Third Order Mode Optically Pumped Semiconductor Laser for an Integrated Twin Photon Source in Quantum Optics
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Third Order Mode Optically Pumped Semiconductor Laser for an Integrated Twin Photon Source in Quantum Optics N. G. Semaltianos, A. De Rossi, V. Berger, B. Vinter, E. Chirlias and V. Ortiz Thales Research and Technology Domaine de Corbeville 91404 Orsay, FRANCE ABSTRACT Lasing action on a third order waveguide mode is demonstrated at room temperature under optical pumping, in a specifically designed quantum well laser structure. The AlGaAs heterostructure involves barriers which ensure that the third order mode has a higher overlap with the single quantum well emitter than the fundamental mode. Third order mode operation of a laser structure opens the way to modal phase matched parametric down conversion inside the semiconductor laser itself. It is a first step towards the realization of semiconductor twin photon laser sources, needed for quantum information experiments. INTRODUCTION Twin photon sources obtained by parametric fluorescence (PF) are a useful tool in quantum cryptography or quantum optics experiments [1-3]. In these experiments PF is obtained from a laser beam with a frequency ωp which enters into a nonlinear crystal and creates twin down generated photons at a frequency ωi=ωs=ωp/2. The whole set-up is in general complicated. The purpose of this work is to study a new type of semiconductor laser in which PF could be obtained in the semiconductor laser itself thus resulting in a highly compact twin photon source. Two criteria must be fulfilled to obtain efficient PF: a high nonlinear coefficient and the possibility to phase match the interaction between the interacting waves [4]. Semiconductors and especially GaAs are very interesting for waveguided nonlinear parametric processes due to their high nonlinear coefficient and the possibility to integrate quantum well (QW) sources with nonlinear interactions. However, III-V semiconductors are not birefringent and alternative phase matching schemes have to be used [5]. Among the different phase matching schemes, modal dispersion phase matching (MDPM) [6,7] is attractive because it is well suited for materials grown by molecular beam epitaxy (MBE) due to the control of the layer thickness homogeneity up to the atomic level. In this method phase matching is obtained by a careful design of a multilayer waveguide in which the effective indices neff of three different guided modes i, j and k satisfy the MDPM condition: neff,i(λp)=1/2[neff,j(λi)+neff,k(λs)]. Figure 1 indicates MDPM in the laser structure which is described in detail below; in this specific design photons on the third order mode (i=TE2) at ωp=775 nm can generate through phase matched PF signal and idler photons at λs,i=2λp=1.55 µm on the fundamental modes (j=TE0 and k=TM0). In addition, the overlap integral [6] between the third order mode and the fundamental one, which gives the efficiency of this nonlinear process, is optimised.
H9.37.1
Al0.3 0Ga0.70 As
3.1 3.0 2.9
TE2
TE0 TM 1
TE1
TM0
TM2 λ=775 nm
effective index
3.3 3.2
λ=1.55 µm
3.4
AlAs 0.8
1.0
1.2
1.4
1.6
1.8
wavelength (µ
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