P. García-Fernández

Synchronization of chaotic semiconductor lasers: application to encoded communications

We numerically show that the synchronization of two chaotic semiconductor lasers is possible when a small amount of output intensity from one Is injected into the other. We also show that a message can be encoded in the chaotic carrier, transmitted by an optical fiber and decoded by a receiver with a very good quality.

Encoded Gbit/s digital communications with synchronized chaotic semiconductor lasers

We numerically study the synchronization of two chaotic semiconductor lasers in a master-slave configuration. To synchronize the lasers, a small amount of output power from the master laser is injected, after propagating through an optical fiber, into the slave laser. We show that the output of the master laser can be used as a chaotic carrier to encode a digital message which can be recovered after propagating long distances. We also check the robustness of this scheme when the two lasers are slightly different.

Non-classical Properties of Non-degenerate Parametric Amplifiers and Oscillators with Pump Depletion and Non-homogeneous Losses Using the Wigner Representation

Abstract The squeezing properties of non-degenerate parametric amplification and oscillation with pump depletion and non-homogeneous absorption losses are studied. A method based in the Wigner representation is used which allows one, within a linearization scheme, to derive directly the Langevin equations for the involved optical fields from their quantum Heisenberg equations. Non-homogeneous absorption losses for the three beams are included in order to analyse the sensitivity of the squeezing spectra to the asymmetry of the losses. Intracavity squeezing spectra are calculated within this method both below- and above-threshold regimes. Special attention is given to the squeezing properties of the phase sum and amplitude difference of the correlated beams and amplitude of a single beam above threshold, where the role of loss asymmetry and pump losses is analysed in detail.

Fiber based dispersion compensation schemes in nonlinear fibers for laser diode pulses in high bit-rate IM/DD systems☆

Abstract The combined effects of chromatic dispersion and self-phase modulation are numerically investigated for a 10 Gbit/s IM/DD system over 100 km of standard single-mode fiber for input signals modeled by stochastic rate equations for single-mode semiconductor lasers. Signal degradation and filtering effects are studied through the monitoring of the eye opening penalty (EOP). It is observed that the shape of the input signal, which depends on the laser parameters, has a major influence on the EOP. Fiber based pre- and post-compensation schemes are compared for different values of the laser parameters and compensation length. In most cases, pre-compensation yields lower eye-opening penalty for the laser pulses analysed.

Analytical study of nonlinear chirped pulses: propagation in dispersive optical fibers

The generation and transmission characteristics of optical pulses with nonlinear chirp are analytically studied. When we compare our results, assuming a Gaussian pulse with a quadratic chirp at the input of a dispersive fiber, with results obtained with the Gaussian model with linear chirp, the position of maximum narrowing is modified and the velocity of broadening of the pulse envelope during the propagation is reduced. Our analytical results are in good agreement with numerical simulation of semiconductor laser pulses. The model could be useful, for example, for dispersion compensation analysis.

Nonclassical properties of nondegenerate parametric oscillators and amplifiers using two-mode operators

Abstract Two-mode quadrature-phase amplitudes are used to describe two-mode squeezing in nondegenerate parametric amplification and oscillation with linear absorption losses. A comparison with the usual description by means of one-mode operators is performed and the relation between two-mode operators and heterodyne detection is discussed. The generalized Fokker-Planck equation for the Wigner quasiprobability distribution has been obtained in terms of the two-mode variables and second-order correlations are discussed. Intra-and inter-beam second-order coherences are given and the intensity fluctuations in the difference of the signal and idler photocurrents calculated. Limits on the simultaneity in the coincidence detection are discussed and finally, it is shown that the quadrature-phase amplitudes are the complex amplitudes for the quantities measured by heterodyne detection.

The effect of loss asymmetry on the nonclassical properties of nondegenerate parametric devices

Abstract The effect of linear absoption loss asymmetry on two-mode squeezing in nondegenerate parametric oscillation and amplification is analysed. The interbeam correlations show time-displaced maxima, which we have analytically identified. The analysis of the intensity difference fluctuations shows that the essential factor governing noise reduction is the proper balancing of the system which, in some cases, may be enhanced by increasing the total losses. Finally, an interesting interplay between loss asymmetry and twin beam frequency splitting arises in the analysis of two-mode quadrature squeezing by means of heterodyne detection. Though no perfect squeezing is possible, we have identified optimal squeezing parameter regions and local minima.

Apodized chirped fibre Bragg gratings for dispersion compensation in a 10 Gbit/s IM-DD semiconductor laser system

Different fibre Bragg grating dispersion compensation schemes are studied for a directly modulated 1550 nm single-mode semiconductor laser signal through a standard nonlinear fibre link. The laser diode is simulated by its stochastic rate equations, while the nonlinear Schrodinger equation is used to simulate the propagation. The optimum length for dispersion compensation after transmission through 100 km SSM fibre is studied. Pulses with a FWHM of the order of 65 ps with any linewidth-enhancement factor are reconstructed using pre-compensation or post-compensation with an apodized 5.75 cm chirped fibre Bragg grating.

Squeezing Parameters in Two-photon Absorption

A comparison is made between exact numerical results of the squeezing parameters in single-mode two-photon absorption with those predicted by short-time calculations. Numerical calculations lead to much higher squeezing and at longer times than those predicted by short-time calculations. The value of the squeezing parameter in the limit of long times and large initial photon numbers coincides in both calculations, as well as in the limit of long times and small initial photon numbers.

Infrared spectra of calcium—strontium arsenate apatites

Abstract The i.r. spectra of the calcium—strontium arsenate apatites have been studied, and the OH, A s O 4 , CO 3 and cation—oxygen fundamental frequencies assigned on the basis of group theoretical arguments. It is seen that CO 3 ions are included in the lattice. It is demonstrated that Ca and Sr undergo continuous ordered migrations throughout the crystal.