1D photonic systems for quantum optics

Following the inspiration of atomic physics, spontaneous emission (SE) control in semiconductors has been first achieved using the Purcell effect that arises in high-Q microcavities. To overcome the tiny operation bandwidth inherent to a resonant effect, we have recently introduced fiber-like photonic nanowires. These monomode waveguides, made of a high refractive index material, ensure a nearly perfect and broadband SE control of an embedded emitter. We are interested in the fundamental mechanisms associated with SE control in these structures, in order to optimize their performance. In addition, we take advantage of their unique properties to realise ultrabright sources of quantum light (single photon sources and sources of entangled photon pairs).

Schematics of a photonic wire

What is a photonic nanowire?

A photonic wire is a monomode waveguide that is made of a high refractive index material, and which is surrounded by a low index cladding (air or vacuum). The large refractive index contrast between the material and the cladding leads to two important and useful effects. First, the guided mode can be confined very tightly in the structure, allowing a good coupling to the embedded emitter. Secondly, a dielectric screening effect inhibits the coupling to the continuum of ‘leaky’ modes. These two effects results in an efficient spontaneous emission control, that is maintained over a large operation bandwidth. We realize and study GaAs wire, with embedded InAs QDs.

> Reference: Friedler et al. Optics Express 17, 2095 (2009) PDF
Research Highlights, Nature Photonics 3, 186 (2009)

Radiative decay of QD embeded in 'small' wires (red) and in optimal diameter wires (blue)

Spontaneous emission control in photonic nanowires

To investigate experimentally these mechanisms, we have performed time-resolved study on individual QD embedded in wires with various dimensions. For a diameter around 250 nm, the coupling to the guided mode dominates the SE process and an increase of the SE rate by a factor of 1.5 is achieved. When the diameter is decreased down to 120 nm, the coupling to this mode vanishes rapidly, thus allowing the coupling to the other radiation modes to be probed. In these conditions, a SE inhibition factor of 16, equivalent to the one obtained in state-of-the-art photonic crystals, is measured. This experimental study confirms the potential of these structures to provide a nearly perfect SE control.

> Reference: Bleuse et al., Phys. Rev. Lett. 106, 103601 (2011) PDF

Elliptical photonic nanowires for single-mode emission

For simple symmetry reasons, a photonic wire with a circular section supports two degenerate guided modes, with linear orthogonal polarizations. For some applications (e.g. single-mode single photon sources, high-beta nanolasers), it is desirable to achieve SE into a single optical mode, with a well defined polarization. We have shown that this ideal situation can be achieved in an anisotropic structure featuring a moderate aspect ratio ( 2).

> Reference: Munsch et al., submitted to Phys. Rev. Lett.

Nature Photonics cover

An ultrabright source of single photons

We have exploited the efficient and broadband SE control provided by photonic nanowires to realize an ultrabright on-demand single-photon source. To this end, one needs to collect efficiently the photons that are emitted in the guided mode supported by the wire. Thus, our source feature a bottom mirror, made of gold plus a thin silica spacer (the tightly confined mode does not behave as a plane wave and requires some tricks to achieve a high modal reflectivity). Furthermore, the upper tip features a conical shape, in order to obtain a directive far-field emission pattern. This device has shown remarkable performance. Under pulsed optical excitation, the probability of collecting a single photon in the microscope objective (N.A.=0.75) reaches the record value of 72% (state-of-the-art at 40%). Moreover, even at the saturation of the QD, the single-photon emission remains very clean: the second order intensity correlation function g^2(0) is below 1%. These results open a wealth of interesting perspectives for the realization of advanced quantum light sources.

> References:

- Claudon et al., Nature Photonics 4, 174 (2010) PDF
Nature photonics cover (March), News and Views, Nature Photonics 4, 132 (2010)

- Friedler et al., Optics Express 17, 2095 (2009) PDF
Research Highlights, Nature Photonics 3, 186 (2009)

- Gregersen et al., Optics Lett. 33, 1693 (2008) PDF
Research Highlights, Nature Photonics 2, 518 (2008)

- Friedler et al., Optics Letters 33, 2635 (2008) PDF

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