Grégoire Beaudoin

Nanoepitaxy of InAs∕InP quantum dots by metalorganic vapor phase epitaxy for 1.55μm emitters

We report here on the structural and optical properties of selectively grown InAs∕InP quantum dots. Our approach combines electron-beam lithography, reactive ion etching, and selective low-pressure metalorganic vapor phase epitaxy, which allows the growth of nanometer-scale InAs quantum dots directly on InP substrate and an improved control of their size uniformity and density. These nanogrown InAs dots exhibit a high-efficiency photoluminescence band pointed at 1.55μm at room temperature.

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 1.06xa0µm and exhibits high output power (>100u2009u2009mW) with a low-divergence diffraction-limited TEM00 beam. It also features a narrow free-running linewidth of <400u2009u2009kHz with high spectral purity (side mode suppression ratio >55u2009u2009dB) and continuous broadband tunability greater than 250xa0GHz (<15u2009u2009V piezo voltage, 6xa0kHz cutoff frequency) with a total tunable range up to 3xa0THz. 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 50xa0W covering the wavelength range from 1057 to 1066xa0nm. Excess intensity noise brought on by the amplification stage is in good agreement with a theoretical model. A low relative intensity noise value of -145u2009u2009dBc/Hz is obtained at 1xa0MHz, and we reach the shot-noise limit above 200xa0MHz.

Pulse train control in an excitable micropillar laser with delayed optical feedback (Conference Presentation)

Recent experiments with an excitable VCSEL micropillar laser with delayed optical feedback demonstrated that the system is able to sustain trains of optical pulses. The laser has two layers of gain and one layer of absorption in the VCSEL cavity, and it is an excitable single longitudinal and transverse mode laser. With optical feedback, a past pulse can trigger a new pulse, creating a pulse train with repetition rate given by the delay time. It is possible to trigger and retime pulses by appropriate external perturbations, in the form of appropriately timed short optical pulses. In particular, several pulse trains can be triggered independently by optical perturbations, and sustained simultaneously in the external cavity, with different timing in between pulses. Such dynamics are also called localised structures, and are investigated here theoretically.nIt has been verified experimentally and theoretically that the phase of the electric field is not relevant. The Yamada model – a well-established system of ordinary differential equations for intensity, gain and absorption – is thus a suitable model. As we show, the Yamada model with delayed intensity feedback describes the pulsing micropillar laser system in good agreement with the experiment.nA bifurcation analysis of this model shows that several pulsing periodic solution with different repetition rates coexist and are stable. Although coexisting pulse trains can seem independent on the timescale of the experiment, we show that they correspond here to extremely long transient dynamics toward one of the stable periodic solutions, with equidistant pulses.

Spiking and pulse train dynamics in a neuromimetic micropillar laser (Conference Presentation)

Processing of information with optical spikes could present an alternative path with a reduced energy consumption. It could also be well suited in the framework of novel brain-inspired computation paradigms. We investigate the spiking and pulse train dynamics in a micropillar laser with integrated saturable absorber. The optically-pumped microcavity laser is based on a specifically optimized design. The solitary laser can emit sub-nanosecond Q-switched pulses above laser threshold. Below threshold, the laser is in the so-called excitable regime, a generic all-or-none kind of response also found in biological neurons. We demonstrate several neuromimetic properties of the micropillar laser including the relative and absolute refractory periods and the temporal summation. The latter gives rise to sensitive and fast coincidence detectors of optical signals.nnIn the configuration with delayed optical feedback, the system is shown experimentally and theoretically to sustain controllable trains of dissipative temporal solitons controlled by adequate optical perturbations. We show that the pulse train can be started or resynchronized (retiming) with a single perturbation and that the system can store a large variety of temporal pulse patterns. We discuss the role of pump noise that may terminate a pulse train. We demonstrate a strong asymmetry in the effect of noise on the switch on and off processes, as well as a peculiar role played by noise timing. Besides its interest as a compact source of controllable pulses, this system can be arranged if needed in arrays leading to interesting prospects for artificial optical neural networks.

Nanostructured diode for infrared photodetection through non degenerate two-photon absorption

Two-photon absorption (TPA) is a third order non-linear process that relies on the quasi-simultaneous absorption of two photons. Therefore, it has been proved to be an interesting tool to measure ultra-fast correlations1 or to design all-optical switches.2 Yet, due to the intrinsically low efficiency of the non-linear processes, these applications rest upon high peak power light sources such as femtosecond and picosecond pulsed laser. However TPA has also been noticed as an appealing new scheme for quantum infrared detection.3, 4 Indeed, typical quantum detection of IR radiation is based on small gap semiconductors that need to be cooled down to cryogenic temperature to achieve sufficient detectivity. TPA enables the absorption of IR photons by wide gap semiconductors when pump photons are provided to complete optical transitions across the gap. Still, the low efficiency of TPA represents a difficulty to detect usual infrared photon fluxes. To tackle this issue, we combined three strategies to improve the detection efficiency. First, it has been proved theoretically and experimentally that using different pump and signal photon energies which is known as non degenerate TPA (NDTPA) help increasing the TPA efficiency by several orders of magnitude.5 Thus we decided to work with different pump and signal wavelength. Secondly, since TPA is a local quasi-instantaneous process, both pump and signal photons must be temporarily and spatially co-localized inside the active medium. We made sure to maximize the overlap of the fields inside our device. Finally, it is well known that TPA has a quadratic dependence with the signal electric fields modulus, so we designed a specific nanostructure to enhance the signal field inside the active medium of the detector.

Coherent and Tunable THz Emission Driven by an Integrated III–V Semiconductor Laser

We demonstrate coherent and tunable THz emission by excitation of a unitraveling-carrier photodiode by a dual-frequency III–V semiconductor laser emitting up to 80xa0mW of optical power around 1xa0 <inline-formula><tex-math notation=LaTeX>

Mechanical tensile strain engineering of Ge for gain achievement

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Recent advances in germanium emission

</tex-math></inline-formula>m. The laser is an optically-pumped vertical-external-cavity surface-emitting laser that operates simultaneously on two transverse Laguerre–Gauss modes. Modes frequency difference is driven by thermal effects, band-filling effects and/or phase masks, allowing THz emission from 50xa0GHz to few THz. To reach THz emission from a pigtailed photodiode, we detail quantitatively how orthogonal transverse modes can be coupled within a single-mode fiber, leading to more than 20% beat efficiency. Coherent THz emission spectrum is presented with a linewidth of about 150xa0kHz for 3-ms acquisition time, and an output power limited by the photodiode (typically 1xa0<inline-formula><tex-math notation=LaTeX>

Invited) Strain Engineering for Optical Gain in Germanium

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Tensile-strained germanium microdisks using Si3N4 stressors

</tex-math></inline-formula>W at 300xa0GHz). Frequency noise is measured for the optical transverse modes along with the THz signal. The latter presents a frequency noise that is about 20-dB lower than the optical ones, thus proving that the dual-frequency concept allows frequency noise reduction by correlating part of the technical noise of the two modes.