Quantum technologies exploit peculiar properties of quantum mechanics, such as superposition and non-classical correlations, to strengthen the performance of classical devices, or to introduce new functionalities. In particular, light-based quantum technologies, thus exploiting photons as quantum information carriers (qubits), are very appealing due to the inherently low decoherence of non-classical state of light. Single photons or entangled photon pairs can be employed to increase computational capability and security of communications by building quantum simulators and implementing quantum cryptography protocols. From an industrial point of view, these light-based qubits are supported by the possibility of integrating thousands of optical components on millimetric chips, thus opening the way towards scalable and diffused quantum-based devices. Integrated quantum photonics provides various versatile platforms for quantum information science practical implementations; among them, silicon stands out for its very good linear and nonlinear optical properties at telecommunication wavelengths and its compatibility with the Complementary Metal-Oxide-Semiconductor (CMOS) industry. Up to now, single photons have been successfully generated through spontaneous four-wave mixing on silicon chips employing micro-resonators to enhance the light-matter interaction, using low-power CW pump lasers. Now, the focus is on the full integration of quantum photonic circuits, i.e. on-chip generation, processing, and detection of photonic qubits. However, it has not been achieved yet due to severe technical challenges that still need to be tackled, such as the suppression before-detection of the intense pump light, done until now only off-chip by means of bulk or fiber-based optical filters. In this thesis, we have tried to face the challenge of the on-chip removal of the pump with a new approach, specifically by filtering the light emitted from a ring resonator with multiple echelle grating (EG) filters. The latter is a curved diffraction grating, mainly used in silicon wafers to multiplex/demultiplex optical networks, which disperses the incident light and focuses it back in optically isolated output channels. Specifically, my work can be divided into three parts: -Design: both the symmetric Add-Drop silicon ring resonator sources and the wavelength filter based on echelle gratings had been designed using several advanced simulation solvers. Their geometrical parameters had been determined according to the extracted effective index of the ring’s waveguide (WG) and the EG’s slab, the ring-WG coupling coefficients, the reflectivity of the distributed brag reflectors placed along the grating, and the performances of the DEMUX. -Fabrication: the fabrication of our 300mm 220nm-Si chip had been carried on inside the CEA-Leti's cleanroom at MINATEC Micro-Nano Technologies Innovation Center (Grenoble), using immersion photolithography, followed by inductively coupled plasma etching and encapsulation with chemical vapor deposition of the silica cladding. -Characterization: preliminary measurements of the passive components had been performed at wafer-level in the Laboratory of Integrated Silicon Photonics (LIPS) of CEA-Leti. The results presented in this thesis comprise the preliminary measurement of the optical spectrum of our resonators, with position and shape analysis of the resonances, resulting in the extraction of Quality-factor of the order of 20000-80000 (around 25000 in resonances at critical-coupling regime). In addition, the performances of the integrated single echelle-grating demultiplexer had been recorded, showing good agreement with designed devices. To conclude, the complete optical characterization and the demonstration of efficient on-chip pump suppression will be carried on at the Laboratory of Quantum Photonics of the University of Pavia as soon as the full fabrication flow will be finished.
Le tecnologie quantistiche sfruttano le proprietà peculiari della meccanica quantistica, come la sovrapposizione e l’entanglement, per migliorare il funzionamento dei dispositivi classici, o per introdurre nuove funzionalità. In particolare, le tecnologie quantistiche basate sull’utilizzo della radiazione elettromagnetica come vettore quantistico di informazione (qubit) hanno grande potenzialità, grazie alla bassa decoerenza degli stati luminosi nonclassici. È il caso di fotoni singoli o coppie di fotoni entangled, i quali possono essere impiegati in simulatori e in protocolli di crittografia quantistici per aumentare le capacità computazionali e la sicurezza delle comunicazioni. Dal punto di vista industriale, è possibile integrare migliaia di componenti ottici su chip millimetrici, aprendo la strada alla diffusione in larga scala di dispositivi quantistici basati su qubit fotonici. La fotonica quantistica integrata fornisce varie piattaforme, e tra queste il silicio si distingue per le sue ottime proprietà ottiche lineari e nonlineari alle lunghezze d'onda delle telecomunicazioni e per la sua compatibilità con l'industria Complementary Metal-Oxide Semiconductor della microelettronica. Finora, la generazione di fotoni singoli su chip di silicio è stata ottenuta attraverso il fenomeno di Spontaneous Four-Wave Mixing all’interno di micro-risonatori, dove si ha una considerevole amplificazione dell'interazione radiazione-materia tale da permettere l’utilizzo di laser in regime continuo a bassa potenza come sorgenti di pompa. Ora, si punta all'integrazione di circuiti fotonici quantistici completi, in cui generazione, manipolazione e acquisizione siano compiuti su un solo chip. Tale obbiettivo non è ancora stato raggiunto, a causa di vari problemi tecnici, tra cui la necessità di rimuovere efficacemente la pompa, cosa che fino ad oggi è stata fatta solo off-chip. In questa tesi, abbiamo cercato di affrontare la questione della rimozione on-chip della pompa con un approccio nuovo: filtrando lo spettro emesso da un micro-risonatore ad anello con una sequenza di Echelle Grating (EG). Quest'ultimo è un reticolo di diffrazione curvo che disperde la luce incidente e la focalizza in canali di uscita otticamente isolati. Più in dettaglio, il lavoro può essere suddiviso in tre parti: -Progettazione: le sorgenti ad anello tipo Add-Drop e il filtro costituito dalla serie di echelle grating sono stati disegnati utilizzando diversi programmi di simulazione. I loro parametri geometrici sono stati determinati in base all'indice effettivo estratto dalla guida d'onda dell'anello e dalla slab dell'EG, ai coefficienti di accoppiamento guida-anello, alla riflettività degli specchi (Distributed Bragg Reflector) distribuiti lungo il reticolo, e alle prestazioni del singolo DEMUX. -Fabbricazione: il nostro chip 300mm 220nm-Si è stato prodotto all'interno della camera pulita di CEA-Leti presso il MINATEC Micro-Nano Technologies Innovation Center (Grenoble), utilizzando fotolitografia a immersione, seguita da inductively coupled plasma etching e rivestimento con silice mediante chemical vapor deposition. -Caratterizzazione: alcune misure preliminari dei dispositivi sono state effettuate sul wafer nel Laboratoire d'intégration Photonique sur silicium (LIPS) di CEA-Leti. I risultati mostrati in questa tesi, comprendono la misura degli spettri ottici dei risonatori, con l'analisi di posizione e forma delle risonanze e estrazione dei loro fattori di qualità (dell'ordine di 20000-80000, circa 25000 per risonanze in regime di critical coupling). Inoltre, è stato testato il singolo EG, il cui comportamento è confrontabile con quello simulato. Per concludere, la caratterizzazione ottica completa e la dimostrazione dell’efficiente soppressione on-chip della pompa saranno effettuate presso il Laboratorio di Fotonica Quantistica dell'Università di Pavia non appena il processo di fabbricazione sarà terminato.
Progettazione di una sorgente di coppie di fotoni entangled integrata su chip di silicio con rimozione della pompa
CONGIA, SARA
2020/2021
Abstract
Quantum technologies exploit peculiar properties of quantum mechanics, such as superposition and non-classical correlations, to strengthen the performance of classical devices, or to introduce new functionalities. In particular, light-based quantum technologies, thus exploiting photons as quantum information carriers (qubits), are very appealing due to the inherently low decoherence of non-classical state of light. Single photons or entangled photon pairs can be employed to increase computational capability and security of communications by building quantum simulators and implementing quantum cryptography protocols. From an industrial point of view, these light-based qubits are supported by the possibility of integrating thousands of optical components on millimetric chips, thus opening the way towards scalable and diffused quantum-based devices. Integrated quantum photonics provides various versatile platforms for quantum information science practical implementations; among them, silicon stands out for its very good linear and nonlinear optical properties at telecommunication wavelengths and its compatibility with the Complementary Metal-Oxide-Semiconductor (CMOS) industry. Up to now, single photons have been successfully generated through spontaneous four-wave mixing on silicon chips employing micro-resonators to enhance the light-matter interaction, using low-power CW pump lasers. Now, the focus is on the full integration of quantum photonic circuits, i.e. on-chip generation, processing, and detection of photonic qubits. However, it has not been achieved yet due to severe technical challenges that still need to be tackled, such as the suppression before-detection of the intense pump light, done until now only off-chip by means of bulk or fiber-based optical filters. In this thesis, we have tried to face the challenge of the on-chip removal of the pump with a new approach, specifically by filtering the light emitted from a ring resonator with multiple echelle grating (EG) filters. The latter is a curved diffraction grating, mainly used in silicon wafers to multiplex/demultiplex optical networks, which disperses the incident light and focuses it back in optically isolated output channels. Specifically, my work can be divided into three parts: -Design: both the symmetric Add-Drop silicon ring resonator sources and the wavelength filter based on echelle gratings had been designed using several advanced simulation solvers. Their geometrical parameters had been determined according to the extracted effective index of the ring’s waveguide (WG) and the EG’s slab, the ring-WG coupling coefficients, the reflectivity of the distributed brag reflectors placed along the grating, and the performances of the DEMUX. -Fabrication: the fabrication of our 300mm 220nm-Si chip had been carried on inside the CEA-Leti's cleanroom at MINATEC Micro-Nano Technologies Innovation Center (Grenoble), using immersion photolithography, followed by inductively coupled plasma etching and encapsulation with chemical vapor deposition of the silica cladding. -Characterization: preliminary measurements of the passive components had been performed at wafer-level in the Laboratory of Integrated Silicon Photonics (LIPS) of CEA-Leti. The results presented in this thesis comprise the preliminary measurement of the optical spectrum of our resonators, with position and shape analysis of the resonances, resulting in the extraction of Quality-factor of the order of 20000-80000 (around 25000 in resonances at critical-coupling regime). In addition, the performances of the integrated single echelle-grating demultiplexer had been recorded, showing good agreement with designed devices. To conclude, the complete optical characterization and the demonstration of efficient on-chip pump suppression will be carried on at the Laboratory of Quantum Photonics of the University of Pavia as soon as the full fabrication flow will be finished.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/14465