A Coupled Optoelectronic Oscillator With Performance Improved by Enhanced Spatial Hole Burning in an Erbium-Doped Fiber

A coupled optoelectronic oscillator (COEO) with performance improved by the enhanced spatial hole burning (SHB) effect in an unpumped erbium-doped fiber (EDF) is proposed and demonstrated. In the proposed COEO, a strong standing-wave forming structure is incorporated to enable large SHB effect in the unpumped EDF, which significantly improves the supermode suppression ratio of the generated optical pulse, and the sidemode suppression ratio and phase noise performance of the generated electrical signal. A 10-GHz COEO is established. A stable optical pulse train is successfully generated with a supermode suppression ratio as high as 75 dB. The system is observed in the lab environment for 1.5 h with no significant variation. Without introducing any long fiber or multiloop structure in the optoelectronic oscillator loop, the sidemode suppression ratio of the 10-GHz RF output reaches 90 dB and the phase noise is about -130 dBc/Hz at 10-kHz offset. The influence of the optical power injected into the EDF, and the effects of the absorption coefficient and length of the EDF on the key parameters of the COEO are investigated and discussed.