Search

A theoretical analysis of the error probability and the precision of Random Modulation-Continuous Wave LIDAR systems is presented. Both the signal to noise ratio prior and after the correlation process are calculated taking into account the main noise sourc es. Analytical expressions for the estimation of the probability of catastrophic errors in the determination of the distances due to random noise peaks are derived. The effect of the signal to noise ratio on the precision is also theoretically evaluated. As illustrative examples, plots for the signal to noise ratio, the error probability and the precision corresponding to a LIDAR system currently developed in our laboratory are presented.

The performance of new three-section master oscillator power amplifiers emitting at around 1.5 ?m has been analyzed in regard with their application as laser sources for a differential absorption lidar. The devices incorporate a modulation section that can be separately driven thus allowing the required random modulation of the laser emission. The bent design of this section together with the tilting of the output facet ensures a stable single-mode emission in the entire range of driving conditions. At the required modulation frequency (12.5 MHz) a square wave emission profile with high optical modulation amplitude and 22 dB extinction ratio is obtained.

Direct optical modulation of a 1.55 ?m three-section Master Oscillator Power Amplifier has been demonstrated. The temporal response, the optical spectra and the optical modulation amplitude have been analyzed as a function of the frequency and the modulating amplitude. For low modulation amplitude, no spectral broadening was observed up to 1.5 GHz. However, at 12.5 MHz an optical broadening of ~ 4 pm was observed for high modulation amplitudes. At this frequency an extinction ratio of 42 dB has been achieved. The modulation amplitude degrades for frequency values higher than 30 MHz. The device performance under modulation at 12.5 MHz is interesting for its application as laser source for CO2 detection by differential absorption LIDAR operating in the Continuous Wave Random Modulation mode.

We theoretically investigate a dynamical regime, experimentally observed in monolithically integrated master oscillator power amplifiers emitting at 1.5 7 μm, consisting in large emission wavelength jumps of the device from the Bragg wavelength to that of the gain peak. Our analysis is based on numerical simulations by means of a travelling wave model that incorporates spatial effects such as spatial hole burning and coupled-cavity effects. Thermal effects are included by considering the optical response of the quantum well active medium within the quasi-equilibrium approximation at finite temperature, with a phenomenological description of the redshift of the gain peak and the changes in the background material refractive index by means of self- and cross-heating coefficients for both sections. We find that whereas the thermally-induced index changes are the responsible of the modal jumps between consecutive modes, the carrier-induced refractive index changes are the responsible of the jumps occurring between the Bragg wavelength and the gain peak.

High power (> 0.5 W) single-mode frequency laser at 1.55 μm are nowadays key components for a large number of applications such as lidar systems, telemetry or free-space communications. For this level of power, the most suitable and available sources are solid-state lasers and fiber lasers. Semiconductor devices, which are more compact and more efficient, have still to demonstrate very high power operation to be a credible competitor. In order to obtain these levels of power with semiconductor devices, the more suitable device seems to be the Master Oscillator Power Amplifier (MOPA). Single-mode emission is generated by a Distributed Feedback laser (DFB) and the signal is then amplified with a Power Amplifier (PA). To avoid complex optical coupling and to simplify the packaging, it is possible to integrate on the same chip the laser and the amplifier. The main challenges are the fabrication of the multi-section device (at least 2 sections: one for the laser and one for the amplifier) and the reduction of the reflections. Indeed the facet and the internal reflections can create multiple cavities behavior and disturb the laser single-mode emission. In this contribution, we report the realization of a 3-section monolithic MOPA on InP.