REAM intensity modulator-enabled 10Gb/s colorless upstream transmission of real-time optical OFDM signals in a single-fiber-based bidirectional PON architecture

Reflective electro-absorption modulation-intensity modulators (REAM-IMs) are utilized, for the first time, to experimentally demonstrate colorless ONUs in single-fiber-based, bidirectional, intensity-modulation and direct-detection (IMDD), optical OFDM PONs (OOFDM-PONs) incorporating 25km SSMFs and OLT-side-seeded CW optical signals. The colorlessness of the REAM-IMs is characterized, based on which optimum REAM-IM operating conditions are identified. In the aforementioned PON architecture, 10Gb/s colorless upstream transmissions of end-to-end realtime OOFDM signals are successfully achieved for various wavelengths within the entire C-band. Over such a wavelength window, corresponding minimum received optical powers at the FEC limit vary in a range as small as <0.5dB. In addition, experimental measurements also indicate that Rayleigh backscattering imposes a 2.8dB optical power penalty on the 10Gb/s over 25km upstream OOFDM signal transmission. Furthermore, making use of on-line adaptive bit and power loading, a linear trade-off between aggregated signal line rate and optical power budget is observed, which shows that, for the present PON system, a 10% reduction in signal line rate can improve the optical power budget by 2.6dB. © 2012 Optical Society of America

Feasibility of Using Bandwidth Efficient Modulation to Upgrade the CMS Tracker Readout Optical Links

Plans to upgrade the LHC after approximately 10 years of operation are currently being considered at CERN. A tenfold increase in luminosity delivered to the experiments is envisaged in the so-called Super LHC (SLHC). This will undoubtedly give rise to significantly larger data volumes from the detectors, requiring faster data readout. The possibility of upgrading the CMS Tracker analog readout optical links using a bandwidth efficient digital modulation scheme for deployment in the SLHC has been extensively explored at CERN. Previous theoretical and experimental studies determined the achievable data rate using a system based on Quadrature Amplitude Modulation (QAM) to be ~3-4Gbit/s (assuming no error correction is used and for an error rate of ~10-9). In this note we attempt to quantify the feasibility of such an upgrade in terms of hardware implementation complexity, applicability to the high energy physics (HEP) environment, technological feasibility and R&D effort required.Comment: CERN CMS Note. 16 pages, 10 figure

Chip-based Brillouin processing for carrier recovery in coherent optical communications

Modern fiber-optic coherent communications employ advanced spectrally-efficient modulation formats that require sophisticated narrow linewidth local oscillators (LOs) and complex digital signal processing (DSP). Here, we establish a novel approach to carrier recovery harnessing large-gain stimulated Brillouin scattering (SBS) on a photonic chip for up to 116.82 Gbit/sec self-coherent optical signals, eliminating the need for a separate LO. In contrast to SBS processing on-fiber, our solution provides phase and polarization stability while the narrow SBS linewidth allows for a record-breaking small guardband of ~265 MHz, resulting in higher spectral-efficiency than benchmark self-coherent schemes. This approach reveals comparable performance to state-of-the-art coherent optical receivers without requiring advanced DSP. Our demonstration develops a low-noise and frequency-preserving filter that synchronously regenerates a low-power narrowband optical tone that could relax the requirements on very-high-order modulation signaling and be useful in long-baseline interferometry for precision optical timing or reconstructing a reference tone for quantum-state measurements.Comment: Part of this work has been presented as a postdealine paper at CLEO Pacific-Rim'2017 and OSA Optic

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

On The Non-linear Distortion Effects in an OFDM-RoF Link

Radio over Fiber (RoF) system is a promising technique for microcell and picocell applications for deployment of future ubiquitous wireless data networks. However, the performance of RoF systems can be severely degraded due to non-linear effects in the channel. Also, Orthogonal Frequency Division Multiplexing (OFDM), as a standard for broadband wireless networks, is being proposed for deployment with RoF systems to facilitate the total performance of a system. In this research, at first, the performance of OFDM-based RoF link with Mach-Zehnder modulator distortion effects has been analyzed at 5.8 GHz. Evaluation of mean-squared error of the proposed OFDM-RoF system was carried out to compare with the conventional single carrier system based RoF link after the modulator distortion case and also for fixed Signal to Noise Ratio (SNR) of 20 dB using undistorted OFDM signal. Later, nominal and offset biasing pre-distortion techniques are applied in proposed system to linearize the OFDM-RoF link. Thus, finally a comparison between the aforementioned pre-distortion techniques applied showed important observation in terms of distortion-free dynamic range and SNR to choose offset pre-distortion technique for our proposed system

SiP-based SSBI cancellation for OFDM

We propose for the first time to use a silicon photonics (SiP) solution for a passive optical network to both reduce signal-signal beat interference (SSBI) and recuperate a part of the downlink carrier for use in the uplink. The Kramers-Kronig (KK) receiver for direct detection of advanced modulation formats overcomes SSBI at the cost of a moderate carrier to signal ratio (>6 dB) and high oversampling (4X). We propose an optical SSBI solution that achieves better performance than KK and requires only standard sampling and low (3 dB) carrier to signal power ratio. The receiver is conceived for the downlink in passive optical networks, where carrier signal must be husbanded for re-use in the uplink. Using cost effective and power efficient SiP, the receiver filters the incoming signal, suppresses SSBI, and routes a portion of the carrier for use in the uplink. We experimentally examine the SSBI suppression in this paper. While previous demonstrations used bulky, discrete components, we achieve significant Q-factor improvement with a simple SiP solution. We examine the optimal frequency offset between the carrier and the microring resonator center frequency. The robustness to frequency drift, as well as the impact of imperfect filtering, is discussed and quantified

Characterization and design of coherent optical OFDM transmission systems based on Hartley Transform

Nowadays, due to huge deployment of optical transport networks, a continuous increase towards higher data rates up to 100 Gb/s and beyond is observed. Furthermore, an evolution of the current optical networks is forecasted, acquiring new functionalities, e.g. elastic spectrum assignment for the optical signals. The target for these new challenges in transmission is to find techniques ready to deal with a growth of demand for bandwidth continuously asked by network operators, for whom the standard systems do not meet the new functionalities while higher rates are being set up. A solution for covering all of those needs is to adapt techniques capable to deal with such enormous data rates, and ensuring the same high efficiency for long distances and mitigate the optical impairments accumulated along the transmission path. Additionally, these transmission techniques are expected to provide some degree of flexibility, in order to enhance the network flexibility. A promising technology that can fully cope with those requires is the coherent optical orthogonal frequency division multiplexing (CO-OFDM). CO-OFDM provides several advantages, namely high sensitivity and spectral efficiency, simple integration and possibility to fully recover a signal in phase, amplitude and polarization. These systems are composed by digital signal processing (DSP) blocks that easily process data and can equalize and compensate the main impairments, providing high tolerance for dispersion effects. However, CO-OFDM systems are not free from drawbacks. Their high peak-to-average power ratio (PAPR) reduce their tolerance to nonlinearities. Furthermore, CO-OFDM systems are sensitive to any frequency shift and phase offset. Hence, a constant envelope optical OFDM (CE-OFDM) is proposed for significantly reducing the PAPR and solving high sensitivity to nonlinear impairments. It consists in a phase modulated discrete multi-tone signal, which is coherently detected at the receiver side. An alternative transform, the discrete Hartley transform, is proposed to speed up calculations in the DSP and eliminate the need to have a Hermitian symmetry. The optical CE-OFDM by its unique flexibility and rate scalability turns out as a great technology applicable to different configurations, ranging from access to core networks. In case of access solutions, several cases are investigated. First, the optical CE-OFDM is applied for radio access network signals delivery by means of a wavelength division multiplexing (WDM) overlay in deployed access architecture. A decomposed radio access network is deployed over an existing standard passive optical network (PON), capable to avoid interference and cross talks with access signals between network clients. The system exhibited narrow channel spacing, while reducing losses fed into the access equipment path. Next, a full duplex 10 Gb/s bidirectional PON transmission over a single wavelength with RSOA based ONU is investigated. The key point of that system is the upstream transmission, which is achieved re-modulating the phase of a downstream intensity modulated signal after proper saturation. The reported sensitivity performances show a power budget matching the PON standards and an OSNR easy to reach on non-amplified PON. Next, a flexible metropolitan area network of up to 100km with traffic add/drop using WDM is investigated. There the narrowing effect of the optical filters is studied. Finally, an elastic upgrade of the existing Telefonica model of the Spanish national core network is proposed. For that, the transceiver architecture is proposed to be operated featuring polarization multiplexing. Respect to the existing fixed grid, the flexible approach (enabled by the CE-OFDM transceiver) results into reduced bandwidth occupancy and low OSNR requirement.Hoy en día, debido al gran despliegue de las redes de ópticas de transporte, se espera un aumento continuado hacia mayores velocidades de datos, hasta 100 Gb/s y más allá. Por otra parte, la evolución que se prevé para las redes ópticas actuales, incluye la adquisición de nuevas funcionalidades, por ejemplo, la asignación del espectro de forma elástica para las señales ópticas. Por tanto, el claro desafío en cuanto a las tecnologías de transmisión es encontrar técnicas preparadas para hacer frente a un crecimiento de la demanda de ancho de banda; demanda que continuamente se incrementa por parte de los operadores de red, para quienes los sistemas estándar no se acaban de ajustar a las nuevas funcionalidades que esperan para la red. Una solución para cubrir todas estas necesidades es la adaptación de técnicas capaces de hacer frente a estas velocidades de datos enormes, y garantizar el mismo nivel de eficiencia para las largas distancias y mitigar las deficiencias ópticas acumuladas a lo largo de la ruta de transmisión. Además, se espera que estas técnicas de transmisión puedan proporcionar cierto grado de flexibilidad, a fin de mejorar y hacer más eficiente la gestión de la red. Una tecnología prometedora que puede hacer frente a estos requisitos es lo que se llama multiplexación por división de frecuencias ortogonales, combinado con la detección óptica coherente (CO-OFDM). CO-OFDM ofrece varias ventajas, entre otras: alta sensibilidad y eficiencia espectral y, sobre todo, la posibilidad de recuperar por completo de una señal en fase, la amplitud y la polarización. Estos sistemas están compuestos por bloques de procesado de señales digitales (DSP) que permiten detectar los datos fácilmente así como también compensar las principales degradaciones, proporcionando alta tolerancia a los efectos de dispersión. Sin embargo, los sistemas CO-OFDM no están exentos de inconvenientes. Su alta relación de potencia de pico a potencia media (PAPR) reduce sensiblemente la tolerancia no linealidades. Por otra parte, los sistemas CO-OFDM son sensibles a cualquier cambio de frecuencia y desplazamiento de fase. Por tanto, se propone un sistema OFDM de envolvente constante (CE-OFDM) para reducir significativamente la PAPR y solucionar la alta sensibilidad a las degradaciones no lineales. Consiste en una señal OFDM modulada en fase, que se detecta coherentemente en el receptor. Una transformada alternativa, la transformada discreta de Hartley, se propone para acelerar los cálculos en el DSP. El sistema CE-OFDM por su flexibilidad y escalabilidad única, resulta una tecnología aplicable a diferentes escenarios, que van desde las redes de acceso hasta las redes troncales. En el caso de las soluciones de acceso, se investigan varios casos. En primer lugar, el CE-OFDM aplica para el desarrollo y soporte de datos de una red radio, reutilizando una red óptica de acceso ya desplegada. A continuación, se investiga la transmisión bidireccional dúplex a 10 Gb / s sobre una sola longitud de onda empleando un RSOA a las unidades de usuario. El punto clave de este sistema es la transmisión en sentido ascendente, que se consigue re-modulando la fase de una señal de intensidad modulada después de saturar de forma adecuada. A continuación, se estudia una red de área metropolitana flexible de hasta 100 km. Concretamente el efecto de concatenación de filtros ópticos es el objetivo de este estudio. Finalmente, se propone una actualización elástica del modelo de Telefónica I+D para la red troncal española. Por ello, se propone operar el CE-OFDM en multiplexación de polarización. Los resultados muestran que esta combinación reduce sensiblemente el empleo de ancho de banda esto como los requisitos de los enlaces transmisión, reduciendo también los costes tanto de desarrollo como de operación y mantenimiento de la red.Avui dia, a causa del gran desplegament de les xarxes de òptiques de transport, s'espera un augment continuat cap a majors velocitats de dades, fins a 100 Gb/s i més enllà. D'altra banda, l'evolució que es preveu per a les xarxes òptiques actuals, inclou l'adquisició de noves funcionalitats, per exemple, assignació de l'espectre de forma elàstica per als senyals òptics. Per tant, el clar desafiament pel que fa a les tecnologies de transmissió és trobar tècniques preparades per fer front a un creixement de la demanda d'ample de banda; demanda que contínuament es fa per part dels operadors de xarxa, per als qui els sistemes estàndard no s'acaben d'ajustar a les noves funcionalitats que esperen per a la xarxa. Una solució per a cobrir totes aquestes necessitats és l'adaptació de tècniques capaces de fer front a aquestes velocitats de dades enormes, i garantir el mateix nivell d'eficiència per a les llargues distàncies i mitigar les deficiències òptiques acumulades al llarg de la ruta de transmissió. A més, s'espera que aquestes tècniques de transmissió puguin proporcionar cert grau de flexibilitat, per tal de millorar i tornar més eficient la gestió de la xarxa. Una tecnologia prometedora que pot fer front a aquests requisits és el que s'anomena multiplexació per divisió de freqüències ortogonals, combinat amb la detecció òptica coherent (CO-OFDM). CO-OFDM ofereix diversos avantatges, entre altres: alta sensibilitat i eficiència espectral i, sobretot, la possibilitat de recuperar per complet d'una senyal en fase, l'amplitud i la polarització. Aquests sistemes estan compostos per blocs de processament de senyals digitals (DSP) que permeten detectar les dades fàcilment així com també compensar les principals degradacions, proporcionant alta tolerància pels efectes de dispersió. No obstant això, els sistemes CO-OFDM no estan exempts d'inconvenients. La seva alta relació de potència de pic a potència mitjana (PAPR) redueix sensiblement la tolerància a no linealitats. D'altra banda, els sistemes de CO-OFDM són sensibles a qualsevol canvi de freqüència i desplaçament de fase. Per tant, es proposa un sistema OFDM d'envolvent constant (CE-OFDM) per a reduir significativament la PAPR i solucionar l'alta sensibilitat a les degradacions no lineals. Consisteix en un senyal OFDM modulat en fase, que es detecta coherentment en el receptor. Una transformada alternativa, la transformada discreta d'Hartley, es proposa accelerar els càlculs en el DSP. El sistema CE-OFDM per la seva flexibilitat i escalabilitat única, resulta una tecnologia aplicable a diferents escenaris, que van des de les xarxes d'accés fins a les xarxes troncals. En el cas de les solucions d'accés, s'investiguen diversos casos. En primer lloc, el CE-OFDM s'aplica per al desplegament i suport de dades d'una xarxa radio, reutilitzant una xarxa òptica d'accés ja desplegada. A continuació, s'investiga la transmissió bidireccional dúplex a 10 Gb/s sobre una sola longitud d'ona emprant un RSOA a les unitats d'usuari. El punt clau d'aquest sistema és la transmissió en sentit ascendent, que s'aconsegueix re-modulant la fase d'un senyal d'intensitat modulada després de saturar-la de forma adequada. A continuació, s'estudia una xarxa d'àrea metropolitana flexible de fins a 100 km. Concretament l'efecte de concatenació de filtres òptics és l'objectiu d'aquest estudi. Finalment, es proposa una actualització elàstica del model de Telefónica I+D per a la xarxa troncal espanyola. Per això, es proposa operar el CE-OFDM en multiplexació de polarització. Els resultats mostren que aquesta combinació redueix sensiblement l'ocupació d'ample de banda això com també els requisits dels enllaços transmissió, reduint també els costos tant de desplegament com d'operació i manteniment de la xarxa