Silicon Modulators, Switches and Sub-systems for Optical Interconnect

Silicon photonics is emerging as a promising platform for manufacturing and integrating photonic devices for light generation, modulation, switching and detection. The compatibility with existing CMOS microelectronic foundries and high index contrast in silicon could enable low cost and high performance photonic systems, which find many applications in optical communication, data center networking and photonic network-on-chip. This thesis first develops and demonstrates several experimental work on high speed silicon modulators and switches with record performance and novel functionality. A 8x40 Gb/s transmitter based on silicon microrings is first presented. Then an end-to-end link using microrings for Binary Phase Shift Keying (BPSK) modulation and demodulation is shown, and its performance with conventional BPSK modulation/ demodulation techniques is compared. Next, a silicon traveling-wave Mach- Zehnder modulator is demonstrated at data rate up to 56 Gb/s for OOK modulation and 48 Gb/s for BPSK modulation, showing its capability at high speed communication systems. Then a single silicon microring is shown with 2x2 full crossbar switching functionality, enabling optical interconnects with ultra small footprint. Then several other experiments in the silicon platform are presented, including a fully integrated in-band Optical Signal to Noise Ratio (OSNR) monitor, characterization of optical power upper bound in a silicon microring modulator, and wavelength conversion in a dispersion-engineered waveguide. The last part of this thesis is on network-level application of photonics, specically a broadcast-and-select network based on star coupler is introduced, and its scalability performance is studied. Finally a novel switch architecture for data center networks is discussed, and its benefits as a disaggregated network are presented

High-speed and Robust Integrated Silicon Nanophotonics for On-Chip Interconnects

Optical interconnects offer advantages over electrical interconnects such as higher bandwidth, low power, reduced interconnects delay, and immunity to electro-magnetic interference and signal crosstalk. However, in order for optical interconnects to be widely adopted, the technology must be made cost effective and must be simple to implement with CMOS electronics. Silicon photonics offers a great promise due to its inexpensive material and its compatibility with the current CMOS fabrication technology. Moreover, Silicon as a platform has the ability to integrate with different types of the optical components such as photodetector, modulator, light source, and waveguide to form a photonics integrated circuit. The goal of this work is to develop and fabricate devices that utilize a hybrid electronic-photonic integration to enable high performance optoelectronic computing and communication systems that overcome the barriers of electronics and dramatically enhance the performance of circuits and systems. We experimentally demonstrate a novel broadband optical time division multiplexer (OTDM) on a silicon chip. The system has a footprint× 700 micrometer and is inherently broadband with a bandwidth of over 100nm making it suitable for high-speed optical networks on chip. Also, we propose and fabricate a novel design to demultiplex the high bit rates of OTDM data using two differentially operated 5Gb/s modulators. Moreover, we propose a high-speed hybrid optical-time-division-multiplexing (OTDM) and wavelength-division-multiplexing (WDM) system that seamlessly generates high bit-rate data (\u3e200Gbit/s) from a low speed (5Gbit/s) quantum-dot mode locked laser pulse source. By utilizing time and wavelength domains, the proposed design is a promising solution for high-speed, compact and low-power consumption optical networks on chip. And finally, we experimentally demonstrate a robust, low insertion loss, compact Silicon ring resonator electro-optic modulator for Binary Phase Shift Key (BPSK) coding/decoding that encodes data in the phase of light. Our design improves significantly over recently demonstrated PSK modulator designs in terms of insertion loss and stability

Control Systems for Silicon Photonic Microring Devices

The continuing growth of microelectronics in speed, scale, and complexity has led to a looming bandwidth bottleneck for traditional electronic interconnects. This has precipitated the penetration of optical interconnects to smaller, more localized scales, in such applications as data centers, supercomputers, and access networks. For this next generation of optical interconnects, the silicon photonic platform has received wide attention for its ability to manifest, more economical, high-performance photonics. The high index contrast and CMOS compatibility of the silicon platform give the potential to intimately integrate small footprint, power-efficient, high-bandwidth photonic interconnects with existing high-performance CMOS microelectronics. Within the silicon photonic platform, traditional photonic elements can be manifested with smaller footprint and higher energy-efficiency. Additionally, the high index contrast allows the successful implementation of silicon microring-based devices, which push the limits on achievable footprint and energy-efficiency metrics. While laboratory demonstrations have testified to their capabilities as powerful modulators, switches, and filters, the commercial implementation of microring-based devices is impeded by their susceptibility to fabrication tolerances and their inherent temperature sensitivity. This work develops and demonstrates methods to resolve the aforementioned sensitivities of microring-based devices. Specifically, the use of integrated heaters to thermally tune and lock microring resonators to laser wavelengths, and the underlying control systems to enable such functionality. The first developed method utilizes power monitoring to show the successful thermal stabilization of a microring modulator under conditions that would normally render it inoperational. In a later demonstration, the photodetector used for power monitoring is co-integrated with the microring modulator, again demonstrating thermal stabilization of a microring modulator and validating the use of defect-enhanced silicon photodiodes for on-chip control systems. Secondly, a generalized method is developed that uses dithering signals to generate anti-symmetric error signals for use in stabilizing microring resonators. A control system utilizing a dithering signal is shown to successfully wavelength lock and thermally stabilize a microring resonator. Characterizations are performed on the robustness and speed of the wavelength locking process when using dithering signals. An FPGA implementation of the control system is used to scale to a WDM microring demultiplexer, demonstrating the simultaneous wavelength locking of multiple microring resonators. Additionally, the dithering technique is adopted to create control systems for microring-based switches, which have traditionally posed a challenging problem due to their multi-state configurations. The aforementioned control systems are rigorously tested for applications with high speed data and analyzed for power efficiency and scalability to show that they can successfully scale to commercial implementations and be the enabling factor in the commercial deployment of microring-based devices

Chip-Scale Microwave Photonic Signal Processing

The use of optical technology can provide unprecedented performance to the generation, distribution, and processing of microwave. Recently, on-chip microwave photonics (MWP) has gained significant interests for its numerous advantages, such as robustness, reconfigurability as well as reduction of size, weight, cost, and power consumption. In this chapter, we review our recent progress in ultracompact microwave photonic signal processing using silicon nanophotonic devices. Using the fabricated silicon waveguide, silicon microring resonators (MRRs) and silicon photonic crystal nanocavities, we demonstrate on-chip analog signal transmission, optically controlled tunable MWP filter, and ultra-high peak rejection notch MWP filter. The performance of analog links and the responses of MWP filters are evaluated in the experiment. In addition, microwave signal multiplication and modulation are also demonstrated based on a silicon Mach-Zehnder modulator in the experiment with favorable operation performance. The demonstrated on-chip analog links, MWP filters, microwave signal multiplication/modulation may help understand on-chip analog signaling and expand novel functionalities of MWP signal processing

Development of Silicon Photonic Multi Chip Module Transceivers

The exponential growth of data generation–driven in part by the proliferation of applications such as high definition streaming, artificial intelligence, and the internet of things–presents an impending bottleneck for electrical interconnects to fulfill data center bandwidth demands. Links now require bandwidths in excess of multiple Tbps while operating on the order of picojoules per bit, in addition to constraints on areal bandwidth densities and pin I/O bandwidth densities. Optical communications built on a silicon photonic platform offers a potential solution to develop power efficient, high bandwidth, low attenuation, small footprint links, all while building off the mature CMOS ecosystem. The development of silicon photonic foundries supporting multi project wafer runs with associated process design kit components supports a path towards widespread commercial production by increasing production volume while reducing fabrication and development costs. While silicon photonics can always be improved in terms of performance and yield, one of the central challenges is the integration of the silicon photonic integrated circuits with the driving electronic integrated circuits and data generating compute nodes such as CPUs, FPGAs, and ASICs. The co-packaging of the photonics with the electronics is crucial for adoption of silicon photonics in datacenters, as improper integration negates all the potential benefits of silicon photonics. The work in this dissertation is centered around the development of silicon photonic multi chip module transceivers to aid in the deployment of silicon photonics within data centers. Section one focuses on silicon photonic integration and highlights multiple integrated transceiver prototypes. The central prototype features a photonic integrated circuit with bus waveguides with WDM microdisk modulators for the transmitter and WDM demuxes with drop ports to photodiodes for the receiver. The 2.5D integrated prototype utilizes a thinned silicon interposer and TIA electronic integrated circuits. The architecture, integration, characterization, performance, and scalability of the prototype are discussed. The development of this first prototype identified key design considerations necessary for designing multi chip module silicon photonic prototypes, which will be addressed in this section. Finally, other multi chip module silicon photonic prototypes will be overviewed. These include a 2.5D integrated transceiver with a different electronic integrated circuit TIA, a 3D integrated receiver, an active interposer network on chip, and a 2.5D integrated transceiver with custom electronic integrated circuits. Section two focuses on research that supports the development of silicon photonic transceivers. The thermal crosstalk from neighboring microdisk modulators as a function of modulator pitch is investigated. As modulators are placed at denser pitches to accommodate areal bandwidth density requirements in transceivers, this thermal crosstalk will become significant. In this section, designs and results from several iterations of custom microring modulators are reported. Custom microring modulators allow for scaling up the number of channels in microring transceivers by offering the ability to fabricate variable resonances and provide a platform for further innovation in bandwidth, free spectral range, and energy efficiency. The designs and results of higher order modulation format modulators, both microring based and Mach Zehnder based, are discussed. High order modulators offer a path towards scaling transceiver total throughput without having to increase the channel counts or component bandwidth. Together, the work in these two sections supports the development of silicon photonic transceivers to aid in the adoption of silicon photonics into data generating systems

Advanced optical modulation and fast reconfigurable en/decoding techniques for OCDMA application

With the explosive growth of bandwidth requirement in optical fiber communication networks, optical code division multiple access (OCDMA) has witnessed tremendous achievements as one of the promising technologies for optical access networks over the past decades. In an OCDMA system, optical code processing is one of the key techniques. Rapid optical code reconfiguration can improve flexibility and security of the OCDMA system. This thesis focuses on advanced optical modulations and en/decoding techniques for applications in fast reconfigurable OCDMA systems and secure optical communications. A novel time domain spectral phase encoding (SPE) scheme which can rapidly reconfigure the optical code and is compatible with conventional spectral domain phase en/decoding by using a pair of dispersive devices and a high speed phase modulator is proposed. Based on this scheme, a novel advanced modulation technique that can simultaneously generate both the optical code and the differential-phase-shift-keying (DPSK) data using a single phase modulator is experimentally demonstrated. A symmetric time domain spectral phase encoding and decoding (SPE/SPD) scheme using a similar setup for both the transmitter and receiver is further proposed, based on which a bit-by-bit optical code scrambling and DPSK data modulation technique for secure optical communications has been successfully demonstrated. By combining optical encoding and optical steganography, a novel approach for secure transmission of time domain spectral phase encoded on-off-keying (OOK)/DPSK-OCDMA signal over public wavelength-division multiplexing (WDM) network has also been proposed and demonstrated. To enable high speed operation of the time domain SPE/SPD scheme and enhance the system security, a rapid programmable, code-length variable bit-by-bit optical code shifting technique is proposed. Based on this technique, security improvements for OOK/DPSK OCDMA systems at data rates of 10Gb/s and 40Gb/s using reconfigurable optical codes of up to 1024-chip have been achieved. Finally, a novel tunable two-dimensional coherent optical en/decoder which can simultaneously perform wavelength hopping and spectral phase encoding based on coupled micro-ring resonator is proposed and theoretically investigated. The techniques included in this thesis could be potentially used for future fast reconfigurable and secure optical code based communication systems

Ultra-wideband indoor communications using optical technology

La communication ultra large bande (UWB) a attiré une énorme quantité de recherches ces dernières années, surtout après la présentation du masque spectral de US Federal Communications Commission (FCC). Les impulsions ultra-courtes permettent de très hauts débits de faible puissance tout en éliminant les interférences avec les systèmes existants à bande étroite. La faible puissance, cependant, limite la portée de propagation des radios UWB à quelques mètres pour la transmission sans fil à l’intérieur d’une pièce. En outre, des signaux UWB reçu sont étendus dans le temps en raison de la propagation par trajet multiple qui résulte en beaucoup d’interférence inter-symbole (ISI) à haut débit. Le monocycle Gaussien, l’impulsion la plus commune dans UWB, a une mauvaise couverture sous le masque de la FCC. Dans cette thèse, nous démontrons des transmet- teurs qui sont capables de générer des impulsions UWB avec une efficacité de puissance élevée. Une impulsion efficace résulte dans un rapport de signal à bruit (SNR) supérieur au récepteur en utilisant plus de la puissance disponible sous le masque spectral de la FCC. On produit les impulsions dans le domaine optique et utilise la fibre optique pour les transporter sur plusieurs kilomètres pour la distribution dans un réseau optique pas- sif. La fibre optique est très fiable pour le transport des signaux radio avec une faible consommation de puissance. On utilise les éléments simples comme un modulateur Mach-Zehnder ou un résonateur en anneau pour générer des impulsions, ce qui permet l’intégration dans le silicium. Compatible avec la technologie CMOS, la photonique sur silicium a un potentiel énorme pour abaisser le coût et l’encombrement des systèmes optiques. La photodétection convertit les impulsions optiques en impulsions électriques avant la transmission sur l’antenne du côté de l’utilisateur. La réponse fréquentielle de l’antenne déforme la forme d’onde de l’impulsion UWB. Nous proposons une technique d’optimisation non-linéaire qui prend en compte la distorsion d’antenne pour trouver des impulsions qui maximisent la puissance transmise, en respectant le masque spectral de la FCC. Nous travaillons avec trois antennes et concevons une impulsion unique pour chacune d’entre elle. L’amélioration de l’énergie des impulsions UWB améliore directement la SNR au récepteur. Les résultats de simulation montrent que les impulsions optimisées améliorent considérablement le taux d’erreur (BER) par rapport au monocycle Gaussien sous propagation par trajet multiple. Notre autre contribution est l’évaluation d’un filtre adapté pour recevoir efficacement des impulsions UWB. Le filtre adapté est synthétisé et fabriqué en technologie microstrip, en collaboration avec l’Université McGill comme un dispositif de bande interdite électromagnétique. La réponse fréquentielle du filtre adapté montre une ex- cellente concordance avec le spectre ciblé de l’impulsion UWB. Les mesures de BER confirment la performance supérieure du filtre adapté par rapport à un récepteur à conversion directe. Le canal UWB est très riche en trajet multiple conduisant à l’ISI à haut débit. Notre dernière contribution est l’étude de performance des récepteurs en simulant un système avec des conditions de canaux réalistes. Les résultats de la simulation montrent que la performance d’un tel système se dégrade de façon significative pour les hauts débits. Afin de compenser la forte ISI dans les taux de transfert de données en Gb/s, nous étudions l’algorithme de Viterbi (VA) avec un nombre limité d’états et un égaliseur DFE (decision feedback equalizer). Nous examinons le nombre d’états requis dans le VA, et le nombre de coefficients du filtre dans le DFE pour une transmission fiable de UWB en Gb/s dans les canaux en ligne de vue. L’évaluation par simulation de BER confirme que l’égalisation améliore considérablement les performances par rapport à la détection de symbole. La DFE a une meilleure performance par rapport à la VA en utilisant une complexité comparable. La DFE peut couvrir une plus grande mémoire de canal avec un niveau de complexité relativement réduit.Ultra-wideband (UWB) communication has attracted an enormous amount of research in recent years, especially after the introduction of the US Federal Communications Commission (FCC) spectral mask. Ultra-short pulses allow for very high bit-rates while low power eliminates interference with existing narrowband systems. Low power, however, limits the propagation range of UWB radios to a few meters for indoors wireless transmission. Furthermore, received UWB signals are spread in time because of multipath propagation which results in high intersymbol interference at high data rates. Gaussian monocycle, the most commonly employed UWB pulse, has poor coverage under the FCC mask. In this thesis we demonstrate transmitters capable of generating UWB pulses with high power efficiency at Gb/s bit-rates. An efficient pulse results in higher signal-to-noise ratio (SNR) at the receiver by utilizing most of the available power under the FCC spectral mask. We generate the pulses in the optical domain and use optical fiber to transport the pulses over several kilometers for distribution in a passive optical network. Optical fiber is very reliable for transporting radio signals with low power consumption. We use simple elements such as a Mach Zehnder modulator or a ring resonator for pulse shaping, allowing for integration in silicon. Being compatible with CMOS technology, silicon photonics has huge potential for lowering the cost and bulkiness of optical systems. Photodetection converts the pulses to the electrical domain before antenna transmission at the user side. The frequency response of UWB antennas distorts the UWB waveforms. We pro- pose a nonlinear optimization technique which takes into account antenna distortion to find pulses that maximize the transmitted power, while respecting the FCC spectral mask. We consider three antennas and design a unique pulse for each. The energy improvement in UWB pulses directly improves the receiver SNR. Simulation results show that optimized pulses have a significant bit error rate (BER) performance improvement compared to the Gaussian monocycle under multipath propagation. Our other contribution is evaluating a matched filter to receive efficiently designed UWB pulses. The matched filter is synthesized and fabricated in microstrip technology in collaboration with McGill University as an electromagnetic bandgap device. The frequency response of the matched filter shows close agreement with the target UWB pulse spectrum. BER measurements confirm superior performance of the matched filter compared to a direct conversion receiver. The UWB channel is very rich in multipath leading to ISI at high bit rates. Our last contribution is investigating the performance of receivers by simulating a system employing realistic channel conditions. Simulation results show that the performance of such system degrades significantly for high data rates. To compensate the severe ISI at gigabit rates, we investigate the Viterbi algorithm (VA) with a limited number of states and the decision feedback equalizer (DFE). We examine the required number of states in the VA, and the number of taps in the DFE for reliable Gb/s UWB trans- mission for line-of-sight channels. Non-line-of-sight channels were also investigated at lower speeds. BER simulations confirm that equalization considerably improves the performance compared to symbol detection. The DFE results in better performance compared to the VA when using comparable complexity as the DFE can cover greater channel memory with a relatively low complexity level