  Oscillators in the GHz frequency range are key building blocks for
telecommunication, timing and positioning applications. Operating directly in
the GHz and compactness while keeping high frequency stability, is still an
up-to-date challenge. Recently, optomechanical crystals, compact by nature,
have demonstrated GHz frequency modes, thus gathering prerequisite features for
using them as oscillators. Here we report on the demonstration, in ambient
atmospheric conditions, of an optomechanical oscillator designed with an
original concept based on bichromatic one-dimensional optomechanical crystal.
Self sustained oscillations directly at 3 GHz are routinely achieved with a low
optical power threshold of 40 $\mu W$ and short-term linewidth narrowed down to
100 Hz in agreement with phase noise measurements (-113 dBc/Hz at 1 MHz from
the carrier) for free running optomechanical oscillators. This oscillator is
made of InGaP, low loss and TPA-free piezoelectric material which makes it
valuable for optomechanics.
