Fourier-transform-limited pulses from gain-switched distributed-Bragg-reflector lasers using simultaneous modulation of gain and phase sections

Fourier-transform-limited pulses ( Delta tau . Delta nu approximately=0.35) have been obtained from a microwave-modulated DBR laser at 1.56 mu m. The chirp of the gain-switched pulse is compensated for by applying a fraction of the microwave signal to the phase section, thereby creating an instantaneous frequency shift of opposite sign. The generation of short coherent pulses from such a monolithic source can be of great interest for long haul soliton transmission.<>     

Diodes lasers en régime de forte modulation sinusoïdale de courant : modélisation et expériences â 1,3 µm

We present a theoretical and experimental study of laser diodes under strong sinusoidal current modulation. Situations where the diodes are biased above threshold are considered. The first part describes different behaviors occurring under strong modulation. The GaAs lasers are compared to the InGaAsP lasers. The major result of numerical calculations shows that the existence of anomalous behaviors (period doubling, chaos,...) can be predicted from the weak-signal response of the laser. In a second part, we report on the expérimentais results obtained with an InGaAsP laser at 1.3 µ.m and their comparison with the theoretical calculations from a rate equation model. This kind of laser does not exhibit any anomalous behaviour under strong modulation, but distorsion effects occur. The calculated spectra of the laser intensity are in excellent agreement with measurements, which validates both the use of the rate equation model and the choice of the laser-parameters. In contrast, the spectral analysis at the optical frequency shows that the optical phase-equation previously used by many authors is uncomplete and that longitudinal and/or transversal variations of the α-factor have to be taken into account.     

Optimum linear pulse compression of a gain-switched 1.5 μm DFBlaser

We report on pulse compression measurements of a 1.5 μm gain-switched strained multi-quantum well distributed feedback semiconductor laser. Experiments with eight normal dispersion fiber lengths show that the optimum compression may be achieved at a dispersion value about half of the one usually calculated using a gaussian pulseshape model. Pulse compression measurements are well reproduced by a simple model involving rate equations. Effective linewidth enhancement factors, α_eff, deduced from this model reveal increasing values with pumping conditions. We show that this nonlinear behaviour is in agreement with an intensity dependence of α_eff     

Mesure automatique des paramétres de bruit des MESFET hyperfréquences

An automatic noise parameter measurement test set is described in two sections : (i) A novel noise parameter extraction procedure from a set of noise figure measurements is developped. The experimental minimum noise figure is no longer required and the sensitivity to measurement incertainties is found to be very low. (ii) An automatic input tuner with a large number of precalibrated and reproducible positions is designed and realized. The last part give examples of broadband (8 to 17 GHz) noise parameters characterization ofmmic GaAsmesfets when both the automatic tuner and the extraction procedure are used.     

High reflectivity Te-doped GaAsSb/AlAsSb Bragg mirror for 1.5 μmsurface emitting lasers

A high reflectivity GaAsSb/AlAsSb Bragg mirror lattice matched to InP is reported. Operation at 1.5 μm is obtained owing to a large Burstein-Moss shift of GaAsSb absorption caused by a strong N-doping up to 10¹⁹ cm^-2. Peak reflectivity up to 94% has been measured with only 11.5 periods     

Picosecond (<2.5 ps) wavelength-tunable ( approximately 20 nm) semiconductor laser pulses with repetition rates up to 12 GHz

A novel technique is used to produce picosecond wavelength-tunable optical pulses from gain-switched Fabry-Perot semiconductor lasers using fibre compression. Experiments are carried out with high power, large modulation-bandwidth lasers at 1.3 mu m. Pulses of 2.5 ps durations with repetition rates up to 12 GHz are obtained. Still shorter pulses ( approximately 1 ps) with higher repetition rates (18 GHz) are shown to be feasible.<>     

Gain compression and phase-amplitude coupling in GaInAs quantum well lasers with three, five and seven wells

The gain compression and phase-amplitude coupling factors are measured along with the differential gain in GaInAs/GaInAsP quantum well lasers with three, five and seven wells. Results are compared with those obtained for a conventional bulk laser of the same quaternary material. The ultimate modulation bandwidth deduced from the measurements is shown to increase with the number of wells. For the seven well laser, the ultimate modulation bandwidth is found to reasonably approach that obtained for the bulk laser while the phase-amplitude coupling factor is 2.6 times smaller.<>     

Autocorrelation at 1.3-1.5 mu m using POM crystal

A nonlinear 3-methyl 4-nitropyridine 1-oxide (POM) crystal is used in a collinear type-I autocorrelator for the measurement of picosecond pulses generated by 1.3-1.55 mu m semi-conductor lasers. Experiments were performed at 1.3 mu m. Measurements of laser pulses with peak powers as low as 300 mu W are reported.<>     

Near-Field Electromagnetic Characterization and Perturbation of Logic Circuits

We propose here a nondestructive electromagnetic (EM) near-field test bench for both EM compatibility and susceptibility of circuits. This setup permits both the collection of the near field and injection without contact of a disturbing EM field, all through a probe. Exhaustive characterizations of probes are undertaken via simulations and experiments. According to their design, they are supposedly linked more to the electric or the magnetic field. Simulations of their EM behavior are undergone to fix their optimal geometries, leading to the best measurement performances. It is shown by both the simulations and the S-parameter measurements that their presence does not interfere with the electric behavior of the device under test. Then, logic circuits are characterized from the EM point of view, with the help of this test bench. Circuits are placed on three different printed boards: one double-sided low-frequency board without a ground plane and two single-sided boards with a ground plane and a design that is more or less optimized. EM near-field mappings highlight the strong field areas of the circuits. The need for a ground plane is highlighted. Field patterns on the traces are linked with those observed on microstrip lines. Then, an EM aggression is injected over a supposed sensitive zone of the circuit. Whichever printed board is considered, a parasitic signal superimposes itself on the output signal of the gates. Deepened studies are undergone to exhaustively explain the phenomena observed.     

Génération ďimpulsions picosecondes avec des lasers à semiconducteur pour les transmissions par soliton sur fibre optique

Recent developments in soliton transmission on optical fiber require picosecond pulses at 1.5 μm which are as close as possible to the Fourier transform limit. In the present paper, semiconductor lasers in pulsed regime are studied for this purpose. Thus, performances achievable by using the most usual methods, mode-locking and gain-switching, are evaluated. The aim of the last part is to discuss the design and performances of sources dedicated to soliton transmission as well as to present the principle of operation of a monolithic source based on a two- or three-section laser. The first results obtained with a three sections dbr laser are given.