25,562 research outputs found
Semiconductor optical amplifiers: performance and applications in optical packet switching [Invited]
Semiconductor optical amplifiers (SOAs) are a versatile core technology and the basis for the implementation of a number of key functionalities central to the evolution of highly wavelength-agile all-optical networks. We present an overview of the state of the art of SOAs and summarize a range of applications such as power boosters, preamplifiers, optical linear (gain-clamped) amplifiers, optical gates, and modules based on the hybrid integration of SOAs to yield high-level functionalities such as all-optical wavelength converters/regenerators and small space switching matrices. Their use in a number of proposed optical packet switching situations is also highlighted
The Measurement of AM noise of Oscillators
The close-in AM noise is often neglected, under the assumption that it is a
minor problem as compared to phase noise. With the progress of technology and
of experimental science, this assumption is no longer true. Yet, information in
the literature is scarce or absent. This report describes the measurement of
the AM noise of rf/microwave sources in terms of Salpha(f), i.e., the power
spectrum density of the fractional amplitude fluctuation alpha. The proposed
schemes make use of commercial power detectors based on Schottky and tunnel
diodes, in single-channel and correlation configuration. There follow the
analysis of the front-end amplifier at the detector output, the analysis of the
methods for the measurement of the power-detector noise, and a digression about
the calibration procedures. The measurement methods are extended to the
relative intensity noise (RIN) of optical beams, and to the AM noise of the
rf/microwave modulation in photonic systems. Some rf/microwave synthesizers and
oscillators have been measured, using correlation and moderate averaging. As an
example, the flicker noise of a low-noise quartz oscillator (Wenzel 501-04623E)
is Salpha = 1.15E-13/f, which is equivalent to an Allan deviation of
sigma_alpha = 4E-7. The measurement systems described exhibit the world-record
lowest background noise.Comment: 39 pages, 22 figures, 8 tables, 21 references, list of symbol
Ultimate on-chip quantum amplifier
We report amplification of electromagnetic waves by a single artificial atom
in open 1D space. Our three-level artificial atom -- a superconducting quantum
circuit -- coupled to a transmission line presents an analog of a natural atom
in open space. The system is the most fundamental quantum amplifier whose gain
is limited by a spontaneous emission mechanism. The noise performance is
determined by the quantum noise revealed in the spectrum of spontaneous
emission, also characterized in our experiments.Comment: 4 pages, 4 figures + supplemenntary materials accepted for
publication in Phys. Rev. Lett
Microwave amplification with nanomechanical resonators
Sensitive measurement of electrical signals is at the heart of modern science
and technology. According to quantum mechanics, any detector or amplifier is
required to add a certain amount of noise to the signal, equaling at best the
energy of quantum fluctuations. The quantum limit of added noise has nearly
been reached with superconducting devices which take advantage of
nonlinearities in Josephson junctions. Here, we introduce a new paradigm of
amplification of microwave signals with the help of a mechanical oscillator. By
relying on the radiation pressure force on a nanomechanical resonator, we
provide an experimental demonstration and an analytical description of how the
injection of microwaves induces coherent stimulated emission and signal
amplification. This scheme, based on two linear oscillators, has the advantage
of being conceptually and practically simpler than the Josephson junction
devices, and, at the same time, has a high potential to reach quantum limited
operation. With a measured signal amplification of 25 decibels and the addition
of 20 quanta of noise, we anticipate near quantum-limited mechanical microwave
amplification is feasible in various applications involving integrated
electrical circuits.Comment: Main text + supplementary information. 14 pages, 3 figures (main
text), 18 pages, 6 figures (supplementary information
Theory Based on Device Current Clipping to Explain and Predict Performance Including Distortion of Power Amplifiers for Wireless Communication Systems
Power amplifiers are critical components in wireless communication systems
that need to have high efficiency, in order to conserve battery life and minimise heat
generation, and at the same time low distortion, in order to prevent increase of bit
error rate due to constellation errors and adjacent channel interference. This thesis is
aimed at meeting a need for greater understanding of distortion generated by power
amplifiers of any technology, in order to help designers manage better the trade-off
between obtaining high efficiency and low distortion. The theory proposed in this
thesis to explain and predict the performance of power amplifiers, including distortion,
is based on analysis of clipping of the power amplifier device current, and it is a
major extension of previous clipping analyses, that introduces many key definitions
and concepts. Distortion and other power amplifier metrics are determined in the form
of 3-D surfaces that are plotted against PA class, which is determined by bias voltage,
and input signal power level. It is shown that the surface of distortion exhibits very
high levels due to clipping in the region where efficiency is high. This area of high
distortion is intersected by a valley that is ‘L’-shaped. The 'L'-shaped valley is subject
to a rotation that depends on the softness of the cut-off of the power amplifier device
transfer characteristic. The distortion surface with rotated 'L'-shaped valley leads to
predicted curves for distortion versus input signal power that match published
measured curves for power amplifiers even using very simple device models. The
distortion versus input signal power curves have types that are independent of
technology. In class C, there is a single deep null. In the class AB range, that is
divided into three sub-ranges, there may be two deep nulls (sub-range AB(B)), a
ledge (sub-range AB(A)) or a shallow null with varying depth (sub-range AB(AB))
IUS/payload communication system simulator configuration definition study
The requirements and specifications for a general purpose payload communications system simulator to be used to emulate those communications system portions of NASA and DOD payloads/spacecraft that will in the future be carried into earth orbit by the shuttle are discussed. For the purpose of on-orbit checkout, the shuttle is required to communicate with the payloads while they are physically located within the shuttle bay (attached) and within a range of 20 miles from the shuttle after they have been deployed (detached). Many of the payloads are also under development (and many have yet to be defined), actual payload communication hardware will not be available within the time frame during which the avionic hardware tests will be conducted. Thus, a flexible payload communication system simulator is required
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