Publication: Contribuciones a las comunicaciones ópticas en espacio libre: utilización de telescopios Cherenkov como receptores y corrección de Beam Wander en comunicaciones cuánticas
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2015-05
Defense date
2015-06-11
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Abstract
Actualmente existe un consenso en que las comunicaciones ópticas en espacio libre constituirán la próxima generación de enlaces inalámbricos de alta velocidad en varios escenarios estratégicos. Esta tesis se centra en los dos donde esta tecnología puede producir un mayor impacto: comunicaciones interplanetarias y comunicaciones cuánticas. Consecuentemente, este trabajo está estructurado en dos bloques. En el primero, se ofrece una propuesta novedosa relacionada con la utilización de telescopios Cherenkov como estaciones receptoras. Las señales que se recibirán en la Tierra desde sondas en espacio profundo en futuras implementaciones de comunicaciones ópticas serán extremadamente débiles y se requerirán nuevas estaciones terrenas para dar soporte a estos enlaces. Esta tesis analiza la viabilidad de utilizar la tecnología desarrollada para los telescopios de rayos gamma que constituirán el observatorio CTA (Cherenkov Telescope Array) en la implementación de una nueva clase de estación terrena receptora. Entre las principales ventajas que brindan estos telescopios se encuentran las mayores aperturas necesarias para superar las limitaciones de potencia que comparte la astronomía terrestre de rayos gamma y las comunicaciones ópticas desde espacio profundo. Además, el elevado número de grandes telescopios que se construirán para CTA hará posible reducir costes unitarios gracias a una producción masiva. El segundo bloque de la tesis se enmarca en las comunicaciones cuánticas en espacio libre y en particular en la distribución de clave cuántica (QKD), que se ha convertido en un nuevo paradigma en el campo de la seguridad de la información. Esta técnica ofrece una forma teóricamente segura de comunicarse a través de un canal inseguro gracias a que es posible detectar la presencia de un intruso. QKD ha demostrado ser una forma fiable de transmitir datos sensibles mediante fibra óptica. Sin embargo, su alternativa no guiada también ofrece importantes ventajas, así como nuevos retos. El más importante es la necesidad de operar bajo una fuerte turbulencia atmosférica y altos niveles de ruido de fondo durante el día. Para mitigar estos efectos normalmente se lleva a cabo un compromiso al diseñar la óptica del receptor, ya que un campo de visión estrecho mejora el rechazo al ruido de fondo, pero aumenta las pérdidas relacionadas con las turbulencias y un campo de visión amplio produce el efecto opuesto. En este segundo bloque de la tesis se propone la utilización de un sistema de corrección de turbulencias para solucionar ambas limitaciones de forma simultánea, y se analizan y experimentan las distintas estrategias para llevar a cabo la implementación e integración con el sistema de QKD.
Free-space optical communication is widely regarded as the next-generation of high-speed wireless communication links in several scenarios. This thesis focuses on the two main applications where this technology can bring the most significant impact: interplanetary communications and quantum communications. Consequently, the dissertation is structured in two sections. In the first one, a novel proposal is suggested regarding to using Cherenkov telescopes as ground-station receivers. The signals that will be received on Earth from future lasercom transmitters in deep-space will be extremely weak and new ground stations will have to be developed in order to adequately support these links. This thesis addresses the feasibility of using the technology developed for the gamma-ray telescopes that will make up the Cherenkov Telescope Array (CTA) observatory in the implementation of a new kind of ground station. Among the main advantages that these telescopes provide are the much larger apertures needed to overcome the power limitation that ground-based gamma-ray astronomy and deep-space optical communication both have. Also, the large number of big telescopes that will be built for CTA will make it possible to reduce unitary costs by economy-scale production. The second section of the thesis is framed in the field of free-space quantum communications. In particular, in quantum key distribution (QKD), which has become a new paradigm in the discipline of information security. This technique offers a theoretically-secure way to communicate over an insecure channel since the presence of an eventual eavesdropper can be detected during the key transmission. QKD has proven to be a reliable way to transmit sensitive data through optical fiber. However, the free-space alternative also brings important advantages, as well as new challenges. The main challenge is the need to operate both under strong atmospheric turbulence and daylight background noise. In order to mitigate these effects, a trade-off is usually required when designing the receiver's optics, since a narrow field-of-view improves background noise rejection, but increases turbulence-related losses and a wide field-of-view produces the opposite effect. In this section of the thesis, a correction system for atmospheric turbulence is proposed to overcome both limitations at the same time, and different strategies are analyzed and experimented to carry out the implementation and integration within the QKD system.
Free-space optical communication is widely regarded as the next-generation of high-speed wireless communication links in several scenarios. This thesis focuses on the two main applications where this technology can bring the most significant impact: interplanetary communications and quantum communications. Consequently, the dissertation is structured in two sections. In the first one, a novel proposal is suggested regarding to using Cherenkov telescopes as ground-station receivers. The signals that will be received on Earth from future lasercom transmitters in deep-space will be extremely weak and new ground stations will have to be developed in order to adequately support these links. This thesis addresses the feasibility of using the technology developed for the gamma-ray telescopes that will make up the Cherenkov Telescope Array (CTA) observatory in the implementation of a new kind of ground station. Among the main advantages that these telescopes provide are the much larger apertures needed to overcome the power limitation that ground-based gamma-ray astronomy and deep-space optical communication both have. Also, the large number of big telescopes that will be built for CTA will make it possible to reduce unitary costs by economy-scale production. The second section of the thesis is framed in the field of free-space quantum communications. In particular, in quantum key distribution (QKD), which has become a new paradigm in the discipline of information security. This technique offers a theoretically-secure way to communicate over an insecure channel since the presence of an eventual eavesdropper can be detected during the key transmission. QKD has proven to be a reliable way to transmit sensitive data through optical fiber. However, the free-space alternative also brings important advantages, as well as new challenges. The main challenge is the need to operate both under strong atmospheric turbulence and daylight background noise. In order to mitigate these effects, a trade-off is usually required when designing the receiver's optics, since a narrow field-of-view improves background noise rejection, but increases turbulence-related losses and a wide field-of-view produces the opposite effect. In this section of the thesis, a correction system for atmospheric turbulence is proposed to overcome both limitations at the same time, and different strategies are analyzed and experimented to carry out the implementation and integration within the QKD system.
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Keywords
Comunicaciones ópticas, Astrofísica nuclear, Telescopio de rayos gamma, Criptografía, Telescopio Cherenkov