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.

Optimization of the conversion efficiency and evaluation of the noise figure of an optical frequency converter based on a dual-pump fiber phase sensitive amplifier.

We propose a new architecture of phase sensitive optical frequency converter based on dual-pump phase sensitive amplification in a highly nonlinear fiber. This frequency converter allows generation of extra tones through nonlinear four-wave mixing between two strong pumps and an input tone. The frequency channel to which the input tone is converted can be chosen by adjusting the phase of the input signal. The conversion efficiency and extinction ratio of this frequency converter are predicted and optimized and its noise figure is calculated using a numerical approach based on the nonlinear Schrödinger equation. A semi-classical noise figure calculation for this approach was used and validated using an analytical fully quantum calculation based on the multi-wave model.

Noise investigation of CW and mode-locked harmonic cavity nanolasers.

We theoretically investigate the noise properties of harmonic cavity nanolasers by introducing a model of coupled equations of evolution of the modes, taking spontaneous emission into account. This model is used to predict the noise among the nanolaser Hermite-Gaussian modes, both in continuous wave and mode-locked regimes. In the first case, the laser noise is described in terms of noise modes, thus illustrating the role of the laser dynamics. In the latter case, this leads to the calculation of the fluctuations of the pulse train parameters. The influence of the different laser parameters, including the amount of saturated absorption and the Henry factors, on the noise of the mode-locked regime is discussed in details.

Effect of linewidth enhancement factor on the generation of optical vortices in a class-A degenerate cavity semiconductor laser.

The dynamical behavior of a one-dimensional ring array of lasers generated in a class-A degenerate cavity semiconductor laser is numerically investigated. The class-A behavior of the laser is obtained by considering a low-loss vertical external cavity surface emitting laser (VECSEL), in which a telescope and a mask allow us to control the geometry and the linear nearest-neighbour coupling between the lasers. The behavior of the lasers is simulated using coupled rate equations, taking the influence of the Henry factor into account. It is shown that the ring array of lasers exhibits multistability. Moreover, by comparison with a class-B semiconductor laser, it is proved that the class-A nature of the laser makes it more robust to the increase of the Henry factor when it comes to generating topological charge carrying arrays of lasers, thus opening new perspectives of application for such lasers.

New method for residual amplitude modulation control in fibered optical experiments.

When locking the frequency of a laser to an optical cavity resonance, the residual amplitude modulation (RAM), which accompanies the phase modulation necessary to build the error signal, is a major limitation to the frequency stability. We show that the popular method demonstrated by Wong and Hall to cancel this effect, based on the measurement of the RAM using an auxiliary detector, is limited in the case of optical setups exhibiting polarization dependent losses and an imperfect polarizer at the modulator output, such as guided-wave optical systems.We propose and demonstrate a new method, using a single photodetector, to generate the two error signals and demonstrate its usefulness in the case of fibered systems.

Microwave-driven generation and group delay control of optical pulses from an ultra-dilute atomic ensemble.

A cyclic atomic level scheme interacting with an optical and a microwave field is proposed for the generation and group-delay control of few-photon optical pulses. Our analysis exploits a hybrid second order-nonlinearity under conditions of electromagnetically induced transparency to generate an optical pulse. The generated pulse can be delayed or advanced through microwave intensity control of the absolute phase of the second-order-nonlinearity. Importantly, this handle on group delay of the generated pulse is number density-independent. Our scheme is thus ideally suited for the generation and control of few-photon optical pulses using ultra-dilute atomic samples. Our results will enable microscopic atomic interface systems that serve as controllable delay channels for both classical and quantum signal processing.

Robustness of mode-locking in harmonic cavity nanolasers subjected to potential distortions.

We theoretically analyze the robustness to potential distortion of mode-locking in a harmonic cavity nanolaser sustaining oscillation of Hermite-Gaussian modes. Different types of imperfections of the harmonic potential that create the Hermite-Gaussian modes are considered: the non-parabolicity of the potential and the possible random errors in the shape of the potential. The influence of the different laser parameters, including the Henry factors of the gain medium and the saturable absorber, on the robustness of the mode-locked regime is discussed in detail.

Directing random lasing emission using cavity exciton-polaritons.

Random lasing is an intriguing phenomenon occurring in disordered structures with optical gain in which light scattering provides the necessary feedback for lasing action. Unlike conventional lasers, random lasing systems emit in all directions due to light scattering. While this property can be desired in some cases, directional emission remains required for most applications. In a vertical microcavity containing the hybrid perovskite CH3NH3PbBr3, we report here the coupling of the emission of a random laser with a cavity polaritonic resonance, resulting in a directional random lasing, whose emission angles can be tuned by varying the cavity detuning and reach values as large as 15.8° and 22.4°.

Mode Locking of the Hermite-Gaussian Modes of a Nanolaser.

Mode locking is predicted in a nanolaser cavity forming an effective photonic harmonic potential. The cavity is substantially more compact than a Fabry-Perot resonator with a comparable pulsing period, which is here controlled by the potential. In the limit of instantaneous gain and absorption saturation, mode locking corresponds to a stable dissipative soliton, which is very well approximated by the coherent state of a quantum mechanical harmonic oscillator. This property is robust against noninstantaneous material response and nonzero phase-intensity coupling.

Phase-sensitive amplification of an optical field using microwaves.

We report phase-sensitive amplification (PSA) of a near-infrared electromagnetic field using room-temperature 85Rb atoms possessing ground-state coherence. Our novelty is in achieving significant optical PSA by manipulating the intensity and phase of a frequency-separated microwave field. PSA is obtained by inducing a three-wave mixing nonlinear process utilising a three-level cyclic scheme in the D1 manifold. We achieve a near-ideal PSA with a gain of 7 dB over a range of 500 kHz bandwidth with very low pump-field intensities and with low optical depths. Such a hybrid, ground-state-coherence-assisted PSA is the first such demonstration using atomic ensembles.

Rotation measurements using a resonant fiber optic gyroscope based on Kagome fiber.

We build a resonant fiber optic gyro based on Kagome hollow-core fiber. A semi-bulk cavity architecture based on an 18-m-long Kagome fiber permits achieving a cavity finesse of 23 with a resonance linewidth of 700 kHz. An optimized Pound-Drever-Hall servo-locking scheme is used to probe the cavity in reflection. Closed-loop operation of the gyroscope permits reaching an angular random walk as small as 0.004°/h and a bias stability of 0.45°/h over 0.5 s of integration time.

Infrared laser threshold magnetometry with a NV doped diamond intracavity etalon.

We propose a hybrid laser system consisting of a semiconductor external cavity laser associated to an intra-cavity diamond etalon doped with nitrogen-vacancy color centers. We consider laser emission tuned to the infrared absorption line that is enhanced under the magnetic field dependent nitrogen-vacancy electron spin resonance and show that this architecture leads to a compact solid-state magnetometer that can be operated at room-temperature. The sensitivity to the magnetic field limited by the photonshot-noise of the output laser beam is estimated to be less than 1 pT/Hz. Unlike usual NV center infrared magnetometry, this method would not require an external frequency stabilized laser. Since the proposed system relies on the competition between the laser threshold and an intracavity absorption, such laser-based optical sensor could be easily adapted to a broad variety of sensing applications based on absorption spectroscopy.

Coherent microwave-to-optical conversion by three-wave mixing in a room temperature atomic system.

We experimentally observe coherent generation of a near-infrared optical field through a three-wave mixing phenomenon in an atomic energy level scheme of Rb85 atoms. This nonlinear generation process in a centro-symmetric thermally broadened atomic system is made possible through a novel interaction between induced electric and magnetic dipoles. The two-photon and three-photon coherence present in our scheme eliminates excited state decoherence. Thus, our scheme represents a minimal optical decoherence scheme which could be used to transfer quantum states between microwave-to-optical frequency regimes with near-unit fidelity.

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.

Phase evolution of the direct detection noise figure of a nondegenerate fiber phase-sensitive amplifier.

We experimentally investigate the evolution of the direct detection noise figure of a nondegenerate phase-sensitive amplifier based on a nonlinear fiber, as a function of the relative phase between the signal, idler, and pump, all other parameters remaining fixed. The use of a fiber with a high stimulated Brillouin scattering threshold permits us to investigate the full range of phase-sensitive gain and noise figure without pump dithering. Good agreement is found with theory, both for signal only and combined signal and idler direct detections.

Ultra-low noise dual-frequency VECSEL at telecom wavelength using fully correlated pumping.

An ultra-low intensity and beatnote phase noise dual-frequency vertical-external-cavity surface-emitting laser is built at telecom wavelength. The pump laser is realized by polarization combining two single-mode fibered laser diodes in a single-mode fiber, leading to a 100% in-phase correlation of the pump noises for the two modes. The relative intensity noise is lower than -140 dB/Hz, and the beatnote phase noise is suppressed by 30 dB, getting close to the spontaneous emission limit. The role of the imperfect cancellation of the thermal effect resulting from unbalanced pumping of the two modes in the residual phase noise is evidenced.

Optimization of a degenerate dual-pump phase-sensitive optical parametric amplifier for all-optical regenerative functionality.

We present a thorough investigation aimed at the optimization of a phase-sensitive optical parametric amplifier capable of simultaneous phase and amplitude regeneration. The regeneration potential, quantified in terms of the phase-sensitive extinction ratio, has been carefully assessed by a scalar model involving high-order waves associated with high-order four-wave mixing processes, going beyond the usual three-wave approach. Additionally, this model permits to unveil the physics involved in the high-order waves assisted regeneration. This permits a multi-dimensional and comprehensive optimization that fully exploits the underlying regenerative capability and expedites the design of a transparent regenerator, showing the potential to act as basic building block in future all-optical processing. We also compare different strategies when such regenerators are configured in concatenation. The approach can be readily applied to virtually any similar applications for different all-optical processing functionalities.

Impact of Reabsorption on the Emission Spectra and Recombination Dynamics of Hybrid Perovskite Single Crystals.

Understanding the surface properties of organic-inorganic lead-based perovskites is of high importance to improve the device's performance. Here, we have investigated the differences between surface and bulk optical properties of CH3NH3PbBr3 single crystals. Depth-resolved cathodoluminescence was used to probe the near-surface region on a depth of a few microns. In addition, we have studied the transmitted luminescence through thicknesses between 50 and 600 µm. In both experiments, the expected spectral shift due to the reabsorption effect has been precisely calculated. We demonstrate that reabsorption explains the important variations reported for the emission energy of single crystals. Single crystals are partially transparent to their own luminescence, and radiative transport is the dominant mechanism for propagation of the excitation in thick crystals. The transmitted luminescence dynamics are characterized by a long rise time and a lengthening of their decay due to photon recycling and light trapping.

30-Hz relative linewidth watt output power 1.65 µm continuous-wave singly resonant optical parametric oscillator.

We built a 1-watt cw singly resonant optical parametric oscillator operating at an idler wavelength of 1.65 µm for application to quantum interfaces. The non resonant idler is frequency stabilized by side-fringe locking on a relatively high-finesse Fabry-Perot cavity, and the influence of intensity noise is carefully analyzed. A relative linewidth down to the sub-kHz level (about 30 Hz over 2 s) is achieved. A very good long term stability is obtained for both frequency and intensity.

Fourier transform-limited optical frequency-modulated continuous-wave interferometry over several tens of laser coherence lengths.

We report on a versatile optical frequency-modulated continuous-wave interferometry technique that exploits wideband phase locking for generating highly coherent linear laser frequency chirps. This technique is based on an ultra-short delay-unbalanced interferometer, which leads to a large bandwidth, short lock time, and robust operation even in the absence of any isolation from environmental perturbations. In combination with a digital delay-matched phase error compensation, this permits the achievement of a range window about 60 times larger than the intrinsic laser coherence length with a 1.25 mm Fourier transform-limited spatial resolution. The demonstrated configuration can be easily applied to virtually any semiconductor laser.