Abstract
Compared to traditional non-linear optical crystals, like BaB2O4, KTiOPO4 or LiNbO3, semiconductor integrated sources of photon pairs may operate at pump wavelengths much closer to the bandgap of the materials. This is also the case for Bragg-reflection waveguides (BRWs) targeting parametric down-conversion (PDC) to the telecom C-band. The large non-linear coefficient of the AlGaAs alloy and the strong confinement of the light enable extremely bright integrated photon pair sources. However, under certain circumstances, a significant amount of detrimental broadband photoluminescence has been observed in BRWs. We show that this is mainly a result of linear absorption near the core and subsequent radiative recombination of electron–hole pairs at deep impurity levels in the semiconductor. For PDC with BRWs, we conclude that devices operating near the long wavelength end of the S-band or the short C-band require temporal filtering shorter than 1 ns. We predict that shifting the operating wavelengths to the L-band reduces the amount of photoluminescence by 70% and making small adjustments in the material composition results in its total reduction of 90%. Such measures enable us to increase the average pump power and/or the repetition rate, which makes integrated photon pair sources with on-chip multi-gigahertz pair rates feasible for future devices.
Highlights
Entangled photons form the basis of many quantum applications, notably in computing and communication [1,2,3,4]
The selected pump laser is coupled into the waveguides via an aspheric lens (AL) or a microscope objective (MO) on one side, the generated parametric down-conversion (PDC) is collimated with another AL at the output facet
There have been previous hypotheses that the background results from impurities in the GaAs substrate [25], which can be verified by comparison with the spatial distribution of the PDC signal
Summary
Entangled photons form the basis of many quantum applications, notably in computing and communication [1,2,3,4]. While some strategies to handle and mitigate detrimental effects are often internal lab-knowledge (e.g. the ubiquitous black masking tape at the right places to shield detectors from background light), others are wellknown techniques and approaches in the experiment or data post-processing. In both bulk and integrated experiments, pulsed operation, time gating, and spectral and spatial filtering are commonly employed [5,6,7,8,9]
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