Complementary Metasurfaces for Guiding Electromagnetic Wave

Metasurfaces can be employed for designing waveguides that confine the electromagnetic energy while they are open structures. In this communication, we introduce a new type of such waveguides, formed by two penetrable metasurfaces having complementary isotropic surface impedances. We theoretically study the guided modes supported by the proposed structure and discuss the corresponding dispersion properties. We show the results for different scenarios in which the surface impedances possess nonresonant or resonant characteristics, and the distance between the two metasurfaces changes from large values to the extreme limit of zero. We also derive and describe the general condition for existence of two modes with orthogonal polarizations having the same phase velocity. In the particular case in which the metasurfaces are complementary and the distance between them is not small, we indicate that such phenomenon occurs within a broad frequency range. This property can be promising for applications in leaky-wave antennas and field focusing.

Dispersion Properties of Photonic Crystals and Silicon Nanostructures Investigated by Fourier-Space Imaging

Jana Jágerská

State-of-the-art nanophotonic devices based on semiconductor technology use total internal reflection or the photonic bandgap effect to reduce the waveguide core dimensions down to hundreds of nanometers, ensuring strong optical confinement within the scale of the wavelength. Within the framework of this thesis, we investigate the light propagation in such devices by direct experimental reconstruction of their dispersion relation ω (k), where ω is the optical frequency and k the wave vector of the supported modes. Knowledge of the dispersion relation provides us with comprehensive information about the guided field, including the number of supported modes, their phase and group velocity as well as the higher order dispersion. As a principal characterization tool, an original experimental technique referred as Fourier-space imaging is used. It is based on far-field analysis of optical signal radiated out of the plane of the structure, which makes it possible to retrieve accurately, non-invasively and in one step the complex dispersion of both the leaky and the truly guided optical modes. The latter is feasible provided that the device is equipped with vanishingly weak grating probes that scatter a small part of the guided light into the light cone. The Fourier-space imaging technique was applied to study the optical properties of a large number of nanophotonic devices, ranging from simple nanowire waveguides to complex photonic crystal structures. In the first part of the work, silicon-on-insulator slot waveguides, coupled ridge waveguides and nanowire waveguide arrays are addressed. Besides the phase and group index dispersion, we investigate the phenomenon of mode splitting in coupled systems, being able to probe the coupling lengths with an accuracy of ±50 nm. In the case of waveguide arrays, beam steering using both thermo-optic effect and wavelength tuning was demonstrated. Concerning the photonic crystal devices, we primarily focus on the phenomenon of slow light propagation in line-defect and coupled-cavity photonic crystal waveguides. The latter represent a special type of a waveguide, which allows for substantial optical signal retardation by evanescent coupling along a chain of photonic crystal cavities. The main motivation was to accurately measure the group index of the slow light modes and recognize the main factors limiting its maximum achievable value. Among others, experimental observation of dispersion curve renormalization, enhanced out-of-plane and back-scattering as well as light localization due to residual disorder were reported. Finally, a detailed experimental study of hollow-core photonic crystal structures intended for optical sensing applications is presented.

EPFL2011

Planar Integrated Sensors on Waveguides for sensing applications

Armando Cosentino, Hans Peter Herzig, Qing Tan

We investigate the use of a metallic nano-cavity on dielectric waveguides for sensing applications. Nowadays the fabrication of metallic structures featured by challenging dimensions is feasible thanks to the most recent technologies such as E-Beam Lithography (EBL) and lift-off [1]. We propose here to study the simulation, fabrication and characterization of such structures at the telecom wavelength (λ=1.55 μm).

2011

On-chip NIR optical spectrometer based on polymeric waveguide and metallic nano-structures

Maurine Malak Karam Awadallah, Irène Philipoussis Fernandez, Toralf Scharf

In this work, we report about optical spectrometry using gold nano-structures printed on a polymer based integrated optical waveguide. The optical waveguide is a single mode buried waveguide, having dimensions of 3x2.2 mu m(2). It is made from a combination of photo-polymerizable materials and is fabricated by photolithography on a glass substrate. To sense the electric field inside the waveguide, a gold nano-coupler array of thin lines (50 nm thick and 8 mu m length) is embedded on top of the aforementioned waveguide. They are produced by E-beam lithography. The array pitch is 2.872 mu m and the number of lines 564, which yields an array of 1.619 mm length. The device is enclosed with a glass superstrate to prevent it from dust and destruction. Both waveguide ports are polished and the output port in particular, is coated with a thin gold layer to assimilate a mirror and hence, it enables the creation of stationary waves inside the structure. The measurement procedure involves light injection using a single mode fiber carrying both visible light (658nm) and infrared light (785nm), used for alignment and measurement purposes respectively. Stationary waves generated inside the guide constitute the spatial interferogram. Locally, light is out-coupled using the nano-couplers and allows measuring the interferogram structure. The resulting pattern is imaged by a vision system involving an optical microscope with a digital camera mounted on-top of it. Signal processing, mainly based on Fast Fourier transform is performed on the captured signal to extract the spectral content of the measured signal.

Spie-Int Soc Optical Engineering2014

Dispersion Properties of Photonic Crystals and Silicon Nanostructures Investigated by Fourier-Space Imaging

Jana Jágerská

EPFL2011