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Single-layer silicon metalens for broadband achromatic focusing and wide field of view
Authors:
Jian Cao,
Sarra Salhi,
Jonathan Peltier,
Jean-René Coudevylle,
Samson Edmond,
Cédric Villebasse,
Etienne Herth,
Laurent Vivien,
Carlos Alonso Ramos,
Daniele Melati
Abstract:
Achieving simultaneous broadband achromatic focusing and a wide field of view remains a significant challenge for metalenses. In this work, we begin with a quadratic phase profile, enabling full field-of-view designs, and apply dispersion engineering to minimize variations of the focal length across wavelengths, thereby substantially reducing both longitudinal and transverse chromatic aberrations.…
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Achieving simultaneous broadband achromatic focusing and a wide field of view remains a significant challenge for metalenses. In this work, we begin with a quadratic phase profile, enabling full field-of-view designs, and apply dispersion engineering to minimize variations of the focal length across wavelengths, thereby substantially reducing both longitudinal and transverse chromatic aberrations. This is accomplished using only the propagation phase in waveguide-like rectangular meta-atoms, without relying on geometric phase contributions. The fabricated singlet metalens experimentally demonstrates a field of view of 86{\textdegree}, along with a tenfold reduction in focal length variations with wavelength compared to a conventional quadratic metalens, achieving a measured relative shift as low as 1.3% across the 1.5 $μ$m - 1.6 $μ$m range (limited by our experimental setup). This improvement also leads to a twofold increase in focusing efficiency relative to the reference metalens. These experimental results validate the effectiveness of our design strategy in simultaneously enhancing the operational bandwidth and field of view of metalenses. The demonstrated performance can directly benefit beam steering applications in the near-infrared wavelength range and provides a path toward achromatic, wide field-of-view metalenses in the visible range for imaging systems
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Submitted 22 July, 2025;
originally announced July 2025.
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On-chip pulse generation at 8 μm wavelength
Authors:
Annabelle Bricout,
Mathieu Bertrand,
Philipp Täschler,
Barbara Schneider,
Victor Turpaud,
Stefano Calcaterra,
Davide Impelluso,
Marco Faverzani,
David Bouville,
Jean-René Coudevylle,
Samson Edmond,
Etienne Herth,
Carlos Alonso-Ramos,
Laurent Vivien,
Jacopo Frigerio,
Giovanni Isella,
Jérôme Faist,
Delphine Marris-Morini
Abstract:
The mid-infrared spectral region holds growing importance for applications such as gas sensing and spectroscopy. Although compact ultrashort pulse laser sources are essential to enable these applications, their realization in this spectral range remains an open challenge. We demonstrate an integrated approach to generate pulses in the mid-infrared based on chirped Bragg gratings engineered to comp…
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The mid-infrared spectral region holds growing importance for applications such as gas sensing and spectroscopy. Although compact ultrashort pulse laser sources are essential to enable these applications, their realization in this spectral range remains an open challenge. We demonstrate an integrated approach to generate pulses in the mid-infrared based on chirped Bragg gratings engineered to compensate for the group delay dispersion of quantum cascade laser frequency comb sources. SiGe graded-index photonic circuits are used for operation around 8 μm wavelength. With this approach, pulses as short as 1.39 picoseconds were obtained, marking a key step towards fully integrated ultrashort pulse sources in the mid-infrared.
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Submitted 12 June, 2025;
originally announced June 2025.
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Reduced lasing thresholds in GeSn microdisk cavities with defect management of the optically active region
Authors:
Anas Elbaz,
Riazul Arefin,
Emilie Sakat,
Binbin Wang,
Etienne Herth,
Gilles Patriarche,
Antonino Foti,
Razvigor Ossikovski,
Sebastien Sauvage,
Xavier Checoury,
Konstantinos Pantzas,
Isabelle Sagnes,
Jérémie Chrétien,
Lara Casiez,
Mathieu Bertrand,
Vincent Calvo,
Nicolas Pauc,
Alexei Chelnokov,
Philippe Boucaud,
Frederic Boeuf,
Vincent Reboud,
Jean-Michel Hartmann,
Moustafa El Kurdi
Abstract:
GeSn alloys are nowadays considered as the most promising materials to build Group IV laser sources on silicon (Si) in a full complementary metal oxide semiconductor-compatible approach. Recent GeSn laser developments rely on increasing the band structure directness, by increasing the Sn content in thick GeSn layers grown on germanium (Ge) virtual substrates (VS) on Si. These lasers nonetheless su…
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GeSn alloys are nowadays considered as the most promising materials to build Group IV laser sources on silicon (Si) in a full complementary metal oxide semiconductor-compatible approach. Recent GeSn laser developments rely on increasing the band structure directness, by increasing the Sn content in thick GeSn layers grown on germanium (Ge) virtual substrates (VS) on Si. These lasers nonetheless suffer from a lack of defect management and from high threshold densities. In this work we examine the lasing characteristics of GeSn alloys with Sn contents ranging from 7 \% to 10.5 \%. The GeSn layers were patterned into suspended microdisk cavities with different diameters in the 4-\SI{8 }{\micro\meter} range. We evidence direct band gap in GeSn with 7 \% of Sn and lasing at 2-\SI{2.3 }{\micro\meter} wavelength under optical injection with reproducible lasing thresholds around \SI{10 }{\kilo\watt\per\square\centi\meter}, lower by one order of magnitude as compared to the literature. These results were obtained after the removal of the dense array of misfit dislocations in the active region of the GeSn microdisk cavities. The results offer new perspectives for future designs of GeSn-based laser sources.
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Submitted 21 December, 2020;
originally announced December 2020.
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Ultra-low threshold cw and pulsed lasing in tensile strained GeSn alloys
Authors:
A. Elbaz,
D. Buca,
N. Von den Driesch,
K. Pantzas,
G. Patriarche,
N. Zerounian,
E. Herth,
X. Checoury,
S. Sauvage,
I. Sagnes,
A. Foti,
R. Ossikovski,
J. -M. Hartmann,
F. Boeuf,
Z. Ikonic,
P. Boucaud,
D. Grutzmacher,
M. El Kurdi
Abstract:
GeSn alloys are the most promising semiconductors for light emitters entirely based on group IV elements. Alloys containing more than 8 at.% Sn have fundamental direct band-gaps, similar to conventional III-V semiconductors and thus can be employed for light emitting devices. Here, we report on GeSn microdisk lasers encapsulated with a SiNx stressor layer to produce tensile strain. A 300nm GeSn la…
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GeSn alloys are the most promising semiconductors for light emitters entirely based on group IV elements. Alloys containing more than 8 at.% Sn have fundamental direct band-gaps, similar to conventional III-V semiconductors and thus can be employed for light emitting devices. Here, we report on GeSn microdisk lasers encapsulated with a SiNx stressor layer to produce tensile strain. A 300nm GeSn layer with 5.4 at.% Sn, which is an indirect band-gap semiconductor as-grown with a compressive strain of -0.32 %, is transformed via tensile strain engineering into a truly direct band-gap semiconductor. In this approach the low Sn concentration enables improved defect engineering and the tensile strain delivers a low density of states at the valence band edge, which is the light hole band. Continuous wave (cw) as well as pulsed lasing are observed at very low optical pump powers. Lasers with emission wavelength of 2.5 um have thresholds as low as 0.8kWcm^-2 for ns-pulsed excitation, and 1.1kWcm^-2 under cw excitation. These thresholds are more than two orders of magnitude lower than those previously reported for bulk GeSn lasers, approaching these values obtained for III-V lasers on Si. The present results demonstrate the feasabiliy and are the guideline for monolithically integrated Si-based laser sources on Si photonics platform.
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Submitted 14 January, 2020;
originally announced January 2020.
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Low power sessile droplet actuation via modulated surface acoustic waves
Authors:
Michael Baudoin,
Philippe Brunet,
Olivier Bou Matar,
Etienne Herth
Abstract:
Low power actuation of sessile droplets is of primary interest for portable or hybrid lab-on-a-chip and harmless manipulation of biofluids. In this paper, we show that the acoustic power required to move or deform droplets via surface acoustic waves can be substantially reduced through the forcing of the drops inertio-capillary modes of vibrations. Indeed, harmonic, superharmonic and subharmonic (…
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Low power actuation of sessile droplets is of primary interest for portable or hybrid lab-on-a-chip and harmless manipulation of biofluids. In this paper, we show that the acoustic power required to move or deform droplets via surface acoustic waves can be substantially reduced through the forcing of the drops inertio-capillary modes of vibrations. Indeed, harmonic, superharmonic and subharmonic (parametric) excitation of these modes are observed when the high frequency acoustic signal (19.5 MHz) is modulated around Rayleigh-Lamb inertio-capillary frequencies. This resonant behavior results in larger oscillations and quicker motion of the drops than in the non-modulated case.
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Submitted 8 March, 2012;
originally announced March 2012.