This paper presents the design and dimensioning optimization of a novel optical network structure, called the PetaWeb, having a total capacity of several Pb/s (10¹⁵ bit/s). Its topology is a superimposition of stars that drastically eases signaling and switching operations. Firstly, we deal with the network model, focusing on the insertion of the time-sharing of the optical channel in network components and in lightpath provisioning. The design problem is jointly a network dimensioning and an assignment problem; we propose for the dimensioning an integer linear programming formulation and a linear resolution algorithm for the assignment. We also propose the use of a quasi-regular topology extracted from the optimized regular topology to reduce costs and improve the network utilization.