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Publications

Publications by CTM

1991

Performance assessment of optical subcarrier multiplexing systems: Implications of laser distortion

Authors
O'Reilly, JJ; Salgado, HM;

Publication
IEEE Global Telecommunications Conference and Exhibition

Abstract
The theory of nonlinear systems based on frequency domain analysis using Volterra series is shown to provide an appropriate means of assessing laser distortion which includes the effects of laser resonance. Hence, it is an appropriate and tractable means of assessing the performance of optical subcarrier multiplexed (SCM) systems. Based on this analysis the performance of SCM systems is examined, with calculation of the carrier-to-intermodulation ratio for an eight-channel SCM system providing an illustrative example.

1991

Distortion analysis of semiconductor lasers. A caution

Authors
O'Reilly, JJ; Salgado, HM;

Publication
Electronics Letters

Abstract
Analytic techniques proposed for distortion analysis are shown not to predict adequately the higher order terms generated by a semiconductor laser diode of relevance to the design and dimensioning of subcarrier multiplexed optical communications systems. A modified analysis which avoids this deficiency is outlined and illustrative results are presented.

1989

THE USE OF POWER DARLINGTON TRANSISTORS IN AN 40KVA UPS SYSTEM - AN IMPROVED SOLUTION

Authors
QUINTAS, A; FARIA, J; MARTINS, A; ARAUJO, A; SILVA, J;

Publication
CONFERENCE RECORD OF THE 1989 IEEE INDUSTRY APPLICATIONS SOCIETY ANNUAL MEETING, PTS 1-2

Abstract
The use of power Darlington transistors for an inverter of a 40-kVA uninterruptible power supply (UPS) system is discussed, and the storage time, dead time, and switching aid network contributions to the total harmonic content of the output voltage are examined. A review of common switching aid circuits, for nominal and short-circuit conditions, is presented, and their limitations are discussed. A solution, conceived specifically for power Darlington transistors, is presented. The solution that fits the most relevant characteristics of this technology is analyzed regarding commutation under nominal conditions, commutation under short-circuit conditions, and contribution to harmonic distortion in the output voltage. Conclusions are drawn about the optimal switching frequency for this type of application. The discussion and conclusions are supported by experimental and simulation results.

1986

SPATIAL-FILTERING AND FREQUENCY COLOR CODING WITH PHOTOREFRACTIVE CRYSTALS

Authors
BERNARDO, LM; SALGADO, HM; SOARES, ODD;

Publication
OPTICA ACTA

Abstract
Image processing can be supported by efficient thick holographic recording media such as photorefractive crystals. A numerical analysis is presented showing how low- and band-pass tunable filtering as well as frequency color coding can be performed with reflection holographic gratings recorded in photorefractive crystals.

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