PUBLICATIONS
Selected Congresses
Fiber-based Infrared Heterodyne Technology for the PFI: On the possibility of breaking the noise temperature quantum limit with cross-correlation
E.A. Michael and F.E. Besser
We present concept and first experimental lab results for a novel heterodyne correlation receiver architecture and demonstrate that it can surpass the standard quantum limit (SQL) for the noise temperature by “correlating out” the local oscillator shot noise made uncorrelated at both receivers due to replacing the laser shot noise by individual beam splitter noise. It is based on two balanced receivers, comprising in total of 4 mixers, and uses an 8-bit digitization FPGA-based 1GHz bandwidth digital correlation between the two receivers. The demonstrated prototype was built for 1550 nm using InGaAs balanced photodiodes. We present here a summary of the results described in detail in a paper accepted at IEEEAccess journal. The extra-sensitivity would lead to heterodyne being better than direct detection for wavelengths beyond 3 microns. We propose therefore this receiver architecture as a building block in a heterodyne technology to be developed for the future Planet Formation Imager Infrared Interferometer (PFI). This paper is a reduced version of a paper accepted at IEEE Access a week before the conference.
Heterodyne versus direct detection -it is not over
Ernest A. Michael, Felipe E. Besser
A semi-classical theory was re-derived in a consistent form for properly comparing direct and heterodyne detection as a function of wavelength. Plots are shown for example cases. We show that heterodyne should be better than direct detection for wavelengths longer than 3 microns, even with a bandwidth disadvantage, since direct detection is more sensitive to ambient temperature background than heterodyne detection. For interferometry the advantage of heterodyne is more pronounced in this case due to the smaller beam filling factors. When we include even the effect of surpassing the noise temperature quantum limit with a novel correlation receiver architecture (see paper 10701-94), the advantage of heterodyne detection becomes irrefutable.
Fiber-based heterodyne infrared interferometry: an instrumentation study platform on the way to the proposed Infrared Planet Formation Imager
Felipe E. Besser, Alfredo Rates, Nicolas Ortega, Miguel I. Pina, Clemente Pollarolo, Mauricio Jofre, Claudio Yanez, Matias Lasen, Nicolas Ramos, Ernest A. Michael
We present concept and first experimental lab results for a low-cost near-infrared heterodyne interferometer based on commercial 1.55μm fiber components with relative phase-stabilization between both telescopes. After a demonstration with 14”-telescopes, the concept should be upgradable to larger numbers of mid- or large-class telescopes. Given that the employed fiber phase stabilization scheme should enable the operation of long baselines, we discuss the applicability of his concept for long-baseline, high telescope number systems (scalability of the concept) and mid-infrared wavelengths. This could finally result in contributions to the design of the large in-frared Planet Formation Imager which is being proposed currently.
Heterodyne versus direct detection—it is not over
Ernest A. Michael, Felipe E. Besser
In this study a rigorous and consistent spectral semi-classical comparison between heterodyne and direct detection for astronomy is presented for single telescopes and interferometers. Triggered from recent instrumental heterodyne developments useful for future infrared interferometers, it was developed because no satisfactory comparison was traceable in literature. As a result, heterodyne and direct detection are of comparable sensitivity for equal bandwidths and integration times. Heterodyne should be much better than direct detection for wavelengths beyond 3 microns even with some bandwidth disadvantage because direct detection is more affected by ambient temperature background than heterodyne detection. Recently, a double-balanced cross-correlation receiver laboratory setup was demonstrated to surpass the quantum limit for the sensitivity in cross-correlation. We show that with this interferometry factor, heterodyne would be clearly more sensitive throughout the infrared spectral range. With this, the only drawback of heterodyne stays a much smaller optical bandwidth. However, ultra-broad band “dispersed heterodyne receivers” based on frequency-comb local oscillators, and eventually additionally ultra-fast mixers, should be the solution.
Fiber-Based Infrared Heterodyne Technology for the PFI: Development of a Prototype Test System
F. E. Besser, N. Ramos, A. Rates, N. Ortega, S. Sepulveda, T. Parvex, M. Piña, C.Pollarolo, R. E. Jara, K. R. Espinoza, A. Rodriguez, A. Becerra, P. Martin, M. D.Cadiz, N. N. Henriquez, J. Carrasco, C. San Martin, C. Rearte, J. Diaz, E. Moreno, and E. A. Michael
We present the concept and experimental development of a low-cost near-infrared heterodyne interferometer prototype based on commercial 1.55 μm fiber components. As the most crucial component of it we characterized a novel sub-shot noise correlation detection system. We are upgrading to a Reconfigurable Open Archi-tecture Computing Hardware, 2nd Generation (ROACH-2) board with the capacity of four parallel 1.25 GHz bandwidth digitization, so that phase closure measurements will be possible. We extended the stabilization of the local oscillator phase between the telescopes to cover the whole acoustic range. For the telescope to single-mode fiber coupling under atmospheric perturbation, we developed a fiber actuator lock-loop for small telescopes and good seeing, and tested an adaptive optics approach for mediocre seeing and/or larger telescopes. We constructed also a frequency comb based laser synthesizer system to include tests on multi-frequency band measurements towards ultra-broad band “dispersed” heterodyne detection systems finally useful for the Planet Formation Imager (PFI).
CONCEPT FOR FIBER-BASED NEAR-INFRARED INTERFEROMETRY OF HIGHEST FREQUENCY RESOLUTION
E. A. Michael, F Besser, R. Prado, L. Pallanca
We are presenting first experimental results for subsystems of a low-cost near-infrared heterodyne interferometer concept based on commercial 1.55μm fiber-components with relative phase-stabilization between both telescopes, a shot noise limited heterodyne scheme with ambient temperature operated photodiodes, an ultra-coherent fiber laser, and a ROACH-based correlator. After we worked on a first demonstration with two 14” amateur telescopes on Betelgeuse, the concept should be upgradable to connect mid- or large-class telescopes, also given that the employed fiber phase stabilization scheme will enable the operation of long baselines.
https://doi.org/10.1117/12.2057203
BCC-Grid versus BS-Grid in the modeling of a sheet of graphene as a surface boundary condition in the context ADE-FDTD
E. Moreno and E.A. Michael
In the fully explicit finite-difference time-domain method the stability condition establishes a relation between the size of the updating time stepping and the spatial mesh size. The tiniest mesh element provides through the stability conditiontime-stepping as well as the simulation duration. In a multi-scale problem, some small volumetric bodies and in particular some thin layers can be treated as a surface boundary condition. This means a no reduction of mesh elements size when the thin layer is discretized and considered in the spatial grid. This is not new, there isreplacement of a graphene layer by a surface boundary condition in standard ADE-FDTD where the simple-cubic grid (SC-Grid) or Yee’s cell is employed as the stencil. However, in relation with the phase velocity body centered cubic grid (BCC-Grid) preserves a higher level of isotropy than SC-Grid along with a similar level of physical dispersion error. BCC-Grid has also a similar level of asymptotic time complexity than SC-Grid and it is more appropriate for describing the thin layer of graphene as a mathematical boundary condition in ADE-FDTD. We transform by means SC-Grid and BCC-Grid a thin layer of graphene located in a sandwich of glass-graphene-metal by a surface boundary condition where the metal is considered asdispersive medium. In this context, we compare the two stencil and demonstrated that BCC-Grid is more appropriate.
Selected Papers
2020
Thermally engineered resistive memories by multilayer dielectric stacks: fabrication, characterization and simulation
M. Maestro-Izquierdo, M. Gonzalez, F. Jimenez-Molinos, E. Moreno, J.B. Roldan, F. Campabadal
In this work, the impact of different HfO2/Al2O3-based multilayer dielectric stack configurations on the electrical characteristics and the resistive switching performance has been systematically investigated in Ni/Insulator/Silicon devices. Significant differences are observed in the electrical characteristics of the fabricated bilayer, trilayer and pentalayer stacks compared to a single HfO2 layer of the same physical thickness. The resistive switching analysis has shown similar low resistance state currents, and set voltages for all the dielectric stack combinations whereas currents at the high resistance state and reset voltages depend on the dielectric stack. The shift of the reset voltage to lower values for HfO2 and Al2O3/HfO2/Al2O3 cases is explained by the results from thermal simulations that reveal that these differences could be associated to the different temperature distributions at the narrowest part of the conductive filament just before the thermally triggered reset process occurs.
Accepted
2019
A CO-multilayer outer atmosphere for eight evolved stars revealed with VLTI/AMBER
M. Hadjara, P. Cruzalèbes, C. Nitschelm, X. Chen, E.A. Michael, E. Moreno
We determine the physical parameters of the outer atmosphere of a sample of eight evolved stars, including the red supergiant α Scorpii, the red giant branch stars α Bootis and γ Crucis, the K giant λ Velorum, the normal M giants BK Virginis and SW Virginis, and the Mira star W Hydrae (in two different luminosity phases) by spatially resolving the stars in the individual carbon monoxide (CO) first overtone lines. We used the Astronomical Multi-BEam combineR (AMBER) instrument at the Very Large Telescope Interferometer (VLTI), in high-resolution mode (λ/Δλ ≈ 12 000) between 2.28 and 2.31 μmμm in the K band. The maximal angular resolution is 10 mas, obtained using a triplet telescope configuration, with baselines from 7 to 48 m. By using a numerical model of a molecular atmosphere in a spherical shells (MOLsphere), called PAMPERO (an acronym for the ‘physical approach of molecular photospheric ejection at high angular resolution for evolved stars’), we add multiple extended CO layers above the photospheric MARCS model at an adequate spatial resolution. We use the differential visibilities and the spectrum to estimate the size (R) of the CO MOLsphere, its column density (NCO) and temperature (Tmol) distributions along the stellar radius. The combining of the χ2 minimization and a fine grid approach for uncertainty analysis leads to reasonable NCO and Tmol distributions along the stellar radius of the MOLsphere.
https://doi.org/10.1093/mnras/stz2240
Comparative study of grids based on the cubic crystal system for the FDTD solution of the wave equation
In this paper, a scalar wave is solved in the fully explicit finite difference time domain scheme for different stencils based on the cubic crystal system. In particular, we study four systems: the simple cubic, the body-centered cubic, the face-centered cubic and the compact packing cubic. In many papers that are focused on the artificial anisotropy induced by these grids in the propagated wave, one candidate is often better than all the others. In this manuscript, we study the stability, the physical phase velocity error and the anisotropy under two views. Firstly, we consider the same burdens or density of nodes per cubic wavelength and secondly we look at the asymptotic case. We also investigate the computational complexity based on several considerations: burdens, asymptotic time and implementation difficulties. Therefore, we pointed out how each problem or application, due to its different characteristics, has an appropriate grid in order to be treated pr operly.
Illumination study of a quantum MIM diode for the mid-infrared
E. Moreno and E.A. Michael
Metal-insulator-metal (MIM) junctions with insulators a few nanometers thick are tunneling diodes able to operate at frequencies up to 1015 Hz. However, their main limitation is their poor harvested current. The quantum tunneling current between the two metals through the potential barrier created by the insulator is inversely proportional to the barrier thickness which corresponds to the insulator thickness. Therefore, in the mid-infrared, the insulator thickness in MIM diodes is several orders of magnitude under the diffraction limit and so the electromagnetic field cannot penetrate the structure. In all papers reviewed, the wave that illuminates the diode inside the junction is transformed into an evanescent one. The only way in which the electromagnetic radiation can be introduced to a reasonable distance within the structure is through a traveling wave of surface plasmon-polaritons. This paper demonstrates that a distributed illumination produced by a beam splitter is the key to creating this traveling wave. The distributed illumination creates a surface-plasmon-polariton traveling-wave (SSP-TW) that is not exponentially attenuated. In addition to creating this wave, we had to match the external electromagnetic stimuli with the SPP-TW velocity. To do so, the illumination must enter the junction from the outside of one of the two metal layers at an appropriate angle consistent with the Kretschmann and Reather prism-based configuration. The use of these two techniques, a particular angle and distributed light, improves the electric field inside the junction, which extends the tunneling event to the entire junction length with the same probability all along the junction. This increases the harvested quantum-tunneling current and the diode responsivity.
Optically-activated cascode configuration for 650 V GaN FET devices and packaging parasitic inductance effects
Z. Hemmat, A. Mojab, E. Moreno, A. Ahmadiparidari, M. Paryavi, M. Alizadeh, E.A. Michael
In this paper, a novel optically-activated cascode structure is proposed to be used with a normally-on gallium nitride (GaN) field-effect transistor (FET) device to achieve an overall normally-off configuration. Using this novel configuration, cost-effective infrared (IR) lasers can be utilized instead of expensive ultraviolet (UV) lasers to activate this structure which includes a wide-bandgap-material device (GaN FET). Furthermore, the effect of parasitic inductance available in the package and connections of this proposed configuration is evaluated using Silvaco TCAD simulations. In practice, one high-power normally-on FET device is connected in series with a low-power optical switch (OS) to make the proposed overall normally-off cascode structure. The capability of being optically-activated for the proposed structure has many advantages over the conventional electrically-activated cascode structures including but not limited to: more immunity to electromagnetic interference (EMI), using only one main bias as the power source, using cost-effective long-wavelength laser instead of expensive short-wavelength lasers to trigger the GaN devices, reduced current and voltage ringing during switching transitions, etc. Comprehensive device modeling and parasitic inductance analysis for this new proposed optical cascode GaN FET device are provided in this work.
Thermal study of multilayer resistive random access memories based on HfO2 and Al2O3 oxides
M. Cazorla, A. Aldana, M. Maestro, M. Bargalló-González, F. Campabadal, E. Moreno, F. Jiménez-Molinos, and J.B. Roldán
An in-depth analysis including both simulation and experimental characterization of resistive random access memories (RRAMs) with dielectric stacks composed of two layers of HfO2 and Al2O3 stacked in different orders is presented. The simulator, which includes the electrodes in the simulation domain, solves the 3D heat equation and calculates the device current. The results are employed to analyze thermal effects in bilayer HfO2 and Al2O3-based RRAMs with electrodes of Ni and Si-n+ during resistive switching (RS) operation. According to simulations and the experimental data, the narrow part of the conductive filaments (CF) is formed in the HfO2 layer in all the cases, and, therefore, no important differences are found in terms of reset voltage if the oxide stack order is changed with respect to the electrodes. This result is attributed to the fact that the heat flux in Al2O3 is higher than in the HfO2 layer and this determines the thermal behavior and RS operation. The heat transfer rate from the conductive filament to the electrodes and the surrounding oxide has been analyzed. The lateral heat flux component from the CF to the oxide is shown to be important with respect to the vertical component (from the CF to the electrodes).
2018
On the possibility of breaking the heterodyne detection quantum noise limit with cross-correlation
EA Michael, FE Besser
The cross-correlation sensitivity of two identical balanced photodiode heterodyne receivers is characterized. Both the balanced photodiodes receive the same weak signal split up equally, a situation equivalent to an astronomical spatial interferometer. A common local oscillator is also split up equally and its phase difference between both the receivers is stabilized. We show by a semi-classical photon deletion theory that the post-detection laser shot noise contributions on both the receivers must be completely uncorrelated in this case of passing three power splitters. We measured the auto- and cross-correlation outputs as a function of the weak signal power (system noise temperature measurement) and obtained a cross-correlation system noise temperature up to 20 times lower than for the auto-correlation system noise temperature of each receiver separately. This is supported by Allan plot measurements showing cross-correlation standard deviations 30 times lower than in auto-correlation. Careful calibration of the source power shows that the auto-correlation (regular) noise temperature of the single balanced receivers is already very near to the quantum limit as expected, which suggests a cross-correlation system noise temperature below the quantum limit. If validated further, this experimentally clear finding will not only be relevant for astronomical instrumentation but also for other fields, such as telecommunications and medical imaging.
E. Moreno, R. Sohrabi, G. Klochok, E. A. Michael
The design process of a photoconductive antenna (PCA), which emits efficiently in the electromagnetic terahertz range, demands some considerations that are discussed through this work. In this work, several essential characteristics of a photoconductive antenna made with LT-GaAS are studied by means of well established commercial software (COMSOL 5.3). An approach to the efficiency is also made through the study of geometry, the laser illumination position, the substrate doping distribution, the direction of the bias applied to the semiconductor, the matching impedance at the laser operating frequency and, finally, the plasmonics effects or penetration laser enhancement due to the use of nano antennas. We study and compare two kinds of structures, one which is quasi-bidimensional or planar and the other which is vertical. Additionally, the photoconductive antennas are also modeled by using a simplified equivalent circuit which helps to understand the antennas’ performance. Therefore, some fundamental parameters, like the transient capacitance between the metal contacts are also studied. Furthermore, we introduce an optimized vertical design which achieves the best results.
An accurate analytical model for nonequilibrium drift-velocity and chord-mobility of In0.53Ga0.47As
E. Moreno and L. Varani
Mobility models are an essential tool for an accurate description of the charge carrier dynamics in semiconductor materials and devices. By means of a simulator based on the Monte Carlo method which has been properly validated, a set of velocity and chord-mobility data was generated for electrons and holes in In0.53Ga0.47As bulk material as a function of electric field and for different concentrations of donors and acceptors. This set has been used to build an accurate velocity and chord-mobility analytical model, the mathematical simplicity of which represents a significant advantage because it provides necessary values by a rapid calculation process without forgoing accuracy. The model can be easily implemented in compact numerical simulations of electronic devices and associated circuits where a fast recovery of the velocity and mobility values corresponding to the local electric field and doping concentration is needed.
2017
Control of deviations and prediction of surface roughness from micro machining of THz waveguides using acoustic emission signals
Griffin, JM (Griffin, James M.) ; Diaz, F (Diaz, Fernanda) ; Geerling, E (Geerling, Edgar) ; Clasing, M (Clasing, Matias) ; Ponce, V (Ponce, Vicente) ; Taylor, C (Taylor, Chris) ; Turner, S (Turner, Sam) ; Michael, EA (Michael, Ernest A.) ; Mena, FP (Mena, F. Patricio) ; Bronfman, L(Bronfman, Leonardo)
By using acoustic emission (AE) it is possible to control deviations and surface quality during micro milling operations. The method of micro milling is used to manufacture a submillimetre waveguide where micro machining is employed to achieve the required superior finish and geometrical tolerances. Submillimetre waveguide technology is used in deep space signal retrieval where highest detection efficiencies are needed and therefore every possible signal loss in the receiver has to be avoided and stringent tolerances achieved. With a sub-standard surface finish the signals travelling along the waveguides dissipate away faster than with perfect surfaces where the residual roughness becomes comparable with the electromagnetic skin depth. Therefore, the higher the radio frequency the more critical this becomes. The method of time frequency analysis (STFT) is used to transfer raw AE into more meaningful salient signal features (SF). This information was then correlated against the measured geometrical deviations and, the onset of catastrophic tool wear. Such deviations can be offset from different AE signals (different deviations from subsequent tests) and feedback for a final spring cut ensuring the geometrical accuracies are met. Geometrical differences can impact on the required transfer of AE signals (change in cut off frequencies and diminished SNR at the interface) and therefore errors have to be minimised to "within 1 mu m. Rules based on both Classification and Regression Trees (CART) and Neural Networks (NN) were used to implement a simulation displaying how such a control regime could be used as a real time controller, be it corrective measures (via spring cuts) over several initial machining passes or, with a micron cut introducing a level plain measure for allowing setup corrective measures (similar to a spirit level).
Broadband near-to-shot-noise suppression of arbitrary cw-laser excess intensity noise in the gigahertz range
Ernest A. Michael and Laurent Pallanca
Broadband near-to-shot-noise suppression of the intensity noise from a continuous-wave (cw) fiber laser at 1550 nm is demonstrated at GHz-frequencies using feed-forward phase-matched destructive noise interference impressed onto the optical signal with a fiber electro-optic power modulator. The scheme is independent of the laser frequency and therefore is suitable for tunable lasers. It can be used with some modifications after an optical fiber-amplifier boosting a cw laser signal. A noise residual of down to 2 dB above the shot-noise was measured, which is about 2 dB below the prediction with a rigorous noise model. While the total laser noise can be removed, inclusive shot noise, because the latter is still 10 dB above the thermal noise, the power splitter introduces some partition noise above the shot level. In that case, a sub-shot-noise suppression scheme should be possible by replacing the photon anti-correlation of the power splitter by the co-correlation obtained from a paired photon or twin beam source.
Implementation of Open Boundary Problems in Photo-Conductive Antennas by Using Convolutional Perfectly Matched Layers
A method to simulate an open boundary problem within the finite difference time domain approach for the emission of photo-conductive antennas is presented here. For this purpose, we use convolutional perfectly matched layers (CPMLs). In these devices, the semiconductor region, where transient currents are present in simulation time, is considered to be an “active” medium. This medium is extended virtually beyond its boundaries or the computational domain limits. We explain in this communication how to simulate the transient state of a semiconductor in a CPML region as well as the potential of the method developed to solve conventional practical applications.
Free-electron THz-reabsorption in distributed photodiode structures
Ultra-fast photodiodes based on vertical p-i-n or uni-traveling (UTC) mesa structures require a highly doped base layer that makes a well-conducting transverse connection between the mesa bottom layer and the bottom metal contacts. To reach the lowest possible THz loss, the question arises on what doping levels would be optimal for this layer. Doping levels of up to approximate to 5 x 10(19) cm(-3) can be reached in InP, corresponding to conductivities of around 8 x 10(5) S m(-1), which is still much lower than those of metal conductors. A full-wave analysis, which is executed in HFSS (TM) and CST Microwave Studio (TM) and reported here, shows that a valley of low loss exists around a conductivity of 5 x 10(4) S m(-1) (estimated doping value approximate to 2 x 10(18) cm(-3)), in the middle of a conductivity range of excessive terahertz absorption, making this value the best choice for the whole frequency range up to 2000 GHz. The results are supported by an analytical solution in a simplified transmission line model. The results are expected to be significant for designing future distributed photonic devices such as traveling-wave (TW) photodiodes.