Ph.D Thesis

Ph.D StudentLevy Etgar
SubjectGeneration of Radiofrequency Signals by Using
Optoelectronic Oscillators
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Moshe Horowitz


Optoelectronic oscillators (OEOs) are hybrid devices that combine electronic and optical components. High-frequency signals whose phase noise is nearly independent of the oscillation frequency can be generated by using an OEO. The low phase noise in such devices is obtained due to the low loss of an optical fiber which serves as a very long length cavity with a very high-Q. Such ultralow phase-noise radio-frequency signals are very important for accurate measurements. Synchronization between two OEOs is used to improve the performance of such devices.

In this thesis we explore the physical properties of the generated signals by OEOs. We discuss these properties both from the engineering aspect, in which we show how the performance of OEOs can be improved, and from the physics aspect, in which we show new phenomena that were not obtained or analyzed before.

In the first part of the thesis we discuss the limits of long-length OEOs and the requirement of coupling between two OEOs. We study how to analyze such systems and show how the performance of two coupled OEOs can be improved. The improvement in the OEO performance was verified experimentally, and an excellent agreement between theory and experiment was obtained.

The conditions under which synchronization between two coupled OEOs can be obtained are discussed theoretically in the second part of the thesis. We show that the amplitude response is required to model coupled delay-line oscillators, even if the coupling is weak. Thus, weakly coupled delay line oscillators can not be accurately modeled by coupled phase oscillator models. We show that the presence of other cavity modes should be taken into account in the stability analysis of the solutions. In particular, we discuss the physical effects that dominate the synchronization region for two weakly-coupled delay-line oscillators with a p/2 coupling-phase, and show new results that were not obtained by previously published models.

In the last part of the thesis we demonstrate experimentally, for the first time, passive mode-locking of an optoelectronic oscillator. Using this device, we were able to generate a single-cycle radio-frequency pulse train with a low jitter: less than 5 ppm of the round-trip duration. The relative phase between the pulse envelope and the carrier is autonomously locked and as a result the pulse waveform is repeated in each round-trip. A theoretical model that reproduces the experimental results is developed and is used to theoretically study the autonomously carrier-envelope phase-locking.