A laser diode for integrated photon pair generation at telecom wavelength

G. Boucher1, A.Orieux1, F. Boitier1, A. Eckstein1, E. Galopin2, A. Lemaître2, C. Manquest1, I. Favero1, G. Leo1 and S. Ducci1

1. Université Paris Diderot, Sorbonne Paris Cité, Laboratoire Matériaux et Phénomènes Quantiques, CNRS-UMR 7162, Case courrier 7021, 75205 Paris Cedex 13, France

2. Laboratoire de Photonique et Nanostructures, CNRS-UPR20, Route de Nozay, 91460 Marcoussis, France

A fully integrated photon pair source is a key element to achieve quantum optics circuitry on chip. Such a source could be easily combined with promising nanophotonic technologies such as plasmonic waveguides [1] or multipath integrated optical interferometer [2]. As mature technologies, semiconductors exhibit a huge potential in terms of integration (electrical pumping, advanced nanostructure design...).

Our device based on AlGaAs waveguides is designed to emit photon pairs at room temperature and telecommunication wavelength. Due to its very high nonlinear coefficient, AlGaAs is a material of choice for this purpose; however, since this semiconductor is not birefringent, phase matching conditions for spontaneous down conversion (SPDC) require an original design. We developed a structure based on modal phase-matching involving pump Bragg mode, as proposed in [3]. Here, we report on an electrically pumped device designed to emit photon pairs around 1.56 µm: second harmonic generation (SHG) and lasing on a Bragg mode around 780 nm under electrical pumping have been observed.

The structure consists of a multilayer AlGaAs ridge waveguide grown by molecular beam epitaxy (Fig. 1 a): two Bragg mirrors provide both a photonic band gap confinement for a TE Bragg mode at 780 nm and total internal reflection claddings for TE and TM modes at 1.56 µm. The structure has been optimized for efficient type-II SPDC and lasing on the TE Bragg mode at room temperature. Lateral confinement is obtained by wet etching of 4 μm-wide and 2 μm-deep ridges along the (011) crystalline axis. Nonlinear properties of the device were tested via a cw SHG experiment both in a passive and an active structure. A single-mode external cavity diode laser beam polarized at 45° with respect to TE and TM modes was injected into the ridge waveguide and the SHG signal on the Bragg mode at 782 nm was measured (Fig. 1 b). The internal SHG efficiency is about 35 %W-1.cm-2.

(a) (b) Fig. 1

A key advantage of this phase-matching scheme is the possibility to insert a quantum well within the structure to obtain an electrically-pumped twin-photons-emitting diode working at room temperature. Our experiments on an electrically-pumped active device show a laser emission at 782 nm on the Bragg mode. The sample was pumped at 10 kHz repetition rate with 150 ns-long electrical pulses. No thermal effects were observed and a laser threshold of ~ 400 mA was measured for a 1.75 mm-long sample. The external laser power collected through a 0.95 N.A. microscope objective is ~ 7.5x10-3 mW/mA, which allows photon pairs generation near the threshold.

In summary, we have demonstrated electrically-pumped lasing on a Bragg mode at 782 nm in an AlGaAs waveguide structure designed for efficient type-II second harmonic generation on the same Bragg mode. Experiments are currently under progress to characterize SPDC at 1.55 µm within the laser diode. These results are very promising for a completely integrated source for quantum communications at room temperature.

References [1] I. I. Smolyaninov, A. V. Zayats, A. Gungor, and C. C. Davis, "Single-Photon Tunneling via Localized Surface Plasmons," Phys. Rev. Lett. 88, 187402 (2002).[2] A. Politi, M. J. Cryan, J. G. Rarity, S. Yu, and J. L. O’Brien, "Silica-on-Silicon Waveguide Quantum Circuits," Science 320, 646 (2008). [3] A. S. Helmy, "Phase matching using Bragg reflection waveguides for monolithic nonlinear optics applications," Opt. Express 14, 1243 (2006).

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