Alexandros Pitilakis

Thermo-optic plasmo-photonic mode interference switches based on dielectric loaded waveguides

We demonstrate an efficient thermo-optic dielectric loaded surface plasmon polariton waveguide (DLSPPW) 2 × 2 switch using a high thermo-optic coefficient polymer and a dual mode interference configuration. Unlike previous configurations relying on single-mode waveguide circuitry, the switch we consider is based on the interference between a plasmonic and a low-damping photonic mode of the DLSPPW, thus leading to the minimization of insertion losses of the device. Switching extinction ratios of 7 dB are measured for a compact 119 μm-long device. The overall device performances are in good agreement with numerical simulations performed using the beam propagation method.

A 320 Gb/s-Throughput Capable 2

We demonstrate a 2 × 2 silicon-plasmonic router architecture with 320 Gb/s throughput capabilities for optical interconnect applications. The proposed router platform relies on a novel dual-ring Dielectric-Loaded Surface Plasmon Polariton (DLSPP) 2 × 2 switch heterointegrated on a Silicon-on-Insulator (SOI) photonic motherboard that is responsible for traffic multiplexing and header processing functionalities. We present experimental results of a Poly-methyl-methacrylate (PMMA)-loaded dual-resonator DLSPP waveguide structure that uses two racetrack resonators of 5.5 μm radius and 4 μ m-long straight sections and operates as a passive add/drop filtering element. We derive its frequency-domain transfer function, confirm its add/drop experimental spectral response, and proceed to a circuit-level model for dual-ring DLSPP designs supporting 2 × 2 thermo-optic switch operation. The validity of our circuit-level modeled 2 × 2 thermo-optic switch is verified by means of respective full vectorial three-dimensional Finite Element Method (3D-FEM) simulations. The router setup is completed by means of two 4 × 1 SOI multiplexing circuits, each one employing four cascaded second order micro-ring configurations with 100 GHz spaced resonances. Successful interconnection between the DLSPP switching matrix and the SOI circuitry is performed through a butt-coupling design that, as shown via 3D-FEM analysis, allows for small coupling losses of as low as 2.6 dB. The final router architecture is evaluated through a co-operative simulation environment, demonstrating successful 2 × 2 routing for two incoming 4-wavelength Non-Return-to-Zero (NRZ) optical packet streams with 40 Gb/s line-rates.

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A comprehensive theoretical analysis of end-fire coupling between dielectric-loaded surface plasmon polariton and rib/wire silicon-on-insulator (SOI) waveguides is presented. Simulations are based on the 3-D vector finite element method. The geometrical parameters of the interface are varied in order to identify the ones leading to optimum performance, i.e., maximum coupling efficiency. Fabrication tolerances about the optimum parameter values are also assessed. In addition, the effect of a longitudinal metallic stripe gap on coupling efficiency is quantified, since such gaps have been observed in fabricated structures. Finally, theoretical results are compared against insertion loss measurements, carried out for two distinct sets of samples comprising rib and wire SOI waveguides, respectively.

2 Silicon-Plasmonic Router Architecture for Optical Interconnects

We demonstrate experimental evidence of the data capture and the low-energy thermo-optic tuning credentials of dielectric-loaded plasmonic structures integrated on a silicon chip. We show 7-nm thermo-optical tuning of a plasmonic racetrack-resonator with less than 3.3 mW required electrical power and verify error-free 10-Gb/s transmission through a 60-μm-long dielectric-loaded plasmonic waveguide.

Interfacing Dielectric-Loaded Plasmonic and Silicon Photonic Waveguides: Theoretical Analysis and Experimental Demonstration

Longitudinal 2 × 2 thermo-optic switches based on dielectric-loaded plasmonic circuitry are thoroughly studied using vectorial numerical tools, i.e., an eigenmode solver and a beam propagation method, implemented with the finite-element technique. The switching configurations studied are based on the Mach-Zehnder interferometer (MZI) and a novel multimode interference (MMI) design. Both components offer improved performance, with respect to comparable microring-based ones, exhibiting larger bandwidth and output port extinction ratio, allowing values up to 30 dB. The reference MZI configuration has better overall performance when compared to the MMI, mainly in terms of available bandwidth.

Data Transmission and Thermo-Optic Tuning Performance of Dielectric-Loaded Plasmonic Structures Hetero-Integrated on a Silicon Chip

Compact polarization control elements based on index-guiding soft-glass photonic crystal fibers infiltrated with nematic liquid crystals are proposed and thoroughly studied. The nematic director profiles at the fibers cross section are consistently calculated by solving the coupled electrostatic and elastic problem, in the context of an analysis on the tunability of liquid-crystal-infiltrated photonic crystal fibers. The fibers dispersive properties and light propagation in the proposed polarization controller are studied by means of a fully anisotropic finite-element-based beam propagation method. The electrically induced evolution of the state of polarization is mapped on the Poincaré sphere. Efficient polarization conversion is demonstrated, with a crosstalk of -50 dB, for a total device length of 4.65 mm and a maximum applied voltage of 150 V. Crosstalk values lower than -20 dB are achieved over a 30 nm window. The proposed devices are envisaged as compact all-in-fiber dynamic polarization controllers.

Longitudinal 2 x 2 Switching Configurations Based on Thermo-Optically Addressed Dielectric-Loaded Plasmonic Waveguides

We demonstrate Wavelength Division Multiplexed (WDM)-enabled transmission of 480Gb/s aggregate data traffic (12x40Gb/s) as well as high-quality 1x2 thermo-optic tuning in Dielectric-Loaded Surface Plasmon Polariton Waveguides (DLSPPWs). The WDM transmission characteristics have been verified through BER measurements by exploiting the heterointegration of a 60 μm-long straight DLSPPW on a Silicon-on-Insulator waveguide platform, showing error-free performance for six out of the twelve channels. High-quality thermo-optic tuning has been achieved by utilizing Cycloaliphatic-Acrylate-Polymer as an efficient thermo-optic polymer loading employed in a dual-resonator DLSPPW switching structure, yielding a 9 nm wavelength shift and extinction ratio values higher than 10 dB at both output ports when heated to 90°C.

In-Line Polarization Controller Based on Liquid-Crystal Photonic Crystal Fibers

We describe a rigorous formalism for the calculation of the nonlinear parameter of arbitrary three-dimensional nanophotonic graphene-comprising waveguides. Graphene is naturally implemented as a zero-thickness conductive sheet, modeled solely by complex linear and nonlinear surface conductivity tensors, whose values are extracted from theoretical models. This representation is compared to the more commonly employed equivalent bulk-medium representation and is found superior. We numerically calculate the nonlinear parameters of several optical waveguide archetypes overlaid with infinite graphene monolayers, including silicon-wire and plasmonic metal-slot and metal-stripe configurations. The metal-slot configuration offers the most promising performance for Kerr-type nonlinear applications. Finally, we apply the same formalism to probe the potential of graphene nanoribbon waveguide nonlinearity in the terahertz band.

0.48Tb/s (12x40Gb/s) WDM transmission and high-quality thermo-optic switching in dielectric loaded plasmonics

Compact voltage-controlled all-in-fiber polarization switches are designed and investigated based on dual-core photonic crystal fibers, by selectively infiltrating one of the fibers cores with a nematic liquid crystal. The electro-optical control of the liquid crystal cores optical properties allows for the splitting of the two orthogonal polarizations, showing crosstalk values lower than -20 dB in a 40 nm window at 1550 nm, for an ultracompact length less than 0.6 mm. With proper selection of the control voltage and the component length, dual-band operation with a crosstalk lower than -20 dB is also demonstrated for the 1300 and 1550 nm telecom bands.

Rigorous calculation of nonlinear parameters in graphene-comprising waveguides

We present recent work that is carried out within the FP7 project PLATON on novel Tb/s switch fabric architectures and technologies for optical interconnect applications, employing heterointegration of plasmonics, silicon photonics and electronics.