New opportunities for integrated microwave photonics

Recent advances in photonic integration have propelled microwave photonic technologies to new heights. The ability to interface hybrid material platforms to enhance light-matter interactions has led to the developments of ultra-small and high-bandwidth electro-optic modulators, frequency synthesizers with the lowest noise, and chip signal processors with orders-of-magnitude enhanced spectral resolution. On the other hand, the maturity of high-volume semiconductor processing has finally enabled the complete integration of light sources, modulators, and detectors in a single microwave photonic processor chip and has ushered the creation of a complex signal processor with multi-functionality and reconfigurability similar to their electronic counterparts. Here we review these recent advances and discuss the impact of these new frontiers for short and long term applications in communications and information processing. We also take a look at the future perspectives in the intersection of integrated microwave photonics with other fields including quantum and neuromorphic photonics

InP integrated optical frequency comb generator using an amplified recirculating loop

A novel realisation of photonically integrated optical frequency comb generation is demonstrated on indium phosphide (InP) using a generic foundry platform. The architecture, based on the amplified recirculating loop technique, consists of cascaded electro-optic phase modulators embedded within a short waveguide loop. While an injected continuous wave laser signal is recirculated by the loop, the modulators are driven with a modulation frequency corresponding to the round-trip loop length frequency. This results in many phase coherent, evenly spaced optical comb lines being generated. The choice of InP as an integration platform allows immediate optical amplification of the modulated signal by embedded semiconductor optical amplifiers, enabling loop losses to be compensated and expanding the comb across broad optical bandwidths. This approach reduces the requirement for external, high-power optical amplifiers, improving the compactness and power efficiency of the full system. The system was modelled to identify off-resonance behaviour, outlining limits in matching both the modulation frequency and seed laser frequency to the round-trip loop frequency for optimal comb line generation to be achieved. The experimental device occupied a fraction of the 6 x 2 mm2 InP chip and operated at round-trip loop frequencies of 6.71 GHz to produce 59 comb lines within a 20 dB power envelope. All comb lines exhibited strong phase coherence as characterised by low composite phase noise measurements of -105 dBc/Hz at 100 kHz. A second device is also presented with a shorter loop length operating at ~10 GHz which generated 57 comb lines. Both loop configurations included short waveguide phase shifters providing a degree of tunability of the free spectral range with a tuning range of 150 MHz for small injection currents of less than 2.5 mA.This research work has been supported by the UK Engineering and Physical Sciences Research Council (EPSRC) through the Integrated Photonics and Electronic Systems (IPES) Centre of Doctoral Training and PICSat project (EPSRC Reference: EP/S000976/1)

Estudio de dispositivos integrados fotónicos para la generación de peines de frecuencias ópticas

Esta tesis presenta los avances realizados en el desarrollo de diferentes estructuras de generación de peines de frecuencias ópticas (OFCG) utilizando plataformas genéricas de integración fotónica. Presentamos el desarrollo, evaluación y caracterización de un circuito integrado fotónico que implementa un generador de peine de frecuencias ópticas basado en un lazo amplificado con modulación de fase. El diseño se basa en los bloques funcionales de una plataforma de integración fotónica genérica. El circuito incluye una fuente interna por medio de un láser DBR (Distributed Bragg Reflector) para estudiar un OFCG totalmente integrado. Describimos el desarrollo de un OFCG basado en un láser anillo mode locked pasivo monolíticamente integrado, fabricado en una plataforma tecnológica de integración fotónica genérica, en una ronda de fabricación (Multi-Project Wafer), compartiendo costos con otros usuarios, utilizando los bloques funcionales estándares ofrecidos. El dispositivo se basa en una estructura láser mode-locked pasivo que incluye un interferómetro Mach-Zehnder (MZI) que controla la planitud del espectro de salida del peine generado, obteniéndose un gran ancho de banda óptico de 1.08 THz. Presentamos el diseño y caracterización experimental de circuitos integrados fotónicos de baja frecuencia para la generación y distribución de patrones de frecuencia y señales de calibración en el rango de 2 GHz y 14 GHz, con baja tasa de repetición de 2.7 GHz. El chip ha sido fabricado sobre la plataforma de integración fotónica genérica. El dispositivo de baja frecuencia, opera bien en régimen mode-locked pasivo o bien en ML híbrido, generando peines eléctricos de estrecho ancho espectral del tono de batido de radiofrecuencia. También exponemos el estudio del ruido de fase en un OFCG. Realizamos las mediciones en el láser mode locked de baja frecuencia, para investigar la calidad y estabilidad de la señal, variando las condiciones de operación del dispositivo tales como: corriente del amplificador, potencia de salida y regímenes de trabajo. Finalmente presentamos las conclusiones obtenidas del trabajo de investigación y planteamos las líneas de trabajo de investigación futuras.This thesis presents the progress made in the development of different optical frequency combs generators (OFCG) using generic photonic integration platforms. We present the design, evaluation and characterization of a photonic integrated circuit that implements an OFCG based on an amplified loop with phase modulation. The design is based on the building blocks of a generic photonic integration platform. The circuit includes an on chip source by means of a Distributed Bragg Reflector (DBR) laser to study fully integrated OFCG. We describe the development of an OFCG based on a monolithically integrated passive mode locked ring laser fabricated in a generic photonic integration platform, in a Multi-Project Wafer (MPW) run, sharing costs with other users and using standardized building blocks. The photonic integrated circuit is based on a passive mode-locked ring laser architecture, which includes a Mach-Zehnder Interferometer (MZI) to flatten the spectral shape of the comb output. We obtain a high optical bandwidth of 1.08 THz. We present the design and experimental characterization of the long cavity photonic integrated circuits to generation and distribution frequency standards and calibration signals. The frequency range of our interest is from 2 GHz to 14 GHz, with low repetition rate (2.7 GHz). The chip was fabricated in a generic photonic integration platform. The long cavity device operates in both regime passive and hybrid modelocked, generating electrical combs with very narrow radio frequency linewidth of the beat note. Also we expose phase noise study in an OFCG. We do the measurements in the long cavity mode locked laser, in order to investigate the quality and stability signal, changing the device operation conditions like as: amplifier current, output power and work regimes. Finally, we present the conclusions of this thesis and propose the future working lines.Programa Oficial de Doctorado en Ingeniería Eléctrica, Electrónica y AutomáticaPresidente: Ana Pilar González Marcos.- Secretario: Horario Lamela Rivera.- Vocal: Pedro Corredera Guillé

High Speed All Optical Switching and Encryption using Ultrafast Devices

The next generation of fiber-optic communication system demands ultra-high speed data processing and switching components. Conventional electro-optical parts have reached their bottleneck both speed-wise and efficiency-wise. The idea of manipulating high speed data in all-optical domain is gaining more popularity. In this PhD dissertation, I showed the design and performance analysis of two kinds of ultra-fast all-optical latches, Set-Reset latch and D-flip-flop, based on two different schemes: (1) cross gain and phase modulation (XGM and XPM) in quantum dot semiconductor optical amplifiers (QD-SOA) and (2) two-photon absorption (TPA) in bulk semiconductor optical amplifiers. Design and simulation of a scheme to realize high speed all-optical encryption and decryption using key-stream generators and XOR gates based on QD-SOA are included in this dissertation. We also proposed and simulated all-optical Boolean logic functions with improved output quality using binary phase shift keyed signal based on QD-SOA. A fiber ring laser system with charcoal nano-particles as saturable absorber inside the cavity has been designed and experimentally demonstrated. This fiber ring laser system can generate optical pulse train @ 20Gb/s with improved stability and smaller pulse width comparing with the system without nano-particles in the cavity

Microwave Photonic Applications - From Chip Level to System Level

Die Vermischung von Mikrowellen- und optischen Technologien – Mikrowellenphotonik – ist ein neu aufkommendes Feld mit hohem Potential. Durch die Nutzung der Vorzüge beider Welten hat die Mikrowellenphotonik viele Anwendungsfälle und ist gerade erst am Beginn ihrer Erfolgsgeschichte. Der Weg für neue Konzepte, neue Komponenten und neue Anwendungen wird dadurch geebnet, dass ein höherer Grad an Integration sowie neue Technologien wie Silicon Photonics verfügbar sind. In diesem Werk werden zuerst die notwendigen grundlegenden Basiskomponenten – optische Quelle, elektro-optische Wandlung, Übertragungsmedium und opto-elektrische Wandlung – eingeführt. Mithilfe spezifischer Anwendungsbeispiele, die von Chipebene bis hin zur Systemebene reichen, wird der elektrooptische Codesign-Prozess veranschaulicht. Schließlich werden zukünftige Ausrichtungen wie die Unterstützung von elektrischen Trägern im Millimeterwellen- und THz-Bereich sowie Realisierungsoptionen in integrierter Optik und Nanophotonik diskutiert.The hybridization between microwave and optical technologies – microwave photonics – is an emerging field with high potential. Benefitting from the best of both worlds, microwave photonics has many use cases and is just at the beginning of its success story. The availability of a higher degree of integration and new technologies such as silicon photonics paves the way for new concepts, new components and new applications. In this work, first, the necessary basic building blocks – optical source, electro-optical conversion, transmission medium and opto-electrical conversion – are introduced. With the help of specific application examples ranging from chip level to system level, the electro-optical co-design process for microwave photonic systems is illustrated. Finally, future directions such as the support of electrical carriers in the millimeter wave and THz range and realization options in integrated optics and nanophotonics are discussed

Photonic Crystal Optical Frequency Combs

Nanophotonics, driven by low processing power and high-density integration, is emerging as the next logical step for photonic integrated circuits. Microwave photonics is a diverse research topic that is set to transform traditional microwave electronics. In this thesis, the two topics are combined by investigating the ability for nanophotonic devices to harbour and generate microwave photonic signals. Generating an optical frequency comb (OFC) plays a vital role in integrated microwave photonics. By investigating the different OFC generation methods as well as the capabilities offered in photonic crystal (PhC) devices, a method to produce an OFC from nanoscale devices is proposed. The proposal is modelled using calculations based on temporal coupled mode theory. Analysis shows that a broadband OFC can be produced using nanoscale devices that favour high-density integration. The experimental results in this thesis are based around three fundamental areas: PhC device fabrication, optical characterisation and microwave photonic characterisation. Each chapter builds towards the overarching theme of microwave photonic signal processing at telecommunication wavelengths in a nanophotonic device. A new fabrication process for etching PhC structures in nonthermalised InP samples is developed. The developed process has excellent applications in fabrication where the use of thermal grease or a high sample stage temperature is impractical. Optical characterisation of the fabricated samples shows the effects of lithographic and photothermal tuning on the cavity mode frequency. Through this analysis, resonant cavity modes can be designed for a working wavelength within the telecommunication bandwidth. Temporal analysis shows that carrier lifetimes from a QD ensemble that spectrally and spatially overlaps with the PhC cavity are greatly reduced. Finally, a new measurement set-up is proposed and analysed for the characterisation of microwave photonic signals in nanoscale devices. It is shown that the integration of an ultra-fast laser and a two-arm Mach-Zehnder interferometer can generate a microwave signal within the spectrum of the ultra-fast laser. This signal is integrated into the standard optical characterisation set-up, where it is used to excite PhC optical devices. The results show that the microwave signal present in the ultra-fast laser can be resolved in the emission spectrum of QDs weakly coupled to a PhC cavity