Integration of electronics and photonics for future applications requires an efficient conversion of electrical to optical signals. The excellent electronic and photonic properties of graphene make it a suitable material for integrated systems with extremely wide operational bandwidth. In this paper, we analyze the novel geometry of modulator based on the rib photonic waveguide configuration with a double-layer graphene placed between a slab and ridge. The theoretical analysis of graphene-based electro-absorption modulator was performed showing that a 3 dB modulation with ~ 600 nm-long waveguide is possible resulting in energy per bit below 1 fJ/bit. The optical bandwidth of such modulators exceeds 12 THz with an operation speed ranging from 160 GHz to 850 GHz and limited only by graphene resistance. The performances of modulators were evaluated based on the figure of merit defined as the ratio between extinction ratio and insertion losses where it was found to exceed 220.

We report preliminary results on the development of compact (length < 100 microm) fiber-coupled dielectric-loaded plasmonic waveguide components, including Mach-Zehnder interferometers (MZIs), waveguide-ring resonators (WRRs) and directional couplers (DCs), whose operation at telecom wavelengths is controlled via the thermo-optic effect by electrically heating the gold stripes of dielectric-loaded plasmonic waveguides. Strong output modulation (> 20%) is demonstrated with MZI- and WRR-based components, and efficient (approximately 30%) rerouting is achieved with DC switches.

Silicon based nonlinear photonics has been extensively researched at telecom wavelengths in recent years. However, studies of Kerr nonlinearity in silicon at mid-infrared wavelengths still remain limited. Here, we report the wavelength dependency of third-order nonlinearity in the spectral range from 1.6 μm to 6 μm, as well as multi-photon absorption coefficients in the same range. The third-order nonlinear coefficient n2 was measured with a peak value of 1.65 × 10(−13) cm2/W at a wavelength of 2.1 μm followed by the decay of nonlinear refractive index n2 up to 2.6 μm. Our latest measurements extend the wavelength towards 6 μm, which show a sharp decrement of n2 beyond 2.1 μm and steadily retains above 3 μm. In addition, the analysis of three-photon absorption and four-photon absorption processes are simultaneously performed over the wavelength range from 2.3 μm to 4.4 μm. Furthermore, the effect of multi-photon absorption on nonlinear figure of merit in silicon is discussed in detail.

A waveguiding configuration for surface plasmon polaritons (SPPs) featuring simultaneously a tight mode confinement and long propagation (several millimeters) at telecom wavelengths is proposed and analyzed using the finite-element method. The configuration represents a long-range dielectric-loaded SPP waveguide (LR-DLSPPW), in which a thin and narrow metal stripe is sandwiched between a square dielectric ridge and a dielectric film supported by a low-index substrate. Considering optical polymers, for example, we calculated that a 15-nm-thick and 500-nm-wide gold stripe placed on a 460 nm thick medium-index (1.49) layer supported by a low-index (1.34) substrate and topped by a 850 × 850 nm(2) high-index (1.535) ridge supports a fundamental LR-DLSPPW mode having width of 1.6 μm and propagating over 3.1 mm at the wavelength λ = 1.55 μm. The proposed configuration allows for easy connection to electrodes enabling, e.g., thermo- or electro-optic control, and is technologically simple being compatible with planar fabrication using UV-lithography.

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Here we propose an original waveguide-integrated plasmonic Schottky photodetector that takes full advantage of a thin metal stripe embedded entirely into a semiconductor. The photodetector is based on the long-range dielectric-loaded surface plasmon polariton waveguide with a metal stripe deposited on top of a semiconductor rib and covered by another semiconductor. As the metal stripe is entirely surrounded by semiconductor, all hot electrons with appropriate k-vectors can participate in transitions that highly enhances the electron transfer, and consequently the internal quantum efficiency. In addition, a high coupling efficiency from the photonic waveguide to the photodetector is simulated exceeding 90 % which enhances the external quantum efficiency. Calculations show that a responsivity exceeding 0.5 A / W can be achieved at telecom wavelength of 1550 nm and the bandwidth can exceed 100 GHz . Furthermore, it is shown that titanium nitride is a perfect material for the photodetector as it provides a low Fermi energy and long electron mean free path that enhance the hot electron transfer to the semiconductor. In addition, it shows reasonable metallic behavior and CMOS compatibility. Measurements showed that the Schottky barrier height between titanium nitride and p-doped silicon reaches 0.69–0.70 eV that matches the optimum signal-to-noise ratio operation calculated at 0.697 eV .

Theoretical investigations of graphene-based electro-optic plasmonic modulators with a dielectric ridge were analyzed and the results were presented. The effects of different ridge materials and different spacer dielectric functions were analyzed, showing that a 3 dB modulation with a 65 nm-long waveguide is possible with dielectric-loaded surface plasmon polariton waveguides (DLSPPWs), resulting in an energy per bit only 0.08 fJ/bit. The figure of merit, defined as the ratio between the extinction ratio and the insertion loss, was found to be about 5.2 with a low refractive index ridge and increased to over 17.3 for a high refractive index Si ridge, compared to 3.5 calculated and measured with photonic graphene-based waveguides. Additionally, it was shown that further improvement in terms of the figure of merit is possible with long-range dielectric-loaded surface plasmon polariton waveguides (LR-DLSPPWs), where it was calculated to exceed 72. For such waveguides, a 3 dB modulation was achieved with 10 μm-long waveguides with an energy per bit of 15.8 fJ/bit. The wavelength dependence of the graphene conductivity and, consequently, the attenuation of the waveguide were analyzed for different chemical potentials. It was shown that gate voltage applied across the graphene layers shifts the attenuation curve to shorter wavelengths, with the 3 dB modulation bandwidth exceeding 15 THz for a 12 μm-long DLSPP waveguide.

Theoretical analysis of thermo-optic (TO) modulation with dielectric-loaded surface plasmon polariton waveguide (DLSPPW) components at telecom wavelength of 1.55 μm is presented with simulations performed using the finite-element method (FEM). The investigated DLSPPW configuration consists of a 1 μm-thick and 1 μm-wide polymer ridge placed on a 50 nm-thin gold stripe and supported by a buffer layer material covering a Si wafer. Our analysis covers a broad range of parameters, including the buffer layer thickness, its thermal conductivity, and the metal stripe width, and takes into account the effect of isolation trenches structured along the heated part of waveguide. The results of our simulations agree well with the reported experimental data and provide valuable information for further development of TO plasmonic components with low switching powers, fast responses and small footprints.