Communication over a waveform channel corrupted by additive white Gaussian noise and by an unknown and arbitrary interference of bounded power is considered, For this channel, an upper bound is presented for the worst...
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Communication over a waveform channel corrupted by additive white Gaussian noise and by an unknown and arbitrary interference of bounded power is considered, For this channel, an upper bound is presented for the worst-case error probability of a communication system comprising a direct-sequence spread spectrum modulator and a nonlinear correlation receiver. It is shown that this bound is exponentially tight as the number of chips used in the modulator becomes large, This bound is evaluated for several detector nonlinearities. Numerical examples and comparisons to the performance of a pure Gaussian noise channel are also given.
We investigate the dispersion-related amplification induced by two counterpropagating waves in a nonlinear fiber and demonstrate that this system can provide broadband (of the order of terahertz) and large (> 10(5)...
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We investigate the dispersion-related amplification induced by two counterpropagating waves in a nonlinear fiber and demonstrate that this system can provide broadband (of the order of terahertz) and large (> 10(5)) amplification even in the presence of absorption, with the pumping significantly below the threshold of instability.
It is demonstrated theoretically that the optical rectification and difference-frequency generation of nonlinear coefficients that are known to exist in asymmetric quantum wells for certain directions of growth do not...
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It is demonstrated theoretically that the optical rectification and difference-frequency generation of nonlinear coefficients that are known to exist in asymmetric quantum wells for certain directions of growth do not vanish even in symmetric quantum wells. The dispersion and anisotropy of the optical rectification coefficient are evaluated, and their magnitude is found to be 1 order larger than for the bulk zinc blende materials. This dramatic change is shown to be caused by the liking of the valence band degeneracy. Practical applications for generating terahertz radiation are considered. (C) 1996 Optical Society of America.
Recently, M. Kelemen (IEEE Trans. Automat. Contr., ***-31, 766-768, Aug. 1986) presented a stability result that deals with the response of a nonlinear system to slowly varying input signals. In this work a proof is g...
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Recently, M. Kelemen (IEEE Trans. Automat. Contr., ***-31, 766-768, Aug. 1986) presented a stability result that deals with the response of a nonlinear system to slowly varying input signals. In this work a proof is given, under a weaker hypothesis on the input signal, by constructing a Lyapunov function that is standard in the control literature. This proof may be more accessible than the other approaches. For completeness, brief proofs of some intermediate results that are regarded as well known are included. A simple example is given to show that this approach can yield explicit bounds in certain situations of interest.
Higher-order effects in femtosecond-pulse propagation in optical fibers are examined. In particular, the specific contributions to nonlinear chirping in the fiber by the higher-order cubic dispersion term and by the s...
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Higher-order effects in femtosecond-pulse propagation in optical fibers are examined. In particular, the specific contributions to nonlinear chirping in the fiber by the higher-order cubic dispersion term and by the shock term are investigated. The effects on the output spectrum of fiber input pulses having an initial chirp and an initial asymmetric pulse shape are also investigated. By comparison to a global description, it is shown that, for optical pulses having reasonable power levels, dispersion effects can be accurately approximated by a Taylor series expansion in the nonlinear Schrodinger equation even for pulses containing two optical cycles.< >
A 25 Mbit/s direct-detectionoptical communicationsystem that used Q = 4 PPM signaling was constructed and its performancemeasured under laboratory conditions. The system used a single mode AlGaAs laser diode (h = 834 ...
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A 25 Mbit/s direct-detectionoptical communicationsystem
that used Q = 4 PPM signaling was constructed and its performance
measured under laboratory conditions. The system used a single mode
AlGaAs laser diode (h = 834 nm) and low-noise silicon avalanche
photodiode (APD). A procedure is given to numerically compute system
performance which uses the nearly exact Webb"s approximation of the
true Conradi distribution for the APD output that does not require
excessive amounts of computer time (a few CPU minuteson VAX 8600
persystem operating point). Comparisonrevealedthat modelingtheAPD
output as a Gaussian process under conditions of negligible background
radiation and low (less than 10-l2A) APD bulk leakagecurrentsleads to
substantial underestimates of optimal APD gain and overestimates of
system bit error probabiiity. Examples are given which illustrate the
breakdown of the Gaussian approximationin assessingsystem perform-
ance. The measured performance of the system was found to be in
excellent agreement with the performancepredicted by the nearly exact
computationalprocedure. This systemachieveda bit error probability of
at a received signal energy corresponding to an average of 60
absorbed photondbit and optimal APD gain of 700.
The main aim in carrying out the calculations of this paper is to show the effects (on performance) of adaptation speed relative to true speed of parameter change. There are three cases that need to be covered: First,...
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The main aim in carrying out the calculations of this paper is to show the effects (on performance) of adaptation speed relative to true speed of parameter change. There are three cases that need to be covered: First, where adaptation speed is relatively slow, second, where it is matched, and, third, where it is faster than the true speed. The computations are generally not straightforward and are accomplished by a perturbation expansion based on stochastic averaging.
The interference of two mutually coherent optical fields with unequal center frequencies generates moving space-charge electric fields inside photoconductive semiconductors that contain deep level traps. The motion of...
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The interference of two mutually coherent optical fields with unequal center frequencies generates moving space-charge electric fields inside photoconductive semiconductors that contain deep level traps. The motion of the internal space-charge field drifts free charge carriers out of the photoconductive sample and results in measurable photocurrents that consist of ac and de components even in the absence of external bias electric fields. The de photocurrent can be expressed as a convolution integral between the baseband power spectrum of the signal optical field and the characteristic impulse response of the photoconductive crystal, provided that the local oscillator has negligible optical linewidth. We have demonstrated experimentally a new kind of optical spectrum analyzer with a resolution bandwidth smaller than 15 kHz by sweeping the local-oscillator center frequency over the spectral region of interest and by subsequent deconvolution of the recorded photocurrent with the characteristic response of the crystal. The scanning range of the analyzer is Limited only by the tuning range of the local oscillator. (C) 1996 Optical Society of America
A low-power and compact VLSI architecture, implementing a bidirectional bit-serial A/D/A (analog-to-digital and digital-to-analog) converter, is presented, Both functions of algorithmic D/A conversion and successive a...
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A low-power and compact VLSI architecture, implementing a bidirectional bit-serial A/D/A (analog-to-digital and digital-to-analog) converter, is presented, Both functions of algorithmic D/A conversion and successive approximation AID conversion are combined into a single device, converting bits in the order from most to least significant. The MSB-first order guarantees robust implementation, relatively insensitive to component mismatches, offsets and nonlinearities. Also, since the A/D conversion makes use of the intermediate D/A conversion results, matched monotonic characteristics are obtained in both directions of conversion. The final D/A result is available at the end of A/D conversion, and can be used directly in applications calling for analog quantization. More general use of the A/D/A converter allows for bidirectional read/write digital access to local analog information in VLSI, The robust architecture supports dense integration of multiple low-power data conversion units along with digital processors or sensory circuitry in a standard CMOS process. Minimum sizing of active and passive devices in the implementation, to obtain optimal area and energy efficiency, is limited by clack feedthrough and finite gain considerations rather than matching requirements, Experimental results from a prototype VLSI implementation are given, Including control logic, the A/D/A cell measures 216 mu m x 315 mu m in a 2-mu m CMOS process, and achieves 8-b untrimmed monotonicity at 200 mu W power consumption for a 20 mu s conversion cycle. This corresponds to 4 nJ of energy dissipated per 8-b converted sample.
Output regulation for a nonlinear plant driven by an exogenous signal is addressed in this paper. In the absence of the standard exosystem hypothesis, we assume availability of the instantaneous values of the exogenou...
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Output regulation for a nonlinear plant driven by an exogenous signal is addressed in this paper. In the absence of the standard exosystem hypothesis, we assume availability of the instantaneous values of the exogenous signal and its first time-derivative for use in the control law. We formulate an approximate output regulation problem and characterize solvability in terms of the existence of a certain invariant manifold. The control law we obtain yields a closed-loop system with output exhibiting ultimate boundedness properties with respect to both the first- and the second-time derivatives of the exogenous signal. Performance characteristics are illustrated by application to the linear case and to specific nonlinear examples.
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