Nowadays it is more essential than ever to encrypt transmitted data to guarantee users’ privacy and the advent of quantum computers threats the hardest classical algorithms implemented. To face this issue, Quantum Key Distribution (QKD) has been proposed, relying on the laws of quantum mechanics. There exist two main approaches which focus on a secure key exchange between legitimate parties: Discrete-Variable (DV) and Continuous-Variable (CV) QKD. The first one transmits single photons through weak laser sources, while the second one encodes information on the light’s quadrature components. In the access network scenario, here represented by Passive Optical Networks (PONs), the classical-quantum channels coexistence and the presence of splitters strongly affect the overall performance, inducing Spontaneous Raman Scattering (SpRS) effect and strong losses. To evaluate which approach outperforms the other, a MATLAB simulator calibrated on the VPI software has been developed, leading to the identification of available quantum bands for different PON standards and set ups and, similarly, to the study of the secret-key rate as function of the travelled distance. DV-QKD results to be very sensitive to SpRS, leading to narrower bands. When a 7.5 km distance is considered, it is able to serve up to 64 users for any PON standard. On the other hand, CV-QKD is less affected by Raman noise thanks to the inherent filtering property of coherent detectors, but it is mainly affected by system’s losses. Indeed no more than 16 users can be served at 7.5 km. Despite this drawback, its maximum SKRs are usually higher than the corresponding DV ones. Finally, the analysis on the travelled distance is reported, showing how DV-QKD is able to reach 20 km when 64 users are served, apart from the XG-PON standard which is less promising, while CV-QKD is often limited to 6 km with 32 users.
Oggigiorno è più che mai essenziale criptare i dati trasmessi per garantire la privacy degli utenti e l’avvento dei computer quantistici minaccia la solidità degli algoritmi classici. Come soluzione è stato proposto lo Scambio di Chiavi Quantistiche, che si basa sulle leggi della meccanica quantistica. Esistono due approcci principali: lo scambio a Variabile Discreta e Continua. Mentre il primo si occupa di trasmettere singoli fotoni attraverso sorgenti laser attenuate, il secondo codifica le informazioni nelle due componenti, quadratura e fase, della luce. Nel contesto di rete di accesso, in questa tesi rappresentato dalle Reti Ottiche Passive, la coesistenza tra canali classici e quantistici e la presenza di splitter influenzano le performance del sistema, attraverso la generazione di rumore Raman Spontaneo e forti perdite. Per poter valutare quale sia l’approccio migliore in diverse circostanze, è stato sviluppato un simulatore MATLAB, calibrato sul software VPI, che permetta l’identificazione delle bande riservate al canale quantistico per diverse configurazioni e standard classici e, similmente, lo studio della velocità di scambio di chiave in funzione della distanza percorsa. L’approccio a Variabile Discreta risulta essere più sensibile al rumore Raman, identificando bande più ristrette, ma meno alle perdite. Per distanze pari a 7.5 km, qualsiasi protocollo classico è in grado di servire 64 utenti. D’altra parte, l’approccio a Variabile Continua è meno sensibile al rumore Raman, grazie al filtraggio intrinseco al ricevitore coerente, ma lo è alle perdite. Infatti non più di 16 utenti sono tollerati a una distanza di 7.5 km. Nonostante ciò, i picchi di velocità di trasmissione sono solitamente maggiori dei corrispondenti a Variabile Discreta. Infine, è riportato il confronto relativo alla massima distanza percorsa, mostrando come, tranne nel caso dello standard XG-PON che presenta performance peggiori, l’approccio a Variabile Discreta sia in grado di raggiungere 20 km servendo 64 utenti, mentre quello a Variabile Continua circa 6 km per 32 utenti.
Discrete and continuous variable quantum key distribution in passive optical networks
Mazza, Eliana
2023/2024
Abstract
Nowadays it is more essential than ever to encrypt transmitted data to guarantee users’ privacy and the advent of quantum computers threats the hardest classical algorithms implemented. To face this issue, Quantum Key Distribution (QKD) has been proposed, relying on the laws of quantum mechanics. There exist two main approaches which focus on a secure key exchange between legitimate parties: Discrete-Variable (DV) and Continuous-Variable (CV) QKD. The first one transmits single photons through weak laser sources, while the second one encodes information on the light’s quadrature components. In the access network scenario, here represented by Passive Optical Networks (PONs), the classical-quantum channels coexistence and the presence of splitters strongly affect the overall performance, inducing Spontaneous Raman Scattering (SpRS) effect and strong losses. To evaluate which approach outperforms the other, a MATLAB simulator calibrated on the VPI software has been developed, leading to the identification of available quantum bands for different PON standards and set ups and, similarly, to the study of the secret-key rate as function of the travelled distance. DV-QKD results to be very sensitive to SpRS, leading to narrower bands. When a 7.5 km distance is considered, it is able to serve up to 64 users for any PON standard. On the other hand, CV-QKD is less affected by Raman noise thanks to the inherent filtering property of coherent detectors, but it is mainly affected by system’s losses. Indeed no more than 16 users can be served at 7.5 km. Despite this drawback, its maximum SKRs are usually higher than the corresponding DV ones. Finally, the analysis on the travelled distance is reported, showing how DV-QKD is able to reach 20 km when 64 users are served, apart from the XG-PON standard which is less promising, while CV-QKD is often limited to 6 km with 32 users.File | Dimensione | Formato | |
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2024_7_Mazza_Tesi.pdf
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2024_7_Mazza_Executive Summary.pdf
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https://hdl.handle.net/10589/222701