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Schilt, Stephane

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Schilt, Stephane
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https://libra.unine.ch/handle/123456789/492

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  • Publication
    Accès libre
    Frequency stability of a dual wavelength quantum cascade laser
    Sargachev, Ilia
    ;
    Maulini, Richard
    ;
    Gresch, Tobias
    ;
    Blaser, Stéphane
    ;
    Bismuto, Alfredo
    ;
    Müller, Antoine
    ;
    Bidaux, Yves
    ;
    Südmeyer, Thomas 
    ;
    Schilt, Stephane 
    We characterized the dual wavelength operation of a distributed Bragg reflector (DBR) quantum cascade laser (QCL) operating at 4.5 μm using two independent optical frequency discriminators. The QCL emits up to 150 mW fairly evenly distributed between two adjacent Fabry-Perot modes separated by ≈11.6 GHz. We show a strong correlation between the instantaneous optical frequencies of the two lasing modes, characterized by a Pearson correlation coefficient of 0.96. As a result, we stabilized one laser mode of the QCL to a N2O transition using a side-of-fringe locking technique, reducing its linewidth by a factor 6.2, from 406 kHz in free-running operation down to 65 kHz (at 1-ms observation time), and observed a simultaneous reduction of the frequency fluctuations of the second mode by a similar amount, resulting in a linewidth narrowing by a factor 5.4, from 380 kHz to 70 kHz. This proof-of-principle demonstration was performed with a standard DBR QCL that was not deliberately designed for dual-mode operation. These promising results open the door to the fabrication of more flexible dual-mode QCLs with the use of specifically designed gratings in the future.
  • Publication
    Accès libre
    All-electrical frequency noise reduction and linewidth narrowing in quantum cascade lasers
    Sargachev, Ilia
    ;
    Maulini, Richard
    ;
    Bismuto, Alfredo
    ;
    Blaser, Stéphane
    ;
    Gresch, Tobias
    ;
    Bidaux, Yves
    ;
    Müller, Antoine
    ;
    Schilt, Stephane 
    ;
    Südmeyer, Thomas 
    A novel all-electrical method of frequency noise reduction in quantum cascade lasers (QCLs) is proposed. Electrical current through the laser was continuously adjusted to compensate for fluctuations of the laser internal resistance, which led to an active stabilization of the optical emission frequency. A reduction of the linewidth from 1.7 MHz in the standard constant current mode of operation down to 480 kHz is demonstrated at 10-ms observation time when applying this method to a QCL emitting at 7.9 μm.
  • Publication
    Accès libre
    Electrically-driven pure amplitude and frequency modulation in a quantum cascade laser
    Shehzad, Atif 
    ;
    Brochard, Pierre 
    ;
    Matthey-De-L'Endroit, Renaud 
    ;
    Blaser, Stéphane
    ;
    Gresch, Tobias
    ;
    Maulini, Richard
    ;
    Muller, Antoine
    ;
    Südmeyer, Thomas 
    ;
    Schilt, Stephane 
    We present pure amplitude modulation (AM) and frequency modulation (FM) achieved electrically in a quantum cascade laser (QCL) equipped with an integrated resistive heater (IH). The QCL output power scales linearly with the current applied to the active region (AR), but decreases with the IH current, while the emission frequency decreases with both currents. Hence, a simultaneous modulation applied to the current of the AR and IH sections with a proper relative amplitude and phase can suppress the AM, resulting in a pure FM, or vice-versa. The adequate modulation parameters depend on the applied modulation frequency. Therefore, they were first determined from the individual measurements of the AM and FM transfer functions obtained for a modulation applied to the current of the AR or IH section, respectively. By optimizing the parameters of the two modulations, we demonstrate a reduction of the spurious AM or FM by almost two orders of magnitude at characteristic frequencies of 1 and 10 kHz compared to the use of the AR current only.
  • Publication
    Accès libre
    Frequency Ageing and Noise Evolution in a Distributed Feedback Quantum Cascade Laser Measured Over a Two-Month Period
    Schilt, Stephane 
    ;
    Tombez, Lionel 
    ;
    Tardy, Camille
    ;
    Bismuto, Alfredo
    ;
    Blaser, Stéphane
    ;
    Maulini, Richard
    ;
    Terazzi, Romain
    ;
    Rochat, Michel
    ;
    Südmeyer, Thomas 
    We report on the evaluation of the frequency stability of a distributed feedback quantum cascade laser (QCL) at 8 µm that was continuously monitored over a 2-month period using a spectroscopic setup. The QCL was operated in continuous wave mode at room temperature (21.4 °C). It was driven by a home-made low-noise controller at a nominal current of ∼600 mA located in the middle of its operation range. Two distinctive behaviors were observed. A monotonous frequency drift of about 1.8 GHz was observed during slightly more than the first month, followed by a stable regime in the second month where the frequency remained within a 100 MHz range. In addition, the electrical flicker noise of the QCL was regularly measured during the same period, and similarly showed two different regimes. The noise regularly decreased at a small rate of about 0.3%/day during the first month, whereas it tends to stabilize during the second month. We believe that an improvement of the QCL contacts over time is responsible for this behavior. After the initial one-month period, the QCL showed a remarkably stable behavior that is beneficial for many applications that require stable long-term operation.
  • Publication
    Accès libre
    An experimental study of noise in midinfrared quantum cascade lasers of different designs
    Schilt, Stephane 
    ;
    Tombez, Lionel 
    ;
    Tardy, Camille
    ;
    Bismuto, Alfredo
    ;
    Blaser, Stéphane
    ;
    Maulini, Richard
    ;
    Terazzi, Romain
    ;
    Rochat, Michel
    ;
    Südmeyer, Thomas 
    We present an experimental study of noise in mid-infrared quantum cascade lasers (QCLs) of differ-ent designs. By quantifying the high degree of correlation occurring between fluctuations of the optical frequency and voltage between the QCL terminals, we show that electrical noise is a powerful and simple mean to study noise in QCLs. Based on this outcome, we investigated the electrical noise in a large set of 22 QCLs emitting in the range of 7.6–8 μm and consisting of both ridge-waveguide and buried-heterostructure (BH) lasers with different geometrical designs and operation parameters. From a statistical data processing based on an analysis of variance, we assessed that ridge-waveguide lasers have a lower noise than BH lasers. Our physical interpretation is that additional current leakages or spare injection channels occur at the interface between the active region and the lateral insulator in the BH geometry, which induces some extra noise. In addition, Schottky-type contacts occurring at the interface between the n-doped regions and the lat-eral insulator, i.e., iron-doped InP, are also believed to be a potential source of additional noise in some BH lasers, as observed from the slight reduction in the integrated voltage noise observed at the laser threshold in several BH-QCLs.
  • Publication
    Accès libre
    Frequency Tuning and Modulation of a Quantum Cascade Laser with an Integrated Resistive Heater
    Gürel, Kutan
    ;
    Schilt, Stephane 
    ;
    Bismuto, Alfredo
    ;
    Bidaux, Yves
    ;
    Tardy, Camille
    ;
    Blaser, Stéphane
    ;
    Gresch, Tobias
    ;
    Südmeyer, Thomas 
    We present a detailed experimental investigation of the use of a novel actuator for frequency tuning and modulation in a quantum cascade laser (QCL) based on a resistive integrated heater (IH) placed close to the active region. This new actuator is attractive for molecular spectroscopy applications as it enables fast tuning of the QCL wavelength with a minor influence on the optical output power, and is electrically-controlled. Using a spectroscopic setup comprising a low-pressure gas cell, we measured the tuning and modulation properties of a QCL emitting at 7.8 μm as a function of the active region and IH currents. We show that a current step applied to the IH enables the laser frequency to be switched by 500 MHz in a few milliseconds, as fast as for a step of the current in the active region, and limited by heat dissipation towards the laser sub-mount. The QCL optical frequency can be modulated up to ∼100 kHz with the IH current, which is one order of magnitude slower than for the QCL current, but sufficient for many spectroscopic applications. We discuss the experimental results using a thermal model of the heat transfer in terms of cascaded low-pass filters and extract the respective cut-off frequencies. Finally, we present a proof-of-principle experiment of wavelength modulation spectroscopy of a N2O transition performed with a modulation of the IH current and show some potential benefits in comparison to QCL current modulation, which results from the reduced associated amplitude modulation.