Microwave Optoelectronic Oscillator with Optical Gain

Optoelectronic oscillators (OEO) are unique compared to radio-frequency (RF) oscillators in that they do not fundamentally require a RF gain element in order to satisfy the amplitude threshold condition for oscillation. All of the energy required for oscillation can be obtained from the optical carrier. This, however, was not initially possible, due to the inefficiency and power limitations on the optical components used in the OEO. Recent improvements driven by the need for optical-RF links have improved modulator and detector technology. Electro-optic modulators (EOM) with ultra-low half-wave voltage (V_pi), and high optical power capabilities, when coupled with high-power photodetectors, have achieved optical links with gain. With sufficient gain from the photonic components in the OEO, the RF loop amplifier becomes unnecessary. Eliminating this amplifier removes one of the major noise contributing elements of the oscillator. Here we present designs and phase noise results of several OEOs, operating at RF frequencies up to 10 GHz, constructed with only optical gain.