32 research outputs found
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Observing mode-dependent wavelength-to-time mapping in few-mode fibers using a single-photon detector array
Wavelength-to-time mapping (WTM)—stretching ultrashort optical pulses in a dispersive medium such that the instantaneous frequency
becomes time-dependent—is usually performed using a single-mode fiber. In a number of applications, such as time-stretch imaging (TSI),
the use of this single-mode fiber during WTM limits the achievable sampling rate and the imaging quality. Multimode fiber based WTM
is a potential route to overcome this challenge and project a more diverse range of light patterns. Here, we demonstrate the use of a twodimensional
single-photon avalanche diode (SPAD) array to image, in a time-correlated single-photon counting (TCSPC) manner, the
time- and wavelength-dependent arrival of different spatial modes in a few-mode fiber. We then use a TCSPC spectrometer with a onedimensional
SPAD array to record and calibrate the wavelength-dependent and mode-dependent WTM processes. The direct measurement
of the WTM of the spatial modes opens a convenient route to estimate group velocity dispersion, differential mode delay, and the effective
refractive index of different spatial modes. This is applicable to TSI and ultrafast optical imaging, as well as broader areas such as
telecommunications
Solitary pulmonary nodule imaging approaches and the role of optical fibre-based technologies
Sub millimetre flexible fibre probe for background and fluorescence free Raman spectroscopy
Using the shifted-excitation Raman difference spectroscopy technique and an
optical fibre featuring a negative curvature excitation core and a coaxial ring
of high numerical aperture collection cores, we have developed a portable,
background and fluorescence free, endoscopic Raman probe. The probe consists of
a single fibre with a diameter of less than 0.25 mm packaged in a
sub-millimetre tubing, making it compatible with standard bronchoscopes. The
Raman excitation light in the fibre is guided in air and therefore interacts
little with silica, enabling an almost background free transmission of the
excitation light. In addition, we used the shifted-excitation Raman difference
spectroscopy technique and a tunable 785 nm laser to separate the fluorescence
and the Raman spectrum from highly fluorescent samples, demonstrating the
suitability of the probe for biomedical applications. Using this probe we also
acquired fluorescence free human lung tissue data
Demonstrating the Use of Optical Fibres in Biomedical Sensing:A Collaborative Approach for Engagement and Education
This paper demonstrates how research at the intersection of physics, engineering, biology and medicine can be presented in an interactive and educational way to a non-scientific audience. Interdisciplinary research with a focus on prevalent diseases provides a relatable context that can be used to engage with the public. Respiratory diseases are significant contributors to avoidable morbidity and mortality and have a growing social and economic impact. With the aim of improving lung disease understanding, new techniques in fibre-based optical endomicroscopy have been recently developed. Here, we present a novel engagement activity that resembles a bench-to-bedside pathway. The activity comprises an inexpensive educational tool ($70) adapted from a clinical optical endomicroscopy system and tutorials that cover state-of-the-art research. The activity was co-created by high school science teachers and researchers in a collaborative way that can be implemented into any engagement development process
Computational Fluorescence Suppression in Shifted Excitation Raman Spectroscopy
Fiber-based Raman spectroscopy in the context of <italic>in vivo</italic> biomedical application suffers from the presence of background fluorescence from the surrounding tissue that might mask the crucial but inherently weak Raman signatures. One method that has shown potential for suppressing the background to reveal the Raman spectra is shifted excitation Raman spectroscopy (SER). SER collects multiple emission spectra by shifting the excitation by small amounts and uses these spectra to computationally suppress the fluorescence background based on the principle that Raman spectrum shifts with excitation while fluorescence spectrum does not. We introduce a method that utilizes the spectral characteristics of the Raman and fluorescence spectra to estimate them more effectively, and compare this approach against existing methods on real world datasets.</p
Biomedical fibre optic time-correlated single-photon counting spectroscopy with CMOS SPAD line arrays
In times of economic constraint, an ageing population and antimicrobial
resistance, medical challenges must be met by exploring new pathways to
improve diagnostics, prevention and specialised treatments. Lung diseases
include a wide range of conditions and exhibit high morbidity and mortality
rates, especially for actively ventilated patients in intensive care units.
The aim of this PhD is to develop systems for endoscopic sensing in size
restricted regions such as the alveolar space in the distal lung. The systems are
based on miniaturised and disposable single optical fibres and a custom CMOS
SPAD line sensor capable of time-resolved single photon detection. Standard
optical fibres are suitable for single-use medical devices and allow access
to remote locations in the lung. Applying advanced time-resolving detector
technology has the potential to overcome common limitations of intensity-based
spectroscopy. Two common sensing technologies – Raman and fluorescence
spectroscopy – are investigated. Fluorescence spectroscopy is a powerful tool
for tissue diagnostics providing insight into the molecular composition and
local environment through changes in the fluorescence intensity, spectral
properties, and lifetime. Raman spectroscopy reveals the chemical ‘fingerprint’
of molecules under investigation, but is impeded by an inherently weak signal.
The visibility of the Raman signal can be significantly enhanced by utilising
the different time profiles of unwanted background signals and the Raman
signal. The systems are exemplified for differentiating normal and abnormal
tissue, detecting pathogens and measuring key physiological parameters such
as pH, facilitated by fluorescent markers and Raman reporters. Time-resolved
fluorescence lifetime spectroscopy successfully demonstrates its potential for
pH-sensing, distinguishing between normal and tumorous tissue, and detecting
fluorescent labelled bacteria, all through a miniaturised optical fibre. Time-gated
Raman spectroscopy enables pH-sensing with Raman reporters, functionalised
gold nanoshells deposited on the fibre tip, with an improved pH sensitivity of
0.06 pH unit
Code and Data accompanying "pH sensing through a single optical fibre using SERS and CMOS SPAD line arrays"
Full exploitation of fibre Raman probes has been limited by the obstruction of weak Raman signals by background fluorescence of the sample and the intrinsic Raman signal of the delivery fibre. Here we utilised functionalised gold nanoshells (NS) to take advantage of the surface-enhanced Raman spectroscopy (SERS) effect to enhance the pH responsive spectrum of 4-mercaptobenzoic acid (MBA), however fibre background is still dominant. Using the photon arrival time-resolving capability of a CMOS single photon avalanche diode (SPAD) based line sensor we recover the SERS spectrum without fibre background in a 10 s measurement. In this manner, pH sensing through a multimode fibre at a low excitation power, that is safe for future in vivo applications, with short acquisition times (10 or 60 s) is demonstrated. A measurement precision of ±0.07 pH units is thus achieved.Katjana, Ehrlich. (2017). Code and Data accompanying "pH sensing through a single optical fibre using SERS and CMOS SPAD line arrays", [dataset]. University of Edinburgh. College of Medicine and Veterinary Medicine. Queen's Medical Research Institute. http://dx.doi.org/10.7488/ds/2241