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# Dual-Comb generation in III-V semiconductor external cavity laser: Dual transverse modes versus degenerated cavities solutions

Mohamed Nadrani, Baptiste Chomet, Adrian Bartolo, Nathan Vigne, Luc Le Gratiet, Grégoire Beaudoin, Konstatinos Pantzas, Isabelle Sagnes, F.

Gonzalez-Posada, Stéphane Blin, et al.

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Mohamed Nadrani, Baptiste Chomet, Adrian Bartolo, Nathan Vigne, Luc Le Gratiet, et al. Dual-Comb generation in III-V semiconductor external cavity laser: Dual transverse modes versus degenerated cavities solutions. Journées Nationales d'Optique Guidée (JNOG 2025), Société Française d'Optique, Jul 2025, Sète, France. hal-05165553

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Submitted on 16 Jul 2025

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Distributed under a Creative Commons Attribution 4.0 International License
Dual-Comb generation in III-V semiconductor external cavity laser:
Dual transverse modes versus degenerated cavities solutions

Mohamed NADRANI¹, Baptiste CHOMET ¹,², Adrián BARTOLO ¹,³, Nathan VIGNE ¹,
Luc LE GRATIET ⁴, Grégoire BEAUDOIN ⁴, Konstatinos PANTZAS ⁴, Isabelle SAGNES ⁴,
Fernando GONZALEZ-POSADA ¹, Stéphane BLIN ¹, Arnaud GARNACHE ¹

¹ Institut d'Electronique et des Systèmes, Université de Montpellier, CNRS UMR 5214, 34090, Montpellier, France

² Laboratoire de Physique de l'Ecole normale supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, Paris, France

³ LP2N, Institut d'Optique Graduate School, CNRS, Université de Bordeaux, 33400 Talence, France

⁴ Centre de Nanosciences et de Nanotechnologies, Université Paris-Saclay, CNRS UMR 9001, 91120 Palaiseau, France

Mohamed.nadrani@umontpellier.fr

RÉSUMÉ

We developed two passively mode-locked dual frequency-combs configurations based on III-V semiconductor VECSEL technology. Operating at a wavelength of 1.06µm, both configurations achieve 1GHz repetition rate with ultrashort pulse durations <5ps. The first configuration is a dual Laguerre-Gaussian (LG) mode oscillator, designed to generate two distinct frequency combs on a single optical axis. The second configuration is a modeless self-imaging cavity, featuring two distinct optical axes in a telecentric configuration to enable coherent dual-comb operation.

KEYWORDS: VECSEL; semiconductor; dual-comb; passively mode-locking;

# 1. INTRODUCTION

Dual frequency-combs have become indispensable tools in various applications, including high-resolution spectroscopy [1], precision astronomical observations [2], and advanced optical metrology [3]. Several methods for generating dual-combs have been explored, such as polarization multiplexing [4] and wavelength or spatial multiplexing [5], [6]. Despite significant progress, there remains a strong demand for compact, efficient systems capable of operating at room temperature while offering versatile configurations tailored to specific applications.

In this work, we developed two distinct dual-comb configurations leveraging III-V semi-
conductor Vertical External-Cavity Surface-Emitting Laser (VECSEL) technology [7], [8].
The first configuration co-locates spatially the two combs using a dual Laguerre-Gauss (LG)
mode oscillator, optimized for terahertz (THz) comb generation via photomixing. The second
configuration separates spatially the two combs in a modeless self-imaging cavity configu-
ration with two optical axesthanks to telecentric design, making it well-suited for applications
in data communication channels.
## 2. DUAL-COMB GENERATION

We demonstrated two passively mode-locked dual-comb configurations in a single VECSEL using a InGaAs/GaAs based optically-pumped gain mirror (1/2-VCSEL) and a fast Semiconductor Saturable Absorber Mirror (SESAM) for an emission at 1.06µm with a pulse duration <5ps at 1GHz repetition rate. Fig. 1 a) shows the cavity design where two lenses are used to control the beam ratio on the gain mirror and the SESAM for a stable mode-locking state, $f_{1,2}$ and $d_{1,2,3}$ are chosen in order to get a stable Laguerre-Gauss (LG) transverse modes oscillations with one optical axis and two transverse states as shown in Fig. 1 b) (up), or a modeless self-imaging cavity with two optical axes as shown in Fig. 1 b) (down). Fig. 1 c) shows the temporal evolution of the dual-comb where the LG₀₀ comb's repetition rate is $f_{rep}=1/T$, and the LG₀₃ comb's one is $f_{rep}+\Delta f$ where T is the roundtrip time of 1ns and $\Delta f \approx 100$kHz.

<figure><img src="image_3.png" /><figcaption>Fig. 1 a) The cavity design consisting of InGaAs/GaAs gain mirror and SESAM structures and two intracavity lenses. b) 2D near-field intensity profile showing the coexistence of the two transverse LG modes (up) and two spatially-localised structures (down). c) 2D map showing the optical intensity in colors during a roundtrip ($T = 1$ns) for $2.25 \times 10^4$ roundtrips.</figcaption></figure>

## 3. CONCLUSION

We will present temporal, optical and radio-frequency characterization of the two configurations that could address different applications such as coherent THz-comb generation at room temperature via photomixing for the dual transverse mode configuration, or multiplexing and data communications for spatially-localized structures since the two spatiotemporal structures are reconfigurable [9].

## 4. SUPPORT

This work was supported in part by Région Occitanie/ Pyrénées-Méditerranée (EMERGENCE program N° 268104 and HERMES platform) and in part by the European Regional Development Fund (FEDER). This work was also supported by ANR under the "Investment for the Future" programs (MUSE STAE ANR-16-IDEX-0006), the SPATIOTERA program (ANR-19-CE24), PICOTE program (ANR-23-CE24-0023-02), KOGIT program (ANR-22-CE92-0009). This work benefits from a France 2030 government grant managed by the ANR (ANR-22-PEEL-0008).
REFERENCES

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