A microwave channelizer and spectroscope based on an integrated optical Bragg-grating Fabry-Perot and integrated hybrid Fresnel lens system

A compact means to separate microwave and millimeter-wave optical signals by RF frequency in real time is demonstrated. The approach is to employ an integrated optical Bragg grating Fabry-Perot (BGFP) device to spatially separate optically modulated microwave signals with high resolution. The compactness is achieved through the use of an integrated optical hybrid diffractive lens beam expander to provide the required optical wavefront to the BGFP. A proof-of-principle measurement was performed from 1 to 23 GHz with peak finesse of 27. The theoretical analysis, fabrication procedure, experimental results, limitations, and improvements are described

Opto-VLSI processing for reconfigurable optical devices

The implementation of Wavelength Division Multiplexing system (WDM) optical fibre transmission systems has the potential to realise this high capacity data rate exceeding 10 Tb/s. The ability to reconfigure optical networks is a desirable attribute for future metro applications where light paths can be set up or taken down dynamically as required in the network. The use of microelectronics in conjunction with photonics enables intelligence to be added to the high-speed capability of photonics, thus realising reconfigurable optical devices which can revolutionise optical telecommunications and many more application areas. In this thesis, we investigate and demonstrate the capability of Opto-VLSI processors to realise a reconfigurable WDM optical device of many functions, namely, optical multiband filtering, optical notch filtering, and reconfigurable-Optical-Add-Drop Multiplexing (ROADM). We review the potential technologies available for tunable WDM components, and discuss their advantages and disadvantages. We also develop a simple yet effective algorithm that optimises the performance of Opto-VLSI processors, and demonstrate experimentally the multi-function WDM devices employing Opto-VLSI processors. Finally, the feasibility of Opto-VLSI-based WDM devices in meeting the stringent requirements of the optical communications industry is discussed

High capacity photonic integrated switching circuits

As the demand for high-capacity data transfer keeps increasing in high performance computing and in a broader range of system area networking environments; reconfiguring the strained networks at ever faster speeds with larger volumes of traffic has become a huge challenge. Formidable bottlenecks appear at the physical layer of these switched interconnects due to its energy consumption and footprint. The energy consumption of the highly sophisticated but increasingly unwieldy electronic switching systems is growing rapidly with line rate, and their designs are already being constrained by heat and power management issues. The routing of multi-Terabit/second data using optical techniques has been targeted by leading international industrial and academic research labs. So far the work has relied largely on discrete components which are bulky and incurconsiderable networking complexity. The integration of the most promising architectures is required in a way which fully leverages the advantages of photonic technologies. Photonic integration technologies offer the promise of low power consumption and reduced footprint. In particular, photonic integrated semiconductor optical amplifier (SOA) gate-based circuits have received much attention as a potential solution. SOA gates exhibit multi-terahertz bandwidths and can be switched from a high-gain state to a high-loss state within a nanosecond using low-voltage electronics. In addition, in contrast to the electronic switching systems, their energy consumption does not rise with line rate. This dissertation will discuss, through the use of different kind of materials and integration technologies, that photonic integrated SOA-based optoelectronic switches can be scalable in either connectivity or data capacity and are poised to become a key technology for very high-speed applications. In Chapter 2, the optical switching background with the drawbacks of optical switches using electronic cores is discussed. The current optical technologies for switching are reviewed with special attention given to the SOA-based switches. Chapter 3 discusses the first demonstrations using quantum dot (QD) material to develop scalable and compact switching matrices operating in the 1.55µm telecommunication window. In Chapter 4, the capacity limitations of scalable quantum well (QW) SOA-based multistage switches is assessed through experimental studies for the first time. In Chapter 5 theoretical analysis on the dependence of data integrity as ultrahigh line-rate and number of monolithically integrated SOA-stages increases is discussed. Chapter 6 presents some designs for the next generation of large scale photonic integrated interconnects. A 16x16 switch architecture is described from its blocking properties to the new miniaturized elements proposed. Finally, Chapter 7 presents several recommendations for future work, along with some concluding remark

Photonic wideband phased array: an optical time steered antenna based on a new true time delay unit

L’attività di ricerca svolta durante il corso di dottorato e descritta dettagliatamente all’interno della tesi è stata diretta al progetto di una innovativa rete ottica di formazione del fascio per antenne a schiera a banda larga esenti dal fenomeno del beam squint. La rete di formazione del fascio proposta è basata sull’utilizzo di un chip ottico integrato modulare che consente di realizzare il True Time Delay implementando switched delay lines. Le caratteristiche del sistema ne consentono l’utilizzo in architetture ad array e a subarray, e la sua modularità rende possibile, in principio, il pilotaggio del sistema radiante, integrando in un unico componente le linee di ritardo di ciascun elemento della schiera. Nella sua prima parte la tesi di dottorato introduce alle antenne ad alte prestazioni richieste dalle moderne applicazioni, focalizzando l’attenzione sui Phased Array, sistemi radianti destinati a svolgere un ruolo di primo piano grazie alla loro flessibilità e potenzialità. Un’analisi ragionata delle soluzioni proposte in letteratura viene, quindi, proposta al fine di evidenziare i principi di funzionamento e le principali problematiche connesse all’implementazione di reti ottiche di formazione del fascio. Inoltre, vengono descritte e discusse le architetture ottiche utilizzate sia per il controllo della fase che per il controllo del ritardo. Successivamente viene presentata la nuova unità ottica integrata di tipo True Time Delay. Le configurazioni di utilizzo del chip ottico studiate e messe a punto durante gli anni del corso di dottorato vengono presentate nel dettaglio, chiarendo le scelte e le strategie di progetto utilizzate in modo da ottimizzare le prestazioni del sistema. Viene presentato il progetto di un prototipo di antenna a schiera basato sul nuovo modulo True Time Delay e un modello accurato dell’intero sistema, implementato allo scopo di verificare il funzionamento dell’antenna e determinarne le prestazioni. Il modello sviluppato tiene in conto delle reali caratteristiche dei dispositivi disponibili in commercio da utilizzarsi all’interno della rete e del sistema radiante, degli inevitabili errori realizzativi relativi a ciascun componente e delle caratteristiche peculiari del nuovo modulo di ritardo. Per compensare gli effetti degli errori suddetti è stata prevista all’interno della rete un’unità di compensazione. Per rendere semplice ed efficace determinarne i parametri è stato sviluppato un algoritmo evolutivo capace di sfruttare al meglio le potenzialità dell’unità così da evitare inutili complessità. Infine, viene proposta una nuova architettura, interamente ottica, di una rete di formazione del fascio per antenne a schiera capaci di irradiare sia fasci somma che fasci differenza beam squint free

Advances in Optical Amplifiers

Optical amplifiers play a central role in all categories of fibre communications systems and networks. By compensating for the losses exerted by the transmission medium and the components through which the signals pass, they reduce the need for expensive and slow optical-electrical-optical conversion. The photonic gain media, which are normally based on glass- or semiconductor-based waveguides, can amplify many high speed wavelength division multiplexed channels simultaneously. Recent research has also concentrated on wavelength conversion, switching, demultiplexing in the time domain and other enhanced functions. Advances in Optical Amplifiers presents up to date results on amplifier performance, along with explanations of their relevance, from leading researchers in the field. Its chapters cover amplifiers based on rare earth doped fibres and waveguides, stimulated Raman scattering, nonlinear parametric processes and semiconductor media. Wavelength conversion and other enhanced signal processing functions are also considered in depth. This book is targeted at research, development and design engineers from teams in manufacturing industry, academia and telecommunications service operators

Optical Switching for Scalable Data Centre Networks

This thesis explores the use of wavelength tuneable transmitters and control systems within the context of scalable, optically switched data centre networks. Modern data centres require innovative networking solutions to meet their growing power, bandwidth, and scalability requirements. Wavelength routed optical burst switching (WROBS) can meet these demands by applying agile wavelength tuneable transmitters at the edge of a passive network fabric. Through experimental investigation of an example WROBS network, the transmitter is shown to determine system performance, and must support ultra-fast switching as well as power efficient transmission. This thesis describes an intelligent optical transmitter capable of wideband sub-nanosecond wavelength switching and low-loss modulation. A regression optimiser is introduced that applies frequency-domain feedback to automatically enable fast tuneable laser reconfiguration. Through simulation and experiment, the optimised laser is shown to support 122×50 GHz channels, switching in less than 10 ns. The laser is deployed as a component within a new wavelength tuneable source (WTS) composed of two time-interleaved tuneable lasers and two semiconductor optical amplifiers. Switching over 6.05 THz is demonstrated, with stable switch times of 547 ps, a record result. The WTS scales well in terms of chip-space and bandwidth, constituting the first demonstration of scalable, sub-nanosecond optical switching. The power efficiency of the intelligent optical transmitter is further improved by introduction of a novel low-loss split-carrier modulator. The design is evaluated using 112 Gb/s/λ intensity modulated, direct-detection signals and a single-ended photodiode receiver. The split-carrier transmitter is shown to achieve hard decision forward error correction ready performance after 2 km of transmission using a laser output power of just 0 dBm; a 5.2 dB improvement over the conventional transmitter. The results achieved in the course of this research allow for ultra-fast, wideband, intelligent optical transmitters that can be applied in the design of all-optical data centres for power efficient, scalable networking

Liquid Crystal Optics For Communications, Signal Processing And 3-d Microscopic Imaging

This dissertation proposes, studies and experimentally demonstrates novel liquid crystal (LC) optics to solve challenging problems in RF and photonic signal processing, freespace and fiber optic communications and microscopic imaging. These include free-space optical scanners for military and optical wireless applications, variable fiber-optic attenuators for optical communications, photonic control techniques for phased array antennas and radar, and 3-D microscopic imaging. At the heart of the applications demonstrated in this thesis are LC devices that are non-pixelated and can be controlled either electrically or optically. Instead of the typical pixel-by-pixel control as is custom in LC devices, the phase profile across the aperture of these novel LC devices is varied through the use of high impedance layers. Due to the presence of the high impedance layer, there forms a voltage gradient across the aperture of such a device which results in a phase gradient across the LC layer which in turn is accumulated by the optical beam traversing through this LC device. The geometry of the electrical contacts that are used to apply the external voltage will define the nature of the phase gradient present across the optical beam. In order to steer a laser beam in one angular dimension, straight line electrical contacts are used to form a one dimensional phase gradient while an annular electrical contact results in a circularly symmetric phase profile across the optical beam making it suitable for focusing the optical beam. The geometry of the electrical contacts alone is not sufficient to form the linear and the quadratic phase profiles that are required to either deflect or focus an optical beam. Clever use of the phase response of a typical nematic liquid crystal (NLC) is made such that the linear response region is used for the angular beam deflection while the high voltage quadratic response region is used for focusing the beam. Employing an NLC deflector, a device that uses the linear angular deflection, laser beam steering is demonstrated in two orthogonal dimensions whereas an NLC lens is used to address the third dimension to complete a three dimensional (3-D) scanner. Such an NLC deflector was then used in a variable optical attenuator (VOA), whereby a laser beam coupled between two identical single mode fibers (SMF) was mis-aligned away from the output fiber causing the intensity of the output coupled light to decrease as a function of the angular deflection. Since the angular deflection is electrically controlled, hence the VOA operation is fairly simple and repeatable. An extension of this VOA for wavelength tunable operation is also shown in this dissertation. A LC spatial light modulator (SLM) that uses a photo-sensitive high impedance electrode whose impedance can be varied by controlling the light intensity incident on it, is used in a control system for a phased array antenna. Phase is controlled on the Write side of the SLM by controlling the intensity of the Write laser beam which then is accessed by the Read beam from the opposite side of this reflective SLM. Thus the phase of the Read beam is varied by controlling the intensity of the Write beam. A variable fiber-optic delay line is demonstrated in the thesis which uses wavelength sensitive and wavelength insensitive optics to get both analog as well as digital delays. It uses a chirped fiber Bragg grating (FBG), and a 1xN optical switch to achieve multiple time delays. The switch can be implemented using the 3-D optical scanner mentioned earlier. A technique is presented for ultra-low loss laser communication that uses a combination of strong and weak thin lens optics. As opposed to conventional laser communication systems, the Gaussian laser beam is prevented from diverging at the receiving station by using a weak thin lens that places the transmitted beam waist mid-way between a symmetrical transmitter-receiver link design thus saving prime optical power. LC device technology forms an excellent basis to realize such a large aperture weak lens. Using a 1-D array of LC deflectors, a broadband optical add-drop filter (OADF) is proposed for dense wavelength division multiplexing (DWDM) applications. By binary control of the drive signal to the individual LC deflectors in the array, any optical channel can be selectively dropped and added. For demonstration purposes, microelectromechanical systems (MEMS) digital micromirrors have been used to implement the OADF. Several key systems issues such as insertion loss, polarization dependent loss, wavelength resolution and response time are analyzed in detail for comparison with the LC deflector approach. A no-moving-parts axial scanning confocal microscope (ASCM) system is designed and demonstrated using a combination of a large diameter LC lens and a classical microscope objective lens. By electrically controlling the 5 mm diameter LC lens, the 633 nm wavelength focal spot is moved continuously over a 48 [micro]m range with measured 3-dB axial resolution of 3.1 [micro]m using a 0.65 numerical aperture (NA) micro-objective lens. The ASCM is successfully used to image an Indium Phosphide twin square optical waveguide sample with a 10.2 [micro]m waveguide pitch and 2.3 [micro]m height and width. Using fine analog electrical control of the LC lens, a super-fine sub-wavelength axial resolution of 270 nm is demonstrated. The proposed ASCM can be useful in various precision three dimensional imaging and profiling applications

Opto-VLSI-based adaptive optical power splitter/combiner for next generation dynamic optical telecommunication networks

The demand for optical power splitters is growing globally, due to the rapid deployment of fibre-to-the-premises, optical metropolitan area network (MAN), and active optical cables for TV/Video signal transport. Optical splitters play an important role in passive optical network (PON) technology by enabling several hundred users to share one optical line terminal. However, current PONs, which use fixed optical power splitters, have limited reconfigurability particularly in adding/dropping users to/from an optical network unit. An adaptive optical power splitter (OPS) can dynamically reallocate the opticalpower in the entire network according to the real-time distribution of users and services, thus providing numerous advantages such as improve an optical network efficiency, scalability, and reliability. An adaptive OPS is also important for realizing self-healing ring-to-ring optical MAN, thus offering automatic communication recovery when line break occurs. In addition, future optical line protection systems will require adaptive optical splitters to switch optical signals from faulty lines to active power lines, avoid the use of optical attenuators and/or amplifiers, and achieve real time line monitoring. An adaptive OPS can also be incorporated in tunable optical dispersion compensators, optical attenuator and optical gain equalizer, and reconfigurable optical switches. This thesis proposes and demonstrates the principle of a novel Opto-VLSI-based adaptive optical splitter/combiner for next generation dynamic optical telecommunication networks. The proposed splitter structure enables an input optical power to be split adaptively into a larger number of output fibre ports, through optimized phase holograms driving the Opto-VLSI processor. The new adaptive optical splitter has additional advantages including lossless operation, adequate inter-port crosstalk, compressed hardware and simple user interface. This thesis demonstrates, in particular, the concept of an adaptive optical power splitter employing an Opto-VLSI processor and a 4-f imaging system experimentally in three stages as follow: (i) a 1×2 adaptive optical power splitter based on an Opto-VLSI processor, a fibre collimator array and 4-f imaging systems (single lens), (ii) a 1×4 adaptive optical power splitter based on an Opto-VLSI processor, a fibre array and 4-f imaging systems (single lens), and (iii) a 1×N lossless adaptive optical power splitter structure integrating an Opto-VLSI processor, optical amplifiers, a fibre array, and an array of 4-f imaging systems (lens array). The thesis also demonstrates the concept of an adaptive optical signal combiner which enables multiple signals to be combined with user-defined weight profiles into a single fibre port. Experimental results demonstrate that an input optical signal can arbitrarily be split into N signals and coupled into optical fibre ports by uploading optimized multicasting phase holograms onto the Opto-VLSI processor. They also demonstrate that N input optical signals can be dynamically combined with arbitrary weights into a single optical fibre port. Excellent agreement between theoretical and experimental results is demonstrated. The total insertion loss of the optical power splitter is only 5 dB. Results also show that the optical amplifiers can compensate for the insertion and splitting losses, thus enabling lossless splitter operation. A crosstalk level around -25 dB and a wavelength spectral range exceeding 40 nm is experimentally realized. In addition, a novel broadband adaptive RF power splitter/combiner based on Opto-VLSI processor is proposed and experimentally demonstrated. By uploading optimized multicasting phase holograms onto the software-driven Opto-VLSI processor, the input RF signal is dynamically split and directed to different output ports, with userdefined splitting ratios. Also, multiple input RF signals can be dynamically combined with arbitrary user-defined weights. As a proof-of-concept demonstration, two input RF signals are dynamically combined with different user-defined weight profiles. We also propose and demonstrate a photonic microwave filter based on the use of an Opto-VLSI-based adaptive optical combiner. The experimental results demonstrate that the developed Opto-VLSI-based adaptive optical combiner can dynamically route multiple input optical signals to a single output, with user-defined weight profiles, thus realising a tunable microwave filter. Overall this Opto-VLSI-based adaptive optical power splitter should allow as many as 32 output ports to be supported while achieving high splitting resolution and dynamic range. This will greatly enhance the efficiency of optical communication networks

Componentes em fibra ótica para comunicações óticas e sensores

Doutoramento em Engenharia FísicaNos últimos anos, a Optoelectrónica tem sido estabelecida como um campo de investigação capaz de conduzir a novas soluções tecnológicas. As conquistas abundantes no campo da óptica e lasers, bem como em comunicações ópticas têm sido de grande importância e desencadearam uma série de inovações. Entre o grande número de componentes ópticos existentes, os componentes baseados em fibra óptica são principalmente relevantes devido à sua simplicidade e à elevada de transporte de dados da fibra óptica. Neste trabalho foi focado um destes componentes ópticos: as redes de difracção em fibra óptica, as quais têm propriedades ópticas de processamento únicas. Esta classe de componentes ópticos é extremamente atraente para o desenvolvimento de dispositivos de comunicações ópticas e sensores. O trabalho começou com uma análise teórica aplicada a redes em fibra e foram focados os métodos de fabricação de redes em fibra mais utilizados. A inscrição de redes em fibra também foi abordado neste trabalho, onde um sistema de inscrição automatizada foi implementada para a fibra óptica de sílica, e os resultados experimentais mostraram uma boa aproximação ao estudo de simulação. Também foi desenvolvido um sistema de inscrição de redes de Bragg em fibra óptica de plástico. Foi apresentado um estudo detalhado da modulação acústico-óptica em redes em fibra óptica de sílica e de plástico. Por meio de uma análise detalhada dos modos de excitação mecânica aplicadas ao modulador acústico-óptico, destacou-se que dois modos predominantes de excitação acústica pode ser estabelecidos na fibra óptica, dependendo da frequência acústica aplicada. Através dessa caracterização, foi possível desenvolver novas aplicações para comunicações ópticas. Estudos e implementação de diferentes dispositivos baseados em redes em fibra foram realizados, usando o efeito acústico-óptico e o processo de regeneração em fibra óptica para várias aplicações tais como rápido multiplexador óptico add-drop, atraso de grupo sintonizável de redes de Bragg, redes de Bragg com descolamento de fase sintonizáveis, método para a inscrição de redes de Bragg com perfis complexos, filtro sintonizável para equalização de ganho e filtros ópticos notch ajustáveis.In the last years, the Optoelectronics has been established as a top field of research able to drive towards new technological solutions. The abundant achievements in the field of optics as well in optical communications have been of great importance and triggered a number of innovations. Among the large group of existing optical components, optical fiber components are mainly relevant due to three factors: their simplicity, their nature as an optical fiber based component and the capability of optical fiber to carry information. In this thesis the focus was on one of these optical components: optical fiber gratings, which have unique optical processing properties and are quite interesting for the development of devices for optical communications and sensing applications. The work started with a theoretical analysis applied to fiber gratings and continues with the most used fiber gratings production methods. The inscription of fiber gratings was also addressed in this work, where an automated inscription setup has been implemented for silica fiber, and experimental results showed a good approximation to the simulation study. Also, the inscription setup for gratings in polymer optical fiber was developed. A detailed analysis of the acousto-optic modulation in fiber gratings in silica and polymer optical fiber was presented. By means of a detailed analysis of the mechanical excitation modes applied to the modulator set, it was noticed that two predominant modes of acoustic excitation can be found in the optical fiber depending on the applied acoustic frequency. Through this characterization, it was possible to develop new applications. Studies and implementation of different devices based on fiber gratings were performed, using acousto-optic effect and regeneration process in optical fiber for photonic applications such as fast add-drop multiplexer, tunability of the fiber Bragg grating group delay, tunable phase-shift fiber Bragg grating, tunable mode coupler, method for inscription of complex fiber Bragg grating profiles, gain equalization filter and adjustable notch filters