Application des lasers fibrés à verrouillage de modes à la génération très haute fréquence à haute pureté spectrale

Vincent Auroux 1
1 LAAS-MOST - Équipe Microondes et Opto-microondes pour Systèmes de Télécommunications
LAAS - Laboratoire d'analyse et d'architecture des systèmes [Toulouse]
Abstract : 2119/5000 Technological development in the field of telecommunications, as well as detection systems, has increased in recent years the need for reference signals presenting a very high spectral purity. The increase in flow rates, the saturation of frequency bands as well as the performances imposed for radar detection have opened the way to the microwave generation by optics. These frequency references are often derived from optoelectronic oscillators (OEO). These oscillators include an element for storing energy through resonators or long fibered delay lines in order to increase their quality factor and thus to achieve performances superior to signals multiplied from low-frequency sources or directly to From microwave oscillators with a dielectric resonator (DRO). An original topology of optoelectronic oscillators was proposed in the late 1990s by an American team: it is a question of replacing the passive resonator requiring a laser locking on the latter by an active resonator, integrating an optical amplifier. This active resonator, a mode-locked laser, allows a coupling between the optical oscillation of the laser and the optoelectronic oscillation. This is called a coupled optoelectronic oscillator (COEO). The performance of the COEO is closely related to the spectral purity of the signal from the mode-locked laser. This work of thesis deals with the study and optimization of these systems. An in-depth study of noise in optical amplifiers was first conducted to determine what type of amplifier to choose for the COEO and under what conditions optical amplification provides minimal phase noise. Then, a 10 GHz COEO was produced with very low phase noise reaching - 132 dBc / Hz at 10 kHz of the carrier. A model has also been implemented, allowing to determine a posteriori the efficiency of the coupling and thus the locking band between the optoelectronic oscillation and the mode-locked laser. This internal coupling depends strongly on the dynamics of the system. However, the various non-linear effects which occur in the semiconductor amplifier and the fibers do not make it possible to obtain an analytical model. An iterative model was then proposed in order to obtain the properties of the slowly variable complex envelope of the frequency comb generated at the output of the laser whose photodetection leads to the RF power generated by the COEO. The COEO generates a comb sufficiently wide to produce RF harmonics greater than the repetition frequency of the mode-locked laser if the longitudinal modes spaced apart from several free spectral intervals (ISL) are in phase. The iterative model developed allows, from the experimental parameters, to determine the optical spectrum as well as the phase distribution within it. It is then possible to increase the power of a harmonic at the output of the photodiode by adding dispersive elements. This frequency multiplication allows the generation of high spectral purity signals in millimeter band. An experimental demonstration at 90 GHz has been proposed, based on a COEO operating at 30 GHz. These results are promising and integration of the COEO into a thermalized housing as well as finer management of fiber dispersion can allow significant improvements in the phase noise of the system.
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Micro et nanotechnologies/Microélectronique. UNIVERSITE TOULOUSE 3 PAUL SABATIER (UT3 PAUL SABATIER), 2017. Français
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Vincent Auroux. Application des lasers fibrés à verrouillage de modes à la génération très haute fréquence à haute pureté spectrale. Micro et nanotechnologies/Microélectronique. UNIVERSITE TOULOUSE 3 PAUL SABATIER (UT3 PAUL SABATIER), 2017. Français. 〈tel-01560899〉

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