Coherent All-Optical Analog Pulse Compression Lidar – COCOA

COCOA is structured into 4 tasks. The first (WP0), supervised by LIPhy in conjunction with Lumibird, is a project management and monitoring task, and covers the definition of general specifications, technical recommendations, and project progress towards the lidar demonstrator. Technology watch, publications and intellectual property will also be attached to WP0, with a view to technological maturation and future commercialization (CNRS Innovation, SATT, European funding....). It is worth noting that such a system could eventually be integrated on a chip. WP1 (supervised by I-FOTON) is devoted to the development of new broadband waveform sources based on electro-optical FSLs. This development is split between LIPhy (single-sideband electro-optical FSLs) and I-FOTON (double-sideband electro-optical FSLs). Full modeling of these systems and their metrological aspects will also be studied. WP2 (supervised by LIPhy) is devoted to the implementation of all-optical analog pulse compression in electro-optical FSLs. Finally, WP3 (I-FOTON) is dedicated to the realization of a demonstrator (TRL 4), i.e. a lidar system enabling 3D profiling under real outdoor conditions.

COCOA has achieved most of its objectives. We have developed dual frequency-shifting loop architectures, using either a unilateral electro-optical frequency shifter or a bi-lateral shifter. For each of these architectures, we have demonstrated their applicability to coherent Lidar. With regard to unilateral FSL, Louis Alliot's thesis enabled us to characterize the properties of the dual-comb, and then to use it for coherent lidar measurements at high spatial resolution (< mm). The phase dependence of the system was well verified. In addition, this work has demonstrated three original results - a priori not expected within the COCOA framework. The Talbot effect in electro-optical FSL enables frequency multiplication of microwave signals (up to 20 GHz) without phase noise degradation. We have also demonstrated slow/fast light effects in FSL. Finally, we have shown that dual-comb techniques can also be used to implement distributed sensors, providing access to the reflectivity profile along a fiber or a line on a surface (vibrometry), for example. The latter application is currently being validated as part of an M2 internship. We have also obtained a large number of results for bi-lateral FSL.

The prospects for COCOA are manifold, involving both sensors and microwave photonics. As far as lidar is concerned, FSLs offer very interesting performance in terms of spatial resolution, but with a modest ambiguity distance (of the order of a metre), making them ideal for profilometry applications. Based on the knowledge we have acquired of coherent lidar techniques, we have obtained funding from the DGA (ANR RACOON project), to build an underwater coherent lidar demonstrator. This project will use the same base as the FSLs developed in COCOA, before a frequency conversion stage to generate frequency combs in the blue-green. Similarly, the interest in FSLs for coherent metrology has led to the creation of the ANR Mechoui project, which aims to characterize parietal pressure in flows using an interrogator based on a double FSL. Applications to microwave photonics mainly involve signal frequency multiplication, and the generation of signals with arbitrary frequency modulation. Work on these functionalities will continue, through the realization of FSLs in integrated optics. Various platforms are currently being studied (SiN/InP hybridization by transfer printing, or lithium niobate). Two projects are currently being submitted for these applications.

Published articles :

L. Alliot de Borggraef and H. Guillet de Chatellus, «Phase-sensitive distributed Rayleigh fiber sensing enabling the real-time monitoring of the refractive index with a sub-cm resolution by all-optical coherent pulse compression,« Opt. Express 31, 1167-1180 (2023)

Hugues Guillet de Chatellus, Goulc’hen Loas, Louis Alliot de Borggraeff, and Marc Brunel, «Slow and fast light effects induced by interference with a control light field,« Opt. Express 32, 35228-35235 (2024)

L. Alliot de Borggraef, and H. Guillet de Chatellus, « Photonics-based microwave frequency multiplier with low phase noise degradation  », soumis (Optics Letters)

Conference presentations :

L. Alliot de Borggraef, V. Carlet, M. Brunel, and H. Guillet de Chatellus, « Radio-frequency Multiplication without Phase Noise Degradation in an Electro-optic Frequency-shifting Loop “, CLEO 2023

L. Alliot de Borggraef, and H. Guillet de Chatellus, « Distributed Rayleigh fiber sensing enabling quantitative monitoring in real time of the refractive index with a sub-cm resolution », CLEO 2023

L. Alliot de Borggraef, and H. Guillet de Chatellus, « Dual-comb interferometry using frequency shifting loops», EOS AN 2023.

M. Brunel et al., « Nonlinear frequency chirps from a stabilized injected phase-modulated fiber laser loop», EOS AN 2023.

L. Alliot de Borggraef, and H. Guillet de Chatellus, « Lidar cohérent à résolution sub-millimétrique à l’aide d’une double boucle à décalage de fréquence», Optique Normandie 2024.

L. Alliot de Borggraef, and H. Guillet de Chatellus, « Multiplication de fréquences GHz à faible dégradation du bruit de phase grâce à une boucle à décalage de fréquence électro-optique », Optique Normandie 2024.

The COCOA (Coherent All-Optical Analog Pulse Compression Lidar) project aims to develop a new coherent lidar system based on frequency shifting loops. This architecture combines optimal performance (range, resolution, security) with great simplicity by overcoming the need for fast electronics, both for the generation of waveforms and for their (all-optical) processing by pulse compression. The project, which brings together two academic partners (LIPhy in Grenoble, FOTON Institute in Rennes) pursues three objectives: (i) to develop new architectures of wideband electro-optical frequency shifting loops (> 40 GHz), (ii) from these architectures, demonstrate a new coherent lidar technique with adjustable resolution (1mm-10cm), based on all-optical analog pulse compression; (iii) build a lidar prototype according to the recommendations of an industrial leader in the sector, Lumibird.