A Widely Tunable Optoelectronic Oscillator Based on Directly Modulated Dual-Mode Laser

A widely tunable optoelectronic oscillator (OEO) based on a directly modulated monolithic integrated dual-mode amplified feedback laser (AFL) is proposed and experimentally demonstrated. In this OEO scheme, the functions of the laser source, the intensity modulator, and the tunable high-
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RF filter are all realized through an AFL chip. On one hand, the beating frequency of the two modes defines the central oscillating frequency, which functions as an active tunable microwave photonic filter. On the other hand, by taking advantage of the photon–photon resonance, the laser has high modulation efficiency around the beating frequency that is far beyond the intrinsic modulation bandwidth of the lasers. It eliminates the use of high-speed external modulators and dramatically reduces the threshold gain of the oscillator. By tuning the injection currents of the laser sections, stable microwave signals that are continuously tunable from 28 to 41 GHz with signal-sideband phase noise below −106 dBc/Hz (at a 10-kHz offset) and threshold electronic gain no more than 27 dB are experimentally realized.