Researcher (M/W) 18 months : Physical modeling of free-space optical telecommunications through scattering atmosphere in MWIR range

Description of the job :
In the applicative context of free space optical telecommunications (FSOT) (see project summary below),
you will be involved in the physical and numerical modeling of optical wave propagation through
complex and turbid atmosphere, and in the performance assessment of balisting photons filtering
approaches in the SWIR and MWIR wavelength ranges. Using realistic applicative scenarii, and medium
characteristics (size distribution of scatterers, type of scatterers, spectroscopic properties, dynamical
properties...), the absorption, scattering and depolarization properties of the medium will be simulated,
relying on analytical models and validated through numerical simulations (vectorial Radiative Transfer
Equation solved with Monte-Carlo simulations). The impact of propagation of light through turbid
atmosphere on the (classical or chaos-based) temporal modulation waveforms encoded onto the light
beam will be also analyzed with similar modeling tools, taking into account the geometrical
characteristics of the telecommunication system (e.g., aperture of the detection device) : this study
should provide an estimate of the maximal range and bandwidth of FSOT as a function of the fog
properties.
Then, you will be in charge of a theoretical and numerical evaluation of the benefits of
ballistic/serpentile photons filtering approaches (polarization or temporal-modulation based) on the
quality of FSOT in the SWIR/MWIR. Relying on the simulation building blocks set up, you will simulate
the implementation of such a serpentile/ballistic photon filtering technique by temporal modulation of
intensity and/or polarization, and analyze the potential gain in telecommunication performance. As far
as possible, these numerical approaches will be backed up by analytical studies of possible performance
gains in modulated signal discrimination, using the tools of statistical information theory. Finally, you
will handle the definition of technological specifications for the design of appropriate optical
phase/polarization modulation devices in the SWIR/MWIR ranges to implement ballistic photons
filtering for FSOT and increase the range and throughput of free-space optical telecommunication
systems in the presence of fog.

Public summary of the collaborative project :
Free-space optical telecommunications (FSOT) in the infrared represent an increasingly attractive alternative to the progressive
saturation of channels dedicated to wireless technologies, and to the growing bandwidth requirements. However, this
promising, rapidly deployable technology is vulnerable to weather conditions such as fog. Indeed, when the optical beam
propagates through a scattering medium, it undergoes absorption and scattering phenomena that attenuate the optical signal
and, at high data rates, cause time elongation of modulation signals. The greater the transmission distance, the greater these
effects, endeavouring communication reliability or bandwidth. In addition, the multiple scattering of the beam means that the
signal can be intercepted by an opposing party at a suitable distance. Securing transmitted data and increasing the range of
encrypted telecommunication systems through turbid environments such as fog is therefore a fundamental challenge for
defense and industrial applications.
The aim of this collaborative project is to propose new telecommunication strategies to significantly increase the range and
throughput of free-space optical telecommunication systems in the presence of fog. Data security will be achieved using a
cryptographic method that exploits the temporal chaos of quantum cascade laser sources. The proposed strategy involves the
combination of three innovative approaches : (i) chaos-based cryptographic encoding ; (ii) ballistic/serpentile photons filtering ;
(iii) wavefront correction through adaptive optics techniques to correct for the effects of scattering. One of OPTOPIRAT's
objectives will also be to compare telecommunication performance at different wavelengths, moving from the near infrared
(SWIR) to mid-infrared (MWIR, LWIR), while covering the main fog conditions (advective and convective).

Laboratory :
Institut Fresnel, UMR 7249 CNRS/Centrale Méditerranée/Aix-Marseille Univ
Contact : Julien Fade, MCF HDR, ECM, DiMABio Team
Email : julien.fade@fresnel.fr
Tel : +33 (0)4 13 95 54 94
Website: https://www.fresnel.fr
Partners :
-
-
ONERA-DOTA (French Aerospace Lab, Optics dpt.), Palaiseau
LTCI Lab, Palaiseau