High-speed Coherent Optical Communication with Isolator-free Heterogeneous Si/III-V Lasers

Coherent optical communication is considered as an indispensable solution to the ever-increasing demand for higher data rates. To reduce the cost and form factor of coherent transceivers, full integration of photonic devices including lasers, modulators, amplifiers, photodetectors, and other components is necessary. However, as fabricating optical isolators on chip remains extremely challenging, optical feedback, which can degrade the coherence of semiconductor lasers, becomes the main obstacle, thwarting large-scale photonic integration. An appealing solution to such a problem is to use semiconductor lasers with intrinsic insensitivity to optical feedback as the integrated light sources. The heterogenous Si/III-V lasers, with their built-in high-Q resonators, are expected to possess a robustness to optical feedback which exceeds by several orders of magnitude compared to commercial III-V distributed feedback (DFB) lasers, which will be validated here. We present data showing that the heterogeneous Si/III-V lasers can preserve their phase coherence under much larger optical feedback and therefore function without severe degradation in isolator-free coherent optical communication systems

Mode-division-multiplexing of multiple Bessel-Gaussian beams carrying orbital-angular-momentum for obstruction-tolerant free-space optical and millimetre-wave communication links

We experimentally investigate the potential of using ‘self-healing’ Bessel-Gaussian beams carrying orbital-angular-momentum to overcome limitations in obstructed free-space optical and 28-GHz millimetre-wave communication links. We multiplex and transmit two beams (l = +1 and +3) over 1.4 metres in both the optical and millimetre-wave domains. Each optical beam carried 50-Gbaud quadrature-phase-shift-keyed data, and each millimetre-wave beam carried 1-Gbaud 16-quadrature-amplitude-modulated data. In both types of links, opaque disks of different sizes are used to obstruct the beams at different transverse positions. We observe self-healing after the obstructions, and assess crosstalk and power penalty when data is transmitted. Moreover, we show that Bessel-Gaussian orbital-angular-momentum beams are more tolerant to obstructions than non-Bessel orbital-angular-momentum beams. For example, when obstructions that are 1 and 0.44 the size of the l = +1 beam, are placed at beam centre, optical and millimetre-wave Bessel-Gaussian beams show ~6 dB and ~8 dB reduction in crosstalk, respectively

Experimental characterization of a 400 Gbit/s orbital angular momentum multiplexed free-space optical link over 120 m

We experimentally demonstrate and characterize the performance of a 400-Gbit/s orbital angular momentum (OAM) multiplexed free-space optical link over 120- meters on the roof of a building. Four OAM beams, each carrying a 100-Gbit/s QPSK channel are multiplexed and transmitted. We investigate the influence of channel impairments on the received power, inter-modal crosstalk among channels, and system power penalties. Without laser tracking and compensation systems, the measured received power and crosstalk among OAM channels fluctuate by 4.5 dB and 5 dB, respectively, over 180 seconds. For a beam displacement of 2 mm that corresponds to a pointing error less than 16.7 μrad, the link bit-error-rates are below the forward error correction threshold of 3.8×10-3 for all channels. Both experimental and simulation results show that power penalties increase rapidly when the displacement increases

Orbital-angular-momentum-multiplexed free-space optical communication link using transmitter lenses

In this paper, we explore the potential benefits and limitations of using transmitter lenses in an orbital-angular-momentum (OAM)-multiplexed free-space optical (FSO) communication link. Both simulation and experimental results indicate that within certain transmission distances, using lenses at the transmitter to focus OAM beams could reduce power loss in OAM-based FSO links and that this improvement might be more significant for higher-order OAM beams. Moreover, the use of transmitter lenses could enhance system tolerance to angular error between transmitter and receiver, but they might degrade tolerance to lateral displacement

In Vivo Near-Infrared Imaging of Fibrin Deposition in Thromboembolic Stroke in Mice

imaging of activated factor XIII (FXIIIa), an important mediator of thrombosis or fibrinolytic resistance. The present study was to investigate the fibrin deposition in a thromboembolic stroke mice model by FXIIIa–targeted near-infrared fluorescence (NIRF) imaging., which were correlated with histology after animal euthanasia. NIRF images and lesion volume.Non-invasive detection of fibrin deposition in ischemic mouse brain using NIRF imaging is feasible and this technique may provide an in vivo experimental tool in studying the role of fibrin in stroke

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Development of SOA-based space switches and photonic integrated circuit interface for optical interconnection networks

With the explosive increase of internet services and diverse applications ranging from video streaming, social networking and cloud computing, the requirements of modern computing platforms keep increasing to satisfy the demand for fast computation, data analysis and processing. This situation poses challenging requirements to the data center/HPC network in terms of throughput, scalability, and power consumption. Optical interconnection network has been proposed as a promising means to meet the increase of communication bandwidth and data throughput with low power consumption. Energy-proportional optical interconnections are enabled by semiconductor optical amplifiers (SOAs) remaining off (or idle) when not routing data. In this work, the physical layer scalability of SOA-based optical space switches configured with different gain and loss is assessed using an experimental recirculating loop. Results demonstrate that for a 13.0-dB gain/loss configuration, optical multi-channel packets successfully propagate through a series of 14 SOAs with a BER < 10-9, which indicates that a single-stage space switch can scale up to 109 ports. Scalability improves for lower gain/loss configuration at the cost of more SOAs per routing path. As expected, scalability is limited by cross-gain modulation (XGM) and optical signal-to-noise ratio (OSNR) degradation, but their detrimental impact depends on the architecture configuration. Furthermore, an SOA model used as a tool to predict the performance degradation of SOA-based space switches is developed and validated. Given the potential on-chip large-scale integration of SOA-based space switches or other optical interconnection networks, high density optical connections are required. In that context, an ultra dense silicon photonics interface for the coupling between optical fiber and photonic integrated circuits (PICs) is designed and fabricated. The designed optical interface consists of compact grating coupler array and nanophotonic waveguides. The simulation results and experimental characterization of chip performance are presented, indicating a potential high capacity optical connection for off-chip and on-chip communications.Avec l'augmentation explosive des services Internet et des applications diverses allant des vidéos en continu, aux réseaux sociaux en passant par l’informatique en nuage, les exigences pour les plates-formes informatiques modernes ne cessent d'augmenter pour satisfaire la demande pour le calcul rapide et l’analyse et le traitement de données. Cette situation crée des exigences complexes sur les centres de données et réseaux HPC en terme de débit, d’extensibilité et de consommation d'énergie. Un réseau d'interconnexion optique à faible consommation d'énergie est proposé comme moyen prometteur pour répondre à l'augmentation de la bande passante et du débit de données pour les communications. Les interconnexions optiques à énergie proportionnelle sont activées par des amplificateurs optiques à semiconducteur (SOA) et sont fermés (ou au repos) lorsqu'elles ne transfèrent pas de données. Dans cette thèse, l'extensibilité de la couche physique des commutateurs optiques spatiaux basés sur des SOA et configurés pour différents gains et pertes est évaluée à l'aide d'une boucle de recirculation expérimentale. Les résultats montrent que pour une configuration de gain / perte de 13.0 dB, des paquets de données optiques et multi-canaux se propagent avec succès à travers une série de 14 SOA avec un taux d'erreur binaire (BER) de moins de 10-9, ce qui indique qu'un commutateur spatial en une seule étape peut s'échelonner jusqu'à 109 ports. L'extensibilité s'améliore pour des configurations à moindre gain / perte, au coût de plus de SOA par chemin de routage. Tel que prévu, l'extensibilité est limitée par la modulation par saturation de gain (XGM) et la dégradation du rapport signal sur bruit optique (OSNR), mais leur impact négatif dépend de l'architecture. En outre, un modèle SOA est élaboré et validé comme outil pour prédire la dégradation de la performances des commutateurs spatiaux SOA. Compte tenu de l'intégration à grande échelle de commutateurs spatiaux SOA ou autres réseaux d'interconnexion optiques sur puce, des connexions optiques à haute densité sont nécessaires. Dans ce contexte, une interface photonique ultra dense sur silicium pour le couplage entre une fibre optique et des circuits photoniques intégrés (PIC) a été conçue et fabriquée. L'interface optique conçue est composée de coupleurs à réseaux compacts et de guides d'onde nanophotoniques. Les résultats de simulation et la caractérisation expérimentale des performances de la puce sont présentés, indiquant une potentielle connexion optique à haute capacité pour les communications sur puce et hors puce