6 research outputs found
Enhanced optical Kerr effect method for a detailed characterization of the third order nonlinearity of 2D materials applied to graphene
Using an enhanced optically heterodyned optical Kerr effect method and a
theoretical description of the interactions between an optical beam, a single
layer of graphene, and its substrate, we provide experimental answers to
questions raised by theoretical models of graphene third-order nonlinear
optical response. In particular, we measure separately the time response of the
two main tensor components of the nonlinear susceptibility, we validate the
assumption that the out-of plane tensor components are small, and we quantify
the optical impact of the substrate on the measured coefficients. Our method
can be applied to other 2D materials, as it relies mainly on the small ratio
between the thickness and the wavelength.Comment: 7 pages, 4 figure
Electrodynamic models of 2D materials: can we match thin film and single sheet approaches?
The electromagnetic properties of 2D materials are modeled either as single
sheets with a surface susceptibility or conductivity, or as thin films of
finite thickness with an effective permittivity. Their intrinsic anisotropy,
however, has to be fully described to reliably predict the optical response of
systems based on 2D materials or to unambiguously interpret experimental data.
In the present work, we compare the two approaches within the transfer matrix
formalism and provide analytical relations between them. We strongly emphasize
the consequences of the anisotropy. In particular, we demonstrate the crucial
role of the choice of the thin film's effective thickness compared with the
parameters of the single sheet approach and therefore the computed properties
of the 2D material under study. Indeed, if the isotropic thin film model with
very low thickness is similar to an anisotropic single sheet with no
out-of-plane response, with larger thickness it matches with a single sheet
with isotropic susceptibility, in the reasonable small phase condition. We
illustrate our conclusions on extensively studied experimental quantities such
as transmittance, ellipsometry and optical contrast, and we discuss
similarities and discrepancies reported in the literature when using single
sheet or thin film models
Nonlinear optics in graphene: Detailed characterization for application in photonic circuits
In the quest for ultrathin materials compatible with CMOS technology for all-optical signal processing applications in integrated photonics, graphene appears to be a promising candidate, with broadband1 optical properties and a high and broadband optical nonlinearity. However, researchers do not agree on the value of its nonlinear refractive index, and commonly used characterization methods do not provide a clear picture of the optical nonlinearity, in terms of its tensor nature or relaxation time. In the first part of this thesis, apart from the previously used Z-scan method, we have also used the ultrafast Optical Kerr Effect method coupled to Optical Heterodyne Detection (OHD-OKE) for the characterization of the third order optical nonlinearity of monolayer CVD graphene at telecom wavelengths. This method allows to separately measure the real and the imaginary part of the third-order nonlinearity, as well as their dynamics. With respect to the Z-scan method, OHD-OKE presents the major advantage of being robust against inhomogeneities of the sample. As such, we have demonstrated that graphene has a negative nonlinear refractive index, contrary to previously reported results. In addition, we have studied the real and imaginary part of graphene’s nonlinearity, when electrostatic gating is applied to change the chemical potential of graphene. Furthermore, we have proposed an enhanced version of the OHD-OKE method, together with the appropriate theoretical framework, in order to extract the tensor elements of the nonlinearity including the out-of-plane tensor elements. In particular, we have measured separately the time response of the two main tensor elements of the nonlinear susceptibility and we have experimentally verified that the out-of-plane tensor components are negligible. In the second part of this thesis, we have investigated, from an experimental point of view, the use of the nonlinear optical response of graphene for all-optical switching applications in integrated photonics. Namely, we have designed simple silicon nitride waveguide structures that constitute basic building blocks of switching devices, which were then fabricated and covered by graphene patches. Finally, we have experimentally tested the graphene-covered structures at low and high power levels and discussed the results.Doctorat en Sciences de l'ingénieur et technologieinfo:eu-repo/semantics/nonPublishe
Characterization of nonlinear optical properties of graphene at telecommunication wavelength
info:eu-repo/semantics/publishe