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arXiv2018

Photonic crystal-Microring resonators for tunable delay lines

In this paper, a new design of optical delay line based on coupled ring resonators in photonic crystals is proposed and analyzed by means of numerical simulation in CST Microwave Studio. The performance of the proposed photonic crystal ring resonator (PhCRR) based coupled resonant optical waveguide (CROW) is compared to: point-defect cavity based coupled cavity waveguides (CCW) in photonic crystal. microring resonator (MRR) based CROW. The suggested design addresses compactness issues of the MRR CROW while offering normalized delay values better than CCW and comparable to MRR CROW. The PhCRR CROW also enhances design flexibility as the PhCRRs support multiple modes and thereby supporting multi-channel transfer/delay application on a single device.

physics.app-ph↗

arXiv2019

Towards integrated metatronics: a holistic approach on precise optical and electrical properties of Indium Tin Oxide

The class of transparent conductive oxides includes the material indium tin oxide (ITO) and has become a widely used material of modern every-day life such as in touch screens of smart phones and watches, but also used as an optically transparent low electrically-resistive contract in the photovoltaics industry. More recently ITO has shown epsilon-near-zero (ENZ) behavior in the telecommunication frequency band enabling both strong index modulation and other optically-exotic applications such as metatronics. However the ability to precisely obtain targeted electrical and optical material properties in ITO is still challenging due to complex intrinsic effects in ITO and as such no integrated metatronic platform has been demonstrated to-date. Here we deliver an extensive and accurate description process parameters of RF-sputtering, showing a holistic control of the quality of ITO thin films in the visible and particularly near-infrared spectral region. We further are able to custom-engineer the ENZ point across the telecommunication band by explicitly controlling the sputtering process conditions. Exploiting this control we design a functional sub-wavelength-scale filter based on lumped circuit-elements, towards the realization of integrated metatronic devices and circuits.

physics.app-ph↗

arXiv2018

Super Damping of Mechanical Vibrations

We report the phenomenon of coherent super decay, where a linear sum of several damped oscillators can collectively decay much faster than the individual ones in the first stage, followed by stagnating ones after more than 90 percent of the energy has already been dissipated. The parameters of the damped oscillators for CSD are determined by the process of response function decomposition, which is to use several slow decay response functions to approximate the response function of a fast decay reference resonator. Evidence established in experiments and in finite element simulations not only strongly supported the numerical investigations, but also uncovered an unexplored region of the tuned mass damper parameter space where TMDs with total mass less than 0.2 percent of a primary free body can damp its first resonance up to a damping ratio of 4.6 percent. Our findings also shed light onto the intriguing underline connections between complex functions with different singular points.

physics.app-ph↗

arXiv2018

Network of thermoelectric nanogenerators for low power energy harvesting

We report the design, elaboration and measurements of an innovative planar thermoelectric (TE) devices made of a large array of small mechanically suspended nanogenerators (nanoTEG). The miniaturized TE generators based on SiN membranes are arranged in series and/or in parallel depending on the expected final resistance adapted to the one of the load. The microstructuration allows, at the same time, a high thermal insulation of the membrane from the silicon frame and high thermal coupling to its environment (surrounding air, radiations). We show a ratio of 60% between the measured effective temperature of the membrane, (and hence of the TE junctions), and the available temperature of the heat source (air). The thermal gradient generated across the TE junction reaches a value as high as 60 kelvin per mm. Energy harvesting with this planar TE module is demonstrated through the collected voltage on the TE junctions when a temperature gradient is applied, showing a harvested power on the order of 0.3 $μ$Watt for a 1 cm 2 chip for an effective temperature gradient of 10 K. The optimization of nanoTEGs performances will increase the power harvested significantly and permit to send a signal by a regular communication protocol and feed basic functions like temperature measurement or airflow sensing.

physics.app-ph↗

arXiv2018

Crystallization-Arrested Viscoelastic Phase Separation in Semiconducting Polymer Gels

Through a combination of rheological characterization and temperature-variable imaging methods, a novel gelation pathway in dilute solutions of a semiconducting polymer to achieve interconnected, crystalline networks with hierarchical porosity is reported. Upon rapid cooling, solutions of regioregular poly(3-hexylthiophene) (RR-P3HT) in ortho-dichlorobenzene formed thermoreversible gels. Temperature-variable confocal microscopy revealed cooling-induced structural rearrangement to progress through viscoelastic phase separation. The phase separation process arrested prematurely during the formation of micron-sized solvent-rich "holes" within the RR-P3HT matrix due to intrachain crystallization. Cryogen-based scanning electron microscopy of RR P3HT gels revealed the existence of an interfibrillar network exhibiting nano-sized pores. Remarkably, these networks formed to equal gel strengths when a third component, either small molecule phenyl C61 butyric acid methyl ester (PCBM) or non-crystallizing regiorandom (Rra)-P3HT, was added to the solution. Organic solar cells in which the active layers were deposited from phase-separated solutions displayed 45% higher efficiency compared to reference cells.

physics.app-ph↗

arXiv2018

Effect of AlN Seed Layer on Crystallographic Characterization of Piezoelectric AlN

Ultrathin aluminum nitride (AlN) films are of great interest for integration into nanoelectromechanical systems for actuation and sensing. Given the direct relationship between crystallographic texture and piezoelectric response, x-ray diffraction has become an important metrology step. However, signals from layers deposited below the piezoelectric (PZE) AlN thin film may skew the crystallographic analysis and give misleading results. In this work, we compare the use of a Ti or AlN seed layer on the crystallographic quality of PZE AlN. We also analyze the influence of several AlN seed layer thicknesses on the rocking curve FWHM of PZE AlN and demonstrate an larger effect of the AlN seed layer on the θ-2θ AlN <0002> crystallographic peak for increasing AlN seed layer thickness.

physics.app-ph↗

arXiv2018

Complex frequency band structure of periodic thermo-diffusive materials by Floquet-Bloch theory

This work deals with the micromechanical study of periodic thermo-diffusive elastic multi-layered materials, which are of interest for the fabrication of solid oxide fuel cells (SOFCs). The focus is on the dynamic regime, that is investigating the dispersive wave propagation within the periodic material. In this framework, a generalization of the Floquet-Bloch theory is adopted, able to determine the complex band structure of such materials. The infinite algebraic linear system, obtained by exploiting both bilateral Laplace transform and Fourier transform, is replaced by its finite counterpart, resulting from a proper truncation at a finite number of considered equations. A regularization technique is herein useful to get rid of the Gibbs phenomenon. The solution of the problem is, finally, found in terms of complex angular frequencies, corresponding to a finite sequence of eigenvalue problems for given values of the wave vector. The paper is complemented by numerical examples taking into account thermo-mechanical coupling. The overall behaviour is found to be strongly influenced by the interaction between thermal and mechanical phenomena.

physics.app-ph↗

arXiv2018

Nano-fabrication and characterization of silicon meta-surfaces provided with Pancharatnam-Berry effect

In this paper, the implementation of optical elements in the form of Pancharatnam-Berry optics is considered. With respect to 3D bulk and diffractive optics, acting on the dynamic phase of light, Pancharatnam-Berry optical elements transfer a phase which is geometric in nature by locally manipulating the polarization state of the incident beam. They can be realized as space-variant sub-wavelengths gratings that behave like inhomogeneous form-birefringent materials. We present a comprehensive work of simulation, realization, and optical characterization at the telecom wavelength of 1310 nm of the constitutive linear grating cell, whose fabrication has been finely tuned in order to get a π-phase delay and obtain a maximum in the diffraction efficiency. The optical design in the infrared region allows the use of silicon as candidate material due to its transparency. In order to demonstrate the possibility to assemble the single grating cells for generating more complex phase patterns, the implementation of two Pancharatnam-Berry optical elements is considered: a blazed grating and an optical vortices demultiplexer.

cond-mat.mtrl-sci↗

arXiv2018

Dynamic asymptotic homogenization for periodic viscoelastic materials

A non-local dynamic homogenization technique for the analysis of a viscoelastic heterogeneous material which displays a periodic microstructure is herein proposed. The asymptotic expansion of the micro-displacement field in the transformed Laplace domain allows obtaining, from the expression of the micro-scale field equations, a set of recursive differential problems defined over the periodic unit cell. Consequently, the cell problems are derived in terms of perturbation functions depending on the geometrical and physical-mechanical properties of the material and its microstructural heterogeneities. A down-scaling relation is formulated in a consistent form, which correlates the microscopic to the macroscopic transformed displacement field and its gradients through the perturbation functions. Average field equations of infinite order are determined by substituting the down-scale relation into the micro-field equation. Based on a variational approach, the macroscopic field equations of a non-local continuum is delivered and the local and non-local overall constitutive and inertial tensors of the homogenized continuum are determined. The problem of wave propagation in case of a bi-phase layered material with orthotropic phases and axis of orthotropy parallel to the direction of layers is investigated as an example. In such a case, the local and non-local overall constitutive and inertial tensors are determined analytically and the dispersion curves obtained from the non-local homogenized model are analysed.

physics.app-ph↗

arXiv2018

Effect of PEG binder on gas sensitivity of ferric oxide films synthesized by spin coating and doctor blade methods

Ferric oxide (Fe2O3) thin films were fabricated on amorphous nonconductive and FTO conductive glass substrates starting from iron acetate nanoparticles by the doctor blade and the spin coating techniques. Thin films of Fe2O3 with and without the PEG binder were investigated. Films were subsequently annealed at 500 0C in air for 1 hour to crystallize the phase Fe2O3. The structural and chemical properties of Fe2O3 thin films were determined using XRD and FTIR. According to XRD, the single phase of Fe2O3 crystallized in the thin film after annealing. The optical band gap of synthesized Fe2O3 thin films were determined by UV-Visible spectrums. Gas sensitivity, respond time and recovery time of Fe2O3 thin films were measured in 1000ppm of CO2 gas using AUTO LAB. Thin films synthesized by the doctor blade method were thicker and more uniform than the thin films prepared by the spin coating technique. Gas sensitivity of Fe2O3 films synthesized by the doctor blade method is slightly higher than that of the films fabricated by the spin coating technique. Fe2O3 films with the PEG binder posses a higher gas sensitivity, lower respond time and lower recovery time compared to films without PEG binder. After adding the PEG binder, the optical band gap of Fe2O3 thin films reduces. The reduction of the activation energy is the reason for the improvement of the gas sensitivity after adding the PEG. However, the peak positions of FTIR do not indicate any significant change due to the adding of the PEG. Adding the binder increased the gas sensitivity of iron oxide by 15.44%. Both FTIR and UV-Visible data confirm the formation of Fe2O3 in the thin film.

cond-mat.mtrl-sci↗

arXiv2018

A 16-pixel NbN nanowire single photon detector coupled with 300 micrometer fiber

Niobium Nitride (NbN) nanowire is the most popular detection material of superconducting nanowire single photon detectors (SNSPDs) for high repetition rate and high efficiency. However, it has been assumed to be difficult for fabricating SNSPDs with arrays over large area, which are critical components of quantum imaging, linear optical quantum computing, satellite laser ranging, and high-speed quantum key distribution. This paper reported a 4*4 pixel NbN SNSPDs array with an equivalent receiving aperture of 300 micrometer associated with beam compression technology, which is the first NbN SNSPD coupled by 300 micrometer fiber according to our knowledge. The designed pixel was compact with a filling factor of 98.5%, resulting in a high quantum efficiency of 94.5%, a system efficiency of 46% for photons coupled from 300 micrometer fiber without optimizing polarization, and a system time resolution of 92 ps. This work demonstrates the feasibility of a large SNSPDs array, and paves the way for developing efficient photon camera with NbN nanowires.

physics.app-ph↗

arXiv2018

Machine learning-based Raman amplifier design

A multi-layer neural network is employed to learn the mapping between Raman gain profile and pump powers and wavelengths. The learned model predicts with high-accuracy, low-latency and low-complexity the pumping setup for any gain profile.

physics.app-ph↗

arXiv2018

Compact Modeling of I-V Characteristics, Temperature Dependency, Variations, and Noise of Integrated, Reproducible Metal-Oxide Memristors

We present a comprehensive phenomenological model for the crossbar integrated metal-oxide continuous-state memristors. The model consists of static and dynamic equations, which are obtained by fitting a large amount of experimental data, collected on several hundred devices. The static equation describes the device current, at non-disturbing voltages, as a sum of three components, representing the average behavior and its device-to-device and temporal variations. All three components are expressed as functions of the applied voltage, ambient temperature, and the current memory state. The dynamic equation models the change in the memory state as a function of the applied voltage stress and the current memory state, and is also expressed as a sum of the average and the device-to-device variation terms. Both equations are explicit, computationally inexpensive, and suitable for SPICE modeling. At the same time, the model has good predictive power, which is supported by the validation results. The presented model is useful for realistic simulations of various mixed-signal computing circuits, such as image compression and image classification applications, discussed in this paper.

physics.app-ph↗

arXiv2018

CMUT on Glass Substrate for Next-Generation Medical Imaging and Beyond

CMUT technology was invented and has been widely researched on silicon substrates. In recent years, fabrication of CMUT on glass substrates has raised significant interests because a number of advantages it can offer. First, parasitic capacitance could be easily reduced since glass is an insulating material. Second, insulation steps required in the silicon-based CMUT fabrication process could be avoided, leading to a reduced fabrication complexity. Third, anodic bonding can be used when the substrate is borosilicate glass, which is a low-temperature bonding technique and has a high tolerance to bonding surface area and roughness in addition to the advantages of silicon wafer bonding. Moreover, glass transparency can enable novel applications beyond pulse-echo ultrasound medical imaging and enlarge the potential markets of CMUTs.

physics.app-ph↗

arXiv2018

Highly enhanced field emission current density of copper oxide coated vertically aligned carbon nanotubes: Role of interface and electronic structure

We report the field emission (FE) properties of Cu coated vertically aligned carbon nanotubes (VACNTs) before and after oxidation. The current density was found to be the maximum (20 mA/cm$^2$) for 3 nm thick Cu coated VACNTs after oxidation. The variation in conventionally monitored parameters like work function and field enhancement factor does not explain the experimentally determined FE current density. A critical analysis of the electronic structure reveals the importance of presence of Cu$_2$O at the interface of CuO and VACNTs, which in turn controls the current density of these films. The highly enhanced FE current density of 3 nm Cu coated VACNTs after oxidation suggests its potential as a next generation electron source in vacuum microelectronic devices.

physics.app-ph↗

arXiv2018

Low-Frequency Noise Reduction Using In-Pixel Chopping To Enhance The Dynamic Range of a CMOS Image Sensor

In this paper, a low-noise CMOS image sensor with enhanced dynamic range (DR), using an in-pixel chopping technique, is presented. The proposed in-pixel chopping technique is used to reduce the low-frequency or 1/f noise of the source follower (SF) in an active pixel sensor (APS), which is a major component of the temporal noise. A conventional 3T active pixel, with n-well/p-sub photodiode (PD), is modified to implement a chopper inside a pixel. A single minimum sized nMOS transistor is used in each pixel, without much compromising in the fill-factor (FF). Using chopping action the low-frequency noise of the source follower is modulated to the chopping frequency (f ch ) which is much higher than the maximum frequency of the input signal frequency band. The up-converted low-frequency noise is eliminated using a column level low-pass filter (LPF), in the later stage. The reduction in the temporal noise also results in an enhanced dynamic range of the image sensor. In addition, the readout consists of a column level high gain chopper amplifier also reduces the non-linearity of the source follower. To validate the proposed technique a prototype sensor consists of a 128x128 sized pixel array with in-pixel chopping and column level read-out circuitry, is fabricated in AMS 0.35 μm CMOS OPTO process. The pixel pitch is 10.5 um (horizontal and vertical both) with a fill-factor of around 30%. The temporal noise is measured as 280 uVrms at the chopping frequency (fch) of 8 MHz, which shows a reduction in the noise power by 11 dB. Due to the reduced noise floor, the dynamic range is enhanced from 65 dB to 76 dB, using the proposed technique.

physics.app-ph↗

arXiv2018

100G Data Center Interconnections with Silicon Dual-Drive Mach-Zehnder Modulator and Direct Detection

In this paper, we experimentally demonstrate that a silicon dual-drive Mach-Zehnder modulator (DD-MZM) has great potential for next-generation data center interconnections (DCIs). For intra-data center interconnections, 120 Gb/s Nyquist 4-ary pulse amplitude modulation (PAM-4) signal is successfully generated with a silicon DD-MZM operating at C-band and transmitted over 2 km standard single-mode fiber (SSMF) with a bit error rate (BER) of 5.55x10-4. For inter-data center interconnections, single sideband (SSB) modulation is chosen to avoid power fading caused by fiber chromatic dispersion and square-law detection. We report the generation and transmission of 112 Gb/s Nyquist SSB PAM-4 signal by using the same silicon DD-MZM and Kramers-Kronig (KK) direct detection. A two-tap digital post filter and maximum likelihood sequence detection (MLSD) are applied to compensate for the limited system bandwidth. After 80 km SSMF transmission, the BER is 2.46x10-3 that is below the 7% HD-FEC threshold of 3.8x10-3. To the best of our knowledge, our work reports the highest single-lane bitrate of 80 km SSB transmission based on a silicon DD-MZM. Our study also shows the feasibility of silicon photonic modulator for DCI applications in the future.

eess.SP↗

arXiv2018

Transmission of Photonic Polarization States through 55-meter Water: Towards Air-to-sea Quantum Communication

Quantum communication has been rapidly developed due to its unconditional security and successfully implemented through optical fibers and free-space air in experiment. To build a complete quantum communication network involving satellites in space and submersibles in ocean, underwater quantum channel has been investigated in both theory and experiment. However, the question of whether the polarization encoded qubit can survive through a long-distance and high-loss underwater channel, which is considered as the restricted area for satellite-borne radio waves, still remains. Here, we experimentally demonstrate the transmission of blue-green photonic polarization states through 55-meter-long water. We prepare six universal quantum states at single photon level and observe their faithful transmission in a large marine test platform. We obtain the complete information of the channel by quantum process tomography. The distance demonstrated in this work reaches a region allowing potential real applications, representing a step further towards air-to-sea quantum communication.

quant-ph↗