Zeno Toffano

Measurement of spectral characteristics of semiconductor laser diodes-effect of injected current modulation and optical feedback

Precision optical spectral lineshape measurements on semiconductor lasers using Michelson and Fabry-Perot interferometers are presented. Measurements ranging from 30 MHz up to 100 GHz give the spectral behavior above and below threshold even for very small emitted optical powers. Variations of the linewidth above and below threshold as a function of injected current are measured and used to evaluate the linewidth enhancement factor and behavior at threshold. The lineshape can differ from the modified Schawlow-Townes almost Lorentzian form for semiconductor lasers above threshold when submitted to operating system conditions such as modulation and optical feedback. Under modulation, line frequency and signal form are modified because of chirping effects. A simple method for chirp evaluation at low frequencies based on lineshape evaluation is proposed. Optical feedback effects are studied as a function of the feedback coefficient C showing various regimes differing for single-mode and multimode laser diodes. >

Linewidth evolution in semiconductor lasers throughout threshold

A detailed experimental and theoretical investigation on the evolution of linewidth Av(I) function of injection current for different structures of semiconductor lasers has been undertaken. Linewidth shows a continuous transition and tends asymptotically on either side to Schawlow-Townes inverse power behaviours. In a small current zone at threshold warping of the linewidth is observed depending on linewidth enhancement factor a and laser structure. Different models including fluctuations are used in order to describe the coherence evolution : asymptotic behaviours by simple linear response model of Van der Pol equation (VdP), continuous evolution by phase transition Landau model (L) and complete description including a using Fokker-Planck field probability density resolution (fp). All models show the same asymptotic behaviour. (fp) seems to be the best-adapted one because it includes intrinsically phase-amplitude coupling. These models lead to a new determination method of spontaneous emission rate R, α, number of photons at saturation Ss and cavity photon lifetime tp by fitting only two direct measurements (linewidth and optical power).RésuméUne étude expérimentale et théorique très approfondie a été effectuée sur l’évolution d’un mode d’oscillation pour différentes structures récentes de laser à semiconducteur en fonction du courant de polarisation. L’évolution de la largeur spectrale montre une variation de la cohérence sans discontinuité au seuil et tend asymptotiquement, au-dessus et au-dessous, vers les comportements de Schawlow-Townes inversement proportionnels à la puissance. Au seuil, sur une gamme de courants étroite, un comportement résonnant plus ou moins marqué, dépendant du facteur d’élargissement spectral a et de la structure du laser est observé. Différents modèles pour décrire l’ évolution continue de la cohérence : méthode de la réponse linéaire appliquée à l’équation de Van der Pol (VdP), modèle des transitions de phase de Landau (l) et résolution de l’équation de Fokker Planck sur la densité de probabilité incluant a (fp) sont utilisés. Le modèle (fp) semble le plus approprié, parce qu’il inclut de façon intrinsèque la notion de couplage phase-amplitude. Ces modèles, par l’ajustement de deux mesures directes (largeur spectrale et puissance optique), constituent une méthode nouvelle de détermination du taux d’émission spontanée R, du facteur a, du nombre de photons à saturation Ss et du temps de vie des photons tp.

Contextual Query Using Bell Tests

Tests are essential in Information Retrieval and Data Mining in order to evaluate the effectiveness of a query. An automatic measure tool intended to exhibit the meaning of words in context has been developed and linked with Quantum Theory, particularly entanglement. Quantum like experiments were undertaken on semantic space based on the Hyperspace Analogue Language HAL method. A quantum HAL model was implemented using state vectors issued from the HAL matrix and query observables, testing a wide range of window sizes. The Bell parameter

Accurate Measurement of RF Exposure from Emerging Wireless Communication Systems

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Linguistics and Quantum Theory: Epistemological Perspectives

, associating measures on two words in a document, was derived showing peaks for specific window sizes. The peaks show maximum quantum violation of the Bell inequalities and are document dependent. This new correlation measure inspired by Quantum Theory could be promising for measuring query relevance.

Quantum Semantic Correlations in Hate and Non-Hate Speeches

We present the design, realization and test of a high bit-rate optical communication system dedicated to underwater operations at the bottom of the sea transmitting data between sensor hubs and remote operated vehicles.

Why quantum computing will be the next turn in information retrieval: a semiotic overview on language and probability

Isotropic broadband probes or spectrum analyzers (SAs) may be used for the measurement of rapidly varying electromagnetic fields generated by emerging wireless communication systems. In this paper this problematic is investigated by comparing the responses measured by two different isotropic broadband probes typically used to perform electric field (E-field) evaluations. The broadband probes are submitted to signals with variable duty cycles (DC) and crest factors (CF) either with or without Orthogonal Frequency Division Multiplexing (OFDM) modulation but with the same root-mean-square (RMS) power. The two probes do not provide accurate enough results for deterministic signals such as Worldwide Interoperability for Microwave Access (WIMAX) or Long Term Evolution (LTE) as well as for non-deterministic signals such as Wireless Fidelity (WiFi). The legacy measurement protocols should be adapted to cope for the emerging wireless communication technologies based on the OFDM modulation scheme. This is not easily achieved except when the statistics of the RF emission are well known. In this case the measurement errors are shown to be systematic and a correction factor or calibration can be applied to obtain a good approximation of the total RMS power.

Entanglement and Semantics : Application to Language Processing

In the context of human exposure to Radio Frequency (RF), measurements of electromagnetic fields are performed, according to standard measurement protocols, using isotropic broadband probes with or without service filters. Two electric field measurement probes are herein examined. Their responses to different typical WIMAX emissions are analysed. Results show that these probes are not accurate enough for the next generation OFDM (Orthogonal Frequency Division Multiplexing) communication systems. A new correction method for these probes is proposed for the evaluation of the RF exposure due to WIMAX systems.