Browsing by Author "Casaubieilh, P."

Now showing 1 - 4 of 4
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    Comparative signal-to-noise analysis of fibre-optic based optical coherence tomography systems
    (Taylor & Francis, 2005-09-20T00:00:00Z) Ford, Helen D.; Beddows, R.; Casaubieilh, P.; Tatam, Ralph P.
    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 are compared with values calculated for typical existing configurations based around Michelson interferometers. Fizeau- based systems incorporating a secondary processing interferometer offer the advantage over current interferometer configurations of down- lead insensitivity, which prevents signal fading and reduces thermal fringe drift. The most basic form of the Fizeau system makes inefficient use of optical power, and has a low SNR compared with the widely used Michelson configuration. However, the results of the analysis described in this paper show that the SNR for more sophisticated Fizeau configurations, incorporating optical circulators and balanced detection systems, can be as high as the value for the most sensitive existing fibre- based OCT systems. Fizeau configurations therefore offer the combined advantages of optimized SNR and down- lead insensitivity, indicating their suitability for use in relatively poorly controlled environments such as in- vivo measurements.
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    Fibre optic fizeau intererometer for optical coherence tomography
    (Cranfield University, 2006) Casaubieilh, P.; Tatam, Ralph P.
    The aim of the project was to develop the Fizeau interferometer configuration to take advantage of the benefits derived from its “downlead insensitivity” to temperature and polarisation fading. This sensing interferometer was investigated and implemented in conjunction with various processing interferometers with the view to achieve optimised performances for Optical Coherence Tomography (OCT) application. A comprehensive theoretical analysis has been carried for Signal-to-Noise ratio of these OCT systems. Balanced detection indenting two detectors with anti-phase signals was also investigated to improve further the SNR. The analysis showed that the SNR (67 dB) of the balanced Fizeau interferometer improved by 30 dB from that of standard Fizeau interferometer implementing a single detector. Experimentally, the best SNR for this configuration was achieved by adding an electronic rectifier based demodulation system for the signal after balanced detection. The OCT systems investigated in this project were developed based on a broadband source operating in the 1550 nm wavelength-band to facilitate improvement in the depth of penetration of light directed into imaged samples. The coherence length or axial resolution in air of the system was 21[micro milli]while the transverse resolution was 18 [micro milli] and focusing depth was 340 [micro milli].
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    Optical coherence tomography with a Fizeau interferometer configuration
    (International Society for Optical Engineering; 1999, 2005-12-31T00:00:00Z) Casaubieilh, P.; Ford, Helen D.; James, Stephen W.; Tatam, Ralph P.; Heidi, Ottevaere; Peter, DeWolf; Diederik, S. Wiersma
    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 eliminates polarisation fading. An optical circulator is used in our system to route light efficiently from the source to the sample, and backscattered light from the sample and the fibre end through to the Mach-Zehnder processing interferometer. The choice of a Mach- Zehnder processing interferometer, from which both antiphase outputs are available, facilitates the incorporation of balanced detection, which often results in a large improvement in the Signal-to-Noise ratio (SNR) compared with the use of a single detector. Balanced detection comprises subtraction of the two antiphase interferometer outputs, implying that the signal amplitude is doubled and the noise is well reduced. It has been discerned that the SNR drops when the refractive index variation at a boundary is small. Several OCT images of samples (resin, resin + crystals, fibre composite) are presented.
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    Optical fibre Fizeau-based OCT
    (SPIE - International Society for Optics and Photonics, 2004-06-09) Casaubieilh, P.; Ford, Helen D.; Tatam, Ralph P.
    An optical fibre, Fizeau configuration Optical Coherence Tomography (OCT) system is presented in this paper. The interferometer is formed between the distal end of the sample-arm fibre and the sample itself. This ensures 'downlead insensitivity' ; polarisation variation is not a problem, as it is in the standard Michelson configuration. Path-length matching is performed by a secondary, bulk-optic scanning Mach-Zehnder interferometer. In this paper, we demonstrate the use of an optical circulator and balanced detection to permit optimum use of the light and maximise the signal-tonoise ratio.