A Few-Mode-Fiber Platform for Quantum Communication Applications

Abstract

Society as we know it today would not have been possible without the explosive and astonishing development of telecommunications systems, and optical fibers have been one of the pillars of these technologies.Despite the enormous amount of data being transmitted over optical networks today, the trend is that the demand for higher bandwidths will also increase. Given this context, a central element in the design of telecommunications networks will be data security, since information can often be confidential or private.Quantum information emerges as a solution to encrypt data by quantum key distribution (QKD) between two users. This technique uses the properties of nature as the fundamentals of operation rather than relying on mathematical constructs to provide data protection. A popular alternative to performing QKD is to use the relative phase between two individual photon paths for information encoding. However, this method was not practical over long distances. The timebin-based scheme was a solution to the previous problem given its practical nature, however, it introduces intrinsic losses due to its design, which increases with the dimension of the encoded quantum system.In this thesis we have designed and tested a fiber-optic platform using spatialdivision-multiplexing techniques. The use of few-mode fibers and photonic lanterns are the cornerstone of our proposal, which also allow us to support orbital angular momentum (OAM) modes. The platform builds on the core ideas of the phasecoded quantum communication system and also takes advantage of the benefits proposed by the time-bin scheme. We have experimentally tested our proposal by successfully transmitting phase-coded single-photon states over 500 m few-mode fiber, demonstrating the feasibility of our scheme. We demonstrated the successful creation of OAM states, their propagation and their successful detection in an all in-fiber scheme. Our platform eliminates the post-selection losses of time-bin quantum communication systems and ensures compatibility with next-generation optical networks and opens up new possibilities for quantum communication. v vi always and I hope we can remain friends forever.To Camilo, one of the brightest people I've ever met, my current roommate and friend. I hope that we continue to have thousands of inspiring conversations and that gravity never fails in our environment.To Yerko, that person who arrives at a very hard time for our country and for my life. If it wasn't for you, I might have fallen into despair many times. Thanks for everything, let the crazy conversations continue for a long time.For Lady Fahrenheit I should write a whole book giving thanks for her influence in my life, so here I will try try to summarize. Thank you for always being there, for giving me the infinite tranquility that I can always count on you, for being my accomplice in so many crazy thoughts. For supporting all my dreams and for being such an intense light in my darkest moments.One paragraph will not do justice to everything I have to say about...