Wide Range Of Bias Currents Research Articles

Large-area TaN superconducting microwire single photon detectors for X-ray detection.

With the development of superconducting nanowire single photon detectors, increasing numbers of important applications are being explored, covering not only low-energy optical photon detection but also high-energy photon and particle detection. In this work, 100-nm-thick TaN superconducting microwire single photon detectors (SMSPDs) with large active areas were prepared for X-ray detection, and their response characteristics to X-rays were studied. The results showed that our TaN SMSPDs were able to detect X-rays at a wide range of bias currents and working temperatures. The detectors could distinguish different energy X-rays under suitable working conditions, and the energy resolving power was strongly related to the bias current.

Current Detection Using a Josephson Parametric Upconverter

We present the design, measurement and analysis of a current sensor based on a process of Josephson parametric upconversion in a superconducting microwave cavity. Terminating a coplanar waveguide with a nanobridge constriction Josephson junction, we observe modulation sidebands from the cavity that enable highly sensitive, frequency-multiplexed output of small currents for applications such as transition-edge sensor array readout. We derive an analytical model to reproduce the measurements over a wide range of bias currents, detunings and input powers. Tuning the frequency of the cavity by more than \SI{100}{\mega\hertz} with DC current, our device achieves a minimum current sensitivity of \SI{8.9}{\pico\ampere\per\sqrt{\hertz}}. Extrapolating the results of our analytical model, we predict an improved device based on our platform, capable of achieving sensitivities down to \SI{50}{\femto\ampere\per\sqrt{\hertz}}}, or even lower if one could take advantage of parametric amplification in the Josephson cavity. Taking advantage of the Josephson architecture, our approach can provide higher sensitivity than kinetic inductance designs, and potentially enables detection of currents ultimately limited by quantum noise.

Quantum Dot Lasers Subject to Polarization-Rotated Optical Feedback

Dynamics of a multimode quantum dot laser with polarization-rotated optical feedback is investigated in a wide range of bias current. The results reveal that the laser is more sensitive to optical feedback when the polarization of feedback beam is rotated a large angle from the original polarization, which is different from the results in DFB lasers. Anticorrelated fluctuations between orthogonal polarizations are observed in a certain range of selected polarizations. Accordingly, dynamics in the total power can be weaker than that in a selected polarization. The anticorrelated polarization dynamics may be related to different polarizations of longitudinal modes.

A V2O5/4H-SiC Schottky diode-based PTAT sensor operating in a wide range of bias currents

A proportional to absolute temperature sensor (PTAT) based on V2O5/4H-SiC (vanadium pentoxide/4H polytype of silicon carbide) Schottky diodes is presented. The linear dependence on temperature of the voltage difference appearing at the terminals of two constant-current forward-biased diodes has been used for thermal sensing in the wide temperature range from T=147K to 400K which extends down the state-of-the art of more than 80K. The proposed sensor shows a sensitivity of 307μV/K, a good reproducibility and a stable linear output also in case of deviation of the two bias currents from the best operating condition.

Wideband Gain MQW-SOA Modeling and Saturation Power Improvement in a Tri-Electrode Configuration

A semiphenomenological wideband model is proposed for both the material gain and the gain coefficient of a multiquantum well semiconductor optical amplifier (MQW-SOA). This analytical model is integrated in an SOA-dedicated simulation tool and validated experimentally over a wide range of bias currents, input powers, and wavelengths. We demonstrate the ability of multielectrode configurations to increase the saturation power of MQW-SOA without sacrificing either their noise figure or their optical gain bandwidth A tri-electrode configuration permits to obtain an enhancement of the MQW-SOA output saturation power of more than 3 dB over 100 nm while maintaining its optical bandwidth (defined at −1 dB) at about 76 nm.

Tungsten-Doped Nb2O5Nanorod Sensor for Toxic and Combustible Gas Monitoring Applications

High power consumption due to the need for elevated operating temperature remains a challenge for metal–oxide gas sensors. This letter presents a tungsten-doped Nb2O5 nanorod sensor suitable for toxic and combustible gas monitoring applications. The fabricated prototype has been experimentally characterized for H2, CH4, and NO2 gases for both static and dynamic performances, under a wide range of bias currents and operating temperatures. Results indicate that the large surface-to-volume ratio of the nanostructured sensing film achieves strong responses even down to room temperature, which is highly advantageous for low-power, heater-free, portable sensing applications.

Subthreshold DC‐gain enhancement by exploiting small size effects of MOSFETs

A pseudo-cascode split-transistor technique is proposed for DC-gain enhancement of amplifiers in the subthreshold by exploiting the small size effects of metal–oxide semiconductor field effect transistors (MOSFETs) including the reverse short-channel effect and the inverse narrow-width effect. It requires no body-biasing and occupies a small area. A compact 114 μm2 two-stage amplifier with pseudo-cascode compensation for in-pixel amplification in vision sensors has been designed using the proposed technique. A total of 10 samples of split-transistors and amplifiers fabricated in an UMC 0.18 μm standard CMOS process were measured. More than half of the tested split-transistors show considerable DC-gain enhancement over a wide range of bias currents and nine amplifiers have increased DC gains larger than 85 dB at about 4 nA power consumption.

Polarization Switching in Long-Wavelength VCSELs Subject to Orthogonal Optical Injection

Polarization switching (PS) appearing in long-wavelength vertical-cavity surface-emitting lasers (VCSELs) subject to orthogonal optical injection is investigated theoretically and experimentally. We have studied the injected optical power required for PS as a function of the frequency detuning between the injected light and the orthogonal linear polarization of the VCSEL. For a wide range of bias currents applied to the device, the injected power required for the occurrence of PS exhibited a minimum and a plateau with respect to the frequency detuning. The minimum (plateau) was found at negative (positive) frequency detuning. The bistable behavior of the polarization is described. Our experimental results confirm the theoretical predictions of Sciamanna and Panajotov. The levels of the minimum and the plateau were observed to increase as higher bias currents were applied to the VCSEL. A first theoretical and experimental observation of the disappearance and further appearance of PS when increasing the injected power in long-wavelength VCSELs is described. This situation is obtained for small levels of negative frequency detuning and for large enough values of applied bias current. A good overall qualitative agreement is found between our theoretical and experimental results.

GaAs-Based Transverse Junction Superluminescent Diodes With Strain-Compensated InGaAs–GaAsP Multiple-Quantum-Wells at 1.1-$\mu$m Wavelength

In this study, we demonstrate a transverse junction superluminescent diode (TJ-SLD) with an engagement of chirped In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As-GaAs <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.9</sub> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.1</sub> strain-compensated multiple-quantum-wells (SC MQWs) at 1.1-μm wavelength. The problem relative to inhomogeneous carrier distribution in each QW, which is a problem in traditional vertical junction SLDs (VJ-SLDs), can be effectively minimized by utilizing the benefit of lateral carrier injection in TJ devices. Our demonstrated device offers significant improvements in threshold current, output power, and optical bandwidths compared to TJ-SLD without SC MQWs. Furthermore, compared with the high-performance ~1-μm VJ-SLDs, this novel device exhibits a comparable output power and 3-dB bandwidth performance with a more stable electroluminescence spectrum, which varies only negligibly under a wide range of bias current.

Large-amplitude coherent spin waves excited by spin-polarized current in nanoscale spin valves

We present spectral measurements of spin-wave excitations driven by direct spinpolarized current in the free layer of nanoscale Ir20Mn80/Ni80Fe20/Cu/Ni80Fe20 spin valves. The measurements reveal that large-amplitude coherent spin wave modes are excited over a wide range of bias current. The frequency of these excitations exhibits a series of jumps as a function of current due to transitions between different localized nonlinear spin wave modes of the Ni80Fe20 nanomagnet. We find that micromagnetic simulations employing the Landau-Lifshitz-Gilbert equation of motion augmented by the Slonczewski spin torque term (LLGS) accurately describe the frequency of the current-driven excitations including the mode transition behavior. However LLGS simulations give qualitatively incorrect predictions for the amplitude of excited spin waves as a function of current.

Vertical-cavity surface-emitting lasers (VCSELs) with high-power and single-spot far-field distributions at 850-nm wavelength by use of petal-shaped light-emitting apertures

In this letter, we demonstrate a vertical-cavity surface-emitting laser (VCSEL) with a petal-shaped light-emitting aperture, which is realized by the Zn-diffusion technique, at a wavelength of 850 nm. The demonstrated device behaves like a two-dimensional VCSEL array and each light-emitting unit can have high coherence of in-phase lasing to form a near fundamental supermode emission. The measured far-field distributions of such a device exhibit single-lobe (spot), high-power (>7.5 mW), and narrow divergence angle (~6deg) performance under a wide range of bias current. The ratio of in-phase lasing mode to total lasing modes, which include isolated single mode, in-phase, and out-of-phase modes, has also been analyzed by the measured far-field distributions and the theoretically calculated patterns

Electrical noise of laser diodes measured over a wide range of bias currents

The electrical noise of commercially available laser diodes, an index guided AlGaInP diode lasing at 635 nm (SDL3038-11) and an InGaAlP-multiquantum well diode lasing at 670 nm (SVL71B), has been investigated over a wide current range of six orders of magnitude. After increasing proportionally with current at small currents (10 nA to 10 μA), the 1/ f noise tends to saturate with increasing current in the range from 10 to 100 μA. For larger operating currents, the 1/ f noise increases again, and with the current proportional to I 2. Different noise sources were discovered below the lasing threshold current. The electrical noise at lower currents must be measured to assess the degradation of the active region of the laser diode.

Suppression of second harmonic distortion in directlymodulateddistributed feedback lasers by external light injection

The suppression of second harmonic distortion in directly modulated semiconductor distributed feedback lasers by optical injection locking has been experimentally demonstrated. Reduction of second harmonic distortion by more than 10 dB has been observed over a wide range of bias currents and modulation frequencies.

Linear arrays of Josephson junctions: A stability analysis of characteristic modes

We have performed a linear stability analysis of two arrays of resistively shunted Josephson junctions: a ladder array and a so-called modified linear array. We find the periodic solutions to be linearly stable for a wide range of bias currents in the absence of a load. This is contrasted with the well-studied globally coupled linear array, where stability of the periodic solutions is a sensitive function of bias current and load parameters. For the ladder array, we have studied the nature of the mesh currents for the different decay modes. Numerical evidence leads us to conclude that the branches of the ladder parallel to the bias current play an important role in helping to damp out perturbed currents. We also compare the long-time dynamics of these Josephson-junction arrays with that of an RL network, which is a ladder of resistors and inductors, and for which the decay rates and mesh currents are calculated exactly. We find that at long times the dynamics of all three arrays are basically identical.

A SQUID gradiometer with trimmable additional positive feedback

A SQUID gradiometer with a glass package and trimmable additional positive feedback (APF) is developed to achieve a low equivalent flux noise over a wide range of bias current. The noise characteristics of a SQUID with APF are investigated by varying the APF gain and the bias current. We found the most suitable APF parameter to achieve low equivalent flux noise over a wide range of bias current. When a SQUID with APF has a co-planar first-order coil whose effective area is , a typical gradiometer noise level of at 100 Hz and at 1 Hz is achieved.

Multiple routes for vortex depinning in amorphous thin film superconductors

ffWe present simulations of vortex dynamics in amorphous two-dimensional thin film superconductors, using a new exact method to evaluate long range interactions between vortices. We find that the onset of vortex motion is dominated by filamentary channels of flow. There are multiple patterns of filamentary flow which are stable in a wide range of bias current. As a consequence, there are multiple steps in the differential resistance, each step corresponding to a different pattern of filamentary flow. This results in a strong history dependence of the depinning current and current voltage characteristics. Our results are in agreement with recent experiments on amorphous Mo{sub 77}Ge{sub 23} thin films.

Granular-aluminum superconducting detector for 6 keV X-rays and 2.2 MeV beta sources

A 2 μm wide superconducting strip of granular aluminum was used to detect the superconducting to normal transitions induced by the absorption of 55Fe, 6 keV X-rays or the passage of electrons from a 90Sr, 2.2 MeV beta source. The count-rate for X-rays reaches almost 70% efficiency over a wide range of bias currents, confirming the potential application for high-spatial-resolution X-ray detectors. We report the first evidence of switching by a 2.2 MeV beta source which emits electrons in the minimum-ionizing range. However, the inability to distinguish between transitions caused by minimum-ionizing electrons and those caused by lower energy, more heavily ionizing electrons emitted by the source, prevented us from demonstrating the full sensitivity of the granular aluminum detector to minimum-ionizing radiation. The switching threshold for X-rays depends on thermal propagation of a normal region which bridges the film width, and a numerical simulation is presented, the simple formulation of which allows extrapolation to other materials and temperatures. The very fast rise-time voltages are accurately described by a thermal propagation model.

Practical 2-dimensional bipolar-transistor-analysis algorithm

Extensions to a 2-dimensional bipolar-transistor-modelling algorithm are described. They enable practical high-frequency silicon devices to be analysed in a time appreciably shorter than previously reported schemes. This allows device properties to be economically explored over a wide range of bias currents and voltages.