Browsing by Author "Wiseman, Kieran B."

Now showing 1 - 6 of 6
  • No Thumbnail Available
    ItemOpen Access
    Data "OFS 2025 Manuscript Data - FSI Humidity Sensors"
    (Cranfield University, 2024-12-13) Wiseman, Kieran B.; James, Steve; Tatam, Ralph
    This research demonstrates a novel approach to distributed humidity sensing using polyimide-coated optical fibres and fibre segment interferometry (FSI). FSI interrogates the cumulative strain along fibre segments formed between pairs of FBG reflectors, significantly enhancing sensitivity by scaling with segment length. Polyimide, a hygroscopic coating material, induces strain on the optical fibre in response to humidity changes, creating measurable phase shifts. Experiments were conducted using an FSI array comprising three 10 mm fibre segments, with polyimide coatings on two segments and the third uncoated for control. This work highlights the advantages of FSI over direct FBG interrogation, including increased sensitivity, scalability, and reduced complexity of interrogation hardware.
  • Thumbnail Image
    ItemOpen Access
    Highly linear, compact and cost-effective sensor probes for displacement measurements using range-resolved interferometry
    (EUSPEN, 2021-06-10) Kissinger, Thomas; Wiseman, Kieran B.; Tatam, Ralph P.
    We demonstrate a novel approach for interferometric displacement and vibration sensing using range-resolved interferometry (RRI). The concept exploits the ability of RRI to reject the signal contributions due to multiple reflections that would otherwise lead to high levels of periodic non-linearity errors, allowing the use of very compact and cost-effective sensor heads based on gradient index (GRIN) lenses, with the presented approach thought to be widely applicable across many precision engineering applications.
  • Thumbnail Image
    ItemOpen Access
    Long-term wavelength stabilisation of widely modulated lasers
    (SPIE, 2023-08-15) Wiseman, Kieran B.; Kissinger, Thomas; Tatam, Ralph P.
    In this paper, we present a novel technique for stabilisation of widely wavelength modulated lasers (>100pm) over long time scales, where modulation depths exceed the spectral width of standard reference features, such as gas absorption lines, by over an order of magnitude. The technique operates by controlling the temporal separation between successive appearances of a gas absorption line on the up and down sweeps of a sinusoidal laser wavelength modulation waveform. The influence of the signal distortions introduced by the laser intensity modulation that are associated with laser diode injection current modulation are also addressed. The technique is applied to a range-resolved interferometric system interrogating a Mach-Zehnder interferometer operating in thermally stable conditions, using an absorption feature from a fibre-coupled gas cell as a reference. Proof-of-principle measurement results achieved using this technique are presented, demonstrating a notional fractional stability of 3.9×10−7 without further correction.
  • Thumbnail Image
    ItemOpen Access
    Optical fibre-coupled displacement and angle measurements using range-resolved interferometry
    (euspen, 2021-07-10) Wiseman, Kieran B.; Kissinger, Thomas; Tatam, Ralph P.
    A novel approach to displacement and angle measurements that uses range-resolved interferometry to interrogate multiple interferometers is presented. Spatially offset beams are multiplexed onto the same delivery fibre using a very simple setup comprising of two stacked beamsplitters and the phase evaluation of these interferometers allows simultaneous measurement of both displacement and angular changes of a target surface. The operating principle of this technique and key design concepts are discussed. This approach, with its simple and compact fibre-coupled optical setup and ease of alignment, expands existing applications of laser interferometry, particularly for space-restricted environments, and its cost-effectiveness will be key to allowing widespread usage.
  • Thumbnail Image
    ItemOpen Access
    Three-dimensional interferometric stage encoder using a single access port
    (Elsevier, 2020-08-30) Wiseman, Kieran B.; Kissinger, Thomas; Tatam, Ralph P.
    We present a novel multi-dimensional positional encoder approach that uses range-resolved interferometry (RRI) to simultaneously interrogate multiple interferometers differing in optical path length, using only a single photo detector and a single diode laser. Employing only stage-mounted non-polarising beamsplitters and reflections from three orthogonal, externally mounted, planar mirrors, three Cartesian measurement directions are formed, that when combined with measurements from a stage-mounted reference reflection, allow for three-dimensional measurements of stage motion obtained via a single access port. Through a variety of movements of a three-dimensional Piezo-electric stage over its nominal stage working range of ± 50 μm, simultaneous measurements of displacements from three orthogonal dimensions are acquired with a 10 kHz quadrature bandwidth, achieving typical displacement noise densities of below 0.4 nm/√Hz with the noise floor dropping to below 0.1 nm/√Hz above 50 Hz, as well as high linearity with cyclic errors amplitudes well below 1 nm in all three directions.
  • Thumbnail Image
    ItemOpen Access
    Two-dimensional remote interferometric stage encoder through a single access port using range-resolved interferometry
    (SPIE, 2019-06-21) Wiseman, Kieran B.; Kissinger, Thomas; Tatam, Ralph P.
    In this work, using our range-resolved interferometry (RRI) signal processing technique, we present a novel approach to multidimensional displacement measurements using only a single optical access port and very simple optical setup. By utilising surface reflections from a stage-mounted moving beamsplitter and two orthogonal stationary reference mirrors, two interferometers for the two Cartesian measurement directions are formed. With RRI, the interferometric phase signals of both interferometers can be independently demodulated, allowing simultaneous measurements of displacement in both dimensions using a single continuous-wave laser diode source and a single photodetector. In this paper, the capabilities of this approach are demonstrated using a proof-of-concept experiment with a multidimensional Piezoelectric stage performing a variety of stage movements. Measurements of displacements over a nominal stage working range of ±50μm are presented, demonstrating independent, simultaneous displacement measurements of two dimensions. The presented measurements show nanometer-level displacement resolutions with typical noise densities of 0.02 nm/√Hz over a 21 kHz bandwidth. It is thought that this approach could offer an interesting alternative to existing interferometric techniques for multi-dimensional metrology, benefiting from both simplicity and cost-effectiveness whilst maintaining the advantages that make optical techniques attractive to scientific and industrial applications.