An integrated circuit includes an active device for confinement of a light flux that is formed in a semiconducting substrate. A confinement rib is separated from two doped zones by two trenches. Each doped zone includes a contacting zone on an upper face. Each trench widens from a bottom wall towards the upper face of the corresponding doped zone. The widening trenches present a sidewall having a tiered profile between the trench and the doped zone. An opposite sidewall presents a straight profile.