Contribution à l'étude d'un oscillateur opto-électronique micro-ondes : applications fondées sur une variation de sa fréquence

The optoelectronic oscillator (OEO) proposed for the first time in 1994 by S. Yao and L. Maleki was the first microwave oscillator including a very long optical fiber and leading to a very high spectral quality. In this thesis we have focused our work on the possible applications of the OEO, a domain which is still not widely explored. The main idea is to study controlled variations of the oscillation frequency and to show the feasibility. of corresponding applications. Two possibilities will be developed in order to act on the signal phase shift and hence on the oscillation frequency. The first one is based on a change of the global optical path of the system. After showing the sensitivity of the system to a variation of the loop length, we have applied this principle for measuring of the refractive index of some chemical solutions leading to an estimated accuracy of five to one thousand. Improving this first realization could lead to gain one magnitude order. For the second method, the optical signal at the output of the fiber is divided into two equivalent parts. By setting a variation of the signal amplitude in one of these two paths it is possible to change the global phase shift after the electronic combining. The first technique is based on a semi-conductor optical amplifier leading to the realization of a voltage controlled OEO whose properties are underlined by implementing a frequency modulation with a modulation index up to 5.4. The second technique is based on using a circulator terminated by an optical fiber interferometer. With a compensation of the thermal effects it is possible to measure for example the absorption coefficient of some liquids.