Spin injection enhancement in CW VECSEL at room temperature using push-pull optical pumping.

We report the enhancement of spin injection efficiency in an external-cavity VCSEL based on a non-resonant pumping coupled with a polarized optical resonant illumination. This double pumping scheme allows both the injection of spin polarized electrons in the conduction band and the selection of the spin orientation for the electron/hole recombination laser process. Experimentally, a flip of the polarization state of the laser is achieved with an ellipticity of +31° (spin down) and -33° (spin up), so an increase of about 50% of the ellipticity is achieved in comparison to an optical non-resonant pumping alone.

Investigation of noise correlations in the phase-locked class-A VECSEL array.

We theoretically and experimentally study the noise correlations in an array of lasers based on a VECSEL (Vertical External Cavity Surface Emitting Laser) architecture. The array of two or three lasers is created inside a planar degenerate cavity with a mask placed in a self-imaging position. Injection from each laser to its neighbors is created by diffraction, which creates a controllable complex coupling coefficient. The noise correlations between the different modes are observed to be dramatically different when the lasers are phase-locked or unlocked. These results are well explained by a rate equation model that takes into account the class-A dynamics of the lasers. This model permits the isolatation of the influence of the complex coupling coefficients and of the Henry α-factor on the noise behavior of the laser array.

Tracking exceptional points above the lasing threshold.

Recent studies on exceptional points (EPs) in non-Hermitian optical systems have revealed unique traits, including unidirectional invisibility, chiral mode switching and laser self-termination. In systems featuring gain/loss components, EPs are commonly accessed below the lasing threshold, i.e., in the linear regime. In this work, we experimentally demonstrate that EP singularities in coupled semiconductor nanolasers can be accessed above the lasing threshold, where they become branch points of a nonlinear dynamical system. Contrary to the common belief that unavoidable cavity detuning impedes the formation of EPs, here we demonstrate that such detuning is necessary for compensating the carrier-induced frequency shift, hence restoring the EP. Furthermore, we find that the pump imbalance at lasing EPs varies with the total pump power, enabling their continuous tracking. This work uncovers the unstable nature of EPs above laser threshold in coupled semiconductor lasers, offering promising opportunities for the realization of self-pulsing nanolaser devices and frequency combs.

Sub-Hz Closed-Loop Electro-Optomechanical Oscillator with Gallium Phosphide Photonic Crystal Integrated on SoI Circuitry.

We report on a new approach of a low phase noise electro-optomechanical oscillator directly working in the GHz frequency range. The developed nanoscale oscillator is a one-dimensional photonic crystal made of gallium phosphide (GaP), heterogeneously integrated on silicon-on-insulator circuitry. Based on the strong interaction between the optical mode at the telecommunication wavelength and the mechanical mode in GHz, ultra-pure mechanical oscillations are enabled and directly imprinted on an optical carrier. Further stabilization is achieved with a delayed optoelectronic feedback loop using integrated electro-mechanical self-injection. We achieve a short-term stability of 0.7 Hz linewidth and a long-term stability with an Allan deviation below 10-7 Hz/Hz at 10 s averaging time, which represents an important step toward fully integrated optomechanical oscillators. Integrability and the low phase noise of this oscillator address some of the most important needs of optoelectronic oscillators and pave the way toward on-chip integrated microwave oscillators for microwave applications such as RADARs.

Brillouin Scattering Selection Rules in Polarization-Sensitive Photonic Resonators.

Spontaneous Brillouin scattering in bulk crystalline solids is governed by the intrinsic selection rules locking the relative polarization of the excitation laser and the Brillouin signal. In this work, we independently manipulate the polarization of the two by employing polarization-sensitive optical resonances in elliptical micropillars to induce a wavelength-dependent rotation of the polarization states. Consequently, a polarization-based filtering technique allows us to measure acoustic phonons with frequencies difficult to access with standard Brillouin and Raman spectroscopies. This technique can be extended to other polarization-sensitive optical systems, such as plasmonic, photonic, or birefringent nanostructures, and finds applications in optomechanical, optoelectronic, and quantum optics devices.

Merging and disconnecting resonance tongues in a pulsing excitable microlaser with delayed optical feedback.

Excitability, encountered in numerous fields from biology to neurosciences and optics, is a general phenomenon characterized by an all-or-none response of a system to an external perturbation of a given strength. When subject to delayed feedback, excitable systems can sustain multistable pulsing regimes, which are either regular or irregular time sequences of pulses reappearing every delay time. Here, we investigate an excitable microlaser subject to delayed optical feedback and study the emergence of complex pulsing dynamics, including periodic, quasiperiodic, and irregular pulsing regimes. This work is motivated by experimental observations showing these different types of pulsing dynamics. A suitable mathematical model, written as a system of delay differential equations, is investigated through an in-depth bifurcation analysis. We demonstrate that resonance tongues play a key role in the emergence of complex dynamics, including non-equidistant periodic pulsing solutions and chaotic pulsing. The structure of resonance tongues is shown to depend very sensitively on the pump parameter. Successive saddle transitions of bounding saddle-node bifurcations constitute a merging process that results in unexpectedly large regions of locked dynamics, which subsequently disconnect from the relevant torus bifurcation curve; the existence of such unconnected regions of periodic pulsing is in excellent agreement with experimental observations. As we show, the transition to unconnected resonance regions is due to a general mechanism: the interaction of resonance tongues locally at an extremum of the rotation number on a torus bifurcation curve. We present and illustrate the two generic cases of disconnecting and disappearing resonance tongues. Moreover, we show how a pair of a maximum and a minimum of the rotation number appears naturally when two curves of torus bifurcation undergo a saddle transition (where they connect differently).

Non-linear dynamics of multimode semiconductor lasers: dispersion-based phase instability and route to single-frequency operation.

Emission dynamics of a multimode broadband interband semiconductor laser have been investigated experimentally and theoretically. Non-linear dynamics of a III-V semiconductor quantum well surface-emitting laser reveal the existence of a modulational instability, observed in the anomalous dispersion regime. An additional unstable region arises in the normal dispersion regime, owing to carrier dynamics, and has no analogy in systems with fast gain recovery. The interplay between cavity dispersion and phase sensitive non-linearities is shown to affect the character of laser emission with phase turbulence, leading to regular self-excited oscillations of mode intensity, self-mode locking, and single-frequency emission stabilized by spectral symmetry breaking. Such physical behavior is a general phenomenon for any laser with a slow gain medium relative to the round trip time, in the absence of spatial inhomogeneities.

Ultra-low-noise microwave to optics conversion in gallium phosphide.

Mechanical resonators can act as excellent intermediaries to interface single photons in the microwave and optical domains due to their high quality factors. Nevertheless, the optical pump required to overcome the large energy difference between the frequencies can add significant noise to the transduced signal. Here we exploit the remarkable properties of thin-film gallium phosphide to demonstrate bi-directional on-chip conversion between microwave and optical frequencies, realized by piezoelectric actuation of a Gigahertz-frequency optomechanical resonator. The large optomechanical coupling and the suppression of two-photon absorption in the material allows us to operate the device at optomechanical cooperativities greatly exceeding one. Alternatively, when using a pulsed upconversion pump, we demonstrate that we induce less than one thermal noise phonon. We include a high-impedance on-chip matching resonator to mediate the mechanical load with the 50-Ω source. Our results establish gallium phosphide as a versatile platform for ultra-low-noise conversion of photons between microwave and optical frequencies.

Metamaterial engineering for optimized photon absorption in unipolar quantum devices.

Metamaterials have played a major role in the development of optoelectronic devices due to their capability of coupling free-space radiation with active materials at the nanometer scale. In particular, unipolar photodetectors display highly improved performances when implemented into patch-antenna arrays. We study light-coupling and absorption in patch-antenna metamaterials by combining an experimental investigation, an analytical approach based on coupled mode theory and numerical simulations in order to understand how the geometrical parameters influence the electromagnetic energy transfer from the free-space to the active material. Our findings are applied to the design of optimized unipolar photodetectors with improved quantum efficiency.

Kardar-Parisi-Zhang universality in a one-dimensional polariton condensate.

Revealing universal behaviours is a hallmark of statistical physics. Phenomena such as the stochastic growth of crystalline surfaces1 and of interfaces in bacterial colonies2, and spin transport in quantum magnets3-6 all belong to the same universality class, despite the great plurality of physical mechanisms they involve at the microscopic level. More specifically, in all these systems, space-time correlations show power-law scalings characterized by universal critical exponents. This universality stems from a common underlying effective dynamics governed by the nonlinear stochastic Kardar-Parisi-Zhang (KPZ) equation7. Recent theoretical works have suggested that this dynamics also emerges in the phase of out-of-equilibrium systems showing macroscopic spontaneous coherence8-17. Here we experimentally demonstrate that the evolution of the phase in a driven-dissipative one-dimensional polariton condensate falls in the KPZ universality class. Our demonstration relies on a direct measurement of KPZ space-time scaling laws18,19, combined with a theoretical analysis that reveals other key signatures of this universality class. Our results highlight fundamental physical differences between out-of-equilibrium condensates and their equilibrium counterparts, and open a paradigm for exploring universal behaviours in driven open quantum systems.

Direct observation of photonic Landau levels and helical edge states in strained honeycomb lattices.

We report the realization of a synthetic magnetic field for photons and polaritons in a honeycomb lattice of coupled semiconductor micropillars. A strong synthetic field is induced in both the s and p orbital bands by engineering a uniaxial hopping gradient in the lattice, giving rise to the formation of Landau levels at the Dirac points. We provide direct evidence of the sublattice symmetry breaking of the lowest-order Landau level wavefunction, a distinctive feature of synthetic magnetic fields. Our realization implements helical edge states in the gap between n = 0 and n = ±1 Landau levels, experimentally demonstrating a novel way of engineering propagating edge states in photonic lattices. In light of recent advances in the enhancement of polariton-polariton nonlinearities, the Landau levels reported here are promising for the study of the interplay between pseudomagnetism and interactions in a photonic system.

Multi-orbital tight binding model for cavity-polariton lattices.

In this work we present a tight-binding model that allows to describe with a minimal amount of parameters the band structure of exciton-polariton lattices. This model based on s and p non-orthogonal photonic orbitals faithfully reproduces experimental results reported for polariton graphene ribbons. We analyze in particular the influence of the non-orthogonality, the inter-orbitals interaction and the photonic spin-orbit coupling on the polarization and dispersion of bulk bands and edge states.

Gallium Phosphide as a Piezoelectric Platform for Quantum Optomechanics.

Recent years have seen extraordinary progress in creating quantum states of mechanical oscillators, leading to great interest in potential applications for such systems in both fundamental as well as applied quantum science. One example is the use of these devices as transducers between otherwise disparate quantum systems. In this regard, a promising approach is to build integrated piezoelectric optomechanical devices that are then coupled to microwave circuits. Optical absorption, low quality factors, and other challenges have up to now prevented operation in the quantum regime, however. Here, we design and characterize such a piezoelectric optomechanical device fabricated from gallium phosphide in which a 2.9 GHz mechanical mode is coupled to a high quality factor optical resonator in the telecom band. The large electronic band gap and the resulting low optical absorption of this new material, on par with devices fabricated from silicon, allows us to demonstrate quantum behavior of the structure. This not only opens the way for realizing noise-free quantum transduction between microwaves and optics, but in principle also from various color centers with optical transitions in the near visible to the telecom band.

Semiconductor disk laser in bi-frequency operation by laser ablation micromachining of a laser mirror.

We present bi-frequency continuous wave oscillation in a semiconductor disk laser through direct writing of loss-inducing patterns onto an intra-cavity high reflector mirror. The laser is a Vertical External Cavity Surface Emitting Laser which is optically pumped by up to 1.1 W of 808 nm light from a fibre coupled multi-mode diode laser, and oscillates on two Hermite-Gaussian spatial modes simultaneously, achieving wavelength separations between 0.2 nm and 5 nm around 995 nm. We use a Digital Micromirror Device (DMD) enabled laser ablation system to define spatially specific loss regions on a laser mirror by machining away the Bragg layers from the mirror surface. The ablated pattern is comprised of two orthogonal lines with the centermost region undamaged, and is positioned in the laser cavity so as to interact with the lasing mode, thereby promoting the simultaneous oscillation of the fundamental and a higher order spatial mode. We demonstrate bi-frequency oscillation over a range of mask gap sizes and pump powers.

Fully-correlated multi-mode pumping for low-noise dual-frequency VECSELs.

We report a fully-correlated multi-mode pumping architecture optimized for dramatic noise reduction of a class-A dual-frequency Vertical External Cavity Surface Emitting Laser (VECSEL). Thanks to amplitude division of a laser diode, the two orthogonally polarized modes emitted by the VECSEL oscillating at 852 nm are separately pumped by two beams exhibiting fully in-phase correlated intensity noises. This is shown to lead to very strong and in-phase correlations between the two lasing modes intensities. As a result, the phase noise power spectral density of the RF beat note generated by the two modes undergoes a drastic reduction of about 10 to 20 dB throughout the whole frequency range from 10 kHz to 20 MHz and falls below the detection floor above a few MHz. A good agreement is found with a model which uses the framework of rate equations coupled by cross-saturation. The remaining phase noise is attributed to thermal effects and additional technical noises and lies mainly within the bandwidth of a phase-locked-loop.

High-power tunable low-noise coherent source at 1.06 µm based on a surface-emitting semiconductor laser.

Exploiting III-V semiconductor technologies, vertical external-cavity surface-emitting laser (VECSEL) technology has been identified for years as a good candidate to develop lasers with high power, large coherence, and broad tunability. Combined with fiber amplification technology, tunable single-frequency lasers can be flexibly boosted to a power level of several tens of watts. Here, we demonstrate a high-power, single-frequency, and broadly tunable laser based on VECSEL technology. This device emits in the near-infrared around 1.06 µm and exhibits high output power (>100 mW) with a low-divergence diffraction-limited TEM00 beam. It also features a narrow free-running linewidth of <400 kHz with high spectral purity (side mode suppression ratio >55 dB) and continuous broadband tunability greater than 250 GHz (<15 V piezo voltage, 6 kHz cutoff frequency) with a total tunable range up to 3 THz. In addition, a compact design without any movable intracavity elements offers a robust single-frequency regime. Through fiber amplification, a tunable single-frequency laser is achieved at an output power of 50 W covering the wavelength range from 1057 to 1066 nm. Excess intensity noise brought on by the amplification stage is in good agreement with a theoretical model. A low relative intensity noise value of -145 dBc/Hz is obtained at 1 MHz, and we reach the shot-noise limit above 200 MHz.

Pulse train interaction and control in a microcavity laser with delayed optical feedback.

We report experimental and theoretical results on the pulse train dynamics in an excitable semiconductor microcavity laser with an integrated saturable absorber and delayed optical feedback. We show how short optical control pulses can trigger, erase, or retime regenerative pulse trains in the external cavity. Both repulsive and attractive interactions between pulses are observed, and are explained in terms of the internal dynamics of the carriers. A bifurcation analysis of a model consisting of a system of nonlinear delay differential equations shows that arbitrary sequences of coexisting pulse trains are very long transients towards weakly stable periodic solutions with equidistant pulses in the external cavity.

A solid-state single-photon filter.

A strong limitation of linear optical quantum computing is the probabilistic operation of two-quantum-bit gates based on the coalescence of indistinguishable photons. A route to deterministic operation is to exploit the single-photon nonlinearity of an atomic transition. Through engineering of the atom-photon interaction, phase shifters, photon filters and photon-photon gates have been demonstrated with natural atoms. Proofs of concept have been reported with semiconductor quantum dots, yet limited by inefficient atom-photon interfaces and dephasing. Here, we report a highly efficient single-photon filter based on a large optical nonlinearity at the single-photon level, in a near-optimal quantum-dot cavity interface. When probed with coherent light wavepackets, the device shows a record nonlinearity threshold around 0.3 ± 0.1 incident photons. We demonstrate that 80% of the directly reflected light intensity consists of a single-photon Fock state and that the two- and three-photon components are strongly suppressed compared with the single-photon one.

Compensation of the residual linear anisotropy of phase in a vertical-external-cavity-surface-emitting laser for spin injection.

We report on the compensation of the linear anisotropy of phase in a vertical-external-cavity surface-emitting laser from 21 to 0.5 mrad with an intracavity PLZT electro-optical ceramic. It allows dynamic and accurate control of the laser linear anisotropy, as well as dynamic control of the laser polarization eigenstates. At the birefringence compensation point, we observe an elliptical polarization state with 41° of ellipticity, rotated from its initial position of 32°. The experimental observations are in close agreement with the theoretical predictions. Finally, we are able to demonstrate control of the polarization state with spin injection.

Vortex Laser based on III-V semiconductor metasurface: direct generation of coherent Laguerre-Gauss modes carrying controlled orbital angular momentum.

The generation of a coherent state, supporting a large photon number, with controlled orbital-angular-momentum L = hl (of charge l per photon) presents both fundamental and technological challenges: we demonstrate a surface-emitting laser, based on III-V semiconductor technology with an integrated metasurface, generating vortex-like coherent state in the Laguerre-Gauss basis. We use a first order phase perturbation to lift orbital degeneracy of wavefunctions, by introducing a weak anisotropy called here "orbital birefringence", based on a dielectric metasurface. The azimuthal symmetry breakdown and non-linear laser dynamics create "orbital gain dichroism" allowing selecting vortex handedness. This coherent photonic device was characterized and studied, experimentally and theoretically. It exhibits a low divergence (<1°) diffraction limited beam, emitting 49 mW output power in the near-IR at λ ≃ 1 µm, a charge l = ±1, … ±4 (>50 dB vortex purity), and single frequency operation in a stable low noise regime (0.1% rms). Such high performance laser opens the path to widespread new photonic applications.