Browsing by Subject "Noise"

Now showing 1 - 12 of 12

Open Access
Analysis of the generation of amplitude-squeezed light with Gaussian-beam degenerate optical parametric amplifiers
(OSA Publishing, 2001-06) Köprülü, K. G.; Aytür, O.
We investigate the generation of amplitude-squeezed states with degenerate optical parametric amplifiers that are pumped by focused Gaussian beams. We present a model that facilitates the calculation of the squeezing level for an experimentally realistic cofiguration in which there is a Gaussian input signal beam that has the same confocal parameter and waist location as the Gaussian pump beam, with no restriction on the interaction length-to-confocal parameter ratio. We show that the 3-dB squeezing limit that was thought to be imposed by the Gaussian pump profile can be exceeded in the (previously uninvestigated) tight-focusing regime. We find the maximum possible amplitude squeezing in this regime to be 4.65 dB. However, it is possible to increase the squeezing level further by spatially filtering the tails of the output signal beam, resulting in squeezing levels in excess of 10 dB. (C) 2001 Optical Society of America.
Open Access
Broadband GaN LNA MMIC development with the micro/nano process development by kink-effect in S22 consideration
(2021-01) Osmanoğlu, Sinan
Broadband low noise ampliﬁers (LNA) are one of the key components of the nu-merous applications such as communication, electronic warfare, and radar. The requirements for higher bandwidth, higher speed, higher survivability, higher re-liability, etc. pushes the technological boundaries. The demand for high per-formance circuit components without a compromise stimulates the utilization of the high-end gallium nitride (GaN) technology to develop better monolithic microwave integrated circuits (MMIC) in a smaller footprint. To support the progress, the development of a proper GaN high electron mobility transistor (HEMT) technology and proper circuit models have become critical. To support the eﬀorts and contribute to the progress, a 0.25 µm microstrip (MS) GaN HEMT technology is developed in Bilkent University Nanotechnology Research Center (NANOTAM). The technology development yields that the MS GaN HEMT tech-nology is capable of supporting ≥4.4 W/mm output power (POUT ), ≥50% power added eﬃciency (PAE), ≥15 dB gain, and ∼1 dB noise ﬁgure (NF ) at 10 GHz. Moreover, the gate structure of the technology is studied by evaluating the kink-eﬀect (KE) in the output reﬂection coeﬃcient (S22) of a HEMT to support the broadband operation. Besides the technology development, the small-signal (SS) and noise equivalent circuit models are studied, and the developed models present high convergence with the measurements. The accuracy of the models contributes to development of the cascode HEMT based LNAs even without fabricating the cascode HEMT. Furthermore, the developed models and the proper gate struc-ture are used to develop the broadband quad-ﬂat no-leads (QFN) packaged GaN LNA MMIC for the mobile radio communications, the military radar, and the commercial radar applications. The results of the circuit models and the GaN LNA MMIC also yield that the developed MS GaN HEMT technology is capable for developing diﬀerent solutions up to 18 GHz.
Open Access
High-power-high-repetition-rate-single-mode Er-Yb-doped fiber laser system
(Optical Society of America, 2012) Pavlov, I.; Ilbey, E.; Dulgergil, E.; Bayri, A.; Ilday, F. O.
We demonstrate an all-fiber-integrated, high-power chirped-pulse-amplification system operating at 1550 nm. The seed source is a soliton fiber laser with 156 MHz repetition rate. Two-stage single mode amplifier provides an amplification of more than 40 dB without significant spontaneous amplified emission. The power amplifier is based on cladding-pumped 10 mu m-core Er-Yb co-doped fiber, the output of which was spliced into standard singlemode fiber. We obtain 10 W average power in a strictly singlemode operation. After dechirping with a grating compressor, near transform-limited, 450 fs-long pulses are obtained. The laser source exhibits excellent short and long-term intensity stability, with relative intensity noise measurements characterizing the short-term stability. (C) 2012 Optical Society of America
Open Access
Junction characteristics and magnetic field dependencies of low noise step edge junction Rf-SQUIDs for unshielded applications
(IEEE, 2003-06) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Bozbey, Ali; Bick, M.; Banzet, M.; Lomparski, D.; Zander, W.; Zhang, Y.; Krause, H-J.
Step edge grain boundary (GB) junctions and rf-SQUIDs have been made using pulsed laser deposited Y-Ba-Cu-O films on crystalline LaAlO3 substrates. The steps were developed using various ion-beam etching processes resulting in sharp and ramp type step structures. Sharp step based GB junctions showed behavior of serial junctions with resistively shunted junction (RSJ)-like I-V characteristics. The ramped type step structures resulted in relatively high critical current, Ic, junctions and noisy SQUIDs. The sharp steps resulted in low noise rf-SQUIDs with a noise level below 140 fT/Hz12/ down to few Hz at 77 K while measured with conventional tank circuits. The Ic of the junctions and hence the operating temperature range of the SQUIDs made using sharp steps was controlled by both the step height and the junction widths. The junction properties of the SQUIDs were also characterized showing RSJ-like characteristics and magnetic field sensitivities correlated to that of the SQUIDs. Two major low and high background magnetic field sensitivities have been observed for our step edge junctions and the SQUIDs made on sharp steps. High quality step edge junctions with low magnetic field sensitivities made on clean sharp steps resulted in low 1/f noise rf-SQUIDs proper for applications in unshielded environment.
Open Access
Noise on noise
(Routledge, 2006) Aracagök, Zafer
[No abstract available]
Open Access
Noise problem in primary schools in Ankara
(1994) Özüpek, Ayşegül
In this study, the problem of noise in primary schools is examined, by indicating the negative effects of this problem on the physiological, psychological, and social well-being of human beings, and on the effectiveness of teaching and learning process. By proving the excessive noise levels in primary schools in Ankara, it is aimed that, to take attentions of specialists to the subject of noise, and to make them consider this problem in the planning of new schools and in the renovation process of older school buildings.
Open Access
Noise, junction characteristics, and magnetic field dependencies of bicrystal grain boundary junction Rf-SQUIDs
(IEEE, 2003) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Bick, M.; Banzet, M.; Zander, W.; Zhang, Y.; Krause, H-J.
Bicrystal grain boundary (GB) Josephson junctions and rf-SQUID's were made of 200 nm thick PLD YBCO films on bi-crystal SrTiO3 substrates. The junction characteristics were studied to investigate optimal parameters in the rf-SQUID) layout designs and the limits imposed by the technology. The I c of 3 to 8 μm wide test junctions scaled with the junction widths, showing clear linear RSJ-like I-V characteristics at 77 K. All the junctions showed hysteretic RCSJ-like behavior at very low temperatures. Classical Josephson flux motion type (long junction) nonlinearity in I-V curves of all the junctions was also observed at lower temperatures with systematic dependence on the junction widths. Measurements of the magnetic field dependence of the Ic of the junctions resulted in junction width dependent well-defined Fraunhofer-pattern like characteristics. The obtained characteristics of the junctions led to feasible criteria for the rf-SQUID layouts with desired device characteristics. Rf-SQUID's were made using designs for optimal performance at 77 K while avoiding large superconducting weak links across the substrate GB. Devices with low noise characteristics and junction field sensitivities proper for operation in environmental background magnetic fields were obtained. A nonsystematic spread of optimal working temperature of the SQUID's were also observed which is associated to the spread of the junction parameters caused by the defects at the GB of substrates.
Open Access
Numerical analysis of multidomain systems: coupled nonlinear PDEs and DAEs with noise
(Institute of Electrical and Electronics Engineers, 2018) Demir, A.; Hanay, Selim
We present a numerical modeling and simulation paradigm for multidomain, multiphysics systems with components modeled both in a lumped and distributed manner. The lumped components are modeled with a system of differential-Algebraic equations (DAEs), whereas the possibly nonlinear distributed components that may belong to different physical domains are modeled using partial differential equations (PDEs) with associated boundary conditions. We address a comprehensive suite of problems for nonlinear coupled DAE-PDE systems including 1) transient simulation; 2) periodic steady-state (PSS) analysis formulated as a mixed boundary value problem that is solved with a hierarchical spectral collocation technique based on a joint Fourier-Chebyshev representation, for both forced and autonomous systems; 3) Floquet theory and analysis for coupled linear periodically time-varying DAE-PDE systems; 4) phase noise analysis for multidomain oscillators; and 5) efficient parameter sweeps for PSS and noise analyses based on first-order and pseudo-Arclength continuation schemes. All of these techniques, implemented in a prototype simulator, are applied to a substantial case study: A multidomain feedback oscillator composed of distributed and lumped components in two physical domains, namely, a nano-mechanical beam resonator operating in the nonlinear regime, an electrical delay line, an electronic amplifier and a sensor-Actuator for the transduction between the two physical domains.
Open Access
Online learning under adverse settings
(2015-05) Özkan, Hüseyin
We present novel solutions for contemporary real life applications that generate data at unforeseen rates in unpredictable forms including non-stationarity, corruptions, missing/mixed attributes and high dimensionality. In particular, we introduce novel algorithms for online learning, where the observations are received sequentially and processed only once without being stored, under adverse settings: i) no or limited assumptions can be made about the data source, ii) the observations can be corrupted and iii) the data is to be processed at extremely fast rates. The introduced algorithms are highly effective and efficient with strong mathematical guarantees; and are shown, through the presented comprehensive real life experiments, to significantly outperform the competitors under such adverse conditions. We develop a novel highly dynamical ensemble method without any stochastic assumptions on the data source. The presented method is asymptotically guaranteed to perform as well as, i.e., competitive against, the best expert in the ensemble, where the competitor, i.e., the best expert, itself is also specifically designed to continuously improve over time in a completely data adaptive manner. In addition, our algorithm achieves a significantly superior modeling power (hence, a significantly superior prediction performance) through a hierarchical and self-organizing approach while mitigating over training issues by combining (taking finite unions of) low-complexity methods. On the contrary, the state-of-the-art ensemble techniques are heavily dependent on static and unstructured expert ensembles. In this regard, we rigorously solve the resulting issues such as the over sensitivity to source statistics as well as the incompatibility between the modeling power and the computational load/precision. Our results uniformly hold for every possible input stream in the deterministic sense regardless of the stationary or non-stationary source statistics. Furthermore, we directly address the data corruptions by developing novel versatile imputation methods and thoroughly demonstrate that the anomaly detection -in addition to being stand alone an important learning problem- is extremely effective for corruption detection/imputation purposes. To that end, as the first time in the literature, we develop the online implementation of the Neyman-Pearson characterization for anomalies in stationary or non-stationary fast streaming temporal data. The introduced anomaly detection algorithm maximizes the detection power at a specified controllable constant false alarm rate with no parameter tuning in a truly online manner. Our algorithms can process any streaming data at extremely fast rates without requiring a training phase or a priori information while bearing strong performance guarantees. Through extensive experiments over real/synthetic benchmark data sets, we also show that our algorithms significantly outperform the state-of-the-art as well as the most recently proposed techniques in the literature with remarkable adaptation capabilities to non-stationarity.
Open Access
Optimal channel switching for average capacity maximization
(IEEE, 2014-05) Sezer, Ahmet Dündar; Gezici, Sinan; İnaltekin, H.
Optimal channel switching is proposed for average capacity maximization in the presence of average and peak power constraints. A necessary and sufficient condition is derived in order to determine when the proposed optimal channel switching approach can or cannot outperform the optimal single channel approach, which performs no channel switching. Also, it is stated that the optimal channel switching solution can be realized by channel switching between at most two different channels. In addition, a low-complexity optimization problem is derived in order to obtain the optimal channel switching solution. Numerical examples are provided to exemplify the derived theoretical results. © 2014 IEEE.
Open Access
Parametric power spectral density analysis of noise from instrumentation in MALDI TOF mass spectrometry
(2007) Shin H.; Mutlu, M.; Koomen J.M.; Markey, M.K.
Noise in mass spectrometry can interfere with identification of the biochemical substances in the sample. For example, the electric motors and circuits inside the mass spectrometer or in nearby equipment generate random noise that may distort the true shape of mass spectra. This paper presents a stochastic signal processing approach to analyzing noise from electrical noise sources (i.e., noise from instrumentation) in MALDI TOF mass spectrometry. Noise from instrumentation was hypothesized to be a mixture of thermal noise, 1/f noise, and electric or magnetic interference in the instrument. Parametric power spectral density estimation was conducted to derive the power distribution of noise from instrumentation with respect to frequencies. As expected, the experimental results show that noise from instrumentation contains 1/f noise and prominent periodic components in addition to thermal noise. These periodic components imply that the mass spectrometers used in this study may not be completely shielded from the internal or external electrical noise sources. However, according to a simulation study of human plasma mass spectra, noise from instrumentation does not seem to affect mass spectra significantly. In conclusion, analysis of noise from instrumentation using stochastic signal processing here provides an intuitive perspective on how to quantify noise in mass spectrometry through spectral modeling.
Open Access
Role of the environmental spectrum in the decoherence and dephasing of multilevel quantum systems
(The American Physical Society, 2005) Hakioǧlu T.; Savran, K.
We examine the effect of multilevels on decoherence and dephasing properties of a quantum system consisting of a nonideal two level subspace, identified as the qubit, and a finite set of higher energy levels above this qubit subspace. The whole system is under interaction with an environmental bath through a Caldeira-Leggett type coupling. The model that we use is an rf-SQUID under macroscopic quantum coherence and coupled inductively to a flux noise characterized by an environmental spectrum. The model interaction can generate dipole couplings which can be appreciable between the qubit and the high levels. The decoherence properties of the qubit subspace is examined numerically using the master equation formalism of the system's reduced density matrix. We calculate the relaxation and dephasing times as the spectral parameters of the environment are varied. We observe that, these calculated time scales receive contribution from all available frequencies in the noise spectrum (even well above the system's resonant frequency scales) stressing the dominant role played by the nonresonant transitions. The relaxation and dephasing and the leakage times thus calculated, strongly depend on the appreciably interacting levels determined by the strength of the dipole coupling. Under the influence of these nonresonant and multilevel effects, the validity of the two level approximation is dictated not by the low temperature as conveniently believed, but by these multilevel dipole couplings as well as the availability of the environmental modes.