In this work, a novel method to obtain all-dielectric toroidal response metasurfaces in the W-band and THz range is demonstrated. Two designs are proposed, a symmetric and asymmetric disk metasurface. The first design is intended to corroborate the theoretical analysis, demonstrating the excitation of a strong toroidal mode resonance at 93.2 GHz. Then, the second design is used to demonstrate that symmetry-breaking variations in the disk dimensions, could lead to birefringent metasurfaces, affecting the polarization of the impinging light. Two structures are designed, a polarization beam splitter and a polarization converter. Such devices are difficult to obtain at the target frequency range with low absorption, so they could be of particular interest for the next generation of 5G communications and THz devices.
Different electro-optical modulator designs based on electromagnetically induced transparency are proposed. A conductor–gap–silicon input waveguide is coupled to microrings-on-disks on each side. A low voltage modulating signal is applied to the modulator in a push-pull configuration, which changes the refractive index of the embedded layer of the electro-optical polymer. The proposed microrings-on-disks and cascaded microring modulators with submicron radii can efficiently modulate the light wave with moderate propagation losses. The microring-on-disk modulator achieved ultrasmall capacitance, 1.06 fF, and low power consumption, 2.12 fJ/bit. Both modulators have low insertion losses and high extinction ratios.
We introduce a compact plasmonic resonator that is capable of generating a Fano resonance in the transmission spectrum. The Fano resonance is observed with its unique lineshape. The proposed design is simple, compact, easy to fabricate and can be easily developed for different applications. The device structure is made of a gold layer, a metalinsulator- metal waveguide, and a rectangular cavity. As an application to the proposed plasmonic resonator, we introduce a gas sensor which is operational at the near infrared spectral range. The sensor possesses a high sensitivity of 1500nm/RIU at the telecom wavelength 1.55μm. FDTD simulation tools were conducted for the optimization of the device structure and obtaining the results.
In this work, we present an electro-optical modulator based on electromagnetically induced transparency (EIT). Our modulator employs a conductor-gap-silicon (CGS) microring resonator on each side of the input waveguide in a pushpull configuration utilizing an embedded electro-optical polymer (EOP). CGS waveguides support hybrid plasmonic modes offering a sound trade-off between mode confinement and propagation loss. The modulator is designed and analyzed using 3D finite difference time domain (FDTD) simulations. To have a high quality resonator, the rings are designed to have moderate waveguide propagation losses and a sub-micron radius of R = 805 nm. With an exact capacitance of just 1.06 fF per single microring resonator and applied voltage of 2 V, the exact energy consumption is estimated to be 4.24 fJ/bit. To the best of our knowledge, this figure represents 40% less power consumption in comparison with different modulators structures. The ultra-small capacitance of the proposed modulator and the instantaneous response of the used polymer make our design suitable for high bit rate applications. At the wavelength of -1550 nm-, the insertion loss is 0.34 dB and the extinction ratio is 10.23 dB.
In this paper we show two approaches to fabricate photonic channels on different substrate technology platforms, in particular silicon and polydimethylsiloxane (PDMS), for flexible photonic integrated circuits. The electro-optic effect and nonlinear optical properties of liquid crystals (LC) allow the realization of low cost and low energy consumption optoelectronic devices operating at both visible and near-infrared wavelengths. High extinction ratio and large tuning range guided wave devices will be presented to be used for both optofluidic and datacom applications, in which both low realization costs and low power consumption are key features. In particular we will show our recent results on polarization independent light propagation in waveguides whose core consists of LC infiltrated in PDMS channels (LC:PDMS waveguides) fully compatible with optofluidic and lab-on-chip microsystems.
In this work we design and theoretically investigate optical switches based on long-range plasmonic directional couplers, which are controlled via the electro-optic effect of nematic liquid crystal layers. Employed numerical tools include a fully-anisotropic finite-element-method, the eigenmode-expansion method, and a rigorous finite-element based calculation of the liquid-crystal molecular reorientation. Both horizontal and vertical configurations are assessed, providing a comparison in terms of key-performance characteristics, such as coupling length, switching voltage, insertion losses, and crosstalk. These tunable plasmonic devices are envisaged as ultra-low power consumption switching elements in integrated platforms for optical inter-chip interconnects.
KEYWORDS: Sensors, Polymers, Data modeling, Neurons, Chemical fiber sensors, Chemical elements, Polymeric sensors, Receptors, Data processing, Olfactory system
Biological olfaction outperforms chemical instrumentation in specificity, response time, detection limit, coding capacity,
time stability, robustness, size, power consumption, and portability. This biological function provides outstanding
performance due, to a large extent, to the unique architecture of the olfactory pathway, which combines a high degree of
redundancy, an efficient combinatorial coding along with unmatched chemical information processing mechanisms. The
last decade has witnessed important advances in the understanding of the computational primitives underlying the
functioning of the olfactory system. EU Funded Project NEUROCHEM (Bio-ICT-FET- 216916) has developed novel
computing paradigms and biologically motivated artefacts for chemical sensing taking inspiration from the biological
olfactory pathway. To demonstrate this approach, a biomimetic demonstrator has been built featuring a large scale sensor
array (65K elements) in conducting polymer technology mimicking the olfactory receptor neuron layer, and abstracted
biomimetic algorithms have been implemented in an embedded system that interfaces the chemical sensors. The
embedded system integrates computational models of the main anatomic building blocks in the olfactory pathway: the
olfactory bulb, and olfactory cortex in vertebrates (alternatively, antennal lobe and mushroom bodies in the insect). For
implementation in the embedded processor an abstraction phase has been carried out in which their processing
capabilities are captured by algorithmic solutions. Finally, the algorithmic models are tested with an odour robot with
navigation capabilities in mixed chemical plumes
This paper reports on linear and nonlinear optical properties of channel waveguides made of micromachined SiO2/Si Vgrooves
filled with nematic liquid crystal E7. Experiments demonstrate operation of the waveguides in the C-band (1530
- 1565 nm). Molecular reorientation of the NLC, induced either by an applied low frequency electric field or by the
electric field of the light itself, changes the LC refractive index distribution then allowing the control of guided light.
Design criteria and techniques of channel waveguides for both
electro-optical and all-optical switching and modulation
will be discussed. Experiments are presented where it is showed that light at 1550 nm, fiber-coupled to the LC
waveguide is optically modulated by an optical beam with an input power below 25 mW. All-optical switching of a
signal at 1510 nm with a contrast over 10 dB is also demonstrated by using a copropagating control signal at 1560 nm.
A model of the waveguide is also presented able to explain linear and nonlinear experimental results.
We present an integrated optical narrowband electrically tunable filter based on the whispering gallery modes of sapphire
microspheres and double ion-exchanged channel BK7 glass waveguides. Tuning is provided by a liquid crystal infiltrated
between the spheres and the glass substrate. By suitably choosing the radii of the spheres and of the circular apertures,
upon which the spheres are positioned, arrays of different filters can be realized on the same substrate with a low cost
industrial process. We evaluate the performance in terms of quality factor, mode spacing, and tuning range by comparing
the numerical results obtained by the numerical finite element modeling approach and with the analytical approach of the
Generalized Lorenz-Mie Theory for various design parameters. By reorienting the LC in an external electrical field, we
demonstrate the tuning of the spectral response of the sapphire microsphere based filter. We find that the value of the
mode spacing remains nearly unchanged for the different values of the applied electric field. An increase of the applied
electric field strength, changes the refractive index of the liquid crystal, so that for a fixed geometry the mode spacing remains unchanged.
A 1D photonic crystal slab based on preferential etching of commercially available silicon-on-insulator wafers is
presented. Compared to dry etching, anisotropic wet etching is more tolerant to errors as it is self-stopping on
crystallographic {111} planes and it produces a more precise geometry with symmetries and homothetic properties, with
surface roughness close to 1 nm. The resulting grooves are infiltrated by low viscosity liquid crystal having large
positive optical anisotropy. The use of slanted grooves provides advantages: first of all the complete filling of slanted
grooves is simplified when compared to vertical walls structures. Furthermore alignment is significantly facilitated.
Indeed the liquid crystal molecules tend to align with their long axis along the submicron grooves. Therefore by forcing
reorientation out of a rest position, the liquid crystal presents a choice of refractive indices to the propagating optical
field. The liquid crystal behavior is simulated by a finite element method, and coupled to a finite difference time domain
method. We investigate different photonic crystal configurations. Large tunability of bandgap edge for TE polarization is
demonstrated when switching the liquid crystal with an applied voltage. We have also studied the use of the same device
geometry as a very compact microfluidic refractometric sensor.
Integrated optic devices using liquid crystals embedded in optical waveguiding structures have advantages in terms of compactness and high performance. Such devices exploits the high electro-optic effect and the good optical properties of liquid crystals, in particular their high birefringence and their low absorption, combined with low loss optical waveguides. Optical switches based on ion-exchanged channel glass waveguides and liquid crystals operating in the C-band used for optical communications have been designed by using beam propagation method. Polarization independent configurations are described and evaluated in terms of crosstalk and losses. Feasibility of tunable optical filters using composites materials made of polymer and nematic liquid crystals to be used in optical communication and sensor systems is demonstrated. Materials and fabrication procedures of both integrated optical switches and filters are also discussed.
A multilayer structure realizing an optical switch with ferroelectric liquid crystal, polymeric buffers and waveguides has been analyzed at the wavelength of 1550 nm, focusing on fabrication and design tolerances. The used liquid crystal FELIX-M4851-025 from Clariant is aligned by Nylon6 and embedded between two polymeric waveguides. ITO is deposited on quartz substrates to apply voltage to the cell and polymeric buffers are employed to reduce ITO absorption losses. The polymers consisted of poly(pentafluorostyrene-co-glycidyl methacrylate). Light is switched between the optical waveguides by reorienting the liquid crystal. Optimization in terms of optical losses and extinction ratios was carried out by varying layer thicknesses, refractive indices of waveguides and buffers, and the angle α between the normal to the smectic layers and the propagation direction. An optimized device with α = 51°, refractive indices of 1.475 and 1.462, thicknesses of 3 and 6 μm for waveguides and buffer, respectively and 4.4 μm for the liquid crystal layer, exhibits an extinction ratio of 59.6 dB with losses as low as 0.8 dB for a length of only 174 μm. A device design using single mode channel waveguides for optical switching matrices has been also carried out.
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