9,267 research outputs found
Nd:YAG development for spaceborne laser ranging system
The results of the development of a unique modelocked laser device to be utilized in future NASA space-based, ultraprecision laser ranger systems are summarized. The engineering breadboard constructed proved the feasibility of the pump-pulsed, actively modelocked, PTM Q-switched Nd:YAG laser concept for the generation of subnanosecond pulses suitable for ultra-precision ranging. The laser breadboard also included a double-pass Nd:YAG amplifier and provision for a Type II KD*P frequency doubler. The specific technical accomplishment was the generation of single 150 psec, 20-mJ pulses at 10 pps at a wavelength of 1.064 micrometers with 25 dB suppression of pre-and post-pulses
A 90 nm CMOS 16 Gb/s Transceiver for Optical Interconnects
Interconnect architectures which leverage high-bandwidth optical channels offer a promising solution to address the increasing chip-to-chip I/O bandwidth demands. This paper describes a dense, high-speed, and low-power CMOS optical interconnect transceiver architecture. Vertical-cavity surface-emitting laser (VCSEL) data rate is extended for a given average current and corresponding reliability level with a four-tap current summing FIR transmitter. A low-voltage integrating and double-sampling optical receiver front-end provides adequate sensitivity in a power efficient manner by avoiding linear high-gain elements common in conventional transimpedance-amplifier (TIA) receivers. Clock recovery is performed with a dual-loop architecture which employs baud-rate phase detection and feedback interpolation to achieve reduced power consumption, while high-precision phase spacing is ensured at both the transmitter and receiver through adjustable delay clock buffers. A prototype chip fabricated in 1 V 90 nm CMOS achieves 16 Gb/s operation while consuming 129 mW and occupying 0.105 mm^2
Metodologia Per la Caratterizzazione di amplificatori a basso rumore per UMTS
In questo lavoro si presenta una metodologia di
progettazione elettronica a livello di sistema,
affrontando il problema della caratterizzazione dello spazio di progetto dell' amplificatore a basso rumore costituente il primo stadio di un front end a conversione diretta per UMTS realizzato in tecnologia CMOS con lunghezza di canale .18u. La metodologia è sviluppata al fine di valutare in modo quantititativo le specifiche ottime di sistema per il front-end stesso e si basa sul concetto di Piattaforma Analogica, che prevede la costruzione di un modello di prestazioni per il blocco analogico basato su
campionamento statistico di indici di prestazioni del blocco stesso, misurati tramite simulazione di dimensionamenti dei componenti attivi e passivi soddisfacenti un set di equazioni specifico della topologia circuitale. Gli indici di prestazioni vengono successivamente ulizzati per parametrizzare modelli comportamentali utilizzati nelle fasi di ottimizzazione a livello di sistema. Modelli comportamentali atti a rappresentare i sistemi RF sono stati pertanto studiati per ottimizzare la scelta delle metriche di prestazioni. L'ottimizzazione dei set di
equazioni atti a selezionare le configurazione di
interesse per il campionamento ha al tempo stesso richiesto l'approfondimento dei modelli di dispositivi attivi validi in tutte le regioni di funzionamento, e lo studio dettagliato della progettazione degli amplificatori a basso rumore basati su degenerazione induttiva. Inoltre,
il problema della modellizzazione a livello di sistema degli effetti della comunicazione tra LNA e Mixer è stato affrontato proponendo e analizzando diverse soluzioni. Il lavoro ha permesso di condurre un'ottimizzazione del front-end UMTS, giungendo a specifiche ottime a livello di sistema per l'amplificatore stesso
Development of an image converter of radical design
A long term investigation of thin film sensors, monolithic photo-field effect transistors, and epitaxially diffused phototransistors and photodiodes to meet requirements to produce acceptable all solid state, electronically scanned imaging system, led to the production of an advanced engineering model camera which employs a 200,000 element phototransistor array (organized in a matrix of 400 rows by 500 columns) to secure resolution comparable to commercial television. The full investigation is described for the period July 1962 through July 1972, and covers the following broad topics in detail: (1) sensor monoliths; (2) fabrication technology; (3) functional theory; (4) system methodology; and (5) deployment profile. A summary of the work and conclusions are given, along with extensive schematic diagrams of the final solid state imaging system product
Quantum shot noise in mesoscopic superconductor-semiconductor heterostructures
Shot noise in a mesoscopic electrical conductor have become one of the most attentiondrawing
subject over the last decade. This is because the shot-noise measurements
provide a powerful tool to study charge transport in mesoscopic systems [1]. While
conventional resistance measurements yield information on the average probability
for the transmission of electrons from source to drain, shot-noise provides additional
information on the electron transfer process, which can not be obtained from resistance
measurements. For example, one can determine the charge ‘q’ of the current
carrying quasi-particles in different systems from the Poisson shot noise SI = 2q�I� [2] where �I� is the mean current of the system. For instance, the quasi-particle
charge is a fraction of the electron charge ‘e’ in the fractional quantum Hall regime
[3, 4, 5]. The multiple charge quanta were observed in an atomic point contact
between two superconducting electrodes [6].
Shot-noise also provides information on the statistics of the electron transfer.
Shot noise in general is suppressed from its classical value SI = 2e�I�, due to the
correlations. In mesoscopic conductors, due to the Pauli principle in fermion statistics,
electrons are highly correlated. As a results, the noise is fully suppressed in the
limit of a perfect open channel T = 1. For the opposite limit of low transmission
T � 1, transmission of electron follows a Poisson process and recovers the Schottky
result SI = 2e�I� [2]. For many channel systems, shot-noise is suppressed to
1/2 × 2e�I� for a symmetric double barrier junction [7, 8], to 1/3 in a disordered
wire [9, 10, 11, 12, 13, 14] and to 1/4 in an open chaotic cavity [15, 16, 17].
When a superconductor is involved, the shot-noise can be enhanced by virtue
of the Andreev reflection process taking place at the interface between a normal
metal and a superconductor. In some limiting cases, e.g. in the tunneling and
disordered limit, the shot-noise can be doubled with respect to its normal state
value [18, 19, 20, 21]. One of the main results of this thesis is an extensive comparison
of our experimental data on conductance and shot noise measurements in a S-N
junction with various theoretical models.
In addition to measure shot-noise in a two-terminal geometry, one can also perform
the fluctuation measurements on multi-terminal conductors. Whereas shotnoise corresponds to the autocorrelation of fluctuations from the same leads, crosscorrelation
measurements of fluctuations between different leads provide a wealth of
new experiments. For example, the exchange-correlations can be measured directly
from these geometry [22]. Experimental attempt in mesoscopic electronic device was
the correlation measurements [14, 23] on electron beam-splitter geometry [24] which
is the analogue to the Hanbury-Brown Twiss (HBT) experiment in optics. In their
experiment, Hanbury-Brown and Twiss demonstrated the intensity-intensity correlations
of the light of a star in order to determine its diameter [25]. They measured
a positive correlations between two different output photon beams as predicted to
the particles obeying Bose-Einstein statistics. This behavior is often called ‘bunching’.
On the other hand, a stream of the particles obeying Fermi-Dirac statistics
is expected to show a anti-bunching behavior, resulting in a negative correlation of
the intensity fluctuations. Latter one was confirmed by a Fermionic version of HBT
experiments in single-mode, high-mobility semiconductor 2DEG systems [14, 23].
Whereas in a single electron picture, correlations between Fermions are always
negative1 (anti-bunching), the correlation signal is expected to become positive if
two electrons are injected simultaneously to two arms and leave the device through
different leads for the coincident detection in both outputs2. One simple example is
the splitting of the cooper pair in a Y-junction geometry in front of the superconductor.
Fig.1.1 shows the possible experimental scheme of the correlation measurement
as described here and the sample realized in an high-mobility semiconductor heterostructures.
Since all three experiments were done3, only one left unfolded, ‘The
positive correlations from the Fermionic system’. The main motivation of this thesis
work was to find a positive correlations in the device shown in Fig.1.1. In a
well defined single channel collision experiment on an electron beam splitter, it has
theoretically been shown that the measured correlations are sensitive to the spin
entanglement [29, 30]. This is another even more exciting issue and we would like
to mention that the experimental quest for positive correlations is important for the
new field of quantum computation and communication in the solid state, [31, 32]
in which entangled electrons play a crucial role. A natural source of entanglement
is found in superconductors in which electrons are paired in a spin-singlet
state. A source of entangled electrons may therefore be based on a superconducting
injector.[33, 34, 27, 35, 36, 37, 38, 38, 39, 40, 41] Even more so, an electronic beamsplitter
is capable of distinguishing entangled electrons from single electrons.[29, 42]
However, the positive correlations have not been observed in solid-state mesoscopic
devices until today. This thesis is organized as follows. Chapter 2 is devoted to the theoretical
background of the electrical transport and the current fluctuations. We introduce
the basic concept of electrical transport and the shot noise in normal state and
superconductor-normal metal (S-N) junction. We also briefly review the theoretical
proposals and arguments about the current-current cross-correlations in threeterminal
systems. In Chapter 3, we describe the sample fabrication techniques which
have been done in our laboratory such as e-beam lithography, metallization and etching.
We present also the characterization of our particular system, niobium (Nb) /
InAs-based 2DEG junction. Chapter 4 describes the reliable low-temperature measurement
technique for detecting the noise. We characterize our measurement setup
using a simple RC-circuit model. In Chapter 5, our main results about the shot
noise of S-N junction are presented in detail
Model for self-consistent analysis of arbitrary MQW structures
Self-consistent computations of the potential profile in complex
semiconductor heterostructures can be successfully applied for comprehensive
simulation of the gain and the absorption spectra, for the analysis of the
capture, escape, tunneling, recombination, and relaxation phenomena and as a
consequence it can be used for studying dynamical behavior of semiconductor
lasers and amplifiers. However, many authors use non-entirely correct ways for
the application of the method. In this paper the versatile model is proposed
for the investigation, optimization, and the control of parameters of the
semiconductor lasers and optical amplifiers which may be employed for the
creation of new generations of the high-density photonic systems for the
information processing and data transfer, follower and security arrangements.
The model is based on the coupled Schredinger, Poisson and drift-diffusion
equations which allow to determine energy quantization levels and wave
functions of charge carriers, take into account built-in fields, and to
investigate doped MQW structures and those under external electric fields
influence. In the paper the methodology of computer realization based on our
model is described. Boundary conditions for each equation and consideration of
the convergence for the method are included. Frequently encountered in practice
approaches and errors of self-consistent computations are described. Domains of
applicability of the main approaches are estimated. Application examples of the
method are given. Some of regularities of the results which were discovered by
using self-consistent method are discussed. Design recommendations for
structure optimization in respect to managing some parameters of AMQW
structures are given.Comment: 12 pages, 2 table, 4 figures, Optics East Symposium, Conference on
Physics and Applications of Optoelectronic Devices, October 25-28, 2004,
Philadelphia, Pennsylvania, US
Development of nine-channel 10-micrometer (Hg, Cd)Te pushbroom IR/CCD system
The engineering development of the 9-channel detector array is documented. The development of the array demonstrates the feasibility of a self scanned multi-element infrared detector focal plane. Procedures for operating the array are outlined
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