Transmetteurs photoniques sur silicium pour les transmissions optiques à grande capacité

Les applications exigeant des très nombreuses données (médias sociaux, diffusion vidéo en continu, mégadonnées, etc.) se développent à un rythme rapide, ce qui nécessite de plus en plus de liaisons optiques ultra-rapides. Ceci implique le développment des transmetteurs optiques intégrés et à bas coût et plus particulirement en photonique sur silicium en raison de ses avantages par rapport aux autres technologies (LiNbO3 et InP), tel que la compatibilité avec le procédé de fabrication CMOS. Les modulateurs optoélectronique sont un élément essentiel dans la communication op-tique. Beaucoup de travaux de recherche sont consacrées au développement de dispositifs optiques haut débit efficaces. Cependant, la conception de modulateurs en photonique sur sili-cium (SiP) haut débit est diffcile, principalement en raison de l'absence d'effet électro-optique intrinsèque dans le silicium. De nouvelles approches et de architectures plus performances doivent être développées afin de satisfaire aux critères réliés au système d'une liaison optique aux paramètres de conception au niveau du dispositif integré. En outre, la co-conception de circuits integrés photoniques sur silicium et CMOS est cruciale pour atteindre tout le potentiel de la technologie de photonique sur silicium. Ainsi cette thèse aborde les défits susmentionnés. Dans notre première contribution, nous préesentons pour la première fois un émetteur phononique sur silicium PAM-4 sans utiliser un convertisseur numérique analog (DAC)qui comprend un modulateur Mach Zehnder à électrodes segmentées SiP (LES-MZM) implémenté dans un procédé photonique sur silicium générique avec jonction PN latérale et son conducteur CMOS intégré. Des débits allant jusqu'à 38 Gb/s/chnnel sont obtenus sans utili-ser un convertisseur numérique-analogique externe. Nous présentons également une nouvelle procédure de génération de délai dans le excitateur de MOS complémentaire. Un effet, un délai robuste aussi petit que 7 ps est généré entre les canaux de conduite. Dans notre deuxième contribution, nous présentons pour la première fois un nouveau fac-teur de mérite (FDM) pour les modulateurs SiP qui inclut non seulement la perte optique et l'efficacité (comme les FDMs précédents), mais aussi la bande passante électro-optique du modulateur SiP (BWEO). Ce nouveau FDM peut faire correspondre les paramètres de conception physique du modulateur SiP à ses critères de performance au niveau du système, facilitant à la fois la conception du dispositif optique et l'optimisation du système. Pour la première fois nous définissons et utilisons la pénalité de puissance du modulateur (MPP) induite par le modulateur SiP pour étudier la dégradation des performances au niveau du système induite par le modulateur SiP dans une communication à base de modulation d'amplitude d'impulsion optique. Nous avons développé l'équation pour MPP qui inclut les facteurs de limitation du modulateur (perte optique, taux d'extinction limité et limitation de la bande passante électro-optique). Enfin, dans notre troisième contribution, une nouvelle méthodologie de conception pour les modulateurs en SiP intégré à haute débit est présentée. La nouvelle approche est basée sur la minimisation de la MPP SiP en optimisant l'architecture du modulateur et le point de fonctionnement. Pour ce processus, une conception en longueur unitaire du modulateur Mach Zehnder (MZM) peut être optimisée en suivant les spécifications du procédé de fabrication et les règles de conception. Cependant, la longueur et la tension de biais du d'éphaseur doivent être optimisées ensemble (par exemple selon vitesse de transmission et format de modulation). Pour vérifier l'approche d'optimisation proposée expérimentale mont, a conçu un modulateur photonique sur silicium en phase / quadrature de phase (IQ) ciblant le format de modulation 16-QAM à 60 Gigabaud. Les résultats expérimentaux prouvent la fiabilité de la méthodologie proposée. D'ailleurs, nous avons augmenté la vitesse de transmission jusqu'à 70 Gigabaud pour tester la limite de débit au système. Une transmission de données dos à dos avec des débits binaires de plus de 233 Gigabit/s/channel est observée. Cette méthodologie de conception ouvre ainsi la voie à la conception de la prochaine génération d'émetteurs intégrés à double polarisation 400+ Gigabit/s/channel.Data-hungry applications (social media, video streaming, big data, etc.) are expanding at a fast pace, growing demand for ultra-fast optical links. This driving force reveals need for low-cost, integrated optical transmitters and pushes research in silicon photonics because of its advantages over other platforms (i.e. LiNbO3 and InP), such as compatibility with CMOS fabrication processes, the ability of on-chip polarization manipulation, and cost effciency. Electro-optic modulators are an essential component of optical communication links and immense research is dedicated to developing effcient high-bitrate devices. However, the design of high-capacity Silicon Photonics (SiP) transmitters is challenging, mainly due to lack of inherent electro-optic effect in silicon. New design methodologies and performance merits have to be developed in order to map the system-level criteria of an optical link to the design parameters in device-level. In addition, co-design of silicon photonics and CMOS integrated circuits is crucial to reveal the full potential of silicon photonics. This thesis addresses the aforementioned challenges. In our frst contribution, for the frst time we present a DAC-less PAM-4 silicon photonic transmitter that includes a SiP lumped-element segmented-electrode Mach Zehnder modula-tor (LES-MZM) implemented in a generic silicon photonic process with lateral p-n junction and its co-designed CMOS driver. Using post processing, bitrates up to 38 Gb/s/channel are achieved without using an external digital to analog converter. We also presents a novel delay generation procedure in the CMOS driver. A robust delay as small as 7 ps is generated between the driving channels. In our second contribution, for the frst time we present a new figure of merit (FOM) for SiP modulators that includes not only the optical loss and effciency (like the prior FOMs), but also the SiP modulator electro-optic bandwidth ( BWEO). This new FOM can map SiP modulator physical design parameters to its system-level performance criteria, facilitating both device design and system optimization. For the frst time we define and employ the modulator power penalty (MPP) induced by the SiP modulator to study the system level performance degradation induced by SiP modulator in an optical pulse amplitude modulation link. We develope a closed-form equation for MPP that includes the SiP modulator limiting factors (optical loss, limited extinction ratio and electro-optic bandwidth limitation). Finally in our third contribution, we present a novel design methodology for integrated high capacity SiP modulators. The new approach is based on minimizing the power penalty of a SiP modulator (MPP) by optimizing modulator design and bias point. For the given process, a unit-length design of Mach Zehnder modulator (MZM) can be optimized following the process specifications and design rules. However, the length and the bias voltage of the phase shifter must be optimized together in a system context (e.g., baud rate and modulation format). Moreover, to verify the proposed optimization approach in experiment, we design an in-phase/quadrature-phase (IQ) silicon photonic modulator targeting 16-QAM modulation format at 60 Gbaud. Experimental results proves the reliability of our proposed methodology. We further push the baud rate up to 70 Gbaud to examine the capacity boundary of the device. Back to back data transmission with bitrates more than 233 Gb/s/channel are captured. This design methodology paves the way for designing the next generation of integrated dual- polarization 400+ Gb/s/channel transmitters

50 GBd PAM4 transmitter with a 55nm SiGe BiCMOS driver and silicon photonic segmented MZM

We demonstrate an optical transmitter consisting of a limiting SiGe BiCMOS driver co-designed and co-packaged with a silicon photonic segmented traveling-wave Mach-Zehnder modulator (MZM). The MZM is split into two traveling-wave segments to increase the bandwidth and to allow a 2-bit DAC functionality. Two limiting driver channels are used to drive these segments, allowing both NRZ and PAM4 signal generation in the optical domain. The voltage swing as well as the peaking of the driver output are tunable, hence the PAM4 signal levels can be tuned and possible bandwidth limitations of the MZM segments can be partially alleviated. Generation of 50 Gbaud and 53 Gbaud PAM4 yields a TDECQ of 2.8 and 3.8 dB with a power efficiency of 3.9 and 3.6 pJ/bit, respectively; this is the best reported efficiency for co-packaged silicon transmitters for short-reach datacenter interconnects at these data rates. With this work, we show the potential of limiting drivers and segmented traveling-wave modulators in 400G capable short-reach optical interconnects

Electro-Photonic Transmitter Front-Ends for High-Speed Fiber-Optic Communication

This thesis addresses basic scientific research in the field of transmitter front-end circuits for electro-optical data communication. First, the theoretical fundamentals are presented and analyzed. Based on the theoretical considerations, conceptual circuit designs are studied. Finally, in order to prove the described concepts, the circuits were experimentally characterized and subsequently compared to other works in the literature. The analysis covers key theoretical aspects regarding transmitter front-end circuits. It starts from the basic physical effects inside a transistor and ends with the design of high-swing modulator drivers. Furthermore, it comprises the fundamentals of optical modulators as well as the integration of the electrical driver with the modulator. First, the concept of a basic monolithically integrated transmitter consisting of a Mach-Zehnder modulator (MZM) and an electrical driver is presented. The circuit reaches a bit-error-free data rate of 37 Gb/s, which is a record among other monolithically integrated transmitters reported in the literature. It was shown that by employing a high-swing driver, high extinction ratios (ER) can be achieved (namely 8.4 dB at 25 Gb/s and 7.6 dB at 35 Gb/s) while using short-length phase shifters (2 mm of length). It was therefore proved that one of the main drawbacks of the MZM-based transmitters, namely their large chip area, can be mitigated by using high-swing drivers, however without sacrificing the ER. Next, an improved modulator driver design is investigated, the focus of the study being the linearity. In addition to a high peak-to-peak differential output voltage swing of 7.2 Vpp,d, the driver achieves record-low total harmonic distortion (THD) values of 1% (at 1 GHz, for the output swing of 6.5 Vpp,d) and 1.7% (at 1 GHz, for the output swing of 7 Vpp,d). Moreover, the driver reaches a bandwidth of 61.2 GHz and shows a high power efficiency when relating its DC power consumption to its output voltage swing. The achievement of a high linearity and bandwidth without an increased power consumption is due to the fact that the bias currents of the emitter-follower (EF) stages are provided by means of resistors instead of the conventional current sources. The two approaches were first analyzed mathematically and subsequently compared by means of circuit simulations. It was shown that the proposed approach for the realization of the EFs – i.e. by means of resistors – allows a reduction of the DC power consumption by 19% compared to the current-source approach for an equivalent performance in terms of linearity and bandwidth. Finally, a modulator driver concept suitable for higher-order modulation formats is studied, namely the 8-level pulse amplitude modulation (PAM-8). The circuit was realized as a 3-bit digital-to-analog converter (DAC), thus being able to yield 8-level output signals. Moreover, the circuit is able to function as a PAM-4 driver as well, thanks to the tunable tail currents of the DAC core. It achieves a symbol rate of 50 Gbaud, which corresponds to a bit rate of 150 Gb/s for the PAM-8 modulation and 100 Gb/s for PAM-4. The study showed that a modulator driver can be realized that is able to switch between different modulation formats (namely PAM-8 and PAM-4), without requiring extra power or additional circuit parts. Moreover, the use of on-chip single-to-differential converters (SDCs) targets the relaxation of the requirements on the stages that precede the driver. Finally, relating its DC power consumption (590 mW, including the SDCs) to its output voltage swing (4 Vpp,d), the driver shows one of the highest power efficiencies among PAM modulator drivers in the literature

Segmented optical transmitter comprising a CMOS driver array and an InP IQ-MZM for advanced modulation formats

Segmented Mach-Zehnder modulators are promising solutions to generate complex modulation schemes in the migration towards optical links with a higher-spectral efficiency. We present an optical transmitter comprising a segmented-electrode InP IQ-MZM, capable of multilevel optical signal generation (5-bit per I/Q arm) by employing direct digital drive from integrated, low-power (1W) CMOS binary drivers. We discuss the advantages and design tradeoffs of the segmented driver structure and the implementation in a 40 nm CMOS technology. Multilevel operation with combined phase and amplitude modulation is demonstrated experimentally on a single MZM of the device for 2-ASK-2PSK and 4-ASK-2-PSK, showing potential for respectively 16-QAM and 64-QAM modulation in future assemblies

Silicon photonic modulators for PAM transmissions

High-speed optical interconnects are crucial for both data centers and high performance computing systems. High power consumption and limited device bandwidth have hindered the move to higher optical transmission speeds. Integrated optical transceivers in silicon photonics (SiP) using pulse-amplitude modulation (PAM) are a promising solution to increase data rates. In this paper, we review recent progress in SiP for PAM transmissions. We focus on materials and technologies available CMOS-compatible photonics processes. Performance metrics of SiP modulators and crucial considerations for high-speed PAM transmissions are discussed. Various driving strategies to achieve optical PAM signals are presented. Some of the state-of-the-art SiP PAM modulators and integrated transmitters are reviewed

DAC-less PAM-4 generation in the O-band using a silicon Mach-Zehnder modulator

International audienceWe demonstrate 20-Gb/s 4-level pulse amplitude modulation (PAM-4) signal generation using a silicon Mach-Zehnder modulator (MZM) in the O-band. The modulator is driven by two independent binary streams, and the PAM-4 signal is thus generated directly on the chip, avoiding the use of power-hungry digital-to-analog converters (DACs). With optimized amplitude levels of the binary signals applied to the two arms of the MZM, a pre-forward error correction (FEC) bit-error rate (BER) as low as 7.6 × 10 −7 is obtained. In comparison with a commercially available LiNbO 3 modulator, the penalty is only 2 dB at the KP4 FEC threshold of 2.2 × 10 −4

QPSK Modulation in the O-Band Using a Single Dual-Drive Mach Zehnder Silicon Modulator

[EN] Keeping up with bandwidth requirements in next generation short- and long-reach optical communication systems will require migrating from simple modulation formats such as on-off keying to more advanced formats such as quaternary phase-shift keying (QPSK). In this paper, we report the first demonstration of QPSK signal generation in the O-band using a silicon dual-drive Mach-Zehnder modulator (DD-MZM). The performance of the silicon DD-MZM is assessed at 20 Gb/s and compared against a similar DD-MZM based on LiNbO3, showing a limited implementation power penalty of only 1.5 dB.This work was supported in part by the European project Plat4m (FP7-2012-318178); European project Cosmicc (H2020-ICT-27-2015- 688516); French Industry Ministry Nano2017 program.Pérez-Galacho, D.; Bramerie, L.; Baudot, C.; Chaibi, M.; Messaoudène, S.; Vulliet, N.; Vivien, L.... (2018). QPSK Modulation in the O-Band Using a Single Dual-Drive Mach Zehnder Silicon Modulator. Journal of Lightwave Technology. 36(18):3935-3940. https://doi.org/10.1109/JLT.2018.2851370S39353940361