Stéphane Ginestar

Via-Hole Less Broadband Grounded Coplanar to Coupled Microstrip Transition for up to 40 GHz

A broadband via-hole less transition from a conductor-backed coplanar waveguide (CBCPW) to a parallel coupled microstrip line (CMS) via microstrip section (MS) is reported in this paper that is realized on a MCL FX-2 substrate (100 μm thick). This transition should find a wide variety of applications due to its demonstrated broadband (from 4.5 GHz up to 39.5 GHz) behavior, ease of fabrication, and low manufacturing cost. In addition, utilization of the MS section between the CBCPW and CMS sections allows putting ground electrode in a different plane than the signal electrodes. This exibility made possible by electromagnetic field coupling between the bottom and top ground planes simplifies the transition manufacturing and facilitates the characterization of optical components driven with CMS line using coplanar probes.

TiO 2 nanoparticles loading on the microwave and optical properties of the electro-optic polymer PMMA-DR1 for optimization of microwave photonic components

Thanks to a very good velocity matching between the microwave signals and optical waves in polymeric materials and progress in the synthesis of high hyperpolarizability chromophores, electro-optic (EO) polymers offer a very attractive possibility to realize low cost photonic microwave components with a very wide bandwidth and a very low driving signal. Indeed, on one hand, the EO coefficient of EO polymers achieves up to 350 pm/V [1], which is much higher than 31 pm/V, that of the popular inorganic EO crystal Lithium Niobate (LiNbO3). On the other hand, RF bandwidth of 110 GHz is demonstrated for stabile E-O polymer based optical Mach-Zehnder (MZ) modulators [2]. We study the influence of dielectric nanoparticles on the microwave and optical properties of the polymers. It consists of a fine tuning of the microwave and optical properties of the EO polymers by loading with dielectric nanoparticles, aiming at improving the bandwidth by reducing the difference between the effective refractive index and dielectric constant [3]. For our investigations, a classical polymer such as poly (methyl methacrylate) (PMMA) filled or not with disperse red 1 (DR1) EO dyes is used as host polymer. Titanium dioxide (TiO2) nanoparticles are chosen due to the transparency of TiO2 at the telecommunication wavelength of 1.55 μm [4]. The 1,1,2-trichloroethane (TCA) is the solvent used for the PMMA polymer matrix, the DR1 chromophore and the polymer-nanoparticles suspensions. The TiO2 nanoparticles are homogeneously incorporated in the EO polymer by an ultrasonic stirring. Different TiO2 nanoparticles contents ranging from 1 to 3wt.% with respect to PMMA are used. A rigorous control of the agglomeration is performed by dynamic light scattering. TEM observations and Raman spectra are used for the classification of the nanoparticles. The thin film necessary for this study is produced by spin coating from the parent solution (PMMA + DR1 + TiO2 + solvent). The first step of our investigation is to study the influence of TiO2 on the microwave dielectric properties (permittivity and loss tangent) up to 10 GHz and the refractive index at telecommunication wavelength of the PMMA as a function of the TiO2 loading. The obtained results show that both the dielectric constant and the refractive index of PMMA and PMMA-DR1 films may be continuously tuned by incorporating TiO2 nanoparticles. This results show a continuous increase of the dielectric constant in the frequency range from 100 MHz to 10 GHz with TiO2 nanoparticles loading, by 22% at 8 GHz from 1 to 3%wt TiO2 nanoparticles with respect to PMMA. Interestingly, the dielectric losses are not increased to the same extent by TiO2 filling (x% at 8 GHz). The refractive index increases with the TiO2 nanoparticles loading by less than 1%. The obtained results will be used to optimize the bandwidth of EO modulator based in polymer by using HFSS software.

Tuning of microwave and optical properties of the electro-optic polymer PMMA-DR1 by loading with SiC nanoparticles for optimization of photonic microwave components

We report on a study of the influence of the Silicon Carbide (SiC) nanoparticles on the microwave and optical properties of electro-optic (EO) polymers. EO polymers are known as much more promising than the popular inorganic EO crystal Lithium Niobate (LiNbO3). Indeed, EO polymers can have larger EO coefficients and permit broader component bandwidths due to a better velocity matching between lightwave and microwave signal. In this study, we use a classical EO polymer constituted of poly(methyl methacrylate) (PMMA) used as host polymer matrix in which Disperse Red 1 (DR1) EO dyes have been dispersed. The obtained results show that both the dielectric constant and the refractive index of PMMA-DR1 films may be continuously tuned by incorporating SiC nanoparticles. Therefore, one can increase component bandwidths by optimizing phase velocity matching between lightwave and microwave signal and improve optical mode coupling.