Jean-Pierre Cariou

Pulsed 1.5-

In this paper, we present the development of an axial aircraft wake vortex light detection and ranging (LIDAR) sensor, working in Mie scattering regime, based on pulsed 1.5-mu m high-brightness large-core fiber amplifier. An end-to-end Doppler heterodyne LIDAR simulator is used for the LIDAR design. The simulation includes the observation geometry, the wake vortex velocity image, the scanning pattern, the LIDAR instrument, the wind turbulence outside the vortex, and the signal processing. An innovative high-brightness pulsed 1.5-mum laser source is described, based on a master oscillator power fiber amplifier (MOPFA) architecture with a large-core fiber. The obtained beam quality is excellent (M 2 = 1.3), and achieved pulsed energy is 120 muJ with a pulse repetition frequency of 12 kHz and a pulse duration of 800 ns. A Doppler heterodyne LIDAR is developed based on this laser source with a high-isolation free-space circulator. The LIDAR includes a real-time display of the wind field. Wind dispersion is postprocessed. Field tests carried out at Orly airport in April 2008 are reported. Axial aircraft wake vortex signatures have been successfully observed and acquired at a range of 1.2 km with axial resolution of 75 m for the first time with fiber laser source.

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In order to optimize their flight conditions, airborne platforms need to know precisely their true airspeed. In helicopters, measuring low air speeds is a severe issue because of the rotor flow. Optical air data sensors are therefore a good alternative to classical pneumatic probes. ONERA is involved for many years in simulation and design of coherent lidar and focuses its last research on eye-safe solid state lidars. This paper describes the study of performance of a reliable compact airborne system based on a 1.5 μm Erbium fiber laser and architecture. The average heterodyne current power is examined for the case of negligible turbulence and truncation effect. The spatial resolution of the measurement is deduced and its behavior versus transmitter beam parameters discussed.

m LIDAR for Axial Aircraft Wake Vortex Detection Based on High-Brightness Large-Core Fiber Amplifier

This paper describes a 1.55 micrometer coherent fiber laser radar designed and developed at ONERA in France. This eye-safe Doppler system uses a 0.5 W codoped Erbium/Ytterbium fiber laser and a compact fiber optical architecture. The system has been tested at distances up to 1 km. Experimental results are presented and performances compared to the theoretical model taking into account atmospheric propagation.

All-fiber 1.5-um CW coherent laser anemometer for in-flight measurements

A pulsed fibre lidar based on 1.5 mum fibre technology has been demonstrated for wake vortex monitoring on airport sites. The wake vortex cores position resolution is plusmn2 m, the error on circulation 10%.

Performance of an erbium laser vibration sensor

Originally developed for telecommunications, fiber lasers are now becoming new effective sources for coherent lidars allowing new instruments to be designed. The advent of the double clad fiber, along with advances in semiconductor pump diode sources, have allowed rapid power scaling of both pulsed and CW fiber sources. The unique capabilities of fiber sources, coupled with significant commercial and academic progress in implementation, have driven fiber technology to enter active remote sensing markets as signal sources and amplification stages for direct detection lidars and coherent lidars as well. Some interesting fiber lasers benefit from a good transmission in the near infrared spectral band. However, useful wavelengths have to be tuned between absorption H20 and CO2 lines. Eye safety may be an issue for atmospheric lidars. Above 1.4 µm, an eye-safe operation is possible even with multi-watt lasers. Low power fiber lasers using single mode fibers have a good spatial quality. However, higher power lasers and amplifiers need larger fiber cores, to store enough energy and to avoid non linear effects. Trade-off between high power, single mode operation, stable polarization and spectral quality need to be considered for coherent lidars.

1.5 μm all fiber pulsed lidar for wake vortex monitoring

AbstractThe measurement range of a coherent wind Doppler lidar (CWDL) along a laser beam is the maximum distance from the lidar where wind speed data are accurately retrieved. It means that, at this distance, a sufficient number of emitted laser photons are backscattered and received by the lidar. Understanding of the propagation of the laser through the atmosphere, and particularly the backscattering and extinction processes from aerosols, is therefore important to estimate the metrological performances of a CWDL instrument. The range is directly related to specific instrument characteristics and atmospheric content, such as the aerosols type, size, and density distributions. Associated with the measurement range is the notion of data availability, which can be defined, at a given range and over a time period, as the percentage number of data retrieved correctly by the CWDL over the total number of measurement attempts.This paper proposes a new approach to predict the CWDL data availability and range of ...

Fiber lasers: new effective sources for coherent lidars

Since air traffic is in constant expansion, a more efficient optimisation of the airports capacity is expected. In this context, the characterization of aircraft hazardous turbulences known as wake vortices with an operational vortex Lidar is one of the major issues for the dynamic distances separation. A study has been probed to develop a hybrid vortex algorithm , i.e that uses both the velocity envelopes and a parametric estimator in the interest of processing time as short as possible. The aim is to make this algorithm exploitable for operational projects. That is why a methodology has been set up to evaluate its precision and its robustness. The results of tests on simulated scenarios of different aircraft vortices and different weather conditions show that this algorithm is able to localize precisely wake vortices and to estimate accurately their circulation in a short time.

Simulation of Doppler Lidar Measurement Range and Data Availability

Cladding-pumped rare-earth-doped fiber laser technologies are currently among the best sources for high power applications. Theses extremely compact and robust sources appoint them as good candidate for aeronautical and space applications. The double-clad (DC) fiber converts the poor beamquality of high-power large-area pump diodes from the 1st cladding to laser light at another wavelength guided in an active single-mode core. High-power coherent MOPA (Master Oscillator Power Amplifier) sources (several 10W CW or several 100W in pulsed regime) will soon be achieved. Unfortunately it also brings nonlinear effects which quickly impairs output signal distortions. Stimulated Brillouin scattering (SBS) and optical parametric amplification (OPA) have been shown to be strong limitations. Based on amplifier modeling and experiments we discuss the performances of these sources.

Development and assessment of a wake vortex characterization algorithm based on a hybrid lidar signal processing

Mid-infrared (IR) lasers are of interest for a variety of applications including environmental sensing, LIDAR and military counter measures. However, this wavelength range lacks powerful, coherent, robust and compact sources. A solution can lie in chalcogenide glasses as host materials for rare earth ions. With an extended infrared transparency, low phonon energy limiting the non radiative multiphonon relaxation rates and suitable rare earth solubility, sulfide glasses based on Ge-Ga-Sb-S system make available radiative transitions in the mid-IR range. The glasses with nominal composition of Ge20Ga5Sb10S65 doped with Er3+ (500 to 10000 ppm) were prepared by means of conventional melting and quenching method. The Er3+, widely studied in glass fibers for near-IR amplification, was initially selected for the transition 4I9/2 to 4I11/2 emitting at around 4.5 &mgr;m in order to demonstrate the ability of this sulfide composition for midinfrared fiber lasers application. In these objectives, absorption and emission spectra have been recorded and the radiative decay lifetime of excited levels (4I9/2, 4I11/2 and 4I13/2) has been determined. These last experimental results were compared with those obtained by Judd-Ofelt model from absorption cross-sections of all observable transitions. Therefore, the 4I9/2 radiative quantum efficiency was estimated at 67 %. The emission cross-section was 2.6x10-21 cm2 at 4.6 &mgr;m obtained by Fütchbauer-Ladenburg theory. The product of measured lifetime and emission cross-section for 4I9/2 -> 4I11/2 transition is about 1.87x10-24 cm2.s is comparable with that for GaLaS glasses. The fiber drawing of the Er3+ doped Ge20Ga5Sb10S65 glasses and measurements of optical losses in mid-IR are currently in progress and first results were presented.

High power pulsed sources based on fiber amplifiers

We propose a new technique using a transmitter with two simultaneous phase correlated wavelengths. Heterodyne signals are correlated to give the Doppler information. The performances of our system are compared to the conventional lidar ones.