  Si photonics has an immense potential for the development of compact and
low-loss opto-electronic oscillators (OEO), with applications in radar and
wireless communications. However, current Si OEO have shown a limited
performance. Si OEO relying on direct conversion of intensity modulated signals
into the microwave domain yield a limited tunability. Wider tunability has been
shown by indirect phase-modulation to intensity-modulation conversion,
requiring precise control of the phase-modulation. Here, we propose a new
approach enabling Si OEOs with wide tunability and direct intensity-modulation
to microwave conversion. The microwave signal is created by the beating between
an optical source and single sideband modulation signal, selected by an
add-drop ring resonator working as an optical bandpass filter. The tunability
is achieved by changing the wavelength spacing between the optical source and
resonance peak of the resonator. Based on this concept, we experimentally
demonstrate microwave signal generation between 6 GHz and 18 GHz, the widest
range for a Si-based OEO. Moreover, preliminary results indicate that the
proposed Si OEO provides precise refractive index monitoring, with a
sensitivity of 94350 GHz RIU and a potential limit of detection of only 10-8
RIU, opening a new route for the implementation of high-performance Si photonic
sensors.
