The possibility of using integrated photonics to scale multiple optical components on a single monolithic chip offers transformative advantages in fields such as communications, computing, bioengineering, and sensing. However, today’s integrated photonic circuits are rudimentary compared to the complexity of modern electronic circuits. Any advancements to efficiently integrate new photonic functionalities bring us closer to replicate the enormous impact of electronic integrated circuits.
Slow light propagation in chip-integrated nanophotonic structures with engineered band dispersion is a highly promising approach for controlling the relative phase of light and for enhancing optical nonlinearities on a chip. A primary goal in this field is to achieve devices with large, approximately constant group index (n_g) over the largest possible bandwidth, thereby enabling multimode and pulsed operation. We present an experimental record high group-index-bandwidth product (GBP) in genetically optimized coupled-cavity-waveguides (CCWs) designed by L3 photonic crystal nanocavities. The resulting designs were realized in SOI buckling-free suspended slabs with CCWs integrating up to 800 coupled nanocavities. The samples were characterized by measuring the CCW transmission, the mode dispersion through Fourier-space imaging, and ng via Mach-Zehnder interferometry. Various nanocavity designs were investigated, with theoretical n_g ranging from 37 to 100. Record high GBP = 0.47 was demonstrated over a bandwidth of 19.5 nm with a homogeneous flat-top transmission profile (variations lower than 10 dB) and losses below 56 dB/ns. Our results open the path towards building enhanced slow-light-based devices such as of slow-light-enhanced spectroscopic interferometers and single-photon buffers.
We optimize a photonic crystal slab for the generation of second harmonic. The optimization consists in two steps. In the first step a regular photonic crystal, consisting in a triangular lattice of circular holes in a dielectric slab, is optimized by allowing for holes of three alternating radii, with the objective of obtaining a high-frequency bandgap doubly resonant with the fundamental one. The second step consists in modeling a L3 defect cavity in such a photonic crystal where, by further varying the radii and positions of a few neighboring holes, doubly resonant modes at the fundamental and second harmonic frequencies are obtained, with maximal Q-factors and field overlap. The structure emerging from this optimization procedure has Q-factors of 3400 for the fundamental mode and of 430 for the doubly resonant one. Due to the localized nature of those modes and hence their large field overlap, efficient second-harmonic generation is expected in a material with a X(2) non-linearity.
We investigate the use of MOVPE-grown ordered nanostructures on non-planar substrates for quantum nano-photonics
and quantum electrodynamics-based applications. The mastering of surface adatom fluxes on patterned GaAs substrates
allows for forming nanostrucutres confining well-defined charge carrier states. An example given is the formation of
quantum dot (QD) molecules tunneled-coupled by quantum wires (QWRs), in which both electron and hole states are
hybridized. In addition, it is shown that the high degree of symmetry of QDs grown on patterned (111)B substrates
makes them efficient entangled-photons emitters. Thanks to the optimal control over their position and emission
wavelength, the fabricated nanostructures can be efficiently coupled to photonic nano-cavities. Low-threshold, optically
pumped QWR laser incorporating photonic crystal (PhC) membrane cavities are demonstrated. Moreover, phononmediated
coupling of QD exciton states to PhC cavities is observed. This approach should be useful for integrating more complex systems of QWRs and QDs for forming a variety of active nano-photonic structures.
We adopt a kinetic theory of polariton non-equilibrium Bose-Einstein condensation, to describe the formation
of off-diagonal long-range order. The theory accounts properly for the dominant role of quantum fluctuations in
the condensate. In realistic situations with optical excitation at high energy, it predicts a significant depletion of
the condensate caused by long-wavelength fluctuations. As a consequence, the one-body density matrix in space
displays a partially suppressed long-range order and a pronounced dependence on the finite size of the system.
The initial dynamics of resonantly excited secondary emission from quantum wells are dominated by Rayleigh scattering due to excitons localized in the disordered quantum well potential. We show experimentally and theoretically how the temporal shape of the early response is related to details of the 2D disorder potential, and we determine the mean amplitude of the fluctuations and the correlation length. Spectral interferometry performed with a single speckle allows to investigate the phase of the electric field emitted by the ensemble of excitons. We find evidence for a correlation between the degree of localization and the fluctuations of the phase as a function of energy.