788 research outputs found
Dispersive Fourier Transformation for Versatile Microwave Photonics Applications
Abstract: Dispersive Fourier transformation (DFT) maps the broadband spectrum of an ultrashort optical pulse into a time stretched waveform with its intensity profile mirroring the spectrum using chromatic dispersion. Owing to its capability of continuous pulse-by-pulse spectroscopic measurement and manipulation, DFT has become an emerging technique for ultrafast signal generation and processing, and high-throughput real-time measurements, where the speed of traditional optical instruments falls short. In this paper, the principle and implementation methods of DFT are first introduced and the recent development in employing DFT technique for widespread microwave photonics applications are presented, with emphasis on real-time spectroscopy, microwave arbitrary waveform generation, and microwave spectrum sensing. Finally, possible future research directions for DFT-based microwave photonics techniques are discussed as well
Spectral broadening of frequency combs via pulse apodization prior to nonlinear propagation
This thesis focuses on specific methods for spectrally broadening large repetition rate frequency combs using the idea that tailoring the shape of the seed pulse prior to nonlinear propagation will result in a spectrally flatter comb. A spectrally flat comb is desired for applications in optical communications, arbitrary waveform generation, and microwave photonic filtering. Three experimental setups using Fourier transform pulse shapers, Dispersion Decreasing Fiber (DDF) or Highly Nonlinear Fiber (HNLF) as the nonlinear propagation media were performed. Simulations employing the Split Step Fourier Method to solve the Nonlinear Schrödinger Equation were performed to analyze the experimental results. The first experiments employed DDF to produce a compressed pulse via Adiabatic Soliton Compression. This pulse was launched into the second stage and HNLF broadened the comb spectrum via Self Phase Modulation. A promising 130nm broadened comb spectrum was returned. The next experiments showed that, by apodizing the pulse produced by the optoelectronic frequency comb generator prior to propagation in HNLF, a flatter broadened comb spectrum was returned. These results were extended to a two-stage setup. The setup used two stages of HNLF. Sech apodization in the first stage and parabolic apodization in the second stage led to promising simulation results. With the insight gained by the simulations, experiments were performed and a flat broadened frequency comb led to applications in RF photonic filtering. An RF photonic phase filter was implemented with the comb generated as the source, and pulse compression experiments were performed
Harnessing optical micro-combs for microwave photonics
In the past decade, optical frequency combs generated by high-Q
micro-resonators, or micro-combs, which feature compact device footprints, high
energy efficiency, and high-repetition-rates in broad optical bandwidths, have
led to a revolution in a wide range of fields including metrology, mode-locked
lasers, telecommunications, RF photonics, spectroscopy, sensing, and quantum
optics. Among these, an application that has attracted great interest is the
use of micro-combs for RF photonics, where they offer enhanced functionalities
as well as reduced size and power consumption over other approaches. This
article reviews the recent advances in this emerging field. We provide an
overview of the main achievements that have been obtained to date, and
highlight the strong potential of micro-combs for RF photonics applications. We
also discuss some of the open challenges and limitations that need to be met
for practical applications.Comment: 32 Pages, 13 Figures, 172 Reference
Photonic Time-Stretch Enabled High Throughput Microwave and MM-Wave Interferometry Applied to Fibre Grating Sensors and Non-Contact Measurement
The research presented in this thesis is focused towards developing real-time, high-speed applications, employing ultrafast optical microwave generation and characterisation techniques. This thesis presents a series of experiments wherein mode-locked laser pulses are utilised. Photonics-based microwave and MM-Wave generation and detection are explored and employed for applications pertaining to fibre grating sensors and non-contact measurement. The application concepts leverage techniques from optical coherence tomography and non-destructive evaluation of turbid media. In particular, I use the principle of dispersion-induced photonic Time-Stretch to slow down high-speed waveforms to speeds usable by state-of-the-art photo-detectors and digital signal processors. The concept of photonic time-stretch is applied to map instantaneous microwave frequency to the time instant of the signal, which in turn is related to spatial location as established by the space-wavelength-time conversions. The experimental methods applied throughout this thesis is based upon Michelson interferometer architecture.
My original contribution to knowledge is the realisation of Photonics-based, single tone, and chirped microwave and MM-Wave pulse generation applied to deciphering physical strain profile along the length of a chirped fibre Bragg grating employed in a Michelson interferometer configuration. This interrogation scheme allows intra-grating high-resolution, high-speed, and temperature independent strain measurement. This concept is further extended to utilise photonic generation of microwave pulses to characterise surface profile information of thin film and thin plate infrared transparent slides of variable thickness setup in a Michelson interferometer architecture. The method basis for photonically generated high-frequency microwave signals utilises the principle of photonic Time-Stretch. The research was conducted in the Photonics Lab at the University of Kent. In addition, the photonically generated microwave/ MM-Wave pulses is utilised as a potential broadband frequency-swept source for non-contact measurement of turbid media. Investigation of the proof-of-concept based on an MM-Wave coherence tomography set-up is implemented at Vrije Universiteit Brussel (VUB), Department of Electronics and Informatics (ETRO)
Photonic processing of microwave signals
La distribution par fibre optique de signaux de type « ultra-wideband (UWB)» requiert le développement de nouvelles technologies photoniques qui seront le sujet d'étude de cette thÚse. Nous commençons avec un démonstration expérimentale d'une technique de sculpture d'impulsions qui offre une solution économique et à faible consommation de puissance pour les systÚmes UWB . Dans cette étude, nous procédons à l'apodisation de deux réseaux Bragg identiques avec une variation de période linéaire qui sont placés aux deux entrées d'un photodétecteur balancé. L'apodisation est réalisée par l'application d'un profile de température à l'aide d'éléments résistif de petite dimensions, ce qui permet une consommation énergétique réduite et une bonne résolution spectrale. Le filtrage spectral d'une source laser puisée suivi d'une conversion fréquence-temps par propagation dans une fibre optique standard permet de générer une impulsion UWB efficace d'un point de vue énergétique pour les communications à courte portée dans la bande spectrale de 3 a 10 GHz. Dans un deuxiÚme temps, pour générer des signaux passe-bande à haute fréquence, nous avons utilisé un laser puisé à commutation de gain. AprÚs la conversion optique/électrique des impulsions en utilisant des filtres optiques et RF appropriés, nous réussissons à générer des signaux large bande dans des bandes spectrales ayant des fréquences centrales de 25, 35 et 45 GHz. Nous examinons diverses configurations de filtres permettant cette conversion selon qu'il y ait ou non transmission dans une fibre optique. Finalement, nous démontrons la détection de signaux RF dans le domaine optique par le design et la fabrication de filtres adaptés. Notre récepteur utilise un modulateur de Mach-Zehnder pour faire la conversion électrique-optique et des filtres à base de réseau de Bragg comme filtres adaptés. Nous examinons la performance du récepteur pour deux conditions de polarisation différentes du Mach-Zehnder. Nous avons conçu des filtres adaptés pour ces deux cas et nous discutons de la performance résultant
Generation and optimization of picosecond optical pulses for use in hybrid WDM/OTDM networks
The burgeoning demand for broadband services such as database queries, home shopping, video-on-demand, remote education, telemedicine and videoconferencing will push the existing networks to their limits. This demand was mainly fueled by the brisk proliferation of Personal Computers (PC) together with the exceptional increases in their storage capacity and processing capabilities and the widespread availability of the internet. Hence the necessity, to develop high-speed optical technologies in order to construct large capacity networks, arises. Two of the most popular multiplexing techniques available in the optical domain that are used in the building of such high capacity networks, are Wavelength Division Multiplexing (WDM) and Optical Time Division Multiplexing (OTDM). However merging these two techniques to form very high-speed hybrid WDM/OTDM networks brings about the merits of both multiplexing technologies.
This thesis examines the development of one of the key components (picosecond optical pulses) associated to such high-speed systems. Recent analysis has shown that RZ format is superior to conventional NRZ systems as it is easier to compensate for dispersion and nonlinear effects in the fibre by employing soliton-like propagation. In addition to this development, the use of wavelength tunability for dynamic provisioning is another area that is actively researched on. Self-seeding of a gain switched Fabry Perot laser is shown to one of the simplest and cost effective methods of generating, transform limited optical pulses that are wavelength tunable over very wide ranges. One of the vital characteristics of the above mentioned pulse sources, is their Side Mode Suppression Ratio (SMSR). This thesis examines in detail how the pulse SMSR affects the performance of high-speed WDM/OTDM systems that employ self-seeded gain-switched pulse sources
Retrieval of phase relation and emission profile of quantum cascade laser frequency combs
The major development recently undergone by quantum cascade lasers has
effectively extended frequency comb emission to longer-wavelength spectral
regions, i.e. the mid and far infrared. Unlike classical pulsed frequency
combs, their mode-locking mechanism relies on four-wave mixing nonlinear
processes, with a temporal intensity profile different from conventional
short-pulses trains. Measuring the absolute phase pattern of the modes in these
combs enables a thorough characterization of the onset of mode-locking in
absence of short-pulses emission, as well as of the coherence properties. Here,
by combining dual-comb multi-heterodyne detection with Fourier-transform
analysis, we show how to simultaneously acquire and monitor over a wide range
of timescales the phase pattern of a generic frequency comb. The technique is
applied to characterize a mid-infrared and a terahertz quantum cascade laser
frequency comb, conclusively proving the high degree of coherence and the
remarkable long-term stability of these sources. Moreover, the technique allows
also the reconstruction of electric field, intensity profile and instantaneous
frequency of the emission.Comment: 20 pages. Submitted to Nature Photonic
Optical frequency comb technology for ultra-broadband radio-frequency photonics
The outstanding phase-noise performance of optical frequency combs has led to
a revolution in optical synthesis and metrology, covering a myriad of
applications, from molecular spectroscopy to laser ranging and optical
communications. However, the ideal characteristics of an optical frequency comb
are application dependent. In this review, the different techniques for the
generation and processing of high-repetition-rate (>10 GHz) optical frequency
combs with technologies compatible with optical communication equipment are
covered. Particular emphasis is put on the benefits and prospects of this
technology in the general field of radio-frequency photonics, including
applications in high-performance microwave photonic filtering, ultra-broadband
coherent communications, and radio-frequency arbitrary waveform generation.Comment: to appear in Laser and Photonics Review
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