Nathalie Vermeulen - Academia.edu (original) (raw)
Papers by Nathalie Vermeulen
Abstract—Numerical calculations based on finite-difference time-domain (FDTD) simulations for met... more Abstract—Numerical calculations based on finite-difference time-domain (FDTD) simulations for metallic nanostructures in a broad optical spectrum require an accurate modeling of the permittivity of dispersive materials. In this paper, we present the algorithms behind B-CALM (Belgium-CAlifornia Light Machine), an open-source 3D-FDTD solver simultaneously operating on multiple Graphical Processing Units (GPUs) and efficiently utilizing multi-pole dispersion models while hiding latency in inter-GPU memory transfers. Our architecture shows a reduction in computing times for multi-pole dispersion models and an almost linear speed-up with respect to the amount of used GPUs. We benchmark B-CALM by computing the absorption efficiency of a metallic nanosphere in a broad spectral range with a six-pole Lorentz model and compare it with Mie theory and with a widely used Central Processing Unit (CPU)-based FDTD simulator. 1.
Journal of Materials Chemistry C, 2018
The use of graphene in optical and photonic applications has gained much attention in recent years.
Scientific Reports, 2017
We present a practical scheme to separate the contributions of the electric quadrupole-like and t... more We present a practical scheme to separate the contributions of the electric quadrupole-like and the magnetic dipole-like effects to the forbidden second order optical nonlinear response of graphene, and give analytic expressions for the second order optical conductivities, calculated from the independent particle approximation, with relaxation described in a phenomenological way. We predict strong second order nonlinear effects, including second harmonic generation, photon drag, and difference frequency generation. We discuss in detail the controllability of these effects by tuning the chemical potential, taking advantage of the dominant role played by interband optical transitions in the response.
Journal of Lightwave Technology, 2016
General rights Copyright and moral rights for the publications made accessible in the public port... more General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
![Research paper thumbnail of Erratum: Third-order nonlinearity of graphene: Effects of phenomenological relaxation and finite temperature [Phys. Rev. B91, 235320 (2015)]](https://attachments.academia-assets.com/104820741/thumbnails/1.jpg)
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SPIE Proceedings, 2016
We numerically investigate the capabilities and advantages of Raman lasers based on integrated si... more We numerically investigate the capabilities and advantages of Raman lasers based on integrated single-crystal diamond ring resonators. To this end, we first model continuous-wave (CW) Raman lasing action while taking into account the lasing directionality, the linear and nonlinear losses, and the coupling of the fields between the bus and ring sections of racetrack-shaped diamond ring resonators. We then consider the design of the ring resonators for a short-wavelength infrared (SWIR) and an ultraviolet (UV) Raman laser. Using our Raman lasing model, we determine the lasing directionality, pump threshold and lasing efficiency of the SWIR and UV devices. We find that both can yield efficient CW operation with SWIR and UV lasing slope efficiencies of 33 % and 65 %, respectively. These results showcase the potential of integrated diamond ring Raman lasers for producing wavelengths that are challenging to generate with other types of integrated lasers.
Laser Physics Letters, 2011
ABSTRACT We report the first demonstration of resonant-grating-based laser wavelength tuning in t... more ABSTRACT We report the first demonstration of resonant-grating-based laser wavelength tuning in the mid-infrared spectral domain and with Littrow mounting of the grating. We show for a mid-infrared Cr:ZnSe laser that this tuning technique is much more wavelength selective than prism-based tuning, while inducing very low cavity losses (around 2%), which are at least two times smaller than in the case of a standard metal grating. Furthermore, the resonant grating allows tuning the Cr:ZnSe laser over as much as 400 nm around a center wavelength of 2.38 µm. This shows the potential of employing Littrow-mounted resonant diffraction gratings for controlling and tuning the emission wavelength of lasers emitting in the mid-infrared spectral domain and other wavelength regions. (© 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) (© 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)
APL Photonics
The first nonlinear-optical experiments with graphene date back over a decade, and a wide range o... more The first nonlinear-optical experiments with graphene date back over a decade, and a wide range of research breakthroughs has been reported since then, particularly on the third-order nonlinearities of the material. Graphene has been shown to exhibit extraordinary saturable absorption properties as well as extremely strong nonlinear refraction effects, both of which hold promise for practical use in nonlinear-optical devices. In this Perspective, after providing a very brief overview of the state of the art, I elaborate on the most relevant material parameters for future research and development activities in this domain, while also highlighting specific features of graphene's linear and nonlinear-optical properties that are sometimes overlooked in experiments. Finally, I present my view on what the opportunities and remaining challenges are in the practical exploitation of graphene for nonlinear-optical applications.
We present a generic approach to determine the phase mismatch for any optical nonlinear process. ... more We present a generic approach to determine the phase mismatch for any optical nonlinear process. When applying this approach, which is based on the evaluation of local phase changes, to Raman- and Kerr-based four-wave mixing in silicon waveguides, we obtain an expression for the phase mismatch which is more accurate as compared to the conventional definition; and which contains additional contributions due to the dispersion of the four-wave-mixing processes. Furthermore, starting from the general propagation equations for the involved pump, Stokes and anti-Stokes waves, we investigate the impact of this four-wave-mixing dispersion in silicon waveguides and examine how it is influenced by changing the frequency difference between the pump and Stokes input waves. We show by means of numerical simulations that, by detuning this frequency difference slightly away from Raman resonance, the four-wave-mixing conversion efficiency can be more than doubled, but can also lead to a decrease in...
Conference on Lasers and Electro-Optics
Graphene exhibits a strong nonlinear-optical refractive response to light pulses, but its impact ... more Graphene exhibits a strong nonlinear-optical refractive response to light pulses, but its impact on the pulses' spatiotemporal evolution is challenging to analyze and predict. We solve this issue using non-perturbative calculations and spectral broadening experiments.
Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF)
We solve the long-standing discrepancy between the theoretically predicted and experimentally obs... more We solve the long-standing discrepancy between the theoretically predicted and experimentally observed performance of nonlinear-optical refraction in graphene. Hereto we study self-phase modulation in silica-core waveguides covered with graphene.
OSA Advanced Photonics Congress (AP) 2020 (IPR, NP, NOMA, Networks, PVLED, PSC, SPPCom, SOF)
We present a closed-form expression that predicts graphene’s nonlinear-optical refractive respons... more We present a closed-form expression that predicts graphene’s nonlinear-optical refractive response induced by optical pulses. Our semianalytical approach allows maintaining the nonlinear-pulse-propagation formalism in graphene-covered waveguides.
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
Measuring the nonlinear coefficient γ of any guiding medium, regardless of the sign and magnitude... more Measuring the nonlinear coefficient γ of any guiding medium, regardless of the sign and magnitude of its group-velocity dispersion parameter β 2 , is challenging because of the lack of general solutions of the nonlinear Schrödinger equation (NLSE). Indeed, existing approaches typically need to disregard chromatic-dispersion effects to determine γ [1] . Here we propose an all-encompassing approach to measure the ratio β 2 /γ and prove our method in polarization-maintaining (PM) and single-mode (SM) fibers with positive and negative β 2 .
Laser & Photonics Reviews
Nature communications, Jan 11, 2018
Graphene is considered a record-performance nonlinear-optical material on the basis of numerous e... more Graphene is considered a record-performance nonlinear-optical material on the basis of numerous experiments. The observed strong nonlinear response ascribed to the refractive part of graphene's electronic third-order susceptibility χ cannot, however, be explained using the relatively modest χ value theoretically predicted for the 2D material. Here we solve this long-standing paradox and demonstrate that, rather than χ-based refraction, a complex phenomenon which we call saturable photoexcited-carrier refraction is at the heart of nonlinear-optical interactions in graphene such as self-phase modulation. Saturable photoexcited-carrier refraction is found to enable self-phase modulation of picosecond optical pulses with exponential-like bandwidth growth along graphene-covered waveguides. Our theory allows explanation of these extraordinary experimental results both qualitatively and quantitatively. It also supports the graphene nonlinearities measured in previous self-phase modulat...
RSC Adv., 2016
We developed a uniform, transparent and low-roughness F4-TCNQ/MEK layer to controllably dope grap... more We developed a uniform, transparent and low-roughness F4-TCNQ/MEK layer to controllably dope graphene with superior optical quality.
Physical Review Applied, 2016
We experimentally demonstrate a negative Kerr nonlinearity for quasi-undoped graphene. Hereto, we... more We experimentally demonstrate a negative Kerr nonlinearity for quasi-undoped graphene. Hereto, we introduce the method of chirped-pulse-pumped self-phase modulation and apply it to graphenecovered silicon waveguides at telecom wavelengths. The extracted Kerr-nonlinear index for graphene equals n2,gr = −10 −13 m 2 /W. Whereas the sign of n2,gr turns out to be negative in contrast to what has been assumed so far, its magnitude is in correspondence with that observed in earlier experiments. Graphene's negative Kerr nonlinearity strongly impacts how graphene should be exploited for enhancing the nonlinear response of photonic (integrated) devices exhibiting a positive nonlinearity. It also opens up the possibility of using graphene to annihilate unwanted nonlinear effects in such devices, to develop unexplored approaches for establishing Kerr processes, and to extend the scope of the "periodic poling" method often used for second-order nonlinearities towards third-order Kerr processes. Because of the generic nature of the chirped-pulse-pumped self-phase modulation method, it will allow fully characterizing the Kerr nonlinearity of essentially any novel (2D) material.
Photonics and Fiber Technology 2016 (ACOFT, BGPP, NP), 2016
We present a novel theoretical framework where dispersive wave emission in normal and anomalous d... more We present a novel theoretical framework where dispersive wave emission in normal and anomalous dispersion is interpreted based on four-wave mixing processes. It is a powerful tool for designing supercontinuum sources along analytical guidelines.
Silicon Photonics and Photonic Integrated Circuits V, 2016
We present the use of femtosecond laser ablation for the removal of monolayer graphene from silic... more We present the use of femtosecond laser ablation for the removal of monolayer graphene from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphenecovered SOI waveguides using the cutback method. This loss contribution is measured to be 0.132 dB/µm.
Abstract—Numerical calculations based on finite-difference time-domain (FDTD) simulations for met... more Abstract—Numerical calculations based on finite-difference time-domain (FDTD) simulations for metallic nanostructures in a broad optical spectrum require an accurate modeling of the permittivity of dispersive materials. In this paper, we present the algorithms behind B-CALM (Belgium-CAlifornia Light Machine), an open-source 3D-FDTD solver simultaneously operating on multiple Graphical Processing Units (GPUs) and efficiently utilizing multi-pole dispersion models while hiding latency in inter-GPU memory transfers. Our architecture shows a reduction in computing times for multi-pole dispersion models and an almost linear speed-up with respect to the amount of used GPUs. We benchmark B-CALM by computing the absorption efficiency of a metallic nanosphere in a broad spectral range with a six-pole Lorentz model and compare it with Mie theory and with a widely used Central Processing Unit (CPU)-based FDTD simulator. 1.
Journal of Materials Chemistry C, 2018
The use of graphene in optical and photonic applications has gained much attention in recent years.
Scientific Reports, 2017
We present a practical scheme to separate the contributions of the electric quadrupole-like and t... more We present a practical scheme to separate the contributions of the electric quadrupole-like and the magnetic dipole-like effects to the forbidden second order optical nonlinear response of graphene, and give analytic expressions for the second order optical conductivities, calculated from the independent particle approximation, with relaxation described in a phenomenological way. We predict strong second order nonlinear effects, including second harmonic generation, photon drag, and difference frequency generation. We discuss in detail the controllability of these effects by tuning the chemical potential, taking advantage of the dominant role played by interband optical transitions in the response.
Journal of Lightwave Technology, 2016
General rights Copyright and moral rights for the publications made accessible in the public port... more General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.
SPIE Proceedings, 2016
We numerically investigate the capabilities and advantages of Raman lasers based on integrated si... more We numerically investigate the capabilities and advantages of Raman lasers based on integrated single-crystal diamond ring resonators. To this end, we first model continuous-wave (CW) Raman lasing action while taking into account the lasing directionality, the linear and nonlinear losses, and the coupling of the fields between the bus and ring sections of racetrack-shaped diamond ring resonators. We then consider the design of the ring resonators for a short-wavelength infrared (SWIR) and an ultraviolet (UV) Raman laser. Using our Raman lasing model, we determine the lasing directionality, pump threshold and lasing efficiency of the SWIR and UV devices. We find that both can yield efficient CW operation with SWIR and UV lasing slope efficiencies of 33 % and 65 %, respectively. These results showcase the potential of integrated diamond ring Raman lasers for producing wavelengths that are challenging to generate with other types of integrated lasers.
Laser Physics Letters, 2011
ABSTRACT We report the first demonstration of resonant-grating-based laser wavelength tuning in t... more ABSTRACT We report the first demonstration of resonant-grating-based laser wavelength tuning in the mid-infrared spectral domain and with Littrow mounting of the grating. We show for a mid-infrared Cr:ZnSe laser that this tuning technique is much more wavelength selective than prism-based tuning, while inducing very low cavity losses (around 2%), which are at least two times smaller than in the case of a standard metal grating. Furthermore, the resonant grating allows tuning the Cr:ZnSe laser over as much as 400 nm around a center wavelength of 2.38 µm. This shows the potential of employing Littrow-mounted resonant diffraction gratings for controlling and tuning the emission wavelength of lasers emitting in the mid-infrared spectral domain and other wavelength regions. (© 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) (© 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)
APL Photonics
The first nonlinear-optical experiments with graphene date back over a decade, and a wide range o... more The first nonlinear-optical experiments with graphene date back over a decade, and a wide range of research breakthroughs has been reported since then, particularly on the third-order nonlinearities of the material. Graphene has been shown to exhibit extraordinary saturable absorption properties as well as extremely strong nonlinear refraction effects, both of which hold promise for practical use in nonlinear-optical devices. In this Perspective, after providing a very brief overview of the state of the art, I elaborate on the most relevant material parameters for future research and development activities in this domain, while also highlighting specific features of graphene's linear and nonlinear-optical properties that are sometimes overlooked in experiments. Finally, I present my view on what the opportunities and remaining challenges are in the practical exploitation of graphene for nonlinear-optical applications.
We present a generic approach to determine the phase mismatch for any optical nonlinear process. ... more We present a generic approach to determine the phase mismatch for any optical nonlinear process. When applying this approach, which is based on the evaluation of local phase changes, to Raman- and Kerr-based four-wave mixing in silicon waveguides, we obtain an expression for the phase mismatch which is more accurate as compared to the conventional definition; and which contains additional contributions due to the dispersion of the four-wave-mixing processes. Furthermore, starting from the general propagation equations for the involved pump, Stokes and anti-Stokes waves, we investigate the impact of this four-wave-mixing dispersion in silicon waveguides and examine how it is influenced by changing the frequency difference between the pump and Stokes input waves. We show by means of numerical simulations that, by detuning this frequency difference slightly away from Raman resonance, the four-wave-mixing conversion efficiency can be more than doubled, but can also lead to a decrease in...
Conference on Lasers and Electro-Optics
Graphene exhibits a strong nonlinear-optical refractive response to light pulses, but its impact ... more Graphene exhibits a strong nonlinear-optical refractive response to light pulses, but its impact on the pulses' spatiotemporal evolution is challenging to analyze and predict. We solve this issue using non-perturbative calculations and spectral broadening experiments.
Advanced Photonics 2018 (BGPP, IPR, NP, NOMA, Sensors, Networks, SPPCom, SOF)
We solve the long-standing discrepancy between the theoretically predicted and experimentally obs... more We solve the long-standing discrepancy between the theoretically predicted and experimentally observed performance of nonlinear-optical refraction in graphene. Hereto we study self-phase modulation in silica-core waveguides covered with graphene.
OSA Advanced Photonics Congress (AP) 2020 (IPR, NP, NOMA, Networks, PVLED, PSC, SPPCom, SOF)
We present a closed-form expression that predicts graphene’s nonlinear-optical refractive respons... more We present a closed-form expression that predicts graphene’s nonlinear-optical refractive response induced by optical pulses. Our semianalytical approach allows maintaining the nonlinear-pulse-propagation formalism in graphene-covered waveguides.
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
Measuring the nonlinear coefficient γ of any guiding medium, regardless of the sign and magnitude... more Measuring the nonlinear coefficient γ of any guiding medium, regardless of the sign and magnitude of its group-velocity dispersion parameter β 2 , is challenging because of the lack of general solutions of the nonlinear Schrödinger equation (NLSE). Indeed, existing approaches typically need to disregard chromatic-dispersion effects to determine γ [1] . Here we propose an all-encompassing approach to measure the ratio β 2 /γ and prove our method in polarization-maintaining (PM) and single-mode (SM) fibers with positive and negative β 2 .
Laser & Photonics Reviews
Nature communications, Jan 11, 2018
Graphene is considered a record-performance nonlinear-optical material on the basis of numerous e... more Graphene is considered a record-performance nonlinear-optical material on the basis of numerous experiments. The observed strong nonlinear response ascribed to the refractive part of graphene's electronic third-order susceptibility χ cannot, however, be explained using the relatively modest χ value theoretically predicted for the 2D material. Here we solve this long-standing paradox and demonstrate that, rather than χ-based refraction, a complex phenomenon which we call saturable photoexcited-carrier refraction is at the heart of nonlinear-optical interactions in graphene such as self-phase modulation. Saturable photoexcited-carrier refraction is found to enable self-phase modulation of picosecond optical pulses with exponential-like bandwidth growth along graphene-covered waveguides. Our theory allows explanation of these extraordinary experimental results both qualitatively and quantitatively. It also supports the graphene nonlinearities measured in previous self-phase modulat...
RSC Adv., 2016
We developed a uniform, transparent and low-roughness F4-TCNQ/MEK layer to controllably dope grap... more We developed a uniform, transparent and low-roughness F4-TCNQ/MEK layer to controllably dope graphene with superior optical quality.
Physical Review Applied, 2016
We experimentally demonstrate a negative Kerr nonlinearity for quasi-undoped graphene. Hereto, we... more We experimentally demonstrate a negative Kerr nonlinearity for quasi-undoped graphene. Hereto, we introduce the method of chirped-pulse-pumped self-phase modulation and apply it to graphenecovered silicon waveguides at telecom wavelengths. The extracted Kerr-nonlinear index for graphene equals n2,gr = −10 −13 m 2 /W. Whereas the sign of n2,gr turns out to be negative in contrast to what has been assumed so far, its magnitude is in correspondence with that observed in earlier experiments. Graphene's negative Kerr nonlinearity strongly impacts how graphene should be exploited for enhancing the nonlinear response of photonic (integrated) devices exhibiting a positive nonlinearity. It also opens up the possibility of using graphene to annihilate unwanted nonlinear effects in such devices, to develop unexplored approaches for establishing Kerr processes, and to extend the scope of the "periodic poling" method often used for second-order nonlinearities towards third-order Kerr processes. Because of the generic nature of the chirped-pulse-pumped self-phase modulation method, it will allow fully characterizing the Kerr nonlinearity of essentially any novel (2D) material.
Photonics and Fiber Technology 2016 (ACOFT, BGPP, NP), 2016
We present a novel theoretical framework where dispersive wave emission in normal and anomalous d... more We present a novel theoretical framework where dispersive wave emission in normal and anomalous dispersion is interpreted based on four-wave mixing processes. It is a powerful tool for designing supercontinuum sources along analytical guidelines.
Silicon Photonics and Photonic Integrated Circuits V, 2016
We present the use of femtosecond laser ablation for the removal of monolayer graphene from silic... more We present the use of femtosecond laser ablation for the removal of monolayer graphene from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphenecovered SOI waveguides using the cutback method. This loss contribution is measured to be 0.132 dB/µm.