Optoelectronic oscillator with dual-loop in the RF domain

An optoelectronic oscillator (OEO) configuration with a unique optical fiber length, followed by a dual-loop in the radiofrequency (RF) domain is proposed and studied. Such a configuration with a unique optical delay followed by an RF time delay enables a reduction in the intensity of unwanted frequencies and a remotely fine frequency tuning. The RF output power spectrum was theoretically studied through a formalism that reveals the role of the relative size of optical and RF time delays. The theoretical analyzes were confirmed by the experimental results. An unwanted frequency intensity is 50 dB below RF OEO output frequency after a reduction of 13 dB. A maximum tuning band equal to 94 MHz with a resolution of 250 kHz was achieved without using an RF external source or additional system. Phase noise of - 117 dBc/Hz is measured for an offset frequency of 100 kHz with an optical fiber length equal to 800 m. The phase noise value obtained is compatible with aeronautical and space systems in the S band. All the achieved results are compared with the single loop OEO configuration.