Maximum Signal Power Research Articles

A transparent optical bus using a chain of remotely pumped erbium-doped fiber amplifiers

A transparent optical bus using a chain of remotely pumped erbium-doped fiber amplifiers is proposed and demonstrated in a four-station implementation. An analytical model which predicts the required parameters for the remotely pumped EDFAs at each station was developed. A maximum signal power variation of 0.3 dB is measured experimentally for each station, in good agreement with the model prediction. Experimental results indicate that the bus can potentially support up to 40 WDM channels, as limited by remotely pumped amplifier saturation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The practical significance of two-dimensional deconvolution in echography

This paper evaluates deconvolution (inverse filtering) as applied to ultrasonic imaging systems, and discusses the obstacles which are encountered employing the technique in practice. A minicomputer is used to generate artifical echo signals, simulating rf signals resulting from a set of point reflectors in a homogeneous medium, as recorded by an electronically focused group-steered linear array scanner. Two-dimensional deconvolution in combination with a Wiener noise reduction filter (i.e., a Wiener-Inverse filter) is applied to these simulated rf signals, which were contaminated with white noise. The efficacy of the Wiener-Inverse filter is defined in terms of its ability to resolve two point reflectors with a lateral spacing equal to the local −6 dB width of the ultrasonic beam. In favorable circumstances, the targets are resolved at signal-to-noise ratios (SNR) better than 20 dB, where SNR is defined as the maximum signal power divided by the average noise power level. Nonlinear effects due to quantization or signal clipping are investigated. In order to improve the resolution of an rf signal with a dynamic range of 40 dB, the input signal should be digitized at a minimum of 12 bits. The problem of signal clipping can be circumvented by oversampling. The two-dimensional Wiener-Inverse filter is defined in terms of both temporal and spatial properties of the insonification. Effects of wave diffraction give rise to a depth-dependent ultrasonic beam. As a result of a misfit of the Wiener-Inverse filter and the local properties of the ultrasonic beam, erroneous noisy texture arises in the image. Adaptation of the Wiener-Inverse filter with respect to the beam properties gives acceptable results, at the expense of a rather large computational effort.

The practical significance of two-dimensional deconvolution in echography.

This paper evaluates deconvolution (inverse filtering) as applied to ultrasonic imaging systems, and discusses the obstacles which are encountered employing the technique in practice. A minicomputer is used to generate artificial echo signals, simulating rf signals resulting from a set of point reflectors in a homogeneous medium, as recorded by an electronically focused group-steered linear array scanner. Two-dimensional deconvolution in combination with a Wiener noise reduction filter (i.e., a Wiener-Inverse filter) is applied to these simulated rf signals, which were contaminated with white noise. The efficacy of the Wiener-Inverse filter is defined in terms of its ability to resolve two point reflectors with a lateral spacing equal to the local -6 dB width of the ultrasonic beam. In favorable circumstances, the targets are resolved at signal-to-noise ratios (SNR) better than 20 dB, where SNR is defined as the maximum signal power divided by the average noise power level. Nonlinear effects due to quantization or signal clipping are investigated. In order to improve the resolution of an rf signal with a dynamic range of 40 dB, the input signal should be digitized at a minimum of 12 bits. The problem of signal clipping can be circumvented by oversampling. The two-dimensional Wiener-Inverse filter is defined in terms of both temporal and spatial properties of the insonification. Effects of wave diffraction give rise to a depth-dependent ultrasonic beam. As a result of a misfit of the Wiener-Inverse filter and the local properties of the ultrasonic beam, erroneous noisy texture arises in the image. Adaptation of the Wiener-Inverse filter with respect to the beam properties gives acceptable results, at the expense of a rather large computational effort.

The signal-handling capacity of the square-wave switched ring modulator

Expressions are derived for the maximum permissible interfering input signal power which may be applied to a square-wave switched resistively terminated ring modulator before the onset of severe cross-modulation distortion in the output spectrum. The effects of source and load mismatch are considered and good agreement demonstrated between theoretical prediction and the measured performance of a typical ring modulator using Schottky barrier diodes.

Power Loss in Propagation Through a Turbulent Medium for an Optical-Heterodyne System with Angle Tracking*

The power loss due to propagation through a turbulent medium is considered for an optical-heterodyne detection system whose axis tracks perfectly the instantaneous direction for maximum signal power. Pertinent to both fixed- and tracking-axis cases, the general expression for power reduction is found to be given correctly by neglecting the angular diffraction spread of the local-oscillator field and using the signal field evaluated on the optical axis. A plane and broad incident wave is assumed. The result for the tracking aperture is indicated to be given correctly by ray optics if L≪a2/λ, where L is the path length in the turbulent medium, a the aperture radius, and λ the signal wavelength, whereas for a fixed aperture the lateral homogeneity of the field is indicated to suffice without this condition. Refractive-index fluctuations are assumed to be described statistically by the usual Kolmogorov spectrum. For moderate aperture (a≲ae), the power reduction factor Γ is found to be given by Γ≃1-s(a/ae)5/3with s = 0.125 for a tracking axis and s = 0.955 for a fixed axis, where a. is ae certain effective radius for the fixed case. If the improvement due to tracking is extrapolated to arbitrary a/ae by conjecture of a fixed factor of increase in the effective radius, the factor of increase in maximum signal-to-noise ratio achievable by tracking is 11.5. To approach the maximum, the frequency response of the tracking system should extend beyond roughly 50 cps.

A level compensator for telephotograph systems

SINCE 1936, a number of different telephotograph systems1 have been operated over the lines of the Bell System on a leased-wire basis. The requirements which a line facility must meet for such service are in several respects more severe than the requirements for voice-message service. Telephotograph- transmission requirements have usually specified that abrupt variations in line net loss should be limited to ±0.2 decibel, single frequency noise power should be at least 50 decibels below maximum signal power, and throughout the useful frequency band (1,200 to 2,600 cycles per second), the envelope delay should be equalized within ±300 microseconds. Such requirements were originally satisfied by using 4-wire H-44-25 side circuits in cable, where available, and elsewhere by using 2-wire open-wire side circuits. These facilities were delay-equalized over the necessary frequency range, and precautions were taken to minimize various transmission disturbances.