MSCA-COFUND-CLEAR-Doc-PhD Position #CD22-27: Passive Modelocking of external cavity MIR Quantum Cascade Laser integrating graphene

The mid-infrared (MIR) spectral region has numerous scientific interests and technological applications. In recent years, by the emergence of quantum cascade lasers (QCLs) as compact, reliable and commercially available semiconductor sources, even more applications have been empowered such as in telecommunication, defense, spectroscopy, etc. These sources can deliver up to hundreds of mW at room temperature. Passive mode-locking in QCLs remains one of the huge challenges because of the fast relaxation time of the excited carriers which is typically in the range of sub-picoseconds. The use of conventional techniques such as the semiconductor saturable absorber mirror is inefficient because the spatial hole burning effect dominates the carrier dynamics. To overcome this effect, longitudinal transition structures with relaxation time around 50 ps were proposed [2]. However, mode-locking is assured with an external modulation at a cavity roundtrip frequency. We demonstrate a passive modelocking ability in MIR QCL by integrating a single-layer graphene used as a saturable absorber [5]. The graphene has been integrated with a highly reflective mirror to increase the internal electric field and achieve the saturation intensity. We have shown that an optimized location corresponds to a distance of a quarter wavelength between the Bragg mirror and the graphene layer for which the electric field intensity attains the maximum value. Without graphene, the QCL operates in a continuous waves mode which means that the mode-locking failure. For a QCL structure with a vertical transition, SHB effect dominates because of the fast recovery time compared to the cavity roundtrip time. With T1=5 ps, multiple pulses per roundtrip are obtained in 2.6 mm cavity length. However, isolated pulses are obtained by reducing the cavity length to 1.8 mm. Thus, passive mode-locking of the MIR QCL is obtained by integrating a graphene reflective mirror but requires shorter cavity length for T1 in the range 0.5 – 1 ps. In this work, external cavity MIR QCL will be investigated for passive modelocking by integrating graphene. Recent work uses diffraction grating compensation which presents a complex configuration method to implement experimentally [4].

We have at Esycom Lab. an expertise on the modeling of semiconductor quantum devices, photonic integrated circuits and more recently quantum cascade lasers in MIR spectral region. We developed a simulation tools to determine the dynamic of the QCL through the resolution of Maxwell-Bloch equations for the gain section [3], [1]. For the graphene layer, Maxwell-Ampere equation has been considered by the determination of a nonlinear conductivity from a saturable absorption coefficient. However, graphene layer can be modeling using Maxwell-Bloch equations which is efficient method for fast light interaction with matter but need to have the graphene physical parameters. Thus, in this PhD work such method will be used from experimental data of graphene. In addition, recent work in [6] proposes to describe graphene as a surface current with no optical thickness. This method was proved experimentally. For modelocking of QCL, saturable absorption effect could be included in such modeling.

Missions:

The first mission consists in implementing Maxwell-Bloch equations or a new method to consider the single-layer graphene in FDTD.

The second aim is to participate to the characterization of frequency COMB QCLs or active modelocking QCL in LPENS (Laboratoire de Physique de l'école Normal Supérieur). This mission will permit to have an access to physical parameters of MIR QCLs to be used for the simulation setup.

The third mission deals with an experimental setup located at Nanyang Technological University (NTU / Cintra Singapore) where a commercial product of external cavity QCL is available. The objective will consist to insert graphene layer within the cavity to determine the effect on the laser dynamic.

The modeling activity will be carried out at the Laboratory of Electronics, Communication System and Microsystems (Esycom, UMR9007) and the experimental activity will be done in LPENS and NTU/Cintra Singapore.

Activities:

Main activities:

• Maxwell-Bloch simulation using Finite-Difference Time-Domain (FDTD) method,

• Comparison of the two-level atom approximation and the multiple-level system,

• Study of MIR QCL with external cavity including graphene,

• Development of simulation tools to study the interaction of light-matter in external laser cavity using Maxwell-Bloch equations,

• Experimental characterization of QCLs, extraction physical parameters from measurement data of graphene layer.

Secondary activities:

• Writing of progress reports on the different results,

• Participation to international and national conferences and writing journal papers.

Candidate profile:

The thesis has a theoretical and an experimental aspects with an important part devoted to quantum/electromagnetic simulations towards device design and development. The work will involve electromagnetic simulations using a finite-difference time-domain method, testing of the realized devices using FTIR spectroscopy for example. The successful applicant will be an energetic individual with interest in semiconductor physics, quantum mechanics. She/he will have completed an undergraduate program in Physics, Optics or Electronic Engineering.

Ability to work in a team and to collaborate in a project context involving international collaborators.

Supervisors :

Catherine Algani: catherine.algani@lecnam.net, Professor Esycom-Cnam

Elodie Richalot: elodie.richalot-taisne@univ-eiffel.fr, Professor Esycom-UGE

Salim Faci: salim.faci@lecnam.net, Associate Professor Esycom-Cnam

References:

[1] A. Outafat et al. “Active Modelocking Improvement of MIR-QCL by Integrating Graphene as a Saturable Absorber”. In IEEE Journal of Quantum Electronics 58, 5 (2022), pp. 1–8. doi:10.1109/JQE.2022.3177220.

[2] A. Outafat et al. “Graphene Saturable Absorber Mirror for Passive Mode-locking of Mid-Infrared QCLs”. Accepted for publication in Optical and Quantum Electronics, doi: https://doi.org/10.21203/rs.3.rs-1991441/v1.

[3] A. Outafat et al. “Passive modelocking MIR quantum cascade laser incorporating self-induced transparency”. Optical and Quantum Electronics 54, 5 (May 2022), p. 283, doi:10.1007/s11082-022-03675-y.

[4] Philipp T ̃aschler et al. “Femtosecond pulses from a mid-infrared quantum cascade laser”. NaturePhotonics 15, 12 (Dec. 2021), pp. 919–924, doi:10.1038/s41566-021-00894-9, doi:https://doi.org/10.1038/s41566-021-00894-9.

[5] Christine Y. Wang et al. “Mode-locked pulses from mid-infrared Quantum Cascade Lasers”. In:Opt.Express17.15 (July 2009), pp. 12929–12943.doi:10.1364/OE.17.012929.

[6] Zhemi Xu et al. “Optical detection of the susceptibility tensor in two-dimensional crystals”. Communications Physics 4, 1 (Sept. 2021), p. 215, doi:10.1038/s42005-021-00711-3.