Access
Characterization of optical fiber imaging bundles for swept-source optical coherence tomography
(Osa Optical Society of America, 2011-02-03T00:00:00Z) Ford, Helen D.; Tatam, Ralph P.
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 potential for miniaturization and inclusion in endoscopic-type systems, since the advantages of employing imaging bundles are most clearly seen in this type of system. The various types of bundle available are described, and the properties of the leached bundles used here are discussed in detail, with reference to their effect upon the performance of OCT systems. Images are displayed from measurements made on a range of samples.
Open Access
Characterization of the response of fibre Bragg gratings fabricated in stress and geometrically induced high birefringence fibres to temperature and transverse load.
(Institute of Physics, 2004-08-01T00:00:00Z) Chehura, Edmon; Ye, Chen-Chun; Staines, Stephen E.; James, Stephen W.; Tatam, Ralph P.
The transverse load and temperature sensitivities of fibre Bragg gratings (FBGs) fabricated in a range of commercially available stress and geometrically induced high birefringent (HiBi) fibres have been experimentally investigated. The wavelength reflected by the FBG in each polarization eigenmode was measured independently and simultaneously using a custom designed interrogation system. The highest transverse load sensitivity, of 0.23 ± 0.02 nm/(N/mm), was obtained with HiBi FBGs fabricated in elliptically clad fibre. This was higher than for any other HiBi fibre, which, coupled with the small diameter of the fibre, makes it a good candidate for an embedded or surface mounted strain sensor. The highest temperature sensitivity of 16.5 ± 0.1 pm °C-1, approximately 27% greater than any other fibre type, was obtained with the HiBi FBG fabricated in Panda fibre. HiBi FBG sensors fabricated in D-clad fibre were the only ones to exhibit identical temperature sensitivities for the slow and fast axes (11.5 ± 0.1 pm °
Open Access
Coherent fibre bundles in full-field swept-source OCT
(2009-02-20T00:00:00Z) Ford, Helen D.; Tatam, Ralph P.; Fujimoto, J. G.; Izatt, J. A.; Tuchin, V. V.
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 investigating a swept-source OCT system incorporating coherent fibre bundles, to allow many measurement points to be addressed, within an area of the sample, without the need for mechanical motion within the endoscope probe. Scanning components are still present at the input of our system, but are no longer required within the flexible ndoscope section. This allows a small-diameter, electrically passive probe to be engineered using off-the-shelf scanning components. A common-path probe design is proposed, in which the bundle is external to the OCT interferometer. This eliminates contrast variations caused by non-controllable differences in the state of polarisation between fibres. Imaging bundle fibres are typically few-moded, which can lead to ghost features and reduced SNR in OCT images, but the common-path configuration also removes cross-mode interference problems, and reduces dispersion artefacts. OCT images of a microscope cover-slip and a sample of spring onion, acquired using the swept-source, bundle-based OCT system are presented. Features peculiar to the inclusion of the fibre bundle are discussed, and directions for future development of the system are outlined.