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Quantum-limited frequency fluctuations in a terahertz laser

Nature Photonics volume 6, pages 525–528 (2012)Cite this article

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Abstract

Quantum cascade lasers1,2 can be considered the primary achievement of electronic band structure engineering, showing how artificial materials can be created through quantum design to have tailor-made properties that are otherwise non-existent in nature. Indeed, quantum cascade lasers can be used as powerful testing grounds of the fundamental physical parameters determined by their quantum nature, including the intrinsic linewidth of laser emission3, which in such lasers is significantly affected by the optical and thermal photon number generated in the laser cavity. Here, we report experimental evidence of linewidth values approaching the quantum limit4,5 in far-infrared quantum cascade lasers. Despite the broadening induced by thermal photons, the measured linewidth results narrower than that found in any other semiconductor laser to date. By performing noise measurements with unprecedented sensitivity levels, we highlight the key role of gain medium engineering6 and demonstrate that properly designed semiconductor-heterostructure lasers can unveil the mechanisms underlying the laser-intrinsic phase noise, revealing the link between device properties and the quantum-limited linewidth.

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Figure 1: Gain media architecture of a BTC terahertz QCL.
Figure 2: Schematic of the experimental set-up.
Figure 3: Frequency noise power spectral density.

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Acknowledgements

This work was partly supported by the Italian Ministry of Education, University, and Research (MIUR) through the programme ‘FIRB–Futuro in Ricerca 2010 RBFR10LULP Fundamental Research on Terahertz Photonic Devices’ and by the Ente Cassa di Risparmio di Firenze and Regione Toscana, through project CTOTUS, in the framework of POR–CReO FESR 2007–2013. The authors thank H.E. Beere and D.A. Ritchie for the growth of the QCL structure, J.H. Xu for technical support and J. Faist for useful discussions.

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Authors and Affiliations

  1. CNR- Istituto Nazionale di Ottica and LENS (European Laboratory for Non-linear Spectroscopy), Via Carrara 1, Sesto Fiorentino (FI), 50019, Italy

    Miriam S. Vitiello, Luigi Consolino, Saverio Bartalini, Andrea Taschin, Massimo Inguscio & Paolo De Natale

  2. NEST, CNR – Istituto Nanoscienze and Scuola Normale Superiore, Piazza San Silvestro 12, Pisa, 56127, Italy

    Miriam S. Vitiello & Alessandro Tredicucci

  3. Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via Carrara 1, Sesto Fiorentino (FI), 50019, Italy

    Massimo Inguscio

Authors
  1. Miriam S. Vitiello
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  2. Luigi Consolino
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  6. Massimo Inguscio
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  7. Paolo De Natale
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Contributions

M.S.V. conceived and performed the experiment, analysed the data, carried out the modelling and wrote the paper. S.B. conceived and performed the experiment, analysed the data and contributed to manuscript preparation. L.C. performed the experiment and analysed the data. P.D. conceived the experiments and contributed to the analysis and manuscript preparation. All authors discussed the results and implications and contributed to the manuscript at various stages.

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Correspondence to Miriam S. Vitiello.

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Vitiello, M., Consolino, L., Bartalini, S. et al. Quantum-limited frequency fluctuations in a terahertz laser. Nature Photon 6, 525–528 (2012). https://doi.org/10.1038/nphoton.2012.145

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