Programmable photonics : an opportunity for an accessible large-volume PIC ecosystem

We look at the opportunities presented by the new concepts of generic programmable photonic integrated circuits (PIC) to deploy photonics on a larger scale. Programmable PICs consist of waveguide meshes of tunable couplers and phase shifters that can be reconfigured in software to define diverse functions and arbitrary connectivity between the input and output ports. Off-the-shelf programmable PICs can dramatically shorten the development time and deployment costs of new photonic products, as they bypass the design-fabrication cycle of a custom PIC. These chips, which actually consist of an entire technology stack of photonics, electronics packaging and software, can potentially be manufactured cheaper and in larger volumes than application-specific PICs. We look into the technology requirements of these generic programmable PICs and discuss the economy of scale. Finally, we make a qualitative analysis of the possible application spaces where generic programmable PICs can play an enabling role, especially to companies who do not have an in-depth background in PIC technology

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

Photonic RF signal processors

The purpose of this thesis is to explore the emerging possibilities of processing radiofrequency (RF) or microwave signals in optical domain, which will be a key technology to implement next-generation mobile communication systems and future optical networks. Research activities include design and modelling of novel photonic architectures for processing and filtering of RF, microwave and millimeter wave signals of the above mentioned applications. Investigations especially focus on two basic functions and critical requirements in advanced RF systems, namely: • Interference mitigation and high Q tunable filters. • Arbitrary filter transfer function generation. The thesis begins with a review on several state-of-the-art architectures of in-fiber RF signal processing and related key optical technologies. The unique capabilities offered by in-fiber RF signal processors for processing ultra wide-band, high-frequency signals directly in optical domain make them attractive options for applications in optical networks and wide-band microwave signal processing. However, the principal drawbacks which have been demonstrated so far in the in-fiber RF signal processors arc their inflexible or expensive schemes to set tap weights and time delay. Laser coherence effects also limit sampling frequency and introduce additional phase-induced intensity noise

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

Enhanced PON Infrastructure Enabled by Silicon Photonics

Les systèmes de courte portée et de détection directe sont le dernier/premier kilomètre de la fourniture des services Internet d'aujourd'hui. Deux cas d'application sont abordés dans cette thèse, l'un concerne l'amélioration des performances des services Internet par la Fibre-To-TheHome ou les réseaux optiques passifs (PONs). L'autre est le radio access network (RAN) pour le fronthaul. Notre objectif pour RAN est de superposer les signaux 5G sur une infrastructure PON. Nous démontrons expérimentalement la génération d'un signal de répartition multiplexée de fréquences orthogonales (OFDM) à bande latérale unique en utilisant un modulateur IQ sur puce basé sur les photoniques au silicium à micro-anneau. Il s'agit d'une solution à coût bas permettant aux PONs d'augmenter les débits de données grâce à l'utilisation d'OFDM. Nous avons généré un signal OFDM à large bande avec un ratio de suppression de bande latérale de plus de 18 dB. Afin de confirmer la robustesse de la dispersion chromatique (CD), nous transmettons le signal généré OFDM SSB dans plus de 20 km de fibre de monomode standard. Aucun fading induit par la CD n'a été observé et le taux d'erreur sur les bits était bon. Nous proposons une solution de photoniques au silicium pour un réseau optique passif afin de mitiger l'interférence de battement signal-signal (SSBI) dans la transmission OFDM, et de récupérer une partie des porteuses de la liaison descendante pour une utilisation dans la liaison montante. Le sous-système recrée les interférences à une entrée du détecteur équilibré ; le signal de données corrompu par SSBI est à la deuxième entrée. L'annulation se produit via la soustraction dans la détection équilibrée. Comme notre solution de photoniques au silicium (SiP) ne peut pas filtrer les signaux idéalement, nous examinons un facteur d'échelle introduit dans la détection équilibrée qui peut balancer les effets de filtrage non idéaux. Nous montrons expérimentalement l'annulation de l'interférence donne de bonnes performances même avec une porteuse faible, soit pour un ratio porteuse/signal ultra bas de 0 dB. Bien que notre solution soit sensible aux effets de la température, notre démonstration expérimentale montre que le réglage de la fréquence résonante peut dériver jusqu'à 12 GHz de la valeur ciblée et présenter toujours de bonnes performances. Nous effectuons des simulations extensives du schéma d'annulation SSBI proposé, et suggérons une diverse conception polarisée pour le sous-système SiP. Nous examinons via la simulation la vulnérabilité à la variation de température et introduisons une nouvelle métrique de performance : Q-facteur minimum garanti. Nous nous servons de cette métrique pour évaluer la robustesse d'annulation SSBI contre la dérive de fréquence induite par les changements de température. Nous maximisons l'efficacité spectrale sous différentes conditions du système en balayant les paramètres de conception contrôlables. Finalement, les résultats de la simulation du système fournissent des indications sur la conception du résonateur micro-anneau, ainsi que sur le choix de la bande de garde et du format de modulation pour obtenir la plus grande efficacité spectrale. Finalement, nous nous concentrons sur la superposition des signaux 5G sur une infrastructure PON pour RAN. Nous expérimentalement validons un sous-système photonique au silicium conçu pour les réseaux optiques passifs avec réutilisation de porteuses et compatibilité radiosur-fibre (RoF) analogique 5G. Le sous-système permet la détection simultanée des signaux RoF et du signal PON transmis dans une seule tranche assignée de longueur d'onde. Tout en maintenant une qualité suffisante de détection des signaux RoF et PON, il n'y a que la puissance minimale de la porteuse qui est extraite pour chaque détection, ce qui conserve ainsi la puissance de la porteuse pour la modulation de liaison montante. Nous réalisons une suppression efficace du signal de liaison descendante en laissant une porteuse propre et forte pour la remodulation. Nous démontrons expérimentalement le signal RoF de liaison montante via un modulateur à micro-anneau. Nous avons détecté avec succès un signal à large bande de 8 GHz et cinq signaux RoF de 125 MHz simultanément. Et deux signaux RoF de 125 MHz sont remodulés sur la même porteuse. Le signal RoF de liaison montante généré est de 13 dB de plus que les signaux de liaison descendante, ce qui indique leur robustesse contre la diaphonie des signaux résiduels de la liaison descendante.Short reach, direct detection systems are the last/first mile of today's internet service provision. Two use cases are addressed in this thesis, one is for enhancing performance of Internet services on fiber-to-the-home or passive optical networks (PON). The other is radio access networks (RAN) for fronthaul. Our focus for RAN is to overlay 5G signals on a PON infrastructure. We experimentally demonstrate the generation of a single-sideband orthogonal frequency division multiplexed (OFDM) signal using an on-chip silicon photonics microring-based IQ modulator. This is a low cost solution enabling PONs to increase data rates through the use of OFDM. We generated a wideband OFDM signal with over 18 dB sideband suppression ratio. To confirm chromatic dispersion (CD) robustness, we transmit the generated SSB OFDM signal over 20 km of standard single mode fiber. No CD-induced fading was observed and bit error rate was good. We propose a silicon photonics solution for a passive optical network to mitigate signal-signal beat interference (SSBI) in OFDM transmission, and to recuperate a part of the downlink carrier for use in the uplink. The subsystem recreates the interference at one balanced detector input; the data signal corrupted with SSBI is at the second input. Cancellation occurs via subtraction in the balanced detection. As our silicon photonics (SiP) solution cannot filter the signals ideally, we examine a scaling factor to be introduced to the balanced detection that can trade-off the non-ideal filtering effects. We show experimentally that the interference is cancelled, allowing good performance even with a weak carrier, that is, for ultra low carrier to signal ratio of 0 dB. Although our solution is sensitive to temperature effects, our experimental demonstration shows the tuning of the resonant frequency can drift by as much as 12 GHz from the targeted value and still provide good performance. We perform extensive simulations of the proposed SSBI cancellation scheme, and suggest a polarization diverse design for the SiP subsystem. We examine via simulation the vulnerability to temperature variation and introduce a new performance metric: minimum guaranteed Qfactor. We use this metric to evaluate the SSBI cancellation robustness against the frequency drift induced by temperature changes. We maximize the spectral efficiency under different system conditions by sweeping the controllable design parameters. Finally the system simulation results provide guidance on the microring resonator design, as well as choice of guard band and modulation format to achieve the highest spectral efficiency. Finally, we turn to focus on overlay 5G signals on a PON infrastructure for RAN. We experimentally validate a silicon photonic subsystem designed for passive optical networks with carrier reuse and 5G analog radio-over-fiber (RoF) compatibility. The subsystem enables the simultaneous detection of RoF signals and a PON signal transmitted in a single assigned wavelength slot. While maintaining sufficient quality of RoF and PON signal detection, only the minimum carrier power is leached off for each detection, thus conserving carrier power for uplink modulation. We realize effective downlink signal suppression to leave a clean and strong carrier for remodulation. We demonstrate experimentally the RoF uplink signal via a micro ring modulator. We successfully detected an 8 GHz broadband signal and five 125 MHz RoF signals simultaneously. And two 125 MHz radio over fiber signals are remodulated onto the same carrier. The generated uplink RoF signal is 13 dB over the downlink signals, indicating their robustness against the crosstalk from residual downlink signals

Intensity based interrogation of optical fibre sensors for industrial automation and intrusion detection systems

In this study, the use of optical fibre sensors for intrusion detection and industrial automation systems has been demonstrated, with a particular focus on low cost, intensity-based, interrogation techniques. The use of optical fibre sensors for intrusion detection systems to secure residential, commercial, and industrial premises against potential security breaches has been extensively reviewed in this thesis. Fibre Bragg grating (FBG) sensing is one form of optical fibre sensing that has been underutilised in applications such as in-ground, in-fence, and window and door monitoring, and addressing that opportunity has been a major goal of this thesis. Both security and industrial sensor systems must include some centralised intelligence (electronic controller) and ideally both automation and security sensor systems would be controlled and monitored by the same centralised system. Optical fibre sensor systems that could be used for either application have been designed, developed, and tested in this study, and optoelectronic interfaces for integrating these sensors with electronic controllers have been demonstrated. The versatility of FBG sensors means that they are also ideal for certain mainstream industrial applications. Two novel transducers have been developed in this work; a highly sensitive low pressure FBG diaphragm transducer and a FBG load cell transducer. Both have been designed to allow interrogation of the optical signal could occur within the housing of the individual sensors themselves. This is achieved in a simple and low cost manner that enables the output of the transducers to be easily connected to standard electronic controllers, such as programmable logic controllers. Furthermore, some of the nonlinear characteristics of FBG sensors have been explored with the aim of developing transducers that are inherently decoupled from strain and temperature interference. One of the major advantages of optical fibre sensors is their ability to be both time division and wavelength division multiplexed. The intensity-based interrogation techniques used here complement this attribute and are a major consideration when developing the transducers and optoelectronic circuits. A time division multiplexing technique, using transmit-reflect detection and incorporating a dual bus, has also been developed. This system architecture enables all the different optical fibre transducers on the network to have the same Bragg wavelength and hence the number of spare replacement transducers required is minimal. Moreover, sensors can be replaced in an online control system without disrupting the network. In addition, by analysing both the transmitted and reflected signals, problems associated with optical power fluctuations are eliminated and the intensity of the sensor signals is increased through differential amplification. Overall, the research addresses the limitations of conventional electrical sensors, such as susceptibility to corrosive damage in wet and corrosive environments, and risk of causing an explosion in hazardous environments, as well as the limitations of current stand-alone optical fibre sensor systems. This thesis supports more alert, reliable, affordable, and coordinated, control and monitoring systems in an on-line environment