117 research outputs found
Spatial and spectral brightness improvement of single-mode laser diode arrays
This thesis addresses the strong need for efficient and compact techniques for brightness
enhancement of laser diode arrays and responds to the challenges created for high
performance optics and techniques for laser characterisation.
A novel optical inter-leaving method for a 7-bar stack of single-mode emitters,
providing a nearly 2-fold improvement in the slow axis beam parameter product,
enabling fibre-coupling, is demonstrated.
A laser-written dual-axis optics approach is used to perform challenging slow axis
collimation combined with fast axis correction for closely-packed 49-single-mode
emitter bars, to provide low-loss collimation with high pointing accuracy of less than
3% and 10% of a beam divergence in the fast and slow axis direction, respectively. This
produces excellent source for application beam-combined laser diode systems.
An emitter-by-emitter simultaneous analysis is used to provide spectra and far
field pointing for all emitters and evaluate the performance of various external cavity
configurations with Volume Holographic Gratings (VHGs). For the ultra-collimated
bars, high efficiency VHG-locking is shown to be maintained over enhanced range of
temperatures (>17˚C) and large laser-VHG distances (>110 mm). Highly effective
feedback enables the use of a folded cavity configuration for wavelength selection over
a range of 8 nm for the full 49-emitter bar, giving a prospect for multi-wavelength
single-VHG-locking of bars for cost-effective spectral combining. An innovative
technique of wavelength stepping by individually-formed folded cavities for 5 and 7
sections along the bar demonstrates a potential to produce a source for high
performance dense spectral beam combining.
In a VHG-based Talbot cavity, eight emitters are coherently locked with a highvisibility
interference pattern at 1W of output power. The results of phase-locking for
full 49-emitter bar show that the slow axis pointing variation of ± 2mrad produces
different supermodes, for a fixed alignment of the cavity, thus it must be additionally
corrected for further improvement
Fiber Optic Sensors and Fiber Lasers
The optical fiber industry is emerging from the market for selling simple accessories using optical fiber to the new optical-IT convergence sensor market combined with high value-added smart industries such as the bio industry. Among them, fiber optic sensors and fiber lasers are growing faster and more accurately by utilizing fiber optics in various fields such as shipbuilding, construction, energy, military, railway, security, and medical.This Special Issue aims to present novel and innovative applications of sensors and devices based on fiber optic sensors and fiber lasers, and covers a wide range of applications of optical sensors. In this Special Issue, original research articles, as well as reviews, have been published
Recent Progress in Optical Fiber Research
This book presents a comprehensive account of the recent progress in optical fiber research. It consists of four sections with 20 chapters covering the topics of nonlinear and polarisation effects in optical fibers, photonic crystal fibers and new applications for optical fibers. Section 1 reviews nonlinear effects in optical fibers in terms of theoretical analysis, experiments and applications. Section 2 presents polarization mode dispersion, chromatic dispersion and polarization dependent losses in optical fibers, fiber birefringence effects and spun fibers. Section 3 and 4 cover the topics of photonic crystal fibers and a new trend of optical fiber applications. Edited by three scientists with wide knowledge and experience in the field of fiber optics and photonics, the book brings together leading academics and practitioners in a comprehensive and incisive treatment of the subject. This is an essential point of reference for researchers working and teaching in optical fiber technologies, and for industrial users who need to be aware of current developments in optical fiber research areas
In-line fibre-optic laser doppler velocimeter using bragg grating interferometric filters as frequency to intensity transducers
Three dimensional complex flows particularly those of turbomachinery present
challenges to current measurement technology in terms of restricted optical access,
measurement accuracy for the on-axis velocity component, the need to resolve flow
turbulence and measurement difficulty from close to surface or intra-channel
measurements in rotating machinery.
A novel non-intrusive in-line fibre-optic laser Doppler velocimeter is presented
specifically for the measurement of the on-axis component of velocity. The
measurement principle is based on a Doppler frequency to intensity transducer in the
form of a fibre-optic Bragg grating based Fabry-Perot interferometric filter. The filters
were fabricated at 514.5 nm but in principle any desired wavelength may be used thus
permitting any laser wavelength source to be used. Filters with appropriate features
were designed with the aid of the theoretical models based on the coupled mode
theory and transfer matrix approach.
The argon-ion laser emission wavelength was locked to a corresponding Doppler
broadened absorption line of molecular iodine vapour while the Fabry-Perot
interferometer phase was controlled in an independent feedback system using digital
lock-in amplifiers. The optical frequency was stabilized to within 10 MHz for at least
one hour while the phase was controlled to an equivalent of (within) ± 3 MHz in
frequency. Both feedback loops utilized custom designed PID electronic circuit
controllers. The bandwidth of the filter was tunable by up to 400 MHz, with a
resolution of between 0.2 ms'1 and 1 ms"1, and a sensitivity range of between 0.5
[GHz]'1 and 1.7 [GHz]'1. In this technique the filter was tuned to the optical
wavelength, rather than tuning the laser wavelength to match the filter. The finished
instrument was applied to the measurement of the on-axis component of velocity, of a
rotating disc, over an available range of up to ± 42 ms'1, limited only by the maximum
velocity of the disc. The detection system was reconfigured for low velocity
measurements at twice the sensitivity over a velocity range of ± 7 ms'1. This technique
demonstrates a unique contribution to fluid dynamics for the measurement of the
traditionally difficult in-line component of velocity.Ph
1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface
A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance
Dual beam swept source optical coherence tomography for microfluidic velocity measurements
Microfluidic flows are an increasing area of interest used for “lab-on-a-chip” bioanalytical
techniques, drug discovery, and chemical processing. This requires optical,
non-invasive flow-visualization techniques for characterising microfluidic flows. Optical
Coherence Tomography (OCT) systems can provide three-dimensional imaging
through reasonably-opaque materials with micrometre resolution, coupled to a single
optical axis point using optical fibre cables. Developed for imaging the human eye,
OCT has been used for the detection of skin cancers and endoscopically in the human
body. Industrial applications are growing in popularity including for the monitoring
of bond-curing in aerospace, for production-line non-destructive-testing, and for
medical device manufacturing and drug encapsulation monitoring.
A dual beam Optical Coherence Tomography system has been developed capable
of simultaneously imaging microfluidic channel structures, and tracking particles
seeded into the flow to measure high velocity flows, using only a single optical access
point. This is achieved via a dual optical fibre bundle for light delivery to the sample
and a custom high-speed dual channel OCT instrument using an akinetic sweep
wavelength laser. The system has 10 μm resolution in air and a sweeping rate of
96 kHz. This OCT system was used to monitor microfluidic flows in 800 μm deep
test chips and Poiseuille flows were observed
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Biosensors for Diagnosis and Monitoring
Biosensor technologies have received a great amount of interest in recent decades, and this has especially been the case in recent years due to the health alert caused by the COVID-19 pandemic. The sensor platform market has grown in recent decades, and the COVID-19 outbreak has led to an increase in the demand for home diagnostics and point-of-care systems. With the evolution of biosensor technology towards portable platforms with a lower cost on-site analysis and a rapid selective and sensitive response, a larger market has opened up for this technology. The evolution of biosensor systems has the opportunity to change classic analysis towards real-time and in situ detection systems, with platforms such as point-of-care and wearables as well as implantable sensors to decentralize chemical and biological analysis, thus reducing industrial and medical costs. This book is dedicated to all the research related to biosensor technologies. Reviews, perspective articles, and research articles in different biosensing areas such as wearable sensors, point-of-care platforms, and pathogen detection for biomedical applications as well as environmental monitoring will introduce the reader to these relevant topics. This book is aimed at scientists and professionals working in the field of biosensors and also provides essential knowledge for students who want to enter the field
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