# Dual femtosecond pumping supercontinuum generation in a highly doped silica glass integrated waveguide

Charbel Khallouf, Lynn Sader, Brent. E. Little, Sai T. Chu, David J. Moss, Roberto Morandotti, J.M. Dudley, Benjamin Wetzel, Thibaut Sylvestre

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Charbel Khallouf, Lynn Sader, Brent. E. Little, Sai T. Chu, David J. Moss, et al., Dual femtosecond pumping supercontinuum generation in a highly doped silica glass integrated waveguide. GDR ELIOS Annual Meeting, Sep 2024, Bordeaux, France. hal-05250394

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Submitted on 29 Sep 2025

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# Dual femtosecond pumping supercontinuum generation in a highly doped silica glass integrated waveguide

C. Khallouf<fnref n="1" />, L. Sader<fnref n="2" />, B. Little<fnref n="3" />, S. T. Chu<fnref n="4" />, D. J. Moss<fnref n="5" />, R. Morandotti<fnref n="6" />, J. M. Dudley<fnref n="1" />, B. Wetzel<fnref n="2" />, and T. Sylvestre<fnref n="1" />

Due to their unique combination of high brightness, multi-octave bandwidth, and fiber delivery, supercontinuum (SC) sources have revolutionized many applications, including optical coherence tomography (OCT), fluorescence imaging, optical sensing, absorption spectroscopy, and optical frequency comb metrology [1]. While SC light has been extensively researched and developed in optical fibers for over three decades, achieving record bandwidths spanning the ultraviolet (UV) to mid-infrared (MIR) wavelength ranges, current efforts have shifted towards developing compact, low-threshold SC sources based on photonic integrated circuits (PICs) [2,3].

We report in this work the first on-chip dual femtosecond pumping SC generation experiment using a highly doped silica glass integrated waveguide from QXP technologies Inc. [3]. The experimental setup is shown in Fig. 1 (a), and the waveguide's output spectra for both pump wavelength at 1040 nm and 1550 nm are plotted as a function of time delays in Figs. (b) and (c), respectively. Key findings include the observation of cross-phase modulation (XPM)-induced frequency shifts contingent on time delays between femtosecond pulses at 1040 nm and 1550 nm, respectively [4]. Significant SC bandwidth enhancement and sideband generation were noted around 705 nm at zero delays (See Figs. 1b and c). The influence of polarization on SC and XPM-induced frequency shifts was pronounced, highlighting its critical role in the process. Additionally, we will present real-time dispersive Fourier transform (DFT) spectra showing a strong instability due to XPM, with a notable increase in high spectral relative intensity noise (RIN) at zero delay. These findings underscore the potential of integrated waveguides in advanced photonic applications.

<figure><img src="image_2.png" /></figure>

Figure 1: Scheme of dual wavelength femtosecond pumping experiment in a 50-cm long high index doped silica integrated waveguide. (b) and (c) show the waveguide output optical spectra of the first and second pumps at 1040 nm and 1550 nm, respectively, for different time delays. The XPM-induced wavelength shift and sideband generation at 705 nm are clearly observable near zero delay for both pumping wavelengths.

## References

[1] T. Sylvestre, E. Genier, A. N. Ghosh, P. Bowen, G. Genty, J. Troles, A. Mussot, A.C. Peacock, M. Klimczak, A.M. Heidt, et al., "Recent advances in supercontinuum generation in specialty optical fibers," JOSA.B 38(12), F90-F103 (2021).

[2] C.-S. Brès, A. D. Torre, D. Grassani, V. Brasch, C. Grillet, and C. Monat, "Supercontinuum in integrated photonics: generation, applications, challenges, and perspectives," Nanophotonics 12(7), 1199-1244 (2023).

[3] D. J. Moss, R. Morandotti, A. Gaeta, M. Lipson, "New CMOS-compatible platforms based on silicon nitride and hydex for nonlinear optics," Nature Photonics 7, 597-607 (07 2013).

[4] T. Schreiber, T. V. Andersen, D. Schimpf, J. Limpert, and A. Tünnermann, "Supercontinuum generation by femtosecond single and dual wavelength pumping in photonic crystal fibers with two zero dispersion wavelengths," Opt. Express 13, 9556-9569 (2005).

<footnote n="1">¹Institut FEMTO-ST, CNRS UMR 6174, Université de Franche-Comté, Besançon, France</footnote>

<footnote n="2">²XLIM Research Institute, CNRS UMR 7252, Université de Limoges, Limoges, France</footnote>

<footnote n="3">³QXP Technologies Inc., Xi’an, China</footnote>

<footnote n="4">⁴Department of Physics, City University of Hong Kong, Hong Kong, China</footnote>

<footnote n="5">⁵Optical Sciences Centre, Swinburne University of Technology, Hawthorn, Victoria, Australia</footnote>

<footnote n="6">⁶INRS-EMT, 1650 Boulevard Lionel-Boulet, Varennes, J3X 1S2, Québec, Canada</footnote>

<footnote>Email: thibaut.sylvestre@univ-fcomte.fr; Benjamin.wetzel@unilim.fr</footnote>