Using far-field optical lithography, a single quantum dot is positioned within a pillar microcavity with a 50 nm accuracy. The lithography is performed in situ at 10 K while measuring the quantum dot emission. Deterministic spectral and spatial matching of the cavity-dot system is achieved in a single step process and evidenced by the observation of strong Purcell effect. Deterministic coupling of two quantum dots to the same optical mode is achieved, a milestone for quantum computing.

Desirable material properties for all-optical χ (3) nonlinear chips are a high Kerr nonlinearity and low linear and nonlinear losses to enable high four-wave mixing (FWM) efficiency and parametric gain. Many material platforms have been investigated showing the different trade-offs between nonlinearity and losses [2][3][4][5][11][12][13][14][15][16] . In addition to good intrinsic material properties, the ability to perform accurate and high yield processing is desirable in order to integrate additional functionalities on the same chip and also to decrease linear losses. Silicon-on-insulator is the model system for integration 2 . It supports a large index contrast and shallow etch depths, enabling patterning submicron structures with smooth sidewalls. However, due to two-photon absorption (TPA) at telecom wavelengths, 19 . Its bandgap can be tailored in such a way that TPA, which is the main detrimental effect for the FWM process, is mitigated and at the same time, the three-photon absorption is low 10 while a high material nonlinearity is maintained. Over the past two decades, efforts have been made to realize efficient nonlinear processes in AlGaAs waveguides [17][18][19] . However, the fabrication of such waveguides with very high and narrow mesa structures becomes very challenging and prevents advanced designs that go beyond simple straight waveguides. In addition, the low vertical index contrast of such waveguides limits the effective nonlinearity.To enhance light confinement and relax the etching process requirements, we propose an AlGaAs-on-insulator (AlGaAsOI) platform as shown in Fig. 1a. In this layout, a thin AlxGa1-xAs layer on top of a low index insulator layer resides on a semiconductor substrate. Wafer bonding and substrate removal are used to realize the structure. In this letter, the aluminium fraction (x) is 17%, which makes the material bandgap 1.63 eV and the refractive index 3.33. Thanks to the large index contrast (~55%) of this layout, light can be confined in a sub-micron waveguide core. As the nonlinear parameter (γ) is highly dependent on the waveguide effective mode area (Aeff) as expressed 2 by γ=2πn2/λAeff, an ultra-high effective nonlinearity of about 660 W -1 m -1 , which is orders of magnitude higher than that of a typical Si3N4 waveguide 5 , can be obtained for an AlGaAsOI waveguide using a cross-section dimension of 320 nm×630 nm (see Methods). In addition, the waveguide dispersion dominates over material dispersion for subwavelength sized waveguides and therefore the group velocity dispersion (GVD) can be engineered from the normal dispersion of bulk material to anomalous dispersion (Fig. 1b), which is required to achieve parametric gain in nonlinear processes in the under-coupled regime and its transmission is shown in Fig. 2c for the transverse electric (TE) mode. Only one mode family with a free spectral range (FSR) of ~0.82 nm (98 GHz) is observed in the spectrum, which implies that the resonator waveguide with anomalous dispersion can be operated in a single-mode state....

Semiconductor lasers in use today rely on mirrors based on the reflection at a cleaved facet or Bragg reflection from a periodic stack of layers. Here, we demonstrate an ultra-small laser with a mirror based on the Fano resonance between a continuum of waveguide modes and the discrete resonance of a nanocavity. The Fano resonance leads to unique laser characteristics. Since the Fano mirror is very narrow-band compared to conventional lasers, the laser is single-mode and in particular, it can be modulated via the mirror. We show, experimentally and theoretically, that nonlinearities in the mirror may even promote the generation of a self-sustained train of pulses at gigahertz frequencies, an effect that was previously only observed in macroscopic lasers. Such a source is of interest for a number of applications within integrated photonics.Keywords: Laser, Photonic-crystal, Fano resonance, Nonlinear optics, Nanocavity, Self-pulsation Conventional semiconductor lasers mirrors are based on a cleaved facet [1] or a Bragg grating, or a two-dimensional grating resonance [2][3][4][5][6][7][8]. In this work, we demonstrate a new concept for lasers, an ultra-small laser with a mirror based on the Fano resonance between a continuum of waveguide modes and the discrete resonance of a nanocavity. The rich physics of Fano resonances [9] has recently been explored in a number of different photonic and plasmonic systems [10,11]. The Fano resonance leads to unique laser characteristics and furthermore represents a very rich dynamical system, which is still to be explored. In particular, since the Fano mirror is very narrow-band compared to conventional lasers, the laser is single-mode and it can be modulated via the mirror. We show, experimentally and theoretically, that nonlinearities in the mirror may even promote the generation of a self-sustained train of pulses at gigahertz frequencies, an effect that was previously only observed in macroscopic lasers [12][13][14][15].The photonic crystal Fano laser (FL) concept is illustrated in Fig. 1(a). The laser cavity is composed of a linedefect waveguide in a photonic crystal (PhC) membrane and two mirrors. The left mirror is a conventional PhC mirror, realized by blocking the PhC waveguide (WG) with air holes [16]. In contrast, the right mirror is due to a Fano interference between the continuum of waveguide modes and the discrete resonance of a side-coupled nanocavity [17]. At resonance, the paths of light through the nanocavity and through the waveguide interfere destructively, leading to a high reflectivity, see Fig. 1(b). If the quality factor (Q-factor) of the nanocavity is dominated by its coupling to the waveguide, rather than by intrinsic losses, the maximum reflectivity of the Fano mirror approaches unity, which is the basis for its use as a laser mirror (see Appendix A.1.). This FL concept was suggested in [18] where it was highlighted that, if such a laser could be realized, it should enable modulation not limited by the relaxation oscillations generic to lasers. Here, we ...

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