6 research outputs found

    Next generation optical access networks and coexistence with legacy PONs

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    Nowadays, Fiber-to-the-Home is one of the most promising solutions to provide broadband services in access networks. However, the fiber is inefficiently used as most of the deployed systems are still based on Time Division Multiplexing Passive Optical Networks (TDM-PONs) providing shared transmission capacities up to 2.5 Gb/s down and 1.25 Gb/s up, among multiple users. Research on high-speed electronics and Wavelength Division Multiplexing (WDM) has allowed the emergence of what is known as the second generation PON (NG-PON2), which specify aggregated capacities up to 40 Gb/s, stacking four channels at symmetric data rates of 10 Gb/s each, for residential scenarios. Nevertheless, the capacity per channel is still shared between multiple users due to the use of TDM. Moreover, the optical spectrum efficiency is low because channels are widely spaced (50 to 100 GHz). In addition, the sensitivity, reach and number of users is limited as consequence of using direct detection (DD) systems. In consequence, and due to the increase in bandwidth demands of new multimedia applications, it is necessary to propose solutions that cope with this tendency and, even more important, that can coexist with legacy systems, being one of the major requirements of network operators to guarantee a smooth and non-disruptive technology migration. In this thesis, a breakthrough technology such as Ultra-Dense WDM (UDWDM) that allows to allocate a large number of channels spaced only by a few GHz is used. This approach consent to envision the concept of Wavelength-to-the-User, where each costumer can be served with dedicated bandwidth links. The key technologies are based on coherent systems, with inherent wavelength selectivity and improved sensitivity compared to DD systems, thanks to the booster action of a tunable local oscillator (LO) laser. Because of cost is the main constraint in access networks, especially at the customer premises equipment (Optical Network Unit - ONU), in this thesis, a new class of coherent transceivers, based on low-cost direct modulated lasers and simplified receiver schemes, are proposed and experimentally tested. Moreover, the issue of coexistence is investigated through theoretical studies and real-time implementations, demonstrating full compatibility with legacy systems. Between the proposed solutions, a simple technique to adjust digitally the direct phase modulation of a distributed feedback (DFB) laser is presented to support flexible transmission rates. Next, several multilevel phase modulation formats for achieving higher transmission rates and better spectral efficiency are experimentally compared. Subsequently, the topic of photonic integration is addressed, demonstrating for the first time an 8-ary hybrid amplitude and phase modulated transmitter (Tx), by using a low-cost, small-footprint and energy efficient dual electro-absorption modulated laser (DEML). Finally, two novel proposals, to reduce the complexity of heterodyne and intradyne detection, are provided to face the typical issue of complexity and high-cost of coherent systems. The former explores the possibility of using only one DFB laser as LO and Tx at the ONU. The later demonstrates for the first time, a novel phase time diversity technique alternating phase modulation at each complex component (in-phase - I and quadrature - Q) achieving a 10 Gb/s' transmission with polarization independence.En la actualidad, la Fibra hasta el Hogar es una de las soluciones m谩s prometedoras para proporcionar servicios de banda ancha en las redes de acceso. Sin embargo, la fibra se usa de manera poco eficiente, ya que la mayor铆a de los sistemas implementados todav铆a est谩n basados en redes 贸pticas pasivas de multiplexaci贸n por divisi贸n en el tiempo (TDM-PON) que brindan capacidades de transmisi贸n compartidas entre m煤ltiples usuarios de hasta 2.5 Gb/s y 1.25 Gb/s. La investigaci贸n en electr贸nica de alta velocidad y la multiplexaci贸n por divisi贸n de longitud de onda (WDM) ha permitido el surgimiento de lo hoy se conoce como PON de segunda generaci贸n (NG-PON2), que especifica capacidades agregadas de hasta 40 Gb/s, apilando cuatro canales a velocidades de datos sim茅tricas de 10 Gb/s cada uno, para escenarios residenciales. Sin embargo, la capacidad por canal todav铆a se comparte entre m煤ltiples usuarios debido al uso de TDM. Adem谩s, la eficiencia en el uso del espectro 贸ptico es baja porque los canales est谩n muy separados (50 a 100 GHz). Asimismo, la sensibilidad, el alcance y el n煤mero de usuarios est谩n limitados debido al uso de sistemas de detecci贸n directa. En consecuencia, y debido al aumento de las demandas de ancho de banda de las nuevas aplicaciones multimedia, es necesario proponer soluciones que respondan a esta tendencia y, lo que es m谩s importante, que puedan coexistir con sistemas heredados, siendo uno de los principales requisitos de los operadores de red para garantizar una migraci贸n de tecnolog铆a fluida y sin interrupciones. En esta tesis, se utiliza una tecnolog铆a de vanguardia, como la multiplexaci贸n por divisi贸n ultra densa de longitud de onda (UDWDM) que permite distribuir un gran n煤mero de canales espaciados solo por unos pocos GHz. Este enfoque permite vislumbrar el concepto de longitud de onda para el usuario, donde cada cliente puede usar enlaces de ancho de banda dedicados. Las tecnolog铆as clave est谩n basadas en los sistemas coherentes, con selectividad de longitud de onda inherente y sensibilidad mejorada en comparaci贸n con los sistemas de detecci贸n directa, gracias al efecto de amplificaci贸n 贸ptica de un l谩ser oscilador local (LO) sintonizable. Debido a que el costo es la principal restricci贸n en las redes de acceso, especialmente del equipo en las instalaciones del cliente (unidad de red 贸ptica - ONU), en 茅sta tesis, una nueva clase de transceptores coherentes, basados en l谩seres de bajo coste modulados directamente y esquemas de recepci贸n simplificados, son propuestos y probados experimentalmente. Adem谩s, el problema de la coexistencia es investigado a trav茅s de estudios te贸ricos y experimentos en tiempo real, demostrando compatibilidad total con los sistemas heredados. Entre las soluciones propuestas, se presenta una t茅cnica simple para ajustar digitalmente la modulaci贸n de fase directa de un l谩ser de retroalimentaci贸n distribuida (DFB), y admitir velocidades de transmisi贸n flexibles. Acto seguido, se comparan experimentalmente varios formatos multinivel de modulaci贸n de fase, para lograr tasas de transmisi贸n m谩s altas y una mejor eficiencia espectral. Posteriormente, se aborda el tema de la integraci贸n fot贸nica, demostrando por primera vez un transmisor (Tx) con modulaci贸n h铆brida de fase y amplitud de ocho puntos, mediante el uso de un dispositivo peque帽o, de bajo coste y eficiente energ茅ticamente, como lo es el l谩ser dual de electro-absorci贸n modulada (DEML). Finalmente, se presentan dos propuestas novedosas para reducir la complejidad de la detecci贸n heterodina e intradina, afrontando el problema t铆pico de la complejidad y alto coste de los sistemas coherentes. La primera explora la posibilidad de usar solo un l谩ser DFB en la ONU, como LO y Tx. La segunda, demuestra por primera vez, una nueva t茅cnica de diversidad fase en el tiempo, que alterna la modulaci贸n de fase en cada componente del plano complejo (fase-I y cuadratura-Q) logrando una transmisi贸n de 10 Gb / s / 位 con independencia de polarizaci贸nPostprint (published version

    Next generation optical access networks and coexistence with legacy PONs

    Get PDF
    Nowadays, Fiber-to-the-Home is one of the most promising solutions to provide broadband services in access networks. However, the fiber is inefficiently used as most of the deployed systems are still based on Time Division Multiplexing Passive Optical Networks (TDM-PONs) providing shared transmission capacities up to 2.5 Gb/s down and 1.25 Gb/s up, among multiple users. Research on high-speed electronics and Wavelength Division Multiplexing (WDM) has allowed the emergence of what is known as the second generation PON (NG-PON2), which specify aggregated capacities up to 40 Gb/s, stacking four channels at symmetric data rates of 10 Gb/s each, for residential scenarios. Nevertheless, the capacity per channel is still shared between multiple users due to the use of TDM. Moreover, the optical spectrum efficiency is low because channels are widely spaced (50 to 100 GHz). In addition, the sensitivity, reach and number of users is limited as consequence of using direct detection (DD) systems. In consequence, and due to the increase in bandwidth demands of new multimedia applications, it is necessary to propose solutions that cope with this tendency and, even more important, that can coexist with legacy systems, being one of the major requirements of network operators to guarantee a smooth and non-disruptive technology migration. In this thesis, a breakthrough technology such as Ultra-Dense WDM (UDWDM) that allows to allocate a large number of channels spaced only by a few GHz is used. This approach consent to envision the concept of Wavelength-to-the-User, where each costumer can be served with dedicated bandwidth links. The key technologies are based on coherent systems, with inherent wavelength selectivity and improved sensitivity compared to DD systems, thanks to the booster action of a tunable local oscillator (LO) laser. Because of cost is the main constraint in access networks, especially at the customer premises equipment (Optical Network Unit - ONU), in this thesis, a new class of coherent transceivers, based on low-cost direct modulated lasers and simplified receiver schemes, are proposed and experimentally tested. Moreover, the issue of coexistence is investigated through theoretical studies and real-time implementations, demonstrating full compatibility with legacy systems. Between the proposed solutions, a simple technique to adjust digitally the direct phase modulation of a distributed feedback (DFB) laser is presented to support flexible transmission rates. Next, several multilevel phase modulation formats for achieving higher transmission rates and better spectral efficiency are experimentally compared. Subsequently, the topic of photonic integration is addressed, demonstrating for the first time an 8-ary hybrid amplitude and phase modulated transmitter (Tx), by using a low-cost, small-footprint and energy efficient dual electro-absorption modulated laser (DEML). Finally, two novel proposals, to reduce the complexity of heterodyne and intradyne detection, are provided to face the typical issue of complexity and high-cost of coherent systems. The former explores the possibility of using only one DFB laser as LO and Tx at the ONU. The later demonstrates for the first time, a novel phase time diversity technique alternating phase modulation at each complex component (in-phase - I and quadrature - Q) achieving a 10 Gb/s' transmission with polarization independence.En la actualidad, la Fibra hasta el Hogar es una de las soluciones m谩s prometedoras para proporcionar servicios de banda ancha en las redes de acceso. Sin embargo, la fibra se usa de manera poco eficiente, ya que la mayor铆a de los sistemas implementados todav铆a est谩n basados en redes 贸pticas pasivas de multiplexaci贸n por divisi贸n en el tiempo (TDM-PON) que brindan capacidades de transmisi贸n compartidas entre m煤ltiples usuarios de hasta 2.5 Gb/s y 1.25 Gb/s. La investigaci贸n en electr贸nica de alta velocidad y la multiplexaci贸n por divisi贸n de longitud de onda (WDM) ha permitido el surgimiento de lo hoy se conoce como PON de segunda generaci贸n (NG-PON2), que especifica capacidades agregadas de hasta 40 Gb/s, apilando cuatro canales a velocidades de datos sim茅tricas de 10 Gb/s cada uno, para escenarios residenciales. Sin embargo, la capacidad por canal todav铆a se comparte entre m煤ltiples usuarios debido al uso de TDM. Adem谩s, la eficiencia en el uso del espectro 贸ptico es baja porque los canales est谩n muy separados (50 a 100 GHz). Asimismo, la sensibilidad, el alcance y el n煤mero de usuarios est谩n limitados debido al uso de sistemas de detecci贸n directa. En consecuencia, y debido al aumento de las demandas de ancho de banda de las nuevas aplicaciones multimedia, es necesario proponer soluciones que respondan a esta tendencia y, lo que es m谩s importante, que puedan coexistir con sistemas heredados, siendo uno de los principales requisitos de los operadores de red para garantizar una migraci贸n de tecnolog铆a fluida y sin interrupciones. En esta tesis, se utiliza una tecnolog铆a de vanguardia, como la multiplexaci贸n por divisi贸n ultra densa de longitud de onda (UDWDM) que permite distribuir un gran n煤mero de canales espaciados solo por unos pocos GHz. Este enfoque permite vislumbrar el concepto de longitud de onda para el usuario, donde cada cliente puede usar enlaces de ancho de banda dedicados. Las tecnolog铆as clave est谩n basadas en los sistemas coherentes, con selectividad de longitud de onda inherente y sensibilidad mejorada en comparaci贸n con los sistemas de detecci贸n directa, gracias al efecto de amplificaci贸n 贸ptica de un l谩ser oscilador local (LO) sintonizable. Debido a que el costo es la principal restricci贸n en las redes de acceso, especialmente del equipo en las instalaciones del cliente (unidad de red 贸ptica - ONU), en 茅sta tesis, una nueva clase de transceptores coherentes, basados en l谩seres de bajo coste modulados directamente y esquemas de recepci贸n simplificados, son propuestos y probados experimentalmente. Adem谩s, el problema de la coexistencia es investigado a trav茅s de estudios te贸ricos y experimentos en tiempo real, demostrando compatibilidad total con los sistemas heredados. Entre las soluciones propuestas, se presenta una t茅cnica simple para ajustar digitalmente la modulaci贸n de fase directa de un l谩ser de retroalimentaci贸n distribuida (DFB), y admitir velocidades de transmisi贸n flexibles. Acto seguido, se comparan experimentalmente varios formatos multinivel de modulaci贸n de fase, para lograr tasas de transmisi贸n m谩s altas y una mejor eficiencia espectral. Posteriormente, se aborda el tema de la integraci贸n fot贸nica, demostrando por primera vez un transmisor (Tx) con modulaci贸n h铆brida de fase y amplitud de ocho puntos, mediante el uso de un dispositivo peque帽o, de bajo coste y eficiente energ茅ticamente, como lo es el l谩ser dual de electro-absorci贸n modulada (DEML). Finalmente, se presentan dos propuestas novedosas para reducir la complejidad de la detecci贸n heterodina e intradina, afrontando el problema t铆pico de la complejidad y alto coste de los sistemas coherentes. La primera explora la posibilidad de usar solo un l谩ser DFB en la ONU, como LO y Tx. La segunda, demuestra por primera vez, una nueva t茅cnica de diversidad fase en el tiempo, que alterna la modulaci贸n de fase en cada componente del plano complejo (fase-I y cuadratura-Q) logrando una transmisi贸n de 10 Gb / s / 位 con independencia de polarizaci贸

    Energy Conservation in Passive Optical Networks: A Tutorial and Survey

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    The Passive Optical Network (PON) has been evolving continuously in terms of architecture and capacity to keep up with the demand for high-speed Internet access in the access network segment. Recently, integration of Software-Defined Networking (SDN), which provides programmable and (logically) centralized network control, with PON has attracted intensive research interest to further enhance PON performance and reduce operational and capital expenditure. Although PON is regarded as an energy-efficient a ccess n etwork s olution, it is a major contributor for increasing energy consumption in the access network segment because of its higher penetration rate than other access network technologies. Over the past several years, the major standardization bodies like IEEE and research communities have engaged in introducing energy-efficient PON solutions. This article familiarizes readers with PON evolution in terms of capacity, architecture, and its integration with virtualization and SDN based control. We present a comprehensive survey of the energy conservation research efforts in PON starting from conventional PON to SDN based PON leveraging virtual and physical network functions. This article also presents contemporary energy-efficient standardization activities in IEEE and ITU. To the best of our knowledge, to date, this article is the first most comprehensive survey on energy saving research and standardization on PON. We summarize the lessons learned from the recent advancements, identify important challenges ahead and outline several future research directions that can contribute to further advancement of energy-efficient PON

    Radio over fiber broadband access networks architectures based on wavelength division multiplexing techniques

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    The recent remarkable growth in bandwidth of both wired optical and wireless access networks supports a burst of new high bandwidth Internet applications such as: peer-topeer file sharing, cloud storage, on-line gaming, video streaming, etc. Within this scenario, the convergence of fixed and wireless access networks offers significant opportunities for network operators to satisfy user demands, and simultaneously reduce the cost of implementing and running separated wireless and wired networks. The integration of wired and wireless network can be accomplished within several scenarios and at several levels. In this thesis we will focus on converged radio over fiber architectures, particularly on two application scenarios: converged optical 60 GHz wireless networks and wireless overlay backhauling over bidirectional colorless wavelength division multiplexing passive optical networks (WDM-PONs). In the first application scenario, optical 60 GHz signal generation using external modulation of an optical carrier by means of lithium niobate (LiNbO3) Mach- Zehnder modulators (MZM) is considered. The performance of different optical modulation techniques, robust against fiber dispersion is assessed and dispersion mitigation strategies are identified. The study is extended to 60 GHz carriers digitally modulated with data and to systems employing subcarrier multiplexed (SCM) mm-wave channels. In the second application scenario, the performance of WDM-PONs employing reflective semiconductor optical amplifiers (RSOAs), transmitting an overlay orthogonal frequency-division multiplexing (OFDM) wireless signal is assessed analytically and experimentally, with the relevant system impairments being identified. It is demonstrated that the intermodulation due to the beating of the baseband signal and wireless signal at the receiver can seriously impair the wireless channel. Performance degradation of the wireless channel caused by the RSOA gain modulation owing to the downstream baseband data is also assessed, and system design guidelines are provided.Universidade do Algarve, Faculdade de Ci锚ncias e Tecnologi

    Radio over fiber broadband access networks architectures based on wavelength division multiplexing techniques

    Get PDF
    The recent remarkable growth in bandwidth of both wired optical and wireless access networks supports a burst of new high bandwidth Internet applications such as: peer-topeer file sharing, cloud storage, on-line gaming, video streaming, etc. Within this scenario, the convergence of fixed and wireless access networks offers significant opportunities for network operators to satisfy user demands, and simultaneously reduce the cost of implementing and running separated wireless and wired networks. The integration of wired and wireless network can be accomplished within several scenarios and at several levels. In this thesis we will focus on converged radio over fiber architectures, particularly on two application scenarios: converged optical 60 GHz wireless networks and wireless overlay backhauling over bidirectional colorless wavelength division multiplexing passive optical networks (WDM-PONs). In the first application scenario, optical 60 GHz signal generation using external modulation of an optical carrier by means of lithium niobate (LiNbO3) Mach- Zehnder modulators (MZM) is considered. The performance of different optical modulation techniques, robust against fiber dispersion is assessed and dispersion mitigation strategies are identified. The study is extended to 60 GHz carriers digitally modulated with data and to systems employing subcarrier multiplexed (SCM) mm-wave channels. In the second application scenario, the performance of WDM-PONs employing reflective semiconductor optical amplifiers (RSOAs), transmitting an overlay orthogonal frequency-division multiplexing (OFDM) wireless signal is assessed analytically and experimentally, with the relevant system impairments being identified. It is demonstrated that the intermodulation due to the beating of the baseband signal and wireless signal at the receiver can seriously impair the wireless channel. Performance degradation of the wireless channel caused by the RSOA gain modulation owing to the downstream baseband data is also assessed, and system design guidelines are provided.Universidade do Algarve, Faculdade de Ci锚ncias e Tecnologi
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