Bragg-reflection waveguides (BRWs) fabricated from AlGaAs provide an interesting non-linear optical platform for photon-pair generation via parametric down-conversion (PDC). In contrast to many conventional PDC sources, BRWs are made of high refractive index materials and their characteristics are very sensitive to the underlying layer structure. First, we show that the design parameters like the phasematching wavelength and the group refractive indices of the interacting modes can be reliably controlled even in the presence of fabrication tolerances. We then investigate, how these characteristics can be taken advantage of when designing quantum photonic applications with BRWs. We especially concentrate on achieving a small differential group delay between the generated photons of a pair and then explore the performance of our design when realizing a Hong-Ou-Mandel interference experiment or generating spectrally multi-band polarization entangled states. Our results show that the versatility provided by engineering the dispersion in BRWs is important for employing them in different quantum optics tasks. arXiv:1809.03167v2 [quant-ph]

In this study, the authors extend Manikas's array bound theory using differential geometry to direction-finding (DF) multiple-input multiple-output (MIMO) radar, and investigate the ultimate DF accuracy, detection and resolution capabilities via the manifold studies on MIMO virtual arrays. The authors derive the expression of the asymptotic normalised mean-square angular error, which is based on Cramer-Rao bounds of azimuth and elevation angles, to explore the ultimate DF accuracy both for one-and two-target cases. Furthermore, in two-target case, the authors derive the expressions of detection and resolution thresholds of directional parameters, respectively. They find that all fundamental limits above are highly dependent on the antenna geometry of DF MIMO radar systems. At last, the fundamental limits of four representative antenna geometries of DF MIMO radars, which are used in most of the current literature, are investigated and compared.

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