Alain Dereux

We demonstrate a CMOS compatible interferometric plasmo-photonic sensor exploiting SisN4 photonic and aluminum (Al) plasmonic stripe waveguides. Experimental evaluation revealed bulk sensitivity of 4764 nm/RIU, holding promise for ultra-sensitive and low cost sensing devices.

Integration of plasmonic waveguides with low-loss photonic platforms have attracted research efforts as the means to benefit from the extra-ordinary features of plasmonics while enhancing the functional portfolio of Photonic Integrated Circuits (PICs). In this work, we review a technology platform that integrates water cladded plasmonic waveguides integrated in a low-loss Si 3 N 4 photonic platform, targeting biosensing applications. Results obtained experimentally and numerically will be presented with respect to propagation losses, interface coupling loss and accumulated phase change per unit length, showing how Surface Plasmon Polariton (SPP) waveguides can be effectively combined with photonic components in order to demonstrate low-cost and ultra-sensitive optical biosensors.

Plasmonics have been identified as an ideal platform for ultra-sensitive, label-free biosensors mainly due to the high field confinement on a metal-dielectric interface and the resulting strong light-matter interaction offered by surface plasmon resonances (SPRs) that can be entirely exposed to test analytes. Well-established SPR-based biosensors exploiting propagating SPRs yield superior specifications regarding bulk sensitivity compared to localized counterparts leading to already commercial available sensor devices. However, most of these systems require bulky prism-based configurations to couple light into the Surface Plasmon Polariton (SPP) mode impeding system miniaturization. In addition, SPR-based sensors suffer from intrinsic high propagation losses restricting the potential for multiple on-chip functionalities. In this context, co-integration of plasmonics with a low-loss photonic platform emerges as a viable solution towards highly sensitive, low-loss and small footprint optical sensors. In this work, we present an ultra-compact, interferometric plasmonic sensor co-integrated on a TiO₂ photonic waveguide platform. The device consists of two access TiO₂ photonic waveguides separated by a gold-based metal stripe which is located on top of an appropriately shorter TiO₂ waveguide layer. Two metal/insulator interfaces are formed at the top (sensing arm) and bottom surfaces (reference arm) of the metal able to support SPP modes which upon excitation through the input photonic waveguide propagate along the two metal surfaces and interfere at the output waveguide realizing a single-arm Mach-Zehnder Interferometer. After optimization of the device in aqueous environment, we achieved sensitivity values as high as 2430 nm/RIU at near-infrared spectrum region for a 65 um long plasmonic stripe.

We report the design and fabrication of titanium dioxide optical waveguides optimized for supercontinuum generation in the mid-infrared. A spectrum spanning from the visible up to 2 µm is experimentally demonstrated.

We demonstrate wavelength-division-multiplexed (WDM) 200 Gb/s (8 × 25 Gb/s) data transmission over 100 μm long aluminum (Al) surface-plasmon-polariton (SPP) waveguides on a Si₃N₄ waveguide platform at telecom wavelengths. The Al SPP waveguide was evaluated in terms of signal integrity by performing bit-error-rate (BER) measurements that revealed error-free operation for all eight 25 Gb/s non-return-to-zero (NRZ) modulated data channels with power penalties not exceeding 0.2 dB at 10⁻⁹. To the best of our knowledge, this is the first demonstration of WDM enabled data transmission over complementary-metal-oxide-semiconductor (CMOS) SPP waveguides fueling future development of CMOS compatible plasmo-photonic devices for on-chip optical interconnections.

Damping distances of surface plasmon polariton modes sustained by different thin titanium nitride (TiN) films are measured at the telecom wavelength of 1.55 μm. The damping distances are correlated to the electrical direct current resistivity of the films sustaining the surface plasmon modes. It is found that TiN/Air surface plasmon mode damping distances drop non-linearly from 40 to 16μm as the resistivity of the layers increases from 28 to 130μΩ.cm, respectively. The relevance of the direct current (dc) electrical resistivity for the characterization of TiN plasmonic properties is investigated in the framework of the Drude model, on the basis of parameters extracted from spectroscopic ellipsometry experiments. By probing a parametric space of realistic values for parameters of the Drude model, we obtain a nearly univocal dependence of the surface plasmon damping distance on the dc resistivity demonstrating the relevance of dc resistivity for the evaluation of the plasmonic performances of TiN at telecom frequencies. Finally, we show that better plasmonic performances are obtained for TiN films featuring a low content of oxygen. For low oxygen content and corresponding low resistivity, we attribute the increase of the surface plasmon damping distances to a lower confinement of the plasmon field into the metal and not to a decrease of the absorption of TiN.

We report on the experimental generation of an octave-spanning supercontinuum in a 2.2 cm-long titanium dioxide optical waveguide with two zero dispersion wavelengths. The resulting on-chip supercontinuum reaches the visible wavelength range as well as the mid-infrared region by using a femtosecond fiber laser pump at 1.64 µm.

We present the design, fabrication and characterization of long-range surface plasmon polariton waveguide arrays with materials, mainly silicones, carefully selected with the aim to be used as mechanically flexible single-mode optical interconnections, the so-called “plasmonic arc” working at 1.55µm. The fabricated plasmonic arcs show a TM/TE polarization ratio of ~25 dB. By using the cut-back method, the straight propagation loss at 1.55µm is estimated to 0.5-1 dB/mm and coupling loss to ~1-2 dB/facet after dicing. In the free-standing S-curved configuration, the bending loss of single cladding plasmonic arc is 2.2-2.8 dB/90° at bending radius 2.5 mm. For double cladding plasmonic arcs, it is decreased to 0.7-1.7 dB/90° for the same radius. The coupling loss with single-mode glass PCB waveguides is estimated to be 1.7 dB/interface in the best condition.

We demonstrate the design, fabrication and the experimental characterization of gold-based plasmonic stripes butt-coupled with Low-Pressure-Chemical-Vapor-Deposition (LPCVD)-based Si$_3$N$_4$waveguides for the excitation of Surface-Plasmon-Polariton (SPP) modes in aqueous environment. Plasmonic gold stripes, in aqueous environment, with cross-sectional dimensions of 100nm$\times$7μm were interfaced with 360nm$\times$800nm Si$_3$N$_4$ waveguides cladded with Low-Temperature-Oxide (LTO), exploiting linear photonic tapers with appropriate vertical (VO) and longitudinal (LO) offsets between the plasmonic and photonic waveguide facets. An interface insertion loss of 2.3$\pm$0.3dB and a plasmonic propagation length (L$_spp$) of 75μm have been experimentally measured at 1.55μm for a VO of 400nm and a LO of 500nm, with simulation results suggesting high tolerance to VO and LO misalignment errors. The proposed integration approach enables seamless co-integration of plasmonic stripes, in aqueous environment, with a low-loss and low-cost LPCVD-based Si$_3$N$_4$ waveguide platform, revealing its strong potential for future employment in biochemical sensing applications.