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 thèse. 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 systèmes 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 deuxième temps, pour générer des signaux passe-bande à haute fréquence, nous avons utilisé un laser puisé à commutation de gain. Après 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

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)

Experimental Investigation Of Ultrawideband Wireless Systems: Waveform Generation, Propagation Estimation, And Dispersion Compensation

Ultrawideband (UWB) is an emerging technology for the future high-speed wireless communication systems. Although this technology offers several unique advantages like robustness to fading, large channel capacity and strong anti-jamming ability, there are a number of practical challenges which are topics of current research. One key challenge is the increased multipath dispersion which results because of the fine temporal resolution. The received response consists of different components, which have certain delays and attenuations due to the paths they took in their propagation from the transmitter to the receiver. Although such challenges have been investigated to some extent, they have not been fully explored in connection with sophisticated transmit beamforming techniques in realistic multipath environments. The work presented here spans three main aspects of UWB systems including waveform generation, propagation estimation, and dispersion compensation. We assess the accuracy of the measured impulse responses extracted from the spread spectrum channel sounding over a frequency band spanning 2-12 GHz. Based on the measured responses, different transmit beamforming techniques are investigated to achieve high-speed data transmission in rich multipath channels. We extend our work to multiple antenna systems and implement the first experimental test-bed to investigate practical challenges such as imperfect channel estimation or coherency between the multiple transmitters over the full UWB band. Finally, we introduce a new microwave photonic arbitrary waveform generation technique to demonstrate the first optical-wireless transmitter system for both characterizing channel dispersion and generating predistorted waveforms to achieve spatio-temporal focusing through the multipath channels

Panoramic-reconstruction temporal imaging for seamless measurements of slowly-evolved femtosecond pulse dynamics

Single-shot real-time characterization of optical waveforms with sub-picosecond resolution is essential for investigating various ultrafast optical dynamics. However, the finite temporal recording length of current techniques hinders comprehensive understanding of many intriguing ultrafast optical phenomena that evolve over a time scale much longer than their fine temporal details. Inspired by the space-time duality and by stitching of multiple microscopic images to achieve a larger field of view in the spatial domain, here a panoramic-reconstruction temporal imaging (PARTI) system is devised to scale up the temporal recording length without sacrificing the resolution. As a proof-of-concept demonstration, the PARTI system is applied to study the dynamic waveforms of slowly-evolved dissipative Kerr solitons in an ultrahigh-Q microresonator. Two 1.5-ns-long comprehensive evolution portraits are reconstructed with 740-fs resolution and dissipative Kerr soliton transition dynamics, in which a multiplet soliton state evolves into stable singlet soliton state, are depicted