Theoretical and experimental investigation of a thin-film waveguide laser amplifier with a lossy cladding

In laser amplifiers using high gain materials such as dyes or semiconductors, the inherent broad-band amplified spontaneous emission (ASE) may strongly saturate the amplifier gain: this yields a severe limitation on the amplification of small signals. We show that this difficulty can be appreciably overcome in an optical waveguide amplifier with a lossy cladding. A theoretical analysis of gain saturation by the ASE noise in a lossy cladding waveguide amplifier is given, and the small-signal gain improvement is stressed. An experiment involving a metal-clad thin-film dye laser amplifier is reported, the results of which are in agreement with the theoretical predictions.     

Volterra functional series expansions for noise in semiconductorlasers

In this paper, we present a full analysis of noise in semiconductor lasers. Time-covariance and cross-covariance functions of all variables governing single-mode semiconductor laser behavior are given including all Langevin noise sources and considering all terms of the laser rate equations, RIN, carrier noise spectrum, frequency noise spectrum, coherence between the FM and AM noise, variance of the phase change and coupling between amplitude and phase are investigated analytically in their more general form. Spectral line shape has been derived showing dissymmetrical satellite lines centered at multiple integers of relaxation frequency around a central line. It is shown that neglecting the shot noise and considering only the carrier contribution in phase dynamics (common procedure) are too general approximations     

Laser RIN calibration by extra noise injection

Laser relative intensity noise (RIN) calibration is presented. Experimental results show the influence of laser RIN on the bit error rate (BER) in a transmission system operating at 600 Mbit/s through a 10 km monomode fibre length, at a wavelength of 1.3 mu m.<>     

New metric for <Emphasis Type="Italic">IQ</Emphasis> imbalance compensation in optical QPSK coherent systems

We report on a simple alternative method for the compensation of quadrature imbalance in optical quadrature phase-shift-keying (QPSK) coherent systems. By introducing a new metric, the phase imbalance can be determined and compensated. The proposed method is theoretically and numerically analyzed. In particular, it is shown that the method exhibits a small bias of estimated phase imbalance value. Thanks to its deterministic property, this bias can be simply compensated by incorporating at the receiver a phase rotator (or phase shift) whose value can be determined based on an analytical analysis. Moreover, the algorithm is also experimentally validated through bit-error-rate and error vector magnitude (EVM) measurements. A good agreement on the performance of the proposed method with that of the Gram–Schmidt orthogonalization procedure is shown in a 20-Gbit/s optical QPSK experiment. The robustness of both methods was verified with up to \(30^\circ \) phase imbalance by comparing the signal with and without phase imbalance compensation. A 10% reduction in EVM is achieved with our method for a high phase imbalance of \(30^\circ \), while the implementation complexity can be reduced owing to the suppression of the use of square-root operators.     

Traitement du signal appliqué aux mesures mécaniques du guide d’ondes hélicoïdal

The authors describe a new measurement method which characterizes the second order statistical properties of the difference between the actual radius of the manufactured helix waveguide and the constant radius of a perfectly cylindrical helix waveguide: this method starts from general results about the analysis of a random surface satisfying to some conditions. The first measurements on some samples of waveguide allow to think that this method could lead to an important simplification of the test of some mechanical characteristics of a waveguide line.     

Étude du comportement d’une modulation numérique à 16 états d’amplitude et de phase (MAQ 16) dans un canal de transmission hertzienne

In this paper the bit error probability for 16 QASK modulation of rectangular type is computed. The method was applied to the design of a 140 Mbit/s radio-link equipment. Filtering, modem impairments, interferences, propagation impairments are taken into account. Bit error probability is given by a Gram — Charlier expansion using only the moments of the intersymbol interference, and avoiding the computation of the probability distribution function itself. Comparison with experimental results is given.     

Coefficients de couplage entre modes dans un guide d’ondes circulaire légèrement déformé

The knowledge of the coupling coefficients in a slightly non cylindrical waveguide is very important because it is the first step in the calculation of the additional attenuation of TE ₀₁ mode due to the perturbation. In practice, it is quite impossible to get a perfectly cylindrical waveguide because of the limits of mechanical accuracy in the manufacturing process. A calculation method of the coupling coefficients is given in this paper and it leads to expression which have been already published, but using a different method. Ideal metallic waveguide, lined waveguide and helix waveguide are considered : in the third case it is shown that the method gives a quite general expression, which can be reduced in a simplified one, already published, in the particular case of the TE ₀₁ mode.     

Quelques résultats théoriques et expérimentaux sur la modulation par déplacement de fréquence à deux états et à phase continue d’indice 0,5 (MSK)

Minimumshift keying modulation seems to be very attractive for digital transmission systems in particular because an only small degradation can be expected on non linear channels. In the first part of this paper, some general features of the signal are recalled. After a theoretical method for the calculation of the bit error rate in presence of inter symbol interference is described; the results are compared with experimental values, obtained with a modulator demodulator build incnet laboratories in Lannion.     

OSNR margin brought by nonlinear regenerators in optical communication links

Computation using a semianalytical model of the optical signal-to-noise ratio margins brought by the introduction of a generic 2R regenerator in an optical transmission link is presented. The optimization of the discriminating level of the regenerator depending on the link conditions is discussed and a regenerator characterization method that can be used in system design is presented.