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A prototypical experiment in cavity quantum electrodynamics involves controlling the light-matter interaction by tuning the frequency of a cavity mode in- and out-of resonance with the frequency of a quantum emitter,1-3 while the field amplitude is generally unaltered. The opposite situation, where one perturbs the spatial pattern of a cavity mode without changing its frequency, has been considered only recently in a few works.4, 5 Changing the amplitude of the field at the emitter's position has important applications, at it allows a real-time control of the light-matter coupling rate, and therefore a direct control of processes such as spontaneous emission and Rabi oscillations. In view of this large potential, in this paper we discuss general design principles that allow obtaining large variations of the electromagnetic field, without change of the frequency, upon an external perturbation of the cavity. We showcase the application of these rules to two photonic structures, a single Fabry-Perot cavity and a coupled three-cavity system. As showed by our analysis and by the examples provided, a small frequency spacing between the modes of the unperturbed cavity is an important requirement to obtain large field variations upon small perturbations. In this regard, a coupled-cavity system, where the frequency spacing is controlled by the interaction rates between the single cavities, constitutes the most promising system to achieve large modulations of the field amplitude.

The generation, manipulation and detection of single photons enable quantum communication, simulation and potentially computing protocols. However scaling to several qubits requires the integration of these functionalities in a single chip. A promising approach to the integration of single-photon sources in a chip is the use of single quantum dots embedded in photonic crystal waveguides or cavities. To this aim, efficient coupling of the emission from single quantum dots in photonic crystal cavities to low-loss ridge-waveguide (RWG) circuits is needed. This is usually hampered by the large mode mismatch between the two systems. In this work the emission of a photonic crystal (PhC) cavity realized on a GaAs/AlGaAs membrane and pumped by quantum dots has been effectively coupled and transferred through a long RWG (~1mm). By continuous tapering in both horizontal and vertical direction, transmission values (fiber-in, fiber-out) around 0.16 and 0.08% for RWG and coupled PhC waveguide-RWG have been achieved, respectively. This corresponds to about 2.8% coupling efficiency between the center of the PhC waveguide and the single-mode output fiber, a value much higher than what is achieved by top collection. It further shows that around 70% of the light in the PhC waveguide is coupled to the RWG. The emission from quantum dots in the cavity has been clearly identified by exciting from the top and collecting the photoluminescence from the cleaved facet of the device 1mm away from the cavity which enables the efficient coupling of single photons to RWG and detector circuits.

The implementation of single-photon detectors in waveguide photonic circuits will open the possibility of experiments in quantum regime that would otherwise be impossible to be implemented using bulk optics. Nanowire superconducting single-photon detectors (SSPDs) are good candidates for integration due to their relative ease of fabrication on top of GaAs heterostructures. In this paper we show the experimental demonstration of single-photon detectors, based on superconducting nanowires, fully integrated with GaAs/AlGaAs ridge waveguides. We will discuss all the major challenges surmounted and all the steps necessary to achieve these results.

We analyze the impact of slow intraband relaxation and strong carrier localization on the characteristics of quantum dot (QD) lasers. Relatively long intraband relaxation times and population filling of the QD ground state lead to carrier pile-up on excited states, reducing the laser efficiency and maximum output power. Strong carrier localization in the QDs and consequently large thermal hopping time within the QD ensemble results in the absence of quasi-thermal equilibrium under lasing conditions, as evidenced by stimulated and spontaneous emission spectra. The impact of these specific physical characteristics of QD active regions on the laser high-frequency modulation properties is analyzed, particularly with regards to the differential gain, the gain compression and the linewidth enhancement factors.

We describe the realization and characterization of nanoscale light emitters comprising one or few semiconductor quantum dots (QDs) in the active region. These devices are intended for use as single-photon sources in fiber-based quantum cryptography systems. The epitaxial growth of low-density QDs emitting at 1300 nm is described, and emission from single QDs is demonstrated through micro-photoluminescence measurements. The realization of QD light-emitting diodes (LEDs) having a submicrometer active area is reported, based on oxidized current apertures. Finally, the integration of nanoscale current injection with high-quality factor optical cavities is described, in view of obtaining efficient single-photon LEDs.

We have designed a one-dimensional photonic bandgap crystal to obtain perfect phase-matching conditions for noncollinear type II quadratic processes. The realized sample was 15 periods of Al (0.3) Ga (0.7) As/Al 2 O 3 , for a total length of 3.5um. Noncollinear type II phase-matching was obtained at 1510nm. We have experimentally verified the band structure characteristic as well as its perfect phase-matching for the noncollinear type II parametric process. Indeed, noncollinear type II second harmonic generation was obtained for the first time in a PBG crystal1. The experiment demonstrated that the breaking of symmetry, which is artificially induced in such a structure, and the field resonance effect give rise to a relatively efficient second harmonic generation even using a naturally isotropic material (AlGaAs). In fact, we report a nonlinear effective coefficient of the sample equal to (52±12) pm/V.

We discuss here the feasibility of an optical parametric oscillator integrated on a GaAs chip, after reviewing the recent frequency conversion experiments using from birefringence in GaAs/oxidized-AlAs (Alox) waveguides. Recently, phase-matching has been demonstrated for the first time in a GaAs-based waveguide, using form birefringence in multilayer heterostructures GaAs/Alox. Birefringence n(TE)- n(TM) from 0.15 to 0.2 have been measured for different GaAs/Alox waveguides, which is sufficient to phase match mid-IR generation between 3 micrometers and 10 micrometers by difference frequency generation form two near-IR beams. A second step was the observation of parametric fluorescence. Results on parametric fluorescence at 2.1 micrometers will be described, in an oxidized AlGaAs form-birefringent waveguide, consisting of a high-index, strongly birefringent GaAs-Alox core embedded in an AlGaAs cladding. One of the most existing perspectives opened with this new type of nonlinear material is the realization of an optical parametric oscillator on a GaAs chip. To this aim, minimization of losses is the most crucial point. A typical calculated value of this threshold is less than 70 mW for 1 cm-1 losses, and with 90 percent reflection coefficients. The level of losses has been reduced from 2 cm-1 in ridges obtained by a standard reactive ion etching technique, to less than 0.5 cm-1 in ridges realized with a more refined reactive ion etching process, using a 'three layer' mask. There is still a need for an improvement of the waveguide fabrication process, before reaching the oscillation threshold.