—We experimentally demonstrate enhanced slow and fast light at GHz frequencies by forced coherent population oscillations (CPOs) in a SOA. This opens the possibility to conceive a controllable RF phase shifter based on this setup. Slow and fast light in a semiconductor optical amplifier (SOA) enables to realize RF phase-shifters which are key components in numerous microwave photonics applications [1], [2]. At GHz frequencies, the achievable phase shift experienced by an optically carried RF signal passing through the SOA has been recently increased up to π by optically filtering out the red-shifted modulation sideband before detection [3]. Moreover, a phase shift of 2π at 19 GHz has also been obtained with this method by cascading several SOAs [4]. However, this method involves the use of a very sharp optical notch filter and is consequently efficient mainly for relatively high frequencies (typically above 5 GHz). Furthermore, the insertion of the optical filter leads to a significant noise enhancement [5]. Besides, Anton et al. have recently predicted that modulating the injection current of the SOA at the same frequency of the signal should enhance the phase shift of the signal [6]. The principle of such forced coherent population oscillations has been experimentally validated in an erbium doped fiber amplifier at very low frequency (20 Hz) [7]. In the present paper, we experimentally extend this concept in a SOA at GHz frequencies. We moreover give a comprehensive theoretical description of this phenomena, based on a comparison with optical filtering technique. To experimentally demonstrate forced coherent population oscillations, we used a reflective SOA developed by Alcatel-Thales III-V lab. and specifically designed to be modulated at high frequencies [8]. The experimental setup is shown in Fig. (a). The microwave signal generated by the Vector Network Analyser (VNA) modulates both the injected current of the SOA and the input optical power. An RF attenuator enables to control the modulation depth of the injected current. The gain and the phase shift introduced by the SOA are P. Berger, J. Bourderionnet, M. Alouini and D. Dolfi are with Thales Research&Technology, 1 av. Augustin Fresnel,