Stefano Azzini

Ultra-low power generation of twin photons in a compact silicon ring resonator

We demonstrate efficient generation of correlated photon pairs by spontaneous four wave mixing in a 5 μm radius silicon ring resonator in the telecom band around 1550 nm. By optically pumping our device with a 200 μW continuous wave laser, we obtain a pair generation rate of 0.2 MHz and demonstrate photon time correlations with a coincidence-to-accidental ratio as high as 250. The results are in good agreement with theoretical predictions and show the potential of silicon micro-ring resonators as room temperature sources for integrated quantum optics applications.

Micrometer-scale integrated silicon source of time-energy entangled photons

Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip, but the devices demonstrated so far require millimeter lengths and pump powers of the order of hundreds of milliwatts to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been proven in these devices. Here we report the first demonstration, to the best of our knowledge, of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell’s inequality by more than seven standard deviations with an internal pair generation exceeding 107  Hz. The source is integrated on a silicon chip, operates at milliwatt and submilliwatt pump power, emits in the telecom band, and outputs into a photonic waveguide. These are all essential features of an entangled state emitter for a quantum photonic network.

From classical four-wave mixing to parametric fluorescence in silicon microring resonators

Four-wave mixing (FWM) can be either stimulated or occur spontaneously. The first process is intrinsically much stronger and well understood through classical nonlinear optics. The latter, also known as parametric fluorescence, can be explained only in the framework of a quantum theory of light. We experimentally demonstrated that, in a microring resonator, there is a simple relation between the efficiencies of these two processes that is independent of the nonlinearity and ring size. In particular, we have shown the average power generated by parametric fluorescence can be immediately estimated from a classical FWM experiment. These results suggest that classical nonlinear characterization of a photonic integrated structure can provide accurate information on its nonlinear quantum properties.

Ultra-low threshold polariton lasing in photonic crystal cavities

The authors show clear experimental evidence of lasing of exciton polaritons confined in L3 photonic crystal cavities. The samples are based on an InP membrane in air containing five InAsP quantum wells. Polariton lasing is observed with thresholds as low as 120 nW, below the Mott transition, while conventional photon lasing is observed for a pumping power one to three orders of magnitude higher.

Stimulated and spontaneous four-wave mixing in silicon-on-insulator coupled photonic wire nano-cavities

We report on four-wave mixing in coupled photonic crystal nano-cavities on a silicon-on-insulator platform. Three photonic wire cavities are side-coupled to obtain three modes equally separated in energy. The structure is designed to be self-filtering, and we show that the pump is rejected by almost two orders of magnitude. We study both the stimulated and the spontaneous four-wave mixing processes: owing to the small modal volume, we find that signal and idler photons are generated with a hundred-fold increase in efficiency as compared to silicon micro-ring resonators.

Generation of time-energy entangled photons on a silicon chip

An integrated source of time-energy entangled photons is demonstrated through resonantly enhanced spontaneous four-wave mixing in a silicon micro-ring resonator. A Franson type set-up is employed to show the quantum interference between photon pairs with a visibility exceeding 90% and a violation of the Bells inequality by more than 10 standard deviations. The high spectral brightness and the extremely small footprint of our source make it suitable for the development of quantum information protocols integrated on chip.

Hybrid metal/semiconductor lasers based on confined Tamm plasmons

Tamm plasmons are interface modes formed at the boundary between a metallic layer and a dielectric Bragg mirror. They present advantages associated both to surface plasmons and to microcavities photonic modes. One of their striking properties is that they can be spatially confined by structuring only the metallic part of the structure, thus reducing the size of the mode and allowing various geometries without altering the optical properties of the active layer. These modes are very good candidates for optimizing the emission properties of semiconductor nanostructures. In particular, due to the relatively low damping and the versatility of the Tamm geometries, they open new perspective for the development of hybrid metal/semiconductor lasers. In this paper, we will show that a laser effect can be achieved in a bidimensional Tamm structure under pulsed optical pumping. We will also demonstrate that the mode can be spatially confined, and that this results in a reduction of the pump power at threshold.

Spontaneous parametric fluorescence in SOI integrated micoresonators

Four-wave mixing can be stimulated or occur spontaneously: the latter effect, also known as parametric fluorescence, can be explained only in the framework of a quantum theory of light, and it is at the basis of many protocols to generate nonclassical states of the electromagnetic field. In this work we report on our experimental study of spontaneous four wave mixing in microring resonators and photonic crystal molecules integrated on a silicon on insulator platform. We find that both structures are able to generate signal and idler beams in the telecom band, at rates of millions of photons per second, under sub-mW pumping. By comparing the experiments on the two structures we find that the photonic molecule is an order of magnitude more efficient than the ring resonator, due to the reduced mode volume of the individual resonators.

Integrated nonlinear optics: from classical to quantum phenomena

We show that the results of classical experiments allow for an accurate prediction of quantum correlated photon-pair generation efficiencies, opening a path to move from classical to quantum nonlinear optics in integrated photonic structures.