Post-Doct Digital design and signal processing for satellite optical com systems

Context

Digital optical telecommunications have made it possible to build very high-speed terrestrial fiber networks, but microwaves are still the main physical layer in satellite communications. While optics have proved their worth on inter-satellite links, satellite-to-ground optical transmissions are currently being considered as part of the equipment for new platforms, particularly those for new satellite constellation programs. The advantages are identical to those of terrestrial links: very high data rate, directional beam, secure communications. Future generations of high-capacity satellites (SATCOM) in low earth orbit (LEO) and geostationary orbit (GEO) will haveto include an optical component to guarantee increased throughput. However, the robustness and resilience ofthe link are highly dependent on atmospheric conditions, in particular cloud cover, optical background noise and atmospheric turbulence. In LEO, the Doppler effect will also have an impact on data availability. All these disturbances compromise the reliability of the link and degrade the signal-to-noise ratio. Various transmitted waveforms and different types of detection have been studied, but complex modulation formats (QPSK, 8PSK,etc.) and coherent detection, as for terrestrial networks, are proving to be the most effective, at the expense ofmore complicated implementation (sensitivity to frequency fluctuations). The CALICO project proposes to study and design a new coherent detection technique at the interface between optics and digital electronics in order tocompensate for the Doppler effect and improve the detection threshold. The objectives are to design a phase-locked loop to recover the phase and amplitude of the signal. To achieve this, an original hybrid approach will beused to recover a carrier and a signal that are as clean as possible as soon as they leave the physical and electronic layer. It involves combining an optical phase-locked loop (OPLL) with digital processing on a DSP.

Main activities

The post-doctoral researcher will contribute to the CALICO project, focusing on the development and optimization of advanced detection techniques for optical satellite communications. Their responsibilities willinclude:

1. Design and Implementation of Control Loop Hardware Architecture

• Develop the hardware architecture for a control loop, from a Simulink model, that integrates anoptical phase-locked loop (OPLL) with digital signal processing (DSP).
• Translate simulation models into optimized hardware designs using VHDL for FPGA implementation.

2. Simulation and Optimization of Hardware Models

• Simulate the control loop using advanced modeling tools to evaluate performance under varying conditions, including Doppler shifts, atmospheric turbulence, and noise.
• Optimize the design to ensure robust operation and low error rates in challenging environmental conditions.

3. Real-Time System Testing on Laser Test Bench

• Conduct real-time tests of the hardware on a dedicated laser test bench to validate system functionality and performance.
• Develop testing protocols and adapt the system to ensure compatibility with experimental setups.

4. Analysis and Scientific Contribution

• Analyze test results to assess the performance of the control loop and identify areas for further improvement.
• Collaborate with the research team to synthesize findings into scientific publications and presentresults at relevant conferences.

This role offers a unique opportunity to contribute to cutting-edge research iat the interface of optics and digital electronics, with potential applications in next-generation satellite communication systems.