PhD defence by Raphaël Daveau

Efficient fiber-coupled single-photon sources based on quantum dots

This work first presents single-photon sources based on quantum dots in photonic-crystal waveguides, with an emphasis on efficient extraction of the photons into an optical fiber. Two chip-to-fiber coupling methods are investigated. The first method investigates end-fire coupling from a tapered waveguide to a lensed fiber, which yields a chip-to-fiber coupling efficiency of 16.6 \%. The second method, evanescent coupling from a tapered waveguide to a microfiber, demonstrates a coupling efficiency from chip to fiber up to 80 %, thereby making a single-photon source with an efficiency on the order of 10-15 %. The source efficiency can be optimized further, which opens a promising future for building a deterministic single-photon source, needed in applications such as boson sampling.

The second part of the work presents a theoretical study of optical refrigeration with coupled quantum wells. The particular energy levels and lifetimes of carriers confined in coupled quantum wells make them efficient media for removing thermal energy from the system when interacting with laser light. This has potential application for cooling small-scale electronic or photonic circuits without cryogenic fluids.

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