Isabelle Sagnes

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.

Monolithic echoless photoconductive switches for high-resolution terahertz time-domain spectroscopy (Conference Presentation)

Interdigitated photoconductive (iPC) switches [1] are powerful and convenient devices for time-resolved spectroscopy, with the ability to operate both as sources and detectors of terahertz (THz) frequency pulses. However, reflection of the emitted or detected radiation within the device substrate itself can lead to echoes that inherently limits the spectroscopic resolution achievable from their use in time-domain spectroscopy (TDS) systems. In this work, we demonstrate a design of low-temperature-grown-GaAs (LT-GaAs) iPC switches for THz pulse detection that suppresses such unwanted echoes [2]. This is realized through the growth of a buried multilayer LT-GaAs structure that retains its ultrafast properties, which after wafer bonding to a metal-coated host substrate, results in an iPC switch with a metal plane buried at a subwavelength depth below the LT-GaAs surface. Using this device as a detector, and coupling it to an echo-less iPC source [3], enables echo-free THz-TDS and high-resolution spectroscopy, with a resolution limited only by the temporal length of the measurement governed by the mechanical delay line used. As a proof-of-principle, the 2(12)-2(21) and the 1(01)-2(12) rotational lines of water vapor have been spectrally resolved, demonstrating a spectral resolution below 10 GHz.nn[1] A. Dreyhaupt, S. Winnerl, T. Dekorsy, M. Helm, Appl. Phys. Lett. 86, 121114 (2005)n[2] K. Maussang, J. Palomo, J.-M. Manceau, R. Colombelli, I. Sagnes, L. H. Li, E. H. Linfield, A. G. Davies, J. Mangeney, J. Tignon, and S. S. Dhillon, Appl. Phys. Lett. 110, 141102 (2017).n[3] K. Maussang, A. Brewer, J. Palomo, J.-M. Manceau, R. Colombelli, I. Sagnes, J. Mangeney, J. Tignon, S.S. Dhillon, IEEE Trans. Terahertz Sci. Technol. 6, 20 (2016)

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>

Single-Frequency Diode-Pumped Vertical-External Cavity Laser at the Caesium D 2 line

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Room temperature laser operation of strained InGaAs/GaAs QW structure monolithically grown by MOCVD on LE-PECVD Ge/Si virtual substrate

</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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InGaAs/GaAs LASERS ON SILICON PRODUCED BY LEPECVD AND MOCVD

</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.

LASER DEVICE WITH A BEAM CARRYING CONTROLLED ORBITAL ANGULAR MOMENTUM

We report on the design and characterization of a single-frequency diode-pumped vertical external-cavity surface-emitting laser emitting at 852 nm for Caesium atomic clock experiments. Up to 120 mW under 1.1 W pumping is achieved.