Single-Sideband Hybrid Opto-Electronic Oscillator

Abstract

Opto-electronic oscillators (OEO) are important building blocks in microwave photonics systems, allowing to obtain low-phase noise optically-carried radiofrequency signals. We have recently demonstrated an OEO scheme based on a monolithic dual-frequency source [1], whose beatnote is self-stabilized using frequency-shifted optical feedback, and a delay line [2]. The main interest of such a setup is that it allows the generation of single-sideband signals, which are thus insensitive to dispersion fading when propagating in optical fibers. The scheme presented in [2] offered good short-term performances. However, it could be affected by mode-hopping due to both the resonant modes of the optical feedback loop, and to those of the optoelectronic loop including the delay line. In the present work, we present significant improvements, namely the complete suppression of mode-hopping, and a significant reduction of the spurs in the phase noise spectrum. This has been obtained by (i) the introduction of a RF interferometer thanks to the use of two delay lines, and (ii) a significant shortening of the optical feedback loop (see Fig. 1(a)) [3].