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Tombez, Lionel

Nom
Tombez, Lionel
Affiliation principale
Fonction
Doctorant
Identifiants
https://libra.unine.ch/handle/123456789/495

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  • Publication
    Accès libre
    Active linewidth-narrowing of a mid-infrared quantum cascade laser without optical reference
    Tombez, Lionel 
    ;
    Schilt, Stephane 
    ;
    Hofstetter, Daniel 
    ;
    Südmeyer, Thomas 
    We report on a technique for frequency noise reduction and linewidth-narrowing of a distributed-feedback mid-IR quantum cascade laser (QCL) that does not involve any optical frequency reference. The voltage fluctuations across the QCL are sensed, amplified and fed back to the temperature of the QCL at a fast rate using a near-IR laser illuminating the top of the QCL chip. A locking bandwidth of 300 kHz and a reduction of the frequency noise power spectral density by a factor of 10 with respect to the free-running laser are achieved. From 2 MHz for the free-running QCL, the linewidth is narrowed below 700 kHz (10 ms observation time).
  • 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.